Conjugation of SUMO to p85 leads to a novel mechanism of PI3K regulation

Class IA phosphatidylinositol 3-kinases (PI3Ks) are composed of p110 catalytic and p85 regulatory subunits. How regulatory subunits modulate PI3K activity remains only partially understood. Here we identified SUMO (small ubiquitin-related modifier) as a new player modulating this regulation. We demonstrate that both p85 beta and p85 alpha are conjugated to SUMO1 and SUMO2. We identified two lysine residues located at the inter-SH2 domain on p85 beta, a critical region required for inhibition of p110, as being required for SUMO conjugation. A SUMOylation-defective mutant p85 beta shows higher activation of the PI3K pathway, and increased cell migration and transformation. Moreover, the cancer-related KS459del mutant in p85 alpha was less efficiently SUMOylated compared with the wild-type protein. Finally, our results show that SUMO modulates p85 tyrosine phosphorylation, a modification correlating with PI3K pathway activation. Thus, SUMO reduces the levels of tyrosine-phosphorylated-p85 while loss of SUMOylation results in increased tyrosine phosphorylation of p85. In summary, we identify SUMO as a new important player in the regulation of the PI3K pathway through modulation of p85.