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bioRxiv · 10.1101/2020.09.17.302448

Insulin inhibits protein phosphatase 2A to impair β-adrenergic receptor function

Sahu, A.·Sun, Y.·Mukherjee, S.·Witherow, C.·Stenson, K.·Tesmer, J. J. G.·Mohan, M.·Naga Prasad, S. N.
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Abstract

Insulin impairs {beta}2-adrenergic receptor ({beta}2AR) function through G protein-coupled receptor kinase 2 (GRK2) by phosphorylation but less is known about dephosphorylation mechanisms mediated by protein phosphatase 2A (PP2A). Pharmacologic or genetic inhibition of phosphoinositide 3-kinase {gamma} (PI3K{gamma}) unexpectedly resulted in significant reduction of insulin-mediated {beta}2AR phosphorylation. Interestingly, {beta}2AR-associated phosphatase activity was inhibited by insulin but was reversed by knock-down of PI3K{gamma} showing negative regulation of PP2A by PI3K{gamma}. Co-immunoprecipitation and surface plasmon resonance studies using purified proteins showed that GRK2 and PI3K{gamma} form a complex and could be recruited to {beta}2ARs as GRK2 interacts with insulin receptor substrate following insulin treatment. Consistently, {beta}-blocker pretreatment did not reduce insulin-mediated {beta}2AR phosphorylation indicating agonist- and G{beta}{gamma}-independent non-canonical regulation of receptor function. Mechanistically, PI3K{gamma} inhibits PP2A activity at the {beta}AR complex by phosphorylating an intracellular inhibitor of PP2A (I2PP2A). Knock-down or CRISPR ablation of endogenous I2PP2A unlocked PP2A inhibition mediating {beta}2AR dephosphorylation showing an unappreciated acute regulation of PP2A in mediating insulin-{beta}2AR cross-talk. SummaryInsulin impairs {beta}2-adrenergic receptor ({beta}2AR) function through G protein-coupled receptor kinase 2 (GRK2). We show that insulin simultaneously inhibits protein phosphatase 2A (PP2A) sustaining {beta}2AR functional impairment. Unexpectedly, releasing PP2A inhibition by PI3K{gamma} preserves {beta}2AR function despite intact insulin-driven GRK2-mechanisms.

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Sahu, A., Sun, Y., Mukherjee, S., Witherow, C., Stenson, K., Tesmer, J. J. G., Mohan, M., Naga Prasad, S. N.. 2020-09-19. Insulin inhibits protein phosphatase 2A to impair β-adrenergic receptor function. https://doi.org/10.1101/2020.09.17.302448

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