Cleavage of human 7-domain VCAM-1 (CD106) by thrombin

Vascular cell adhesion molecule 1 (VCAM-1, CD106) is expressed as a type I transmembrane integrin counter-receptor on activated endothelium and mediates white blood cell attachment. The alternatively spliced 7-domain (7d) form of VCAM-1 contains a potential thrombin cleavage site. Thrombin proteolysis of 7d-VCAM-1 may help regulate adhesive activity ofVCAM-1. We determined whether 7d-VCAM-1 is proteolyzed and rendered inactive by thrombin. Recombinant extracellular domain of 7d-VCAM-1 was cleaved by thrombin to generate 33- and 44-kDa products. Cleavage was in the sequence PGPR/IAAQIG near the N-terminal border of the alternatively spliced fourth immunoglobulin (Ig)-like module. There was no cleavage of 6d-VCAM-1 lacking the fourth module. Expression of full-length 7d-VCAM-1 presented on Chinese hamster ovary (CHO) monolayers, as detected by flow cytometry with an antibody directed to Ig-like modules 1-3, was reduced by thrombin treatment whereas there was no reduction in the expression of full-length 6d-VCAM-1. Adhesion of blood eosinophils to full-length 7d-VCAM-1 was reduced after treatment of CHO cells with thrombin, whereas adhesion to full-length 6d-VCAM-1 was not affected. We conclude that cleavage of 7d-VCAM-1 by thrombin is a potential mechanism for differential regulation of VCAM-1 splice forms in white blood cell adhesion and trafficking.