Expression of the DNA repair enzyme, N-methylpurine-DNA glycosylase (MPG) in astrocytic tumors

Abstract

BACKGROUND: DNA is continuously damaged due to exposure to alkylating compounds or oxygen free radicals generated during normal cellular metabolism as well as to environmental mutagens. Several studies have shown that N-methylpurine-DNA-glycosylase (MPG) mRNA levels were lower in adult brain than in other tissues. Terminally differentiated and nonproliferating cells have a lower DNA repair capacity than proliferating cells from various organs, embryo, ovary and testis. If the DNA repair are not efficient, the damaged DNA may lead to tumorigenesis or cell death. This study was designed to investigate the association of tumorigenesis with MPG in astrocytic tumors. MATERIALS AND METHODS: MPG mRNA expression and localization in astrocytic tumors and tumor-adjacent brain tissues was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and RNA in situ hybridization. The expression and intracellular localization of MPG protein was determined by immunohistochemistry. RESULTS: MPG mRNA expression in RT-PCR was slightly higher in astrocytic tumor tissues than in brain tissues adjacent to tumor and in astrocytic tumor tissues, regardless of the tumor grades. MPG protein localization in immunohistochemical study was detected only in the nucleus of all tumor tissues. Interestingly, in brain tissues adjacent to tumor, immunohistochemical staining for MPG was not observed either in the nucleus or the cytoplasm. However, we could not detect MPG protein in the brain tissues adjacent to the tumor although MPG mRNA was detected in the tissues. CONCLUSION: These results suggest an MPG's role in human astrocytic tumors and raise the possibility that the altered MPG expression and intracellular localization could be associated with astrocytic tumorigenesis.