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Biochemistry Research International
Volume 2012 (2012), Article ID 831940, 8 pages
http://dx.doi.org/10.1155/2012/831940
Research Article

Sumoylation of Human Translationally Controlled Tumor Protein Is Important for Its Nuclear Transport

Department of Biomedical Sciences, College of Medicine, University of Illinois, Rockford, IL 61107, USA

Received 23 December 2011; Revised 8 February 2012; Accepted 10 February 2012

Academic Editor: Jacek Kubiak

Copyright © 2012 Gnanasekar Munirathinam and Kalyanasundaram Ramaswamy. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Translationally controlled tumor protein (TCTP) lacks nuclear bipartite localization signal sequence; yet TCTP is present abundantly in the nucleus. At present it is not known how TCTP gets transported to the nucleus. Sequence analyses showed that all TCTPs described to date have putative small ubiquitin-like modifier (SUMO) motifs. Since SUMO modification plays an important role in the nuclear transport of proteins, we evaluated whether SUMO motifs are important for transport of TCTP into the nucleus. We show that TCTP exists in sumoylated form in cytoplasm and nucleus of mammalian cells. Point mutation of lysine residue in the SUMO motif compromised the ability of TCTP to get sumoylated in vitro. When cells were transfected with FLAG-tagged mutated TCTP, nuclear transport of TCTP was inhibited confirming that sumoylation is critical for the nuclear transport of TCTP. Our previous studies demonstrated that TCTP can function as an antioxidant protein in the nucleus. When we mutated TCTP at the SUMO motif the antioxidant function of TCTP was compromised. Results presented in this study thus show that sumoylation plays an important role in the transport of TCTP into the nucleus where they function as antioxidant protein.