RhoB Promotes γH2AX Dephosphorylation and DNA Double-Strand Break Repair

Abstract

Unlike other Rho GTPases, RhoB is rapidly induced by DNA damage, and its expression level decreases during cancer progression. Because inefficient repair of DNA double-strand breaks (DSBs) can lead to cancer, we investigated whether camptothecin, an anticancer drug that produces DSBs, induces RhoB expression and examined its role in the camptothecin-induced DNA damage response. We show that in camptothecin-treated cells, DSBs induce RhoB expression by a mechanism that depends notably on Chk2 and its substrate HuR, which binds to RhoB mRNA and protects it against degradation. RhoB-deficient cells fail to dephosphorylate γH2AX following camptothecin removal and show reduced efficiency of DSB repair by homologous recombination. These cells also show decreased activity of protein phosphatase 2A (PP2A), a phosphatase for γH2AX and other DNA damage and repair proteins. Thus, we propose that DSBs activate a Chk2-HuR-RhoB pathway that promotes PP2A-mediated dephosphorylation of γH2AX and DSB repair. Finally, we show that RhoB-deficient cells accumulate endogenous γH2AX and chromosomal abnormalities, suggesting that RhoB loss increases DSB-mediated genomic instability and tumor progression.

ACKNOWLEDGMENTS

We thank Y. Pommier for Chk2-WT and Chk2-KD HCT15 cells and for stimulating discussions; G. C. Prendergast for WT and RhoB^−/− mice; A. Peyret-Lacombe, J. Cherier, R. Gence, and I. Lajoie-Mazenc for preparing primary mouse dermal fibroblast cells from these mice; and L. Trouilh from the GenoToul Biochips platform for her kind help in the analyses of CGH arrays. We also thank S. Cabantous, E. Nicolas, and C. E. Redon for critically reading the manuscript.

This research was supported by grants from the Ligue Nationale Contre le Cancer and the Region Midi-Pyrénées.

We declare that we have no conflicts of interest.