Rodriguez Laura, Nogales Aitor, Iqbal Munir, Perez Daniel R, Martinez-Sobrido Luis
Department of Microbiology and Immunology, University of Rochester, Rochester, NY, United States.
Agencia Española de Medicamentos y Productos Sanitarios, Madrid, Spain.
Front Microbiol. 2018 Oct 24;9:2546. doi: 10.3389/fmicb.2018.02546. eCollection 2018.
H9N2 influenza A viruses (IAV) are considered low pathogenic avian influenza viruses (LPAIV). These viruses are endemic in poultry in many countries in Asia, the Middle East and parts of Africa. Several cases of H9N2-associated infections in humans as well as in pigs have led the World Health Organization (WHO) to include these viruses among those with pandemic potential. To date, the processes and mechanisms associated with H9N2 IAV adaptation to mammals are poorly understood. The non-structural protein 1 (NS1) from IAV is a virulence factor that counteracts the innate immune responses. Here, we evaluated the ability of the NS1 protein from A/quail/Hong Kong/G1/97 (HK/97) H9N2 to inhibit host immune responses. We found that HK/97 NS1 protein counteracted interferon (IFN) responses but was not able to inhibit host gene expression in human or avian cells. In contrast, the NS1 protein from earlier H9N2 IAV strains, including the first H9N2 A/turkey/Wisconsin/1/1966 (WI/66), were able to inhibit both IFN and host gene expression. Using chimeric constructs between WI/66 and HK/97 NS1 proteins, we identified the region and amino acid residues involved in inhibition of host gene expression. Amino acid substitutions L103F, I106M, P114S, G125D and N139D in HK/97 NS1 resulted in binding to the 30-kDa subunit of the cleavage and polyadenylation specificity factor (CPSF30) and, in consequence, inhibition of host gene expression. Notably, changes in the same amino acid residues resulted in the lack of inhibition of host gene expression by WI/66 NS1. Importantly, our results identified a new combination of amino acids required for NS1 binding to CPSF30 and inhibition of host gene expression. These results also confirm previous studies demonstrating strain specific differences in the ability of NS1 proteins to inhibit host gene expression.
H9N2甲型流感病毒（IAV）被认为是低致病性禽流感病毒（LPAIV）。这些病毒在亚洲、中东和非洲部分地区的许多国家的家禽中呈地方性流行。几例人类以及猪感染H9N2的病例已导致世界卫生组织（WHO）将这些病毒列入具有大流行潜力的病毒之中。迄今为止，与H9N2 IAV适应哺乳动物相关的过程和机制仍知之甚少。IAV的非结构蛋白1（NS1）是一种毒力因子，可对抗先天性免疫反应。在此，我们评估了来自A/鹌鹑/香港/G1/97（HK/97）H9N2的NS1蛋白抑制宿主免疫反应的能力。我们发现HK/97 NS1蛋白可对抗干扰素（IFN）反应，但无法抑制人源或禽源细胞中的宿主基因表达。相比之下，包括首个H9N2 A/火鸡/威斯康星/1/1966（WI/66）在内的早期H9N2 IAV毒株的NS1蛋白能够同时抑制IFN和宿主基因表达。通过构建WI/66和HK/97 NS1蛋白之间的嵌合构建体，我们确定了参与抑制宿主基因表达的区域和氨基酸残基。HK/97 NS1中的氨基酸替换L103F、I106M、P114S、G125D和N139D导致与切割和聚腺苷酸化特异性因子（CPSF30）的30 kDa亚基结合，进而抑制宿主基因表达。值得注意的是，相同氨基酸残基的变化导致WI/66 NS1无法抑制宿主基因表达。重要的是，我们的结果确定了NS1与CPSF30结合以及抑制宿主基因表达所需的新氨基酸组合。这些结果也证实了先前的研究，即NS1蛋白抑制宿主基因表达的能力存在毒株特异性差异。
