Retinoic acid down-regulates the expression of the vasoactive intestinal polypeptide receptor type-1 in human breast carcinoma cell lines.

Four breast carcinoma cell lines (T47D, ZR-75-1, MDA-MB-231, and MCF-7) were tested for regulation of the expression of vasoactive intestinal polypeptide receptor type-1 (VIP-R1). In all four cell lines, retinoic acid (RA) treatment caused a fast and marked decrease in VIP-R1 mRNA level as examined by Northern blots. Cycloheximide pretreatment attenuated the effect from 3- to 2-fold, indicating that existing proteins can mediate the decreasing effect of RA, but to attain the maximal effect new protein synthesis might be needed. Transcriptional inhibition with Actinomyocin D showed that RA did not influence the VIP-R1 mRNA half-life, indicating that the decreasing effect of RA on the mRNA level is due to transcriptional inhibition. In agreement with the observations on mRNA level, we found that the VIP receptor number was reduced 3-fold from 88 to 32 fmol/10(6) cells in T47D cells and from 222 to 73 fmol/10(6) cells in MDA-MB-231 cells upon RA treatment for 72 h. The promoter and 5'-flanking region of the VIP-R1 gene were cloned from a human placental cosmid library, and 2.5 kb were sequenced to search for regulatory elements. Our results, therefore, imply that the regulation of VIP-R1 gene expression by RA could have a role in human mammary tumor biology.