INVOLVEMENT OF ETS-RELATED PROTEINS IN HORMONE-INDEPENDENT MAMMARY CELL-SPECIFIC GENE-EXPRESSION

Regulatory regions have been located in the 5' flanking sequence of th e mouse whey acidic protein gene which contribute to its tissue- and s tage-specific expression in the mammary gland. They can be functionall y separated into elements which mediate the action of lactogenic hormo nes prolactin and glucocorticoids and elements which control mammary c ell-specific transcription in the absence of hormones. By mutational a nalysis, we have located a site in the whey acidic protein promoter be tween -120 and -100 which is important for hormone-independent promote r function. In stably transfected HC11 mammary epithelial cells, the h ormone-independent activity of the mutated promoter was reduced 40-fol d, whereas the capability to respond to lactogenic hormones was retain ed. The site was specifically recognised by two nuclear factors contai ned in extracts of cultivated mammary epithelial cells of mammary glan ds. Electrophoretic mobility shift assay, DNase I footprinting and met hylation interference experiments indicated a relation of both factors to the Ets family of DNA-binding proteins. One of these factors also recognised a functionally important site in the mammary cell-specific enhancer of the mouse mammary tumor virus long terminal repeat. The re sults suggest that factors related to the Ets family are important det erminants in mammary cell-specific gene expression.