ESSENTIAL FUNCTIONS OF EZRIN IN MAINTENANCE OF CELL-SHAPE AND LAMELLIPODIAL EXTENSION IN NORMAL AND TRANSFORMED FIBROBLASTS

Background: Changes in cell shape and motility are important manifesta tions of oncogenic transformation, hut the mechanisms underlying these changes and key effector molecules in the cytoskeleton remain unknown . The Fos oncogene induces expression of ezrin, the founder member of the ezrin/radixin/moesin (ERM) protein family, but not expression of t he related ERM proteins, suggesting that ezrin has a distinct role in cell transformation. ERM proteins have been suggested to link the plas ma membrane to the actin-based cytoskeleton and are substrates and anc horing sites for a variety of protein kinases. Here, we examined the r ole of ezrin in cellular transformation. Results: Fos-mediated transfo rmation of Rat-1 fibroblasts resulted in an increased expression and h yperphosphorylation of ezrin, and a concomitant increased association of ezrin with the cortical cytoskeleton. We lagged ezrin with green fl uorescent protein and examined its distribution in normal and Fos-tran sformed fibroblasts: ezrin was concentrated at the leading edge of ext ending pseudopodia of Fos-transformed Rat-1 cells, and was mainly cyto solic in normal Rat-1 cells. Functional ablation of ezrin by micro-CAL I (chromophore-assisted laser inactivation) blocked plasma-membrane ru ffling and motility of Fos-transformed fibroblasts. Ablation of ezrin in normal Rat-1 cells caused a marked collapse of the leading edge of the cell, Conclusion: Ezrin plays an important role in pseudopodial ex tension in Fos-transformed Rat-1 fibroblasts, and maintains cell shape . in normal Rat-1 cells, The increased expression, hyperphosphorylatio n and subcellular redistribution of ezrin upon fibroblast transformati on coupled with ifs roles in cell shape and motility suggest a critica l role for ezrin in oncogenic transformation.