CURCUMIN REGULATES LOW-LINEAR ENERGY TRANSFER γ-RADIATION-INDUCED NFκB-DEPENDENT TELOMERASE ACTIVITY IN HUMAN NEUROBLASTOMA CELLS

Purpose: We recently reported that curcumin attenuates ionizing radiation (IR)-induced survival signaling and proliferation in human neuroblastoma cells. Also, in the endothelial system, we have demonstrated that NF kappa B regulates IR-induced telomerase activity (TA). Accordingly, we investigated the effect of curcumin in inhibiting IR-induced NF kappa B-dependent hTERT transcription, TA, and cell survival in neuroblastoma cells. Methods and Materials: SK-N-MC or SH-SY5Y cells exposed to IR and treated with curcumin (10-100 nM) with or without IR were harvested after I h through 24 h. NF kappa B-dependent regulation was investigated either by luciferase reporter assays using pNF kappa B-, pGL3-354-, pGL3-347-, or pUSE-I kappa B alpha-Luc, p50/p65, or RelA siRNA-transfected cells. NF kappa B activity was analyzed using an electrophoretic mobility shift assay and hTERT expression using the quantitative polymerase chain reaction. TA was determined using the telomerase repeat amplification protocol assay and cell survival using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltertrazolium bromide and clonogenic assay. Results: Curcumin profoundly inhibited IR-induced NF kappa B. Consequently, curcumin significantly inhibited IR-induced TA and hTERT mRNA at all points investigated. Furthermore, IR-induced TA is regulated at the transcriptional level by triggering telomerase reverse transcriptase (TERT) promoter activation. Moreover, NF kappa B becomes functionally activated after IR and mediates TA upregulation by binding to the kappa B-binding region in the promoter region of the TERT gene. Consistently, elimination of the NF kappa B-recognition site on the telomerase promoter or inhibition of NF kappa B by the I kappa B alpha mutant compromises IR-induced telomerase promoter activation. Significantly, curcumin inhibited IR-induced TERT transcription. Consequently, curcumin inhibited hTERT mRNA and TA in NF kappa B overexpressed cells. Furthermore, curcumin enhanced the IR-induced inhibition of cell survival. Conclusions: These results strongly suggest that curcumin inhibits IR-induced TA in an NF kappa B dependent manner in human neuroblastoma cells. (C) 2011 Elsevier Inc.