Transcription factor RUNX1 regulates coagulation factor XIII-A (): decreased platelet-megakaryocyte expression and clot contraction in haplodeficiency.

Background: Germline haplodeficiency (RHD) is associated with thrombocytopenia, platelet dysfunction, and predisposition to myeloid malignancies. Platelet expression profiling of an RHD patient showed decreased , encoding for the A subunit of factor (F)XIII a transglutaminase that cross-links fibrin and induces clot stabilization. FXIII-A is synthesized by hematopoietic cells, megakaryocytes, and monocytes.

Objectives: To understand RUNX1 regulation of expression in platelets/megakaryocytes and the mechanisms and consequences of decreased in RHD.

Methods: We performed studies in platelets, human erythroleukemia (HEL) cells, and human CD34+ cell-derived megakaryocytes including on clot contraction in cells following small inhibitor RNA knockdown (KD) of RUNX1 or F13A1.

Results: Platelet mRNA and protein were decreased in our index patient and in 2 siblings from an unrelated family with RHD. Platelet-driven clot contraction was decreased in the patient and affected daughter. Promoter studies in HEL cells showed that regulates transcription RUNX1 overexpression increased, and small inhibitor RNA RUNX1 KD reduced promoter activity and protein. Following or KD, clot contraction by HEL cells was decreased, as were FXIII-A surface expression, myosin light chain phosphorylation, and PAC1 antibody binding upon activation. expression and clot contraction were impaired in downregulation in human megakaryocytes.

Conclusion: RUNX1 regulates platelet-megakaryocyte expression, which is decreased in RHD, reflecting regulation of a coagulation protein by a hematopoietic transcription factor. Platelet and megakaryocyte clot contraction is decreased in RHD, related to multiple impaired mechanisms including expression myosin phosphorylation, and αβ activation.