Phosphatidylinositol-3 kinase (PI3 kinase) is a lipid kinase that is activated in the cascade of signal transduction events involved in the initiation of cell growth. It catalyzes the production of a family of phosphoinositides (PI(3)P, PI(3,4)P2, and PI(3,4,5)P3) with phosphate at the D-3 position on the inositol ring. Thus, this enzyme differs from PI4 kinase and PI(4)P5-kinase, which are involved in the production of PI(4,5)P2, the substrate for phospholipase C (PLC). PLC hydrolyzes PI(4,5)P2 to diacylglycerol and inositol-1,4,5-trisphosphate (InsP3), which elevates intracellular free calcium concentration by releasing calcium from InsP3-sensitive intracellulular stores. However, the PLCs that have been characterized do not hydrolyze the products of the PI3 kinase (Serunian et al. 1989; Lips et al. 1989). Recent work from several laboratories has demonstrated that ligand-activated protein tyrosine kinases form tight complexes with their cytosolic targets, and these complexes remain intact through immunoprecipitation protocols (for review, see Cantley et al. 1991)....
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Soltoff et al. (1992) studied this question.