Association of CBFA2 mutation with decreased platelet PKC-theta and impaired receptor-mediated activation of GPIIb-IIIa and pleckstrin phosphorylation: proteins regulated by CBFA2 play a role in GPIIb-IIIa activation.
The mechanisms by which agonists activate glycoprotein (GP) IIb-IIIa function remain unclear. We have reported data on a patient with thrombocytopenia and impaired receptor-mediated aggregation, phosphorylation of pleckstrin (a protein kinase C [PKC] substrate), and activation of the GPIIb-IIIa complex. Abnormalities in hematopoietic transcription factors have been associated with thrombocytopenia and platelet dysfunction. To define the molecular mechanisms, we amplified from patient platelet RNA exons 3 to 6 of core-binding factor A2 (CBFA2) cDNA, which encompasses the DNA-binding Runt domain; a 13-nucleotide (nt) deletion was found (796-808 nt). The gDNA revealed a heterozygous mutation (G>T) in intron 3 at the splice acceptor site for exon 4, leading to a frameshift with premature termination in the Runt domain. On immunoblotting, platelet CBFA2, PKC-, albumin, and IgG were decreased, but pleckstrin, PKC-alpha, -betaI, -betaII, -eta, -epsilon, -delta, and -zeta, and fibrinogen were normal. Our conclusions are that (1) CBFA2 mutation is associated with not only thrombocytopenia, but also impaired platelet protein phosphorylation and GPIIb-IIIa activation; (2) proteins regulated by CBFA2 are required for inside-out signal transduction-dependent activation of GPIIb-IIIa; and (3) we have documented the first deficiency of a human PKC isozyme (PKC-), suggesting a major role of this isozyme in platelet production and function.
Sun
Liansheng
L
Division of Hematology and Thromboembolic Diseases, Temple University School of Medicine, 3400 N Broad St, OMS 300, Philadelphia, PA 19140, USA.
Mao
Guangfen
G
Rao
A Koneti
AK
D000595:Amino Acid Sequence; D001483:Base Sequence; D001792:Blood Platelets / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D005260:Female; D016368:Frameshift Mutation; D006579:Heterozygote; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000097:blood / Q000172:deficiency* / Q000235:genetics; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011493:Protein Kinase C / Q000097:blood / Q000172:deficiency* / Q000235:genetics; D000074121:Protein Kinase C-theta; D012333:RNA, Messenger / Q000097:blood / Q000235:genetics; D015398:Signal Transduction; D013921:Thrombocytopenia / Q000097:blood / Q000235:genetics
D001798:Blood Proteins; D018076:DNA, Complementary; D007527:Isoenzymes; D010750:Phosphoproteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D012333:RNA, Messenger; C039077:platelet protein P47; C076233:PRKCQ protein, human; D011493:Protein Kinase C; D000074121:Protein Kinase C-theta