A type II phosphoinositide 3-kinase is stimulated via activated integrin in platelets. A source of phosphatidylinositol 3-phosphate.
We have observed that aggregation of human platelets, caused by activation of integrin alphaIIb beta3 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 alphaIIb beta3-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 alphaIIb beta3 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.
Zhang
J
J
Kimmel Cancer Institute and Cardeza Foundation for Hematologic Research, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Banfić
H
H
Straforini
F
F
Tosi
L
L
Volinia
S
S
Rittenhouse
S E
SE
D000730:Androstadienes / Q000494:pharmacology; D001792:Blood Platelets / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology; D002154:Calpain / Q000037:antagonists & inhibitors; D004789:Enzyme Activation / Q000502:physiology; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000145:classification / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis / Q000378:metabolism; D010974:Platelet Aggregation / Q000502:physiology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000819:agonists*; D011480:Protease Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D000730:Androstadienes; D002118:Calcium; D002154:Calpain; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011480:Protease Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D013755:Tetradecanoylphorbol Acetate; D000077191:Wortmannin; C060974:phosphatidylinositol 3,4,5-triphosphate; C060980:phosphatidylinositol 3,4-diphosphate; C055525:phosphatidylinositol 3-phosphate; C494918:AKT1 protein, human