DNA repair pathway to come under further scrutiny with new funding

Martin Cohn and his DPhil student David Lopez Martinez have secured funding to enable them to continue to explore how an important DNA damage pathway is regulated.

The funding for a MRC transition fellowship will support David as he moves from DPhil to postdoc position. In particular, David will be able to probe an unexpected control step in the Fanconi anemia (FA) DNA repair pathway that he and his colleagues discovered, helping him to secure his next career move.

David began his research career in the UK in 2013 with a Masters at UCL supported by a prestigious La Caixa scholarship, which won him the best student prize for the MSc Biomedical Sciences. With support from theClarendon Fund and the MRC, and subsequently from the Fundación Mutua Madrileña, he began a DPhil with Martin Cohn in 2014 to explore how the FA DNA repair pathway is controlled.

Over the past 4 years, David's work, which combines human cell based assays with technically challenging in vitro studies using purified proteins, has revealed a new layer of complexity to the FA repair pathway. This pathway repairs a very harmful form of damage in the DNA called inter-strand crosslinks (ICLs), largely during DNA replication as the replication fork passes along the DNA and arrests at the ICL. A protein complex called FANCD2/FANCI is at the centre of the process and its recruitment onto the DNA is tightly regulated. Transfer of ubiquitin onto FANCD2 and FANCI by a process of monoubiquitination is known to be a key component of this step.

However, as David and his colleagues found, this is not the only way that the step is regulated. They have shown that FANCD2 is also regulated through phosphorylation by the CK2 protein kinase, which prevents recruitment of FANCD2 to ICLs. Phosphorylation dramatically reduces the affinity of the FANCD2/FANCI complex towards DNA, inhibits monoubiquitination and blocks activation of the FA pathway and subsequent repair. The researchers suggest that this additional step could act as a safeguard to prevent the repair pathway becoming activated when no damage has occurred.

With the new funding, David will be able to answer a number of questions about the newly identified step, beyond the end of his DPhil studies. These include how phosphorylation of FANCD2 reduces the affinity of the FANCD2/FANCI complex for DNA, and the identity of the phosphatase responsible for dephosphorylation and activation of the complex. Some of David's findings are about to be submitted for publication to form his fifth publication whilst a student in Martin Cohn's laboratory (1-4).

David said: "I am very grateful to the MRC for their support during my DPhil and now for the transition to postdoc. Thanks to their help we have managed to show how phosphorylation can be key to regulating DNA binding of repair factors - for example the FANCD2/FANCI complex - which could be critical in numerous events such as replication, recombination and repair of DNA."

"I'm delighted to see David receive this prestigious support," added Martin. "He has made major discoveries during his DPhil studies and I am certain that he will continue to thrive in his future scientific career."

References

1. Motnenko, A., Liang, C.C., Yang, D, Lopez-Martinez, D., Yoshikawa, Y., Zhan, B., Ward, K.E., Tian, J., Haas, W., Spingardi, P., Kessler, B.M., Kriaucionis, S., Gygi, S.P. and Cohn, M.A. (2018). Identification of UHRF2as a novel DNA interstrand crosslink sensor protein. PLoS Genetics. (In press).
    
2. Liang, C.C., Li, Z., Lopez-Martinez, D., Nicholson, W.V., Venien-Bryan, C., and Cohn, M.A. (2016). The FANCD2-FANCI complex is recruited to DNAinterstrand crosslinks before monoubiquitination of FANCD2. Nature Communications 7, 12124.
    
3. Lopez-Martinez, D., Liang, C.C., and Cohn, M.A. (2016). Cellularresponse to DNA interstrand crosslinks: the Fanconi anemia pathway. Cellular and Molecular Life Sciences 73, 3097-3114.
    
4.  Schwab, R.A., Nieminuszczy, J., Shah, F., Langton, J., Lopez-Martinez, D., Liang, C.C., Cohn, M.A., Gibbons, R.J., Deans, A.J., and Niedzwiedz, W. (2015). The Fanconi Anemia Pathway Maintains Genome Stability by Coordinating Replication and Transcription. Molecular Cell 60, 351-361.

Jane Itzhaki,
16th October 2018