A CRISPR-Cas9 screen identifies LAPTM4A (lysosomal protein transmembrane 4 alpha) as a key host barrier against PRRSV infection.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) manipulates host intracellular processes, particularly macroautophagy/autophagy and lysosomal function, to facilitate its replication and spread. However, the precise host factors and molecular mechanisms by which PRRSV remodels the autophagy-lysosome axis remain poorly defined. Here, we performed a CRISPR-Cas9 knockout screen targeting 1,332 genes involved in protein degradation, metabolism, and vesicular trafficking, and identified LAPTM4A (lysosomal protein transmembrane 4 alpha) as a critical antiviral factor involved in the lysosomal pathway. A yeast two-hybrid screen identified LAPTM4A as an interactor of PRRSV GP5 (glycoprotein 5). Mechanistically, GP5 recruits the E3 ubiquitin ligase NEDD4 and the autophagy receptor SQSTM1/p62 to promote K63-linked polyubiquitination of LAPTM4A, leading to its autophagic degradation. This selective degradation activates the AMPK-ULK1-MAP1LC3/LC3 signaling cascade, initiating autophagy while facilitating MTOR-lysosome colocalization, thereby suppressing TFEB nuclear translocation and transcription of lysosome-related genes. The resulting incomplete autophagic flux enhances viral replication. Additionally, in terms of host defense, LAPTM4A maintains lysosomal homeostasis by restraining excessive autophagy through AMPK-ULK1-LC3 signaling and promoting TFEB-dependent lysosomal gene expression by impairing the binding of RPTOR/raptor to MTOR, thus providing broad antiviral protection against multiple RNA viruses. Collectively, our findings identify LAPTM4A as a central regulator of lysosome-autophagy homeostasis and reveal a viral strategy that dismantles this defense axis to facilitate infection.Abbreviations: ATG5: autophagy related 5; AMPK: adenosine 5'-monophosphate (AMP)-activated protein kinase; Baf A1: bafilomycin A1; CHX: cycloheximide; Co-IP: co-immunoprecipitation; DMVT library: protein degradation, metabolism, and vesicular trafficking library; LAPTM4A: lysosomal protein transmembrane 4 alpha; MAGeCK: model-based analysis of genome-wide CRISPR-Cas9 knockout; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; NC: negative control; PAMs: porcine alveolar macrophages; PRKAA/AMPKα: protein kinase AMP-activated catalytic subunit alpha; PRRSV: porcine reproductive and respiratory syndrome virus; qRT-PCR: quantitative real-time PCR; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; TCID50: 50% tissue culture infective dose; TFEB: transcription factor EB; Ub: ubiquitin; ULK1: unc-51 like autophagy activating kinase 1; WT: wild type.