Multiple protein forms of the human breast tumor-associated epithelial membrane antigen (EMA) are generated by alternative splicing and induced by hormonal stimulation

Cloning and sequencing of epithelial membrane antigen (EMA) has demonstrated the existence of a variable number of tandem repeats (VNTR) flanked by unique sequences, and alternative splicing has been proposed to result in secreted and membrane-bound antigenic forms. Antisense oligonucleotides, specific for the VNTR region and various alternative splice forms, were used as probes to define EMA transcripts in poly A+ RNA from a mucinous breast tumor cell line. The BT549 line has been shown to exhibit enhanced expression and secretion of EMA when the cells are cultivated in a medium supplemented with hydrocortisone and insulin, and Northern blot analysis demonstrated that EMA-related RNA transcripts are commensurately enhanced. As a result of the large increase in EMA RNA levels, two major transcripts in BT549 have been identified as coding for either the secreted or transmembrane EMA forms and two antigenic forms have been immunoprecipitated from BT549 cell layer and medium translation products.