DEMONSTRATION BY DNA FINGERPRINT ANALYSIS OF GENOMIC INSTABILITY IN MOUSE BALB 3T3 CELLS DURING CELL-TRANSFORMATION

We employed DNA fingerprint analysis to monitor DNA rearrangements in BALB 3T3 cells transformed spontaneously or by treatment with 3-methylcholanthrene (MCA) and UV-C. The effect of 22-O-tetradecanoyl-phorbol-13-acetate (TPA) in combination with MCA was also examine d. Twenty-three spontaneously transformed cells, 28 induced transformed cells (18 by 1 mu g/ml MCA, six by 5 mu g/ml MCA, and four by UV-C), and 31 non-transformed subclones were isolated from parental BALB 3T3 A31-1-1 cells. The DNAs were digested with HinfI and subjected to DNA fingerprint analysis with three multi-locus minisatellite probes, Per-6, Core, and Ins. Per-6 was the most effective probe for detecting DNA rearrangements. Rearranged bands detected by the Per-6 probe were observed in 9/31 (29%) of non-transformed subclones, 14/23 (61%) of spontaneously transformed cells, 16/18 (89%) of cells transformed by 1 mu g/ml of MCA, 6/6 (100%) of cells transformed by 5 mu g/ml MCA, and 4/4 (100%) of UV-C-transformed cells. Higher numbers of DNA rearrangements (greater than or equal to 3) occurred most frequently in the induced transformed cells. TPA enhanced the frequency of DNA rearrangements in cells transformed by MCA. These data indicate that (1) genomic DNA in BALB 3T3 cells is unstable and susceptible to rearrangement, (2) its instability is elevated during cell transformation, and (3) MCA and UV-C induce DNA rearrangements, and TPA enhances the effect of the former, probably via the recombination process. DNA fingerprint analysis is valuable for monitoring genomic instability during cell transformation.