Variant estrogen receptor-alpha messenger RNA expression in hormone-independent human breast cancer cells

T5-PRF cells are insensitive to the growthstimulatory effects of estrogen while still retaining expression of estrogen receptor- (ER-). In the apparent absence of ligand, T5-PRF cells have a 3·60·5 (...)-fold increased basal ER- activity and elevated basal progesterone receptor levels compared with the parent, estrogen-sensitive, T5 cells. Long-range ER- reverse transcription-PCR was performed to characterize variant ER- mRNA expression in the two cell lines. An increased relative expression of an exon 3/4-deleted ERmRNA variant was found in T5-PRF. Recombinant expression of this ER- variant resulted in