Somatic Mutations in p85α Promote Tumorigenesis through Class IA PI3K Activation

Abstract

SUMMARY Members of the mammalian phosphoinositide-3-OH kinase (PI3K) family of proteins are critical regulators of various cellular process including cell survival, growth, proliferation and motility. Oncogenic activating mutations in the p110α catalytic subunit of the heterodimeric p110/p85 PI3K enzyme are frequent in human cancers. Here we show the presence of frequent mutations in p85α in colon cancer, a majority of which occurs in the inter-Src homology-2 (iSH2) domain. These mutations uncouple and retain p85α's p110-stabilizing activity, while abrogating its p110-inhibitory activity. The p85α mutants promote cell survival, Akt activation, anchorage independent cell growth, and oncogenesis in a p110-dependent manner. SIGNIFICANCE Somatic mutations in the catalytic p110α subunit of PI3K are common in cancers. In this study, we show the occurrence of frequent mutations in the regulatory p85α subunit of PI3K in human cancers. Our data demonstrate an alternate mechanism for PI3K-pathway activation and oncogenesis resulting from the impaired regulation of p110 activity by mutant p85α. Further, p85α mutations are likely to be useful as diagnostic markers for identification of p110-dependent tumors that may not carry an activating p110α mutation, but are candidates for targeted treatment with PI3K pathway inhibitors that are in development.

Cancer-derived mutations in the regulatory subunit p85α of phosphoinositide 3-kinase function through the catalytic subunit p110α

“…The p85 mutant-expressing cells show enhanced signaling through the PI3K pathway, as evidenced by the phosphorylation of Akt and 4E-BP. Expression of mutant or WT exogenous p85 in CEF also induces elevated levels of p110α by stabilizing the catalytic subunit (17,29). The observations are in agreement with published studies on p85 mutants that used different cellular systems (17,19).…”

“…These mutations show oncogenic potency in cell culture and elevated levels of downstream signaling and operate through the p110α isoform of the catalytic subunit of class I PI3K. Our observations extend recent studies of the p85α mutants using different cell systems (17,19) by providing quantitative data on the oncogenic potency of the mutations and by presenting evidence that suggests a unique role of p110α for the p85 mutation-induced gain of function in PI3K activity. …”

“…The mutations cluster in the inter-SH2 (iSH2) domain of p85α, involving residues that interact with the C2 domain of the catalytic subunit p110α (15,17). The iSH2-C2 domain interaction has an inhibitory effect on enzyme activity, and the mutations in the iSH2 domain of p85α could weaken this interaction and release the inhibition of PI3K activity (15,(17)(18)(19). A similar mechanism has been proposed for the gain-of-function mutations in the helical domain of p110α that alleviate an inhibitory interaction with the N-terminal SH2 domain (nSH2) of p85α (20).…”

Disruption of PH–kinase domain interactions leads to oncogenic activation of AKT in human cancers

“…Coding exons of AKT1, AKT2 and AKT3 were amplified and sequenced as described before (Dataset S6) (35). Retroviral constructs expressing WT and mutant AKT were used to generate stable BaF3, MCF10A, and NIH 3T3 cell lines for studying signaling, transformation and modeling oncogenesis in vivo.…”

“…Previous studies have shown that BaF3 cells stably expressing oncogenes promote a leukemia-like disease when implanted in mice, leading to reduced overall survival (34,35). Because the AKT1 mutants cooperate with active MEK1 to promote factor-independent growth of BaF3 cells (Figs.…”