Role of estrogen receptor(ER)β in modulating ERα SERM complexes in MDA-MB-231 breast cancer cells

Stable transfection of cDNA's for mutant ERα have been used to evaluate the estrogen-like properties of selective estrogen receptor modulators(SERMs) at a transforming growth factor α (TGFα) gene target in MDA-MB-231 breast cancer cells [H. Liu et al. Cancer Res 61:3632-3639,2001]. However, the cells are ERβ positive (Vladusci et al. Cancer Res 58:210-214, 1998), and it is possible that ERβ could modulate SERM ERα complexes. We have evaluated the array of ERβ subtypes present in MDA-MB-231 cells and determined the relative proportion of ERα to ERβ in transfectants.Method: RT-PCR was used to amplify ERβ from MDA-MB-231 cells. ERβ wild type and subtypes were cloned and sequenced. Primers and probes were designed to determine the relative proportion of ERα and total ERβ in MDA-MB-231 and stable transfectants containing D351 ER(WT), D351Y ER, D351G ER, using real time PCR (TaqMan). Result: Studies showed that neither SERMs nor E, induce TGFα in MDA-MB-231 cells without stable transfection of ERα. A whole variety of ERβ variants were cloned and sequenced including ERβ wild type. Δ3, Δ5, Δ6, Δ3,5, and Δ5,6 splicing isoforms. ERα was virtually undetectable in MDA-MB-231, but readily detected in stable transfectants. Relative proportion of ERα in the total ER mRNAs in transfectants were 98.7%(D351), 99.9%(D351Y), 99.9%(D351G). Conclusion: We describe novel exon deletions for ERβ in MDA-MB-231 breast cancer cells and confirm WT ERβ by cloning and sequencing. Although it has been proposed that ERβ can modulate SERM ERα complexes, the low relative levels measured in stable transfectants precludes a significant role in the structure-function relationships of SERMs at TGFα gene.