| Gene information | Literature | Expression | lncRNA | Mutation | Homolog |
Basic Information | |
|---|---|
Gene ID | 580 |
Name | BARD1 |
Synonymous | BRCA1 associated RING domain 1;BARD1;BRCA1 associated RING domain 1 |
Definition | BRCA1-associated RING domain gene 1|BRCA1-associated RING domain protein 1 |
Position | 2q35 |
Gene type | protein-coding |
Title | Abstract |
| Oncogenic BARD1 isoforms expressed in gynecological cancers. | BARD1 is required for protein stability and tumor suppressor functions of BRCA1, which depend on the ubiquitin ligase activity of the BRCA1-BARD1 heterodimer. The NH(2)-terminal RING domains of both proteins act as interaction modules and form a ubiquitin ligase, which has functions in DNA repair, cell cycle checkpoint regulation, and mitosis. Interestingly, up-regulated expression of truncated BARD1 isoforms was found to be associated with poor prognosis in breast and ovarian cancers and, in a hormonally regulated fashion, in the human cytotrophoblast, a cell type with properties reminiscent of cancer cells. We therefore performed reverse transcription-PCR to determine the structure of BARD1 isoforms in cell lines derived from hormone-dependent and hormone-independent cancers. We found a specific combination of isoforms, generated by differential splicing and alternative transcription initiation, mostly lacking the BRCA1 interaction domain, in gynecologic but not hematologic cancer cell lines. To investigate the prevalence of BARD1 isoforms in tumors, we applied immunohistochemistry to ovarian cancers, using antibodies distinguishing full-length BARD1 and isoforms. expression of NH(2) terminally truncated BARD1 was correlated with advanced stage of cancer, and expression of spliced isoforms was typical for clear cell carcinoma, the ovarian cancer with worst prognosis, suggesting a role of BARD1 isoforms in cancer progression. To challenge this hypothesis, we silenced BARD1 isoforms in ovarian cancer cells that lacked wild-type BARD1 by siRNA interference, which led to a complete proliferation arrest. Thus, BARD1 isoform expression is required for cancer cell proliferation, which is compatible with the notion that BARD1 isoforms act as cancer maintenance genes. |
| Expression of oncogenic BARD1 isoforms affects colon cancer progression and correlates with clinical outcome. | BACKGROUND: Colon cancer predisposition is associated with mutations in BRCA1. BRCA1 protein stability depends on binding to BARD1. In different cancers, expression of differentially spliced BARD1 isoforms is correlated with poor prognosis and decreased patient survival. We therefore suspected a role of BARD1 isoforms in colon cancer. METHODS: We performed immunohistochemistry in 168 colorectal cancers, using four antibodies directed against differentially expressed regions of BARD1. We determined structure and relative expression of BARD1 mRNA isoforms in 40 tumour and paired normal peri-tumour tissues. BARD1 expression was correlated with clinical outcome. RESULTS: BARD1 isoforms were expressed in 98% of cases and not correlated with BRCA1. BARD1 mRNA isoforms were upregulated in ALL tumours as compared with paired normal peri-tumour tissues. Non-correlated expression and localisation of different epitopes suggested insignificant expression of full-length (FL) BARD1. expression of N- and C-terminal epitopes correlated with increased survival, but expression of epitopes mapping to the middle of BARD1 correlated with decreased survival. Middle epitopes are present in oncogenic BARD1 isoforms, which have pro-proliferative functions. Correlated upregulation of only N- and C-terminal epitopes reflects the expression of isoforms BARD1delta and BARD1phi. CONCLUSION: Our results suggest that BARD1 isoforms, but not FL BARD1, are expressed in colon cancer and affect its progression and clinical outcome. |