RESUMO
During fasting, induction of hepatic gluconeogenesis is crucial to ensure proper energy homeostasis. Such induction is dysregulated in type 2 diabetes, resulting in the development of fasting hyperglycemia. Hormonal and nutrient regulation of metabolic adaptation during fasting is mediated predominantly by the transcriptional coactivator peroxisome proliferative activated receptor γ coactivator 1α (PGC-1α) in concert with various other transcriptional regulators. Although CITED2 (CBP- and p300-interacting transactivator with glutamic acid- and aspartic acid-rich COOH-terminal domain 2) interacts with many of these molecules, the role of this protein in the regulation of hepatic gluconeogenesis was previously unknown. Here we show that CITED2 is required for the regulation of hepatic gluconeogenesis through PGC-1α. The abundance of CITED2 was increased in the livers of mice by fasting and in cultured hepatocytes by glucagon-cAMP-protein kinase A (PKA) signaling, and the amount of CITED2 in liver was higher in mice with type 2 diabetes than in non-diabetic mice. CITED2 inhibited the acetylation of PGC-1α by blocking its interaction with the acetyltransferase general control of amino acid synthesis 5-like 2 (GCN5). The consequent downregulation of PGC-1α acetylation resulted in an increase in its transcriptional coactivation activity and an increased expression of gluconeogenic genes. The interaction of CITED2 with GCN5 was disrupted by insulin in a manner that was dependent on phosphoinositide 3-kinase (PI3K)-thymoma viral proto-oncogene (Akt) signaling. Our results show that CITED2 functions as a transducer of glucagon and insulin signaling in the regulation of PGC-1α activity that is associated with the transcriptional control of gluconeogenesis and that this function is mediated through the modulation of GCN5-dependent PGC-1α acetylation. We also found that loss of hepatic CITED2 function suppresses gluconeogenesis in diabetic mice, suggesting it as a therapeutic target for hyperglycemia.
