Pur beta promotes hepatic glucose production by increasing Adcy6 transcription

Objective: Enhanced glucagon signaling and hepatic glucose production (HGP) can account for hyperglycemia in patients with obesity and type 2 diabetes. However, the detailed molecular mechanisms underlying the enhanced HGP in these patients are not fully understood. Here, we identify Pur beta as a positive regulator of HGP and study its molecular mechanisms in the regulation of HGP both in vivo and in vitro. Methods: Adenovirus-mediated knockdown or overexpression of Purb was performed in either primary hepatocytes or the livers of db/db mice. Glucose metabolism, insulin sensitivity, and HGP were determined by glucose, insulin, and lactate tolerance tests, respectively. Pur beta/ADCY6 protein levels, glucagon signaling (p-CREB/CREB), and insulin signaling (p-Akt/Akt) were measured by immunoblotting. Gene expression was measured by RNA-seq and real-time quantitative polymerase chain reaction. Luciferase reporter and chromatin immunoprecipitation assays were used to study the interaction between Pur beta and the Adcy6 promoter. Results: Pur beta was abnormally elevated in obese mice and was also increased under fasting conditions or via the glucagon signaling pathway, which promoted HGP by increasing Adcy6 expression. Liver-specific knockdown of Pur beta in db/db mice significantly ameliorated hyperglycemia and glucose intolerance by suppressing the glucagon/ADCY6/cAMP/PKA/CREB signaling pathway. Consistent with this observation, the knockdown of Purb also inhibited glucose production in isolated primary hepatocytes by inhibiting the glucagon/ADCY6/cAMP/PKA/CREB signaling pathway, whereas the overexpression of Pur beta promoted glucose production by activating this signaling pathway. Mechanistically, Purb directly binds to the promoter of the Adcy6 gene and thereby promotes its transcription. Conclusions: Taken together, these results illustrate a new model in which Pur beta functions to regulate the glucagon/ADCY6/cAMP/PKA/CREB signaling pathway to help maintain glucose homeostasis. (C) 2019 The Author(s). Published by Elsevier GmbH.