Phosphorylates PtdIns and PtdIns4P with a preference for PtdIns (PubMed:10805725, PubMed:9830063, PubMed:11533253). Does not phosphorylate PtdIns(4,5)P2 (PubMed:9830063). May be involved in EGF and PDGF signaling cascades (PubMed:10805725). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol 4-phosphate) + ATP = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-3,4-bisphosphate) + ADP + H(+) a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + ATP = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-3-phosphate) + ADP + H(+) Activated by GRB2. Part of a complex with ERBB2 and EGFR. Part of a complex with phosphorylated EGFR and GRB2. Interacts with phosphorylated EGFR and PDGFR, maybe indirectly. Interacts with GRB2. Found mostly in the microsome, but also in the plasma membrane and cytosol. Nuclear in testis. Expressed in columnar and transitional epithelia, mononuclear cells, and ganglion cells (at protein level). Widely expressed, with highest levels in thymus and placenta and lowest in peripheral blood, skeletal muscle and kidney. Belongs to the PI3/PI4-kinase family. It is uncertain whether Met-1 or Met-26 is the initiator.