DNA double strand break repair and human disease

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Research areas:

1. Regulation double strand break repair pathway choice: relevance in cancer development and treatment.
2.  Role of CtIP in double strand break repair and human disease

Our studies are performed with human cell cultures.



Regulation double strand break repair pathway choice: relevance in cancer development and treatment.

Double strand breaks (DSBs) play an extremely relevant role in the biology of cancer. As potent citotoxic lesions - one unrepaired DSB is enough to either kill a cell or induce terminal arrest - they are the molecular base of radiotherapies and many chemotherapies. These treatments are especially successful as many cancer cells harbour mutations on genes in the DSBs repair pathways. Such mutations are favoured in many malignancies, as erroneous repair of DSBs are a major source of genomic instability, a phenomenon associated with cancer development. Therefore, alterations in the DSBs repair pathways are usually selected early on during cancer development, and they facilitate tumour progression. This double role of DSBs in both, the genesis of cancer and the treatment of cancer makes the understanding of the mechanisms that control their repair of capital importance in cancer research.


DSBs are repaired by two major mechanisms that compete for the same substrate. Both ends of the DSB can be simple re-joined with little or no processing, a mechanism known as non-homologous end-joining (NHEJ). NHEJ is a fast, simple way to repair DSBs, but the lack of a proofreading activity makes it an extremely inaccurate and mutagenic repair pathway. On the other hand, DSBs can be processed and engaged in a more complex repair pathway called homologous recombination (HR). This pathway uses the information present in a homologue sequence, usually the sister chromatid, to ensure accurate repair. Despite being generally an extremely accurate pathway, in some circumstances, i.e. when the sister chromatid is absent in G1 cells, can lead to chromosomal rearrangements such as inversions, deletions or translocations. A third, minor mechanism, called Microhomology mediated end joining (MMEJ) or alternative end-joining, share similarities with both HR and NHEJ. While the complete inability to repair DSBs leads to embryonic lethality and cell death, mutations that hamper either NHEJ or HR, are frequently found in many cancers genetic or genetically inherited syndromes with cancer predisposition. This association between DSBs and cancer is usually explained as an increased genomic instability associated with lack of DSBs repair. However, erroneously repaired DSBs – and not unrepaired DSBs – could also contribute to the observed genomic instability.

Despite the relevance of the proper DSB repair choice, little is known about the way is regulated. In eukaryotes, a major point of control is the position on the cell cycle. G0 and G1 cells rely almost exclusively on NHEJ and MMEJ for DSB repair. However, S and G2 cells activate the HR pathway. In addition, the complexity of the breaks seems important for the repair choice. Clean breaks are promptly repaired by NHEJ. On the contrary “dirty”, complex breaks, are most likely repaired by HR. Although many other factors probably contribute to this choice, they are still unknowns. Our goal is to try to further understand the molecular basis of the DSB repair choice and its relevance in human disease.

Role of CtIP in double strand break repair and human disease

CtIP is multifunctional protein involved, among other things, in the early steps of HR and the control the choice of DSB repair pathway. CtIP activation is essential for HR and requires, among other modification, phosphorylation at Thr 847 by cyclin-dependent kinases. Mutations that impair such phosphorylation, i.e. inactive CtIP versions that reduce HR, but also mutations that mimic constitutive phosphorylation, i.e. hyper-active CtIP mutants that increase HR and reduce NHEJ, lead to hyper-sensitivity to DSBs and an increase of chromosome instability. Strikingly, both reduced and increased CtIP levels have been associated with cancer.


CtIP is a multifunctional protein involved in several processes through interaction with many different partners. Such functions/partners include, among others, transcription repression (due to interaction with the transcription repressor CtBP), checkpoint activation (via interaction with the oncogenes Retinoblastoma and Brca1, and the proliferation factor PCNA) and DSB repair by HR (interaction with Brca1 and the DSB repair factor MRN complex). It is noteworthy that many of these CtIP interactors have been associated with tumorigenesis. Some of these interactions seem to be constitutive – CtBP -, while others are cell cycle regulated - Rb, Brca1 and MRN –. Therefore, CtIP is a key component in the response to DNA DSBs and the preservation of genomic stability that integrate multiple cell-cycle dependent signals. Despite its relevance, nothing is known on the crosstalk between the different CtIP interactions and functions. By using combinations of specific CtIP mutants that block specific interactions, we are gaining additional knowledge about the role of CtIP as a key regulator of the DNA damage response in the context of the cell cycle and it relevance in human disease.


Selected Publications:

Huertas, P. DNA resection in eukaryotes: deciding how to fix the break. Nat Struct Mol Biol 17, 11-6.

Huertas, P. & Jackson, S.P. Human CtIP mediates cell cycle control of DNA end resection and double strand break repair. J Biol Chem 284, 9558-65 (2009).

Huertas, P., Cortes-Ledesma, F., Sartori, A.A., Aguilera, A. & Jackson, S.P. CDK targets Sae2 to control DNA-end resection and homologous recombination. Nature 455, 689-92 (2008).