Characterization of SV40-transformed xeroderma pigmentosum cell lines for their usability in HPRT mutation studies

We have characterized six SV40-transformed xeroderma pigmentosum cell lines (XP20S and XP12BE derived from female donors, XP12RO-SV, XP3BR/12SV, XP4PA-SV and XP8CAC-SV from male donors) for their usability in HPRT mutation studies. All cell lines exhibit hypersensitivity, compared with MRC5CV1 cells, towards the cytotoxic action of UV-irradiation. They were all shown to be heteronuclear and hyperdiploid with pronounced variability in chromosome number. Fluorescence in situ hybridization (FISH) with an X-chromosomal library (X-chromosome painting) and BrdUrd-labelling of late-replicating X-chromosomes demonstrated the presence of variable numbers of X-chromosomes and additional X-chromosomal material and suggested the presence of more than one genetically active HPRT allele in the majority of cells of five cell lines. The cell line XP8CAC-SV (complementation group C) seemed to be most suitable for HPRT mutation studies due to its near-diploid karyotype with only one X-chromosome in the majority of cells. From this cell line, a clonal subline was established (XP8CAC-SV-C1) which revealed the same UV-hypersensitivity as the parental cell line and a near-diploid karyotype with one X-chromosome in 94% of the metaphases. Molecular analysis of the HPRT gene gave a normal PCR amplification pattern for all exons and the normal wild-type sequence of the cDNA. HPRT tests with (+)-anti-benzo[a]pyrene-7,8-diol-9,10-oxide [(+)-anti-BPDE] showed a reproducible, concentration related increase in mutant frequencies. Compared with results with MRC5CV1 cells, the obtained data indicate spontaneous and (+)-anti-BPDE-induced hypermutability of the XP line. XP8CAC-SV-C1 thus represents a permanent XP cell line with characteristic cellular XP features which is convenient for studying the influence of deficient excision repair on HPRT mutant frequencies and mutation spectra.