Estradiol down regulates expression of vasoactive intestinal polypeptide receptor type-1 in breast cancer cell lines

Three breast carcinoma cell lines were tested for 17 beta -estradiol (E-2) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (V PAC(1)) expression. In all three, E-2 was found to down-regulate the mRNA l evel. We studied T47D cells in more details and found a 25 and 70% decrease in the VPAC(1) mRNA level upon 7 and 48 h of E-2 treatment, respectively. The number of vasoactive intestinal polypeptide (VIP) binding sites was red uced 66% upon treatment with E-2 for 72 h. After cycloheximide pretreatment , the E-2 mediated mRNA reduction was attenuated from 50% to 25% after 24 h suggesting the effect to be at least partly independent of protein synthes is. Experiments with the transcriptional inhibitor actinomycin D showed tha t E-2 did not influence the VPAC(1) mRNA half-life while nuclear run-on exp eriments indicated that E-2 decreased the VPAC(1) transcription rate. Two a ntiestrogens: ICI 182 780 (ICI) and 4-hydroxy-tamoxifen (4-OHT) mediated a concentration dependent inhibition of E-2's effect on the mRNA level. Trans ient transfection with reporter-gene constructs containing various portions of the VPAC(1) 5'-flanking sequence revealed the most proximal 100 bp to b e essential for the basal transcriptional activity. However, E-2 did not in fluence the expression of the reporter gene using up to 3250 bp of the VPAC (1) 5'-flariking region. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.