Inhibition of Protein Phosphatase 2A Activity by PI3Kγ Regulates β-Adrenergic Receptor Function

SummaryPhosphoinositide 3-kinase γ (PI3Kγ) is activated by G protein-coupled receptors (GPCRs). We show here that PI3Kγ inhibits protein phosphatase 2A (PP2A) at the β-adrenergic receptor (βAR, a GPCR) complex altering G protein coupling. PI3Kγ inhibition results in significant increase of βAR-associated phosphatase activity leading to receptor dephosphorylation and resensitization preserving cardiac function. Mechanistically, PI3Kγ inhibits PP2A activity at the βAR complex by phosphorylating an intracellular inhibitor of PP2A (I2PP2A) on serine residues 9 and 93, resulting in enhanced binding to PP2A. Indeed, enhanced phosphorylation of β2ARs is observed with a phosphomimetic I2PP2A mutant that was completely reversed with a mutant mimicking dephosphorylated state. siRNA depletion of endogenous I2PP2A augments PP2A activity despite active PI3K resulting in β2AR dephosphorylation and sustained signaling. Our study provides the underpinnings of a PI3Kγ-mediated regulation of PP2A activity that has significant consequences on receptor function with broad implications in cellular signaling.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (375 K)Download as PowerPoint slideHighlights► PI3Kγ inhibits βAR resensitization by regulating PP2A activity ► PI3Kγ inhibits PP2A activity by phosphorylating I2PP2A on Serine 9 and 93 ► Phosphorylation of I2PP2A leads to its agonist-mediated interaction with PP2A ► siRNA-targeted depletion of I2PP2A results in βAR resensitization