Fibronectin potentiates actin polymerization in thrombin‐activated platelets

Abstract

The effect of fibronectin on the polymerization state of actin was studied. Triton X‐100‐insoluble cytoskeleton was prepared from thrombin‐activated platelets, and the conversion of G‐actin into F‐actin was monitored by an assay involving DNase I inhibition by G‐actin. It was found that fibronectin bound to membrane receptors decreased the level of platelet G‐actin. This observation suggests that in the presence of fibronectin a larger amount of F‐actin becomes incorporated into the Triton X‐100‐insoluble cytoskeleton. At the same molar concentration, fibrinogen only slightly increased actin polymerization, whereas bovine serum albumin at a much higher concentration caused a small inhibition of actin immobilization. Our data show that fibronectin, through interaction with the platelet actomyosin fibrillar system, facilitates actin polymerization into the cytoskeleton.