DYNAMICS OF ACTIVE LAMELLAE IN CULTURED EPITHELIAL-CELLS - EFFECTS OFEXPRESSION OF EXOGENOUS N-RAS ONCOGENE

We examined the functional consequences of cellular transformation of rat IAR-2 epithelial cells, by a mutant N-ras oncogene, on the dynamic s of active lamellae, structures that play an important role in cell m otility, adhesion, and surface-receptor capping, Lamellar activity was assessed by measuring the rate of outer-edge pseudopodial activity an d by analyzing the motility of Con A-coated beads placed on lamellar s urfaces with optical tweezers, Although transformation dramatically af fected the shape and size of active cellular lamellae, there was littl e detectable effect on either pseudopodial activity or bead movement, To investigate the potential relationship between functional lamellar activity and the microtubule cytoskeleton, lamellar activity was exami ned in nontransformed and transformed cells treated with the microtubu le-disrupting drug nocodazole, In the absence of microtubules, transfo rmed cells were less polarized and possessed decreased rates of pseudo podial and bead motility. On the basis of these observations, it is su ggested that ras-induced transformation of epithelial cells consists o f two cytoskeletal modifications: overall diminished actin cytoskeleta l dynamics in lamellae and reorganization of the microtubule cytoskele ton that directs pseudopodial activity to smaller polarized lamellae.