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Publication Abstract from PubMed

Somatic missense mutations in PIK3CA, which encodes the p110alpha catalytic subunit of phosphoinositide 3-kinases, occur frequently in human cancers. Activating mutations spread across multiple domains, some of which are located at inhibitory contact sites formed with the regulatory subunit p85alpha. PIK3R1, which encodes p85alpha, also has activating somatic mutations. We find a strong correlation between lipid kinase and lipid-binding activities for both wild-type (WT) and a representative set of oncogenic mutant complexes of p110alpha/p85alpha. Lipid binding involves both electrostatic and hydrophobic interactions. Activation caused by a phosphorylated receptor tyrosine kinase (RTK) peptide binding to the p85alpha N-terminal SH2 domain (nSH2) induces lipid binding. This depends on the polybasic activation loop as well as a conserved hydrophobic motif in the C-terminal region of the kinase domain. The hotspot E545K mutant largely mimics the activated WT p110alpha. It shows the highest basal activity and lipid binding, and is not significantly activated by an RTK phosphopeptide. Both the hotspot H1047R mutant and rare mutations (C420R, M1043I, H1047L, G1049R and p85alpha-N564D) also show increased basal kinase activities and lipid binding. However, their activities are further enhanced by an RTK phosphopeptide to levels markedly exceeding that of activated WT p110alpha. Phosphopeptide binding to p110beta/p85alpha and p110delta/p85alpha complexes also induces their lipid binding. We present a crystal structure of WT p110alpha complexed with the p85alpha inter-SH2 domain and the inhibitor PIK-108. Additional to the ATP-binding pocket, an unexpected, second PIK-108 binding site is observed in the kinase C-lobe. We show a global conformational change in p110alpha consistent with allosteric regulation of the kinase domain by nSH2. These findings broaden our understanding of the differential biological outputs exhibited by distinct types of mutations regarding growth factor dependence, and suggest a two-tier classification scheme relating p110alpha and p85alpha mutations with signalling potential.Oncogene advance online publication, 28 November 2011; doi:10.1038/onc.2011.532.

Regulation of lipid binding underlies the activation mechanism of class IA PI3-kinases.,Hon WC, Berndt A, Williams RL Oncogene. 2011 Nov 28. doi: 10.1038/onc.2011.532. PMID:22120714^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.