Auli Karhu | University of Helsinki (original) (raw)

Papers by Auli Karhu

Cancers, Feb 23, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Endocrine connections, May 1, 2018

Objective: Recently, mutations in KCNQ1, a potassium channel gene usually linked to long QT syndr... more Objective: Recently, mutations in KCNQ1, a potassium channel gene usually linked to long QT syndrome, were reported to cause maternally inherited gingival fibromatosis and growth hormone deficiency (GHD). Expression of the mutated KCNQ1 with the auxiliary potassium channel subunit KCNE2 was shown to reduce pituitary hormone secretion in functional experiments. Here, we investigated if germline mutations in KCNQ1 and KCNE2 were present in patients with somatotropinomas, which represent a model of growth hormone excess. Design and methods: KCNQ1 and KCNE2 were screened for germline mutations in 53 patients with acromegaly by Sanger sequencing. Effects of the variants were predicted by in silico tools. Results: Only deep intronic and synonymous polymorphisms were detected in KCNQ1. These findings were likely insignificant based on in silico predictions and the variants' frequencies in the general population. In KCNE2, a heterozygous c.22A>G, p.(Thr8Ala) mutation with unknown significance was found in three patients. It was present in the database controls with a frequency of 0.0038. Conclusions: KCNQ1 or KCNE2 mutations do not appear to account for somatotropinoma formation, although larger patient series are needed to validate the findings. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

European journal of endocrinology, Nov 1, 2009

Objective: Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) were recently sho... more Objective: Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) were recently shown to confer a pituitary adenoma predisposition in patients with familial isolated pituitary adenomas (FIPA). We report a large Samoan FIPA kindred from Australia/New Zealand with an R271W mutation that was associated with aggressive pituitary tumors. Design and methods: Case series with germline screening of AIP and haplotype analyses among R271W families. Results: This previously unreported kindred consisted of three affected individuals that either presented with or had first symptoms of a pituitary macroadenoma in late childhood or adolescence. The index case, a 15-year-old male with incipient gigantism and his maternal aunt, had somatotropinomas, and the maternal uncle of the index case had a prolactinoma. All tumors were large (15, 40, and 60 mm maximum diameter) and two required transcranial surgery and radiotherapy. All three affected subjects and ten other unaffected relatives were found to be positive for a germline R271W AIP mutation. Comparison of the single nucleotide polymorphism patterns among this family and two previously reported European FIPA families with the same R271W mutation demonstrated no common ancestry. Conclusions: This kindred exemplifies the aggressive features of pituitary adenomas associated with AIP mutations, while genetic analyses among three R271W FIPA families indicate that R271W represents a mutational hotspot that should be studied further in functional studies.

Gene Expression, Feb 1, 2007

Fumarate hydratase (FH) is an enzyme of the mitochondrial tricarboxylic acid cycle (TCAC). Here w... more Fumarate hydratase (FH) is an enzyme of the mitochondrial tricarboxylic acid cycle (TCAC). Here we report the characterization of a novel FH variant (FHv) that contains an alternative exon 1b, thus lacking the mitochondrial signal sequence. Distinct from mitochondrial FH, FHv localized to cytosol and nucleus and lacked FH enzyme activity. FHv was expressed ubiquitously in human fetal and adult tissues. Heat shock and prolonged hypoxia increased FHv expression in a cell line (HTB115) by nine-and fourfold, respectively. These results suggest that FHv has an alternative function outside the TCAC related to cellular stress response.

Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characteri... more Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characterized; apart from mutations in the stimulatory Gα protein (Gαs encoded by GNAS) causing activated cAMP synthesis, pathogenic variants are rarely found in growth hormone–secreting pituitary tumors (somatotropinomas). The purpose of the current work was to clarify how genetic and epigenetic alterations contribute to the development of somatotropinomas by conducting an integrated copy number alteration, whole-genome and bisulfite sequencing, and transcriptome analysis of 21 tumors. Somatic mutation burden was low, but somatotropinomas formed two subtypes associated with distinct aneuploidy rates and unique transcription profiles. Tumors with recurrent chromosome aneuploidy (CA) were GNAS mutation negative (Gsp−). The chromosome stable (CS) –group contained Gsp+ somatotropinomas and two totally aneuploidy-free Gsp− tumors. Genes related to the mitotic G1–S-checkpoint transition were differentially expressed in CA- and CS-tumors, indicating difference in mitotic progression. Also, pituitary tumor transforming gene 1 (PTTG1), a regulator of sister chromatid segregation, showed abundant expression in CA-tumors. Moreover, somatotropinomas displayed distinct Gsp genotype–specific methylation profiles and expression quantitative methylation (eQTM) analysis revealed that inhibitory Gα (Gαi) signaling is activated in Gsp+ tumors. These findings suggest that aneuploidy through modulated driver pathways may be a causative mechanism for tumorigenesis in Gsp− somatotropinomas, whereas Gsp+ tumors with constitutively activated cAMP synthesis seem to be characterized by DNA methylation activated Gαi signaling.Implications:These findings provide valuable new information about subtype-specific pituitary tumorigenesis and may help to elucidate the mechanisms of aneuploidy also in other tumor types.

Journal of the Endocrine Society, Jul 23, 2019

Context: Parathyroid carcinoma (PC) is extremely rare. Prognosis is poor, with no known evidence-... more Context: Parathyroid carcinoma (PC) is extremely rare. Prognosis is poor, with no known evidence-based systemic therapies. We previously reported complete remission in a patient with metastasized parathyroid carcinoma and high tumor MGMT promoter methylation status who was treated with temozolomide. Objective: To study MGMT promoter methylation status in an additional set of aggressive parathyroid tumors. Design/Setting: The study included 12 patients: 7 with sporadic and 5 with familial primary hyperparathyroidism (two of the latter carried a CDC73 gross deletion). Patient 9 is the previously described patient with PC and high MGMT methylation status. Her daughter (patient 12) had surgery for severe primary hyperparathyroidism due to atypical parathyroid adenoma during pregnancy. Eleven patients thus had PC and one had atypical parathyroid adenoma. MGMT promoter methylation status was determined from DNA extracted from primary (n 5 10) or metastatic (n 5 2) tumors. A mean methylation level .20% was considered high. Patient 11 had metastatic PC and received temozolomide cycles. Results: Only the previously published patient (patient 9) had high tumor MGMT promoter methylation status. This was not a characteristic of the atypical parathyroid adenoma of the daughter (patient 12). Patient 11 (CDC73 intragenic deletion) has disseminated PC, low MGMT promoter methylation, and stable disease on follow-up after temozolomide treatment. Conclusion: High MGMT promoter methylation status seems rare in PC. However, as demonstrated in other neuroendocrine tumors, some patients with disseminated PC might benefit from temozolomide. Demonstration of high methylation status could be a predictor of positive response to temozolomide treatment.

European journal of endocrinology, Feb 1, 2017

Introduction: In sporadic acromegaly, downregulation of AIP protein of the adenomas associates wi... more Introduction: In sporadic acromegaly, downregulation of AIP protein of the adenomas associates with invasive tumor features and reduced responsiveness to somatostatin analogues. AIP is a regulator of Ga i signaling, but it is not known how the biological function of the Ga i pathway is controlled. Aim: To study GNAS and AIP mutation status, AIP and Ga i-2 protein expressions, Ki-67 proliferation indices and clinical parameters in patients having primary surgery because of acromegaly at a single center between years 2000 and 2010. Results: Sixty patients (F/M, 31/29), mean age 49 (median 50), mean follow-up 7.7 years (range 0.6-14.0) underwent primary surgery. Four adenoma specimens (6.8%) harbored an AIP and 21 (35.6%) an activating GNAS (Gsp+) mutation. Altogether 13/56 (23%) adenomas had low AIP protein levels, and 14/56 (25%) low Ga i-2 staining. In regression modeling, AIP expression associated with Ga i-2 (P = 2.33 × 10 −9) and lower Ki-67 (P = 0.04). In pairwise comparison, low AIP protein predicted high GH at last follow-up (mean 7.7 years after surgery, q = 0.045). Extent of treatments given for acromegaly associated with higher preoperative GH (P = 7.94 × 10 −4), KNOSP (P = 0.003) and preoperative hypopituitarism (P = 0.03) and remission at last follow-up with change in 3-month postoperative IGF1 (P = 2.07 × 10 −7). Conclusions: We demonstrate, for the first time, that AIP protein expression associates with Ga i-2 protein intensities in sporadic somatotropinomas, suggesting a joint regulation on somatostatin signaling. Low AIP level associates with higher proliferative activity and predicts high GH concentrations after long-term follow-up. The AIP mutation rate of 6.8% is fairly high, reflecting the genetic composition of the Finnish population.

Oncogene, Apr 10, 2003

We have allelotyped a series of 104 Finnish colorectal cancers (CRCs) using 372 polymorphic marke... more We have allelotyped a series of 104 Finnish colorectal cancers (CRCs) using 372 polymorphic markers spaced, on average, at 10 cM intervals, and have made a comparison of the differences in the frequency of allelic imbalance (AI) between familial and sporadic cases. Differences in the frequency of allelic imbalance (loss of heterozygosity or amplification) at a number of loci were detected and these were evaluated through analysis of additional series of cancers using specific markers. The most consistent difference was observed at chromosome 20q13.1-13.3 characterized by a two fold difference between familial and nonfamilial disease in a total of 99 familial and 186 sporadic Finnish cases. This difference was not observed in a UK set of 67 familial and 96 sporadic CRCs. The genome-wide effort resulted in a large data set giving clues to the location of putative CRC predisposition genes in the genome. The approach provides an alternative strategy for detecting cancer predisposition genes solely reliant on the molecular analysis of single cases obviating the requirement to collect multiple samples from families.

PLOS ONE, Oct 7, 2014

Pituitary adenomas are neoplasms of the anterior pituitary lobe and account for 15-20% of all int... more Pituitary adenomas are neoplasms of the anterior pituitary lobe and account for 15-20% of all intracranial tumors. Although most pituitary tumors are benign they can cause severe symptoms related to tumor size as well as hypopituitarism and/or hypersecretion of one or more pituitary hormones. Most pituitary adenomas are sporadic, but it has been estimated that 5% of patients have a familial background. Germline mutations of the tumor suppressor gene aryl hydrocarbon receptorinteracting protein (AIP) predispose to hereditary pituitary neoplasia. Recently, it has been demonstrated that AIP mutations predispose to pituitary tumorigenesis through defective inhibitory GTP binding protein (Ga i) signaling. This finding prompted us to examine whether germline loss-of-function mutations in inhibitory guanine nucleotide (GTP) binding protein alpha (GNAI) loci are involved in genetic predisposition of pituitary tumors. To our knowledge, this is the first time GNAI genes are sequenced in order to examine the occurrence of inactivating germline mutations. Thus far, only somatic gain-offunction hot-spot mutations have been studied in these loci. Here, we have analyzed the coding regions of GNAI1 , GNAI2, and GNAI3 in a set of young sporadic somatotropinoma patients (n = 32; mean age of diagnosis 32 years) and familial index cases (n = 14), thus in patients with a disease phenotype similar to that observed in AIP mutation carriers. In addition, expression of Ga i proteins was studied in human growth hormone (GH), prolactin (PRL), adrenocorticotropic hormone (ACTH)-secreting and non-functional pituitary tumors. No pathogenic germline mutations affecting the Ga i proteins were detected. The result suggests that loss-of-function mutations of GNAI loci are rare or nonexistent in familial pituitary adenomas.

Oncogene, Oct 9, 2006

Hereditary non-polyposis colorectal cancer (HNPCC) is caused by germline mutations in mismatch re... more Hereditary non-polyposis colorectal cancer (HNPCC) is caused by germline mutations in mismatch repair (MMR) genes, mostly MLH1 and MSH2. Somatic inactivation of the wild-type allele of the respective MMR gene is required for tumor development. Unexpectedly, a recent study utilizing DNA from paraffin-embedded tissue material detected frequent loss of the mutant MMR gene allele in HNPCC tumors. Dual role for loss of heterozygosity (LOH) was proposed. If somatic loss of the wild-type MMR gene allele had occurred through point mutation or promoter hypermethylation, frequent somatic deletions at the region of the MMR gene locus, perhaps targeting other relevant cancer genes, could quite commonly lead to loss of the mutant allele. To test this hypothesis, we studied a population-based series of 25 fresh-frozen HNPCC tumors with a germline mutation in MLH1 or MSH2 for LOH. Fourteen of the 25 tumors (56%) showed LOH at the respective locus, and all 14 losses targeted the wild-type allele (P ¼ 0.00006). These results strongly support the traditional two-hit model of HNPCC gene inactivation.

International Journal of Cancer, Jun 29, 2010

It is estimated that up to 35% of colorectal cancers (CRC) can be explained by hereditary factors... more It is estimated that up to 35% of colorectal cancers (CRC) can be explained by hereditary factors. However, genes predisposing to highly penetrant CRC syndromes account for only a small fraction of all cases. Thus, most CRCs still remain molecularly unexplained. A recent systematic sequencing study on well-annotated human protein coding genes identified 280 somatically mutated candidate cancer genes (CAN genes) in breast and colorectal cancer. It is estimated that 8% of all reported cancer genes show both somatic and germline mutations. Therefore, the identified CAN genes serve as a distinct set of candidates for being involved in hereditary susceptibility. The aim of this study was to evaluate the role of colorectal CAN genes in familial CRC. Samples from 45 familial CRCs without known cancer predisposing mutations were screened for somatic and germline variants in 15 top-ranked CAN genes. Six of the genes were found to be somatically mutated in our tumor series. We identified 22 nonsynonymous somatic mutations of which the majority was of missense type. In germline, three novel nonsynonymous variants were identified in the following genes: CSMD3, EPHB6 and C10orf137, and none of the variants were present in 890 population-matched healthy controls. It is possible that the identified germline variants modulate predisposition to CRC. Functional validation and larger sample sets, however, will be required to clarify the role of the identified germline variants in CRC susceptibility.

International Journal of Cancer, Jan 15, 2006

In a previous genome-wide effort we identified a novel candidate colorectal cancer (CRC) suscepti... more In a previous genome-wide effort we identified a novel candidate colorectal cancer (CRC) susceptibility locus by allelotyping tumors from familial and sporadic CRC patients. Familial cases harbored amplifications significantly more frequently in 20q13, indicating the presence of a putative oncogene within the amplicon. A kinase-encoding AURKA is located in 20q13 and recently a Phe31Ile (91T > A) change of AURKA was suggested to function as a low penetrance tumor-susceptibility factor. Association analysis suggested an increased cancer risk in 91A homozygous individuals. In addition, tumors from heterozygous individuals showed preferential amplification of 91A allele and were more aneuploid, important findings that have not been confirmed to date. To evaluate whether AURKA is a target for the observed 20q13 amplifications, we assessed the frequency of the 91T > A change and possible preferential amplification of either allele in 125 familial and 110 sporadic Finnish CRC cases. We observed a preferential amplification of 91A with a significant difference between the alleles in the familial group (p = 0.03). Furthermore, a trend between younger age at diagnosis and genotype in the familial group was observed (p = 0.06). Other possible AURKA germline variants were screened by sequencing 10 of the familial cases. The frequency and amplification patterns of the observed variants were assessed in a larger set of familial and sporadic CRC but no evidence on tumorigenic role of the other sequence alterations was obtained. Thus our results support the importance of AURKA 91A as a low penetrance CRC susceptibility factor.

Endocrinology, Sep 1, 1997

Gastroenterology, Sep 1, 2013

Microsatellite instability can be found in approximately 15% of all colorectal cancers. To detect... more Microsatellite instability can be found in approximately 15% of all colorectal cancers. To detect new oncogenes we sequenced the exomes of 25 colorectal tumors and respective healthy colon tissue. Potential mutation hot spots were confirmed in 15 genes; ADAR, DCAF12L2, GLT1D1, ITGA7, MAP1B, MRGPRX4, PSRC1, RANBP2, RPS6KL1, SNCAIP, TCEAL6, TUBB6, WBP5, VEGFB, and ZBTB2; these were validated in 86 tumors with microsatellite instability. ZBTB2, RANBP2, and PSRC1 also were found to contain hot spot mutations in the validation set. The form of ZBTB2 associated with colorectal cancer increased cell proliferation. The mutation hot spots might be used to develop personalized tumor profiling and therapy.

The evolution of microsatellites was studied within and between the pine species. Sequences showe... more The evolution of microsatellites was studied within and between the pine species. Sequences showed that microsatellites do not necessarily mutate in a stepwise fashion and that size homoplasy is common due to flanking sequence and repeat area changes within and between the species. Thus, some assumptions of statistical methods based on changes in repeat numbers may not hold. Sequences from cross-species amplifications revealed evidence of duplications of microsatellite loci in pines. On two independent occasions, the repeat area of the microsatellite had undergone a rapid expansion during the last 10-25 million of years. Microsatellite markers were used together with other molecular markers (allozymes, RFLPs, RAPDs, rDNA RFLPs) and an adaptive trait (date of bud set) to study patterns of genetic variation in Scots pine (Pinus sylvestris) in Finland. All molecular markers showed high level of within population variation, while differentiation among populations was low (F ST = 0.02). Of the total variation in bud set, 36.4 % was found among the populations which experience a steep climatic gradient. Thus, the markers applied were poor predictors of population differentiation of the quantitative trait studied The distribution of genetic variation was studied in five natural populations of radiata pine (Pinus radiata), species which has gone through bottlenecks in the past. Null allele frequencies were estimated and used in later analyses. Microsatellites showed high level of variability within populations (H e = 0.68-0.77). Allele length distributions and average number of alleles per locus showed some traces of bottlenecks. Instead, comparison of observed genetic diversities and expected diversities suggested post-bottleneck expansion of populations. Genetic differentiation (F ST and R ST) among populations was over 10 %, reflecting situation in the isolated radiata pine populations. Using microsatellites and a newly developed Bayesian method, individual inbreeding coefficients were estimated in five populations of radiata pine. Most individuals were outbred while some were selfed. Presumably, in ancestral radiata pine populations the recessive deleterious alleles have been eliminated after bottlenecks and the mating system has changed as a consequence.

International Journal of Cancer, Sep 10, 2020

Pituitary adenomas (PAs) are intracranial tumors associated with significant morbidity due to hor... more Pituitary adenomas (PAs) are intracranial tumors associated with significant morbidity due to hormonal dysregulation, mass effects and have a heavy treatment burden. Growth hormone (GH)-secreting PAs (somatotropinomas) cause acromegaly-gigantism. Genetic forms of somatotropinomas due to germline AIP mutations (AIPmut+) have an early onset and are aggressive and resistant to treatment with somatostatin analogs (SSAs), including octreotide. The molecular underpinnings of these clinical features remain unclear. We investigated the role of miRNA dysregulation in AIPmut + vs AIPmut− PA samples by array analysis. miR-34a and miR-145 were highly expressed in AIPmut+ vs AIPmut− somatotropinomas. Ectopic expression of AIPmut (p.R271W) in Aip −/− mouse embryonic fibroblasts (MEFs) upregulated miR-34a and miR-145, establishing a causal link between AIPmut and miRNA expression. In PA cells (GH3), miR-34a overexpression promoted proliferation, clonogenicity, migration and suppressed apoptosis, whereas miR-145 moderately affected proliferation and apoptosis. Moreover, high miR-34a expression increased intracellular cAMP, a critical mitogenic factor in PAs. Crucially, high miR-34a expression significantly blunted octreotide-mediated GH inhibition and antiproliferative effects. miR-34a directly targets Gnai2 encoding Gαi2, a G protein subunit inhibiting cAMP production. Accordingly, Gαi2 levels were significantly lower in AIPmut+ vs AIPmut− PA. Taken together, somatotropinomas with AIP mutations overexpress miR-34a, which in turn

Molecular Cancer Research, Dec 1, 2019

Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characteri... more Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characterized; apart from mutations in the stimulatory Ga protein (Ga s encoded by GNAS) causing activated cAMP synthesis, pathogenic variants are rarely found in growth hormone-secreting pituitary tumors (somatotropinomas). The purpose of the current work was to clarify how genetic and epigenetic alterations contribute to the development of somatotropinomas by conducting an integrated copy number alteration, whole-genome and bisulfite sequencing, and transcriptome analysis of 21 tumors. Somatic mutation burden was low, but somatotropinomas formed two subtypes associated with distinct aneuploidy rates and unique transcription profiles. Tumors with recurrent chromosome aneuploidy (CA) were GNAS mutation negative (Gsp À). The chromosome stable (CS)-group contained Gsp þ somatotropinomas and two totally aneuploidy-free Gsp À tumors. Genes related to the mitotic G 1-S-checkpoint transition were differentially expressed in CA-and CS-tumors, indicating difference in mitotic progression. Also, pituitary tumor transforming gene 1 (PTTG1), a regulator of sister chromatid segregation, showed abundant expression in CA-tumors. Moreover, somatotropinomas displayed distinct Gsp genotypespecific methylation profiles and expression quantitative methylation (eQTM) analysis revealed that inhibitory Ga (Ga i) signaling is activated in Gsp þ tumors. These findings suggest that aneuploidy through modulated driver pathways may be a causative mechanism for tumorigenesis in Gsp À somatotropinomas, whereas Gsp þ tumors with constitutively activated cAMP synthesis seem to be characterized by DNA methylation activated Ga i signaling. Implications: These findings provide valuable new information about subtype-specific pituitary tumorigenesis and may help to elucidate the mechanisms of aneuploidy also in other tumor types.

BMC Cancer, Sep 17, 2008

Background: MYH11 (also known as SMMHC) encodes the smooth-muscle myosin heavy chain, which has a... more Background: MYH11 (also known as SMMHC) encodes the smooth-muscle myosin heavy chain, which has a key role in smooth muscle contraction. Inversion at the MYH11 locus is one of the most frequent chromosomal aberrations found in acute myeloid leukemia. We have previously shown that MYH11 mutations occur in human colorectal cancer, and may also be associated with Peutz-Jeghers syndrome. The mutations found in human intestinal neoplasia result in unregulated proteins with constitutive motor activity, similar to the mutant myh11 underlying the zebrafish meltdown phenotype characterized by disrupted intestinal architecture. Recently, MYH1 and MYH9 have been identified as candidate breast cancer genes in a systematic analysis of the breast cancer genome. Methods: The aim of this study was to investigate the role of somatic MYH11 mutations in two common tumor types; breast and prostate cancers. A total of 155 breast cancer and 71 prostate cancer samples were analyzed for those regions in MYH11 (altogether 8 exons out of 42 coding exons) that harboured mutations in colorectal cancer in our previous study. Results: In breast cancer samples only germline alterations were observed. One prostate cancer sample harbored a frameshift mutation c.5798delC, which we have previously shown to result in a protein with unregulated motor activity. Conclusion: Little evidence for a role of somatic MYH11 mutations in the formation of breast or prostate cancers was obtained in this study.

PubMed, 2003

Mutations in the currently known mismatch repair genes cannot explain all cases of hereditary non... more Mutations in the currently known mismatch repair genes cannot explain all cases of hereditary nonpolyposis colorectal cancer (HNPCC), and novel predisposing genes are actively sought. Recently, mutations in the DNA repair gene EXO1 have been implicated in HNPCC. One truncating and several missense changes were observed in familial colorectal cancer (CRC) cases but not in controls. We evaluated a series of European CRC patients and population controls to clarify whether EXO1 variants may indeed predispose to familial CRC. Several variants observed in patients were also observed in controls with similar frequencies, including the truncating variant proposed previously to be a disease-causing mutation. Thus, little evidence was obtained to support a major causative role of EXO1 in HNPCC, although we cannot exclude a role for EXO1 as a low penetrance cancer susceptibility or modifying gene.

American Journal of Pathology, Dec 1, 2009

Germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene predispose to ... more Germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene predispose to the development of pituitary adenomas. Here, we characterized AIP mutation positive (AIPmut؉) and AIP mutation negative (AIPmut؊) pituitary adenomas by immunohistochemistry. The expressions of the AIPrelated proteins aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT), cyclin-dependent kinase inhibitor 1B encoding p27(Kip1), and hypoxiainducible factor 1-␣ were examined in 14 AIPmut؉ and 53 AIPmut؊ pituitary adenomas to detect possible expression differences. In addition, the expression of CD34, an endothelial and hematopoietic stem cell marker, was analyzed. We found ARNT to be less frequently expressed in AIPmut؉ pituitary adenomas (P ‫؍‬ 0.001), suggesting that AIP regulates the ARNT levels. AIP small interfering RNA-treated HeLa, HEK293, or Aip-null mouse embryonic fibroblast cells did not show lowered expression of ARNT. Instead, in the pituitary adenoma cell line GH3, Aip silencing caused a partial reduction of Arnt and a clear increase in cell proliferation. We also observed a trend for increased expression of nuclear AHR in AIPmut؉ samples , although the difference was not statistically significant (P ‫؍‬ 0.06). The expressions of p27(Kip1), hypoxia-inducible factor 1-␣, or CD34 did not differ between tumor types. The present study shows that the expression of ARNT protein is significantly reduced in AIPmut؉ tumors. We suggest that the downregulation of ARNT may be connected to an imbalance in AHR/ARNT complex formation arising from aberrant cAMP signaling.

Cancers, Feb 23, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Endocrine connections, May 1, 2018

Objective: Recently, mutations in KCNQ1, a potassium channel gene usually linked to long QT syndr... more Objective: Recently, mutations in KCNQ1, a potassium channel gene usually linked to long QT syndrome, were reported to cause maternally inherited gingival fibromatosis and growth hormone deficiency (GHD). Expression of the mutated KCNQ1 with the auxiliary potassium channel subunit KCNE2 was shown to reduce pituitary hormone secretion in functional experiments. Here, we investigated if germline mutations in KCNQ1 and KCNE2 were present in patients with somatotropinomas, which represent a model of growth hormone excess. Design and methods: KCNQ1 and KCNE2 were screened for germline mutations in 53 patients with acromegaly by Sanger sequencing. Effects of the variants were predicted by in silico tools. Results: Only deep intronic and synonymous polymorphisms were detected in KCNQ1. These findings were likely insignificant based on in silico predictions and the variants' frequencies in the general population. In KCNE2, a heterozygous c.22A>G, p.(Thr8Ala) mutation with unknown significance was found in three patients. It was present in the database controls with a frequency of 0.0038. Conclusions: KCNQ1 or KCNE2 mutations do not appear to account for somatotropinoma formation, although larger patient series are needed to validate the findings. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

European journal of endocrinology, Nov 1, 2009

Objective: Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) were recently sho... more Objective: Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) were recently shown to confer a pituitary adenoma predisposition in patients with familial isolated pituitary adenomas (FIPA). We report a large Samoan FIPA kindred from Australia/New Zealand with an R271W mutation that was associated with aggressive pituitary tumors. Design and methods: Case series with germline screening of AIP and haplotype analyses among R271W families. Results: This previously unreported kindred consisted of three affected individuals that either presented with or had first symptoms of a pituitary macroadenoma in late childhood or adolescence. The index case, a 15-year-old male with incipient gigantism and his maternal aunt, had somatotropinomas, and the maternal uncle of the index case had a prolactinoma. All tumors were large (15, 40, and 60 mm maximum diameter) and two required transcranial surgery and radiotherapy. All three affected subjects and ten other unaffected relatives were found to be positive for a germline R271W AIP mutation. Comparison of the single nucleotide polymorphism patterns among this family and two previously reported European FIPA families with the same R271W mutation demonstrated no common ancestry. Conclusions: This kindred exemplifies the aggressive features of pituitary adenomas associated with AIP mutations, while genetic analyses among three R271W FIPA families indicate that R271W represents a mutational hotspot that should be studied further in functional studies.

Gene Expression, Feb 1, 2007

Fumarate hydratase (FH) is an enzyme of the mitochondrial tricarboxylic acid cycle (TCAC). Here w... more Fumarate hydratase (FH) is an enzyme of the mitochondrial tricarboxylic acid cycle (TCAC). Here we report the characterization of a novel FH variant (FHv) that contains an alternative exon 1b, thus lacking the mitochondrial signal sequence. Distinct from mitochondrial FH, FHv localized to cytosol and nucleus and lacked FH enzyme activity. FHv was expressed ubiquitously in human fetal and adult tissues. Heat shock and prolonged hypoxia increased FHv expression in a cell line (HTB115) by nine-and fourfold, respectively. These results suggest that FHv has an alternative function outside the TCAC related to cellular stress response.

Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characteri... more Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characterized; apart from mutations in the stimulatory Gα protein (Gαs encoded by GNAS) causing activated cAMP synthesis, pathogenic variants are rarely found in growth hormone–secreting pituitary tumors (somatotropinomas). The purpose of the current work was to clarify how genetic and epigenetic alterations contribute to the development of somatotropinomas by conducting an integrated copy number alteration, whole-genome and bisulfite sequencing, and transcriptome analysis of 21 tumors. Somatic mutation burden was low, but somatotropinomas formed two subtypes associated with distinct aneuploidy rates and unique transcription profiles. Tumors with recurrent chromosome aneuploidy (CA) were GNAS mutation negative (Gsp−). The chromosome stable (CS) –group contained Gsp+ somatotropinomas and two totally aneuploidy-free Gsp− tumors. Genes related to the mitotic G1–S-checkpoint transition were differentially expressed in CA- and CS-tumors, indicating difference in mitotic progression. Also, pituitary tumor transforming gene 1 (PTTG1), a regulator of sister chromatid segregation, showed abundant expression in CA-tumors. Moreover, somatotropinomas displayed distinct Gsp genotype–specific methylation profiles and expression quantitative methylation (eQTM) analysis revealed that inhibitory Gα (Gαi) signaling is activated in Gsp+ tumors. These findings suggest that aneuploidy through modulated driver pathways may be a causative mechanism for tumorigenesis in Gsp− somatotropinomas, whereas Gsp+ tumors with constitutively activated cAMP synthesis seem to be characterized by DNA methylation activated Gαi signaling.Implications:These findings provide valuable new information about subtype-specific pituitary tumorigenesis and may help to elucidate the mechanisms of aneuploidy also in other tumor types.

Journal of the Endocrine Society, Jul 23, 2019

Context: Parathyroid carcinoma (PC) is extremely rare. Prognosis is poor, with no known evidence-... more Context: Parathyroid carcinoma (PC) is extremely rare. Prognosis is poor, with no known evidence-based systemic therapies. We previously reported complete remission in a patient with metastasized parathyroid carcinoma and high tumor MGMT promoter methylation status who was treated with temozolomide. Objective: To study MGMT promoter methylation status in an additional set of aggressive parathyroid tumors. Design/Setting: The study included 12 patients: 7 with sporadic and 5 with familial primary hyperparathyroidism (two of the latter carried a CDC73 gross deletion). Patient 9 is the previously described patient with PC and high MGMT methylation status. Her daughter (patient 12) had surgery for severe primary hyperparathyroidism due to atypical parathyroid adenoma during pregnancy. Eleven patients thus had PC and one had atypical parathyroid adenoma. MGMT promoter methylation status was determined from DNA extracted from primary (n 5 10) or metastatic (n 5 2) tumors. A mean methylation level .20% was considered high. Patient 11 had metastatic PC and received temozolomide cycles. Results: Only the previously published patient (patient 9) had high tumor MGMT promoter methylation status. This was not a characteristic of the atypical parathyroid adenoma of the daughter (patient 12). Patient 11 (CDC73 intragenic deletion) has disseminated PC, low MGMT promoter methylation, and stable disease on follow-up after temozolomide treatment. Conclusion: High MGMT promoter methylation status seems rare in PC. However, as demonstrated in other neuroendocrine tumors, some patients with disseminated PC might benefit from temozolomide. Demonstration of high methylation status could be a predictor of positive response to temozolomide treatment.

European journal of endocrinology, Feb 1, 2017

Introduction: In sporadic acromegaly, downregulation of AIP protein of the adenomas associates wi... more Introduction: In sporadic acromegaly, downregulation of AIP protein of the adenomas associates with invasive tumor features and reduced responsiveness to somatostatin analogues. AIP is a regulator of Ga i signaling, but it is not known how the biological function of the Ga i pathway is controlled. Aim: To study GNAS and AIP mutation status, AIP and Ga i-2 protein expressions, Ki-67 proliferation indices and clinical parameters in patients having primary surgery because of acromegaly at a single center between years 2000 and 2010. Results: Sixty patients (F/M, 31/29), mean age 49 (median 50), mean follow-up 7.7 years (range 0.6-14.0) underwent primary surgery. Four adenoma specimens (6.8%) harbored an AIP and 21 (35.6%) an activating GNAS (Gsp+) mutation. Altogether 13/56 (23%) adenomas had low AIP protein levels, and 14/56 (25%) low Ga i-2 staining. In regression modeling, AIP expression associated with Ga i-2 (P = 2.33 × 10 −9) and lower Ki-67 (P = 0.04). In pairwise comparison, low AIP protein predicted high GH at last follow-up (mean 7.7 years after surgery, q = 0.045). Extent of treatments given for acromegaly associated with higher preoperative GH (P = 7.94 × 10 −4), KNOSP (P = 0.003) and preoperative hypopituitarism (P = 0.03) and remission at last follow-up with change in 3-month postoperative IGF1 (P = 2.07 × 10 −7). Conclusions: We demonstrate, for the first time, that AIP protein expression associates with Ga i-2 protein intensities in sporadic somatotropinomas, suggesting a joint regulation on somatostatin signaling. Low AIP level associates with higher proliferative activity and predicts high GH concentrations after long-term follow-up. The AIP mutation rate of 6.8% is fairly high, reflecting the genetic composition of the Finnish population.

Oncogene, Apr 10, 2003

We have allelotyped a series of 104 Finnish colorectal cancers (CRCs) using 372 polymorphic marke... more We have allelotyped a series of 104 Finnish colorectal cancers (CRCs) using 372 polymorphic markers spaced, on average, at 10 cM intervals, and have made a comparison of the differences in the frequency of allelic imbalance (AI) between familial and sporadic cases. Differences in the frequency of allelic imbalance (loss of heterozygosity or amplification) at a number of loci were detected and these were evaluated through analysis of additional series of cancers using specific markers. The most consistent difference was observed at chromosome 20q13.1-13.3 characterized by a two fold difference between familial and nonfamilial disease in a total of 99 familial and 186 sporadic Finnish cases. This difference was not observed in a UK set of 67 familial and 96 sporadic CRCs. The genome-wide effort resulted in a large data set giving clues to the location of putative CRC predisposition genes in the genome. The approach provides an alternative strategy for detecting cancer predisposition genes solely reliant on the molecular analysis of single cases obviating the requirement to collect multiple samples from families.

PLOS ONE, Oct 7, 2014

Pituitary adenomas are neoplasms of the anterior pituitary lobe and account for 15-20% of all int... more Pituitary adenomas are neoplasms of the anterior pituitary lobe and account for 15-20% of all intracranial tumors. Although most pituitary tumors are benign they can cause severe symptoms related to tumor size as well as hypopituitarism and/or hypersecretion of one or more pituitary hormones. Most pituitary adenomas are sporadic, but it has been estimated that 5% of patients have a familial background. Germline mutations of the tumor suppressor gene aryl hydrocarbon receptorinteracting protein (AIP) predispose to hereditary pituitary neoplasia. Recently, it has been demonstrated that AIP mutations predispose to pituitary tumorigenesis through defective inhibitory GTP binding protein (Ga i) signaling. This finding prompted us to examine whether germline loss-of-function mutations in inhibitory guanine nucleotide (GTP) binding protein alpha (GNAI) loci are involved in genetic predisposition of pituitary tumors. To our knowledge, this is the first time GNAI genes are sequenced in order to examine the occurrence of inactivating germline mutations. Thus far, only somatic gain-offunction hot-spot mutations have been studied in these loci. Here, we have analyzed the coding regions of GNAI1 , GNAI2, and GNAI3 in a set of young sporadic somatotropinoma patients (n = 32; mean age of diagnosis 32 years) and familial index cases (n = 14), thus in patients with a disease phenotype similar to that observed in AIP mutation carriers. In addition, expression of Ga i proteins was studied in human growth hormone (GH), prolactin (PRL), adrenocorticotropic hormone (ACTH)-secreting and non-functional pituitary tumors. No pathogenic germline mutations affecting the Ga i proteins were detected. The result suggests that loss-of-function mutations of GNAI loci are rare or nonexistent in familial pituitary adenomas.

Oncogene, Oct 9, 2006

Hereditary non-polyposis colorectal cancer (HNPCC) is caused by germline mutations in mismatch re... more Hereditary non-polyposis colorectal cancer (HNPCC) is caused by germline mutations in mismatch repair (MMR) genes, mostly MLH1 and MSH2. Somatic inactivation of the wild-type allele of the respective MMR gene is required for tumor development. Unexpectedly, a recent study utilizing DNA from paraffin-embedded tissue material detected frequent loss of the mutant MMR gene allele in HNPCC tumors. Dual role for loss of heterozygosity (LOH) was proposed. If somatic loss of the wild-type MMR gene allele had occurred through point mutation or promoter hypermethylation, frequent somatic deletions at the region of the MMR gene locus, perhaps targeting other relevant cancer genes, could quite commonly lead to loss of the mutant allele. To test this hypothesis, we studied a population-based series of 25 fresh-frozen HNPCC tumors with a germline mutation in MLH1 or MSH2 for LOH. Fourteen of the 25 tumors (56%) showed LOH at the respective locus, and all 14 losses targeted the wild-type allele (P ¼ 0.00006). These results strongly support the traditional two-hit model of HNPCC gene inactivation.

International Journal of Cancer, Jun 29, 2010

It is estimated that up to 35% of colorectal cancers (CRC) can be explained by hereditary factors... more It is estimated that up to 35% of colorectal cancers (CRC) can be explained by hereditary factors. However, genes predisposing to highly penetrant CRC syndromes account for only a small fraction of all cases. Thus, most CRCs still remain molecularly unexplained. A recent systematic sequencing study on well-annotated human protein coding genes identified 280 somatically mutated candidate cancer genes (CAN genes) in breast and colorectal cancer. It is estimated that 8% of all reported cancer genes show both somatic and germline mutations. Therefore, the identified CAN genes serve as a distinct set of candidates for being involved in hereditary susceptibility. The aim of this study was to evaluate the role of colorectal CAN genes in familial CRC. Samples from 45 familial CRCs without known cancer predisposing mutations were screened for somatic and germline variants in 15 top-ranked CAN genes. Six of the genes were found to be somatically mutated in our tumor series. We identified 22 nonsynonymous somatic mutations of which the majority was of missense type. In germline, three novel nonsynonymous variants were identified in the following genes: CSMD3, EPHB6 and C10orf137, and none of the variants were present in 890 population-matched healthy controls. It is possible that the identified germline variants modulate predisposition to CRC. Functional validation and larger sample sets, however, will be required to clarify the role of the identified germline variants in CRC susceptibility.

International Journal of Cancer, Jan 15, 2006

In a previous genome-wide effort we identified a novel candidate colorectal cancer (CRC) suscepti... more In a previous genome-wide effort we identified a novel candidate colorectal cancer (CRC) susceptibility locus by allelotyping tumors from familial and sporadic CRC patients. Familial cases harbored amplifications significantly more frequently in 20q13, indicating the presence of a putative oncogene within the amplicon. A kinase-encoding AURKA is located in 20q13 and recently a Phe31Ile (91T > A) change of AURKA was suggested to function as a low penetrance tumor-susceptibility factor. Association analysis suggested an increased cancer risk in 91A homozygous individuals. In addition, tumors from heterozygous individuals showed preferential amplification of 91A allele and were more aneuploid, important findings that have not been confirmed to date. To evaluate whether AURKA is a target for the observed 20q13 amplifications, we assessed the frequency of the 91T > A change and possible preferential amplification of either allele in 125 familial and 110 sporadic Finnish CRC cases. We observed a preferential amplification of 91A with a significant difference between the alleles in the familial group (p = 0.03). Furthermore, a trend between younger age at diagnosis and genotype in the familial group was observed (p = 0.06). Other possible AURKA germline variants were screened by sequencing 10 of the familial cases. The frequency and amplification patterns of the observed variants were assessed in a larger set of familial and sporadic CRC but no evidence on tumorigenic role of the other sequence alterations was obtained. Thus our results support the importance of AURKA 91A as a low penetrance CRC susceptibility factor.

Endocrinology, Sep 1, 1997

Gastroenterology, Sep 1, 2013

Microsatellite instability can be found in approximately 15% of all colorectal cancers. To detect... more Microsatellite instability can be found in approximately 15% of all colorectal cancers. To detect new oncogenes we sequenced the exomes of 25 colorectal tumors and respective healthy colon tissue. Potential mutation hot spots were confirmed in 15 genes; ADAR, DCAF12L2, GLT1D1, ITGA7, MAP1B, MRGPRX4, PSRC1, RANBP2, RPS6KL1, SNCAIP, TCEAL6, TUBB6, WBP5, VEGFB, and ZBTB2; these were validated in 86 tumors with microsatellite instability. ZBTB2, RANBP2, and PSRC1 also were found to contain hot spot mutations in the validation set. The form of ZBTB2 associated with colorectal cancer increased cell proliferation. The mutation hot spots might be used to develop personalized tumor profiling and therapy.

The evolution of microsatellites was studied within and between the pine species. Sequences showe... more The evolution of microsatellites was studied within and between the pine species. Sequences showed that microsatellites do not necessarily mutate in a stepwise fashion and that size homoplasy is common due to flanking sequence and repeat area changes within and between the species. Thus, some assumptions of statistical methods based on changes in repeat numbers may not hold. Sequences from cross-species amplifications revealed evidence of duplications of microsatellite loci in pines. On two independent occasions, the repeat area of the microsatellite had undergone a rapid expansion during the last 10-25 million of years. Microsatellite markers were used together with other molecular markers (allozymes, RFLPs, RAPDs, rDNA RFLPs) and an adaptive trait (date of bud set) to study patterns of genetic variation in Scots pine (Pinus sylvestris) in Finland. All molecular markers showed high level of within population variation, while differentiation among populations was low (F ST = 0.02). Of the total variation in bud set, 36.4 % was found among the populations which experience a steep climatic gradient. Thus, the markers applied were poor predictors of population differentiation of the quantitative trait studied The distribution of genetic variation was studied in five natural populations of radiata pine (Pinus radiata), species which has gone through bottlenecks in the past. Null allele frequencies were estimated and used in later analyses. Microsatellites showed high level of variability within populations (H e = 0.68-0.77). Allele length distributions and average number of alleles per locus showed some traces of bottlenecks. Instead, comparison of observed genetic diversities and expected diversities suggested post-bottleneck expansion of populations. Genetic differentiation (F ST and R ST) among populations was over 10 %, reflecting situation in the isolated radiata pine populations. Using microsatellites and a newly developed Bayesian method, individual inbreeding coefficients were estimated in five populations of radiata pine. Most individuals were outbred while some were selfed. Presumably, in ancestral radiata pine populations the recessive deleterious alleles have been eliminated after bottlenecks and the mating system has changed as a consequence.

International Journal of Cancer, Sep 10, 2020

Pituitary adenomas (PAs) are intracranial tumors associated with significant morbidity due to hor... more Pituitary adenomas (PAs) are intracranial tumors associated with significant morbidity due to hormonal dysregulation, mass effects and have a heavy treatment burden. Growth hormone (GH)-secreting PAs (somatotropinomas) cause acromegaly-gigantism. Genetic forms of somatotropinomas due to germline AIP mutations (AIPmut+) have an early onset and are aggressive and resistant to treatment with somatostatin analogs (SSAs), including octreotide. The molecular underpinnings of these clinical features remain unclear. We investigated the role of miRNA dysregulation in AIPmut + vs AIPmut− PA samples by array analysis. miR-34a and miR-145 were highly expressed in AIPmut+ vs AIPmut− somatotropinomas. Ectopic expression of AIPmut (p.R271W) in Aip −/− mouse embryonic fibroblasts (MEFs) upregulated miR-34a and miR-145, establishing a causal link between AIPmut and miRNA expression. In PA cells (GH3), miR-34a overexpression promoted proliferation, clonogenicity, migration and suppressed apoptosis, whereas miR-145 moderately affected proliferation and apoptosis. Moreover, high miR-34a expression increased intracellular cAMP, a critical mitogenic factor in PAs. Crucially, high miR-34a expression significantly blunted octreotide-mediated GH inhibition and antiproliferative effects. miR-34a directly targets Gnai2 encoding Gαi2, a G protein subunit inhibiting cAMP production. Accordingly, Gαi2 levels were significantly lower in AIPmut+ vs AIPmut− PA. Taken together, somatotropinomas with AIP mutations overexpress miR-34a, which in turn

Molecular Cancer Research, Dec 1, 2019

Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characteri... more Somatic driver mechanisms of pituitary adenoma pathogenesis have remained incompletely characterized; apart from mutations in the stimulatory Ga protein (Ga s encoded by GNAS) causing activated cAMP synthesis, pathogenic variants are rarely found in growth hormone-secreting pituitary tumors (somatotropinomas). The purpose of the current work was to clarify how genetic and epigenetic alterations contribute to the development of somatotropinomas by conducting an integrated copy number alteration, whole-genome and bisulfite sequencing, and transcriptome analysis of 21 tumors. Somatic mutation burden was low, but somatotropinomas formed two subtypes associated with distinct aneuploidy rates and unique transcription profiles. Tumors with recurrent chromosome aneuploidy (CA) were GNAS mutation negative (Gsp À). The chromosome stable (CS)-group contained Gsp þ somatotropinomas and two totally aneuploidy-free Gsp À tumors. Genes related to the mitotic G 1-S-checkpoint transition were differentially expressed in CA-and CS-tumors, indicating difference in mitotic progression. Also, pituitary tumor transforming gene 1 (PTTG1), a regulator of sister chromatid segregation, showed abundant expression in CA-tumors. Moreover, somatotropinomas displayed distinct Gsp genotypespecific methylation profiles and expression quantitative methylation (eQTM) analysis revealed that inhibitory Ga (Ga i) signaling is activated in Gsp þ tumors. These findings suggest that aneuploidy through modulated driver pathways may be a causative mechanism for tumorigenesis in Gsp À somatotropinomas, whereas Gsp þ tumors with constitutively activated cAMP synthesis seem to be characterized by DNA methylation activated Ga i signaling. Implications: These findings provide valuable new information about subtype-specific pituitary tumorigenesis and may help to elucidate the mechanisms of aneuploidy also in other tumor types.

BMC Cancer, Sep 17, 2008

Background: MYH11 (also known as SMMHC) encodes the smooth-muscle myosin heavy chain, which has a... more Background: MYH11 (also known as SMMHC) encodes the smooth-muscle myosin heavy chain, which has a key role in smooth muscle contraction. Inversion at the MYH11 locus is one of the most frequent chromosomal aberrations found in acute myeloid leukemia. We have previously shown that MYH11 mutations occur in human colorectal cancer, and may also be associated with Peutz-Jeghers syndrome. The mutations found in human intestinal neoplasia result in unregulated proteins with constitutive motor activity, similar to the mutant myh11 underlying the zebrafish meltdown phenotype characterized by disrupted intestinal architecture. Recently, MYH1 and MYH9 have been identified as candidate breast cancer genes in a systematic analysis of the breast cancer genome. Methods: The aim of this study was to investigate the role of somatic MYH11 mutations in two common tumor types; breast and prostate cancers. A total of 155 breast cancer and 71 prostate cancer samples were analyzed for those regions in MYH11 (altogether 8 exons out of 42 coding exons) that harboured mutations in colorectal cancer in our previous study. Results: In breast cancer samples only germline alterations were observed. One prostate cancer sample harbored a frameshift mutation c.5798delC, which we have previously shown to result in a protein with unregulated motor activity. Conclusion: Little evidence for a role of somatic MYH11 mutations in the formation of breast or prostate cancers was obtained in this study.

PubMed, 2003

Mutations in the currently known mismatch repair genes cannot explain all cases of hereditary non... more Mutations in the currently known mismatch repair genes cannot explain all cases of hereditary nonpolyposis colorectal cancer (HNPCC), and novel predisposing genes are actively sought. Recently, mutations in the DNA repair gene EXO1 have been implicated in HNPCC. One truncating and several missense changes were observed in familial colorectal cancer (CRC) cases but not in controls. We evaluated a series of European CRC patients and population controls to clarify whether EXO1 variants may indeed predispose to familial CRC. Several variants observed in patients were also observed in controls with similar frequencies, including the truncating variant proposed previously to be a disease-causing mutation. Thus, little evidence was obtained to support a major causative role of EXO1 in HNPCC, although we cannot exclude a role for EXO1 as a low penetrance cancer susceptibility or modifying gene.

American Journal of Pathology, Dec 1, 2009

Germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene predispose to ... more Germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene predispose to the development of pituitary adenomas. Here, we characterized AIP mutation positive (AIPmut؉) and AIP mutation negative (AIPmut؊) pituitary adenomas by immunohistochemistry. The expressions of the AIPrelated proteins aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT), cyclin-dependent kinase inhibitor 1B encoding p27(Kip1), and hypoxiainducible factor 1-␣ were examined in 14 AIPmut؉ and 53 AIPmut؊ pituitary adenomas to detect possible expression differences. In addition, the expression of CD34, an endothelial and hematopoietic stem cell marker, was analyzed. We found ARNT to be less frequently expressed in AIPmut؉ pituitary adenomas (P ‫؍‬ 0.001), suggesting that AIP regulates the ARNT levels. AIP small interfering RNA-treated HeLa, HEK293, or Aip-null mouse embryonic fibroblast cells did not show lowered expression of ARNT. Instead, in the pituitary adenoma cell line GH3, Aip silencing caused a partial reduction of Arnt and a clear increase in cell proliferation. We also observed a trend for increased expression of nuclear AHR in AIPmut؉ samples , although the difference was not statistically significant (P ‫؍‬ 0.06). The expressions of p27(Kip1), hypoxia-inducible factor 1-␣, or CD34 did not differ between tumor types. The present study shows that the expression of ARNT protein is significantly reduced in AIPmut؉ tumors. We suggest that the downregulation of ARNT may be connected to an imbalance in AHR/ARNT complex formation arising from aberrant cAMP signaling.