Over-expression of TSC-22 (TGF-beta stimulated clone-22) markedly enhances5-fluorouracil-induced apoptosis in a human salivary gland cancer cell line

We have recently isolated TSC-22 (transforming growth factor-beta-stimulate d clone-22) cDNA as an anticancer, drug-inducible (with vesnarinone) gene i n a human salivary gland cancer cell line, TYS. We have also reported that TSC-22 negatively regulates the growth of TYS cells and that down-regulatio n of TSC-22 in TYS cells plays a major role in salivary gland tumorigenesis (Nakashiro et at, 1998). In this study, we transfected TYS cells with an e xpression Vector encoding the TSC-22-GFP (green fluorescent protein) fusion protein, and we established TSC-22-GFP-expressing TYS cell clones. Next, w e examined (a) the subcellular localization of the fusion protein, (b) the sensitivity of the transfectants to several anticancer drugs (5-fluorouraci l, cis-diaminedichoroplatinum, peplomycin), and (c) induction of apoptotic cell death in the transfectants by 5-fluorouracil treatment. The TSC-22-GFP fusion protein was clearly localized to the cytoplasm, but not to the nucl eus. Over-expression of the TSC-22-GFP fusion protein did not affect cell g rowth, but significantly increased the sensitivity of the cells to the anti cancer drugs (p < 0.01; one-way ANOVA). Furthermore, over-expression of the TSC-22-GFP fusion protein markedly enhanced 5-fluorouracil-induced apoptos is. These findings suggest that over-expression of TSC-22-GFP protein in PI S cells enhances the chemosensitivity of the cells via induction of apoptos is.