Differential expression of an estrogen receptor messenger RNA containing exon 1′ sequences in MCF-7 breast cancer cell line stocks

The presence of an exon 1′ sequence in the estrogen receptor alpha (ERα) mRNA was detected in different stocks of ER-positive MCF-7 human breast cancer cells by reverse transcriptase polymerase chain reaction (RT-PCR) and ribonuclease protection analysis (RPA), but not by Northern blot analysis. This mRNA, however, was not detectable in ERα-positive ZR-75-1 or ERα-negative MDA-MB-231 breast cancer cells, suggesting that exon 1′ ER mRNA is differentially expressed in some but not all ER-positive cell lines, and then, only at very low levels.