NEDD4-induced degradative ubiquitination of phosphatidylinositol 4-phosphate 5-kinase α and its implication in breast cancer cell proliferation.

Phosphatidylinositol 4-phosphate 5-kinase (PIP5K) family members generate phosphatidylinositol 4,5-bisphosphate (PIP2), a critical lipid regulator of diverse physiological processes. The PIP5K-dependent PIP2 generation can also act upstream of the oncogenic phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Many studies have demonstrated various mechanisms of spatiotemporal regulation of PIP5K catalytic activity. However, there are few studies on regulation of PIP5K protein stability. Here, we examined potential regulation of PIP5K alpha a PIP5K isoform, via ubiquitin-proteasome system, and its implication for breast cancer. Our results showed that the ubiquitin ligase NEDD4 (neural precursor cell expressed, developmentally down-regulated gene 4) mediated ubiquitination and proteasomal degradation of PIP5K, consequently reducing plasma membrane PIP2 level. NEDD4 interacted with the C-terminal region and ubiquitinated the N-terminal lysine 88 in PIP5K alpha. In addition, PIP5K alpha gene disruption inhibited epidermal growth factor (EGF)-induced Akt activation and caused significant proliferation defect in breast cancer cells. Notably, PIP5K alpha K88R mutant that was resistant to NEDD4-mediated ubiquitination and degradation showed more potentiating effects on Akt activation by EGF and cell proliferation than wild-type PIP5K alpha. Collectively, these results suggest that PIP5K alpha is a novel degradative substrate of NEDD4 and that the PIP5K alpha-dependent PIP2 pool contributing to breast cancer cell proliferation through PI3K/Akt activation is negatively controlled by NEDD4.