ADAM17 is an essential attachment factor for classical swine fever virus

Classical swine fever virus (CSFV) is an important pathogen in the swine industry. Virion attachment is mediated by envelope proteins Erns and E2, and E2 is indispensable. Using a pull-down assay with soluble E2 as the bait, we demonstrated that ADAM17, a disintegrin and metalloproteinase 17, is essential for CSFV entry. Loss of ADAM17 in a permissive cell line eliminated E2 binding and viral entry, but compensation with pig ADAM17 cDNA completely rescued these phenotypes. Similarly, ADAM17 silencing in primary porcine fibroblasts significantly impaired virus infection. In addition, human and mouse ADAM17, which is highly homologous to pig ADAM17, also mediated CSFV entry. The metalloproteinase domain of ADAM17 bound directly to E2 protein in a zinc-dependent manner. A surface exposed region within this domain was mapped and shown to be critical for CSFV entry. These findings clearly demonstrate that ADAM17 serves as an essential attachment factor for CSFV.

Author summary Classical swine fever virus (CSFV) is a highly pathogenic RNA virus belonging to Flaviviridae family that can cause deadly classical swine fever (CSF) among pigs. In this study, we identified ADAM17 as a binding partner for CSFV envelope protein E2 using biochemical approaches. Knockout of ADAM17 rendered permissive porcine cells resistant to CSFV infection, which could be reversed by complementing ADAM17 cDNA. The metalloproteinase domain of ADAM17 directly bound to CSFV E2 in a zinc-dependent manner in vitro, within which a 45 amino-acid region played key roles in mediating CSFV entry. Discovery the essential attachment factor for CSFV will provide a mechanistic understanding of cell tropism and pathogenesis of pestiviruses and facilitate development of antiviral agents against CSFV.