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BRCA1-independent ubiquitination of FANCD2
Cassandra J Vandenberg1, Fanni Gergely, Chong Yi Ong
1Protein & Nucleic Acid Chemistry Division, MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom.
Abstract:
Monoubiquitination of the FANCD2 protein is a key step in the Fanconi anemia (FA) tumor suppressor pathway, coinciding with this molecule's accumulation at sites of genome damage. Strong circumstantial evidence points to a requirement for the BRCA1 gene product in this step. Here, we show that the purified BRCA1/BARD1 complex, together with E1 and UbcH5a, is sufficient to reconstitute the monoubiquitination of FANCD2 in vitro. Although siRNA-mediated knockdown of BRCA1 in human cells results in defective targeting of FANCD2 to sites of DNA damage, it does not lead to a defect in FANCD2 ubiquitination. Furthermore, ablation of the RING finger domains of either BRCA1 or BARD1 in the chicken B cell line DT40 also leaves FANCD2 modification intact. Consequently, while BRCA1 affects the accumulation of FANCD2 at sites of DNA damage, BRCA1/BARD1 E3 ligase activity is not essential for the monoubiquitination of FANCD2.
Insights
BRCA1/BARD1 complex can monoubiquitinate FANCD2 protein in vitro. However, BRCA1 is not essential for FANCD2 ubiquitination in cells, despite its role in DNA damage response.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Monoubiquitination of FANCD2 protein is crucial for the Fanconi anemia (FA) tumor suppressor pathway.
- BRCA1 is strongly implicated in FANCD2 monoubiquitination and its accumulation at DNA damage sites.
Purpose of the Study:
- To investigate the role of the BRCA1/BARD1 complex in FANCD2 monoubiquitination.
- To determine if BRCA1/BARD1 E3 ligase activity is essential for FANCD2 modification.
Main Methods:
- In vitro reconstitution of FANCD2 monoubiquitination using purified BRCA1/BARD1 complex, E1, and UbcH5a.
- siRNA-mediated knockdown of BRCA1 in human cells.
- Functional analysis of BRCA1 and BARD1 RING finger domains in DT40 cells.
Main Results:
- The purified BRCA1/BARD1 complex is sufficient for in vitro FANCD2 monoubiquitination.
- BRCA1 knockdown impairs FANCD2 targeting to DNA damage sites but not its ubiquitination.
- Ablation of BRCA1/BARD1 RING finger domains does not affect FANCD2 modification.
Conclusions:
- BRCA1/BARD1 E3 ligase activity is not essential for FANCD2 monoubiquitination.
- BRCA1 influences FANCD2 accumulation at DNA damage sites, but its role in ubiquitination is independent of its E3 ligase function.