GPR143 directs virus-induced cell vacuolation via MKK6-p38 pathway in teleost

Cytoplasmic vacuolization is a well-known morphological phenomenon observed in vertebrate cells after exposure to bacterial or viral pathogens. Studies on cytoplasmic vacuolization focused on its role in cell death and survival processes. However, little is known about the mechanism of cytoplasmic vacuolization formation. Nervous necrosis virus (NNV), a devastating and multispecies marine virus affecting multiple species, induces pronounced cytoplasmic vacuoles in brain during infection. G protein-coupled receptors (GPCRs) are critical in regulating autophagosomes and generating vacuolation. Here, we investigated the specific role of G protein-coupled receptor (GPR) 143 in mediating RGNNV-induced cellular vacuolation in the central nervous system of teleost. We observed that it enhanced red-spotted grouper NNV (RGNNV)-induced cytoplasmic vacuolation through intracellular binding to the RGNNV capsid protein. GPR143 significantly influenced the binding of autophagosomes and lysosomes. Further analysis revealed that RGNNV enhanced the interaction of GPR143 with MKK6, which phosphorylation of p38 mitogen-activated protein kinase. This phosphorylation subsequently activated the mTOR pathway, augmenting the binding of autophagosomes and lysosomes and resulting in cytoplasmic vacuolation. Finally, GPR143-mutant zebrafish demonstrated diminished brain vacuolation and reduced fry mortality. These findings suggest that RGNNV–GPR143 interaction activated the MKK6–p38–mTOR pathway, fostering autophagosome and lysosome binding that leads to cytoplasmic vacuolation. Targeting the GPR143-mediated pathway may provide a new therapeutic strategy for virus-induced cellular vacuolation.

细胞质空泡化（Cytoplasmic vacuolization）是脊椎动物细胞暴露于细菌或病毒病原体后所观测到的一类经典形态学现象。针对细胞质空泡化的研究多聚焦于其在细胞死亡与存活进程中的作用，但目前对其形成机制仍知之甚少。神经坏死病毒（Nervous necrosis virus, NNV）是一种可侵染多物种的毁灭性海洋病毒，感染宿主后可在其脑部诱导显著的细胞质空泡形成。G蛋白偶联受体（G protein-coupled receptors, GPCRs）在调控自噬体（autophagosomes）形成及空泡化进程中发挥关键作用。本研究探讨了G蛋白偶联受体143（G protein-coupled receptor 143, GPR143）在介导硬骨鱼中枢神经系统中由红斑石斑鱼神经坏死病毒（red-spotted grouper NNV, RGNNV）诱导的细胞空泡化中的具体功能。实验结果显示，GPR143可通过与RGNNV衣壳蛋白（capsid protein）在细胞内结合，增强红斑石斑鱼神经坏死病毒诱导的细胞质空泡化。GPR143可显著影响自噬体与溶酶体（lysosomes）的结合过程。进一步分析表明，RGNNV可增强GPR143与MKK6的相互作用，进而介导p38丝裂原活化蛋白激酶（p38 mitogen-activated protein kinase）的磷酸化。该磷酸化事件随后可激活mTOR信号通路（mammalian target of rapamycin, mTOR），强化自噬体与溶酶体的结合，最终引发细胞质空泡化。最后，GPR143基因突变型斑马鱼的脑部空泡化程度显著降低，幼鱼死亡率也有所下降。上述研究结果表明，RGNNV与GPR143的相互作用可激活MKK6-p38-mTOR信号通路，促进自噬体与溶酶体的结合，最终导致细胞质空泡化的发生。靶向GPR143介导的信号通路，或许可为病毒诱导的细胞空泡化提供全新的治疗策略。