Lack of correlation between ATM protein expression and tumour cell radiosensitivity

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Abstract
Purpose: Cells derived from individuals in which the ataxia telangiectasia (ATM) gene is mutated are hypersensitive to ionizing radiation. Whether differences in ATM protein levels exist among human malignant glioma cell lines and whether such differences are correlated with cellular radiosensitivity were determined. Materials and methods: Polyclonal antibodies were raised to separate regions of the ATM protein. ATM protein expression in human malignant glioma cell lines, SV40 transformed normal human fibroblasts and SV40 transformed AT fibroblasts was analysed by Western blotting. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to assess the presence of ATM transcript. Results: While ATM protein was detected in all cell extracts, significant differences in the level of expression were observed. There was no apparent correlation between cellular radiosensitivity and differences in ATM protein levels in these human glioma cells. Extremely low levels of ATM protein were observed in M059J cells, which provide the only example of DNA-dependent protein kinase (DNA-PKcs) deficiency in a cell line of human origin. Conclusions: Variations in the levels of ATM protein are insufficient to explain the differences in cellular radiosensitivity observed in a panel of human malignant glioma cell lines.