PHOSPHORYLATION OF THE GROWTH ARREST-SPECIFIC PROTEIN GAS2 IS COUPLEDTO ACTIN REARRANGEMENTS DURING GO-]G1 TRANSITION IN NIH 3T3 CELLS

Growth arrest-specific (Gas2) protein has been shown to be a component of the microfilament system, that is highly expressed in growth arres ted mouse and human fibroblasts and is hyperphosphorylated upon serum stimulation of quiescent cells. (Brancolini, C., S. Bottega, and C. Sc hneider. 1992. J. Cell Biol. 117:1251-1261). In this study we demonstr ate that the kinetics of Gas2 phosphorylation, during Go-->G1 transiti on, as induced by addition of 20% FCS to serum starved NIH 3T3 cells, is temporally coupled to the reorganization of actin cytoskeleton. To better dissect the relationship between Gas2 phosphorylation and the m odification of the microfilament architecture we used specific stimuli for bothmembrane ruffling (PDGF and PMA) and stress fiber formation ( L-alpha-lysophosphatidic acid LPA) (Ridley, A. J., and A. Hall. 1992. Cell. 70:389-399). All of them, similarly to 20% FCS, are able to down regulate Gas2 biosynthesis. PDGF and PMA induce Gas2 hyperphosphorylat ion that is temporally coupled with the appearance of membrane rufflin g where Gas2 localizes. On the other hand LPA, a specific stimulus for stress fiber formation, fails to induce a detectable Gas2 hyperphosph orylation. Thus, Gas2 hyperphosphorylation is specifically correlated with the formation of membrane ruffling possibly implying a role of Ga s2 in this process.