Expression of wild-type estrogen receptor beta and variant isoforms in human breast cancer

It has been shown in previous studies that a variety of estrogen receptor ( ER) beta mRNA transcripts are expressed in human breast cancer cell lines a nd tumors, To complement the RNA expression studies, we have developed ER-b eta-specific antibodies to characterize ER-beta protein expression in breas t cancer cell lines and tumors. Monoclonal antibodies were made against a p eptide representing the first 18 amino acids of the longest ER-beta open re ading frame reported to date, and polyclonal antibodies were made against a peptide within the ER-beta B domain. By Western blot analysis, we show tha t ER-beta protein is expressed in all cancer cell lines tested and in three of five breast tumor samples. The breast cancer cell lines showed variatio n in the size of the expressed ER-beta protein. The Longest form detected w as consistent with the 530-amino acid, full-length ER-beta sequence. Shorte r ER-beta isoforms were detected in the ER-alpha-negative MDA-MB-231 and MD A-MB-435 breast cancer cell lines, likely corresponding to previously descr ibed COOH-terminal RNA variant isoforms.