The WASH-complex subunit Strumpellin regulates integrin IIb3 trafficking in murine platelets

The platelet specific integrin alpha IIb beta 3 mediates platelet adhesion, aggregation and plays a central role in thrombosis and hemostasis. In resting platelets, alpha IIb beta 3 is expressed on the membrane surface and in intracellular compartments. Upon activation, the number of surface-expressed alpha IIb beta 3 is increased by the translocation of internal granule pools to the plasma membrane. The WASH complex is the major endosomal actin polymerization-promoting complex and has been implicated in the generation of actin networks involved in endocytic trafficking of integrins in other cell types. The role of the WASH complex and its subunit Strumpellin in platelet function is still unknown. Here, we report that Strumpellin-deficient murine platelets display an approximately 20% reduction in integrin alpha IIb beta 3 surface expression. While exposure of the internal alpha IIb beta 3 pool after platelet activation was unaffected, the uptake of the alpha IIb beta 3 ligand fibrinogen was delayed. The number of platelet alpha-granules was slightly but significantly increased in Strumpellin-deficient platelets. Quantitative proteome analysis of isolated alpha IIb beta 3-positive vesicular structures revealed an enrichment of protein markers, which are associated with the endoplasmic reticulum, Golgi complex and early endosomes in Strumpellin-deficient platelets. These results point to a so far unidentified role of the WASH complex subunit Strumpellin in integrin alpha IIb beta 3 trafficking in murine platelets.