Systems-oriented immunology and inflammation research

The idea that death can save lives is indeed a truism, but for complex organisms there is a significant protective mechanism in the background. Apoptosis is the name for the “suicide programme”, with which injured, old, mutated or dangerous cells can be deactivated in human tissue. But this suicide program can be misused by pathogens – or it can get out of control. You can read here how scientists are seeking to understand and make use of programmed cellular death in a cooperative research group within the Institute for Molecular and Clinical Immunology at the Otto-von-Guericke University Magdeburg and the HZI.

Current Projects

Saureus in 3T3

Apoptosis can be initiated by death receptors, a subgroup of the tumor necrosis factor receptor (TNFR) superfamily, with CD95 (APO-1/Fas) being a prototypical family member. CD95 plays a crucial role in a number of immunological processes like the T cell-dependent immune response, but also in tumor development. For quite some time our research team investigates the regulation of CD95-mediated apoptosis in immune and tumor cells. One important regulator of CD95 signaling e.g. is the cellular FLICE-inhibitory protein (c-FLIP).

A critical property of immune cells is that they are able to distinguish between self and non-self structures. Autoreactive cells, which may give rise to autoimmune diseases such as type I diabetes or multiple sclerosis, are usually clonally deleted by apoptosis in a process called negative selection. We analyzed the gene expression profile of thymocytes during negative selection and identified two interesting genes, IkBNS and Gadd45b, which regulate the NF-kB pathway and MAP kinases, respectively. These two factors will be analyzed in the future.

CD95 signaling – regulation by c-FLIP

Two main apoptosis signaling pathways are described, which are known as extrinsic and intrinsic apoptosis pathway. The intrinsic or mitochondrial pathway is regulated by members of the Bcl-2 family. On the other hand, the extrinsic pathway is initiated by so called death receptors, a subgroup of the TNF receptor superfamily. Upon binding of its cognate ligand, death receptors oligomerize and recruit cytoplasmic signaling molecules such as the adapter protein FADD as well as pro-caspase-8 and pro-caspase-10 into a death-inducing signaling complex (DISC). These initiator caspases are activated at the DISC due to dimerization initiating a cascade of cleavage events leading to demise of the cell. The activation of initiator caspases at the DISC can be counteracted by FLIP proteins. Next to viral homologs, three cellular isoforms have been described, which are called c-FLIPlong, c-FLIPshort and c-FLIPR. In the past we concentrated on the biochemical mechanism of apoptosis inhibition by c-FLIP. We especially addressed the question, how resistance and sensitivity of primary human T cells is regulated. Here we could show that the resistance of short-term activated T cells is regulated on multiple levels. Next to an inability to efficiently form a DISC, short-term activated T cells upregulate anti-apoptotic proteins such as Bcl-xL and c-FLIPshort, while c-FLIPlong plays only a minor role. Furthermore, we could show that c-FLIP expression in T cells is mainly regulated by the NFAT pathway, which can be inhibited by cyclosporine A and FK506. The development of specific c-FLIP inhibitors may lead to better immune suppressive drugs, which may show less toxicity compared to cyclosporine A. In order to investigate the poorly characterized c-FLIPR isoform, we cloned the mouse homolog and performed a detailed structure function analysis. Using point and deletion mutants, we could show that despite a striking structural identity cellular and viral FLIP proteins use different biochemical mechanisms to inhibit caspase activation at the DISC. Last but not least, we identified a single nucleotide polymorphism (SNP) within the human c-FLIP gene, which determines expression of c-FLIPshort and c-FLIPR. Of note, the latter isoform is much weaker expressed due to inefficient translation. Therefore, one could assume that c-FLIPR is less efficient in apoptosis inhibition. Surprisingly, we found that the c-FLIPR allele is associated with the development of follicular lymphoma. The function of the different c-FLIP isoforms in the immune system and in tumorigenesis will be analyzed in the future.

IkBNS – an unusual inhibitor of NF-kB

IkBNS belongs to the family of inhibitory proteins of the transcription factor NF-kB and is poorly characterized so far. It is different from the prototypical family member IkBa since (1) it is an inducible protein, (2) it is a nuclear protein, (3) it is not marked by phosphorylation for proteasomal degradation, and (4) it can have next to an inhibitory function also a positive effect on NF-kB-dependent gene expression. We identified HDAC proteins as novel binding partners for IkBNS and now investigate their functional relationship. Since HDACs can induce chromatin condensation and, thus, play an important role in the epigenetic control of gene expression, which is deregulated in certain diseases, we want to analyze whether and how IkBNS influences chromatin modifications. The recruitment of HDACs via IkBNS to chromatin could be one mechanism of how this IkB protein inhibits transcription. In the same line, we want to identify direct target genes of IkBNS. Moreover, we are analyzing the role of IkBNS in the development of T helper cells.

Gadd45b – ein Regulator von MAP Kinasen in Apoptose und Autophagie


In einer globalen Suche nach Genen, die an der negativen Selektion von T-Zellen im Thymus beteiligt sind, haben wir mittels DNA-Array-Technologie das Gen Gadd45b identifiziert. Die starke Induktion von Gadd45b durch den T-Zell-Rezeptor haben wir mittlerweile in mehreren in vitro und in vivo Modellen bestätigen können. Des Weiteren konnte gezeigt werden, dass das Gadd45b Protein eine Signalkaskade anschaltet, die letztlich zu einer lang anhaltenden Aktivierung der MAP Kinase p38 führt. Diese Kinase spielt eine wichtige Rolle bei Entzündungsprozessen aber auch beim programmierten Zelltod. Für die Aufklärung der physiologischen Funktion des Gadd45b Gens steht uns eine Gadd45b knock-out Maus zur Verfügung, mit deren Hilfe wir die Funktion des Gadd45b Proteins in vivo untersuchen können. Darüber hinaus wurde damit begonnen, ein transgenes Mausmodell zu etablieren, in dem das Gadd45b Gen gewebsspezifisch an- und ausgeschaltet werden kann. Schließlich haben wir beobachtet, dass Gadd45b in NIH/3T3 Zellen Autophagie, einen lysosomalen Signalweg zum Abbau langlebiger Proteine und Organelle, beeinflusst. Interessanterweise kann Autophagie sowohl zum Überleben einer Zelle beitragen, als auch zu einem nicht-apoptotischen Zelltod führen. Die molekularen Mechanismen zwischen dem Gadd45b-Signalweg und der Autophagie sollen in Zukunft untersucht werden.



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