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Coexpression of wild-type and variant oestrogen receptor mRNAs in a panel of human breast cancer cell lines
C G Castles1, D M Klotz, S A Fuqua
1Department of Medicine/Oncology, University of Texas Health Science Center at San Antonio 78284, USA.
Abstract:
Wild-type as well as variant oestrogen receptor (ER) mRNAs with exon 5 and 7 deleted were identified in a panel of human breast tumour cell lines by reverse transcriptase-polymerase chain reaction followed by dideoxynucleotide sequence analysis, and then quantitated by ribonuclease protection analysis. All cell lines categorised as ER+ by ligand-binding analysis expressed both wild-type and variant ER transcripts. Most cell lines classified as ER- did not express any ER transcript. However, three ER- cell lines (BT-20, MDA-MB-330 and T47Dco) expressed both wild-type and variant transcripts. A differential pattern of expression of wild type to variant was seen in both ER+ and ER- cell lines, however this pattern was not paralleled by differences in ligand-binding activity. Breast tumour cell lines previously classified as ER- expressed significantly lower levels of ER transcripts than did their ER+ counterparts. In view of these findings, as well as earlier reports that the exon 5 deletion ER variant encodes a dominant-positive receptor, it seems clear that some cell lines are misclassified as ER-, and express both wild-type and variant ER mRNAs, and that the overexpression of this variant may account, in part, for their oestrogen-independent phenotype.
Insights
This study identified both wild-type and variant estrogen receptor (ER) transcripts in human breast cancer cell lines. Some estrogen receptor-negative cell lines may be misclassified, potentially explaining their estrogen-independent growth.
Area of Science:
- Molecular Biology
- Oncology
- Genetics
Background:
- Estrogen receptor (ER) status is crucial for breast cancer classification and treatment.
- ER variants may influence receptor function and cellular phenotype.
- Accurate ER assessment is vital for therapeutic decisions.
Purpose of the Study:
- To investigate the expression of wild-type and variant ER transcripts in human breast tumor cell lines.
- To correlate ER transcript expression with ER protein levels and ligand-binding activity.
- To identify potential misclassification of ER-negative cell lines.
Main Methods:
- Reverse transcriptase-polymerase chain reaction (RT-PCR) for ER transcript detection.
- Dideoxynucleotide sequence analysis for transcript characterization.
- Ribonuclease protection assay (RPA) for ER transcript quantification.
Main Results:
- Wild-type and variant ER transcripts (lacking exons 5 and 7) were detected in ER-positive cell lines.
- Three ER-negative cell lines (BT-20, MDA-MB-330, T47Dco) also expressed both ER transcript types.
- ER-negative cell lines generally showed lower ER transcript levels than ER-positive lines.
- Differential expression patterns of wild-type to variant ER were observed but did not correlate with ligand-binding activity.
Conclusions:
- Some breast tumor cell lines classified as ER-negative may express both wild-type and variant ER mRNAs.
- The exon 5 deletion ER variant may contribute to an estrogen-independent phenotype.
- Potential misclassification of ER status in some cell lines warrants further investigation.