RECONSTITUTION OF ESTROGEN-DEPENDENT TRANSCRIPTIONAL ACTIVATION OF ANADENOVIRAL TARGET GENE IN SELECT REGIONS OF THE RAT MAMMARY-GLAND

Estrogen regulates proliferation and morphogenesis of mammary ductal e pithelium by interacting with a specific intracellular estrogen recept or (ER) that acts as a hormone-dependent transcriptional regulator of gene expression. The mechanisms by which ER regulates transcription in response to estrogen have been analyzed extensively in tissue culture and in cell-free systems. These studies have demonstrated that the tr anscriptional activity of ER is strongly influenced by cellular contex t and highlight the need to address ER transcriptional activity in an appropriate cellular background. Thus, to gain insight into the mechan istic role of ER in mammary epithelial morphogenesis, we have used an adenoviral gene delivery strategy to introduce an estrogen-responsive reporter gene into the mammary epithelium and to monitor the activity of endogenous ERs in their natural environment where cellular context including stromalepithelial interactions can be taken into account. Us ing this approach, we first demonstrated highly efficient adenoviral d elivery throughout the mammary epithelium using a beta-galactosidase ( beta gal) reporter gene under the control of the constitutively active cytomegalovirus (CMV) promoter. Next, we constructed an adenoviral ve ctor by substituting the CMV promoter with an estrogen-dependent promo ter fragment-linked beta gal (Ad-ERE-tk-beta gal). This adenoviral rep orter system provides evidence that ER positive mammary epithelial cel ls display a differential sensitivity in a region-specific manner towa rd estrogen induction. Our data suggest that the availability of facto r(s) other than ER is necessary for ER-mediated gene activation and ma y be important in modulating the differential responses of mammary epi thelial cells to estrogen.