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 glyceroneogenesis. 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 ؊2086 and ؊888 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 PPAR␥2, previously identified as a regulator of the adipocyte P2 enhancer, binds in a heterodimeric complex with RXR␣ to the PEPCK 5-flanking region at two sites, termed PCK1 (bp ؊451 to ؊439) and PCK2 (bp ؊999 to ؊987). Forced expression of PPAR␥2 and RXR␣ 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 PPAR␥2 binding site (PCK2) abolishes both the activity of the enhancer in adipocytes and its ability to be activated by PPAR␥2 and RXR␣. These results establish a role for PPAR␥2 in the adipose expression of the PEPCK gene and suggest that this factor functions as a coordinate regulator of multiple adipocyte-specific genes.Phosphoenolpyruvate carboxykinase (PEPCK [EC 4.1.1.32]) catalyzes the conversion of oxaloacetate to phosphoenolpyruvate, the rate-limiting step in gluconeogenesis and glyceroneogenesis. The PEPCK gene is expressed at high levels in liver, kidney, and white and brown fat (37). Expression is regulated at the transcriptional level by multiple hormones and second messengers, including insulin, glucocorticoids, retinoic acid, thyroid hormone, and cyclic AMP (10, 21, 33). Hormonal and dietary regulation of PEPCK gene transcription is tissue specific. For example, PEPCK expression in the liver is linked to blood glucose concentration, whereas in the kidney it is primarily regulated by physiologic acid-base status. In the liver and kidney, expression is stimulated by glucocorticoids and cyclic AMP and inhibited by insulin (33). In adipose tissue, however, glucocorticoids are inhibitory (25).The complexity of its transcriptional regulation makes PEPCK an attractive model for the study of hormone-linked and tissue-specific gene expression. The regions of the PEPCK promoter important for the hormonal and dietary regulation of this gene in liver have been analyzed in detail. A complex hormone response region extending from bp Ϫ460 to Ϫ349 from the transcriptional start site contains elements important for response to glucocorticoids, insulin and retinoic acid (14,16,24,26). A thyroid hormone response element (10) and a cyclic AMP response element (31) are located a...

Acute and selective regulation of glyceroneogenesis and cytosolic phosphoenolpyruvate carboxykinase in adipose tissue by thiazolidinediones in type 2 diabetes

“…The demonstration that PPARγ ligands acutely regulate PCK1 expression in human adipose tissue agrees with what has been shown earlier by our laboratory and others in rodent adipocytes or adipose tissue [32,43,44]. We show additionally here that PCK1 transcription is the affected step in human adipose tissue and that no post-transcriptionnal effect occurs in response to the thiazolidinedione.…”

The role of oxygen availability in embryonic development and stem cell function

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Metabolic action of peroxisome proliferator-activated receptor γ agonism in rats with exogenous hypercorticosteronemia

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