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Transcriptional signatures are an indispensible source of correlative information on disease-related molecular alterations on a genome-wide level. Numerous candidate genes involved in disease and in factors of predictive, as well as of prognostic, value have been deduced from such molecular portraits, e.g. in cancer. However, mechanistic insights into the regulatory principles governing global transcriptional changes are lagging behind extensive compilations of deregulated genes. To identify regulators of transcriptome alterations, we used an integrated approach combining transcriptional profiling of colorectal cancer cell lines treated with inhibitors targeting the receptor tyrosine kinase (RTK)/RAS/mitogen-activated protein kinase pathway, computational prediction of regulatory elements in promoters of co-regulated genes, chromatin-based and functional cellular assays. We identified commonly co-regulated, proliferation-associated target genes that respond to the MAPK pathway. We recognized E2F and NFY transcription factor binding sites as prevalent motifs in those pathway-responsive genes and confirmed the predicted regulatory role of Y-box binding protein 1 (YBX1) by reporter gene, gel shift, and chromatin immunoprecipitation assays. We also validated the MAPK-dependent gene signature in colorectal cancers and provided evidence for the association of YBX1 with poor prognosis in colorectal cancer patients. This suggests that MEK/ERK-dependent, YBX1-regulated target genes are involved in executing malignant properties.

BackgroundAbundance of commensals constituting the intestinal microbiota (IM) affects the immune system and predisposes to a variety of diseases, including intestinal infections, cancer, inflammatory and metabolic disorders. Housing conditions determine the IM and can hence influence the immune system. We analyzed how both variables affect the IM of four immune-compromized mouse lines kept under different housing conditions.Methodology/Principal FindingsWe investigated the IM composition in mice by quantitative 16S rRNA RT-PCR analysis of the main fecal bacterial groups (Enterobacteriaceae, enterococci, lactobacilli, bifidobacteria, Bacteroides/Prevotella (BP) spp., Clostridium leptum and coccoides groups). Mice were homozygous (HO) or heterozygous (HE) for a targeted inactivating mutation of either the IFN-γ Receptor (R), IFN-γ, Rag1 or IL-4 genes. Overall, differences in IM composition were subtle. However, in the SPF-barrier, total eubacterial loads were higher in Rag1 HE versus Rag1 HO mice as well as in IFN-γR HE versus IFN-γR HO and WT animals. Although absent in WT mice, bifidobacterial loads were higher in HO and HE IFN-γ and Rag1 as well as IL-4 HO mice. Furthermore, BP was slightly lower in HO and HE IFN-γR and IFN-γ mice as well as in IL-4 HO mice as compared to WT controls. Interestingly, IM compositions were comparable in WT mice when kept in individual ventilated cages (IVC) or open cages (OC). IFN-γ HO and HE mice, however, had higher enterobacteria and BP loads, but lacked bifidobacteria when kept in OC versus IVC, as was the case in HO and HE Rag1 mice. In addition, Rag1 HO mice harbored higher clostridial loads when housed in OC as compared to IVC. Unexpectedly, lactobacilli levels were higher in IFN-γR mice when kept in OC versus IVC.Conclusion/SignificanceHousing-dependent and immune-deficiency mediated changes in intestinal microbiota composition were rather subtle but may nevertheless impact immunopathology in experimental models.

To study mechanisms of T cell-mediated rejection of B cell lymphomas, we developed a murine lymphoma model wherein three potential rejection antigens, human c-MYC, chicken ovalbumin (OVA), and GFP are expressed. After transfer into wild-type mice 60–70% of systemically growing lymphomas expressing all three antigens were rejected; lymphomas expressing only human c-MYC protein were not rejected. OVA expressing lymphomas were infiltrated by T cells, showed MHC class I and II upregulation, and lost antigen expression, indicating immune escape. In contrast to wild-type recipients, 80–100% of STAT1-, IFN-γ-, or IFN-γ receptor-deficient recipients died of lymphoma, indicating that host IFN-γ signaling is critical for rejection. Lymphomas arising in IFN-γ- and IFN-γ-receptor-deficient mice had invariably lost antigen expression, suggesting that poor overall survival of these recipients was due to inefficient elimination of antigen-negative lymphoma variants. Antigen-dependent eradication of lymphoma cells in wild-type animals was dependent on cross-presentation of antigen by cells of the tumor stroma. These findings provide first evidence for an important role of the tumor stroma in T cell-mediated control of hematologic neoplasias and highlight the importance of incorporating stroma-targeting strategies into future immunotherapeutic approaches.

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5120 Overexpression of the proto-oncogene c-myc due to chromosomal translocation is the hallmark of Burkitt-lymphoma. The evolving high grade lymphoma is dependent on the overexpression of c-myc, which provides the necessary signal to drive uncontrolled proliferation. Therefore loss of function or recognition of c-myc overexpressing cells by c-MYC specific T-cells should result in killing of the target and a halt to lymphoma progression. C-myc is also expressed in a variety of other human malignancies. Peptide prediction reveals several potential foreign epitopes in the context of murine H2b due to 87% homology between human and mouse c-MYC. In this study we explored whether the human c-myc gene product can be a target for T-cell therapy. Wildtype C57BL/6 mice were immunized with recombinant human c-MYC protein in combination with incomplete Freund′s adjuvans and CpG, and were boosted at various time points thereafter using either c-MYC protein or 40mer peptides encompassing the non homologous regions. Control animals were vaccinated with recombinant GFP or OVA protein. C-MYC vaccinated animals displayed a higher IFNg release upon re-stimulation with c-MYC pulsed dendritic cells compared to control vaccinated animals. In ELISPOT assays we observed a higher number of IFNg positive cells (299±17 vs. 122±8.5 (GFP vaccinated) vs. 66±8.5 (OVA vaccinated)). Vaccination using single peptides revealed that peptides spanning the region from amino acid 87-123, 216-255 and 334-376 produced similar results. In addition, using a human c-MYC specific ELISA we were able to detect c-MYC specific antibodies in serum from immunized mice in a concentration up to 40mg/l. Using established cell lines from l-hu-c-myc transgenic mice, where the human c-myc gene is overexpressed due to the juxtaposition of elements of the immunoglobuline lambda locus as found in t(8;22) of Burkitt's lymphoma, we investigated whether vaccination with human c-MYC protein would influence lymphoma growth in a lymphoma transfer model. Animals were s.c. challenged with 0.1 Mio 291cells overexpressing human c-MYC and were monitored for lymphoma growth. C-MYC vaccinated animals (n=15) displayed a delay in tumor onset and a significantly better disease free survival (28 vs. 22 days, p=0.012) compared to control (OVA) vaccinated animals (n=10). This delayed growth was associated with an increased number of infiltrating CD3+/Perforin+ cells. However, all mice eventually succumbed to lymphoma growth, indicating that the T-cell response was not sufficient to control lymphoma growth in the long term. From these data we conclude that the human c-MYC is a possible target antigen for T-cells, but responses are weak and presumably low in frequency. Disclosures No relevant conflicts of interest to declare.

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