Porcine circovirus type 2 (PCV2) capsid protein (Cap) was previously reported to interact with nucleosome assembly protein 1-like 4 (NAP1L4). The biological function of Cap-NAP1L4 interaction is unknown. Here, we demonstrated that PCV2 Cap could directly interact with NAP1L4, which the amino acid residues 124–279 of NAP1L4 were responsible for the interaction. Furthermore, over-expression of NAP1L4 down-regulated the expression of PCV2 Cap and Rep. DNA copies and virus titers were also decreased in NAP1L4 over-expressed PK15 cells. While, knockout of NAP1L4 through CRISPR/Cas9 technology in PK15 cells could up-regulate the mRNA and protein levels of PCV2 Cap and Rep. PCV2 genomic DNA copies and virus titers were also increased in NAP1L4-knockdown/-knockout PK15 cells compared with wild type PK15 cells. In addition, NAP1L4 depletion was demonstrated to facilitate cytosolic carboxypeptidase-like protein 5 (CCP5) and cytosolic carboxypeptidase 6 (CCP6) expression, which could activate cGAS to promote IFN-β production. Indeed, knockout of NAP1L4 was also confirmed to increase IFN-β expression. And IFN-β stimulation could promote PCV2 replication in PK15 cells. Taken together, our findings suggest that NAP1L4 interacts with PCV2 Cap and inhibits PCV2 replication through regulating IFN-β production. Our study provides theoretical basis for further study of PCV2.

以前有报道称猪圆环病毒2型（PCV2）衣壳蛋白（Cap）与核小体装配蛋白1-like 4（NAP1L4）相互作用。Cap-NAP1L4相互作用的生物学功能是未知的。在这里，我们证明了PCV2 Cap可以直接与NAP1L4相互作用，其中NAP1L4的氨基酸残基124-279负责相互作用。此外，NAP1L4的过表达下调了PCV2 Cap和Rep的表达。在过表达的NAP1L4的PK15细胞中，DNA拷贝和病毒滴度也降低了。而通过CRISPR / Cas9技术在PK15细胞中敲除NAP1L4可以上调PCV2 Cap和Rep的mRNA和蛋白质水平。与野生相比，NAP1L4-nockdown / -knockout PK15细胞中PCV2基因组DNA拷贝和病毒滴度也增加了PK15型细胞。此外，NAP1L4耗竭被证明促进胞质羧肽酶样蛋白5（CCP5）和胞质羧肽酶6（CCP6）的表达，可以激活cGAS来促进IFN-β的产生。实际上，也证实了敲除NAP1L4可以增加IFN-β的表达。IFN-β刺激可以促进PCV2在PK15细胞中的复制。两者合计，我们的发现表明NAP1L4与PCV2 Cap相互作用并通过调节IFN-β的产生抑制PCV2复制。本研究为进一步研究PCV2提供了理论依据。IFN-β刺激可以促进PCV2在PK15细胞中的复制。两者合计，我们的发现表明NAP1L4与PCV2 Cap相互作用并通过调节IFN-β的产生抑制PCV2复制。本研究为进一步研究PCV2提供了理论依据。IFN-β刺激可以促进PCV2在PK15细胞中的复制。两者合计，我们的发现表明NAP1L4与PCV2 Cap相互作用并通过调节IFN-β的产生抑制PCV2复制。本研究为进一步研究PCV2提供了理论依据。