MOESIN INTERACTS WITH THE CYTOPLASMIC REGION OF INTERCELLULAR-ADHESION MOLECULE-3 AND IS REDISTRIBUTED TO THE UROPOD OF T-LYMPHOCYTES DURING CELL POLARIZATION

During activation, T lymphocytes become motile cells, switching from a spherical to a polarized shape. Chemokines and other chemotactic cyto kines induce lymphocyte polarization with the formation of a uropod in the rear pole, where the adhesion receptors intercellular adhesion mo lecule-1 (ICAM-1), ICAM-3, and CD44 redistribute. We have investigated membrane-cytoskeleton interactions that play a key role in the redist ribution of adhesion receptors to the uropod. Immunofluorescence analy sis showed that the ERM proteins radixin and moesin localized to the u ropod of human T lymphoblasts treated with the chemokine RANTES (regul ated on activation, normal T cell expressed, and secreted), a polariza tion-inducing agent; radixin colocalized with arrays of myosin II at t he neck of the uropods, whereas moesin decorated the most distal part of the uropod and colocalized with ICAM-1, ICAM-3, and CD44 molecules. Two other cytoskeletal proteins, beta-actin and alpha-tubulin, cluste red at the cell leading edge and uropod, respectively, of polarized ly mphocytes. Biochemical analysis showed that moesin coimmunoprecipitate s with ICAM-3 in T lymphoblasts stimulated with either RANTES or the p olarization-inducing anti-ICAM-3 HP2/19 mAb, as well as in the constit utively polarized T cell line HSB-2. In addition, moesin is associated with CD44, but not with ICAM-1, in polarized T lymphocytes. A correla tion between the degree of moesin-ICAM-3 interaction and cell polariza tion was found as determined by immunofluorescence and immunoprecipita tion analysis done in parallel. The moesin-ICAM-3 interaction was spec ifically mediated by the cytoplasmic domain of ICAM-3 as revealed by p recipitation of moesin with a GST fusion protein containing the ICAM-3 cytoplasmic tail from metabolically labeled Jurkat T cell lysates. Th e interaction of moesin with ICAM-3 was greatly diminished when RANTES -stimulated T lymphoblasts were pretreated with the myosin-disrupting drug butanedione monoxime, which prevents lymphocyte polarization. Alt ogether, these data indicate that moesin interacts with ICAM-3 and CD4 4 adhesion molecules in uropods of polarized T cells; these data also suggest that these interactions participate in the formation of links between membrane receptors and the cytoskeleton, thereby regulating mo rphological changes during cell locomotion.