Host cell barriers to the early phase of immunodeficiency virus replication explain the current distribution of these viruses among human and non-human primate species. Human immunodeficiency virus type 1 (HIV-1), the cause of acquired immunodeficiency syndrome (AIDS) in humans, efficiently enters the cells of Old World monkeys but encounters a block before reverse transcription. This species-specific restriction acts on the incoming HIV-1 capsid and is mediated by a dominant repressive factor. Here we identify TRIM5alpha, a component of cytoplasmic bodies, as the blocking factor. HIV-1 infection is restricted more efficiently by rhesus monkey TRIM5alpha than by human TRIM5alpha. The simian immunodeficiency virus, which naturally infects Old World monkeys, is less susceptible to the TRIM5alpha-mediated block than is HIV-1, and this difference in susceptibility is due to the viral capsid. The early block to HIV-1 infection in monkey cells is relieved by interference with TRIM5alpha expression. Our studies identify TRIM5alpha as a species-specific mediator of innate cellular resistance to HIV-1 and reveal host cell components that modulate the uncoating of a retroviral capsid.

The host restriction factor TRIM5␣ mediates species-specific, early blocks to retrovirus infection; susceptibility to these blocks is determined by viral capsid sequences. Here we demonstrate that TRIM5␣ variants from Old World monkeys specifically associate with the HIV type 1 (HIV-1) capsid and that this interaction depends on the TRIM5␣ B30.2 domain. Human and New World monkey TRIM5␣ proteins associated less efficiently with the HIV-1 capsid, accounting for the lack of restriction in cells of these species. After infection, the expression of a restricting TRIM5␣ in the target cells correlated with a decrease in the amount of particulate capsid in the cytosol. In some cases, this loss of particulate capsid was accompanied by a detectable increase in soluble capsid protein.Inhibiting the proteasome did not abrogate restriction. Thus, TRIM5␣ restricts retroviral infection by specifically recognizing the capsid and promoting its rapid, premature disassembly.

Retroviruses encounter dominant postentry restrictions in cells of particular species. Human immunodeficiency virus type 1 (HIV-1) is blocked in the cells of Old World monkeys by TRIM5␣, a tripartite motif (TRIM)protein composed of RING, B-box 2, coiled-coil, and B30.2(SPRY) domains. Rhesus monkey TRIM5␣ (TRIM5␣ rh ) more potently blocks HIV-1 infection than human TRIM5␣ (TRIM5␣ hu ). Here, by studying chimeric TRIM5␣ proteins, we demonstrate that the major determinant of anti-HIV-1 potency is the B30.2(SPRY) domain. Analysis of species-specific variation in TRIM5␣ has identified three variable regions (v1, v2, and v3) within the B30.2 domain. The TRIM5␣ proteins of Old World primates exhibit expansion, duplication, and residue variation specifically in the v1 region. Replacement of three amino acids in the N terminus of the TRIM5␣ hu B30.2 v1 region with the corresponding TRIM5␣ rh residues resulted in a TRIM5␣ molecule that restricted HIV-1 nearly as efficiently as wild-type TRIM5␣ rh . Surprisingly, a single-amino-acid change in this region of TRIM5␣ hu allowed potent restriction of simian immunodeficiency virus, a phenotype not observed for either wild-type TRIM5␣ hu or TRIM5␣ rh . Some of the chimeric TRIM5␣ proteins that are >98% identical to the human protein yet mediate a strong restriction of HIV-1 infection may have therapeutic utility. These observations implicate the v1 variable region of the B30.2(SPRY) domain in TRIM5␣ rh antiviral potency.The primate lentiviruses include human immunodeficiency virus type 1 (HIV-1) and HIV-2 and simian immunodeficiency viruses (SIVs) (2,5,7,8,11). HIV-1 and HIV-2 infect humans, HIV-1-like viruses infect chimpanzees, and SIV variants infect African monkeys. Humans infected by HIV-1 and HIV-2 and Asian macaques infected by certain SIV strains (SIV mac ) often develop life-threatening immunodeficiency due to depletion of CD4-positive T lymphocytes (9,19).HIV and SIV tropism is determined by cell-type-specific and species-specific host factors. Following entry into the host cell, uncoating of the viral core, reverse transcription, nuclear access, and integration of the viral DNA into the host genome must occur to establish a permanent infection (1,10,33). Early postentry restrictions to retrovirus infection can determine tropism at the species level. HIV-1 encounters a postentry block in Old World monkeys, whereas SIV mac is blocked in most New World monkey cells (15,16,27). These species-specific restrictions occur prior to or concurrent with reverse transcription; at most, low levels of early reverse transcripts are made in restricted cells (6,15,20,27). The viral determinant of susceptibility to these blocks is the capsid protein (6,13,18,22,23,30). The early restriction of HIV-1 and SIV is mediated by dominant host factors, the activities of which can be titrated by the introduction of virus-like particles containing proteolytically processed capsid proteins of the restricted viruses (3,4,6,12,22,31,32). Thus, in the cells of specific monkey species, host restricti...

Summary The 2013-2015 West African epidemic of Ebola virus disease (EVD) reminds us how little is known about biosafety level-4 viruses. Like Ebola virus, Lassa virus (LASV) can cause hemorrhagic fever with high case fatality rates. We generated a genomic catalog of almost 200 LASV sequences from clinical and rodent reservoir samples. We show that whereas the 2013-2015 EVD epidemic is fueled by human-to-human transmissions, LASV infections mainly result from reservoir-to-human infections. We elucidated the spread of LASV across West Africa and show that this migration was accompanied by changes in LASV genome abundance, fatality rates, codon adaptation, and translational efficiency. By investigating intrahost evolution, we found that mutations accumulate in epitopes of viral surface proteins, suggesting selection for immune escape. This catalog will serve as a foundation for the development of vaccines and diagnostics.

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Tripartite motif (TRIM) proteins are composed of RING, B-box 2, and coiled coil domains. Some TRIM proteins, such as TRIM5␣, also possess a carboxy-terminal B30.2(SPRY) domain and localize to cytoplasmic bodies. TRIM5␣ has recently been shown to mediate innate intracellular resistance to retroviruses, an activity dependent on the integrity of the B30.2 domain, in particular primate species. An examination of the sequences of several TRIM proteins related to TRIM5 revealed the existence of four variable regions (v1, v2, v3, and v4) in the B30.2 domain. Species-specific variation in TRIM5␣ was analyzed by amplifying, cloning, and sequencing nonhuman primate TRIM5 orthologs. Lineage-specific expansion and sequential duplication occurred in the TRIM5␣ B30.2 v1 region in Old World primates and in v3 in New World monkeys. We observed substitution patterns indicative of selection bordering these particular B30.2 domain variable elements. These results suggest that occasional, complex changes were incorporated into the TRIM5␣ B30.2 domain at discrete time points during the evolution of primates. Some of these time points correspond to periods during which primates were exposed to retroviral infections, based on the appearance of particular endogenous retroviruses in primate genomes. The results are consistent with a role for TRIM5␣ in innate immunity against retroviruses.

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TRIM5alpha and TRIMCyp are retroviral restriction factors that, like other members of the tripartite motif (TRIM) family, contain RING, B-box 2 and coiled-coil domains. We found that both proteins are rapidly turned over, with half-lives of 50-60 min. Polyubiquitylation and rapid degradation of TRIM5alpha depended upon intact RING and B-box 2 domains. A chimera consisting of monkey TRIM5alpha with a RING domain of human TRIM21 exhibited a half-life of 210 min, yet potently restricted human immunodeficiency virus; therefore, rapid turnover of TRIM5alpha is not required for its antiretroviral activity. TRIM5alpha forms cytoplasmic bodies that contain other polyubiquitylated proteins, heat shock proteins and dynein, and thus resemble aggresome precursors. Consistent with this interpretation, proteasomal inhibitors triggered the formation of TRIM5alpha(rh)-containing aggresomes in a microtubule-dependent manner. Thus, TRIM5alpha levels in the cell are maintained by continuous synthesis and rapid proteasome-mediated degradation, imbalances in which result in the formation of pre-aggresomal cytoplasmic bodies.