RNF5在卡波氏肉瘤相关疱疹病毒感染与致病中的作用和机制

Infection of Kaposi's sarcoma-associated herpesvirus (KSHV)causes Kaposi`s sarcoma (KS),the most common neoplasm in untreated AIDS patient,which was characterized by proliferation of spindle-shaped endothelial cells, infiltration by inflammatory cells, and striking neo-angiogenesis. KSHV establishes latent infection in the majority of spindle cells, but lytic replications occur in small fraction. It is well documented that the lytic cycle plays critical roles in KS pathogenesis by providing paracrine inflammatory cytokines and angiogenic factors for tumor progression. Autophagy, inflammatory factors and massive cellular signaling pathways are required for infection/replication and pathogenesis of KSHV. And KSHV employs several extracellular surface receptors and intracellular proteins for triggering a variety of cellular signal cascades and reprograming cellular transcriptome. ER-bound E3 ligase RNF5 (RING finger protein 5) have been identified as the negative regulator involved in antiviral innate immunity by tageting MAVS, which was hijacked by MHV68, a murine model hepersvirus for KSHV, to regulate the inflammatory cytokines and immune cell infiltration.Recently we found RNF5 negatively regulates autophagy by targeting ATG4B to limit basal autophagy and influence susceptibility to bacterial Infection. In addition, we recently charactorized EphA2 as a novel substrate of RNF5 by which RNF5 regulates EphrinA1-meidated internation/degradation of EphA2 that acts as a cellular receptor of KSHV and mediator of KSHV entry/trafficking in endothial cells. Given three processes (inflammation,autophagy and entry/trafficking) have been demonstrated to play critical roles in KSHV infection and pathogenesis, however, the role of RNF5 and the relationships with three targets in KSHV infection and pathogenesis have not yet been characterized. We hypothesis that RNF5 controls infection and pathogenesis of KSHV through entry/trafficking, autophagy and inflammatory response by targeting EphA2, ATG4B and MAVS respectively. This study will determine the role of RNF5 in KSHV infection and tumorigenesis (Aim 1), the regulation and functions of EphA2,ATG4B and MAVS in these proceses (Aim 2) and the key signal pathways of EphA2 receptor, autophagy and unresolved inflammation in oncogenesis caused by KSHV infection (Aim 3). The results of this study will shed light on KSHV pathogenesis and identify novel therapeutic targets for KSHV associated diseases.

KSHV感染导致的卡波氏肉瘤是HIV患者中常见的恶性肿瘤。KSHV感染后大部分建立潜伏感染，少部分进入裂解复制，而后者在致病过程中起重要作用，诱导肿瘤发生所必需的炎症因子和血管生成因子。自噬反应、炎症因子和许多细胞信号途径为KSHV感染和致病所必需，病毒利用多个细胞表面受体和细胞内蛋白激活一系列的细胞信号和重编细胞转录。研究已表明RNF5调控MAVS和抗病毒免疫；最近我们发现RNF5限制ATG4B和自噬反应进而影响细菌感染，以及RNF5调控EphA2受体。炎症反应、自噬反应和EphA2在KSHV感染和致病中具有重要作用，但RNF5在其中的作用尚未有研究。本项目将研究RNF5对KSHV感染和诱导肿瘤的影响，EphA2、ATG4B和MAVS介导的EphA2受体途径、自噬反应和炎症反应在其中的作用，揭示RNF5调控KSHV感染和致病的作用机制，增强对KSHV感染和致病机理的认识和揭示新的治疗靶点。

RNF5是一种18kD的E3泛素化连接酶，在调控自噬反应和天然免疫中发挥重要作用，并在乳腺癌和黑色素瘤中高表达，调控肿瘤细胞的谷氨酰胺代谢和对化疗药物紫杉醇的敏感性。Ephrin受体是一类酪氨酸激酶受体家族，在细胞粘附、细胞通讯和肿瘤发生等过程中发挥重要作用，研究已经证明该家族的一个重要成员EphA2是KSHV感染的内皮细胞受体和调控KSHV病毒在内皮细胞内转运入核的关键蛋白。本项目揭示了这两种重要蛋白之间的直接相互作用和在KSHV感染和致病中的重要功能。我们发现RNF5可与EphA2结合、调控其泛素化和在细胞内的降解，并发现RNF5调控EphA2多个位点的磷酸化修饰；从而RNF5通过EphA2途径调控KSHV病毒对内皮细胞的感染、感染细胞的生长和转化；在异体移植肿瘤模型中降低RNF5表达显著抑制肿瘤的生长，免疫组化分析表明抑制RNF5显著增强肿瘤组织中的EphA2含量，基因芯片分析发现这种抑制作用可能与EphA2介导的细胞粘附和Ephrin配体依赖的肿瘤抑制功能密切相关。因此我们的发现阐明了RNF5通过EphA2途径抑制KSHV感染和复制、促进KSHV感染细胞的转化和肿瘤的生长、在这种病毒感染和致病过程中发挥重要作用的分子机制。