| Summary: | 博士 === 國立陽明大學 === 微生物及免疫學研究所 === 105 === Tuberculosis (TB), a disease caused by Mycobacterium tuberculosis (Mtb) infection, remains the leading cause of death from a single infectious agent globally. Host genetic factors have been shown to contribute to Mtb infection outcomes in both humans and experimental animal models. However, how these factors affect the infection remains largely unknown. SP110, an interferon-induced nuclear protein, belongs to the SP100/SP140 protein family. The studies in this thesis show that SP110b, an SP110 isoform, modulated nuclear factor-κB (NF-κB) activity, resulting in the down-regulation of tumor necrosis factor alpha (TNFα) production and concomitant up-regulation of NF-κB-induced anti-apoptotic gene expression, thereby suppressing IFNγ-mediated monocyte/macrophage cell death. A reduction in TNFα expression was also observed in mice expressing Ipr1, the mouse homolog of human SP110b; however, this reduction was not observed in Ipr1-deficient mice that have more severe necrotic lung lesions, less efficient Mtb growth control in the lungs, and a shorter survival duration after Mtb infection. Moreover, the genetic characterization of TB patients demonstrated that the epistatic interaction of SP110 with the NFκB1 and TNFα genes exhibited a much more pronounced association with TB susceptibility. These findings suggest that SP110b may serve as a potential target for host-directed therapy aiming to manipulate the host innate immunity to protect against TB. The studies in this thesis also provide experimental data illustrating the SP110 protein domains that are responsible for its functions. The results of reporter assays demonstrated that SP110 isoforms have different regulatory effects on NF-κB-mediated transcription, supporting the notion that SP110 isoforms may have distinct cellular functions. Analysis of deletion mutants of SP110 showed that the interaction of the N-terminal fragment (amino acids 1-276) of SP110 with p50, a subunit of NF-κB, in the cytoplasm plays a crucial role in the down-regulation of the p50-driven TNFα promoter activity in the nucleus, while the middle and C-terminal regions of SP110 localize it to various cellular compartments. Surprisingly, a nucleolar localization signal (NoLS) that contains one monopartite nuclear localization signal (NLS) and one bipartite NLS was identified in the middle region of SP110. The identification of a cryptic NoLS in the SP110 suggests that although this protein forms nuclear speckles in the nucleoplasm, it may be directed into the nucleolus to carry out distinct functions under certain cellular conditions.
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