miR-17-5p inhibits classical swine fever virus replication by targeting the PKD2-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 miR-17-5p inhibits CSFV replication through an autophagy-dependent mechanism by targeting polycystin-2 (PKD2), 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 miR-17-5p expression. Functional assays revealed that miR-17-5p exerts antiviral effects by directly binding to the 3'-UTR of PKD2, as confirmed by bioinformatics prediction and dual-luciferase reporter assays. Silencing of PKD2 recapitulated the antiviral effect of miR-17-5p overexpression, while PKD2 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, PKD2 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 PKD2 or autophagy regulation.