engleski

Filamin A regulates thrombopoietin c-Mpl receptor function.

Filamin A (FlnA) is a large cytoplasmic protein that crosslinks actin filament networks and links membrane glycoproteins and signaling proteins to the underlying cytoskeleton. We have previously shown that FlnA is critical for platelet production and survival since mice that specifically lack FlnA in their platelets (FlnA loxP-PF4-Cre) have macrothrombocytopenia, due to rapid platelet clearance and an altered megakaryocyte (MK) maturation program. MKs deficient in FlnA more rapidly convert their proplatelets into large platelets. FlnA loxP-PF4-Cre mice have a marked increase in MK numbers in bone marrow and spleen, increased thrombopoietin (TPO) plasma levels and 35% of their circulating platelets are reticulated indicating increased thrombopoiesis. Duration and amplitude of TPO receptor (c-Mpl) signaling is a highly regulated process that is crucial for MK differentiation. Here we show that c-Mpl binds to the actin cytoskeleton in bone marrow derived MKs upon TPO stimulation in a dose dependent manner and is inhibited by actin depolymerizing drug, lantranculin A. Linkage of c-Mpl receptor to the actin cytoskeleton was dependent on FlnA since c-Mpl was mostly in soluble, F-actin unbound fraction of the cell in FlnA KO MKs. Immunofluorescence analysis revealed partial colocalization of FlnA and c-Mpl in WT MKs. In addition, TPO stimulation induced Ser2152 phosphorylation of FlnA, redistributing and disconnecting of phospho-filamin A from actin cytoskeleton. Moreover, surface expression of c-Mpl receptor was markedly decreased in both FlnA KO MK and platelets, suggesting a role for FlnA in stabilizing/recycling c-Mpl on the cell surface

thrombopoetin; c-Mpl; filamin A; megakaryocytes

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