ZMPSTE24 is a novel intrinsic immune protein that restricts a broad-spectrum of viruses

Virus entry begins with attachment to cell-surface receptors and ends with delivery of the viral genome into the cytoplasm. Many enveloped viruses are ferried deep into the cytoplasm through endocytic vesicles and utilize the low pH endosomal environment to activate the fusion process between viral and cellular membranes. Higher vertebrates evolved interferon-induced transmembrane proteins (IFITM) to impede endocytic penetration by a broad spectrum of RNA viruses. However, the molecular mechanism by which IFITM proteins hinder viral entry is not well elucidated. To address the antiviral mechanism of IFITM, we hypothesize that type I interferon (IFN) induces recruitment of co-factors to the IFITM3 protein complex. Proteomic analysis of IFITM3-FLAG protein complex in HEK293 cells revealed that IFN induced IFITM3 to recruit ZMPSTE24, the 7-pass transmembrane zinc metalloprotease whose function in cytoplasmic organelles is not defined. Contrary to IFITM, ZMPSTE24 mRNA and protein expression are not regulated by IFN. But consistent with IFITM, ZMPSTE24 restricts both RNA and DNA viruses using endocytic entry, including influenza A, vesicular stomatitis, sindbis, Ebola, cowpox and vaccinia viruses. Antiviral activity requires ZMPSTE24 endosomal localization and is independent of its protease activity. Furthermore, ZMPSTE24 is recruited to endosomes by IFITM and block viral endocytic entry. These findings identify a new role for ZMPSTE24 as a broad-spectrum intrinsic antiviral protein and the downstream antiviral effector of IFITM.