ATM-NFκB axis-driven TIGAR regulates sensitivity of glioma cells to radiomimetics in the presence of TNFα

摘要

Gliomas are resistant to radiation therapy, as well as to TNF α induced killing. Radiation-induced TNF α triggers Nuclear factor κ B (NF κ B)-mediated radioresistance. As inhibition of NF κ B activation sensitizes glioma cells to TNF α -induced apoptosis, we investigated whether TNF α modulates the responsiveness of glioma cells to ionizing radiation-mimetic Neocarzinostatin (NCS). TNF α enhanced the ability of NCS to induce glioma cell apoptosis. NCS-mediated death involved caspase-9 activation, reduction of mitochondrial copy number and lactate production. Death was concurrent with NF κ B, Akt and Erk activation. Abrogation of Akt and NF κ B activation further potentiated the death inducing ability of NCS in TNF α cotreated cells. NCS-induced p53 expression was accompanied by increase in TP53-induced glycolysis and apoptosis regulator (TIGAR) levels and ATM phosphorylation. siRNA-mediated knockdown of TIGAR abrogated NCS-induced apoptosis. While DN-I κ B abrogated NCS-induced TIGAR both in the presence and absence of TNF α , TIGAR had no effect on NF κ B activation. Transfection with TIGAR mutant (i) decreased apoptosis and γ H2AX foci formation (ii) decreased p53 (iii) elevated ROS and (iv) increased Akt/Erk activation in cells cotreated with NCS and TNF α . Heightened TIGAR expression was observed in GBM tumors. While NCS induced ATM phosphorylation in a NF κ B independent manner, ATM inhibition abrogated TIGAR and NF κ B activation. Metabolic gene profiling indicated that TNF α affects NCS-mediated regulation of several genes associated with glycolysis. The existence of ATM-NF κ B axis that regulate metabolic modeler TIGAR to overcome prosurvival response in NCS and TNF α cotreated cells, suggests mechanisms through which inflammation could affect resistance and adaptation to radiomimetics despite concurrent induction of death.