Regulation of PECAM-1 in endothelial cells during cell growth and migration

Endothelial cells (EC) that form the inner lining of blood vessels remain q uiescent in the normal adult vasculature except during angiogenesis and ree ndothelialization, which result in EC proliferation and migration. EC place d in culture at subconfluent density also undergo cell multiplication and m ovement. This report demonstrates that whereas in confluent EC in a compact monolayer, the EC-EC adhesion molecule platelet-endothelial cell adhesion molecule-1 (PECAM-1) is strongly expressed at cell borders, little or no PE CAM-1 immunostaining Is detected in sparse or migrating cultured EC. Consis tent with this observation, steady-state PECAM-1 mRNA expression was much l ower in subconfluent EC than in confluent EC. The absence of PECAM-1 expres sion in sparse EC appeared not to be linked to ability to proliferate, sinc e PECAM-1 expression remained low even in the presence of nitric oxide (NO) or mitomycin C, agents that inhibit EC growth. However, another growth-inh ibitory agent, TGF-beta1, did not alter PECAM-1 staining. Based on these ob servations, it is hypothesized that cell-associated mechanical forces under lying cell tensegrity regulate PECAM-1 expression.