Subcellular localization of RhoA and ezrin at membrane ruffles of human endothelial cells: Differential role of collagen and fibronectin

Endothelial cells and the regulation of their migration are of prime import ance in many physiological and pathological processes such as angiogenesis. RhoA, an important Rho family member known to trigger actin reorganization , has been shown to mediate the formation of focal adhesions and stress fib ers in quiescent fibroblasts. However, recent studies have emphasized its f unctional diversity and its implication in migration or metastatic processe s in different cell types other than fibroblasts. Its role in endothelial c ells is little known. In this study, we were interested by analyzing in hum an endothelial cells the subcellular redistribution of endogenous RhoA and the reorganization of cytoskeletal actin induced by two important extracell ular matrix proteins, collagen and fibronectin. This paper shows a transloc ation of RhoA and its association with cortical actin in focal contact doma ins at membrane ruffles and at lamellipodia of spread or migrating endothel ial cells, in the absence of any soluble mitogen stimulation. Furthermore, RhoA was found colocalized with ezrin, a member of the ERM family proteins newly described as important membrane-actin cytoskeleton linkers, at early membrane ruffles of endothelial cells spread on collagen but not on fibrone ctin. The present study points out that extracellular matrix, depending on the nature of its components, may promote distinct assemblies of focal cont act constitutive proteins and strongly suggests that endothelial RhoA, like Rad, may be an important mediator of matrix signaling pathway regulating e ndothelial cell adhesiveness and motility, independently of growth factor s timulation. (C) 1999 Academic Press.