Akt phosphorylates insulin receptor substrate (IRS) to limit PI3K-mediated PI(3,4,5)P3 synthesis

The phosphoinositide 3-kinase (PI3K)-Akt network is tightly controlled by feedback mechanisms that regulate signal flow and ensure signal fidelity. Here, we show that Akt itself engages negative feedback by phosphorylating insulin receptor substrate (IRS) 1 and 2 on a number of residues. Mechanistically this serves to deplete plasma membrane-localised IRS1/2 and reduce its interaction with the insulin receptor. Together these events limit plasma membrane associated PI3K and phosphatidylinositol (3,4,5)-trisphosphate (PIP3) synthesis. We identified two Akt-dependent phosphorylation sites in IRS2 at S306 (S303 in mouse) and S577 (S573 in mouse) that are key drivers of this negative feedback. These findings establish another mechanism by which the kinase Akt auto-regulates its activity, through post-translational modification of the IRS scaffold that in turn controls PIP3 levels.