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

Abstract

Cancer-specific mutations in the iSH2 (inter-SH2) and nSH2 (Nterminal SH2) domains of p85α, the regulatory subunit of phosphatidylinositide 3-kinase (PI3K), show gain of function. They induce oncogenic cellular transformation, stimulate cellular proliferation, and enhance PI3K signaling. Quantitative determinations of oncogenic activity reveal large differences between individual mutants of p85α. The mutant proteins are still able to bind to the catalytic subunits p110α and p110β. Studies with isoform-specific inhibitors of p110 suggest that expression of p85 mutants in fibroblasts leads exclusively to an activation of p110α, and p110α is the sole mediator of p85 mutant-induced oncogenic transformation. The characteristics of the p85 mutants are in agreement with the hypothesis that the mutations weaken an inhibitory interaction between p85α and p110α while preserving the stabilizing interaction between p85α iSH2 and the adapter-binding domain of p110α.oncogenic transformation | target of rapamycin T he phosphoinositide 3-kinase (PI3K) signaling pathway is deregulated in most human cancers by differential gene expression, amplification, or mutation. Of particular interest are mutations that occur in the catalytic subunit p110α of class I PI3K, because they confer a strong gain of function upon the enzyme, resulting in enhanced catalytic activity, constitutive signaling, and oncogenicity in vitro and in vivo (1-8). There have also been early reports of cancer-specific mutations in p85α, a regulatory subunit of class I PI3K (9-14). Such mutations gained high significance by recent comprehensive genomic analyses of glioblastomas (15,16). Approximately 9% of these tumors harbor a mutation in p85α. 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).We have studied mutations in p85α (referred to as p85). Most of these were identified in a genomic characterization of glioblastoma (15) and map to the iSH2 domain of p85; one was an engineered mutation that maps to the nSH2 domain of p85. 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. ResultsCancer-Derived Mutations of p85 Induce Oncogenic Transform...

A biochemical mechanism for the oncogenic potential of the p110β catalytic subunit of phosphoinositide 3-kinase

“…Given that phosphopeptide activation of Class IA PI3-kinase involves a disinhibition of p110 (10), the partial loss of p85 inhibition in p110β would be expected to lead to a corresponding loss of activation when tyrosine phosphorylated proteins bind to the p85 nSH2 domain. This prediction also is consistent with a recent study showing that p85 mutations disrupting either the nSH2-helical domain interface or the iSH2-C2 domain interface act primarily through p110α rather than p110β (26). Although we observed ≈50% less phosphopeptide activation of p85/p110β dimers as compared with p85/p110α dimers in vitro, Nurnberg and coworkers (27) reported similar levels of phosphopeptide activation of p85/p110α and p85/p110β dimers.…”

The p110α and p110β isoforms of PI3K play divergent roles in mammary gland development and tumorigenesis

“…In particular, we wanted to determine whether there is a difference between p110b inhibition as opposed to p110b deletion on oncogenic signals driven by MT or HER2/Neu. To investigate this, we isolated primary mammary tumor cells from tumorbearing MMTV-MT or MMTV-NeuT mice and subjected these cells to inhibitor studies using GDC-0941, a pan-PI3K inhibitor (Raynaud et al 2009); A66, a p110a-selective inhibitor (Sun et al 2010); and TGX-221, a p110b-selective inhibitor (Jackson et al 2005). We first determined that the amounts of p110a or p110b activity associated with the MT/p85 or NeuT/HER3/p85 complexes were not altered when cells were treated with these PI3K inhibitors (Supplemental Fig.…”

Phosphoinositide 3-Kinase (PI3K(p110α)) Directly Regulates Key Components of the Z-disc and Cardiac Structure

“…PIK75 has been used previously to study the role of PI3K(p110␣) but has some off-target activity (19,25). A66 is considered a more highly specific and selective inhibitor for p110␣ (20,21). The specificity of both inhibitors at different doses (0.1-100 M) was tested in NRVM with or without IGF1.…”