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 a RHD patient showed decreased encoding for the A subunit of factor XIII, a transglutaminase that cross-links fibrin and induces clot stabilization. FXIII-A is synthesized by hematopoietic cells, megakaryocytes and monocytes.

AIMS

To understand RUNX1 regulation of expression in platelet/megakaryocyte and the mechanisms and consequences of decreased in RHD.

METHODS

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

RESULTS

Platelet mRNA and protein were decreased in our index patient and in two 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 (si)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 binding upon activation. expression and clot contraction were impaired on downregulation in human megakaryocytes.

CONCLUSIONS

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 αII β activation. - Platelets and thrombopoiesis.

ESSENTIALS

RUNX1 regulates expression of FXIII-A chain ( in megakaryocytes (MK) and platelets. Platelet and MK expression and clot contraction are decreased in deficiency. MK clot contraction, myosin phosphorylation and PAC1-binding are impaired in deficiency. Defective clot contraction in RHD arises from defects in multiple platelet-MK mechanisms.