Effects of cross-linked profilin :beta/gamma-actin on the dynamics of the microfilament system in cultured cells

There is evidence that the profilin:actin complex is the immediate precurso r in the formation of actin filaments in cells. This paper describes the ce ll morphology and microfilament distribution after microinjection of covale ntly cross-linked proflin:beta/gamma-actin (PxA) in two different cell line s. injected cells were either kept unstimulated or stimulated with platelet -derived growth factor (PDGF) before fixation and visualization of filament ous actin. After injection of low doses of PxA, the cells displayed an acti n organization characterized by a clearance of diffuse fluorescence from a region immediately interior of ruffling edges and the appearance of small d ots of fluorescence in the same region. At higher concentrations, PxA effec tively inhibited outgrowth of lamellae and microspikes, and there was a dra stic reduction of actin staining in the zone behind the advancing edge. Thi s effect is reminiscent of the effect of cytochalasin B on fibroblasts and the growth cone of neuronal cells. As in these cases, there remained a rim of actin-dependent fluorescence on the very edge of the membrane lamella, p articularly in the PxA-treated fibroblasts. The interference of PxA with th e formation of surface structures was pronounced after PDGF stimulation. He re, PxA effectively eliminated the enhancement of the ruffling activity in the cell edges and on the dorsal surface of the cells. In contrast to PxA, injection of non-cross-linked profilin:beta/gamma-actin had no apparent eff ect on cell morphology and microfilament distribution except for an increas ed concentration of filamentous actin in one of the cell lines. (C) 2000 Ac ademic Press.