Oncogenic mutations ofPIK3CAlead to increased membrane recruitment driven by reorientation of the ABD, p85 and C-terminus

Abstract

PIK3CA encoding the phosphoinositide 3-kinase (PI3K) p110α catalytic subunit is frequently mutated in cancer. The mechanisms underlying PI3K activation on membranes, and how oncogenic mutations distributed throughout p110α increase kinase activity is undefined. Using a synergy of biochemical assays and hydrogen deuterium exchange mass spectrometry (HDX-MS), we reveal unique regulatory mechanisms underlying PI3K activation. Engagement of p110α on membranes leads to disengagement of the ABD domain of p110α from the catalytic core, and the C2 domain from the iSH2 domain of the p85 regulatory subunit. PI3K activation also requires reorientation of the C-terminus, with mutations that alter the inhibited conformation of the C-terminus increasing membrane binding. Mutations at the C-terminus (M1043I/L, H1047R, G1049R, and N1068KLKR) activate p110α through distinct mechanisms, with this having important implications for mutant selective inhibitor development. This work reveals unique mechanisms underlying oncogenic mutants activate PI3K and explains how double mutants can synergistically increase PI3K activity.