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Transcriptional Regulation of the GPX1 Gene by TFAP2C and Aberrant CpG Methylation in Human Breast Cancer

ABSTRACT: The complexity of gene regulation has created obstacles to defining mechanisms that establish the patterns of gene expression characteristic of the different clinical phenotypes of breast cancer. Transcription factor TFAP2C plays a critical role in the regulation of both estrogen receptor-alpha (ERα) and c-ErbB2/HER2 (Her2). Herein, we performed chromatin immunoprecipitation and direct sequencing (ChIP-seq) for TFAP2C in four breast cancer cell lines representing different clinical phenotypes. Comparing the genomic binding sites for TFAP2C in the various cell lines, we identified that glutathione peroxidase (GPX1) is regulated by TFAP2C through an AP-2 regulatory region in the promoter of the GPX1 gene. Knock-down of TFAP2C, but not the related factor TFAP2A, resulted in an abrogation of GPX1 expression. Selenium-dependent GPX activity correlated with endogenous GPX1 expression, and overexpression of exogenous GPX1 induced GPX activity and significantly increased resistance to tert-butyl hydroperoxide. Methylation of the CpG island encompassing the AP-2 regulatory region was identified in cell lines where TFAP2C failed to bind the GPX1 promoter and GPX1 expression was unresponsive to TFAP2C. Furthermore, in cell lines where GPX1 promoter methylation was associated with gene silencing, treatment with 5-aza-dC (an inhibitor of DNA methylation) resulted in activation of GPX1 RNA and protein expression. Methylation of the GPX1 promoter was identified in approximately 20% of primary breast cancers and a highly significant correlation between TFAP2C and GPX1 expression was confirmed when considering only those tumors with an unmethylated promoter, whereas the related factor, TFAP2A, failed to demonstrate a correlation. The results demonstrate that TFAP2C regulates the expression of GPX1, which influences the redox state and sensitivity to oxidative stress induced by peroxides. Given the established role of GPX1 in breast cancer, the results provide an important mechanism for TFAP2C to further influence oncogenesis and progression of breast carcinoma cells.

ORGANISM(S): Homo sapiens

PROVIDER: GSE36351 | GEO | 2012/09/12

SECONDARY ACCESSION(S): PRJNA153311

REPOSITORIES: GEO

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Project description:The complexity of gene regulation has created obstacles to defining mechanisms that establish the patterns of gene expression characteristic of the different clinical phenotypes of breast cancer. Transcription factor TFAP2C plays a critical role in the regulation of both estrogen receptor-alpha (ERM-NM-1) and c-ErbB2/HER2 (Her2). Herein, we performed chromatin immunoprecipitation and direct sequencing (ChIP-seq) for TFAP2C in four breast cancer cell lines representing different clinical phenotypes. Comparing the genomic binding sites for TFAP2C in the various cell lines, we identified that glutathione peroxidase (GPX1) is regulated by TFAP2C through an AP-2 regulatory region in the promoter of the GPX1 gene. Knock-down of TFAP2C, but not the related factor TFAP2A, resulted in an abrogation of GPX1 expression. Selenium-dependent GPX activity correlated with endogenous GPX1 expression, and overexpression of exogenous GPX1 induced GPX activity and significantly increased resistance to tert-butyl hydroperoxide. Methylation of the CpG island encompassing the AP-2 regulatory region was identified in cell lines where TFAP2C failed to bind the GPX1 promoter and GPX1 expression was unresponsive to TFAP2C. Furthermore, in cell lines where GPX1 promoter methylation was associated with gene silencing, treatment with 5-aza-dC (an inhibitor of DNA methylation) resulted in activation of GPX1 RNA and protein expression. Methylation of the GPX1 promoter was identified in approximately 20% of primary breast cancers and a highly significant correlation between TFAP2C and GPX1 expression was confirmed when considering only those tumors with an unmethylated promoter, whereas the related factor, TFAP2A, failed to demonstrate a correlation. The results demonstrate that TFAP2C regulates the expression of GPX1, which influences the redox state and sensitivity to oxidative stress induced by peroxides. Given the established role of GPX1 in breast cancer, the results provide an important mechanism for TFAP2C to further influence oncogenesis and progression of breast carcinoma cells. 4 ChIP-Seq data for TFAP2C in human breast carcinoma cell lines MCF-7, BT-474, MDA-MB-453 and SKBR-3.

Project description:Abstract: A subset of HER2 breast cancers with amplification of the TFAP2C gene locus becomes addicted to AP-2g. We sought to define AP-2g-regulated genes that control growth and invasiveness by comparing HER2 cell lines with differential response to TFAP2C knockdown. A set of 68 differentially expressed genes was identified, which included CDH5 and CDKN1A. Pathway analysis implicated the MAPK13/p38δ and retinoic acid regulatory nodes, which were confirmed to display divergent responses. The AP-2g gene signature was highly predictive of outcome in HER2-positive breast cancer patients. We conclude that AP-2g regulates a set of genes in HER2 breast cancer that drive cancer growth and invasiveness and that the AP-2g gene signature can predict outcome of patients with HER2 breast cancer. Results: Using an optimized data analysis workflow, we mapped about 50-75 million sequence reads per sample to the human genome Human Feb.2009 (GRCh37/hg19) (hg19). By RNA-seq analysis, knockdown of TFAP2C in HCC1954 with siRNA (compared to NT siRNA) identified 364 genes with significantly altered expression. To further create specificity for AP-2gamma-regulated genes, RNA-seq analysis was performed comparing expression in shHCC1954 with shTFAP2C cells vs. shNT; this analysis identified 8,986 genes with significantly altered expression. The two data sets were subsequently compared to identify a set of genes that were consistently altered with knockdown of TFAP2C by siRNA and shRNA. This comparison confirmed the identification of 152 AP-2gamma target genes in HCC1954 cells. Because HCC1954 demonstrated opposite growth regulation and invasiveness with knockdown of TFAP2C compared to SKBR3, we hypothesized that the AP-2gamma target genes responsible for growth and invasion would be differentially regulated with knockdown of TFAP2C in HCC1954 versus SKBR3. Hence, RNA-seq analysis was performed in SKBR3 after knockdown of TFAP2C with siRNA; in this analysis, a total of 3814 genes were significantly altered. The pattern of expression for the 152 AP-2gamma target genes identified in HCC1954 was subsequently compared to expression changes in SKBR3. Of note, only 79 of the 152 TFAP2C target genes in HCC1954 were found to change expression significantly in the RNA-seq data set from SKBR-3. Conclusions: Knockdown of TFAP2C with co-knockdown of CDH5 in SKBR-3 confirmed no significant effect on invasion, though there was a slight reduction in invasiveness with knockdown of CDH5 that failed to reach statistical significance (p=0.12). These findings support the conclusion that regulation of CDH5 and CDKN1A contribute to alterations of proliferation and invasiveness induced by knockdown of TFAP2C.

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Transcriptional Regulation of the GPX1 Gene by TFAP2C and Aberrant CpG Methylation in Human Breast Cancer

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