Research Report 2010 - MDC

Robert KudernatschLi-Min LiuAna MilojkovicAnnika MüerAnja MüllerTim OverkampThomas PretzschThoma RathjenTechnical AssistantsAnja RichterAntje RichterJosephine RußKerstin Dietze*Jana Roßius**part of the period reportedcancer therapies. Our studies therefore deal with questionssuch as how cell cycle stress responses includinganticancer therapies and oncogene deregulation feedinto the mitochondrial death pathway. We recentlyestablished that Nbk stabilizes the anti-apoptotic multidomainprotein Mcl-1 that acts as an endogenousinhibitor of Bak. This fully explains the entirely Baxdependent induction of apoptosis by Nbk. Ongoingwork addresses the transcriptional control of Nbkexpression and its functional involvement in the regulationof cell death following ER stress responses.Regulation of the Bak pathway by Mcl-1 (but not Bcl-x L )is of general relevance for targeted cancer therapy andwas shown to mediate TRAIL resistance in Bax deficientcarcinoma cells.Cell cycle and apoptosisUsing the apoptosis, cell cycle arrest and senescenceinducing tumor suppressor gene p14 ARF expression as amodel system, we explore the intricate interconnectionsbetween cell cycle stress responses and apoptosisinduction. P14 ARF expression is induced upon cellularstress, especially following deregulation of oncogenes.While physical interaction of p14 ARF with numerous regulatoryproteins, induction of p53-dependent cell cyclephenomena and cellular senescence by p14 ARF are wellestablished, little is known how p14 ARF induces celldeath. Notably, we established that the induction ofmitochondrial apoptosis by p14 ARF is entirely independentfrom p53 and Bax in p53-deficient cells where Bakcan fully complement for Bax function. Apoptosis ismediated, at least in p53-proficient cells, via the BH3-only protein Puma/bbc3 and relies on procaspase-3 forcell death execution. In contrast to apoptosis induction,the triggering of a G1 cell cycle arrest (and presumablypremature cellular senescence) by p14 ARF is entirelydependent on p53 and p21 CIP/WAF-1 , indicating that the signalingpathways for p14 ARF -induced G1 arrest and apoptosisinduction dissociate upstream of p53. Noteworthy,loss of p21 and/or 14-3-3σ strongly enhances apoptosisinduction by p14 ARF . Nonetheless, we recently demonstratedthat, in the absence of functional p53 and/orp21, p14 ARF triggers a G2 cell cycle arrest by downregula-Function of BH3-only proteins as death sensors. A: BH3-only proteinsact as functional interface between death signals and the mitochondrialapoptosis pathway. Anti-apoptotic Bcl-2 proteins put an at least duallayer of protection on activation of Bax/Bak that redistribute upon activationto form pores in the outer mitochondrial membrane for therelease of pro-apoptotic factors such as cytochrome c. B: Conditionaladenoviral expression of Nbk induces redistribution of Bax (EGFP, green)to mitochondria (TOM20, red) and a punctuate formation of Bax clustersdue to oligomerization. Blue colour: DAPI stained nuclei.Mitochondria fragment and cluster around the nucleus in apoptoticcells (on condition) as compared to the control (off).tion of cdc2-kinase activity, protein expression, andcytoplasmic localization in these cells whereas p14 ARF islocalized to the nucleus, i.e. mediates cdc2 sequestrationand induction of mitochondrial apoptosis throughan indirect mechanism. Such p53-independent mechanismsof p14 ARF induced apoptosis and arrest in the celldivision cycle represent fail-safe mechanisms thatallow for efficient growth suppression following inductionof p14 ARF -mediated stress responses in p53 pathwaydeficient cells.Selected PublicationsHossbach J, Michalsky E, Henklein P, Jaeger M, Daniel PT, Preissner R.Inhibiting the inhibitors: Retro-inverso Smac peptides. Peptides. 2009 Aug12. [Epub ahead of print]Gillissen B, Essmann F, Hemmati P, Richter A, Richter A, Öztop I,Chinnadurai G, Dörken B and Daniel PT. Mcl-1 mediates the Bax dependencyof Nbk/Bik-induced apoptosis. J Cell Biol 2007, 179: 701-15.Hemmati PG, Normand G, Gillissen B, Wendt J, Dörken B, Daniel PT.Cooperative effect of p21Cip1/WAF-1 and 14-3-3s on cell cycle arrest andapoptosis induction by p14ARF. Oncogene 2008, 27:6707-19.Daniel PT, Koert U, Schuppan J. Apoptolidin: induction of apoptosis by anatural product. Angew Chem Int Ed Engl. 2006, 45:872-93.Sturm I, Stephan C, Gillissen B, Siebert R, Janz M, Radetzki S, Jung K,Loening S, Dörken B, Daniel PT. Loss of the tissue-specific proapoptoticBH3-only protein Nbk/Bik is a unifying feature of renal cell carcinoma.Cell Death Differ. 2006, 13:619-27.Cancer Research 133