The Viral Chemokine MCK-2 of Murine Cytomegalovirus Promotes Infection as Part of a gH/gL/MCK-2 Complex

Human cytomegalovirus (HCMV) forms two gH/gL glycoprotein complexes, gH/gL/gO and gH/gL/pUL(128,130,131A), which determine the tropism, the entry pathways and the mode of spread of the virus. For murine cytomegalovirus (MCMV), which serves as a model for HCMV, a gH/gL/gO complex functionally homologous to the HCMV gH/gL/gO complex has been described. Knock-out of MCMV gO does impair, but not abolish, virus spread indicating that also MCMV might form an alternative gH/gL complex. Here, we show that the MCMV CC chemokine MCK-2 forms a complex with the glycoprotein gH, a complex which is incorporated into the virion. We could additionally show that mutants lacking both, gO and MCK-2 are not able to produce infectious virus. Trans-complementation of these double mutants with either gO or MCK-2 showed that both proteins can promote infection of host cells, although through different entry pathways. MCK-2 has been extensively studied in vivo by others. It has been shown to be involved in attracting cells for virus dissemination and in regulating antiviral host responses. We now show that MCK-2, by forming a complex with gH, strongly promotes infection of macrophages in vitro and in vivo. Thus, MCK-2 may play a dual role in MCMV infection, as a chemokine regulating the host response and attracting specific target cells and as part of a glycoprotein complex promoting entry into cells crucial for virus dissemination.

人类巨细胞病毒（Human cytomegalovirus，HCMV）可形成两种gH/gL糖蛋白复合物：gH/gL/gO与gH/gL/pUL(128,130,131A)，二者决定了该病毒的宿主嗜性、入侵途径与传播模式。作为HCMV研究模型的鼠巨细胞病毒（murine cytomegalovirus，MCMV），其所含的gH/gL/gO复合物与HCMV的gH/gL/gO复合物功能同源，已有相关报道。敲除MCMV的gO基因虽会削弱病毒传播能力，但无法完全阻断病毒播散，这提示MCMV或许也存在替代性的gH/gL复合物。本研究证实，MCMV的CC趋化因子MCK-2可与糖蛋白gH形成复合物，且该复合物可被整合至病毒粒子中。我们进一步发现，同时缺失gO与MCK-2的双突变株无法产生具有感染性的病毒。对上述双突变株进行反式互补实验，分别补充gO或MCK-2后结果显示，两种蛋白均可通过不同的入侵途径促进宿主细胞感染。此前已有其他研究团队在体内（in vivo）对MCK-2开展了广泛研究，证实其可招募特异性细胞以促进病毒播散，并调控抗病毒宿主免疫应答。本研究现证实，MCK-2通过与gH形成复合物，可在体外（in vitro）与体内（in vivo）显著促进巨噬细胞感染。因此，MCK-2在MCMV感染过程中可能发挥双重作用：一方面作为趋化因子调控宿主免疫应答并招募特定靶细胞，另一方面作为糖蛋白复合物的组分，促进病毒入侵对病毒播散至关重要的宿主细胞。