posted on 2012-08-20, 00:00authored byGnanasekar Munirathinam, Kalyanasundaram Ramaswamy
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.
Funding
This work was supported by Public Health Service Grants AI-64745 and AI-39066 from NIAID.