Treeck, O., Pfeiler ,G., Horn, F., Federhofer, B., Houlihan, H., Vollmer, A., and Ortmann, O.
Notes: This study identified two novel transcript variants of the estrogen receptor ERβ that were expressed in the ERα-negative breast cancer cell line MDA-MD-231. These variants were identified after amplification of ERβ transcripts from the breast cancer cell line by RT-PCR. The amplification products were then excised from gels and subcloned into the pTARGET™ Mammalian Expression Vector prior to sequencing. COS1 cells, which do not express the estrogen receptor, were then stably transfected with full-length ERβ or one of the splice variants and the effects on cell proliferation, apoptosis, and estrogen response were evaluated. In COS1 cells expressing either ERβ or the transcript variants cell proliferation decreased and basal apoptosis (caspase 3/7 activity) increased, compared to cells transfected with vector alone. Exposure to therapeutic doses of tamoxifen induced apoptosis in cells expressing the full-length ERβ but not in cells expressing either of the variant isoforms. (3618)