Projekt

The aberrant activation of antigen receptor signaling is frequently observed in lymphoma, but whether these activities are sufficient for lymphomagenesis remains unclear. We previously demonstrated that expression of the fusion protein ITK-SYK mimics qualitative aspects of a constitutively active T cell receptor (TCR) signal in vitro and that conditional ITK-SYK transgenic mice develop PTCL with 100% penetrance. Here, we want to understand whether ITK-SYK-driven lymphomas depend on additional signaling input via the TCR, how acute ITK-SYK signaling is initially counter-regulated in non-transformed T cells and which lymphomagenic events finally disrupt such tumor suppressive pathways.

Chronic lymphocytic leukemia (CLL) is characterized by an expansion of monoclonal B cells that carry autoreactive B cell receptors and exerts complex alterations within the associated immune cell compartment. Autoreactive B cells would normally undergo negative selection. The proposal aims to define whether mutations that activate NF-κB signaling, in particular MyD88 and Notch1, inhibit negative selection and thereby allow autoreactive B lymphocytes to transform to CLL. Furthermore, this study aims to elucidate the role of NF-κB activation via innate immune receptors in the myeloid cell compartment within the CLL microenvironment.

The CXCR4-CXCL12 pathway regulates migration and proliferation of hematopoietic stem and progenitor cells in the bone marrow niche and is essential for normal B-cell lymphopoiesis. We have established a first-in-man targeting of CXCR4 by a CXCR4-specific peptide. This proposal aims at identifying the role and mechanisms of aberrant CXCR4 activity in lymphomagenesis including novel mouse models, forward genomic screening, analysis of disturbed BCR signaling and resistance mechanisms towards BCR pathway targeting drugs. Aberrant CXCR4 expression and function is also recurrently observed in solid tumors, where it is associated with cancer cell dissemination and poor prognosis. The project will thus extend the studies to solid cancer models within this CRC.

We identified novel and recurrent hotspot mutations in Cathepsin S (CTSS) as a previously unrecognized link between aberrant intracellular immune signaling and the immune microenvironment in follicular lymphoma (FL). CTSS is a cysteine protease that is highly expressed in immune cells and plays critical roles in antigen presentation and Toll-like receptor (TLR) signaling. Our previous data show that these mutations are gain-of-function and activate tumor-promoting pathways, including deregulation of TLR and MHC-II signaling. Our project will utilize in vitro and in vivo models to define the underlying molecular mechanisms, as well as the functional and clinical implications of aberrant CTSS activity in FL.

The transcription factor c-Rel, central to innate and adaptive immune responses, is directly implicated in oncogenesis. However, the mechanisms by which c-Rel alterations drive human hematopoietic and solid cancers remain unresolved. To address this issue, we established mice that allow for cell type-specific enhanced c-Rel expression and visualization. We will employ these and complementary loss of function models as well as advanced proteomic approaches to define tumor cell-intrinsic roles of c-Rel signaling in lymphoma and colorectal cancer, as well as mechanisms and consequences of c-Rel activity within the tumor immune environment.

Activation of NF-κB is strongly regulated by signaling cascades that depend on protein phosphorylation and degradative and non-degradative functions of the ubiquitin system. We identified the orphan F-Box protein FBXO21 as a prime candidate for the long-sought p50 ubiquitin ligase, and found overexpression of FBXO21 in human B cell malignancies. This project will mechanistically dissect the FBXO21-p50 axis in the context of lymphoma development and maintenance. In parallel, we will explore the overall role of F-box family ubiquitin ligases and their counter players, the deubiquitylases, in NF-κB control and cancer-linked aberrations thereof using functional genetic screens and proteomic approaches.

Chronic B-cell receptor signaling activates the MALT1 protease to drive survival of the activated B cell-type of diffuse large B cell lymphomas (ABC DLBCL). Here, we will unravel the MALT1 upstream regulation as well as downstream mechanisms that link MALT1 to proliferation and survival of lymphoma cells. More precisely, we will elucidate the function of MALT1 phosphorylation sites in ABC DLBCL that we have recently identified. Further, MALT1 restricts posttranscriptional gene regulation in an acute immune response. We will determine the functional relevance and consequences of MALT1-catalyzed cleavage of RNA regulators Regnase-1 and Roquin in DLBCL.

High-grade inflammation in chronic inflammatory bowel disease (IBD) and smoldering tumor-elicited inflammation are key drivers of colorectal cancer, but the mechanisms that link inflammatory signaling to intestinal carcinogenesis are insufficiently understood. Since polymorphisms in Card9 are associated with human IBD, we have studied the function of Card9 in colitis-associated cancer (CAC). Deficiency for Card9 amongst others results in impaired tumor development and defective tumor cell-intrinsic STAT3 activation. Here, we want to define the mechanism of Card9 signaling during CAC and investigate the functions and consequences of these pathways for tumor-elicited inflammation in oncogene-driven colon cancer.

In project P10, myeloid leukemias will be used as models of transformed innate cells that retain the capacity to sense inflammation in order to investigate consequences of aberrant inflammatory signal integration and necroptotic cell death on malignant transformation. To drive chronic leukocyte activation and to investigate the roles of distinct TNF receptor and necroptotic pathways on oncogenesis in vivo, as well as the functions of coordinated cytokine signaling within leukemia initiating cells, they will utilize mice expressing an AML-associated mutation in the gene encoding the FLT3 cytokine receptor.

Unfolded protein responses (UPR) of the endoplasmic reticulum is associated with intestinal inflammation and tumorigenesis. We created novel mouse models in which epithelial cell-specific activation of the UPR pathway is enforced using constitutively active forms of activating transcription factor 6 (ATF6). Using germ-free mice, we made the striking observation that the presence of microbiota in the context of aberrant UPR activation is necessary for spontaneous colon tumor formation. In the proposed project, they will study which innate immune receptors and pathways are engaged by the microbiota and synergize with epithelial cell-specific UPR to promote tumorigenesis.

Inflammatory signals induced by tumor cells or the host environment are closely linked to cancer progression and treatment resistance. Our preliminary data suggest that the mutational make-up of the primary tumor dictates the pro- and anti-tumorigenic immune response, which in turn determines tumor progression and survival. We aim to systematically decipher inflammatory pathways in subtypes of intestinal cancer and to evaluate the contribution of different immune cell subsets and inflammatory signals to cancer initiation and progression.

To discover hitherto unknown immune signalling components promoting intestinal tumorigenesis, we propose to conduct genome-wide genetic screens in mice. Using our PiggyBac transposon tools, we will perform insertional mutagenesis in four intestinal cancer subentities. Newly discovered immune signalling genes will be functionally validated using CRISPR/Cas9 somatic genome engineering in mice. In addition, transcriptome-based analyses of up to 1000 transposon-induced tumors will discover genotype-immunophenotype relationships. These studies will provide comprehensive insights into the landscapes of cell-intrinsic and extrinsic immune signalling components in intestinal cancer.

Type I interferons (IFN-I) induced by innate immune signaling pathways in immune and tumor cells are emerging as intriguing determinants of both anti-melanoma responses as well as immune escape and resistance mechanisms. In this proposal, we aim to understand the distinct contribution of IFN-I inducing nucleic acid receptor pathways in tumor and host cells during development and immunosurveillance of melanoma as well as to identify the mechanisms that drive disease resistance.

IL-1α and IL-1β are cytokines with pleiotropic activities that have been associated with inflammation, tissue repair and the regulation of adaptive immune responses. IL-1 secretion in the context for chronic inflammation has also been linked to the development and progression of cancer, most prominently malignant melanoma. In this project, we will dissect the role of IL-1 activation and secretion for melanoma dedifferentiation and progression both within the microenvironment, as well as within the tumor itself. We expect that these studies will allow us to dissect the pleiotropic role of IL-1 signaling in cancer, using melanoma as a model system.

While a large array of paracrine factors is hypothesized to determine the local cross-talk between cancer cells and the immune system, only a few of these factors have been identified and characterized because current technologies are insufficiently developed. To overcome these obstacles, Meissner (P16) develops sophisticated quantitative mass spectrometry-based approaches including cell type-specific labeling with amino acid precursors. These technologies will allow the first unbiased and system-wide characterization of cancer – immune cell cross-talk ex vivo and in co-culture in vitro. Using transgenic mouse models, these technologies will be adapted and utilized for in vivo analyses and applied to study the paracrine information exchange between macrophages and cancer cells. Together, this project will generate new hypotheses about how immune-derived factors control melanoma and intestinal cancer cell proliferation and phenotype.

Phenotypic plasticity of melanoma cells in response to proinflammatory signals seems to play a critical role in resistance towards current immunotherapies. We observed an accumulation of melanoma-associated mast cells, which provide a potent source for proinflammatory mediators. Therefore, by using mouse models and defined patient-derived material we will analyze the function of mast cell networks and mast cell-intrinsic signals through the FcεR, TLRs or NF-κB as well as their impact on pathogenesis, progression and resistance to therapy of melanoma.

The tumor microenvironment is highly enriched in sodium chloride, but the effect of tonicity signals on anti-tumor immune cell responses remains unexplored. We have shown that hypertonicity modulates T cell signaling and induces a paralyzed anti-inflammatory T cell phenotype. Although this newly-discovered mechanism has dramatic implications for tumor control, the molecular sensors and effectors that couple hypertonicity to T cell paralysis are unclear. The project will investigate how a sodium chloride rich tumor microenvironment impairs productive TCR signals and T cell effector functions in humans with a particular focus on melanoma.

Metabolic cues affect lymphocyte activation, tumor immune control and can be tumor-promoting. As a consequence of Western diet and subsequent metabolic syndrome, non-alcoholic fatty liver disease is the most frequent liver disease. It progresses to non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) with high incidence. We have generated a mouse model that recapitulates the pathophysiology of human NASH and HCC. We found that aberrantly activated lymphocytes drive NASH and HCC, and validated these observations in humans. Our project will investigate the role of BCR-/TCR- and innate immune signaling (e.g. TLRs and inflammasome) in NASH and HCC.