Boutchueng-Djidjou M, Collard-Simard G, Fortier S, Hebert SS, Kelly I, Landry CR, Faure RL

Insulin is internalized with its cognate receptor into the endosomal apparatus rapidly after binding to hepatocytes. We performed a bioinformatic screen of Golgi/endosome (G/E) hepatic protein fractions and found that ATIC, which is a rate limiting enzyme in the de novo purine biosynthesis pathway, and PTPLAD1 are associated with IR ...

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internalisation. The IR interactome (IRGEN) connects ATIC to AMPK within the G/E protein network (GEN). 45% of the IRGEN have common heritable variants associated with type 2 diabetes, including ATIC and AMPK. We show that PTPLAD1 and AMPK are rapidly compartmentalised within the plasma membrane (PM) and G/E fractions after insulin stimulation and that ATIC later accumulates in the G/E fraction. Using an in vitro reconstitution system and siRNA mediated partial knockdown of ATIC and PTPLAD1 in HEK293 cells, we show that both ATIC and PTPLAD1 affect IR tyrosine phosphorylation and endocytosis. We further show that insulin stimulation and ATIC knockdown readily increase the level of AMPKThr172 phosphorylation in IR complexes. We observed that IR internalisation was markedly decreased after AMPKα2 knockdown, and treatment with the ATIC substrate AICAR, which is an allosteric activator of AMPK, increased IR endocytosis in cultured cells and in the liver. These results suggest the presence of a signalling mechanism that senses adenylate synthesis, ATP levels and IR activation states and that acts in regulating IR autophosphorylation and endocytosis.

Date: Feb. 16, 2015

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