v-Jun downregulates the SPARC target gene by binding to the proximal promoter indirectly through sp1/3 (original) (raw)
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V-Jun is a Transcriptional Activator, but Not in All Cell-Lines
Nucleic Acids Research, 1988
The recently isolated v-jun oncogene encodes a protein with sequence homology to the transcription factor AP1, as well as a similar DNA binding specificity. We show, by expressing v-jun in F9 embryocarcinoma cells, that v-jun is also a transcriptional activator. However, v-jun expression does not activate transcription in several other cell-lines, suggesting that cellspecific factors are required for v-jun activity.
Proceedings of the National Academy of Sciences, 1992
The viral Jun protein (v-Jun) transforms chicken embryo fibroblasts (CEF) more effectively than its cellular counterpart (c-Jun). In certain cell types v-Jun is also a stronger transcriptional activator than c-Jun. These functional differences between v-Jun and c-Jun result from a deletion in v-Jun (referred to as "delta deletion") that seems to weaken the interaction of Jun with a negative cellular regulator molecule. These observations suggested that the oncogenicity of v-Jun may be due to an enhanced ability to activate transcription of target genes. To test this hypothesis, we constructed several deletions in the delta domain of chicken c-Jun and determined their transforming and transactivating properties. Surprisingly, we found an inverse correlation between the ability of the mutants to transform CEF and to transactivate the collagenase and transin promoters in CEF. In contrast, there was no significant effect of the delta mutations in c-Jun on transactivation in F9 murine embryonal carcinoma cells. The function of the delta region is therefore cell-type specific. The inverse correlation between transformation and transactivation in CEF suggests that the strong growth-promoting effect of v-Jun may be related to a failure to activate the transcription of growth attenuating genes.
Frequent inactivation of SPARC by promoter hypermethylation in colon cancers
International Journal of Cancer, 2007
Epigenetic modification of gene expression plays an important role in the development of human cancers. The inactivation of SPARC through CpG island methylation was studied in colon cancers using oligonucleotide microarray analysis and methylation specific PCR (MSP). Gene expression of 7 colon cancer cell lines was evaluated before and after treatment with the demethylating agent 5-aza-2 0deoxycytidine (5Aza-dC) by oligonucleotide microarray analysis. Expression of SPARC was further examined in colon cancer cell lines and primary colorectal cancers, and the methylation status of the SPARC promoter was determined by MSP. SPARC expression was undetectable in 5 of 7 (71%) colorectal cancer cell lines. Induction of SPARC was demonstrated after treatment with the demethylating agent 5Aza-dC in 5 of the 7 cell lines. We examined the methylation status of the CpG island of SPARC in 7 colon cancer cell lines and in 20 test set of colon cancer tissues. MSP demonstrated hypermethylation of the CpG island of SPARC in 6 of 7 cell lines and in all 20 primary colon cancers, when compared with only 3 of 20 normal colon mucosa. Immunohistochemical analysis showed that SPARC expression was downregulated or absent in 17 of 20 colon cancers. A survival analysis of 292 validation set of colorectal carcinoma patients revealed a poorer prognosis for patients lacking SPARC expression than for patients with normal SPARC expression (56.79% vs. 75.83% 5-year survival rate, p 5 0.0014). The results indicate that epigenetic gene silencing of SPARC is frequent in colon cancers, and that inactivation of SPARC is related to rapid progression of colon cancers.
Regulation of the junB gene by v-src
Molecular and cellular biology, 1992
The proteins encoded by cellular and viral src genes are believed to be involved in the transmission of mitogenic signals, the nuclear recipients of which are largely unknown. In this work, we report that four different v-src-transformed cell lines from three different species possess elevated levels of junB transcripts. Transient expression of junB promoter-chloramphenicol acetyltransferase constructs in NIH 3T3 cells was used to demonstrate that the increase in junB transcripts was specifically associated with v-src expression and could not be recapitulated with a c-src, v-H-ras, or v-raf expression vector. Deletion mutants were used to localize the v-src-responsive region in the junB promoter to a 121-nucleotide region encompassing the CCAAT and TATAA elements. This region is distinct from one in the 5' untranslated region of the junB gene which is required to maintain its high-level basal expression. Point mutagenesis of the junB TATAA box completely abolished v-src responsi...
Molecular Cancer, 2010
BackgroundSecreted protein, acidic and rich in cysteine (SPARC) is a matricellular protein that mediates cell-matrix interactions. It has been shown, depending on the type of cancer, to possess either pro- or anti-tumorigenic properties. The transcriptional regulation of the SPARC gene expression has not been fully elucidated and the effects of anti-cancer drugs on this process have not been explored.ResultsIn the present study, we demonstrated that chromatin remodeling factor Brg-1 is recruited to the proximal SPARC promoter region (-130/-56) through an interaction with transcription factor Sp1. We identified Brg-1 as a critical regulator for the constitutive expression levels of SPARC mRNA and protein in mammary carcinoma cell lines and for SPARC secretion into culture media. Furthermore, we found that Brg-1 cooperates with Sp1 to enhance SPARC promoter activity. Interestingly, fenretinide [N-4(hydroxyphenyl) retinamide, 4-HPR], a synthetic retinoid with anti-cancer properties, wa...
Molecular mechanisms underlying the divergent roles of SPARC in human carcinogenesis
Carcinogenesis, 2014
Communication between the cell and its surrounding environment, consisting of proteinaceous (non-living material) and extracellular matrix (eCM), is important for biophysiological and chemical signaling. This signaling results in a range of cellular activities, including cell division, adhesion, differentiation, invasion, migration and angiogenesis. The eCM non-structural secretory glycoprotein called secreted protein, acidic and rich in cysteine (SPARC), plays a significant role in altering cancer cell activity and the tumor's microenvironment (TMe). However, the role of SPARC in cancer research has been the subject of controversy. This review mainly focuses on recent advances in understanding the contradictory nature of SPARC in relation to eCM assembly, cancer cell proliferation, adhesion, migration, apoptosis and tumor growth.
Oncology Reports, 2007
Secreted protein acidic and rich in cysteine (SPARC) is a secreted matricellular glycoprotein involved in crucial processes that occur during cancer. This study explored the occurrence of deregulated expression of SPARC in endometrial carcinomas, since it has been associated with the progression of other tumor types. We analyzed the expression of SPARC in endometrial carcinomas by TaqMan, Western blotting and immunohistochemistry. The CpG island methylation status of SPARC was evaluated by bisulfite sequencing method. A significant down-regulation of SPARC mRNA expression (p<0.001) was observed in endometrial tumor tissues, regardless of their microsatellite instability status (MSI). The downregulation can be accounted for by aberrant hypermethylation of its CpG-rich region, since we demonstrate that SPARC is a frequent target of this epigenetic event in this pathology. Although, differential expression of SPARC is already known in other cancer types, we report that down-regulation of the SPARC gene in endometrial tumors, formed by at least 80% of epithelial tumor cells, contrasts with a frequent overexpression of SPARC protein, with strong immunoreactivity in stromal cells. These results indicate a cell type specific expression of SPARC in endometrial carcinomas. Accumulation of SPARC protein in most tumors compared to normal tissues (p<0.025), suggests an important role in the carcinogenesis of endometrial tumors. SPARC overexpression can be a useful molecular tool that may contribute to the diagnosis of this disease.
The c-Jun Dimerization Protein 2 Inhibits Cell Transformation and Acts as a Tumor Suppressor Gene
Journal of Biological Chemistry, 2003
The c-Jun dimerization protein, JDP2, is a member of the AP-1 (activating protein-1) family of the basic leucine zipper transcription factors. JDP2 can bind 12-O-tetradecanoylphorbol-13-acetate (TPA)-responsive element and cAMP-responsive element DNA response elements, resulting in the inhibition of transcription. Although the role of AP-1 in cell proliferation and malignant transformation is well established, the role of JDP2 in this process is of subject to debate. On the one hand, JDP2 was shown to inhibit cyclin D transcription and promote differentiation of skeletal muscle and osteoclast cells. On the other hand, JDP2 was shown to partially transform chicken embryo fibroblast and was identified in a screen for oncogenes able to collaborate with the loss of p27 kip cyclin-dependent inhibitor to induce lymphomas. Using cell transformation assays in NIH3T3 cells and injection of prostate cancer cell lines overexpressing JDP2 into severe combined immuno-deficient (SCID) mice, we show for the first time the potential role of JDP2 in inhibition of cell transformation and tumor suppression. The mechanism of tumor suppressor action of JDP2 can be partially explained by the generation of inhibitory AP-1 complexes via the increase of JunB, JunD, and Fra2 expression and decrease of c-Jun expression.
Current Biology, 1998
Stimulation of c-Jun transcriptional activity via phosphorylation mediated by the stress-activated or c-Jun amino-terminal (SAPK/JNK) subgroup of mitogen-activated protein kinases (MAP kinases) is thought to depend on a kinase-docking site (the delta region) within the amino-terminal activation domain, which is deleted from the oncogenic derivative, v-Jun [1-3]. This mutation markedly enhances v-Jun oncogenicity [4,5]; however, its transcriptional consequences have not been resolved. In part, this reflects uncertainty as to whether binding of SAPK/JNK inhibits c-Jun function directly [6,7] or, alternatively, serves to facilitate and maintain the specificity of positive regulatory phosphorylation [8]. Using a two-hybrid approach, we show that SAPK/JNK stimulates c-Jun transactivation in yeast and that this depends on both catalytic activity and physical interaction between the kinase and its substrate. Furthermore, c-Jun is active when tethered to DNA via SAPK/JNK, demonstrating that kinase binding does not preclude transactivation. Taken together, these results suggest that SAPK/JNK acts primarily as a positive regulator of c-Jun transactivation in situ, and that loss of the docking site physically uncouples v-Jun from this control. This loss-of-function model accounts for the deficit of v-Jun regulatory phosphorylation and repression of TPA response element (TRE)-dependent transcription observed in v-Jun-transformed cells and predicts that an important property of the oncoprotein is to antagonise SAPK/JNK-dependent gene expression.