A New Complementation Group of Mitomycin C-hypersensitive Chinese Hamster Cell Mutants That Closely Resembles the Phenotype of Panconi Anemia Cells1

Three Mitomycin C (MMC)-hypersensitive mutants (CL-V1B, CL-V5B, and CL-V101B) were isolated from Chinese hamster V79B cells by the replica plating technique. In comparison to the parental cell line, CL-V1B, CL-V5B, and CL-V101B show about a 22-, 32-, and 13-fold increased sensitivity to MMC, respectively (judged by the D10). These mutants are also sensitive to other DNA cross-linking agents, such as 1,2,3,4-diepoxybutane (9-, 19-, and 12-fold, respectively) and cis-diamminedichloroplatinum(II) (17-, 12-, and 6-fold, respectively). CL-V5B and CL-V101B display an exclusive sensitivity to DNA cross-linking agents, whereas CL-V1B also shows an increased sensitivity to monofunctional alkylating agents, such as methyl methanesulfonate (3-fold) and ethyl methanesulfonate (2-fold), and UV254nm (2-fold). Approximately 2-3-fold higher levels of spontaneous chromosomal aberrations are found in these three mutants in comparison to wild-type V79B cells. At a MMC survival level of 80%, CL-V5B demonstrates a 16-fold higher level of MMCinduced chromosomal damage than V79B. Despite phenotypical hetero geneity within this group of mutants, hybrid clones derived after fusion remained MMC sensitive, indicating that these mutants belong to the same complementation group. To determine whether the mutants repre sent a new complementation group among other Chinese hamster cell mutants that also display hypersensitivity to MMC, CL-V1B cells were fused with mutants representing different complementation groups i.e., irsi, irs3, irslSF, UV20, UV41, V-H4, and V-C8 cells. In all cases, the derived hybrids regained MMC sensitivity similar to wild-type cells, indicating that the CL-V1B mutant represents a new complementation group. The phenotype of CL-V1B, CL-V5B, and CL-V101B cells closely resembles the phenotype of Panconi anemia cells, suggesting that these hamster mutants could be defective in a gene that is involved in this disorder.