Ebola virus (EBOV) and Marburg virus (MARV) belong to theFiloviridae family and can cause outbreaks of severe hemorrhagic fever, with high mortality rates in humans. The EBOV VP40 (eVP40) and MARV VP40 (mVP40) matrix proteins play a central role in virion assembly and egress, such that independent expression of VP40 leads to the production and egress of virus-like particles (VLPs) that accurately mimic the budding of infectious virus. Late (L) budding domains of eVP40 recruit host proteins (e.g., Tsg101, Nedd4, and Alix) that are important for efficient virus egress and spread. For example, the PPxY-type L domain of eVP40 and mVP40 recruits the host Nedd4 E3 ubiquitin ligase via its WW domains to facilitate budding. Here we sought to identify additional WW domain host interactors and demonstrate that the PPxY L domain motif of eVP40 interacts specifically with the WW domain of the host E3 ubiquitin ligase ITCH. ITCH, like Nedd4, is a member of the HECT class of E3 ubiquitin ligases, and the resultant physical and functional interaction with eVP40 facilitates VLP and virus budding. Identification of this novel eVP40 interactor highlights the functional interplay between cellular E3 ligases, ubiquitination, and regulation of VP40-mediated egress.
IMPORTANCE
The unprecedented magnitude and scope of the recent 2014-2015 EBOV outbreak in West Africa and its emergence here in the United States and other countries underscore the critical need for a better understanding of the biology and pathogenesis of this emerging pathogen. We have identified a novel and functional EBOV VP40 interactor, ITCH, that regulates VP40-mediated egress. This virus-host interaction may represent a new target for our previously identified small-molecule inhibitors of virus egress.F iloviruses continue to cause severe outbreaks of hemorrhagic fever in humans, and there are currently no approved vaccines or therapeutics to combat Ebola virus (EBOV) and Marburg virus (MARV) infections. A better understanding of the interplay between EBOV and host cells will provide new insights into EBOV pathogenesis and identify novel targets for antiviral intervention. EBOV VP40 (eVP40) is the major virion structural protein that plays a crucial role in the assembly and budding of both virus-like particles (VLPs) and infectious virions. Indeed, eVP40 recruits multiple host proteins to facilitate late stages of virion assembly and egress (1-9). For example, the well-described late (L) budding domain motifs (PTAP and PPxY) of eVP40 mediate the recruitment of ESCRT and ESCRT-associated proteins that facilitate complete and efficient virus-cell separation (2, 4, 10-16).The PPxY core motif recruits WW domain-bearing proteins with diverse functions (17-25). In previous work, we and others demonstrated that the viral PPxY motif within eVP40, MARV VP40 (mVP40), and other viral matrix proteins interacts specifically with WW domains of host Nedd4, a HECT family E3 ubiquitin (Ub) ligase that is linked with the cellular ESCRT machinery (1,3,5,8,9,(26)(27)(28)(29)...