Jarle Bruun | Oslo University Hospital, Norwegian Radiumhospitalet (original) (raw)

Papers by Jarle Bruun

Research paper thumbnail of Phosphorylation of the Transactivation Domain of Pax6 by Extracellular Signal-regulated Kinase and p38 Mitogen-activated Protein Kinase

The Journal of Biological Chemistry, May 21, 1999

The transcription factor Pax6 is required for normal development of the central nervous system, t... more The transcription factor Pax6 is required for normal development of the central nervous system, the eyes, nose, and pancreas. Here we show that the transactivation domain (TAD) of zebrafish Pax6 is phosphorylated in vitro by the mitogen-activated protein kinases (MAPKs) extracellular-signal regulated kinase (ERK) and p38 kinase but not by Jun N-terminal kinase (JNK). Three of four putative proline-dependent kinase phosphorylation sites are phosphorylated in vitro. Of these sites, the serine 413 (Ser 413 ) is evolutionary conserved from sea urchin to man. Ser 413 is also phosphorylated in vivo upon activation of ERK or p38 kinase. Substitution of Ser 413 with alanine strongly decreased the transactivation potential of the Pax6 TAD whereas substitution with glutamate increased the transactivation. Reporter gene assays with wild-type and mutant Pax6 revealed that transactivation by the full-length Pax6 protein from paired domain-binding sites was strongly enhanced (16-fold) following co-transfection with activated p38 kinase. This enhancement was largely dependent on the Ser 413 site. ERK activation, however, produced a 3-fold increase in transactivation which was partly independent of the Ser 413 site. These findings provide a starting point for further studies aimed at elucidating a post-translational regulation of Pax6 following activation of MAPK signaling pathways.

Research paper thumbnail of 540 Post-translational mechanisms involved in downregulation of the gap junction protein Connexin43 in colorectal cancer

European Journal of Cancer Supplements, 2010

Tamoxifen resistance and tamoxifen agonistic effect were induced mainly via ERK pathway activatio... more Tamoxifen resistance and tamoxifen agonistic effect were induced mainly via ERK pathway activation, while the PI3K pathway is linked to cell proliferation. Conclusions: Our data provided the first evidence for the causal role of IGF-1R signaling in acquired anti-estrogen resistance and agonistic action of tamoxifen in human breast cancer cells.

Research paper thumbnail of MiR-9, -31, and -182 deregulation promote proliferation and tumor cell survival in colon cancer

Neoplasia (New York, N.Y.), 2012

Several microRNAs (miRNAs) are known to be deregulated in colon cancer, but the mechanisms behind... more Several microRNAs (miRNAs) are known to be deregulated in colon cancer, but the mechanisms behind their potential involvement on proliferation and tumor cell survival are unclear. The present study aimed to identify miRNAs with functional implications for development of colon cancer. The cell proliferation and apoptosis were examined following perturbations of miRNA levels by employing a comprehensive miRNA library screen. miRNAs nominated for relevance to colon cancer were validated on expression and functional levels. By integrating the effect of miRNA up-regulation with the endogenous miRNA expression levels within the HT29, HCT116, and SW480 colon cancer cell lines, we identified miRNAs controlling cell proliferation (n = 53) and apoptosis (n = 93). From these functionally nominated miRNAs, we narrowed the list to 10 oncogene- and 20 tumor suppressor-like miRNAs that were also differentially expressed between colon cancer (n = 80) and normal colonic mucosa (n = 20). The differen...

Research paper thumbnail of Smad ubiquitination regulatory factor-2 controls gap junction intercellular communication by modulating endocytosis and degradation of connexin43

Journal of Cell Science, 2012

Gap junctions consist of arrays of intercellular channels that enable adjacent cells to communica... more Gap junctions consist of arrays of intercellular channels that enable adjacent cells to communicate both electrically and metabolically. Gap junction channels are made of a family of integral membrane proteins called connexins, of which the best-studied member is connexin43. Gap junctions are dynamic plasma membrane domains, and connexin43 has a high turnover rate in most tissue types. However, the mechanisms involved in the regulation of connexin43 endocytosis and transport to lysosomes are still poorly understood. Here, we demonstrate by live-cell imaging analysis that treatment of cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) induces endocytosis of subdomains of connexin43 gap junctions. The internalized, connexin43-enriched vesicles were found to fuse with early endosomes, which was followed by transport of connexin43 to the lumen of early endosomes. The HECT E3 ubiquitin ligase smad ubiquitination regulatory factor-2 (Smurf2) was found to be recruited to connexin43 gap junctions in response to TPA treatment. Depletion of Smurf2 by small interfering RNA resulted in enhanced levels of connexin43 gap junctions between adjacent cells and increased gap junction intercellular communication. Smurf2 depletion also counteracted the TPA-induced endocytosis and degradation of connexin43. Collectively, these data identify Smurf2 as a novel regulator of connexin43 gap junctions.

Research paper thumbnail of The Gap Junction Channel Protein Connexin 43 Is Covalently Modified and Regulated by SUMOylation

Journal of Biological Chemistry, 2012

Background: Gap junctions are intercellular plasma membrane domains enriched in channels that pro... more Background: Gap junctions are intercellular plasma membrane domains enriched in channels that provide direct communication between adjacent cells. Results: The gap junction channel protein connexin 43 is posttranslationally modified by SUMOylation. Conclusion: SUMOylation of connexin 43 is a novel mechanism for regulating gap junctions. Significance: The study has important implications for understanding how gap junctions are regulated under normal and pathological conditions. gian Research Council. . The abbreviations used are: Cx43, connexin43; SUMO, small ubiquitin-related modifier; SENP, SUMO/sentrin-specific peptidase.

Research paper thumbnail of Connexins in colorectal cancer pathogenesis

International Journal of Cancer, 2014

The connexins constitute a family of integral membrane proteins that form channels between adjace... more The connexins constitute a family of integral membrane proteins that form channels between adjacent cells. These channels are assembled in plasma membrane domains known as gap junctions and enable cells to directly exchange ions and small molecules. Intercellular communication via gap junctions plays important roles in regulating cell growth and differentiation and in maintaining tissue homeostasis. This type of cell communication is often impaired during cancer development, and several members of the connexin protein family have been shown to act as tumor suppressors. Emerging evidence suggests that the connexin protein family has important roles in colorectal cancer development. In the normal colonic epithelial tissue, three connexin isoforms, connexin 26 (Cx26), Cx32 and Cx43, have been shown to be expressed at the protein level. Colorectal cancer development is associated with loss of connexin expression or relocalization of connexins from the plasma membrane to intracellular compartments. Downregulation of connexins in colorectal carcinomas at the transcriptional level involves cancerspecific promoter hypermethylation. Recent studies suggest that Cx43 may constrain growth of colon cancer cells by interfering with the Wnt/b-catenin pathway. There is also increasing evidence that the connexins may have potential as prognostic markers in colorectal cancer. This review discusses the role of connexins in colorectal cancer pathogenesis, as well as their potential as prognostic markers and targets in the prevention and treatment of the disease.

Research paper thumbnail of A novel transcript, VNN1-AB , as a biomarker for colorectal cancer

International Journal of Cancer, 2014

Colorectal cancer is a global health challenge with high incidence rate and mortality. The patien... more Colorectal cancer is a global health challenge with high incidence rate and mortality. The patients' prognosis is strongly associated with disease stage and currently there is a need for improved prognostic and predictive biomarkers. In this study, novel colorectal cancer-specific transcript structures were nominated from whole transcriptome sequencing of seven colorectal cancer cell lines, two primary colorectal carcinomas with corresponding normal colonic mucosa and 16 normal tissues. The nominated transcripts were combined with gene level outlier expression analyses in a cohort of 505 colorectal cancers to identify biomarkers with capacity to stratify colorectal cancer subgroups. The transcriptome sequencing data and outlier expression analysis revealed 11 novel colorectal cancer-specific exon-exon junctions, of which 3 were located in the gene VNN1. The junctions within VNN1 were further characterized using rapid amplification of cDNA ends (RACE) and the prevalence of the subsequently characterized novel transcript, VNN1-AB, was investigated by real-time RT-PCR in 291 samples of miscellaneous origins. VNN1-AB was not present in any of the 43 normal colorectal tissue samples investigated, but in 5 of the 6 polyps, and 102 of the 136 (75%) colorectal cancers. We have identified a novel transcript of the VNN1 gene, with an organ-confined complete specificity for colorectal neoplasia.

Research paper thumbnail of Connexin43 acts as a colorectal cancer tumor suppressor and predicts disease outcome

International Journal of Cancer, 2012

This article is the first to show that loss of connexin43 (Cx43) expression in colorectal tumors ... more This article is the first to show that loss of connexin43 (Cx43) expression in colorectal tumors is correlated with significantly shorter relapse-free and overall survival. Cx43 was further found to negatively regulate growth of colon cancer cells, in part by enhancing apoptosis. In addition, Cx43 was found to colocalize with b-catenin and reduce Wnt signaling. The study represents the first evidence that Cx43 acts as a colorectal cancer tumor suppressor and that loss of Cx43 expression during colorectal cancer development is associated with reduced patient survival. The study has important implications for the assessment of Cx43 as a prognostic marker and target in colorectal cancer prevention and therapy. Gap junctions consist of intercellular channels that permit direct transfer of ions and small molecules between adjacent cells. The gap junction channel protein Cx43 plays important roles in cell growth control and differentiation and is frequently dysregulated in human cancers. However, the functional importance and clinical relevance of Cx43 in cancer development has remained elusive. Here, we show that Cx43 is downregulated or aberrantly localized in colon cancer cell lines and colorectal carcinomas, which is associated with loss of gap junction intercellular communication. The in situ protein expression of Cx43 was analyzed in colorectal tumors in a cohort of 674 patients and related to established clinicopathological variables and survival. A subgroup of the patients had weak or no expression of Cx43 in tumors. Loss of Cx43 expression was significantly correlated with shorter relapse-free and overall survival. Loss of Cx43 further identified a high-risk subgroup among stage I and stage II patients with reduced relapse-free and overall survival. Ectopic expression of Cx43 in the colon cancer cell line HT29 was associated with reduced growth in monolayer and soft agar cultures and in tumor xenografts. Cx43 was found to colocalize with b-catenin and negatively regulate the Wnt signaling pathway, and expression of Cx43 was associated with increased levels of apoptosis. Altogether, these data indicate that Cx43 is a colorectal cancer tumor suppressor protein that predicts clinical outcome.

Research paper thumbnail of 508 Identification of Fusion Transcripts in Colorectal Cancer by Combined RNA-seq and Exon Microarray Analyses

European Journal of Cancer, 2012

Research paper thumbnail of Antibody crossreactivity between the tumour suppressor PHLPP1 and the proto-oncogene β-catenin

Research paper thumbnail of NEDD4 is overexpressed in colorectal cancer and promotes colonic cell growth independently of the PI3K/PTEN/AKT pathway

Cellular Signalling, 2013

Colorectal cancer NEDD4 PI3K AKT PTEN Ubiquitin Ubiquitination controls multiple cellular process... more Colorectal cancer NEDD4 PI3K AKT PTEN Ubiquitin Ubiquitination controls multiple cellular processes relevant to cancer pathogenesis. Using Gene Set Enrichment Analysis of an mRNA transcriptome dataset, we have identified genes encoding components of the ubiquitin system that are differentially expressed in colorectal cancers as compared to normal colonic mucosa. Among the significantly overexpressed genes was NEDD4 (neural precursor cell-expressed developmentally down-regulated 4), the prototype member of the HECT (homologous to E6AP C-terminus) E3 ubiquitin ligase family. Previous studies have shown that NEDD4 may act as an oncoprotein by inducing ubiquitination and degradation of the tumor suppressor protein PTEN (phosphatase and tensin homolog). To investigate its functional importance in colorectal cancer, HCT-15 and LoVo colon cancer cells were depleted of NEDD4 by small interfering RNA. The depletion resulted in reduced growth and altered cell morphology in both cell lines. However, NEDD4 depletion did not affect the PTEN protein level or PI3K/AKT signaling pathway activation. Moreover, ectopic expression of NEDD4 did not influence the PTEN subcellular localization or protein level. Collectively, these data demonstrate that NEDD4 is overexpressed in colorectal cancers, and suggest that NEDD4 promotes growth of colon cancer cells independently of PTEN and PI3K/AKT signaling.

Research paper thumbnail of Common fusion transcripts identified in colorectal cancer cell lines by high-throughput RNA sequencing

Translational Oncology, 2013

Colorectal cancer (CRC) is the third most common cancer disease in the Western world, and about 4... more Colorectal cancer (CRC) is the third most common cancer disease in the Western world, and about 40% of the patients die from this disease. The cancer cells are commonly genetically unstable, but only a few low-frequency recurrent fusion genes have so far been reported for this disease. In this study, we present a thorough search for novel fusion transcripts in CRC using high-throughput RNA sequencing. From altogether 220 million paired-end sequence reads from seven CRC cell lines, we identified 3391 candidate fused transcripts. By stringent requirements, we nominated 11 candidate fusion transcripts for further experimental validation, of which 10 were positive by reverse transcription-polymerase chain reaction and Sanger sequencing. Six were intrachromosomal fusion transcripts, and interestingly, three of these, AKAP13-PDE8A, COMMD10-AP3S1, and CTB-35F21.1-PSD2, were present 20 of 21 analyzed cell lines and in, respectively, 18, 61, and 48 (17%-58%) of 106 primary cancer tissues. These three fusion transcripts were also detected in 2 to 4 of 14 normal colonic mucosa samples (14%-28%). Whole-genome sequencing identified a specific genomic breakpoint in COMMD10-AP3S1 and further indicates that both the COMMD10-AP3S1 and AKAP13-PDE8A fusion transcripts are due to genomic duplications in specific cell lines. In conclusion, we have identified AKAP13-PDE8A, COMMD10-AP3S1, and CTB-35F21.1-PSD2 as novel intrachromosomal fusion transcripts and the most highly recurring chimeric transcripts described for CRC to date. The functional and clinical relevance of these chimeric RNA molecules remains to be elucidated.

Research paper thumbnail of Prognostic Significance of β-Catenin, E-Cadherin, and SOX9 in Colorectal Cancer: Results from a Large Population-Representative Series

Frontiers in oncology, 2014

Robust biomarkers that can precisely stratify patients according to treatment needs are in great ... more Robust biomarkers that can precisely stratify patients according to treatment needs are in great demand. The literature is inconclusive for most reported prognostic markers for colorectal cancer (CRC). Hence, adequately reported studies in large representative series are necessary to determine their clinical potential. We investigated the prognostic value of three Wnt signaling-associated proteins, β-catenin, E-cadherin, and SOX9, in a population-representative single-hospital series of 1290 Norwegian CRC patients by performing immunohistochemical analyses of each marker using the tissue microarray technology. Loss of membranous or cytosolic β-catenin and loss of cytosolic E-cadherin protein expression were significantly associated with reduced 5-year survival in 903 patients who underwent major resection (722 evaluable tissue cores) independently of standard clinicopathological high-risk parameters. Pre-specified subgroup analyses demonstrated particular effect for stage IV patient...

Research paper thumbnail of Regulator of chromosome condensation 2 identifies high-risk patients within both major phenotypes of colorectal cancer

Clinical cancer research : an official journal of the American Association for Cancer Research, Jan 24, 2015

Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite ... more Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite instable (MSI) tumors have significantly better prognosis than patients with microsatellite stable (MSS) tumors. Considerable variation in disease outcome remains a challenge within each subgroup, and our purpose was to identify biomarkers that improve prediction of CRC prognosis. Mutation analyses of 42 MSI target genes were performed in two independent MSI tumor series (n=209). Markers that were significantly associated with prognosis in the Test series were assessed in the Validation series, followed by functional and genetic explorations. The clinical potential was further investigated by immunohistochemistry in a population-based CRC series (n=903). We identified the cell cycle gene Regulator of Chromosome Condensation 2 (RCC2) as a cancer biomarker. We found a mutation in the 5'UTR region of RCC2 that in univariate and multivariate analyses was significantly associated with imp...

Research paper thumbnail of Exome Sequencing of Bilateral Testicular Germ Cell Tumors Suggests Independent Development Lineages

Neoplasia, 2015

Intratubular germ cell neoplasia, the precursor of testicular germ cell tumors (TGCTs), is hypoth... more Intratubular germ cell neoplasia, the precursor of testicular germ cell tumors (TGCTs), is hypothesized to arise during embryogenesis from developmentally arrested primordial germ cells (PGCs) or gonocytes. In early embryonal life, the PGCs migrate from the yolk sac to the dorsal body wall where the cell population separates before colonizing the genital ridges. However, whether the malignant transformation takes place before or after this separation is controversial. We have explored the somatic exome-wide mutational spectra of bilateral TGCT to provide novel insight into the in utero critical time frame of malignant transformation and TGCT pathogenesis. Exome sequencing was performed in five patients with bilateral TGCT (eight tumors), of these three patients in whom both tumors were available (six tumors) and two patients each with only one available tumor (two tumors). Selected loci were explored by Sanger sequencing in 71 patients with bilateral TGCT. From the exome-wide mutational spectra, no identical mutations in any of the three bilateral tumor pairs were identified. Exome sequencing of all eight tumors revealed 87 somatic non-synonymous mutations (median 10 per tumor; range 5-21), some in already known cancer genes such as CIITA, NEB, platelet-derived growth factor receptor α (PDGFRA), and WHSC1. SUPT6H was found recurrently mutated in two tumors. We suggest independent development lineages of bilateral TGCT. Thus, malignant transformation into intratubular germ cell neoplasia is likely to occur after the migration of PGCs. We reveal possible drivers of TGCT pathogenesis, such as mutated PDGFRA, potentially with therapeutic implications for TGCT patients.

Research paper thumbnail of Regulator of chromosome condensation 2 identifies high-risk patients within both major phenotypes of colorectal cancer

Clinical cancer research : an official journal of the American Association for Cancer Research, Jan 24, 2015

Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite ... more Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite instable (MSI) tumors have significantly better prognosis than patients with microsatellite stable (MSS) tumors. Considerable variation in disease outcome remains a challenge within each subgroup, and our purpose was to identify biomarkers that improve prediction of CRC prognosis. Mutation analyses of 42 MSI target genes were performed in two independent MSI tumor series (n=209). Markers that were significantly associated with prognosis in the Test series were assessed in the Validation series, followed by functional and genetic explorations. The clinical potential was further investigated by immunohistochemistry in a population-based CRC series (n=903). We identified the cell cycle gene Regulator of Chromosome Condensation 2 (RCC2) as a cancer biomarker. We found a mutation in the 5'UTR region of RCC2 that in univariate and multivariate analyses was significantly associated with imp...

Research paper thumbnail of Prognostic Significance of β-Catenin, E-Cadherin, and SOX9 in Colorectal Cancer: Results from a Large Population-Representative Series

Frontiers in oncology, 2014

Robust biomarkers that can precisely stratify patients according to treatment needs are in great ... more Robust biomarkers that can precisely stratify patients according to treatment needs are in great demand. The literature is inconclusive for most reported prognostic markers for colorectal cancer (CRC). Hence, adequately reported studies in large representative series are necessary to determine their clinical potential. We investigated the prognostic value of three Wnt signaling-associated proteins, β-catenin, E-cadherin, and SOX9, in a population-representative single-hospital series of 1290 Norwegian CRC patients by performing immunohistochemical analyses of each marker using the tissue microarray technology. Loss of membranous or cytosolic β-catenin and loss of cytosolic E-cadherin protein expression were significantly associated with reduced 5-year survival in 903 patients who underwent major resection (722 evaluable tissue cores) independently of standard clinicopathological high-risk parameters. Pre-specified subgroup analyses demonstrated particular effect for stage IV patient...

Research paper thumbnail of Inhibition of connexin43 gap junction channels by the endocrine disruptor ioxynil

Toxicology and Applied Pharmacology, 2010

Research paper thumbnail of Phosphorylation of the Transactivation Domain of Pax6 by Extracellular Signal-regulated Kinase and p38 Mitogen-activated Protein Kinase

The Journal of Biological Chemistry, May 21, 1999

The transcription factor Pax6 is required for normal development of the central nervous system, t... more The transcription factor Pax6 is required for normal development of the central nervous system, the eyes, nose, and pancreas. Here we show that the transactivation domain (TAD) of zebrafish Pax6 is phosphorylated in vitro by the mitogen-activated protein kinases (MAPKs) extracellular-signal regulated kinase (ERK) and p38 kinase but not by Jun N-terminal kinase (JNK). Three of four putative proline-dependent kinase phosphorylation sites are phosphorylated in vitro. Of these sites, the serine 413 (Ser 413 ) is evolutionary conserved from sea urchin to man. Ser 413 is also phosphorylated in vivo upon activation of ERK or p38 kinase. Substitution of Ser 413 with alanine strongly decreased the transactivation potential of the Pax6 TAD whereas substitution with glutamate increased the transactivation. Reporter gene assays with wild-type and mutant Pax6 revealed that transactivation by the full-length Pax6 protein from paired domain-binding sites was strongly enhanced (16-fold) following co-transfection with activated p38 kinase. This enhancement was largely dependent on the Ser 413 site. ERK activation, however, produced a 3-fold increase in transactivation which was partly independent of the Ser 413 site. These findings provide a starting point for further studies aimed at elucidating a post-translational regulation of Pax6 following activation of MAPK signaling pathways.

Research paper thumbnail of 540 Post-translational mechanisms involved in downregulation of the gap junction protein Connexin43 in colorectal cancer

European Journal of Cancer Supplements, 2010

Tamoxifen resistance and tamoxifen agonistic effect were induced mainly via ERK pathway activatio... more Tamoxifen resistance and tamoxifen agonistic effect were induced mainly via ERK pathway activation, while the PI3K pathway is linked to cell proliferation. Conclusions: Our data provided the first evidence for the causal role of IGF-1R signaling in acquired anti-estrogen resistance and agonistic action of tamoxifen in human breast cancer cells.

Research paper thumbnail of MiR-9, -31, and -182 deregulation promote proliferation and tumor cell survival in colon cancer

Neoplasia (New York, N.Y.), 2012

Several microRNAs (miRNAs) are known to be deregulated in colon cancer, but the mechanisms behind... more Several microRNAs (miRNAs) are known to be deregulated in colon cancer, but the mechanisms behind their potential involvement on proliferation and tumor cell survival are unclear. The present study aimed to identify miRNAs with functional implications for development of colon cancer. The cell proliferation and apoptosis were examined following perturbations of miRNA levels by employing a comprehensive miRNA library screen. miRNAs nominated for relevance to colon cancer were validated on expression and functional levels. By integrating the effect of miRNA up-regulation with the endogenous miRNA expression levels within the HT29, HCT116, and SW480 colon cancer cell lines, we identified miRNAs controlling cell proliferation (n = 53) and apoptosis (n = 93). From these functionally nominated miRNAs, we narrowed the list to 10 oncogene- and 20 tumor suppressor-like miRNAs that were also differentially expressed between colon cancer (n = 80) and normal colonic mucosa (n = 20). The differen...

Research paper thumbnail of Smad ubiquitination regulatory factor-2 controls gap junction intercellular communication by modulating endocytosis and degradation of connexin43

Journal of Cell Science, 2012

Gap junctions consist of arrays of intercellular channels that enable adjacent cells to communica... more Gap junctions consist of arrays of intercellular channels that enable adjacent cells to communicate both electrically and metabolically. Gap junction channels are made of a family of integral membrane proteins called connexins, of which the best-studied member is connexin43. Gap junctions are dynamic plasma membrane domains, and connexin43 has a high turnover rate in most tissue types. However, the mechanisms involved in the regulation of connexin43 endocytosis and transport to lysosomes are still poorly understood. Here, we demonstrate by live-cell imaging analysis that treatment of cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) induces endocytosis of subdomains of connexin43 gap junctions. The internalized, connexin43-enriched vesicles were found to fuse with early endosomes, which was followed by transport of connexin43 to the lumen of early endosomes. The HECT E3 ubiquitin ligase smad ubiquitination regulatory factor-2 (Smurf2) was found to be recruited to connexin43 gap junctions in response to TPA treatment. Depletion of Smurf2 by small interfering RNA resulted in enhanced levels of connexin43 gap junctions between adjacent cells and increased gap junction intercellular communication. Smurf2 depletion also counteracted the TPA-induced endocytosis and degradation of connexin43. Collectively, these data identify Smurf2 as a novel regulator of connexin43 gap junctions.

Research paper thumbnail of The Gap Junction Channel Protein Connexin 43 Is Covalently Modified and Regulated by SUMOylation

Journal of Biological Chemistry, 2012

Background: Gap junctions are intercellular plasma membrane domains enriched in channels that pro... more Background: Gap junctions are intercellular plasma membrane domains enriched in channels that provide direct communication between adjacent cells. Results: The gap junction channel protein connexin 43 is posttranslationally modified by SUMOylation. Conclusion: SUMOylation of connexin 43 is a novel mechanism for regulating gap junctions. Significance: The study has important implications for understanding how gap junctions are regulated under normal and pathological conditions. gian Research Council. . The abbreviations used are: Cx43, connexin43; SUMO, small ubiquitin-related modifier; SENP, SUMO/sentrin-specific peptidase.

Research paper thumbnail of Connexins in colorectal cancer pathogenesis

International Journal of Cancer, 2014

The connexins constitute a family of integral membrane proteins that form channels between adjace... more The connexins constitute a family of integral membrane proteins that form channels between adjacent cells. These channels are assembled in plasma membrane domains known as gap junctions and enable cells to directly exchange ions and small molecules. Intercellular communication via gap junctions plays important roles in regulating cell growth and differentiation and in maintaining tissue homeostasis. This type of cell communication is often impaired during cancer development, and several members of the connexin protein family have been shown to act as tumor suppressors. Emerging evidence suggests that the connexin protein family has important roles in colorectal cancer development. In the normal colonic epithelial tissue, three connexin isoforms, connexin 26 (Cx26), Cx32 and Cx43, have been shown to be expressed at the protein level. Colorectal cancer development is associated with loss of connexin expression or relocalization of connexins from the plasma membrane to intracellular compartments. Downregulation of connexins in colorectal carcinomas at the transcriptional level involves cancerspecific promoter hypermethylation. Recent studies suggest that Cx43 may constrain growth of colon cancer cells by interfering with the Wnt/b-catenin pathway. There is also increasing evidence that the connexins may have potential as prognostic markers in colorectal cancer. This review discusses the role of connexins in colorectal cancer pathogenesis, as well as their potential as prognostic markers and targets in the prevention and treatment of the disease.

Research paper thumbnail of A novel transcript, VNN1-AB , as a biomarker for colorectal cancer

International Journal of Cancer, 2014

Colorectal cancer is a global health challenge with high incidence rate and mortality. The patien... more Colorectal cancer is a global health challenge with high incidence rate and mortality. The patients' prognosis is strongly associated with disease stage and currently there is a need for improved prognostic and predictive biomarkers. In this study, novel colorectal cancer-specific transcript structures were nominated from whole transcriptome sequencing of seven colorectal cancer cell lines, two primary colorectal carcinomas with corresponding normal colonic mucosa and 16 normal tissues. The nominated transcripts were combined with gene level outlier expression analyses in a cohort of 505 colorectal cancers to identify biomarkers with capacity to stratify colorectal cancer subgroups. The transcriptome sequencing data and outlier expression analysis revealed 11 novel colorectal cancer-specific exon-exon junctions, of which 3 were located in the gene VNN1. The junctions within VNN1 were further characterized using rapid amplification of cDNA ends (RACE) and the prevalence of the subsequently characterized novel transcript, VNN1-AB, was investigated by real-time RT-PCR in 291 samples of miscellaneous origins. VNN1-AB was not present in any of the 43 normal colorectal tissue samples investigated, but in 5 of the 6 polyps, and 102 of the 136 (75%) colorectal cancers. We have identified a novel transcript of the VNN1 gene, with an organ-confined complete specificity for colorectal neoplasia.

Research paper thumbnail of Connexin43 acts as a colorectal cancer tumor suppressor and predicts disease outcome

International Journal of Cancer, 2012

This article is the first to show that loss of connexin43 (Cx43) expression in colorectal tumors ... more This article is the first to show that loss of connexin43 (Cx43) expression in colorectal tumors is correlated with significantly shorter relapse-free and overall survival. Cx43 was further found to negatively regulate growth of colon cancer cells, in part by enhancing apoptosis. In addition, Cx43 was found to colocalize with b-catenin and reduce Wnt signaling. The study represents the first evidence that Cx43 acts as a colorectal cancer tumor suppressor and that loss of Cx43 expression during colorectal cancer development is associated with reduced patient survival. The study has important implications for the assessment of Cx43 as a prognostic marker and target in colorectal cancer prevention and therapy. Gap junctions consist of intercellular channels that permit direct transfer of ions and small molecules between adjacent cells. The gap junction channel protein Cx43 plays important roles in cell growth control and differentiation and is frequently dysregulated in human cancers. However, the functional importance and clinical relevance of Cx43 in cancer development has remained elusive. Here, we show that Cx43 is downregulated or aberrantly localized in colon cancer cell lines and colorectal carcinomas, which is associated with loss of gap junction intercellular communication. The in situ protein expression of Cx43 was analyzed in colorectal tumors in a cohort of 674 patients and related to established clinicopathological variables and survival. A subgroup of the patients had weak or no expression of Cx43 in tumors. Loss of Cx43 expression was significantly correlated with shorter relapse-free and overall survival. Loss of Cx43 further identified a high-risk subgroup among stage I and stage II patients with reduced relapse-free and overall survival. Ectopic expression of Cx43 in the colon cancer cell line HT29 was associated with reduced growth in monolayer and soft agar cultures and in tumor xenografts. Cx43 was found to colocalize with b-catenin and negatively regulate the Wnt signaling pathway, and expression of Cx43 was associated with increased levels of apoptosis. Altogether, these data indicate that Cx43 is a colorectal cancer tumor suppressor protein that predicts clinical outcome.

Research paper thumbnail of 508 Identification of Fusion Transcripts in Colorectal Cancer by Combined RNA-seq and Exon Microarray Analyses

European Journal of Cancer, 2012

Research paper thumbnail of Antibody crossreactivity between the tumour suppressor PHLPP1 and the proto-oncogene β-catenin

Research paper thumbnail of NEDD4 is overexpressed in colorectal cancer and promotes colonic cell growth independently of the PI3K/PTEN/AKT pathway

Cellular Signalling, 2013

Colorectal cancer NEDD4 PI3K AKT PTEN Ubiquitin Ubiquitination controls multiple cellular process... more Colorectal cancer NEDD4 PI3K AKT PTEN Ubiquitin Ubiquitination controls multiple cellular processes relevant to cancer pathogenesis. Using Gene Set Enrichment Analysis of an mRNA transcriptome dataset, we have identified genes encoding components of the ubiquitin system that are differentially expressed in colorectal cancers as compared to normal colonic mucosa. Among the significantly overexpressed genes was NEDD4 (neural precursor cell-expressed developmentally down-regulated 4), the prototype member of the HECT (homologous to E6AP C-terminus) E3 ubiquitin ligase family. Previous studies have shown that NEDD4 may act as an oncoprotein by inducing ubiquitination and degradation of the tumor suppressor protein PTEN (phosphatase and tensin homolog). To investigate its functional importance in colorectal cancer, HCT-15 and LoVo colon cancer cells were depleted of NEDD4 by small interfering RNA. The depletion resulted in reduced growth and altered cell morphology in both cell lines. However, NEDD4 depletion did not affect the PTEN protein level or PI3K/AKT signaling pathway activation. Moreover, ectopic expression of NEDD4 did not influence the PTEN subcellular localization or protein level. Collectively, these data demonstrate that NEDD4 is overexpressed in colorectal cancers, and suggest that NEDD4 promotes growth of colon cancer cells independently of PTEN and PI3K/AKT signaling.

Research paper thumbnail of Common fusion transcripts identified in colorectal cancer cell lines by high-throughput RNA sequencing

Translational Oncology, 2013

Colorectal cancer (CRC) is the third most common cancer disease in the Western world, and about 4... more Colorectal cancer (CRC) is the third most common cancer disease in the Western world, and about 40% of the patients die from this disease. The cancer cells are commonly genetically unstable, but only a few low-frequency recurrent fusion genes have so far been reported for this disease. In this study, we present a thorough search for novel fusion transcripts in CRC using high-throughput RNA sequencing. From altogether 220 million paired-end sequence reads from seven CRC cell lines, we identified 3391 candidate fused transcripts. By stringent requirements, we nominated 11 candidate fusion transcripts for further experimental validation, of which 10 were positive by reverse transcription-polymerase chain reaction and Sanger sequencing. Six were intrachromosomal fusion transcripts, and interestingly, three of these, AKAP13-PDE8A, COMMD10-AP3S1, and CTB-35F21.1-PSD2, were present 20 of 21 analyzed cell lines and in, respectively, 18, 61, and 48 (17%-58%) of 106 primary cancer tissues. These three fusion transcripts were also detected in 2 to 4 of 14 normal colonic mucosa samples (14%-28%). Whole-genome sequencing identified a specific genomic breakpoint in COMMD10-AP3S1 and further indicates that both the COMMD10-AP3S1 and AKAP13-PDE8A fusion transcripts are due to genomic duplications in specific cell lines. In conclusion, we have identified AKAP13-PDE8A, COMMD10-AP3S1, and CTB-35F21.1-PSD2 as novel intrachromosomal fusion transcripts and the most highly recurring chimeric transcripts described for CRC to date. The functional and clinical relevance of these chimeric RNA molecules remains to be elucidated.

Research paper thumbnail of Prognostic Significance of β-Catenin, E-Cadherin, and SOX9 in Colorectal Cancer: Results from a Large Population-Representative Series

Frontiers in oncology, 2014

Robust biomarkers that can precisely stratify patients according to treatment needs are in great ... more Robust biomarkers that can precisely stratify patients according to treatment needs are in great demand. The literature is inconclusive for most reported prognostic markers for colorectal cancer (CRC). Hence, adequately reported studies in large representative series are necessary to determine their clinical potential. We investigated the prognostic value of three Wnt signaling-associated proteins, β-catenin, E-cadherin, and SOX9, in a population-representative single-hospital series of 1290 Norwegian CRC patients by performing immunohistochemical analyses of each marker using the tissue microarray technology. Loss of membranous or cytosolic β-catenin and loss of cytosolic E-cadherin protein expression were significantly associated with reduced 5-year survival in 903 patients who underwent major resection (722 evaluable tissue cores) independently of standard clinicopathological high-risk parameters. Pre-specified subgroup analyses demonstrated particular effect for stage IV patient...

Research paper thumbnail of Regulator of chromosome condensation 2 identifies high-risk patients within both major phenotypes of colorectal cancer

Clinical cancer research : an official journal of the American Association for Cancer Research, Jan 24, 2015

Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite ... more Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite instable (MSI) tumors have significantly better prognosis than patients with microsatellite stable (MSS) tumors. Considerable variation in disease outcome remains a challenge within each subgroup, and our purpose was to identify biomarkers that improve prediction of CRC prognosis. Mutation analyses of 42 MSI target genes were performed in two independent MSI tumor series (n=209). Markers that were significantly associated with prognosis in the Test series were assessed in the Validation series, followed by functional and genetic explorations. The clinical potential was further investigated by immunohistochemistry in a population-based CRC series (n=903). We identified the cell cycle gene Regulator of Chromosome Condensation 2 (RCC2) as a cancer biomarker. We found a mutation in the 5'UTR region of RCC2 that in univariate and multivariate analyses was significantly associated with imp...

Research paper thumbnail of Exome Sequencing of Bilateral Testicular Germ Cell Tumors Suggests Independent Development Lineages

Neoplasia, 2015

Intratubular germ cell neoplasia, the precursor of testicular germ cell tumors (TGCTs), is hypoth... more Intratubular germ cell neoplasia, the precursor of testicular germ cell tumors (TGCTs), is hypothesized to arise during embryogenesis from developmentally arrested primordial germ cells (PGCs) or gonocytes. In early embryonal life, the PGCs migrate from the yolk sac to the dorsal body wall where the cell population separates before colonizing the genital ridges. However, whether the malignant transformation takes place before or after this separation is controversial. We have explored the somatic exome-wide mutational spectra of bilateral TGCT to provide novel insight into the in utero critical time frame of malignant transformation and TGCT pathogenesis. Exome sequencing was performed in five patients with bilateral TGCT (eight tumors), of these three patients in whom both tumors were available (six tumors) and two patients each with only one available tumor (two tumors). Selected loci were explored by Sanger sequencing in 71 patients with bilateral TGCT. From the exome-wide mutational spectra, no identical mutations in any of the three bilateral tumor pairs were identified. Exome sequencing of all eight tumors revealed 87 somatic non-synonymous mutations (median 10 per tumor; range 5-21), some in already known cancer genes such as CIITA, NEB, platelet-derived growth factor receptor α (PDGFRA), and WHSC1. SUPT6H was found recurrently mutated in two tumors. We suggest independent development lineages of bilateral TGCT. Thus, malignant transformation into intratubular germ cell neoplasia is likely to occur after the migration of PGCs. We reveal possible drivers of TGCT pathogenesis, such as mutated PDGFRA, potentially with therapeutic implications for TGCT patients.

Research paper thumbnail of Regulator of chromosome condensation 2 identifies high-risk patients within both major phenotypes of colorectal cancer

Clinical cancer research : an official journal of the American Association for Cancer Research, Jan 24, 2015

Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite ... more Colorectal cancer (CRC) has high incidence and mortality worldwide. Patients with microsatellite instable (MSI) tumors have significantly better prognosis than patients with microsatellite stable (MSS) tumors. Considerable variation in disease outcome remains a challenge within each subgroup, and our purpose was to identify biomarkers that improve prediction of CRC prognosis. Mutation analyses of 42 MSI target genes were performed in two independent MSI tumor series (n=209). Markers that were significantly associated with prognosis in the Test series were assessed in the Validation series, followed by functional and genetic explorations. The clinical potential was further investigated by immunohistochemistry in a population-based CRC series (n=903). We identified the cell cycle gene Regulator of Chromosome Condensation 2 (RCC2) as a cancer biomarker. We found a mutation in the 5'UTR region of RCC2 that in univariate and multivariate analyses was significantly associated with imp...

Research paper thumbnail of Prognostic Significance of β-Catenin, E-Cadherin, and SOX9 in Colorectal Cancer: Results from a Large Population-Representative Series

Frontiers in oncology, 2014

Robust biomarkers that can precisely stratify patients according to treatment needs are in great ... more Robust biomarkers that can precisely stratify patients according to treatment needs are in great demand. The literature is inconclusive for most reported prognostic markers for colorectal cancer (CRC). Hence, adequately reported studies in large representative series are necessary to determine their clinical potential. We investigated the prognostic value of three Wnt signaling-associated proteins, β-catenin, E-cadherin, and SOX9, in a population-representative single-hospital series of 1290 Norwegian CRC patients by performing immunohistochemical analyses of each marker using the tissue microarray technology. Loss of membranous or cytosolic β-catenin and loss of cytosolic E-cadherin protein expression were significantly associated with reduced 5-year survival in 903 patients who underwent major resection (722 evaluable tissue cores) independently of standard clinicopathological high-risk parameters. Pre-specified subgroup analyses demonstrated particular effect for stage IV patient...

Research paper thumbnail of Inhibition of connexin43 gap junction channels by the endocrine disruptor ioxynil

Toxicology and Applied Pharmacology, 2010