Quantitative In Vivo Proteomics of Metformin Response in Liver Reveals AMPK-Dependent and -Independent Signaling Networks

Abstract

Summary: Metformin is the front-line treatment for type 2 diabetes worldwide. It acts via effects on glucose and lipid metabolism in metabolic tissues, leading to enhanced insulin sensitivity. Despite significant effort, the molecular basis for metformin response remains poorly understood, with a limited number of specific biochemical pathways studied to date. To broaden our understanding of hepatic metformin response, we combine phospho-protein enrichment in tissue from genetically engineered mice with a quantitative proteomics platform to enable the discovery and quantification of basophilic kinase substrates in vivo. We define proteins whose binding to 14-3-3 are acutely regulated by metformin treatment and/or loss of the serine/threonine kinase, LKB1. Inducible binding of 250 proteins following metformin treatment is observed, 44% of which proteins bind in a manner requiring LKB1. Beyond AMPK, metformin activates protein kinase D and MAPKAPK2 in an LKB1-independent manner, revealing additional kinases that may mediate aspects of metformin response. Deeper analysis uncovered substrates of AMPK in endocytosis and calcium homeostasis. : Metformin is a potential anti-aging and anti-cancer therapy and a treatment for diabetes. Stein et al. investigate metformin-induced signaling in the liver, using 14-3-3 binding to identify phosphorylation events acting as dominant regulators of target protein activity. Kinases (PKD, MK2) activated by metformin independent of LKB1/AMPK and other targets of metformin are identified. Keywords: metformin, AMPK3, diabetes, aging, STIM1, calcium, PKD1, LKB1, liver, kinases