TRIM28 Is an E3 Ligase for ARF-Mediated NPM1/B23 SUMOylation That Represses Centrosome Amplification

Abstract

The tumor suppressor ARF enhances the SUMOylation of target proteins; however, the physiological function of ARF-mediated SUMOylation has been unclear due to the lack of a known, associated E3 SUMO ligase. Here we uncover TRIM28/KAP1 as a novel ARF-binding protein and SUMO E3 ligase for NPM1/B23. ARF and TRIM28 cooperate to SUMOylate NPM1, a nucleolar protein that regulates centrosome duplication and genomic stability. ARF-mediated SUMOylation of NPM1 was attenuated by TRIM28 depletion and enhanced by TRIM28 overexpression. Coexpression of ARF and TRIM28 promoted NPM1 centrosomal localization by enhancing its SUMOylation and suppressed centrosome amplification; these functions required the E3 ligase activity of TRIM28. Conversely, depletion of ARF or TRIM28 increased centrosome amplification. ARF also counteracted oncogenic Ras-induced centrosome amplification. Centrosome amplification is often induced by oncogenic insults, leading to genomic instability. However, the mechanisms employed by tumor suppressors to protect the genome are poorly understood. Our findings suggest a novel role for ARF in maintaining genome integrity by facilitating TRIM28-mediated SUMOylation of NPM1, thus preventing centrosome amplification.

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.01064-14.

ACKNOWLEDGMENTS

We thank Kenji Fukasawa for providing NPM1 (PabN1) antibody, Yanping Zhang for ARF deletion plasmids, NPM1 plasmids, and wild-type, p53^−/−, p53^−/−; Mdm2^−/−, ARF^−/−, and p53^−/−; ARF^−/− MEFs, Mikael Lindström for NPM1 plasmids, and Mathijs Voorhoeve for ARF shRNA construct. We also thank David M. Virshup for critical reading of the manuscript. We thank Rachel Han Shufen and Lee Guan Hwee Bernard for providing technical help. We thank Pickersgill & Andersen, Life Science Editors, for editorial assistance.

S.H.N., Y.I., J.A., and K.I. performed the experiments. K.T. performed mass spectrometry analysis. M.K., A.K.G., and S.H.L. performed metaphase spread analysis. S.H.N., Y.I., and K.I. designed the experiments and wrote the manuscript.

This work was supported by funding from Duke-NUS Graduate Medical School Singapore core grant (to K.I.) and Singapore Ministry of Health's National Medical Research Council grant (NMRC/GMS/1303/2011 to K.I.).