HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Association of CBFA2 mutation with decreased platelet PKC- 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, I, II, , , , and , 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 GPIIbIIIa; 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. (Blood. 2004;103:948-954)