Analysis of estrogen-induced genes in breast cancer

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We found that estrogen increased the activity and protein levels of choline kinase in DMBA-induced rat mammary carcinoma. Choline kinase gene was expected to be regulated by estrogen or by factor induced by estrogen. To investigate the activation mechanism of the enzyme, we carried out two experiments. First, we isolated and characterized rat choline kinase gene. The 5'region of choline kinase gene showed features not only of a typical housekeeping gene but also of a gene regulated by a various kind of regulatory factors. In fact, the carcinogen 3-methylcholanthrene, and hepatotoxic carbon tetrachloride induced this enzyme in rat liver. However, neither estrogen responsive element norits similar sequence of the estrogen binds was found between 5'region and the beginning of the first intron of this gene. Second, we obtained cDNAs from mRNA induced by estrogen in DMBA-induced rat mammary carcinoma and in human breast cancer cell line MCF-7 implanted in nude mice. Total RNA was extracted from these tumors in the presence or absence of estrogen. cDNA was synthesized by reverse transcription and used to polymerase chain reaction with a various pair of primers. Reaction products were separated by electrophoresis and differentially displayd in parallel. We obtained 13 cDNAs of estrogen-induced genes from rat tumors and 39 cDNAs of these from MCF-7 tumors. We are analyzing these cDNAs. We will elucidate the mechanism of choline kinase activation and growth regulation by estrogen.