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Session 3: Transcriptional control Poster 5
Role of MDC1 in NF-kappaB activation by DNA double-strand breaks.
Helene Sabatel, Jacques Piette and Yvette Habraken.
Laboratory of Virology and Immunology, Signal Transduction Unit, GIGA-R,
University of Liège, 4000 Liège, Belgium. helene.sabatel@student.ulg.ac.be,
jpiette@ulg.ac.be, yvette.habraken@ulg.ac.be
Many anticancer treatments, such as ionizing radiation (IR) and DNA topoisomerase I and II,
induce apoptosis in tumor cells by generating DNA double strand breaks (DSB). ATM kinase,
rapidly activated by DSB, orchestrates different aspects of the DNA Damage Response: cell
cycle arrest, DSB repair and transcription factors activation. Both NF-kappaB and p53 are
activated by DSB, controlling anti- and pro-apoptotic signals and therefore affecting cell
survival and the outcome of the cancer treatment.
In this work, the importance of MDC1 (Mediator DNA damage checkpoint 1) in the DNA
damage signalling to NF-!B is studied. As expected, MDC1 reduction by siRNAs resulted in
a smaller number of nuclear foci after IR and Camptothecin treatments. We observed that
reduced MDC1 level leads to a reduction of NF-!B nuclear translocation after both
treatments. NF-!B transactivation potential was assessed with two reporter systems; either a
transiently transfected !B-Luc reporter plasmid or a stably integrated !B-GFP reporter. In
both cases, we noticed a large reduction of the transcriptionnal activity in cells treated with
siRNA-MDC1. The reduction was however less important than the one observed in cells
treated with an siRNA-ATM. Mefs WT and KO for MDC1 were tested for NF-!B activation
by IR and Camptothecin. However, as Mefs WT did not activate NF-!B following DNA
damage we could not use this model. The effect of the deletion of different domains of MDC1
is also analysed to determine by which way this protein interferes with NF-kappaB signalling
pathway (foci dependent or independent manner).
In summary, our data indicate that deletion of MDC1 has an impact on NF-!B activation after
both IR and Camptothecin treatments contrarily to the disruption of NBS/Mre/Rad50 complex
that affects only IR signalling under the tested conditions.
Financial supports: IAP 6/18, Centre anti-cancéreux de l’ULg, FRS-FNRS, F.R.S.M
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