Induction of Membrane Ruffling and Fluid-Phase Pinocytosis in Quiescent Fibroblasts by <i>ras</i> Proteins

TLDR

Expression of the ras oncogene is thought to be one of the contributing events in the initiation of certain types of human cancer. The study aimed to identify cellular activities directly triggered by ras proteins. The authors microinjected human H‑ras proteins into quiescent rat embryo fibroblasts and examined early consequences. Within 30 minutes to 1 hour after injection, ras proteins induced marked surface ruffling and fluid‑phase pinocytosis, with the oncogenic form producing effects lasting over 15 hours and the proto‑oncogenic form lasting 3 hours; the stimulation was dose‑dependent and accompanied by phospholipase A2 activation, suggesting these rapid membrane changes are primary events in ras action.

Abstract

Expression of the ras oncogene is thought to be one of the contributing events in the initiation of certain types of human cancer. To determine the cellular activities that are directly triggered by ras proteins, the early consequences of microinjection of the human H- ras proteins into quiescent rat embryo fibroblasts were investigated. Within 30 minutes to 1 hour after injection, cells show a marked increase in surface ruffles and fluid-phase pinocytosis. The rapid enhancement of membrane ruffling and pinocytosis is induced by both the proto-oncogenic and the oncogenic forms of the H- ras protein. The effects produced by the oncogenic protein persist for more than 15 hours after injection, whereas the effects of the proto-oncogenic protein are short-lived, being restricted to a 3-hour interval after injection. The stimulatory effect of the ras oncogene protein on ruffling and pinocytosis is dependent on the amount of injected protein and is accompanied by an apparent stimulation of phospholipase A 2 activity. These rapid changes in cell membrane activities induced by ras proteins may represent primary events in the mechanism of action of ras proteins.