THE ROLE OF TRANSFORMING GROWTH-FACTOR-BETA IN THE REGULATION OF ESTROGEN-RECEPTOR EXPRESSION IN THE MCF-7 BREAST-CANCER CELL-LINE

The role of transforming growth factor-beta 1 (TGF beta 1) in the regu lation of estrogen receptor (ER) expression in MCF-7 cells was investi gated. After treatment of the cells with 100 pm TGF beta 1, ER protein declined by about 30% at 6 h from a concentration of 413.5 fmol/mg pr otein in control cells to 289.5 fmol/mg protein in treated cells. The concentration of receptor remained suppressed for 24 h. Scatchard anal ysis demonstrated that the decrease in ER protein corresponded to a de crease in estradiol-binding sites, with no effect on the binding affin ity of the ER. The dissociation constant of the estradiol-En complex w as 0.117 nM in TGF beta 1-treated cells compared to 0.155 nM in contro l cells. Treatment with TGF beta 1 did not influence the half-life of the ER. In TGFpl-treated cells, as well as in control cells, the half- life of the receptor was approximately 4 h. In contrast to the effect on ER concentration, TGF beta 1 treatment resulted in a greater decrea se in the steady state level of ER messenger RNA (similar to 75%) at 6 h. By 24 h, a small recovery in the amount of messenger RNA was obser ved. Transcription run-on experiments demonstrated a decrease of appro ximately 70% in the level of ER gene transcription at 3 h. Transient t ransfections using an ER promoter-chloramphenicol acetyltransferase co nstruct demonstrated that after TGF beta 1 treatment, chloramphenicol acetyltransferase activity decreased by 50%, suggesting that TGF beta 1 inhibition of the ER gene transcription is mediated through the ER p romoter. Although treatment with TGF beta 1 decreased the ER concentra tion, the growth Factor had no effect on the activity of ER, as measur ed by its effects on estradiol induction of progesterone receptor and pS2, suggesting that TGF beta 1 does not inhibit proliferation of MCF- 7 cells by blocking ER activity.