Interferons (IFNs) induce the expression of interferon-stimulated genes (ISGs) for defense against numerous viral infections, including classical swine fever virus (CSFV). However, the mechanisms underlying the effect of ISGs on CSFV infection are rarely reported. In this study, we demonstrate that IFN-α treatment induces upregulation of ISG15 and thus attenuates CSFV replication. To determine whether ISG15 is critical for controlling CSFV replication, we established porcine alveolar macrophages (PAMs) with stable overexpression or knockdown of ISG15. Overexpression of Flag-ISG15 significantly prevented CSFV replication, whereas loss of ISG15 led to abnormal proliferation of CSFV. Furthermore, upregulated ISG15 promoted beclin-1 (BECN1) ISGylation and dysfunction and subsequently inhibited autophagy, which is indispensable for CSFV replication. In addition, HECT and RLD domain containing E3 ubiquitin protein ligase 5 (HERC5), which functions to catalyze conjugation of ISG15 protein, was confirmed to interact with BECN1. Collectively, these results indicate that IFN-α restricts CSFV replication through ISG15-mediated BECN1 ISGylation and autophagy inhibition, providing insight into the mechanism of CSFV replication control by type I IFN. This mechanism may not be the only antiviral mechanism of ISG15; nonetheless, this study may contribute to the development of CSFV treatment and prevention strategies.

中文翻译：

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ISG15对猪肺泡巨噬细胞中经典猪瘟病毒复制的抗病毒活性是通过ISG酰化BECN1抑制自噬来实现的。

干扰素（IFN）诱导干扰素刺激基因（ISG）的表达，以防御多种病毒感染，包括经典猪瘟病毒（CSFV）。但是，很少报道了ISG对CSFV感染产生影响的潜在机制。在这项研究中，我们证明IFN-α治疗诱导ISG15上调，从而减弱CSFV复制。为了确定ISG15对于控制CSFV复制是否至关重要，我们建立了具有稳定的ISG15过表达或敲除能力的猪肺泡巨噬细胞（PAM）。Flag-ISG15的过表达显着阻止了CSFV复制，而ISG15的缺失导致CSFV异常增殖。此外，上调的ISG15促进了beclin-1（BECN1）ISG的功能化和功能障碍，并随后抑制了自噬，这对于CSFV复制是必不可少的。此外，已证实含有E3泛素蛋白连接酶5（HERC5）的HECT和RLD结构域可催化ISG15蛋白的结合，并与BECN1相互作用。总体而言，这些结果表明，IFN-α通过ISG15介导的BECN1 ISGylation和自噬抑制作用来限制CSFV复制，从而深入了解I型IFN控制CSFV复制的机制。该机制可能不是ISG15的唯一抗病毒机制；尽管如此，这项研究可能有助于发展CSFV的治疗和预防策略。这些结果表明，IFN-α通过ISG15介导的BECN1 ISGylation和自噬抑制作用来限制CSFV复制，从而为I型IFN控制CSFV复制的机制提供了见识。该机制可能不是ISG15的唯一抗病毒机制；尽管如此，这项研究可能有助于发展CSFV的治疗和预防策略。这些结果表明，IFN-α通过ISG15介导的BECN1 ISGylation和自噬抑制作用来限制CSFV复制，从而为I型IFN控制CSFV复制的机制提供了见识。该机制可能不是ISG15的唯一抗病毒机制；尽管如此，这项研究可能有助于发展CSFV的治疗和预防策略。