Transcriptional regulation of the proximal promoter of the murine pyruvate carboxylase gene in liver cells

Abstract

Pyruvate carboxylase (PC) plays a crucial role in intermediary metabolism i.e. gluconeogenesis, lipogenesis and insulin secretion. Mammalian PC genes are regulated by 2 promoters, the proximal (P1) and the distal (P2) promoters which mediate alternative transcription in tissue‐specific manner. P1 promoter is active in liver and adipocytes while the P2 is active in pancreatic islets. In islets, P2 promoter is regulated by Sp1/Sp3, USF1, 2 and Foxa2 while P1 promoter is regulated by the PPARgamma. P1 is active in both liver and adipocytes, suggesting that this promoter is regulated by the distinct sets of liver and adipocyte transcription factors. To investigate this, we identify the liver‐specific transcription factors that regulate PC expression. We generate a series of 5’‐nested deletion mutants of the 2.3 kb P1 promoter of the mouse PC gene followed by transient transfection in HepG2 cells. This result showed the presence of 3 regulatory regions, located in regions A (−166/−80), B (−166/−256) and C (−335/−603). Region A contains 3 sites for Sp1/Sp3 while the region C contains a putative binding site for the liver‐enrich nuclear factor, HNF4alpha which could potentially bind to its responsive element identical to the PPRE. We are investigating the molecular interaction between HNF4 alpha to this site as well as identifying the nuclear proteins that bind region B of the P1 promoter.