Kang Soowon, Brulois Kevin, Choi Youn Jung, Zhang Shaoyan, Jung Jae U
Department of Infection Biology, Global Center for Pathogen and Human Health Research, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA.
Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
J Med Virol. 2025 Jan;97(1):e70179. doi: 10.1002/jmv.70179.
Kaposi's sarcoma-associated herpesvirus (KSHV) employs diverse mechanisms to subvert host immune responses, contributing to its infection and pathogenicity. As an immune evasion strategy, KSHV encodes the Membrane-Associated RING-CH (MARCH)-family E3 ligases, K3, and K5, which target and remove several immune regulators from the cell surface. In this study, we investigate the impact of K3 and K5 on lymphotoxin receptor (LTβR) ligands, LTβ and LIGHT, which are type II transmembrane proteins and function as pivotal immune mediators during virus infection. Upon co-expression of viral MARCH proteins with LTβR ligands, we showed that K3 and K5 selectively targeted LTβ, but not LIGHT, for the downregulation of surface expression. Specifically, K3 and K5 E3 ligases interacted with the transmembrane domain of LTβ. Intriguingly, K3 interacted with an immature form of LTβ, whereas K5 targeted the fully mature form. Subsequent biochemical analyses revealed that K3 disrupted the initial steps of N-glycosylation maturation of LTβ. This interference resulted in the sequestration of LTβ within the endoplasmic reticulum, impeding its trafficking to the plasma membrane. Consequently, the K3-mediated downregulation of LTβ surface expression suppressed the LTβR downstream signaling pathway. These findings uncover a novel mechanism by which KSHV K3 E3 ligase inhibits the membrane trafficking pathway of the LTβ inflammatory ligand through glycosylation interference, potentially evading LTβR-mediated antiviral immunity.
卡波西肉瘤相关疱疹病毒（KSHV）采用多种机制来颠覆宿主免疫反应，这有助于其感染和致病性。作为一种免疫逃逸策略，KSHV编码膜相关RING-CH（MARCH）家族的E3连接酶K3和K5，它们靶向并从细胞表面去除几种免疫调节因子。在本研究中，我们调查了K3和K5对淋巴毒素受体（LTβR）配体LTβ和LIGHT的影响，LTβ和LIGHT是II型跨膜蛋白，在病毒感染期间作为关键的免疫介质发挥作用。在病毒MARCH蛋白与LTβR配体共表达时，我们发现K3和K5选择性地靶向LTβ而非LIGHT，以下调其表面表达。具体而言，K3和K5 E3连接酶与LTβ的跨膜结构域相互作用。有趣的是，K3与未成熟形式的LTβ相互作用，而K5靶向完全成熟的形式。随后的生化分析表明，K3破坏了LTβ的N-糖基化成熟的初始步骤。这种干扰导致LTβ在内质网中滞留，阻碍其转运到质膜。因此，K3介导的LTβ表面表达下调抑制了LTβR下游信号通路。这些发现揭示了一种新机制，即KSHV K3 E3连接酶通过糖基化干扰抑制LTβ炎症配体的膜转运途径，可能逃避LTβR介导的抗病毒免疫。
