The peroxisome proliferator-activated receptor-γ regulates murine pyruvate carboxylase gene expression in vivo and in vitro

Pyruvate carboxylase ( PC) plays a crucial role in various metabolic pathways, including gluconeogenesis, lipogenesis, and glucose-induced insulin secretion. Here we showed for the first time that the PC gene is transcriptionally regulated by peroxisome proliferator-activated receptor-gamma (PPAR gamma) in vitro and in vivo in white and brown adipose tissue. PC mRNA and protein are markedly increased during differentiation of 3T3-L1 cells and HIB-1B, in parallel with the expression of the adipogenic transcription factors, CCAAT-enhancer binding protein alpha, PPAR gamma 1, and PPAR gamma 2. Tumor necrosis factor-alpha, a cytokine that blocks differentiation of 3T3- L1 cells, suppressed PC expression. Co-transfection studies in 3T3-L1 preadipocytes or HEK293T cells with a 2.3-kb promoter fragment of mouse PC gene linked to a luciferase reporter construct and with plasmids overexpressing retinoid X receptor alpha/PPAR gamma 1 or retinoid X receptor alpha/ PPAR gamma 2 showed a 6 - 8-fold increase above the basal promoter activity. Furthermore, treatment of these transfected cells with the PPAR gamma agonist doubled the promoter activity. Mutation of the putative PPAR-response element-( -386/-374) of this 2.3-kb PC promoter fragment abolished the PPAR gamma response. Gel shift and chromatin immunoprecipitation assays demonstrated that endogenous PPAR gamma binds to this functional PPAR-response element of the PC promoter. Mice with targeted disruption of the PPAR gamma 2 gene displayed similar to 50 - 60% reduction of PC mRNA and protein in white adipose tissue. Similarly, in brown adipose tissue of PPAR gamma 2-deficient mice subjected to cold exposure, PC mRNA was 40% lower than that of wild type mice. Impaired in vitro differentiation of white adipocytes of PPAR gamma 2 knock-out mice was also associated with a marked reduction of PC mRNA. Our findings identified PC as a PPAR gamma-regulated gene and suggested a role for PPAR gamma regulating intermediary metabolism.