Phosphoinositide 3-kinase gamma and p85/phosphoinositide 3-kinase in platelets. Relative activation by thrombin receptor or beta-phorbol myristate acetate and roles in promoting the ligand-binding function of alphaIIbbeta3 integrin.
Platelets exposed to thrombin or thrombin receptor agonist peptide (SFLLRN) activate phospholipase C and protein kinase C (PKC), and accumulate 3-phosphorylated phosphoinositides (3-PPI) as a function of the activation and relocalization of two cytoskeletally-associated phosphoinositide 3-kinases (PI 3-K): p85/PI 3-K and PI 3-Kgamma. We now report that exposure of platelets to PKC-activating beta-phorbol myristate acetate (betaPMA) does not stimulate PI 3-Kgamma, but rather stimulates p85/PI 3-K, which associates with the cytoskeleton. Wortmannin is an inhibitor of both PI 3-Ks, known to act with more potency on p85/PI 3-K. betaPMA-stimulated 3-PPI accumulation is more sensitive to wortmannin (IC50 = 1.3 nM) than is SFLLRN- or thrombin-stimulated 3-PPI accumulation (IC50 = 10 nM). The activity of p85/PI 3-K in immunoprecipitates or in cytoskeletal fractions is inhibited more potently by exposure of platelets to wortmannin than is the activity of PI 3-Kgamma. betaPMA or SFLLRN promotes the conversion of platelet integrin alphaIIb/beta3 into a fibrinogen-binding form required for platelet aggregation. Activation of alphaIIb/beta3 in response to betaPMA or SFLLRN is inhibited by wortmannin with an IC50 of 1 nM in each case. Wortmannin inhibits neither activation of alphaIIb/beta3 by ligand-induced binding site antibody (anti-LIBS6 Fab) nor anti-LIBS6 Fab-induced platelet aggregation in the presence of fibrinogen, indicating that this type of "outside-in" signaling by alphaIIb/beta3 is largely PI 3-K-independent. We conclude that p85/PI 3-K, in preference to PI 3-Kgamma, contributes to activation of alphaIIb/beta3 when the thrombin receptor or PKC is stimulated.
Zhang
J
J
Department of Pharmacology/Jefferson Cancer Institute, Philadelphia, Pennsylvania 19107, USA.
Zhang
J
J
Shattil
S J
SJ
Cunningham
M C
MC
Rittenhouse
S E
SE
D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000097:blood*; D010974:Platelet Aggregation / Q000187:drug effects; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D018179:Receptors, Thrombin / Q000819:agonists / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; D008024:Ligands; D010446:Peptide Fragments; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D018179:Receptors, Thrombin; C082835:thrombin receptor peptide (42-47); D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D013755:Tetradecanoylphorbol Acetate; D000077191:Wortmannin