SP110 與轉錄因子 NF-κB 交互作用之探討

Abstract

肺結核 (Tuberculosis) 係由結核分枝桿菌 (Mycobacterium tuberculosis) 所引起，目前是世界上最嚴重的公共衛生問題之一。根據先前文獻的證據顯示肺結核的感染輕重與宿主的基因可能有很大的關係。經過努力找尋，近年來科學家們發現在小鼠模式上找到 Ipr1 (intracellular pathogen resistance 1) 基因，其可能參與調控宿主先天免疫反應來幫助對抗結核分枝桿菌。而在人類身上也找到和 Ipr1蛋白具同源性的SP110 蛋白，其是核質體 (nuclear bodies) 組成成分之一，亦被報導參與細胞轉錄調控。SP110 主要的異構體有 SP110a、SP110b 及 SP110c。NF-κB 訊息傳導路徑主要是活化免疫反應的相關基因，在免疫反應中是至關重要的。所以我們想研究 SP110 是否會參與 NF-κB 的轉錄調控。NF-κB 轉錄因子家族總共有五個成員，分別是 RelA (p65)、RelB、c-Rel、NF-κB 1 (p105/p50) 及NF-κB 2 (p100/p52)，兩個成員間皆可以形成偶合體 (dimer)。我們觀察到大量表現 SP110a、SP110b 及 SP110c會負向調控 NF-κB 的轉錄活性，即使是共同大量表現 RelA 的情況下亦有輕微負向調控。另外，我們的資料顯示，SP110 蛋白的C端片段可能會幫助 RelA 形成homodimer 而提高轉錄活性。然而，在 NF-κB 訊息傳導路徑引發發炎反應最主要的轉錄複合體 RelA-p50 heterodimer大量表現情況下，SP110 並沒有對該複合體有很明顯的負向調控。綜合以上，SP110 會負向調控以RelA homodimer為主的轉錄活性，而在 RelA-p50 heterodimer 則沒有明顯的負向調控。

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is one of the most serious infectious diseases in the world. It is evident that host genetic factors may control the disease outcome of the infection. Previous studies have identified Ipr1 (intracellular pathogen resistance 1) gene, which locates on mouse chromosome 1, as a genetic factor regulating the host innate immunity against Mtb infection. Expression of the Ipr1 gene limited Mtb multiplication and facilitated apoptotic cell death of the Mtb-infected macrophages. The closest homologue of mouse Ipr1 protein is human SP110 protein, which is a component of nuclear bodies. The SP110 protein forms at least three isoforms, SP110a, SP110b, and SP110c, and may be involved in the regulation of cell division, cell death and immune system. The NF-κB transcription factor is a protein complex controlling the transcription of many genes that play a key role in regulating the immune response to infection. NF-κB represents homo- and heterodimers of five different family members: RelA (p65), RelB, c-Rel, p50/p105 (NF-κB 1), and p52/p100 (NF-κB 2). We observed that the overexpression of SP110a, SP110b, and SP110c down-regulated the transcriptional activity mediated by NF-κB and that co-overexpressed RelA with three SP110 isoforms also did it slightly. Furthermore, our data showed that the transcriptional activity of RelA homodimer was up-regulated through interacting with the C-terminal fragments of SP110 protein. But there seemed to be very limited effect of SP110 on down-regulating RelA-p50 heterodimer which is the major NF-κB complex controlling the inflammatory response.