PPARγ2 Regulates Adipose Expression of the Phosphoenolpyruvate Carboxykinase Gene

Abstract

Phosphoenolpyruvate carboxykinase (PEPCK) is expressed at high levels in liver, kidney, and adipose tissue. This enzyme catalyzes the rate-limiting step in hepatic and renal gluconeogenesis and adipose glyceroneogen-esis. The regulatory factors important for adipose expression of the PEPCK gene are not well defined. Previous studies with transgenic mice established that the region between bp 22086 and 2888 is required for expression in adipose tissue but not for expression in liver or kidney tissue. We show here that a DNA fragment containing this region can function as an enhancer and direct differentiation-dependent expression of a chloramphenicol acetyltransferase gene from a heterologous promoter in cultured 3T3-F442A preadipocytes and adipocytes. We further demonstrate that the adipocyte-specific transcription factor PPARγ2, previously identified as a regulator of the adipocyte P2 enhancer, binds in a heterodimeric complex with RXRα to the PEPCK 5′-flanking region at two sites, termed PCK1 (bp 2451 to 2439) and PCK2 (bp 2999 to 2987). Forced expression of PPARγ2 and RXRα activates the PEPCK enhancer in non-adipose cells. This activation is potentiated by peroxisome proliferators and fatty acids but not by 9-cis retinoic acid. Mutation of the PPARγ2 binding site (PCK2) abolishes both the activity of the enhancer in adipocytes and its ability to be activated by PPARγ2 and RXRα. These results establish a role for PPARγ2 in the adipose expression of the PEPCK gene and suggest that this factor functions as a coordinate regulator of multiple adipocyte-specific genes.