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Mapping of HNF4α binding sites, acetylation of histone H3 and expression in Caco2 cells

ABSTRACT: Background & Aims: The role of HNF4α has been extensively studied in hepatocytes and pancreatic β cells, but emerging evidence indicates that HNF4α is a key regulator of intestinal epithelial cell differentiation as well. The aim of the present work is to identify HNF4α target genes in the intestine in order to elucidate the role of HNF4α in differentiation of the intestinal epithelial cells. Results: One thousand one hundred and seventy-six genes were identified as HNF4α targets, many of which have not previously been described as being regulated by HNF4α. The 1,176 genes contributed significantly to gene ontology (GO) pathways categorized by lipid and amino acid transport and metabolism. A thorough analysis of Cdx-2, trehalase, and cingulin promoters verified that these genes are regulated by HNF4α. In each case we were able to identify a functional HNF4α binding site in their promoters. Conclusions: HNF4α regulation of the Cdx-2 promoter unravels a transcription factor network also including HNF1α and β, all of which are transcription factors involved in intestinal development and gene expression. Keywords: ChIP-CHIP and expression data

ORGANISM(S): Homo sapiens

PROVIDER: GSE7745 | GEO | 2007/05/10

SECONDARY ACCESSION(S): PRJNA99859

REPOSITORIES: GEO

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Project description:HNF4α is a nuclear receptor regulating the transcription of genes involved mainly in development, cell differentiation and metabolism. Opposite functions for the two classes of P1 and P2 isoforms of HNF4α have recently been highlighted. These classes include 12 variants of HNF4α that can be expressed by the use of two promoters and by alternative splicing. Until now, the characterization of this transcription factor has ignored this diversity and has remained confined to the study of a fraction of the isoforms. We therefore wanted to clarify the situation by specifically characterizing the transcriptional functions of the 12 isoforms of HNF4α. We have generated for this purpose stable lines expressing each isoform of HNF4α in HCT 116 cells. We analyzed the whole transcriptome associated with each isoform by sequencing RNA, as well as their proteome by a BioID approach coupled to quantitative mass spectrometry. We noted major differences in the transcriptional function of the 12 isoforms. The α4, α5 and α6 isoforms have been characterized for the first time, and show a greatly reduced transcriptional potential. We have shown that these isoforms are unable to recognize the consensus response element of HNF4α. The α1 and α2 isoforms are the most potent regulators of gene expression, while the α3 isoform exhibits significantly reduced activity. Several transcription factors and coregulators have been identified as potential specific partners for certain HFH4α isoforms. The IRF-2BP2 co-repressor interacts specifically with isoforms which include the long form of the F domain of HNF4α. This specific interaction could explain the large number of genes modulated negatively by α1 and α2 compared to α3. The analysis integrating the vast amount of transcriptomic and proteomic data allows the identification of transcriptional regulatory mechanisms specific to certain isoforms, demonstrating the importance of considering all isoforms which can have diverse functions.

Project description:Background Worldwide, gastric cancer is the fourth most common malignancy and the most common cancer in East Asia. Development of targeted therapies for this disease has focused on a few known oncogenes but has had limited effects. Objective To determine oncogenic mechanisms and novel therapeutic targets specific for gastric cancer by identifying commonly dys-regulated genes from the tumors of both Asian-Pacific and Caucasian patients. Design We generated transcriptomic profiles of 22 Caucasian gastric cancer tumors and their matched non-cancerous samples, and performed an integrative analysis across different gastric cancer gene expression datasets. We examined the inhibition of commonly overexpressed oncogenes and their constituent signaling pathways by RNAi and/or pharmacologic inhibition. Results We found that HNF4α upregulation was a key signaling event in gastric tumors from both Caucasian and Asian patients, and HNF4α antagonism was antineoplastic. Perturbation experiments in GC tumor cell lines and xenograft models further demonstrated that HNF4α is downregulated by AMPKα signaling and the AMPK agonist metformin; blockade of HNF4α activity resulted in cyclin downregulation, cell cycle arrest, and tumor growth inhibition. HNF4α also regulated WNT signaling through its target gene WNT5A, a potential prognostic marker of diffuse type gastric tumors. Conclusions Our results indicate that HNF4α is a targetable oncoprotein in gastric cancer, is regulated by AMPK signaling through AMPKα, and resides upstream of WNT signaling. HNF4α may regulate “metabolic switch” characteristic of a general malignant phenotype and its target WNT5A has potential prognostic values. The AMPKα-HNF4α-WNT5A signaling cascade represents a potentially targetable pathway for drug development. Integrative analysis of Caucasian and Asian-Pacific gastric tumor expression datasets (including newly generated transcriptomic profiling of 22 tumors in this study) revealed a relatively small common sets of highly overexpressed genes.

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Mapping of HNF4α binding sites, acetylation of histone H3 and expression in Caco2 cells

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