Bat and pig Interferon-Induced Transmembrane Protein 3 restrict cell entry by influenza virus and lyssaviruses

Interferon-induced transmembrane protein 3 (IFITM3) is a restriction factor which

blocks cytosolic entry of numerous viruses that utilise acidic endosomal entry

pathways. In humans and mice, IFITM3 limits influenza-induced morbidity and

mortality. Although many IFITM3-sensitive viruses are zoonotic, whether IFITMs

function as antiviral restriction factors in mammalian species other than humans and

mice is unknown. Here, IFITM3 orthologues in the microbat Myotis myotis and the pig

(Sus scrofa domesticus) were identified using rapid amplification of cDNA ends. Amino

acid residues known to be important for IFITM3 function were conserved in the pig and

bat orthologues. Ectopically-expressed pig and microbat IFITM3 co-localised with

transferrin (early endosomes) and CD63 (late endosomes/multivesicular bodies) and

trafficked from the plasma membrane into endosomes following live cell staining. Pig

and microbat IFITM3 restricted cell entry mediated by multiple influenza HA subtypes

and lyssavirus G proteins. Expression of pig or microbat IFITM3 in A549 cells reduced

influenza virus yields and nucleoprotein expression. Conversely siRNA knockdown of

IFITM3 in pig NPTr cells and primary microbat cells enhanced virus replication,

demonstrating that these genes are functional in their species of origin at endogenous

levels. In sum, we show that IFITMs function as potent broad-spectrum antiviral

effectors in two mammals - pigs and bats - identified as major reservoirs for emerging

viruses.