Radiosensitivity of lymphoblastoid cell lines with a heterozygous BRCA1 mutation is not detected by the comet assay and pulsed field gel electrophoresis

Abstract

Lymphoblastoid cell lines (LCL) with a heterozygous mutation in the breast cancer susceptibility gene BRCA1 have been repeatedly used to elucidate the biological consequences of such a mutation with respect to radiation sensitivity and DNA repair deficiency. Our previous results indicated that LCL with a BRCA1 mutation do not generally show the same chromosomal mutagen sensitivity in the micronucleus test as lymphocytes with the same BRCA1 mutation. To further study the radiosensitivity of LCL with a BRCA1 mutation, we now performed comparative investigations with the alkaline (pH 13) and the neutral (pH 8.3) comet assay and pulsed field gel electrophoresis (PFGE). These tests are commonly used to determine the repair capacity for DNA double strand breaks (DNA-DSB). Six LCL (three established from women with a heterozygous BRCA1 mutation and three from healthy controls) were investigated. Induction (2 and 5 Gy) of gamma-ray-induced DNA damage and its repair (during 60 min after irradiation) was measured with the alkaline and neutral comet assay. Comparative experiments were performed with PFGE determining the induction of DNA-DSB by 10-50 Gy gamma-irradiation and their repair during 6 h. There was no significant difference between LCL with and without BRCA1 mutation in any of these experiments. Therefore, using these methods, no indication for a delayed repair of DNA-DSB in LCL with a BRCA1 mutation was found. However, these results do not generally exclude DNA-DSB repair deficiency in these cell lines because the methods applied have limited sensitivity and only measure the speed but not the fidelity of the repair process.