Functional phenotype of phosphoinositide 3-kinase p85alpha-null platelets characterized by an impaired response to GP VI stimulation.
Phosphoinositide 3-kinases (PI3Ks), a family of lipid kinases comprising 3 classes with multiple isoforms, have been shown to participate in different phases of platelet signaling. To investigate the roles that enzymes play in platelet function in vivo and determine which isoforms are important for particular signaling events, we analyzed platelet function of gene knockout mice deficient in the p85alpha regulatory subunit of heterodimeric class IA PI3K. The kinase activity of p85alpha-/- platelets was only 5% of the activity of platelets from wild-type littermates. Platelet aggregation induced by adenosine diphosphate (ADP), thrombin, U46619, phorbol 12-myristate 13-acetate (PMA), or botrocetin was not defective in p85alpha-/- mice, compared with wild-type animals. In contrast, aggregation induced by collagen and collagen-related peptide (CRP) was partially but readily impaired in p85alpha-/- mice. Both P-selectin expression and fibrinogen binding in response to CRP were also decreased to a similar extent in p85alpha-/- platelets. Platelets from p85alpha-/- mice appeared to spread poorly over a CRP-coated surface with intact filopodial protrusions. Significant attenuation of CRP-induced tyrosine phosphorylation in known PI3K effectors such as Btk, Tec, PKB/Akt, and phospholipase Cgamma2 were observed with p85alpha-/- platelets, whereas no alteration was noted in upstream molecules of Syk, LAT, and SLP-76. Considered as a whole, these results provide the first genetic evidence that PI3K p85alpha plays a significant role in platelet function, almost exclusively in the glycoprotein (GP) VI/Fc receptor gamma chain complex-mediated signaling pathway.
Watanabe
Naohide
N
Blood Center, Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan.
Nakajima
Hideaki
H
Suzuki
Hidenori
H
Oda
Atsushi
A
Matsubara
Yumiko
Y
Moroi
Masaaki
M
Terauchi
Yasuo
Y
Kadowaki
Takashi
T
Suzuki
Harumi
H
Koyasu
Shigeo
S
Ikeda
Yasuo
Y
Handa
Makoto
M
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology* / Q000502:physiology / Q000648:ultrastructure; D002352:Carrier Proteins / Q000494:pharmacology; D003094:Collagen / Q000494:pharmacology; D003435:Crotalid Venoms / Q000494:pharmacology; D005340:Fibrinogen / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019007:P-Selectin / Q000096:biosynthesis; D010455:Peptides; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D010980:Platelet Membrane Glycoproteins / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology
D002352:Carrier Proteins; D003435:Crotalid Venoms; D019007:P-Selectin; D010455:Peptides; D010980:Platelet Membrane Glycoproteins; C435908:collagen-related peptide; C098341:platelet membrane glycoprotein VI; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C030961:botrocetin; D005340:Fibrinogen; D003094:Collagen; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D013917:Thrombin; D013755:Tetradecanoylphorbol Acetate