T-cell immunoglobulin and mucin domain 1 (TIM-1) is a receptor for Zaire Ebolavirus and Lake Victoria Marburgvirus
Edited* by Robert A. Lamb, Northwestern University, Evanston, IL, and approved April 7, 2011 (received for review December 21, 2010)
The glycoproteins (GP) of enveloped viruses facilitate entry into the host cell by interacting with specific cellular receptors. Despite extensive study, a cellular receptor for the deadly filoviruses Ebolavirus and Marburgvirus has yet to be identified and characterized. Here, we show that T-cell Ig and mucin domain 1 (TIM-1) binds to the receptor binding domain of the Zaire Ebola virus (EBOV) glycoprotein, and ectopic TIM-1 expression in poorly permissive cells enhances EBOV infection by 10- to 30-fold. Conversely, reduction of cell-surface expression of TIM-1 by RNAi decreased infection of highly permissive Vero cells. TIM-1 expression within the human body is broader than previously appreciated, with expression on mucosal epithelia from the trachea, cornea, and conjunctiva—tissues believed to be important during in vivo transmission of filoviruses. Recognition that TIM-1 serves as a receptor for filoviruses on these mucosal epithelial surfaces provides a mechanistic understanding of routes of entry into the human body via inhalation of aerosol particles or hand-to-eye contact.
ARD5, a monoclonal antibody against the IgV domain of TIM-1, blocked EBOV binding and infection, suggesting that antibodies or small molecules directed against this cellular receptor may provide effective filovirus antivirals.
The Filoviridae family of viruses is composed of two genera, Ebolavirus and Marburgvirus, which cause hemorrhagic fever in humans and nonhuman primates. Infection with some strains of filoviruses causes fatality in 50–90% of human cases (1). The viral glycoprotein (GP) of Ebolavirus, which consists of surface-exposed subunit GP1 attached to membrane-bound subunit GP2 by a disulfide bond (2), mediates binding to, penetration of, and fusion with host-cell membranes (3, 4). Pseudovirions bearing Ebolavirus GP transduce a broad range of cells through interactions that require the GP1 receptor-binding domain (RBD) (5–8). Upon internalization into low-pH endosomes, the filovirus GP1 is proteolyzed by cathepsins B and L, leading to GP2-dependent fusion of the viral and host membranes (9–12).
Several proteins enhance filovirus entry in host cells, including the C-type lectins L-SIGN, DC-SIGN, and hMGL, as well as RhoB/C, integrin α5β1, folate receptor-α, and the tyrosine kinase receptor Axl (13–26); however, because none of these molecules has been shown to interact with the RBD of the filovirus GP1, it is unlikely that any of these proteins serve as a receptor for this family of viruses. Thus, we used gene correlation analysis to search for additional potential receptors. Here, we identify T-cell Ig and mucin domain 1 (TIM-1), which interacts with Zaire ebolavirus (EBOV) GP and enhances EBOV infection by 10- to 30-fold upon expression, providing strong evidence that TIM-1 serves as a receptor for EBOV. As we found that TIM-1 is expressed on a number of mucosal epithelial surfaces, we propose that TIM-1/EBOV interactions may serve as a conduit for filovirus entry into the human body.