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Identification of BAF57 mutations in human breast cancer cell lines
Evangelos Kiskinis1, Juana M García-Pedrero, M Angeles Villaronga
1Institute of Reproductive and Developmental Biology, Imperial College London, London, UK.
Abstract:
Accumulating genetic and biochemical evidences support a role for the SWI/SNF chromatin-remodeling complex in cancer development and multiple core subunits of these complexes have been found to function as tumor suppressor genes. The core SWI/SNF subunit BAF57 mediates direct interactions with estrogen and androgen receptors (ER and AR) regulating their transcriptional activity. BAF57 gene maps to chromosome band 17 q21 in close proximity to the BRCA1 gene. This locus has been associated with frequent loss of heterozygosity (LOH) and allelic imbalance in breast cancers; however, BRCA1 mutations are rare events in sporadic breast cancer with LOH in the region, suggesting that another tumor suppressor gene resides in this area. All these reasons prompted us to screen for mutations in the BAF57 gene using a panel of the most commonly used human breast cancer cell lines. All cell lines analysed contain wild-type copies of BAF57 gene with the only exception of the breast ductal carcinoma cell line BT549. Sequencing of genomic DNA and cDNA generated from BT549 mRNA demonstrated the presence of a CA dinucleotide insertion in exon 5 of BAF57. The absence of wild-type BAF57 alleles indicates that this is a biallelic inactivating mutation that causes a frameshift and as a consequence a premature stop codon leading to a truncated BAF57 protein. A functional characterisation of the truncated BAF57 showed that it has lost the ability to bind to ER but still binds to the nuclear receptor coactivator SRC1e. Furthermore, we observed that the expression of the truncated BAF57 increased the ability of SRC1e to potentiate transcriptional activation by ERalpha, suggesting that mutations in BAF57 could contribute to the oncogenic transformation in breast cancer cells.
Insights
A mutation in the BAF57 gene was identified in breast cancer cells, leading to a truncated protein that may contribute to oncogenic transformation by altering estrogen receptor activity.
Area of Science:
- Genetics
- Molecular Biology
- Oncology
Background:
- The SWI/SNF chromatin-remodeling complex plays a role in cancer, with subunits acting as tumor suppressors.
- BAF57, a core SWI/SNF subunit, interacts with estrogen and androgen receptors, influencing their transcriptional activity.
- The BAF57 gene is located near BRCA1 at chromosome 17q21, a region frequently altered in breast cancer.
Purpose of the Study:
- To investigate mutations in the BAF57 gene in human breast cancer cell lines.
- To understand the functional consequences of BAF57 mutations in breast cancer development.
Main Methods:
- Screening of BAF57 gene mutations in a panel of breast cancer cell lines.
- DNA and cDNA sequencing of the BAF57 gene in the BT549 cell line.
- Functional characterization of the truncated BAF57 protein, including receptor binding assays and transcriptional activity analysis.
Main Results:
- A biallelic inactivating mutation (CA dinucleotide insertion in exon 5) was found in the BAF57 gene of the BT549 breast ductal carcinoma cell line.
- This mutation results in a truncated BAF57 protein lacking estrogen receptor (ER) binding ability but retaining SRC1e binding.
- The truncated BAF57 enhanced SRC1e's potentiation of ERalpha transcriptional activation.
Conclusions:
- Mutations in the BAF57 gene can lead to a non-functional protein that may contribute to breast cancer oncogenesis.
- The altered interaction of truncated BAF57 with ERalpha and SRC1e suggests a novel mechanism in breast cancer development.
