Porcine reproductive and respiratory syndrome virus hijacks the non-canonical enzymatic function of PHGDH to arrest autophagic flux for viral replication

Viruses frequently hijack host metabolic enzymes to fuel replication. However, the mechanisms underlying this hijacking and utilization of metabolic enzymes remain poorly understood. In this study, we report a sophisticated mechanism by which porcine reproductive and respiratory syndrome virus (PRRSV) exploits a non-canonical enzymatic function of PHGDH (phosphoglycerate dehydrogenase) to modulate macroautophagy/autophagy. We demonstrate that PRRSV infection recruits the transcription factor ZNF143 (zinc finger protein 143) to transcriptionally repress PHGDH expression. Importantly, the antiviral restriction activity of PHGDH is entirely uncoupled from its canonical enzymatic role in serine biosynthesis. Mechanistically, PHGDH depletion triggers the initiation of autophagy via the AMP-activated protein kinase (AMPK)-ULK1 (unc-51 like autophagy activating kinase 1) signaling axis; however, it paradoxically arrests autophagic flux at the autophagosome-lysosome fusion stage. PHGDH is identified as a critical scaffold that facilitates the assembly of the autophagic soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex; its downregulation disrupts the interaction between STX17 (syntaxin 17) and SNAP29 (synaptosome associated protein 29), thereby blocking autophagosome-lysosome fusion. This induction of incomplete autophagy creates a favorable cytosolic niche for viral replication. Furthermore, the antiviral effect of PHGDH is also observed in two other swine pathogens, porcine epidemic diarrhea virus (PEDV) and pseudorabies virus (PRV). Collectively, these findings revealed that viruses weaponized the moonlighting function of a metabolic enzyme to dismantle autophagic flux, highlighting PHGDH as a broad-spectrum antiviral target that bridged metabolism and membrane trafficking.