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

Abstract

The female hormone 17beta-estradiol is involved in the development 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 17beta-estradiol enhances the onset of genomic rearrangements, a type of genomic instability, in minisatellite sequences of malignant 10T1/2 mouse cells. Two malignant clones, X-ray-9 and F-17a, previously transformed in vitro by X-rays (600 cGys), and two non-transformed 10T1/2 mouse cell subclones (10T1/2b and 10T1/2c) were divided into two groups. The first group was incubated in the presence of 10(-5) M of 17beta-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 17beta-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 10T1/2b and 10T1/2c cells, no genomic rearrangements were induced by the hormone. After the withdrawal of 17beta-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 enhancement of genomic instability in malignant 10T1/2 mouse cells suggests that 17beta-estradiol may accelerate the accumulation of mutations, and therefore may represent a mechanism by which the female hormone contributes to breast cancer development.