FKBP8 inhibits influenza a virus infection by degrading viral M2 protein in lysosomes.

Influenza A virus (IAV) remains a major threat to global public health, causing seasonal epidemics and occasional pandemics with significant morbidity and mortality. M2 (matrix protein 2), a key IAV envelope protein with ion channel activity, is critical for viral uncoating, genome release, and virion assembly. Here, we identified FKBP8 (FK506 binding protein 8) as a host restriction factor targeting IAV. Overexpression of FKBP8 inhibited IAV replication, while FKBP8 knockdown/knockout enhanced viral susceptibility. Mechanistically, FKBP8 interacted with M2 from diverse IAV strains via high-affinity binding between its tetratricopeptide repeat (TPR) domain and the LC3-interacting region (LIR) of M2, inhibiting viral entry. Importantly, FKBP8 mediated M2 degradation through the lysosomal pathway, not via translational inhibition, as shown by cycloheximide and lysosomal inhibitor (BafA1 and CQ) experiments. FKBP8 recruited RAB7A and LAMP1 to form a FKBP8-RAB7A-LAMP1-M2 complex, facilitating M2 transport to lysosomes. Additionally, FKBP8 interacted with envelope proteins of other enveloped RNA viruses, suggesting broad-spectrum antiviral potential. Our findings reveal FKBP8 as a conserved IAV restriction factor and its mechanism, providing insights for antiviral drug development.Abbreviations: AA: amino acids; AP-MS: affinity tag purification-mass spectrometry; BCL2: B cell leukemia/lymphoma 2; BafA1: bafilomycin A1; MbFKBP8: Myotis brandtii FK506 binding protein 8; CHX: cycloheximide; CQ: chloroquine; CTD: cytoplasmic tail domain; ED: ectodomain; EV: empty vector; FKBP8: FK506 binding protein 8; FL: full length; HCIPs: high-confidence interacting proteins; HsFKBP8: Homo sapiens FKBP prolyl isomerase 8; IAV: influenza A virus; LIR: LC3-interacting region; LAMP1: lysosomal-associated membrane protein 1; M2: matrix protein 2; MOI: multiplicity of infection; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MmFKBP8: Mus musculus FK506 binding protein 8; NP: nucleoprotein; PA: polymerase acidic; PB1: polymerase basic 1; PB2: polymerase basic 2; PPIase: peptidyl-prolyl cis-trans isomerase; KO: knockout; RdRps: RNA-dependent RNA polymerases; RAB7A: RAB7, member RAS oncogene family; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; TRIM41: tripartite motif-containing 41; TMD: transmembrane domain; vRNP: viral ribonucleoprotein.