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Radiobiology and DNA Repair

Patrick Calsou

Group Leader

DNA double-strand breaks are the most deleterious lesions in the genome, as they may prove lethal if unrepaired, or promote tumor development when misrepaired. Our research subject is the repair of these DNA lesions by end-joining reactions in human cells, with emphasis on molecular mechanism, balance between repair pathways, influence of the chromatin context and selection of repair modulators.

photoequipecalsou2.jpegThe Radiobiology and DNA Repair team is specialized in deciphering and targeting pathways that repair DNA double-stranded breaks (DSBs) in human. Disruption of the sugar-phosphate chain in both strands of DNA leads to the DNA lesion the most dangerous for cell integrity. DSBs are doubly linked to cancer: on one hand they promote translocations and mutations that can initiate tumorigenesis and on the other hand, they determine the cytotoxicity of ionizing radiation used in radiotherapy and of several anticancer molecules used in chemotherapy such as topoisomerases inhibitors. The toxicity of DSBs is counteracted by an adapted cellular response in which DNA repair is a key component. Depending on partially known parameters, the choice is made between two prominent types of repair: ligation of the break ends according to the Non-Homologous End Joining (NHEJ) pathway, or recombination with a homologous DNA sequence according to the Homologous Recombination pathway (HR).

During the last two decades also emerged a highly error-prone repair process named alternative end-joining (A-EJ), that we have been among the first ones to identify (Audebert et al., 2004; Frit et al., 2014). DSB repair takes part in cancer resistance to anticancer treatments based on radiotherapy or genotoxic drugs. Thus pharmacological inhibition of DSB repair mechanisms offers new avenues for anticancer drugs, as exemplified by the recent approval of PARP inhibitors to treat HR-defective cancers.


In brief, our double aim is to contribute to the molecular knowledge of DSBs repair and regulation, and to propose therapeutic applications in oncology. The team deals concurrently with:


1/ basic questions concerning the characterization of molecular details of end-joining mechanisms and connections with other cellular pathways, including in the special cellular contexts of telomeres and centromeres.


2/ translational issues regarding :

- isolation of end-joining inhibitors using combined virtual screening, molecular dynamics and biophysical and biochemical techniques;

- control of the balance between repair pathways as radio- or chemo-sensitization strategies by phenotypic screening of small regulator molecules;

- exploration of the mechanism of action of small molecules by crossing a chemoproteomic approach with the sequencing of haploid cells made resistant to these molecules.


Main Publications

Nemoz C et al. (2018) XLF and APLF bind Ku80 at two remote sites to ensure DNA repair by non-homologous end joining. Nat Struct Mol Biol 25:971 


Bombarde O et al. (2017) The DNA-Binding Polyamine Moiety in the Vectorized DNA Topoisomerase II Inhibitor F14512 Alters Reparability of the Consequent Enzyme-Linked DNA Double-Strand Breaks. Mol Cancer Ther 16:2166


Chanut, P et al. (2016) Coordinated nuclease activities counteract Ku at single-ended DNA double-strand breaks. Nat Commun 7:12889


Yuan Y et al. (2015) Single-stranded DNA oligomers stimulate error-prone alternative repair of DNA double-strand breaks through hijacking Ku protein. Nucleic Acids Res 43:10264


Britton S et al. (2014) DNA damage triggers SAF-A and RNA biogenesis factors exclusion from chromatin coupled to R-loops removal. Nucleic Acids Res 42:9047



Mainpub.pngCells containing the XLF protein marked in green (left) are irradiated by laser to create DNA breaks along thin lines. The proteins are recruited in one minute on the parallel lines drawn by the laser (right). © PCalsou



Patrick Calsou

INSERM Research director

Sébastien Britton

CNRS Research associate

Nadia Barboule

CNRS Research associate

Philippe Frit

CNRS Research associate

Dennis Gomez

CNRS Research associate

Florence Larminat

CNRS Research associate

Research Assistants

Christine Delteil

CNRS Engineer

Carine Racca

CNRS Technician

Jean-Baptiste Izquierdo

research assistant of the Occitanie Region

PhD Students

Angelique Pipier

Fellow of the Agence Nationale de la Recherche

Alexandrine Rozié

Fellow of the Agence Nationale de la Recherche

(members of the RAD group in bold characters, publications>2009)


  • Frit, P, V Ropars, M Modesti, JB Charbonnier, and P Calsou. 2019. Plugged into the Ku-DNA hub: The NHEJ network. Prog Biophys Mol Biol. doi:10.1016/j.pbiomolbio.2019.03.001  (Pubmed) (invited review)
  • Pipier A., A De Rache, C Modeste, S Amrane, E Mothes-Martin, JL Stigliani, P Calsou, JL Mergny, G Pratviel, and D Gomez. 2019. G-Quadruplex binding optimization by gold(iii) insertion into the center of a porphyrin. Dalton Trans.
    doi: 10.1039/c8dt04703k (Pubmed)
  • Rozie, A., C. Santos, I. Fabing, P. Calsou, S. Britton*, Y. Genisson, and S. Ballereau*. (2018). Alkyne-Tagged Analogue of Jaspine B: New Tool for Identifying Jaspine B Mode of Action. Chembiochem. DOI: 10.1002/cbic.201800496. (PubMed) Article selected for ChemBioChem cover.


  • Nemoz C.#, Ropars V.#, Frit P.#, Gontier A., Drevet P., Yu J., Guerois R., Pitois A., Comte A., Delteil C., Barboule N., Legrand P., Baconnais S., Yin Y., Tadi S., Barbet-Massin E., Berger I., Le Cam E., Modesti M., Rothenberg E., Calsou P.* and Charbonnier J.-B.* (2018) XLF and APLF bind to Ku80 on two remote sites to ensure DNA repair by non-homologous end-joining. Nat. Struct. Mol. Biol. 25:971-980 (PubMed) (CEA press release) (CNRS press release). F1000PRIME recommended.
  • Bombarde, O., Larminat, F., Gomez, D., Frit, P., Racca, P., Gomes, B., Guilbaud, N., Calsou, P. (2017). The DNA binding polyamine moiety in the vectorized DNA topoisomerase II inhibitor F14512 alters reparability of the consequent enzyme-linked DNA double strand breaks, Mol Cancer Ther, 16:2166-77 (PubMed)
  • Chanut P, Britton S , Coates J, Jackson SP and Calsou P (2016) Coordinated nuclease activities release Ku from single-ended DNA double strand breaks. Nat Commun 7:12889 (PubMed) (CNRS news release)
  • Hegde M, Dutta A, Yang C, Mantha A, Hegde P, Pandey A, Sengupta S, Yu Y, P Calsou, Chen DJ, Lees-Miller S and S Mitra (2016) Scaffold Attachment Factor A (SAF-A) and Ku Temporally Regulate Repair of Radiation-induced Clustered Genome Lesions. Oncotarget 7:54430-54444 (PubMed)
  • Menchon G, Bombarde O, Trivedi M, Negrel A, Inard C, Giudetti B, Baltas M, Milon A, Modesti M, Czaplicki G and Calsou P (2016) Structure-Based Virtual Ligand Screening on the XRCC4/DNA Ligase IV Interface. Sci Rep 6:22878 (PubMed)
  • Yuan Y, Britton S, Delteil C, Coates J, Jackson SP, Barboule N, Frit P and Calsou P (2015) Single-stranded DNA oligomers stimulate error-prone alternative repair of DNA double-strand breaks through hijacking Ku protein. Nucleic Acids Res 43:10264-10276 (PubMed) (CNRS news release)
  • Lamaa A, Le Bras M, Skuli N, Britton S, Frit P, Calsou P, Prats H, Cammas A and Millevoi S (2016) A novel cytoprotective function for the DNA repair protein Ku in regulating p53 mRNA translation and function. EMBO Rep 17:508-518 (PubMed)
  • Chabalier-Taste C, Brichese L, Racca C, Canitrot Y, Calsou P and Larminat F (2016) Polo-like kinase 1 mediates BRCA1 phosphorylation and recruitment at DNA double-strand breaks. Oncotarget 19:2269-2283 (PubMed)
  • Douglas P, Ye R, Morrice N, Britton S, Trinkle-Mulcahy L and Lees-Miller SP. (2015) Phosphorylation of SAF-A/hnRNP-U Serine 59 by Polo-Like Kinase 1 Is Required for Mitosis. Mol Cell Biol 35:2699-2713 (PubMed)
  • Sabater L, Nicolau-Travers ML, De Rache A, Prado E, Dejeu J, Bombarde O, Lacroix J, Calsou P, Defrancq E, Mergny JL, Gomez D* and Pratviel G* (2015) The nickel(II) complex of guanidinium phenyl porphyrin, a specific G-quadruplex ligand, targets telomeres and leads to POT1 mislocalization in culture cells. J Biol Inorg Chem 20:729-738 (PubMed) (*corresponding authors)
  • Brown JS, Lukashchuk N, Sczaniecka-Clift M, Britton S, le Sage C, Calsou P, Beli P, Galanty Y and Jackson SP (2015) Neddylation Promotes Ubiquitylation and Release of Ku from DNA-Damage Sites. Cell Rep 11:704-714 (PubMed)
  • Di Paolo A, Racca CCalsou P and Larminat F (2014) Loss of BRCA1 impairs centromeric cohesion and triggers chromosomal instability. FASEB J 28:5250-5261 (PubMed)
  • Britton S#, Dernoncourt E#, Delteil C, Froment C, Schiltz O, Salles B, Frit P* and Calsou P* (2014). DNA damage triggers SAF-A and RNA biogenesis factors exclusion from chromatin coupled to R-loops removal. Nucleic Acids Res 42:9047-9062 (PubMed) (#equal contribution, *corresponding authors)
  • Frit PBarboule NYuan YGomez D and Calsou P (2014) Alternative End-Joining pathway(s): Bricolage at DNA breaks. DNA Repair 17:81-97 (PubMed)
  • Cottarel J, Frit PBombarde O, Salles B, Négrel A, Bernard S, Jeggo PA, Lieber MR, Modesti M andCalsou P (2013) A noncatalytic function of the ligation complex during nonhomologous end joining. J Cell Biol 200:173-186 (PubMed)
  • E Gicquel, JP Souchard, F Magnusson, J Chemaly, P Calsou and P Vicendo (2013) Role of intercalation and redox potential in DNA photosensitization by ruthenium(II) polypyridyl complexes: assessment using DNA repair protein tests. Photochem Photobiol Sci 12:1517-1526 (PubMed)
  • Cheng QBarboule NFrit PGomez DBombarde O, Couderc B, Ren G-S, Salles B and Calsou P(2011) Ku counteracts mobilization of PARP1 and MRN in chromatin damaged with DNA double-strand breaks. Nucleic Acids Res 39:9605-9619 (PubMed)
  • Romera C, Bombarde O, Bonnet R, Gomez D, Dumy P, Calsou P, Gwan JF, Lin JH, Defrancq E and Pratviel G (2011) Improvement of porphyrins for G-quadruplex DNA targeting. Biochimie 93:1310-1317 (PubMed)
  • Ye J, Lenain C, Bauwens S, Rizzo A, Saint-Léger A, Poulet A, Benarroch D, Magdinier F, Morere J, Amiard S, Verhoeyen E, Britton S, Calsou P, Salles B, Bizard A, Nadal M, Salvati E, Sabatier L, Wu Y, Biroccio A, Londoño-Vallejo A, Giraud-Panis MJ and Gilson E (2010) TRF2 and Apollo cooperate with Topoisomerase 2α to protect human telomeres from replicative damage. Cell 142:230-242 (PubMed)
  • Gomez D, Guédin A, Mergny J.L, Salles B, Riou J.F, Teulade-Fichou MP and Calsou P (2010) A G-quadruplex structure within the 5’-UTR of TRF2 mRNA represses translation in human cells. Nucleic Acids Res 38:7187-7198 (PubMed)
  • Bombarde O, Boby C, Gomez DFrit P, Giraud-Panis MJ, Gilson E, Salles B and Calsou P (2010) TRF2/RAP1 and DNA-PK mediate a double protection against joining at telomeric ends. EMBO J 29:1573-1584 (PubMed)
  • Britton S, Froment C, Frit P, Monsarrat B, Salles B and Calsou P (2009) Cell Nonhomologous End Joining capacity controls SAF-A phosphorylation by DNA-PK in response to DNA double-strand breaks inducers. Cell Cycle 8:3717-3722 (PubMed) (comment by K Meek in Cell Cycle 8:3809)
  • Britton SFrit P, Biard D, Salles B and Calsou P (2009) ARTEMIS nuclease facilitates apoptotic chromatin cleavage. Cancer Res 69:8120-8126 (PubMed)
  • Wu PY, Frit P*, Meesala S, Dauvillier S, Modesti M, Andres SN, Huang Y, Sekiguchi J, Calsou P, Salles B and Junop MS* (2009) Structural and functional interaction between the human DNA repair proteins DNA Ligase IV and XRCC4. Mol Cell Biol 29:3163-3172 (*corresponding authors) (PubMed)






  • 2018-2020 Labellisation Ligue Nationale Contre le Cancer "“ Cassures double-brin de l'ADN : mécanismes de réparation et connexions thérapeutiques en oncologie ”
  • 2018 Programme Prématuration Région Occitanie "OPTIBREAK" (Collaboration with Pascal demange, Lionel Mourey, Yves Génission)
  • 2017 ANR "NHEJ LIG4" (collaboration with Mauro Modesti and Jean-Baptiste Charbonnier"
  • 2017 Fondation ARC.  "Development of new anticancer agents based on the dialkynylcarbinol pharmacophore". 
  • 2017 ANR JCJC.  "Drugging DNA repair complexes". 
  • 2016 IDEX "Fishing out the intracellular target of novel antitumor pharmacophores bio-inspired from marine sponge" (collaboration with Y. Génisson and R. Chauvin)
  •  2016 ANR Projet G4-TopIPro (collaboration with E. Defrancq and J.-F. Riou)
  •  2016 Cancéropôle Grand Sud-Ouest – Soutien à l’Emergence (Cibles pharmacologiques de la Jaspine B)
  •  2016 Cancéropôle Grand Sud-Ouest – Soutien à l’Emergence (G4POPSTAR, collaboration with G. Pratviel and S. Millevoi)
  •  2016 Electricité de France - Conseil de Radioprotection
  •  2015 Electricité de France - Conseil de Radioprotection