Trapping of genes induced upon growth arrest after treatment with antiestrogen or retinoids using retroviral promoter trap

Although chemopreventive anti‐steroids such as the antiestrogens are thought to act through competitive inhibition of agonist binding to estrogen receptors, it has been postulated that the estrogen receptor changes its conformation when bound to a strong antiestrogen such as ICI‐164,384. We hypothesized that such conformationally changed receptors could bind specific recognition sequences in the genome and activate specific genes that might be involved in growth arrest. In order to identify such genes with a functional assay, we used a retroviral gene trap U3lacZ. We have now isolated MCF‐7 breast cancer cell line clones in which the lacZ reporter gene is inserted into the genes activated by either ICI‐164,384 or retinoic acid. One such clone, B4, was further characterized. In B4, lacZ activity is induced by ICI‐164,384 or trans‐retinoic acid, and repressed after treatment with estradiol. Cloning of the 5′‐flanking genomic sequence in this clone will be possible using polymerase chain reaction.