Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.
PLoS Pathog. 2022 Jul 1;18(7):e1010676. doi: 10.1371/journal.ppat.1010676. eCollection 2022 Jul.
Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma (KS)-associated herpesvirus, is involved etiologically in AIDS-associated KS, primary effusion lymphoma (PEL), and multicentric Castleman's disease, in which both viral latent and lytic functions are important. HHV-8 encodes four viral interferon regulatory factors (vIRFs) that are believed to contribute to viral latency (in PEL cells, at least) and/or to productive replication via suppression of cellular antiviral and stress signaling. Here, we identify vIRF-1 interactions with signal transducer and activator of transcription (STAT) factors 1 and 2, interferon (IFN)-stimulated gene factor 3 (ISGF3) cofactor IRF9, and associated signal transducing Janus kinases JAK1 and TYK2. In naturally infected PEL cells and in iSLK epithelial cells infected experimentally with genetically engineered HHV-8, vIRF-1 depletion or ablation, respectively, led to increased levels of active (phosphorylated) STAT1 and STAT2 in IFNβ-treated, and untreated, cells during lytic replication and to associated cellular-gene induction. In transfected 293T cells, used for mechanistic studies, suppression by vIRF-1 of IFNβ-induced phospho-STAT1 (pSTAT1) was found to be highly dependent on STAT2, indicating vIRF-1-mediated inhibition and/or dissociation of ISGF3-complexing, resulting in susceptibility of pSTAT1 to inactivating dephosphorylation. Indeed, coprecipitation experiments involving targeted precipitation of ISGF3 components identified suppression of mutual interactions by vIRF-1. In contrast, suppression of IFNβ-induced pSTAT2 was effected by regulation of STAT2 activation, likely via detected inhibition of TYK2 and its interactions with STAT2 and IFN type-I receptor (IFNAR). Our identified vIRF-1 interactions with IFN-signaling mediators STATs 1 and 2, co-interacting ISGF3 component IRF9, and STAT-activating TYK2 and the suppression of IFN signaling via ISGF3, TYK2-STAT2 and TYK2-IFNAR disruption and TYK2 inhibition represent novel mechanisms of vIRF function and HHV-8 evasion from host-cell defenses.
人类疱疹病毒 8 型（HHV-8），也称为卡波济肉瘤（KS）相关疱疹病毒，在病因上与艾滋病相关的 KS、原发性渗出淋巴瘤（PEL）和多中心卡斯特曼病有关，其中病毒潜伏和裂解功能都很重要。HHV-8 编码四个病毒干扰素调节因子（vIRFs），这些因子被认为有助于病毒潜伏（至少在 PEL 细胞中）和/或通过抑制细胞抗病毒和应激信号来进行有性复制。在这里，我们鉴定了 vIRF-1 与信号转导和转录激活因子（STAT）因子 1 和 2、干扰素（IFN）刺激基因因子 3（ISGF3）共因子 IRF9 以及相关信号转导 Janus 激酶 JAK1 和 TYK2 的相互作用。在天然感染的 PEL 细胞中和实验感染遗传工程 HHV-8 的 iSLK 上皮细胞中，vIRF-1 的耗尽或缺失分别导致在裂解复制过程中 IFNβ 处理和未经处理的细胞中活性（磷酸化）STAT1 和 STAT2 的水平升高，并导致相关的细胞基因诱导。在用于机制研究的转染 293T 细胞中，发现 vIRF-1 对 IFNβ 诱导的磷酸化 STAT1（pSTAT1）的抑制高度依赖于 STAT2，表明 vIRF-1 介导的 ISGF3 复合物抑制和/或解离，导致 pSTAT1 易受到失活去磷酸化的影响。事实上，涉及 ISGF3 成分靶向沉淀的共沉淀实验鉴定了 vIRF-1 对相互作用的抑制。相比之下，通过 STAT2 激活的调节来抑制 IFNβ 诱导的 pSTAT2，可能是通过检测到 TYK2 及其与 STAT2 和 IFN 型受体（IFNAR）的相互作用的抑制。我们鉴定的 vIRF-1 与 IFN 信号转导介质 STATs 1 和 2、相互作用的 ISGF3 成分 IRF9 以及 STAT 激活的 TYK2 的相互作用，以及通过 ISGF3、TYK2-STAT2 和 TYK2-IFNAR 破坏和 TYK2 抑制 IFN 信号的抑制作用，代表了 vIRF 功能和 HHV-8 逃避宿主细胞防御的新机制。
