We are analyzing the regulation of cytokine and chemokine gene expression in lymphoid cells. We have chosen IFN-gamma gene expression as a model system for analysis of the control of gene expression in T cells and NK cells. We are continuing to dissect the regions of the human IFN-g genomic DNA to determine which regions enhance/repress gene transcription in response to extracellular signals. In particular, we are utilizing NK cell lines to elucidate the mechanisms, both transcriptional and post-transcriptional, by which interleukins 2,4,12,13,15,18 induce or inhibit IFN-g gene expression. Overall, our data indicate that multiple DNA binding protein family members interact with the human IFN-g genomic DNA and that control of IFN-g gene expression involves 5' and intronic transcriptional control regions as well as DNA methylation and mRNA stability/nuclear localization. We are now investigating the role of STAT proteins in regulating IFN-g expression. We are also characterizing the biochemical pathways involved in the synergistic induction of IFN-g gene expression in response to IL-2 + IL-12 and IL-2 + IL-18. In an extension of these studies, the NCI Laboratory of Genomic Diversity has identified polymorphisms in the IFN-g genomic DNA and other cytokine/chemokine genes that might result in altered gene expression. We are currently evaluating the effect of these single nucleotide changes on the transcriptional regulation of these genes.In another aspect of CMIS research, we have utilized IFN-g KO mice to identify a novel NK cell population that produces IL-13 and IL-5 in response to IL-2 and IL-18. This cytokine expression profile suggests that this NK population may play a role in influencing humoral immunity. Ongoing studies are focused on characterizing the biochemical/molecular signaling pathways utilized by these cells, determining their function in vivo and defining the molecular pathways involved in the IL-2 and IL-18 induction of the IL-13 gene.
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