RESUMO
TRIP-Br1 oncoprotein is known to be involved in many vital cellular functions. In this study, we examined the role of TRIP-Br1 in hypoxia-induced cell death. Exposure to the overcrowded and CoCl2-induced hypoxic conditions increased TRIP-Br1 expression at the protein level in six breast cancer cell lines (MCF7, MDA-MB-231, T47D, Hs578D, BT549, and MDA-MB-435) but resulted in no significant change in three normal cell lines (MCF10A, MEF and NIH3T3). Our result revealed that CoCl2-induced hypoxia stimulated apoptosis and autophagy, in which TRIP-Br1 expression was found to be upregulated. Interestingly, TRIP-Br1 silencing in the MCF7 and MDA-MB-231 cancer cells accelerated apoptosis and destabilization of XIAP under the CoCl2-induced hypoxic condition, implying that TRIP-Br1 may render cancer cells resistant to apoptosis through the stabilization of XIAP. We also propose that TRIP-Br1 seems to be upregulated at least partly as a result of the inhibition of PI3K/AKT signaling pathway and the overexpression of HIF-1α. In conclusion, our findings suggest that TRIP-Br1 functions as an oncogenic protein by providing cancer cells resistance to the hypoxia-induced cell death.
Assuntos
Neoplasias da Mama/metabolismo , Cobalto/toxicidade , Regulação para Baixo , Resistencia a Medicamentos Antineoplásicos , Proteínas Nucleares/metabolismo , Transativadores/metabolismo , Animais , Apoptose , Hipóxia Celular , Linhagem Celular Tumoral , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Células MCF-7 , Camundongos , Células NIH 3T3 , Fatores de Transcrição , Regulação para Cima , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/metabolismoRESUMO
TRIP-Br1 oncogenic protein has been shown to have multiple biological functions in cells. In this study, we demonstrate that TRIP-Br1 functions as an oncoprotein by inhibiting autophagy, apoptosis, and necroptosis of cancer cells and eventually helping them to survive under the nutrient/serum starved condition. TRIP-Br1 expression level was significantly increased in conditions with low levels of nutrients. Nutrient depleted conditions were induced by culturing cancer cells until they were overcrowded with high cell density or in media deprived of glucose, amino acids, or serum. Among them, serum starvation significantly enhanced the expression of TRIP-Br1 only in all tested breast cancer cell lines (MCF7, MDA-MB-231, T47D, MDA-MB-435, Hs578D, BT549, and MDA-MB-435) but not in the three normal cell lines (MCF10A, HfCH8, and NIH3T3). As compared with the control cells, the introduction of TRIP-Br1 silencing siRNA into MCF7 and MDA-MB-231 cells accelerated cell death by inducing apoptosis and necroptosis. In this process, TRIP-Br1 confers resistance to serum starvation-induced cell deaths by stabilizing the XIAP protein and inhibiting cellular ROS production. Moreover, our data also show that the intracellular increase of TRIP-Br1 protein resulting from serum starvation seems to occur in part through the blockage of PI3K/AKT signaling pathway.
Assuntos
Aminoácidos/deficiência , Apoptose , Autofagia , Neoplasias da Mama/metabolismo , Glucose/deficiência , Proteínas Nucleares/metabolismo , Transativadores/metabolismo , Animais , Neoplasias da Mama/genética , Neoplasias da Mama/patologia , Sobrevivência Celular , Meios de Cultura Livres de Soro/metabolismo , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Células MCF-7 , Camundongos , Células NIH 3T3 , Necrose , Proteínas Nucleares/genética , Fosfatidilinositol 3-Quinase/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Interferência de RNA , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Fatores de Tempo , Transativadores/genética , Fatores de Transcrição , Transfecção , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/metabolismoRESUMO
TRIP-Br3 and TRIP-Br1 have shown to have important biological functions. However, the function of TRIP-Br3 in tumorigenesis is not well characterized compared to oncogenic TRIP-Br1. Here, we investigated the function of TRIP-Br3 in tumorigenesis by comparing with that of TRIP-Br1. Under nutrient/serum starvation, TRIP-Br3 expression was down-regulated slightly in cancer cells and significantly in normal cells. Unexpectedly, TRIP-Br1 expression was greatly up-regulated in cancer cells but not in normal cells. Moreover, TRIP-Br3 activated autophagy while TRIP-Br1 inactivated it under serum starvation. In spite of different expression and roles of TRIP-Br3 and TRIP-Br1, both of them alleviate cell death by directly binding to and stabilizing XIAP, a potent apoptosis inhibitor, through blocking its ubiquitination. Taken together, we propose that TRIP-Br3 primarily activates the autophagy and suppresses apoptosis in nutrient sufficient condition. However, the prolonged extreme stressful condition of nutrient starvation causes a dramatic decrease of TRIP-Br3, which in turn induces apoptosis by destabilizing XIAP. Up-regulated TRIP-Br1 in cancer cells compensates this effect and delays apoptosis. This can be explained by the competitive alternative binding of TRIP-Br3 and TRIP-Br1 to the BIR2 domain of XIAP. In an extended study, our immunohistochemical analysis revealed a markedly lower level of TRIP-Br3 protein in human carcinoma tissues compared to normal epithelial tissues, implying the role of TRIP-Br3 as a tumor suppressor rather than onco-protein.