RESUMEN
Previous study revealed that the protective effect of TIGAR in cell survival is mediated through the increase in PPP (pentose phosphate pathway) flux. However, it remains unexplored if TIGAR plays an important role in DNA damage and repair. This study investigated the role of TIGAR in DNA damage response (DDR) induced by genotoxic drugs and hypoxia in tumor cells. Results showed that TIGAR was increased and relocated to the nucleus after epirubicin or hypoxia treatment in cancer cells. Knockdown of TIGAR exacerbated DNA damage and the effects were partly reversed by the supplementation of PPP products NADPH, ribose, or the ROS scavenger NAC. Further studies with pharmacological and genetic approaches revealed that TIGAR regulated the phosphorylation of ATM, a key protein in DDR, through Cdk5. The Cdk5-AMT signal pathway involved in regulation of DDR by TIGAR defines a new role of TIGAR in cancer cell survival and it suggests that TIGAR may be a therapeutic target for cancers.
Asunto(s)
Proteínas de la Ataxia Telangiectasia Mutada/genética , Quinasa 5 Dependiente de la Ciclina/genética , Daño del ADN/genética , Reparación del ADN/genética , Péptidos y Proteínas de Señalización Intracelular/genética , Vía de Pentosa Fosfato/genética , Transducción de Señal/genética , Proteínas Reguladoras de la Apoptosis , Línea Celular Tumoral , Núcleo Celular/efectos de los fármacos , Núcleo Celular/genética , Núcleo Celular/metabolismo , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/genética , Daño del ADN/efectos de los fármacos , Reparación del ADN/efectos de los fármacos , Epirrubicina/farmacología , Células Hep G2 , Humanos , Hipoxia/genética , Hipoxia/metabolismo , NADP/genética , Vía de Pentosa Fosfato/efectos de los fármacos , Monoéster Fosfórico Hidrolasas , Fosforilación/efectos de los fármacos , Fosforilación/genética , Especies Reactivas de Oxígeno/metabolismo , Transducción de Señal/efectos de los fármacosRESUMEN
The p53-induced glycolysis and apoptosis regulator (TIGAR) inhibits glycolysis, resulting in higher intracellular NADPH, lower reactive oxygen species (ROS) and autophagy activity. In this study, we investigated whether TIGAR might exert dual impacts on cancer cell survival based on its ability to inhibit both apoptosis and autophagy. In liver or lung cancer cells treated with the anticancer drug epirubicin, TIGAR levels increased in a dose- and time-dependent manner. TIGAR silencing enhanced epirubicin-induced elevations in ROS levels and apoptosis rates, in a manner that was blocked by ectopic addition of NADPH or N-acetyl cysteine. These findings were correlated with reduced tumorigenicity and increased chemosensitivity in mouse xenograft tumor assays. In parallel, TIGAR silencing also enhanced the epirubicin-induced activation of autophagy, in a manner that was also blocked by ectopic addition of NADPH. Notably, TIGAR silencing also licensed epirubicin-mediated inactivation of the mTOR pathway, suggesting TIGAR also exerted a negative impact on autophagy. However, genetic or pharmacologic inhibition of autophagy increased epirubicin-induced apoptosis in TIGAR-silenced cells. Overall, our results revealed that TIGAR inhibits both apoptosis and autophagy, resulting in a dual impact on tumor cell survival in response to tumor chemotherapy. Cancer Res; 74(18); 5127-38. ©2014 AACR.