Cytoplasmic TSC-22 (transforming growth factor-beta-stimulated clone-22) markedly enhances the radiation sensitivity of salivary gland cancer cells

We transfected a salivary gland cancer cell line, TYS, with three different forms of TSC-22 (transforming growth factor-beta-stimulated clone-22) gene: full-length TSC-22 (TSC-22FL) containing nuclear export signal, TSC-box and leucine zipper, truncated TSC-22 (TSC-22LZ) containing only TSC-box and leucine zipper, and truncated TSC-22 with nuclear localization signal (NLS-TSC-22LZ). High expression of TSC-22FL in the cytoplasm markedly enhanced the radiation-sensitivity of TYS cells, while, moderate expression of TSC-22FL marginally affected the radiation-sensitivity. TSC-22LZ, which was expressed in the cytoplasm and the nucleus, enhanced the radiation-sensitivity of TYS cells irrespective to its expression level. NLS-TSC-22LZ, which was expressed only in the nucleus, marginally affected the radiation-sensitivity of the cells even at high expression level. Interestingly, cytoplasmic TSC-22 translocates to nucleus concomitant with radiation-induced apoptosis. These results suggest that cytoplasmic localization of TSC-22 and translocation of TSC-22 from cytoplasm to nucleus is important for regulating the cell death signal after irradiation-induced DNA damage.