Biology subjects

Naga Prasad, S. N.

Publications and source records attributed to Naga Prasad, S. N..

3 recordsLinked to original sources

bioRxiv2020

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

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.

biochemistry↗

bioRxiv2020

Chemotherapeutic cardiotoxicity is associated with elevated β1-adrenergic receptor density

ObjectiveTo understand the underlying pathways that promote cardiotoxicity following chemotherapy. BackgroundAnthracyclines are associated with cardiotoxicity which could be potentiated with use of complementary agents (like anti-ERBB2 inhibitors) which together afford robust anti-neoplastic effects. Anthracyclines lead to oxidative stress and thought to induce cardiotoxicity. However, interventions reducing oxidative stress in patients have been unsuccessful suggesting mechanisms beyond oxidative stress. Despite {beta}-adrenergic receptors ({beta}ARs) being key regulators of cardiac function, nothing is known about their role in chemotherapy-mediated cardiotoxicity. Methods{beta}1 and/or {beta}2-AR density was assessed in end-stage human heart failure patient samples either due to anthracycline cardiotoxicity or non-anthracycline dilated cardiomyopathy (DCM). Since ERBB2 inhibition is integral to overall chemotherapeutic arsenal, we assessed {beta}1- and/or {beta}2-AR density, cardiac function by echocardiography and immunohistochemistry in mice following ERBB2-specific inhibitor AG825. ResultsSelective increase in cardiac {beta}1AR density is observed in end-stage human heart failure patient samples due to anthracycline cardiotoxicity as well as in ERBB2 inhibitor-treated mice. ConclusionsElevated {beta}1AR density may be the key common underlying mechanism which is altered in response to chemotherapy promoting cardiac dilation of otherwise healthy hearts. HighlightsIn contrast to downregulation of {beta}1-adrenergic receptors ({beta}1AR) in end-stage human heart failure, anthracycline cardiotoxicity-mediated failure is associated with selective increase in {beta}1AR density. ERBB2 inhibitor (AG825) treatment in mice results in cardiac dilation and selective rise in {beta}1AR density showing that increased {beta}1AR density in the heart could be a common mechanism underlying cardiotoxicity.

pharmacology and toxicology↗

bioRxiv2020

beta-blocker reverses inhibition of beta-2 adrenergic receptor resensitization by hypoxia

Ischemia/hypoxia is major underlying cause for heart failure and stroke. Although beta-adrenergic receptor ({beta}AR) is phosphorylated in response to hypoxia, less is known about the underlying mechanisms. Hypoxia results in robust GRK2-mediated {beta}2AR phosphorylation but does not cause receptor internalization. However, hypoxia leads to significant endosomal-{beta}2AR phosphorylation accompanied by inhibition of {beta}2AR-associated protein phosphatase 2A (PP2A) activity impairing resensitization. Phosphoinositide 3-kinase {gamma} (PI3K{gamma}) impedes resensitization by phosphorylating endogenous inhibitor of protein phosphatase 2A, I2PP2A that inhibits PP2A activity. Hypoxia increased PI3K{gamma} activity leading to significant phosphorylation of I2PP2A resulting in inhibition of PP2A and consequently resensitization. Surprisingly, {beta}-blocker abrogated hypoxia-mediated {beta}2AR phosphorylation instead of phosphorylation in normoxia. Subjecting mice to hypoxia leads to significant cardiac dysfunction and {beta}2AR phosphorylation showing conservation of non-canonical hypoxia-mediated pathway in vivo. These findings provide mechanistic insights on hypoxia-mediated {beta}AR dysfunction which is rescued by {beta}-blocker and will have significant implications in heart failure and stroke.

biochemistry↗