DETECTION OF WILD-TYPE AND EXON-5-DELETED SPLICE VARIANT ESTROGEN-RECEPTOR (ER) MESSENGER-RNA IN ER-POSITIVE AND ER-NEGATIVE BREAST-CANCER CELL-LINES BY REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION

Using reverse transcription (RT)/PCR we have shown that four breast ca ncer cell lines expressed oestrogen receptor (ER) mRNA, irrespective o f whether they were assessed as ER-positive (MCF-7 and BT-474) or ER-n egative (MDA-MB-231 and BT-20) by enzyme immunoassay (EIA). In additio n to the wild type (WT) form, they were all found to express the exon 5-deleted variant (V) form of ER mRNA by RT/PCR; this is thought to co de for a truncated constitutively active protein. By Northern blot ana lysis only the ER-positive cell lines (MCF-7 and BT-474) were found to express detectable levels of ER mRNA. Oestradiol-induced growth was f ound only in the ER-positive (by EIA) cell lines. These results confir m that the differences between ER-positive and ER-negative cell lines are quantitative rather than qualitative. As low levels of ER mRNA cou ld be detected by RT/PCR, this may reflect the greater sensitivity of this approach. The presence of exon 5-deleted V form ER mRNA in additi on to the WT form in all four breast cancer cell lines may allow these lines to be used to assess differential regulation of transcription a nd the impact of this on their oestrogen dependence.