EUROPEAN RADIATION RESEARCH 2012

The nucleotide pool sanitization enzyme hMTH1 protects cells from mutation induced by UVA

16 Oct 2012, 18:15

15m

Hall "E" (Vietri sul Mare)

oral (15 minutes) Non-Ionizing Radiation Non-Ionizing Radiation

Speaker

Ms Asal Fotouhi (Centre for Radiation Protection Research, Department of Genetics, Microbiology and Toxicology, Stockholms university)

Description

The exact mechanism by which UVA radiation induces mutations is not yet fully understood. It is known that UVA can induce different types of DNA damage via production of free radicals. Free radicals that react with nucleic acids may give rise to mutations, sister chromatid exchanges and chromosomal aberrations. UVA can also oxidize dNTPs in the nucleotide pool. Oxidized dNTPs such as 8-oxodGTP and 8-oxodATP can be incorporated into the DNA during replication and cause mutations. This process can be inhibited by the nucleotide pool sanitization mechanism, mediated by the hMTH1 protein, in which oxidized dNTP is dephosphorylated to dNMP (e.g., 8-oxo-dGTP to 8-oxo-dGMP). 8-oxo-dGMP dephosphorylates to 8-oxo-dG which is then excreted to the extracellular matrix. The aim of this study was to investigate the protective role of hMTH1 toward UVA induced cytotoxicity and mutagenicity. For this purpose human B lymphoblastoid cell line (TK6) was transfected with shRNA directed against hMTH. The expression level of hMTH1 in the transfected cells was investigated by Western blot technique. A mutation frequency assay was done to study mutation frequency induced by UVA in the transfected and non-transfected TK6 cells. In transfected TK6 cells, a significantly increased level of mutations was observed after UVA irradiation. (Fotouhi A. et al., 2011). To investigate what types of mutations that are induced by UVA in the transfected and non-transfected cells, mutations spectra in the Thymidine kinase (Tk) gene was determined. The most prominent type of mutation found was base pair substitutions, more precisely GC>AT transitions in non-transfected exposed TK6 cells whereas AT>GC transitions dominated in transfected TK6 cells. The results imply that UVA induces mutations primarily by oxidizing 8-oxodATP in the nucleotide pool.