Abstract
Impairment of gluconeogenesis is a key factor responsible for hyperglycemia in patients with type 2 diabetes. As an important member of the suppressors of cytokine signaling (SOCS) protein family, many physiological functions of cytokine-inducible SH2-containing protein (CISH) have been described; however, the role of hepatic CISH in gluconeogenesis is poorly understood. In the present study, we observed that hepatic CISH expression was reduced in fasted wild-type (WT) mice. Overexpression of CISH decreased glucose production in mouse primary hepatocytes, while silencing of CISH had the opposite effects. In addition, adenovirus-mediated hepatic CISH overexpression resulted in improved glucose tolerance and decreased gluconeogenesis in WT and leptin receptor-deficient diabetic (db/db) mice. In contrast, adenovirus-mediated hepatic CISH knockdown impaired glucose tolerance and increased gluconeogenesis in WT mice. We also generated liver-specific CISH knockout (LV-CISH KO) mice and discovered that these mice had a similar phenotype in glucose tolerance and gluconeogenesis as mice injected with adenoviruses that knockdown CISH expression. Mechanistically, we found that CISH overexpression decreased and CISH knockdown increased the mRNA and protein levels of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase 1 (PEPCK), two key enzymes involved in gluconeogenesis, in vitro, and in vivo. Moreover, we discovered that the phosphorylation of cAMP-responsive element binding protein 1 (CREB), a transcription factor of G6pase and Pepck, was required for regulating gluconeogenesis by CISH. Taken together, this study identifies hepatic CISH as an important regulator of gluconeogenesis. Our results also provide important insights into the metabolic functions of the SOCS protein family and the potential targets for the treatment of diabetes.