A single element in the phosphoenolpyruvate carboxykinase gene mediates thiazolidinedione action specifically in adipocytes

Phosphoenolpyravate carboxykinase (PEPCK) is the key enzyme in glyceroneogenesis, an important metabolic pathway that functions to restrain the release of non-esterified fatty acids (NEFAs) from adipocytes. The antidiabetic drugs known as thiazolidinediones (TZDs) are thought to achieve some of their benefits by lowering elevated plasma NEFAs. Moreover, peroxisome proliferator activated receptor gamma (PPAR gamma) mediates the antidiabetic effects of TZDs, though many TZD responses appear to occur via PPAR gamma -independent pathways. PPAR gamma is required for adipocyte PEPCK expression, hence PEPCK could be a major target gene for the antidiabetic actions of TZDs. If ere we used tissue culture and transfection assays to confirm that the TZD, rosiglitazone, stimulates PEPCK gene transcription specifically in adipocytes. We made the novel observation that this effect was by far the most rapid and robust among several other genes expressed in adipocytes. Adipocytes were transfected with a PEPCK/chloramphenicol acetyltransferase chimeric gene, in which either of the two previously discovered PPAR gamma /retinoid X receptor alpha response elements, PCK2 and gAF1/PCK1, had been inactivated by mutagenesis. We demonstrate that PCK2 alone is a bona fide thiazolidinedione response element. We show also that the regulation of PEPCK by PPARs is cell-specific and isotype-specific since rosiglitazone induces PEPCK gene expression selectively in adipocytes, and PPAR alpha- and PPAR beta -speciflc activators are inefficient. Hence, TZDs could lower plasma NEFAs via PPAR gamma and PEPCK by enhancing adipocyte glyceroneogenesis. (C) 2001 Societe francaise de biochimie et biologie moleculaire/Editions scientifiques et medicales Elsevier SAS. All rights reserved.