Tim-1 and Tim-4 mediate entry of the human Kaposi's sarcoma-associated herpesvirus and the related rhesus monkey rhadinovirus

Abstract

Kaposis sarcoma-associated herpesvirus (KSHV) is a human tumor virus. It is associated with Kaposis sarcoma, primary effusion lymphoma, and multicentric Castlemans disease. KSHV is known to interact with several different receptors, among them heparan sulfate proteoglycans, Eph family receptors, and integrins. We mutated the closely related rhesus monkey rhadinovirus in the known receptor interaction sites for Eph family and Plexin domain containing proteins and found it to still replicate on certain cells. This lytic virus was then used as a selection agent in a genome-wide CRISPR knockout screen, which identified TIM1 and NRP1 as host dependency factors. NRP1 is also host factor for the related Epstein-Barr virus and was recently reported to promote KSHV infection, which we confirm even if it functions with low efficiency on most cells and became functional only after ablation of the Eph receptor interaction. Further analysis through overexpression demonstrated that Tim-1 and the related Tim-4 are strong mediators of RRV and KSHV infection, in particular in the absence of other receptor interactions and even more pronounced for a KSHV mutant deleted in glycoprotein K8.1. Both Tim-1 and Tim-4 are heavily O-glycosylated phosphatidylserine (PS) receptors. For KSHV in particular, experiments with mutated Tim-1 and comparison to Ebola virus glycoprotein-driven entry indicate that the interaction with Tim-1 occurs through PS-binding by Tim-1 and suggest additional interaction in a PS-independent manner. The mucin-like domain of Tim-1 is required for optimal receptor function. The use of Tim proteins for entry is a novelty for herpesviruses and underscores the unique biology of KSHV and RRV.