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Novel mutations in the estrogen receptor messenger RNA in human breast cancers
1Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Abstract:
One mechanism that has been suggested to play a role in the progression of human breast cancer from hormone dependence to independence is the expression or altered expression of mutant and/or variant forms of estrogen receptor (ER). Two major types of variant ER messenger (m)RNA have been identified in human breast biopsy samples so far: truncated transcripts and exon deleted transcripts. In this study we provide data indicating the existence of a novel type of abnormal ER mRNA. These transcripts were identified as larger than wild-type ER mRNA RT-PCR products in 9.4% of 212 human breast tumors analyzed. The data suggest nucleotide insertions are present in ER mRNA of some breast tumors. Cloning and sequencing of the larger RT-PCR products showed three different types: a complete duplication of exon 6 occurring in 7.5% of tumors; a complete duplication of both exons 3 and 4 occurring in 1 tumor; and a 69 nucleotide insertion between exons 5 and 6 occurring in 3 tumors. Open reading frame analysis suggested that exon 6 duplicated transcripts encoded a 51.4 kDa ER-like protein truncated just after exon 6 sequences; the exon 3 and 4 duplicated transcript encoded a 83.3 kDa protein containing duplication of ER amino acid residues encoded by exons 3 and 4; the 69 nucleotide insertion was inframe, adding 23 novel amino acid residues between residues 412 and 413 of the normal ER protein to produce a 68.8 kDa protein. It is unknown if these novel ER-like mRNAs are stably translated in vivo. Any resulting protein would be structurally altered, however, possibly resulting in altered function.
Insights
Researchers discovered novel, larger estrogen receptor (ER) messenger RNA variants in human breast tumors. These abnormal transcripts, potentially leading to altered ER protein function, may play a role in breast cancer progression.
Area of Science:
- Molecular Biology
- Oncology
- Genetics
Background:
- Estrogen receptor (ER) plays a crucial role in human breast cancer development and progression.
- Variant and mutant forms of ER are implicated in the transition from hormone-dependent to hormone-independent breast cancer.
- Previously identified ER messenger RNA (mRNA) variants include truncated and exon-deleted transcripts.
Purpose of the Study:
- To investigate the existence and nature of novel abnormal estrogen receptor (ER) mRNA transcripts in human breast tumors.
- To characterize the structural alterations and potential functional implications of these newly identified ER mRNA variants.
Main Methods:
- Reverse transcription-polymerase chain reaction (RT-PCR) was employed to analyze ER mRNA from 212 human breast tumor samples.
- Larger-than-wild-type RT-PCR products were cloned and sequenced to identify specific structural abnormalities.
- Open reading frame analysis was performed to predict the protein products encoded by the variant transcripts.
Main Results:
- Novel, larger ER mRNA transcripts were detected in 9.4% of the analyzed breast tumors.
- Three distinct types of transcript alterations were identified: complete duplication of exon 6 (7.5% of tumors), duplication of exons 3 and 4 (1 tumor), and a 69-nucleotide insertion between exons 5 and 6 (3 tumors).
- Predicted protein products from these variants exhibit altered molecular weights and amino acid sequences compared to the normal ER protein.
Conclusions:
- The study identified a novel class of abnormal estrogen receptor (ER) mRNA transcripts in human breast tumors, characterized by nucleotide insertions or duplications.
- These findings suggest that altered ER mRNA structures, potentially leading to structurally modified ER-like proteins, may contribute to breast cancer progression.
- Further research is needed to determine if these novel ER-like mRNAs are translated in vivo and to elucidate the functional consequences of any resulting altered proteins.