<i>miR-17-5p</i> inhibits classical swine fever virus replication by targeting the <i>PKD2</i> -regulated AMPK/mTOR autophagy pathway

Classical swine fever virus (CSFV) remains a major threat to the global swine industry, yet the involvement of host miRNAs in its pathogenic mechanisms is not fully understood. In this study, we demonstrate for the first time that <i>miR-17-5p</i> inhibits CSFV replication through an autophagy-dependent mechanism by targeting polycystin-2 (<i>PKD2</i>), a key calcium channel protein that regulates the AMPK/mTOR signaling pathway. Using the PK-15 cell model, we found that CSFV infection significantly upregulates <i>miR-17-5p</i> expression. Functional assays revealed that <i>miR-17-5p</i> exerts antiviral effects by directly binding to the 3'-UTR of <i>PKD2</i>, as confirmed by bioinformatics prediction and dual-luciferase reporter assays. Silencing of <i>PKD2</i> recapitulated the antiviral effect of <i>miR-17-5p</i> overexpression, while <i>PKD2</i> reconstitution restored viral replication by activating AMPK signaling and suppressing mTOR activity, thereby significantly enhancing autophagic flux - as evidenced by increased LC3-II/I ratio and decreased p62 levels. Mechanistically, <i>PKD2</i> regulates intracellular calcium dynamics, modulating the AMPK/mTOR-autophagy axis to promote CSFV proliferation. This work uncovers a novel host antiviral mechanism in which a miRNA controls virus-induced autophagy via calcium signaling. To our knowledge, this is the first report to establish the pivotal role of miRNA-mediated calcium signaling modulation in flavivirus-host interactions. These findings provide a mechanistic framework and potential therapeutic targets for anti-CSFV interventions focused on <i>PKD2</i> or autophagy regulation.