RasGAP-Associated Endoribonuclease G3BP: Selective RNA Degradation and Phosphorylation-Dependent Localization

Abstract

Mitogen activation of mRNA decay pathways likely involves specific endoribonucleases, such as G3BP, a phosphorylation-dependent endoribonuclease that associates with RasGAP in dividing but not quiescent cells. G3BP exclusively cleaves between cytosine and adenine (CA) after a specific interaction with RNA through the carboxyl-terminal RRM-type RNA binding motif. Accordingly, G3BP is tightly associated with a subset of poly(A)⁺ mRNAs containing its high-affinity binding sequence, such as the c-myc mRNA in mouse embryonic fibroblasts. Interestingly, c-myc mRNA decay is delayed in RasGAP-deficient fibroblasts, which contain a defective isoform of G3BP that is not phosphorylated at serine 149. A G3BP mutant in which this serine is changed to alanine remains exclusively cytoplasmic, whereas a glutamate for serine substitution that mimics the charge of a phosphorylated serine is translocated to the nucleus. Thus, a growth factor-induced change in mRNA decay may be modulated by the nuclear localization of a site-specific endoribonuclease such as G3BP.

ACKNOWLEDGMENTS

H.T., I.G., and K.C. contributed equally to this work.

We are grateful to Edouard Bertrand, George Lutfalla, and Gilles Uzé for technical assistance and helpful discussions. We thank N. Taylor, B. Hipskind, and J. Soret for pertinent comments on the manuscript.

This work was supported by Association pour la Recherche sur le Cancer (ARC) and the CNRS. Special thanks go to Fabienne Parker for purified recombinant proteins. H.T. was supported by graduate fellowships from the Ministère de l' Education Nationale, de la Recherche et de la Technologie (MENRT) and ARC. K.C. and I.G. were supported by fellowships from Rhône Poulenc Rorer.