Allelic imbalance at 11p15.5-15.4 correlated with c-Ha-ras mutation during radiation-induced neoplastic transformation of human breast epithelial cells

Breast cancer is the most frequent malignancy in women throughout much of the developed world and is associated with a multistage process involving a number of genetic mutations and their corresponding cellular phenotypic alterations. It has already been shown that neoplastic transformation of a spontaneously immortalized human breast epithelial (MCF-10F) cell line by radiation, in combination with estrogen, represents a successful model in studying the molecular and biological alterations that may contribute to the tumorigenic process. In the present study, the incidence of allelic alterations (microsatellite instability/loss of heterozygosity) on chromosome 11 in different radiation-induced primary and secondary tumorigenic cell lines, relative to the control MCF-10F cells was investigated. We identified 3 regions of the chromosome 11 (11p15-p15.5, 11q13 and 11q23) that showed high incidence of LOH among these tumor cell lines and suggested a potential role for these chromosomal regions in breast carcinogenesis. Among them, locus 11p15.5, where c-Ha-ras oncogene is located, had incidence of allelic imbalance between 25-40%. Furthermore, direct sequencing analysis of codons 12 and 61 of the c-Ha-ras oncogene identified various point mutations. These data highlight the importance of chromosome 11 in radiation induced malignant transformation of human breast epithelial cells and suggest the usefulness of the model in uncovering specific derangements during breast cancer progression.