RESUMO
BACKGROUND: Dietary factors influence tumor formation and progression. Vitamin E is a dietary anti-oxidant capable of eliminating free radical damage, inducing apoptosis and decreasing oncogene expression. Therefore, Vitamin E may be a strong candidate for cancer prevention and/or chemotherapeutic intervention. Since telomerase, a ribonucleoprotein uniquely expressed in over 95% of cancers, plays an important role in cellular immortalization, cell growth and tumor progression, the present study investigated the effects of Vitamin E on telomerase activity in human ovarian cancer. METHODS: Normal and malignant ovarian surface epithelial (OSE) cells were cultured with and without D-alpha tocopheryl acetate (Vitamin E). MTS and Western immunoblot assays were used to examine the effect of Vitamin E on cell growth, survival and cytotoxicity. PCR-ELISA, RT-PCR and luciferase reporter assays were performed to determine the effect of Vitamin E on telomerase activity. RESULTS: Vitamin E suppressed endogenous telomerase activity in ovarian cancer cells, but had no similar effects in telomerase-negative normal OSE cells. Vitamin E also reduced hTERT-mRNA transcript levels and reduced hTERT promoter activity maximally targeting the -976 to -578bp promoter regions. In addition, Vitamin E improved cisplatin-mediated cytotoxicity as evidenced by reduced cancer cell growth and increased cleaved caspase 3 activity. In contrast, Vitamin E protected telomerase-negative OSE cells from cisplatin-mediated cytotoxicity as evidenced by decreased cleaved caspase 3 activity. CONCLUSION: Our data suggest that, by suppressing telomerase activity, Vitamin E may be an important protective agent against ovarian cancer cell growth as well as a potentially effective therapeutic adjuvant.
Assuntos
Antioxidantes/farmacologia , Neoplasias Ovarianas/enzimologia , Telomerase/antagonistas & inibidores , Vitamina E/farmacologia , Antineoplásicos/farmacologia , Western Blotting , Caspase 3/metabolismo , Proliferação de Células/efeitos dos fármacos , Cisplatino/farmacologia , Eletroforese em Gel de Poliacrilamida , Ensaio de Imunoadsorção Enzimática , Feminino , Humanos , Neoplasias Ovarianas/genética , Neoplasias Ovarianas/patologia , Regiões Promotoras Genéticas/genética , RNA Mensageiro/metabolismo , RNA Neoplásico/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Telomerase/genética , Células Tumorais Cultivadas/efeitos dos fármacosRESUMO
There is growing evidence that accelerated telomeric attrition and/or aberrant telomerase activity contributes to pathogenesis in a number of diseases. Likewise, there is increasing interest to develop new therapies to restore or replace dysfunctional cells characterized by short telomeric length using telomerase-positive counterparts or stem cells. While telomerase adds telomeric repeats de novo contributing to enhanced proliferative capacity and lifespan, it may also increase cellular survival by conferring resistance to apoptosis. Consequently, we sought to determine the involvement of telomerase for reduced apoptosis using ovarian surface epithelial cells. We found that expression of hTERT, the catalytic component of telomerase, was sufficient and specific to reduce caspase-mediated cellular apoptosis. Further, hTERT expression reduced activation of caspases 3, 8, and 9, reduced expression of pro-apoptotic mitochondrial proteins t-BID, BAD, and BAX and increased expression of the anti-apoptotic mitochondrial protein, Bcl-2. The ability of telomerase to suppress caspase-mediated apoptosis was p-jnk dependent since abrogation of jnk expression with jip abolished resistance to apoptosis. Consequently, these findings indicate that telomerase may promote cellular survival in epithelial cells by suppressing jnk-dependent caspase-mediated apoptosis.
