A Type II Phosphoinositide 3-Kinase Is Stimulated via Activated Integrin in Platelets

• Published in: The Journal of biological chemistry 1998-06, Vol.273 (23), p.14081-14084
• Main Authors: Zhang, Jun, Banfic, Hrvoje, Straforini, Francesca, Tosi, Lara, Volinia, Stefano, Rittenhouse, Susan E.
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.23.14081

We have observed that aggregation of human platelets, caused by activation of integrin αIIbβ3 and its consequent binding of fibrinogen, stimulates a novel pathway for synthesis of phosphatidylinositol 3,4bisphosphate, thereby activating protein kinase B/Akt. Such synthesis depends upon both the generation of phosphatidylinositol 3-phosphate (PtdIns3P), which is sensitive to wortmannin (IC50 7 nm) and calpain inhibitors, and the phosphorylation of PtdIns3P by PtdIns3P 4-kinase. We now report that a recently characterized C2 domain-containing phosphoinositide 3-kinase isoform (HsC2-PI3K) is present in platelets and a leukemic cell line (CHRF-288) derived from megakaryoblasts, and is likely to be responsible for the stimulated synthesis of PtdIns3P observed in platelets. HsC2-PI3K, identifiable by Western blotting and immunoprecipitatable activity, is sensitive to wortmannin (IC50 6–10 nm), requires Mg2+, and shows strong preference for PtdIns over PtdIns4P or phosphatidylinositol 4,5-bisphosphate as substrate. HsC2-PI3K is activated severalfold when platelets aggregate in an αIIbβ3-dependent manner or when platelet or CHRF-288 lysates are incubated with Ca2+. Activation is prevented by calpain inhibitors. CHRF-288, which cannot undergo activation of αIIbβ3 and thereby aggregate in response to platelet agonists, do not generate PtdIns3P or activate HsC2-PI3K under conditions that stimulate other phosphoinositide 3-kinases. HsC2-PI3K may thus be an important effector for integrin-dependent signaling.