Abstract 682: The mechanism of PI3Kα activation by SH2 release

Abstract

Abstract Phosphoinositide 3-kinase α (PI3Kα) is a ubiquitous kinase mediating signaling cascades important for cell survival, proliferation and protein synthesis. It phosphorylates PIP2 to PIP3, to which downstream Akt kinase binds to execute singling. PI3Kα dysfunction has been extensively implicated in cancers. The kinase activity of PI3Kα is controlled by the interactions between its catalytic p110 and regulatory p85 subunits. The interactions of the SH2 domains in the p85 subunit, particularly nSH2, with p110 are key factors in PI3Kα inhibition. Release of the SH2 domains from the p110 subunit, is promoted by factors including phosphotyrosine peptides (RTK), calmodulin (CaM), and oncogenic mutations, thereby activating PI3Kα. Our recent data show that both phosphorylated and unphosphorylated CaMs are capable of binding to the SH2 domains, nSH2 and cSH2, thus promoting the PI3K activation. Despite numerous seminal publications over the past two decades, the mechanism of PI3Kα activation is still a mystery. The large distance between the PIP2 binding sites and the ATP pocket in the crystal structure suggests that the solved PI3Kα structure represents the inactive conformation. What is the activated conformation of PI3Kα, and how PI3Kα switches from the inactive to the active conformation in response to stimulus are the significant mechanistic questions. We employ the large-scale molecular dynamics (MD) simulations to visualize the PI3Kα activation stimulated by the release of SH2 domains in the p85 subunit at the atomic resolution. Our trajectories show that release of the nSH2 domain initiates a “switch-like” conformational change of the iSH2 domain, extracting the ATP from its pocket to the PIP2 binding sites, eventually leading to an activated conformation. This dynamic process is initiated by the break of salt-bridges between iSH2 and helical domains induced by the nSH2 release, and further facilitated by the various residues in activation loop of p110 subunit including His-917, Lys-802 and Lys-776 and in iSH2 of p85 subunit including Arg-461 and Arg-465. The release of the cSH2 domain in PI3Kα has a minor effect. This work, which for the first time uncovers the mechanism of PI3Kα activation at atomic resolution, is expected to promote cancer drug design from a mechanistic dynamic standpoint view. Funded by Frederick National Laboratory for Cancer Research, National Institutes of Health, under contract HHSN261200800001E. Citation Format: Mingzhen Zhang, Hyunbum Jang, Ruth Nussinov. The mechanism of PI3Kα activation by SH2 release [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 682.