A Novel Phosphorylation-Dependent RNase Activity of GAP-SH3 Binding Protein: a Potential Link between Signal Transduction and RNA Stability

ABSTRACT

A potential p120 GTPase-activating protein (RasGAP) effector, G3BP (RasGAP Src homology 3 [SH3] binding protein), was previously identified based on its ability to bind the SH3 domain of RasGAP. Here we show that G3BP colocalizes and physically interacts with RasGAP at the plasma membrane of serum-stimulated but not quiescent Chinese hamster lung fibroblasts. In quiescent cells, G3BP was hyperphosphorylated on serine residues, and this modification was essential for its activity. Indeed, G3BP harbors a phosphorylation-dependent RNase activity which specifically cleaves the 3′-untranslated region of human c-myc mRNA. The endoribonuclease activity of G3BP can initiate mRNA degradation and therefore represents a link between a RasGAP-mediated signaling pathway and RNA turnover.

ACKNOWLEDGMENTS

This work was supported by the BioAvenir Program (Ministère de la Recherche et de l’Espace, Ministère de l’Industrie et du Commerce Extérieur) and the Centre National de la Recherche Scientifique (Biologie Cellulaire: du Normal au Pathologique).

We are grateful to R. Hipskind, N. Taylor, P. Jeanteur, and M. Sitbon for numerous stimulating discussions and helpful comments on the manuscript. We thank A. Dugue and S. Bouvier for expert technical assistance and J. L. Veyrune for kindly providing plasmid pkSGMW1.