Virus-Specific Effects of TRIM5α _rh RING Domain Functions on Restriction of Retroviruses

Abstract

T he replication of human immunodeficiency virus type 1 (HIV-1) is potently blocked in Old World monkeys at an early postentry step, prior to reverse transcription (1, 2). In 2004, TRIM5␣ was identified as the major host factor that mediates this block (3). Since this discovery, the TRIM5 proteins of multiple mammalian species have been characterized, and the range of restricted viruses has expanded to include a variety of retroviruses (lentiviruses, a betaretrovirus, a gammaretrovirus, and spumaviruses) (4-16). A TRIM5 variant, TRIMCyp, which arose as a result of retrotransposition events involving TRIM5 and cyclophilin A, exhibits distinct restriction activities and has been identified in New World owl monkeys and some Old World macaque species (17-22). The wide existence of restricting TRIM5 variants suggests that they are part of a novel, widespread mechanism of innate immunity.TRIM5 proteins block viral infection in a species-specific manner. Rhesus monkey TRIM5␣ (TRIM5␣ rh ) potently blocks infection by HIV-1, whereas human TRIM5␣ (TRIM5␣ hu ) only modestly restricts HIV-1 infection but potently blocks infection of N-tropic murine leukemia virus (N-MLV) (3,5,8,9,15). The mechanism of TRIM5-mediated restriction is still not completely understood. Retroviral sensitivity is determined by viral capsid proteins; TRIM5␣ has been shown to bind directly to in vitroassembled HIV-1 capsid-nucleocapsid (CA-NC) complexes, which resemble authentic viral cores (23-25). Interactions between TRIM5 proteins and viral capsids promote the uncoating of sensitive viruses, as the level of particulate capsids is decreased in the cytosol of cells expressing a restricting TRIM5␣ protein (25,26). Recent electron microscopic studies (27) demonstrated that purified TRIM5␣ proteins spontaneously form a large hexagonal lattice structure on the HIV-1 capsid, which is composed of smaller CA hexameric units. This observation has led to the hypothesis that a slight mismatch between the geometry of the TRIM5␣ rh hexagonal lattice and that of the capsid could lead to disassembly of the capsid (27). Some investigators have reported that proteasome inhibitors relieve the TRIM5␣-mediated block of viral reverse transcription but not infection, implying a two-step restriction mechanism that requires the proteasome (28, 29). Degradation of TRIM5 proteins was also observed in the presence of saturating levels of sensitive viruses, suggesting that the TRIM5␣-capsid complexes are targeted for degradation; however, changes in capsid protein stability or accumulation of ubiquitinated TRIM5␣ proteins were not observed upon HIV-1 infection (30). Recognition of the retroviral capsid by TRIM5␣ has been shown to promote innate immune signaling by catalyzing the synthesis of unattached K63 ubiquitin chains (31).TRIM5␣ is a member of the tripartite motif (TRIM) protein family (32). TRIM proteins all contain a RING domain, one or two B-box domains, and a coiled-coil domain. TRIM5␣, in addition, contains a B30.2/SPRY domain at the C terminus (32, 33). The B30.2...

The Human Antiviral Factor TRIM11 Is under the Regulation of HIV-1 Vpr

“…This process required the E3 ubiquitin ligase activity of the RING domain of TRIM5α to facilitate the higher-order association of its dimers for capsid binding [47]. Our results also demonstrated that TRIM11 could lead to decreased HIV-1 reverse transcripts and that the RING domain was necessary for the inhibitory activity of TRIM11 during this step.…”

Structural studies of postentry restriction factors reveal antiparallel dimers that enable avid binding to the HIV-1 capsid lattice

“…Deletion of the coiled-coil region prevents stable binding of the retroviral CA protein (21), whereas the B-box promotes cooperative CA binding by mediating higherorder Trim5α self-association (30). Disruption or removal of the RING domain interferes with proteasome interactions, delaying the block in virus replication until after reverse transcription has occurred, but can also affect higher-order RF association (31).…”

Binding of the rhesus TRIM5α PRYSPRY domain to capsid is necessary but not sufficient for HIV-1 restriction

“…The RING domain of TRIM5α rh is an E3 ubiquitin ligase (Diaz-Griffero et al, 2006a; Kar et al, 2008; Kim et al, 2011; Langelier et al, 2008; Li et al, 2013; Lienlaf et al, 2011; Maegawa et al; Pertel et al, 2011; Yamauchi et al, 2008). The E3-ligase activity of TRIM5α is correlated to the ability of TRIM5α to block HIV-1 (Lienlaf et al, 2011).…”