Glyoxalase I inhibition induces apoptosis in irradiated MCF-7 cells via a novel mechanism involving Hsp27, p53, NF-kB

BACKGROUND: Glyoxalase I (GI) metabolizes methylglyoxal (MG) and MG-derived advanced glycation end products (AGEs), known to cause apoptosis. Radiotherapy is an important modality widely used in cancer treatment. Exposure of cells to ionizing radiation (IR) results in a number of complex biological responses, including programmed cell death. The present study was aimed at investigating whether, and through which molecular mechanism, GI was involved in IR-induced apoptosis. METHODS: Apoptosis was evaluated by TdT-mediated dUTP nick-end labeling (TUNEL) and DNA fragmentation assays by agarose gel electrophoresis. Real-time TaqMan polymerase chain reaction, western blot and spectrophotometric methods were used to study transcript or protein levels, or specific activity, respectively. RESULTS: IR induced a dramatic reactive oxygen species (ROS)-mediated inhibition of GI, leading to Hsp27-identified argpyrimidine protein accumulation that, in a mechanism involving p53 and NF-kB, triggered an apoptotic mitochondrial pathway. GI inhibition occurred both at functional and transcriptional level, this latter occurring via ERK1/2 MAPK and ERα modulation. CONCLUSION: IR-induced ROS-mediated GI inhibition resulted in a mitochondrial apoptotic pathway via a novel mechanism involving Hsp27, p53 and NF-kB in irradiated MCF-7 cells.