The human liver fatty acid binding protein (FABP1) gene is activated by FOXA1 and PPAR??; And repressed by C/EBP??: Implications in FABP1 down-regulation in nonalcoholic fatty liver disease

摘要

Liver fatty acid binding protein (FABP1) prevents lipotoxicity of free fatty acids and regulates fatty acid trafficking and partition. Our objective is to investigate the transcription factors controlling the human FABP1 gene and their regulation in nonalcoholic fatty liver disease (NAFLD). Adenovirus-mediated expression of multiple transcription factors in HepG2 cells and cultured human hepatocytes demonstrated that FOXA1 and PPAR?? are among the most effective activators of human FABP1, whereas C/EBP?? is a major dominant repressor. Moreover, FOXA1 and PPAR?? induced re-distribution of FABP1 protein and increased cytoplasmic expression. Reporter assays demonstrated that the major basal activity of the human FABP1 promoter locates between - 96 and - 229 bp, where C/EBP?? binds to a composite DR1-C/EBP element. Mutation of this element at - 123 bp diminished basal reporter activity, abolished repression by C/EBP?? and reduced transactivation by HNF4??. Moreover, HNF4?? gene silencing by shRNA in HepG2 cells caused a significant down-regulation of FABP1 mRNA expression. FOXA1 activated the FABP1 promoter through binding to a cluster of elements between - 229 and - 592 bp, whereas PPAR?? operated through a conserved proximal element at - 59 bp. Finally, FABP1, FOXA1 and PPAR?? were concomitantly repressed in animal models of NAFLD and in human nonalcoholic fatty livers, whereas C/EBP?? was induced or did not change. We conclude that human FABP1 has a complex mechanism of regulation where C/EBP?? displaces HNF4?? and hampers activation by FOXA1 and PPAR??. Alteration of expression of these transcription factors in NAFLD leads to FABP1 gen repression and could exacerbate lipotoxicity and disease progression. ? 2013 Elsevier B.V.