Oxidative Stress Decreases Phosphatidylinositol 4,5-Bisphosphate Levels by Deactivating Phosphatidylinositol-4-phosphate 5-Kinase β in a Syk-dependent Manner

Phosphatidylinositol 4,5-bisphosphate (PIP2) has many essential functions and its homeostasis is highly regulated. We previously found that hypertonic stress increases PIP2 by selectively activating the beta isoform of the type I phosphatidylinositol phosphate 5-kinase (PIP5K beta) through Ser/Thr dephosphorylation and promoting its translocation to the plasma membrane. Here we report that hydrogen peroxide (H2O2) also induces PIP5K beta Ser/Thr dephosphorylation, but it has the opposite effect on PIP2 homeostasis, PIP5K beta function, and the actin cytoskeleton. Brief H2O2 treatments decrease cellular PIP2 in a PIP5K beta-dependent manner. PIP5K beta is tyrosine phosphorylated, dissociates from the plasma membrane, and has decreased lipid kinase activity. In contrast, the other two PIP5K isoforms are not inhibited by H2O2. We identified spleen tyrosine kinase (Syk), which is activated by oxidants, as a candidate PIP5K beta kinase in this pathway, and mapped the oxidant-sensitive tyrosine phosphorylation site to residue 105. The PIP5K beta Y105E phosphomimetic is catalytically inactive and cytosolic, whereas the Y105F non-phosphorylatable mutant has higher intrinsic lipid kinase activity and is much more membrane associated than wild type PIP5K beta. These results suggest that during oxidative stress, as modeled by H2O2 treatment, Syk-dependent tyrosine phosphorylation of PIP5K beta is the dominant post-translational modification that is responsible for the decrease in cellular PIP2.