Breast Cancer Cells: Regulation of Expression by a Progestin -Hydroxysteroid Dehydrogenase Gene Expression in Human

The expression of the 17/3-hydroxysteroid dehydrogenase (17-HSD) gene in a series of human breast cancer cell lines was studied by Northern blot hybridization with a cDNA probe and by a time-resolved immunofluorometric assay using polyclonal antibodies against the enzyme pro tein. The 17-HSD enzyme protein concentration was measured in the 800 x g cell extract. A high concentration was measured in the BT-20 cell line, corresponding to one-fourth of the average concentration in placenta! tissue. Western blot analysis indicated that the antigen corre sponded to a single M, 35,000 band. In 2 other cell lines (MDA-MB361 and T-47D), the 17-HSD protein concentration was much lower, but still measurable, whereas in the remaining 5 cell lines (HBL-100, MCF7, MDA-MB-231, MDA-MB-468, and ZR-75-1) it was below the detec tion limit of the assay. Treatment of the cells for 5 days with the synthetic progestin, ORG2058, resulted in an increase of the 17-HSD protein concentration only in the T-47D cell line. By Northern blot analysis, a low level of 2.3-kilobase inKNA transcripts was detected in all 8 cell lines. In addition, a 1.3-kilobase 17-HSD mRNA was present in the samples from the 3 cell lines containing measurable amounts of 17-HSD protein in the cell extract, and the band intensities were proportional to the amount of protein measured with the immunofluorometric assay. Only in the 1-471) cell line did progestin treatment correspond to an increased amount of the 17-HSD 1.3-kilobase mRNA. These results suggest that the 1.3-kilobase mRNA for 17-HSD is the form most closelyassociated with protein expression and is also the only form responding to the progestin induction of the 17-HSD gene.