Moesin, the major ERM protein of lymphocytes and platelets, differs from ezrin in its insensitivity to calpain

The ERM proteins, ezrin, radixin and moesin, provide regulated linkage of t he cytoskeleton with the plasma membrane, particularly in cell surface proj ections. Ezrin and moesin were found co-expressed, and radixin was not dete cted, in human blood lymphocytes, monocytes and neutrophils. Moesin is the quantitatively dominant ERM protein in these cells and the only one in plat elets. Because Ca signaling pathways involving calpain cleavages are import ant in blood cells, we examined ERM protein sensitivity to this protease. A striking difference was discovered: sensitivity of ezrin and resistance of moesin (and radixin) to calpain. In intact stimulated lymphocytes, ezrin w as cleaved, while moesin was not, strongly suggesting that differential sen sitivity to calpain contributes to specialized functions of these proteins. (C) 1999 Federation of European Biochemical Societies.