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The kinase MK2 in DNA replication upon genotoxic stress and chemotherapy

dc.contributor.advisorDobbelstein, Matthias Prof.
dc.contributor.authorKöpper, Frederikde
dc.description.abstractDNA-Schäden stellen eine ständige Bedrohung der Genomintegrität dar. In Zellen haben sich von einem komplexen Signalnetzwerk kontrollierte Programme entwickelt, um mit diesen Läsionen zurechtzukommen und zu verhindern, dass Tumore entstehen. Diese zellulären Prozesse und die von ihnen regulierten Signalkaskaden bilden die Antwort auf DNA-Schäden (engl.: DNA damage response, DDR). Während viele Aspekte der DDR bis ins Detail untersucht worden sind, ist wenig darüber bekannt, wie Zellen auf genotoxischen Stress während der DNA-Replikation reagieren. Wir stellen in dieser Arbeit eine bislang unbekannte Funktion der Kinase MK2 in der Kontrolle der Replikation nach genotoxischem Stress während der S-Phase vor. MK2 ist ursprünglich als Mediator der allgemeinen Signaltransduktion nach Stress identifiziert worden, neuere Studien berichten jedoch von einer MK2-Funktion in der checkpoint-Signalisierung. In unserem Labor wurde bereits entdeckt, dass MK2 für die effiziente Phosphorylierung der Histon-Variante H2AX (genannt γH2AX), einem Kennzeichen der DDR, nach Schädigung der DNA durch ultraviolette (UV) Strahlung notwendig ist. Dieser Befund weistde
dc.titleThe kinase MK2 in DNA replication upon genotoxic stress and chemotherapyde
dc.title.translatedDie Kinase MK2 in der DNA-Replikation nach genotoxischem Stress und Chemotherapiede
dc.contributor.refereeDobbelstein, Matthias Prof.
dc.subject.dnb570 Biowissenschaften, Biologiede
dc.subject.gokWF 200de
dc.description.abstractengDNA damage constitutes a constant threat to genomic integrity. Cells evolved programs controlled by a complex signaling network to cope with these lesions in order to avoid tumorigenesis. These cellular processes and the signaling cascades that regulate them form the DNA damage response (DDR). Whereas many aspects of the DDR have been investigated in great detail, comparably little is known about how cells respond to genotoxic stress during DNA replication. Here, we identify a hitherto unknown function for the kinase MK2 in the control of replication upon genotoxic stress in S-phase. Originally described as a mediator of general stress signaling in the p38/MK2 pathway, recent studies reported a role of MK2 in checkpoint signaling. In our lab MK2 was previously found to be required for efficient phosphorylation of the histone variant H2AX (yielding γH2AX), a hallmark of the DDR, upon DNA damage induced by ultraviolet (UV) irradiation. This suggests a more general function of the kinase in the DDR than anticipated. We now report that depletion or inhibition of MK2 protects cells from the consequences of UV-induced DNA damage, and mice with genetic ablation of MK2 and its relative MK3 display strongly reduced apoptosis in the skin after UV irradiation. As UV-induced DNA damage mainly affects cells during replication but also in other phases of the cell cycle, we tested whether DNA damage induced by the S-phase-specific drug gemcitabine elicited an MK2-dependent DDR, as well. We found that inhibition or depletion of MK2 indeed reduces the accumulation of γH2AX and increases cell viability following gemcitabine treatment, and this effect cannot be attributed to cell cycle modulation by MK2. MK2 inhibition also rescues slow replication fork progression and increased origin firing caused by gemcitabine, demonstrating that the kinase affects replication in response to DNA damage in S-phase. We furthermore observed that MK2 is required for the genotoxic effects caused by inhibition or depletion of the essential checkpoint kinase Chk1 and that MK2 inhibition also alleviates deregulated replication caused by inhibition of Chk1. Such antagonistic activity between the two kinases comes as a surprise as both share the same target phosphorylation motif. We speculate that MK2 and Chk1 target different proteins, mediated by specific interaction partners not shared between the two. In search for the mechanism underlying the effect of MK2 on replication, we did not find any influence on regulators of origin firing, arguing that MK2 acts directly at the replication fork. The rescue of gemcitabine-induced slow fork speed by MK2 inhibition suggests that the kinase controls lesion bypass mechanisms. Accordingly, we observed that the rescue of deregulated replication by MK2 inhibition depends on translesion synthesis (TLS). We speculate that MK2 directly targets components of the TLS machinery, thereby repressing TLS. In conclusion, our data for the first time reveal an activity of MK2 in replication upon DNA damage. MK2 is required for slow fork speed and increased origin firing upon replicative stress, and this activity depends on TLS. We propose that MK2 balances the DDR by repressing TLS to limit the mutagenic effects of this lesion bypass mechanism, promoting DNA repair or cell death. These findings also identify the p38/MK2 pathway as a potential drug target as enhanced MK2 activation might sensitize cells to
dc.contributor.coRefereeWienands, Jürgen Prof.
dc.subject.topicBiology (incl. Psychology)de
dc.subject.gerreplikativer Stressde
dc.subject.gerultraviolette Strahlungde
dc.subject.engreplicative stressde
dc.subject.engultraviolet irradiationde
dc.subject.engnucleoside analoguesde
dc.subject.engDNA replicationde
dc.subject.engtranslesion synthesisde
dc.affiliation.instituteBiologische Fakultätde

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