Expression and subcellular localization of thymosin beta15 following kainic acid treatment in rat brain

Thymosin beta15 (Tbeta15) is a pleiotropic factor which exerts multiple roles in the development of nervous system and brain diseases. In this study, we found that the expressions of Tbeta15 mRNA and protein were substantially increased in several brain regions including hippocampal formation and cerebral cortex, following kainic acid (KA)-evoked seizures in rat. Interestingly, a subset of cortex neurons exhibited nuclear Tbeta15 immunoreactivity upon KA treatment. Furthermore, translocation of Tbeta15 from cytosol to nuclei was observed in cultured neurons or HeLa cells during staurosporine (STS)-induced apoptosis, which was also verified by time-lapse imaging of YFP-tagged Tbeta15. It appeared that localization of Tbeta15 is restricted to the cytosol in normal condition by its G-actin-interacting domain, because site-directed mutagenesis of this region resulted in the nuclear localization of Tbeta15 in the absence of STS treatment. To explore the role of nuclear Tbeta15, we enforced Tbeta15 to localize in the nuclei by fusion of Tbeta15 with nuclear localization signal (NLS-Tbeta15). However, overexpression of NLS-Tbeta15 did not alter the viability of cells in response to STS treatment. Collectively, these results suggest that nuclear localization of Tbeta15 is a controlled process during KA or STS stimulation, although its functional significance is yet to be clarified.