Summary
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
of VCAM-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 fulllength 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.
Keywords
Adhesion molecules - adhesion receptors/integrins - leukocyte function/activation
- leukocyte trafficking/recruitment - thrombin