Investigation of the function of the IKK2/NF-kappaB-pathway in c-MYC-induced lymphomagenesis

Prosurvival activity of NF-kappaB is essential for many hematological malignancies like Hodgkins lymphoma (HL), diffuse large B-cell lymphoma (DLBCL), mucosa associated lymphoid tissue (MALT) lymphoma, multiple myeloma (MM) and many others. For Burkitts lymphoma (BL), a malignancy caused by overexpressed MYC in B-cells, the contribution of the NF-kappaB pathway for growth and survival of the tumor cells remained elusive. In the present study it could be demonstrated that in MYC-driven murine B-cell lymphomas and human BL the activation of NF-kappaB is impaired. In lymphoma cell lines established from a conditional c-MYC expressing mouse model it was shown that the NF-kappaB pathway is dispensable for tumor growth and generally downregulated. Furthermore, several extrinsic stimuli generally inducing NF-kappaB activity failed to activate this pathway. In addition, inhibition of NF-kappaB by an IkappaBalpha superrepressor provided a selective advantage for MYC-driven lymphoma cells in an in vivo competition assay. Genetic activation of the NF-kappaB pathway by introduction of a constitutively active IkappaB-kinase 2 (IKK2) induced cell aggregation, growth inhibition and apoptosis in MYC-driven lymphomas. Extending our analysis to human BL cell lines we found that NF-kappaB activation induced similar effects by enhancing cell aggregation and apoptosis. The induced cell death was death receptor-mediated and specific for BL cells. Gene expression profiling revealed that induction of IKK2 activity resulted in prominent upregulation of cell adhesion molecules and Fas death receptor. Subsequently, it could be demonstrated that Fas-resistant BL cell lines are sensitized to Fas-mediated death by NF-kappaB activation

Cytokine Imbalance after Measles Virus Infection Has No Correlation with Immune Suppression▿

Measles virus infection leads to immune suppression. A potential mechanism is the reduction of interleukin 12 (IL-12) secretion during acute measles, resulting in a TH2 response. Studies in humans have reported conflicting results, detecting either a TH2 or a TH1 response. We have investigated the correlation between a TH2 response and immune suppression in specific-pathogen-free inbred cotton rats which were infected with measles vaccine and wild-type viruses. After infection of bone marrow-derived macrophages with wild-type virus, IL-12 secretion was reduced in contrast to the level for vaccine virus infection. In bronchoalveolar lavage cells, IL-12 secretion was suppressed after infection with both wild-type and vaccine virus on days 2, 4, and 6 and was detectable on days 8 and 10. After stimulation of mediastinal lymph node and spleen cells with UV-inactivated measles virus at various time points after infection, gamma interferon but no IL-4 was found. After stimulation with phorbol myristate acetate-ionomycin, high gamma interferon and low IL-4 levels were detected. To investigate whether the secretion of IL-4 contributes to immune suppression, a recombinant vaccine virus was created which secretes cotton rat IL-4. After infection with this recombinant virus, IL-4 secretion was enhanced. However, neither inhibition of concanavalin A-stimulated spleen cells nor keyhole limpet hemocyanin-specific proliferation of spleen cells was altered after infection with the recombinant virus in comparison to the levels with the parental virus. Our data indicate that measles virus infection leads to a decrease in IL-12 secretion and an increase in IL-4 secretion, but this does not seem to correlate with immune suppression

The IKK2/NF-kappa B pathway suppresses MYC-induced lymphomagenesis

Deregulated c-MYC is found in a variety of cancers where it promotes proliferation as well as apoptosis. In many hematologic malignancies, enhanced NF-kappa B exerts prosurvival functions. Here we investigated the role of NF-kappa B in mouse and human c-MYC-transformed lymphomas. The NF-kappa B pathway is extinguished in murine lymphoma cells, and extrinsic stimuli typically inducing NF-kappa B activity fail to activate this pathway. Genetic activation of the NF-kappa B pathway induces apoptosis in these cells, whereas inhibition of NF-kappa B by an I kappa B alpha superrepressor provides a selective advantage in vivo. Furthermore, in human Burkitt lymphoma cells we find that NF-kappa B activation induces apoptosis. NF-kappa B up-regulates Fas and predisposes to Fas-induced cell death, which is caspase-8 mediated and can be prevented by CFLAR overexpression. We conclude that c-MYC overexpression sensitizes cells to NF-kappa B-induced apoptosis, and persistent inactivity of NF-kappa B signaling is a prerequisite for MYC-mediated tumorigenesis. We could also show that low immunogenicity and Fas insensitivity of MYC-driven lymphoma cells are reversed by activation of NF-kappa B. Our observations provide a molecular explanation for the described absence of the NF-kappa B signaling in Burkitt lymphoma and question the applicability of NF-kappa B inhibitors as candidates for treatment of this cancer. (Blood. 2009; 114: 2448-2458