Immune surveillance and therapy of lymphomas driven by Epstein-Barr virus protein LMP1 in a mouse model.

B cells infected by Epstein-Barr virus (EBV), a transforming virus endemic in humans, are rapidly cleared by the immune system, but some cells harboring the virus persist for life. Under conditions of immunosuppression, EBV can spread from these cells and cause life-threatening pathologies. We have generated mice expressing the transforming EBV latent membrane protein 1 (LMP1), mimicking a constitutively active CD40 coreceptor, specifically in B cells. Like human EBV-infected cells, LMP1+ B cells were efficiently eliminated by T cells, and breaking immune surveillance resulted in rapid, fatal lymphoproliferation and lymphomagenesis. The lymphoma cells expressed ligands for a natural killer (NK) cell receptor, NKG2D, and could be targeted by an NKG2D-Fc fusion protein. These experiments indicate a central role for LMP1 in the surveillance and transformation of EBV-infected B cells in vivo, establish a preclinical model for B cell lymphomagenesis in immunosuppressed patients, and validate a new therapeutic approach.

Ultraviolet-radiation-induced inflammation promotes angiotropism and metastasis in melanoma.

Intermittent intense ultraviolet (UV) exposure represents an important aetiological factor in the development of malignant melanoma. The ability of UV radiation to cause tumour-initiating DNA mutations in melanocytes is now firmly established, but how the microenvironmental effects of UV radiation influence melanoma pathogenesis is not fully understood. Here we report that repetitive UV exposure of primary cutaneous melanomas in a genetically engineered mouse model promotes metastatic progression, independent of its tumour-initiating effects. UV irradiation enhanced the expansion of tumour cells along abluminal blood vessel surfaces and increased the number of lung metastases. This effect depended on the recruitment and activation of neutrophils, initiated by the release of high mobility group box 1 (HMGB1) from UV-damaged epidermal keratinocytes and driven by Toll-like receptor 4 (TLR4). The UV-induced neutrophilic inflammatory response stimulated angiogenesis and promoted the ability of melanoma cells to migrate towards endothelial cells and use selective motility cues on their surfaces. Our results not only reveal how UV irradiation of epidermal keratinocytes is sensed by the innate immune system, but also show that the resulting inflammatory response catalyses reciprocal melanoma-endothelial cell interactions leading to perivascular invasion, a phenomenon originally described as angiotropism in human melanomas by histopathologists. Angiotropism represents a hitherto underappreciated mechanism of metastasis that also increases the likelihood of intravasation and haematogenous dissemination. Consistent with our findings, ulcerated primary human melanomas with abundant neutrophils and reactive angiogenesis frequently show angiotropism and a high risk for metastases. Our work indicates that targeting the inflammation-induced phenotypic plasticity of melanoma cells and their association with endothelial cells represent rational strategies to specifically interfere with metastatic progression.

Antagonistic TSC22D1 variants control BRAF(E600)-induced senescence.

Oncogene-induced cellular senescence (OIS) is an increasingly recognized tumour suppressor mechanism that confines the outgrowth of neoplastic cells in vivo. It relies on a complex signalling network, but only few components have been identified so far. Gene-expression profiling revealed a >100-fold increase in the levels of the transcription factor and putative tumour suppressor gene TGFß-stimulated clone 22 (TSC22D1) in BRAF(E600)-induced senescence, in both human fibroblasts and melanocytes. Only the short TSC22D1 transcript was upregulated, whereas the abundance of the large protein variant was suppressed by proteasomal degradation. The TSC22D1 protein variants, in complex with their dimerization partner TSC22 homologue gene 1 (THG1), exerted opposing functions, as selective depletion of the short form, or conversely, overexpression of the large variant, resulted in abrogation of OIS. This was accompanied by the suppression of several inflammatory factors and p15(INK4B), with TSC22D1 acting as a critical effector of C/EBPß. Our results demonstrate that the differential regulation of antagonistic TSC22D1 variants is required for the establishment of OIS and suggest distinct contributions of TSC22 family members to the progression of BRAF(E600)-driven neoplasia.

B-cell expansion and lymphomagenesis induced by chronic CD40 signaling is strictly dependent on CD19.

CD40, a member of the TNF receptor family, is expressed on all mature B cells and on most B-cell lymphomas. Recently, we have shown that constitutive activation of CD40 signaling in B cells induced by a fusion protein consisting of the transmembrane part of the Epstein-Barr viral latent membrane protein 1 (LMP1) and the cytoplasmic part of CD40 (LMP1/CD40) drives B-cell lymphoma development in transgenic mice. Because LMP1/CD40-expressing B cells showed an upregulation of CD19, we investigated CD19's function in CD40-driven B-cell expansion and lymphomagenesis. Here, we demonstrate that ablation of CD19 in LMP1/CD40 transgenic mice resulted in a severe loss and reduced lifespan of mature B cells and completely abrogated development of B-cell lymphoma. CD19 is localized to lipid rafts and constitutively activated by the LMP1/CD40 fusion protein in B cells. We provide evidence that the improved survival and malignant transformation of LMP1/CD40-expressing B cells are dependent on activation of the MAPK Erk that is mediated through CD19 in a PI3K-dependent manner. Our data suggest that constitutively active CD40 is dependent on CD19 to transmit survival and proliferation signals. Moreover, we detected a similarly functioning prosurvival pathway involving phosphorylated CD19 and PI3K-dependent Erk phosphorylation in human diffuse large B-cell lymphoma cell lines. Our data provide evidence that CD19 plays an important role in transmitting survival and proliferation signals downstream of CD40 and therefore might be an interesting therapeutic target for the treatment of lymphoma undergoing chronic CD40 signaling.

Near-genomewide RNAi screening for regulators of BRAF(V600E) -induced senescence identifies RASEF, a gene epigenetically silenced in melanoma.

The activation of oncogenes in primary cells blocks proliferation by inducing oncogene-induced senescence (OIS), a highly potent in vivo tumor-suppressing program. A prime example is mutant BRAF, which drives OIS in melanocytic nevi. Progression to melanoma occurs only in the context of additional alteration(s) like the suppression of PTEN, which abrogates OIS. Here, we performed a near-genomewide short hairpin (sh)RNA screen for novel OIS regulators and identified by next generation sequencing and functional validation seven genes. While all but one were upregulated in OIS, depletion of each of them abrogated BRAF(V) (600E) -induced arrest. With genome-wide DNA methylation analysis, we found one of these genes, RASEF, to be hypermethylated in primary cutaneous melanomas but not nevi. Bypass of OIS by depletion of RASEF was associated with suppression of several senescence biomarkers including senescence-associated (SA)-ß-galactosidase activity, interleukins, and tumor suppressor p15(INK) (4B) . Restoration of RASEF expression inhibited proliferation. These results illustrate the power of shRNA OIS bypass screens and identify a potential novel melanoma suppressor gene.

Multiplex ligation-dependent probe amplification (MLPA) in tumor diagnostics and prognostics.

The increasing knowledge about genetic alterations and molecular biomarkers in cancer initiation and progression opens new possibilities for the treatment of various types of cancer. This requires the inclusion of sensitive, and preferably multiplex, methods for the detection of molecular genetic alterations in the toolbox of classic pathology. Multiplex ligation-dependent probe amplification (MLPA) is a multiplex polymerase chain reaction-based method that can detect changes in the gene copy number status, DNA methylation, and point mutations simultaneously. MLPA probes recognize target sequences of only 50 to 100 nucleotides in length. This makes it possible to use MLPA even on highly fragmented DNA, and allows the detection of small deletions encompassing only a single exon. MLPA is a reliable, cost-effective, and robust method that can be performed using a standard thermocycler and capillary electrophoresis equipment, generating results within 24 hours with a short hands-on working time. Up to 50 different genomic locations can be tested in a single reaction, which can be sufficient to detect those genetic alterations that are of diagnostic and prognostic significance in a certain tumor entity. In the last years, MLPA has been used successfully in tumor diagnostics and in cancer research. This review gives an overview on the collected experience of MLPA applications on tumor DNA, about the advantages but also potential pitfalls and limitations of this technique.

LMP1 signaling can replace CD40 signaling in B cells in vivo and has unique features of inducing class-switch recombination to IgG1.

The Epstein-Barr virus (EBV) protein LMP1 is considered to be a functional homologue of the CD40 receptor. However, in contrast to the latter, LMP1 is a constitutively active signaling molecule. To compare B cell-specific LMP1 and CD40 signaling in an unambiguous manner, we generated transgenic mice conditionally expressing a CD40/LMP1 fusion protein, which retained the LMP1 cytoplasmic tail but has lost the constitutive activity of LMP1 and needs to be activated by the CD40 ligand. We show that LMP1 signaling can completely substitute CD40 signaling in B cells, leading to normal B-cell development, activation, and immune responses including class-switch recombination, germinal center formation, and somatic hypermutation. In addition, the LMP1-signaling domain has a unique property in that it can induce class-switch recombination to IgG1 independent of cytokines. Thus, our data indicate that LMP1 has evolved to imitate T-helper cell function allowing activation, proliferation, and differentiation of EBV-infected B cells independent of T cells.

Constitutive CD40 signaling in B cells selectively activates the noncanonical NF-kappaB pathway and promotes lymphomagenesis.

CD40, a member of the tumor necrosis factor (TNF) receptor family, plays an essential role in T cell-dependent immune responses. Because CD40 is widely expressed on the surface of tumor cells in various B cell malignancies, deregulated CD40 signaling has been suggested to contribute to lymphomagenesis. In this study, we show that B cell-specific expression of a constitutively active CD40 receptor, in the form of a latent membrane protein 1 (LMP1)/CD40 chimeric protein, promoted an increase in the number of follicular and marginal zone B cells in secondary lymphoid organs in transgenic mice. The B cells displayed an activated phenotype, prolonged survival and increased proliferation, but were significantly impaired in T cell-dependent immune responses. Constitutive CD40 signaling in B cells induced selective and constitutive activation of the noncanonical NF-kappaB pathway and the mitogen-activated protein kinases Jnk and extracellular signal-regulated kinase. LMP1/CD40-expressing mice older than 12 mo developed B cell lymphomas of mono- or oligoclonal origin at high incidence, thus showing that the interplay of the signaling pathways induced by constitutive CD40 signaling is sufficient to initiate a tumorigenic process, ultimately leading to the development of B cell lymphomas.