Effect of sodium butyrate on estrogen receptor and epidermal growth factor receptor gene expression in human breast cancer cell lines.

Estrogen receptor (ER) binding has been shown to decrease in breast cancer cell lines exposed to sodium butyrate; however, the underlying mechanisms are unknown. In MCF-7 breast cancer cells, butyrate caused a rapid time- and concentration-dependent decrease in ER mRNA levels, apparent by 3 h at 3 mM butyrate. ER gene transcription rate was decreased and cycloheximide co-treatment did not relieve this inhibitory effect, suggesting that the butyrate effect was not dependent on ongoing protein synthesis. In both MCF-7 and T-47D cells the decrease in ER mRNA was mirrored by an increase in the level of epidermal growth factor receptor (EGF-R) mRNA. A marked inverse relationship exists between ER and EGF-R in human breast cancer biopsies and cell lines, and the reciprocal modulation of these genes by butyrate suggests that the expression of ER and EGF-R may be co-regulated. This relationship was further investigated in lines expressing only one or the other receptor. In the ER-positive EGF-R-negative line, MDA-MB-134-VI, butyrate exposure decreased ER mRNA levels, implying that the regulation of ER mRNA by butyrate is independent of EGF-R expression. However, butyrate decreased EGF-R mRNA in two ER-negative lines, MDA-MB-231 and HBL-100. As this effect differed from that in ER-positive lines, the regulation of EGF-R may depend on the expression of ER. The possibility that ER and EGF-R gene expression are closely linked has implications in the understanding of progression of human breast cancers to a hormone-independent phenotype and for the use of ER and EGF-R levels as independent prognostic indicators.