Enhancement of genomic instability by 17-estradiol in minisatellite sequences of X-ray-transformed mouse 10T1/2 cells. Carcinogenesis

The female hormone 17P-estradiol is involved in the devel-opment of breast cancer, an effect usually attributed to its capacity to stimulate the replication of preneoplastic and malignant cells. In this study, we report that 17p*-estradiol enhances the onset of genomic rearrangements, a type of genomic instability, in minisatellite sequences of malignant 10TV2 mouse cells. Two malignant clones, X-ray-9 and F-17a, previously transformed in vitro by X-rays (600 cGys), and two non-transformed lOT'A mouse cell subclones (10TV2b and 10T'/2c) were divided into two groups. The first group was incubated in the presence of 10 5 M of 17p*-estradiol (dissolved in ethanol) for 5 days, while the second group was incubated for the same period in culture media containing 0.1 % of ethanol. After the incubation both groups of cells were then subcloned, and their DNA was extracted and analyzed with the DNA fingerprinting assay using the probe M (core sequence: 5'-AGGC). A high frequency of genomic rearrangements was observed in the transformed subclones treated with 17p*-estradiol. Nine deletions or additions in minisatellite alleles were observed in six F-17a subclones, while 28 of those genomic rearrangements were found in the 12 X-ray-9 malignant subclones. On the other hand, for the non-transformed 10T72b and IOTV2C cells, no genomic rearrangements were induced by the hormone. After the withdrawal of 170-estradiol from the transformed clone X-ray-9, no new genomic rearrangements were detected; while a second incubation with the hormone induced new deletions or additions in minisatellite alleles. This preferential enhance-ment of genomic instability in malignant 10T'/2 mouse cells suggests that 17p*-estradiol may accelerate the accumulation of mutations, and therefore may represent a mechanism by which the female hormone contributes to breast cancer development