Abstract
OBJECTIVE: Mutations in the hematopoietic transcription factor RUNX1 cause thrombocytopenia and impaired platelet function. In a patient with a heterozygous mutation in RUNX1, we have described decreased platelet pleckstrin phosphorylation and protein kinase C- (PKC-, gene PRKCQ) associated with thrombocytopenia, impaired platelet aggregation, and dense granule secretion. Little is known regarding regulation of PKC- in megakaryocytes and platelets. We have addressed the hypothesis that PRKCQ is a direct transcriptional target of RUNX1. METHODS AND RESULTS: In a chromatin immunoprecipitation assay using megakaryocytic cells, there was RUNX1 binding in vivo to PRKCQ promoter region -1225 to -1056 bp containing a RUNX1 consensus site ACCGCA at -1088 to -1069 bp; an electrophoretic mobility shift assay showed RUNX1 binding to the specific site. In RUNX1 overexpression studies, PKC- protein expression and promoter activity were enhanced; mutation of RUNX1 site showed decreased activity even with RUNX1 overexpression. Lastly, PRKCQ promoter activity and PKC- protein were decreased by short interfering RNA knockdown of RUNX1. CONCLUSIONS: Our results provide the first evidence that PRKCQ is regulated at the transcriptional level by RUNX1 in megakaryocytic cells and a mechanism for PKC- deficiency associated with RUNX1 haplodeficiency.