Transcription Factor RUNX1 Regulates Platelet PCTP (Phosphatidylcholine Transfer Protein): Implications for Cardiovascular Events

Background: PCTP (phosphatidylcholine transfer protein) regulates the intermembrane transfer of phosphatidylcholine. Higher platelet PCTP expression is associated with increased platelet responses on activation of protease-activated receptor 4 thrombin receptors noted in black subjects compared with white subjects. Little is known about the regulation of plateletPCTP . Haplodeficiency of RUNX1, a major hematopoietic transcription factor, is associated with thrombocytopenia and impaired platelet responses on activation. Platelet expression profiling of a patient with aRUNX1 loss-of-function mutation revealed a 10-fold downregulation of thePCTP gene compared with healthy controls.Methods: We pursued the hypothesis thatPCTP is regulated by RUNX1 and thatPCTP expression is correlated with cardiovascular events. We studied RUNX1 binding to thePCTP promoter using DNA-protein binding studies and human erythroleukemia cells and promoter activity using luciferase reporter studies. We assessed the relationship betweenRUNX1 andPCTP in peripheral blood RNA andPCTP and death or myocardial infarction in 2 separate patient cohorts (587 total patients) with cardiovascular disease.Results: Platelet PCTP protein in the patient was reduced by ≈50%. DNA-protein binding studies showed RUNX1 binding to consensus sites in ≈1 kB ofPCTP promoter.PCTP expression was increased withRUNX1 overexpression and reduced withRUNX1 knockdown in human erythroleukemia cells, indicating thatPCTP is regulated by RUNX1. Studies in 2 cohorts of patients showed thatRUNX1 expression in blood correlated withPCTP gene expression;PCTP expression was higher in black compared with white subjects and was associated with future death/myocardial infarction after adjustment for age, sex, and race (odds ratio, 2.05; 95% confidence interval 1.6–2.7;P <0.0001).RUNX1 expression is known to initiate at 2 alternative promoters, a distal P1 and a proximal P2 promoter. In patient cohorts, there were differential effects ofRUNX1 isoforms onPCTP expression with a negative correlation in blood betweenRUNX1 expressed from the P1 promoter andPCTP expression.Conclusions: PCTP is a direct transcriptional target of RUNX1.PCTP expression is associated with death/myocardial infarction in patients with cardiovascular disease. RUNX1 regulation ofPCTP may play a role in the pathogenesis of platelet-mediated cardiovascular events.