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

Abstract

Three breast carcinoma cell lines were tested for 17β-estradiol (E 2) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (VPAC 1) expression. In all three, E 2 was found to down-regulate the mRNA level. 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 reduced 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 synthesis. Experiments with the transcriptional inhibitor actinomycin D showed that E 2 did not influence the VPAC 1 mRNA half-life while nuclear run-on experiments indicated that E 2 decreased the VPAC 1 transcription rate. Two antiestrogens: ICI 182 780 (ICI) and 4-hydroxy-tamoxifen (4-OHT) mediated a concentration dependent inhibition of E 2's effect on the mRNA level. Transient transfection with reporter-gene constructs containing various portions of the VPAC 1 5′-flanking sequence revealed the most proximal 100 bp to be essential for the basal transcriptional activity. However, E 2 did not influence the expression of the reporter gene using up to 3250 bp of the VPAC 1 5′-flariking region.