Mutations in the SHP gene are associated with mild obesity in Japanese subjects (28)

Mutations in the SHP gene are associated with mild obesity in Japanese subjects (28). relieved the metformin- and Ad-CA-AMPK-mediated repression of hepatic Osalmid gluconeogenic enzyme gene expression in primary rat hepatocytes. In conclusion, our results suggest that a delayed effect of metformin-mediated induction of SHP gene expression inhibits CREB-dependent hepatic gluconeogenesis. Keywords:AMP-activated Kinase (AMPK), CREB, Gluconeogenesis, Glucose Metabolism, Nuclear Receptors, Transcription Coactivators == Introduction == Glucose homeostasis is regulated by the opposing actions of insulin and glucagon (13), and glucose production in the liver is controlled primarily by gluconeogenesis (4). The regulation of hepatic gluconeogenesis involves the transcriptional regulation of key metabolic enzymes, including PEPCK6and G6Pase. The gluconeogenic program is largely regulated at the level of transcription and the process is coordinated by CREB via its direct binding to the cAMP-response element (CRE) site on the promoter of PEPCK, G6Pase, or PGC-1 (PPAR coactivator-1) (5). Metformin Rabbit Polyclonal to BAX has been shown to activate AMP-activated protein kinase (AMPK) via an LKB1-dependent mechanism (6). AMPK is a serine/threonine kinase that functions as an intracellular energy sensor and has been implicated in the modulation of glucose and fatty acid metabolism (7). AMPK is activated by physiological stimuli, including exercise, muscle contraction, and hormones, such as adiponectin and leptin, as well as by physiological stresses, glucose Osalmid deprivation, hypoxia, oxidative stress, and osmotic shock conditions (8,9). In the liver, activation of AMPK suppresses hepatic gluconeogenesis acutely by direct phosphorylation of its substrates, including CREB-binding protein (CBP) (10), CRTC2 (11), and GSK3 (glycogen synthase kinase 3) (12). Recent studies also suggest that AMPK induces SHP gene expression and inhibits hepatic gluconeogenic gene expression in animal models (13,14). Orphan nuclear receptor SHP (NR0B2) lacks a typical nuclear receptor DNA-binding domain and is expressed predominantly in the liver, whereas nominal expression is also detected in the heart, lung, pancreas, spleen, kidney, smooth muscle, testis, and ovary (15,16). SHP is a transcriptional repressor of a number of nuclear receptors and transcription factors, including estrogen receptor (ER) (17,18), ER-related receptor (19), glucocorticoid receptor (20), androgen receptor (21), forkhead transcription factor FoxA2 (HNF3) (22), HNF4 (hepatocyte nuclear factor 4) (23), HNF6 (hepatocyte nuclear factor 6) (24), CCAAT/enhancer-binding protein (25), and BETA2/NeuroD (26). SHP expression is regulated by several other members of the nuclear receptor superfamily, including the orphan nuclear receptors SF-1, LRH-1, ER-related receptor , and the bile acid receptor FXR (16). SHP plays a crucial role in regulating glucose metabolism (13,27). Mutations in the SHP gene are associated with mild obesity in Japanese subjects (28). Metformin, hepatocyte growth factor, Osalmid and sodium arsenite increase SHP gene expression and inhibit the PEPCK and G6Pase gene expression; fenofibrate inhibits PAI-1 expression through induction of SHP (13,14,29,30). The basic leucine zipper (bZIP) protein CREB binds to CREs that contain the 5-TGACGTCA-3 consensus motif and activate the transcription of CRE-bearing genes, such as G6Pase and PEPCK (31). CREB coactivator CRTC2 significantly contributes to the CRE-dependent transcriptional activation of hepatic gluconeogenesis (11). Under feeding or in the presence of insulin, CRTC2 is located in the cytoplasm via its phosphorylation at Ser171by members of Osalmid the AMPK family of Ser/Thr kinase, including AMPK and SIK1 (salt-inducible kinase 1) (11,32). Fasting triggers activation of cAMP-dependent protein kinase (PKA) to promote dephosphorylation and nuclear entry of CRTC2, which results in the increased occupancy of CRTC2 over promoters of PEPCK, G6Pase, or PGC-1 and activation of the entire gluconeogenic program in mouse liver or in rat primary hepatocytes (33,34). Indeed, knock-out of CRTC2 decreases circulating glucose concentrations during fasting, due to the attenuation of the gluconeogenic gene expression (35). In this study, we have demonstrated that AMPK inhibits phosphorylation-defective mutant CRTC2 (S171A)-dependent hepatic gluconeogenesis. SHP inhibits CRE promoter activity by direct interaction with CREB, thus inhibiting the recruitment of CRTC2 on the chromatin. Metformin or constitutively active AMPK inhibits not only WT CRTC2 but also S171A-dependent activation of hepatic gluconeogenic genes, whereas knockdown of SHP negated these effects, suggesting that AMPK could regulate CREBCRTC2-dependent gluconeogenesis via an alternative mechanism by activating transcription of SHP. Taken together, our result suggests that SHP is.