Downregulation of TREM-like transcript (TLT)-1 and collagen receptor α2 subunit, two novel RUNX1-targets, contributes to platelet dysfunction in familial platelet disorder with predisposition to acute myelogenous leukemia.

GLEMBOTSKY AC.; SLIWA D.; BLUTEAU D.; BALAYN N.; MARIN OYARZUN CP.; RAIMBAULT A,; BORDAS M.; DROIN N.; PIROZHKOVA I.; WASHINGTON V.; GOETTE NP.; MARTA RF.; FAVIER R.; RASLOVA H.; HELLER PG.

Conferencia; Cell Biology of Megakaryocytes and Platelets Gordon Research Conference; 2019

Germline RUNX1 mutations lead to thrombocytopenia and platelet dysfunction in familial platelet disorder with predisposition to acute myelogenous leukemia (FPD/AML). Multiple aspects of platelet function are impaired in these patients, associated with altered expression of genes regulated by RUNX1. We aimed to identify RUNX1-targets involved in platelet function by combining transcriptome analysis of patient and shRUNX1-transduced megakaryocytes. Downregulated genes included TREM-like transcript (TLT)-1 (TREML1) and the integrin subunit α2 (ITGA2) of collagen receptor α2β1, which are involved in platelet aggregation and adhesion, respectively. RUNX1 binding to regions enriched for H3K27Ac marks was demonstrated for both genes using chromatin immunoprecipitation. Cloning of these regions upstream of the respective promoters in lentivirus allowing mCherry reporter expression showed that RUNX1 positively regulates TREML1 and ITGA2 and this regulation was abrogated after deletion of RUNX1 sites. TLT-1 content was reduced in patient megakaryocytes and platelets. A blocking anti-TLT-1 antibody was able to block aggregation of normal but not patient platelets, whereas recombinant soluble TLT-1 potentiated fibrinogen binding to patient platelets, pointing to a role for TLT-1 deficiency in the platelet function defect. Low levels of α2 integrin subunit were demonstrated in patient platelets and megakaryocytes, coupled with reduced platelet and megakaryocyte adhesion to collagen, both under static and flow conditions. In conclusion, we show that gene expression profiling of RUNX1 knock-down or mutated megakaryocytes provides a suitable approach to identify novel RUNX1-targets, among which downregulation of TREML1 and ITGA2 clearly contribute to the platelet phenotype of FPD/AML.