Dysregulated expression of tumor necrosis factor (TNF) has been implicated in multiple disease states, including asthma, allergy, arthritis, cardiovascular diseases, inflammatory bowel disease, diabetes, eczema, lupus, several different forms of cancer, and multiple infectious diseases including sepsis, tuberculosis (TB), and HIV-1. While TNF transcription is induced by a wide range of stimuli associated with cellular activation during infection, stress, and inflammation, work in our laboratory has shown that the mechanisms of TNF gene regulation are distinct for different cell types and for different stimuli. This exquisite cell-type and stimulus-specific transcription is directed by a highly conserved, compact, and modular proximal promoter region, where distinct sets of transcription factors assemble into higher order secondary structures, or enhanceosomes. More recently, we have shown that this specificity extends to the chromatin environment of the TNF locus, where conserved functional genetic regions are associated with cell type- and stimulus-specific DNase hypersensitivity sites (HSSs), intrachromosomal interactions, and interactions with the nuclear matrix. The identification of potential therapeutic targets to control TNF expression in specific cell types and in response to specific stimuli presents a highly attractive alternative to current TNF inhibitors that function in a non-specific, systemic fashion. The first hypothesis that will be tested in this proposal is that the cell type- and stimulus-specific chromatin environment of the TNF locus is a critical regulator in the control of TNF gene transcription in primary human cells. We will characterize the features of the chromatin environment of the TNF locus in human T cells and macrophages, including the location of constitutive and transient DNase I HSSs, histone modifications, protein-DNA contacts, and nucleosome positioning, associated with the stimulated and unstimulated state of these cells. Our studies will examine the impact of multiple physiologically relevant stimuli in T cells and monocytes. The second hypothesis that will be tested in this proposal is that specific factors establish higher-order chromatin interactions and impact DNA topology at the TNF locus in the control of TNF gene expression. We will determine the role of NFATp in the formation of activation-dependent intracrhomosomal interactions in T cells. Through integration of wild-type and mutant TNF/LT loci into cell lines, we will test the impact of specific HSSs upon TNF gene transcription. These cells type-specific HSSs contain matrix attachment regions that interact with topoisomerase II as well as a potential region involved in the transition of Z-to-B-form DNA. These HSSs potentially promote TNF gene transcription by counteracting transcription-induced supercoiling by flanking genes. Thus, these studies will not only elucidate novel mechanisms in the control of TNF gene regulation that may have broader implications for eukaryotic gene transcription, but also delineate potential clinical checkpoints for the control of TNF expression.
Too much or too little tumor necrosis factor (TNF) protein influences a variety of diseases, including asthma, allergy, arthritis, sepsis, tuberculosis, and AIDS. Although current blockers of TNF have been used effectively in certain autoimmune diseases, these therapies are limited because of their lack of specificity and ensuing complications. By focusing our studies on the initial steps involved in the activation of the TNF gene in different kinds of cells, we hope to discover new therapeutic targets that allow for highly specific control of TNF protein levels.
