Loss of Fv-1 restriction in Balb/3T3 cells following infection with a single N tropic murine leukemia virus particle

Dodding

Yap

et al. 2007

MBoC

Tripartite motif (TRIM)5␣ has recently been identified as a host restriction factor that has the ability to block infection by certain retroviruses in a species-dependent manner. One interesting feature of this protein is that it is localized in distinct cytoplasmic clusters designated as cytoplasmic bodies. The potential role of these cytoplasmic bodies in TRIM5␣ function remains to be defined. By using fluorescent fusion proteins and live cell microscopy, we studied the localization and dynamics of TRIM5␣ cytoplasmic bodies. This analysis reveals that cytoplasmic bodies are highly mobile, exhibiting both short saltatory movements and unidirectional long-distance movements along the microtubule network. The morphology of the cytoplasmic bodies is also dynamic. Finally, photobleaching and photoactivation analysis reveals that the TRIM5␣ protein present in the cytoplasmic bodies is very dynamic, rapidly exchanging between cytoplasmic bodies and a more diffuse cytoplasmic population. Therefore, TRIM5␣ cytoplasmic bodies are dynamic structures more consistent with a role in function or regulation rather than protein aggregates or inclusion bodies that represent dead-end static structures. INTRODUCTIONThe species-specific tropism of many retroviruses is determined by cellular restriction factors present in the cells of the host. One of the most well characterized restriction factors is the murine Fv1 gene, which prevents infection by particular strains of murine leukemia virus (MLV) (Best et al., 1996; for review, see Bieniasz, 2004;Goff, 2004). It is known that restriction by Fv1 involves the recognition of a capsid determinant in MLV (DesGroseillers et al., 1983;Kozak and Chakraborti, 1996). Analysis of Fv1 restriction indicates that restricted MLV strains can generate reverse transcription products but that they are unable to complete subsequent steps in infection (Pryciak and Varmus, 1992) and also that this restriction of infection is saturable, because it can be overcome with high levels of virus (Pincus et al., 1975;Duran-Troise et al., 1977).A similar restriction to human immunodeficiency virus 1 (HIV-1) infection in primates has also been well characterized; and recently, the cellular factor present in the cells of Old World monkeys responsible for restricting infection by HIV-1 was cloned and identified as the cytoplasmic body component tripartite motif (TRIM)5␣ . Restriction of HIV-1 infection by TRIM5␣ resembles restriction of MLV infection by Fv1 in many ways. TRIM5␣-mediated restriction is saturable with high multiplicity of infection (MOI), and the specificity of TRIM5␣-mediated HIV-1 restriction is governed by the recognition of a capsid determinant in the restricted virus similar to the case of Fv1-mediated restriction of MLV infection (Towers et al., 2000;Cowan et al., 2002;Owens et al., 2003Owens et al., , 2004Hatziioannou et al., 2004). However, TRIM5␣-mediated restriction differs from Fv1-mediated restriction in that TRIM5␣-mediated restriction is manifested earlier in the infectious pathway, b...

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

TRIM5α Cytoplasmic Bodies Are Highly Dynamic Structures

Dodding

Yap

et al. 2007

MBoC

“…Furthermore, MLV strains restricted by Fv1 can generate reverse transcription (RT) products but do not successfully integrate into the host-cell chromosome (4). This restriction to infection is also saturable because high levels of affected virus can overcome restriction (5,6).…”

mentioning

confidence: 99%

Proteasome inhibitors uncouple rhesus TRIM5α restriction of HIV-1 reverse transcription and infection

Anderson

Proc. Natl. Acad. Sci. U.S.A.

et al. 2006

246

292

“…Conversely, Fv1 b permits B-MLV infection but restricts N-MLV infection (27). Restriction resulted in an early block to MLV infection after reverse transcription (RT) but before integration into the host cell genome (16,28) and could be overcome or saturated by excess amounts of incoming, affected virus (11,27). The gene responsible for mediating this restriction encodes a protein with homology to the Gag protein of the ERV-L family of endogenous retroviruses (4), although its precise mechanism of action remains unclear.…”

mentioning

confidence: 99%

Proteasome Inhibition Reveals that a Functional Preintegration Complex Intermediate Can Be Generated during Restriction by Diverse TRIM5 Proteins

Anderson

et al. 2006

J Virol

152

199

The primate TRIM5 proteins constitute a class of restriction factors that prevent host cell infection by retroviruses from different species. The TRIM5 proteins act early after virion entry and prevent viral reverse transcription products from accumulating. We recently found that proteasome inhibitors altered the rhesus monkey TRIM5␣ restriction of human immunodeficiency virus type 1 (HIV-1), allowing reverse transcription products to accumulate even though viral infection remained blocked. To assess whether sensitivity to proteasome inhibitors was a common feature of primate TRIM5 proteins, we conducted a similar analysis of restriction mediated by owl monkey TRIM-cyclophilin A (CypA) or human TRIM5␣. Similar to rhesus monkey TRIM5␣ restriction, proteasome inhibition prevented owl monkey TRIM-CypA restriction of HIV-1 reverse transcription, even though HIV-1 infection and the output of 2-LTR circles remained impaired. Likewise, proteasome inhibition alleviated human TRIM5␣ restriction of N-tropic murine leukemia virus reverse transcription. Finally, HIV-1 reverse transcription products escaping rhesus TRIM5␣ restriction by proteasome inhibition were fully competent for integration in vitro, demonstrating that TRIM5␣ likely prevents the viral cDNA from accessing chromosomal target DNA. Collectively, these data indicate that the diverse TRIM5 proteins inhibit retroviral infection in multiple ways and that inhibition of reverse transcription products is not necessary for TRIM5-mediated restriction of retroviral infection.