Smooth muscle cells on the move: the battle for actin
Authors: P. A. Doevendans, G. van Eys
Journal: Cardiovascular Research (2002)

composed of a N-terminal FERM domain (F: four point issue.one protein), a central a-domain and a C-terminal tail domain.Inactivated moesin is folded such that the FERM domain bites and holds the tail.Upon phosphorylation of 1. Introduction moesin the protein unfolds, whereafter the FERM domain binds to specific sites in the membrane (like for instance Restenosis has been troubling patients and cardiologists, CD44, CD43, ICAM-1, ICAM-2 and L-selectin in lymphofollowing percutaneous transluminal coronary angioplasty cytes), while the tail interacts with F-actin [3,4].The (PTCA), since the technique was introduced [1].De-activated protein therefore connects F-actin to the plasma differentiation, migration and proliferation of smooth membrane.Blindt et al. [2] showed the increased expresmuscle cell (SMC) can cause a new obstructive lesion, at sion of moesin following PTCA in pigs.Furthermore, in the site of the mechanical intravascular balloon interven-cell culture experiments they showed increased invasive tion.Gradually our knowledge about SMC mobility is potential in human SMC, Mel Im (melenoma metastatic increasing.This mobility is the consequence of SMC cell line) and HepG2 cells upon moesin overexpression.(de)differentiation.The ability of these cells to switch fromThe migration potential is reduced by blocking moesin in a contractile to a synthetic / proliferative phenotype has Mel Im cells, using antisense molecules [2].In this paper, been a prime target of research in the cardiovascular field.there is no information provided on the phosphorylation Although the different phenotypes of SMC have been state of moesin, neither are we informed about the known for years, the underlying signalling, changes in behaviour of ezrin and radixin.The marked effects of gene expression and protein activation and the mechanism interventions on moesin expression levels seem surprising of cell mobility adaptation, still remain to be resolved.since in moesin-deficient mice no phenotype could be Also the keys to the maintenance of SMC (de)differentia-detected.This is probably due to redundancy of the ERM tion are currently unknown.Many clues indicate a crucial proteins although under physiologic conditions the various role for actin stabilisation and assembly regulating pro-ERM proteins are expressed in different tissues [5].In teins.these mice the behaviour and function of platelets, fibroblasts and mast cells was measured, but no changes were observed.Even fibroblast migration was comparable 2. Moesin expression and function in wild-type and moesin-deficient mice.The lack of phenotypical abnormalities could be related to the fact that In this issue important work is reported on the role of these moesin-deficient mice (and isolated cells) were never moesin, one of the actin binding proteins on SMC mobility challenged.by Blindt et al. [2].The moesin gene is positioned on the Several lines of evidence suggest that moesin could be X-chromosome and part of a protein family indicated by the family member responding to cell stress.For instance, ERM (ezrin, radixin and moesin).All three proteins are in lymphocytes the interaction of moesin with the membrane bound L-selectin protein is mediated by PKC activation, whereas the interaction of ezrin with L-selectin is not