Mitochondrial localisation of hTERT protects against nuclear DNA damage and mitochondrial ROS production after endogenous and exogenous stress

Abstract

Under oxidative stress condition, telomerase catalytic subunit can shuttle from the nucleus and localises within mitochondria. hTERT can improve mitochondrial functions and contribute to a decreased oxidative stress suggesting an entirely new function of telomerase in protecting mitochondria and cells under stress. However, there are still many questions about the mechanism and what factors influence the protective function of telomerase. In this study we investigated the kinetic exclusion of hTERT, the catalytic subunit of telomerase, in various cell lines under different oxidative stress conditions. We also used organelle specific hTERT localisation vectors to model hTERT localisation and investigated a correlation between hTERT location, nuclear DNA damage and ROS production. We found that cells excluded endogenous hTERT from the nucleus in a heterogeneous fashion independently of the cell types. Importantly, nuclear DNA damage showed a significant correlation with the localisation of hTERT. Cells where hTERT remained in the nucleus displayed high DNA damage while cells which excluded hTERT from the nucleus displayed no or very low DNA damage. Our results from specific hTERT localisation vectors specified that mitochondrial localisation of hTERT protects the nucleus from DNA damage and did not showed any sign of apoptosis induction while nuclear localisation of hTERT correlated with higher amounts of DNA damage and apoptosis. Moreover, mitochondrial localisation of hTERT decreased mitochondrial ROS generation levels directly after both endogenous and exogenous stress which we interpret as the reason for the prevention of nuclear DNA damage. Additionally, we analysed whether p53 status might influence the protective function of telomerase. Our results in an isogenic cell pair of glioblastoma cells showed that p53 status does not prominently influence the protective function of mitochondrial hTERT under low stress condition. However, nuclear hTERT of cells which contained inactive p53 displayed a significantly higher nuclear DNA damage than cells which contained an active p53 and this became more pronounced when stress levels were increased. We hypothesise that telomerase localisation might possibly interact with p53 when a cancer cell is under stress condition. However, the molecular mechanism for that is unknown. Our results demonstrate a novel link between mitochondrial localisation of hTERT, decrease of mitochondrial ROS generation and the protective capacity of hTERT to nuclear DNA from damage after stress treatments.