USP18 modulates the sensing of HIV-1

HIV-1（人类免疫缺陷病毒1型）的RNA和cDNA可以分别被巨噬细胞和树突状细胞表达的内体Toll样受体和胞质传感器cGAS识别和感受。cGAS-cDNA相互作用诱导cGAMP产生，其刺激STING二聚化和活化。STING介导TBK 1活化，随后磷酸化IRF 3，驱动IFN-α/β诱导。IFN-α/β通过IFN-α受体1和2（IFNAR 1/2）返回信号，诱导过多的IFN刺激基因（ISG），包括ISG 15和p21。p21通过激活SAMHD 1限制性功能和抑制参与从头dNTP生物合成的关键酶而表现出抗逆转录病毒活性。ISG 15通过激活细胞因子来阻断病毒感染，从而显示抗病毒活性。USP 18是ISG 15特异性的异肽酶，并负调节IFN信号传导。USP 18还通过以蛋白酶依赖性和非依赖性方式介导TAK 1和NEMO去泛素化来消除NF-κB信号传导。尽管USP 18通过负调节I型和III型IFN在先天免疫应答中起重要作用，并介导关键抗病毒蛋白的去ISG化，但其在先天靶细胞中的HIV-1感染、识别和传感中的作用尚未被探索。在SPP 1923的框架内，我们在我们的第一篇出版物中表明，HIV-1诱导USP 18表达，USP 18的存在通过废除p21抗病毒功能有助于HIV-1复制。在后续工作中，我们提供了USP 18介导的p21抗病毒活性消除的机制细节。我们证实p53是HIV-1可诱导的。然而，USP 18通过其蛋白酶活性积累了错误折叠的显性负性p53，这消除了野生型p53对p21的反式激活，导致细胞内dNTP池扩大，使SAMHD 1失活，并增加了HIV-1逆转录产物。此外，IFNAR 2的耗竭显著增加了HIV-1的复制。目前还不清楚USP 18介导的HIV-1感知阻断背后的分子和细胞机制，以及IFNAR 2的缺失如何增强先天性靶细胞中的HIV-1复制。然而，我们观察到USP 18与IRF-3和NF-κB信号通路的关键蛋白之间的相互作用。此外，在HIV-1感染的分化THP-1细胞中，USP 18的存在增加了IκBα，并降低了磷酸化IRF-3的表达。这些观察结果和我们正在进行的HIV-1传感途径的详细实验研究可能为确定USP 18在HIV-1先天免疫传感中的作用提供线索。

The RNA and cDNA of HIV-1 (human immunodeficiency virus type 1) can be recognized and sensed by macrophage and dendritic cell-expressed endosomal Toll-like receptors and cytosolic sensor, cGAS respectively. cGAS-cDNA interaction induces cGAMP production, which stimulates STING dimerization and activation. STING mediates TBK1 activation, which subsequently phosphorylates IRF3, driving IFN-α/β induction. IFN-α/β signals back via the IFN-α receptor 1 and 2 (IFNAR1/2), inducing a plethora of IFN stimulated gene (ISGs), including ISG15 and p21. p21 exhibits antiviral activity against retroviruses by activating SAMHD1 restriction function and repressing key enzymes involved in de novo dNTP biosynthesis. ISG15 exhibits antiviral activity by activating cellular factors required to block viral infection through ISGylation.USP18 is an ISG15-specific isopeptidase, and negatively regulates IFN signaling. USP18 also abrogates NF-κB signaling by mediating TAK1 and NEMO deubiquitination in a protease dependent and independent manner. Although USP18 plays an important role in innate immune responses by negatively regulating type I and III IFNs and mediates deISGylation of key antiviral proteins, its role in HIV-1 infection, recognition and sensing in innate target cells has not been explored. Within the framework of SPP1923, we showed in our first publication that HIV-1 induces USP18 expression and the presence of USP18 contributes to HIV-1 replication by abrogating p21 antiviral function. In a follow-up work, we provided a mechanistic detail to USP18-mediated abrogation of p21 antiviral activity. We confirmed that p53 is HIV-1-inducible. However, USP18, by its protease activity, accumulated misfolded dominant negative p53, which abrogated wild type p53 transactivation of p21 leading to an expanded intracellular dNTP pool, inactivated SAMHD1 and increased HIV-1 reverse transcription products.Despite USP18-mediated increased HIV-1 reverse transcripts, differentiated myeloid THP-1 cells failed to sense HIV-1, leading to low IFN and ISGs induction. Further, depletion of IFNAR2 increased significantly HIV-1 replication. The molecular and cellular mechanism behind the USP18-mediated block to HIV-1 sensing and how the absence of IFNAR2 enhances HIV-1 replication in innate target cells is currently not understood. However, we observed an interaction between USP18 and key proteins of the IRF-3 and the NF-κB signaling pathways. In addition, the presence of USP18 increased IκBα and reduced the expression of phosphorylated IRF-3 in HIV-1 infected differentiated THP-1 cells. These observations and our ongoing detailed experimental investigation in the HIV-1 sensing pathway may provide clues to identifying the role of USP18 in innate immune sensing of HIV-1.