EZRIN NH2-TERMINAL DOMAIN INHIBITS THE CELL EXTENSION ACTIVITY OF THECOOH-TERMINAL DOMAIN

Overexpression in insect cells of the full coding sequence of the huma n membrane cytoskeletal linker ezrin (1-586) was compared with that of a NH2-terminal domain (ezrin 1-233) and that of a COOH-terminal domai n (ezrin 310-586). Ezrin (1-586), as well as ezrin (1-233) enhanced ce ll adhesion of infected Sf9 cells without inducing gross morphological changes in the cell structure. Ezrin (310-586) enhanced cell adhesion and elicited membrane spreading followed by microspike and lamellipod ia extensions by mobilization of Sf9 cell actin. Moreover some microsp ikes elongated into thin processes, up to 200 mu m in length, resembli ng neurite outgrowths by a mechanism requiring microtubule assembly. K inetics of videomicroscopic and drug-interference studies demonstrated that mobilization of actin was required for tubulin assembly to proce ed. A similar phenotype was observed in CHO cells when a comparable ez rin domain was transiently overexpressed. The shortest domain promotin g cell extension was localized between residues 373-586. Removal of re sidues 566-586, involved in in vitro actin binding (Turunen, O., T. Wa hlstrom, and A. Vaheri. 1994. J. Cell Biol. 126:1445-1453), suppressed the extension activity. Coexpression of ezrin (1-233) with ezrin (310 -586) in the same insect cells blocked the constitutive activity of ez rin COOH-terminal domain. The inhibitory activity was mapped within ez rin 115 first NH2-terminal residues. We conclude that ezrin has proper ties to promote cell adhesion, and that ezrin NH2-terminal domain nega tively regulates membrane spreading and elongation properties of ezrin COOH-terminal domain.