Transcription Factor RUNX1 Regulates Platelet <i>PCTP</i> (Phosphatidylcholine Transfer Protein): Implications for Cardiovascular Events: Differential Effects of RUNX1 Variants.

Abstract

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 platelet <i>PCTP</i>. 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 a <i>RUNX1</i> loss-of-function mutation revealed a 10-fold downregulation of the <i>PCTP</i> gene compared with healthy controls. We pursued the hypothesis that <i>PCTP</i> is regulated by RUNX1 and that <i>PCTP</i> expression is correlated with cardiovascular events. We studied RUNX1 binding to the <i>PCTP</i> promoter using DNA-protein binding studies and human erythroleukemia cells and promoter activity using luciferase reporter studies. We assessed the relationship between <i>RUNX1</i> and <i>PCTP</i> in peripheral blood RNA and <i>PCTP</i> and death or myocardial infarction in 2 separate patient cohorts (587 total patients) with cardiovascular disease. Platelet PCTP protein in the patient was reduced by ≈50%. DNA-protein binding studies showed RUNX1 binding to consensus sites in ≈1 kB of <i>PCTP</i> promoter. <i>PCTP</i> expression was increased with <i>RUNX1</i> overexpression and reduced with <i>RUNX1</i> knockdown in human erythroleukemia cells, indicating that <i>PCTP</i> is regulated by RUNX1. Studies in 2 cohorts of patients showed that <i>RUNX1</i> expression in blood correlated with <i>PCTP</i> gene expression; <i>PCTP</i> 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; <i>P</i><0.0001). <i>RUNX1</i> expression is known to initiate at 2 alternative promoters, a distal P1 and a proximal P2 promoter. In patient cohorts, there were differential effects of <i>RUNX1</i> isoforms on <i>PCTP</i> expression with a negative correlation in blood between <i>RUNX1</i> expressed from the P1 promoter and <i>PCTP</i> expression. <i>PCTP</i> is a direct transcriptional target of RUNX1. <i>PCTP</i> expression is associated with death/myocardial infarction in patients with cardiovascular disease. RUNX1 regulation of <i>PCTP</i> may play a role in the pathogenesis of platelet-mediated cardiovascular events.