Project area I

P01: The role of acid sphingomyelinase (Asm) in T cell responses during tumor development and radiation treatment

• Prof. Dr. Wiebke Hansen

Institute of Medical Microbiology, E-Mail: wiebke.hansen@uk-essen.de

• Prof. Dr. Jan Buer

Institute of Medical Microbiology, E-Mail: jan.buer@uk-essen.de

• Prof. Dr. Adriana Haimovitz-Friedman

Memorial-Sloan-Kettering Cancer Center, NY, USA,
E-Mail: a-haimovitz-friedman@ski-mskcc.org

The acid sphingomyelinase (Asm)/ ceramide pathway is involved in several cellular processes including mechanisms contributing to tumorigenesis. Recent studies showed that tumor cell lines implanted in Asm-deficient (Asm^-/-) mice showed a double growth rate as compared to their growth rate in wild-type (wt) mice and that these tumors are resistant to radiotherapy. The role of Asm in T cell activity in this differential control of tumor growth by the host is unknown. Preliminary data revealed that increased tumor growth in Asm^-/- mice is accompanied by a decreased activation status of tumor-infiltrating T cells compared to wt lymphocytes suggesting that Asm deficiency modulates T cell function. Therefore, the main focus of this project is to define the role of Asm specifically in the T cell compartment for tumor development in non-treated and gamma-radiation (RT)-treated mice. For this purpose we will make use of Asm-deficient mice and mice displaying a modulated Asm expression specifically in T cells (Asm^fl/fl and Asm^tr/tr transgenic mice crossed with CD4-cre mice). By the use of these mouse models we aim to analyze the impact of Asm/ceramide on T cell function during tumorigenesis and moreover, elucidate whether CD4⁺ T cells, CD8⁺ T cells, and Tregs are involved in the resistance of Asm^-/- mice to RT. 

P02: Sphingolipid signals regulate hypoxia inducible factor 1 in endothelial cells and macrophages after single-dose radiation therapy

• Prof. Dr. Joachim Fandrey

Institute of Physiology , E-Mail: joachim.fandrey@uni-due.de

• Prof. Dr. Zvi Fuks

Memorial-Sloan-Kettering Cancer Center, NY, USA,
E-Mail: fuksz@mskcc.org

• Prof. Dr. Adriana Haimovitz-Friedman

Memorial-Sloan-Kettering Cancer Center, NY, USA, 
E-Mail: a-haimovitz-friedman@ski-mskcc.org

Recent evidence suggests that lipid signaling plays an important role in single dose radiation therapy (SDRT). SDRT is an emerging clinical modality dependent on technological advances of image-guidance radiation therapy (IGRT) and intensity modulation radiation therapy (IMRT) capable of curing radioresistant cancer. Activation of acid sphingomyelinase (Asm) specifically in tumor host cells determines efficacy of SDRT, although underlying molecular mechanisms mediating this biology require definition. Hypoxia in tumors interferes with radiotherapy and it is the hypoxic tumor tissue where hypoxia inducible factor 1 (HIF-1) drives gene expression. To define targets of the Asm in this setting, we tested whether the HIF-pathway is controlled by the Asm/ceramide system. Our data show that Asm is involved in regulation of expression of both HIF- 1α and HIF-2α isoforms and is required for the HIF-1 response in activated macrophages. We will therefore investigate (i) whether and how the host Asm/ceramide pathway regulates HIF-1 activation in tumor cells and (ii) whether Asm/ceramide-regulated HIF-1α in TAMs and HIF-2α endothelial cells of the tumor host are important for tumor response to SDRT.

P03: Signaling via ceramide-enriched membrane platforms

• Prof Dr. Katrin Anne Becker-Flegler

Institute of Molecular Biology , E-Mail: katrin.becker-flegler@uni-due.de

• Prof. Dr. Adriana Haimovitz-Friedman

Memorial-Sloan-Kettering Cancer Center, NY, USA, 
E-Mail: a-haimovitz-friedman@ski-mskcc.org

Many stress stimuli rapidly activate acid sphingomyelinase (ASM), which releases ceramide from sphingomyelin in the plasma membrane. Ceramide forms microdomains that fuse to large macrodomains that serve to cluster specific proteins. For instance, genetic deficiency of Cftr in epithelial cells or infection of epithelial cells with Pseudomonas aeruginosa (P. aeruginosa) results in the generation of ceramide-enriched membrane domains (CRMs) that serve to cluster and activate CD95, thereby killing the cells (1-3). Here, we aim to identify the mechanisms by which CD95 clusters in CRMs after P. aeruginosa infection and to determine whether this mechanism can be generalized to other forms of ceramide-triggered death. We will (i) define the amino acids or motifs in CD95 that mediate its clustering within CRMs. The sequences will be mutated to test their significance for P. aeruginosa/CD95-induced cell death. (ii) Next, we will test whether the structural determinants that mediate CD95 clustering in CRMs can be generalized to the clustering of other molecules within CRMs. We will infect cells with P. aeruginosa or treat them with chemotherapeutic drugs that induce the formation of CRMs. We will identify novel molecules that cluster in CRMs or directly interact with ceramide after application of these stimuli, will define the structures that mediate clustering, and the biological significance of their clustering in CRMs for infection and chemotherapy.