Early Events in Foamy Virus—Host Interaction and Intracellular Trafficking

Abstract

Here we review viral and cellular requirements for entry and intracellular trafficking of foamy viruses (FVs) resulting in integration of viral sequences into the host cell genome. The virus encoded glycoprotein harbors all essential viral determinants, which are involved in absorption to the host membrane and triggering the uptake of virus particles. However, only recently light was shed on some details of FV’s interaction with its host cell receptor(s). Latest studies indicate glycosaminoglycans of cellular proteoglycans, particularly heparan sulfate, to be of utmost importance. In a species-specific manner FVs encounter endogenous machineries of the target cell, which are in some cases exploited for fusion and further egress into the cytosol. Mostly triggered by pH-dependent endocytosis, viral and cellular membranes fuse and release naked FV capsids into the cytoplasm. Intact FV capsids are then shuttled along microtubules and are found to accumulate nearby the centrosome where they can remain in a latent state for extended time periods. Depending on the host cell cycle status, FV capsids finally disassemble and, by still poorly characterized mechanisms, the preintegration complex gets access to the host cell chromatin. Host cell mitosis finally allows for viral genome integration, ultimately starting a new round of viral replication.

Cocirculation of Two env Molecular Variants, of Possible Recombinant Origin, in Gorilla and Chimpanzee Simian Foamy Virus Strains from Central Africa

“…SFV uses heparin sulfate to attach to target cells (47,48), but the receptor for SFV is still unknown (64). Interference studies showed that one cellular receptor is used by all SFVs (44)(45)(46).…”

Equine Infectious Anemia Virus Gag Assembly and Export Are Directed by Matrix Protein through trans -Golgi Networks and Cellular Vesicles

“…Gag proteins are central to the assembly of all retroviruses. Their expression in appropriate cells is sufficient to generate extracellular VLPs (with the exception of foamy virus, the assembly and budding of which rely on the envelope glycoproteins) (4,29). To determine the targeting sites of the EIAV and HIV-1 Gag proteins, 293T cells were transfected with EIAV or HIV-1 Gag-GFP plasmids.…”

Eleventh International Foamy Virus Conference—Meeting Report

“…For example, there is no release of a free protease moiety but instead protease activation is mediated by binding to the defined genomic RNA sequence protease-activating RNA motif (PARM) and subsequent dimerization of the Pol polyproteins. For an introduction into the topic, see [20,21,22]. …”

“…FV replication is inhibited by IFN-α, -β, and -γ. Two possible escape mechanisms from the antiviral action of IFNs have been described for FVs: the low lysine content of the Gag protein conferring partial resistance to IFN-α in primary cells and the synthesis of an miRNA inhibiting response to IFN [27]; (3) most steps of the FV life cycle are sensitive to the action of major IFN-induced restriction factors, including the alpha isoform of tripartite motif-containing protein 5 (TRIM5α), apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like (APOBEC), interferon-induced 35 kDa protein (IFP35), TRIM19, and Tetherin [20,31]; (4) regarding the adaptive immune effectors, FV-virus specific T lymphocytes have not been described thus far. Neutralizing antibodies against cell-free FV are detected in most animal and human hosts.…”