TRIM5alpha Degradation via Autophagy Is Not Required for Retroviral Restriction Journal Article

Authors: Imam, S; Talley, S; Nelson, R. S.; Dharan, A; O'Connor, C; Hope, T. J.; Campbell, E. M.
Article Title: TRIM5alpha Degradation via Autophagy Is Not Required for Retroviral Restriction
Abstract: TRIM5alpha is an interferon-inducible retroviral restriction factor that prevents infection by inducing the abortive disassembly of capsid cores recognized by its C-terminal PRY/SPRY domain. The mechanism by which TRIM5alpha mediates the disassembly of viral cores is poorly understood. Previous studies demonstrated that proteasome inhibitors abrogate the ability of TRIM5alpha to induce premature core disassembly and prevent reverse transcription; however, viral infection is still inhibited, indicating that the proteasome is partially involved in the restriction process. Alternatively, we and others have observed that TRIM5alpha associates with proteins involved in autophagic degradation pathways, and one recent study found that autophagic degradation is required for the restriction of retroviruses by TRIM5alpha. Here, we show that TRIM5alpha is basally degraded via autophagy in the absence of restriction-sensitive virus. We observe that the autophagy markers LC3b and lysosome-associated membrane protein 2A (LAMP2A) localize to a subset of TRIM5alpha cytoplasmic bodies, and inhibition of lysosomal degradation with bafilomycin A1 increases this association. To test the requirement for macroautophagy in restriction, we examined the ability of TRIM5alpha to restrict retroviral infection in cells depleted of the autophagic mediators ATG5, Beclin1, and p62. In all cases, restriction of retroviruses by human TRIM5alpha, rhesus macaque TRIM5alpha, and owl monkey TRIM-Cyp remained potent in cells depleted of these autophagic effectors by small interfering RNA (siRNA) knockdown or clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 genome editing. Collectively, these results are consistent with observations that the turnover of TRIM5alpha proteins is sensitive to autophagy inhibition; however, the data presented here do not support observations that the inhibition of autophagy abrogates retroviral restriction by TRIM5 proteins. IMPORTANCE: Restriction factors are a class of proteins that inhibit viral replication. Following fusion of a retrovirus with a host cell membrane, the retroviral capsid is released into the cytoplasm of the target cell. TRIM5alpha inhibits retroviral infection by promoting the abortive disassembly of incoming retroviral capsid cores; as a result, the retroviral genome is unable to traffic to the nucleus, and the viral life cycle is extinguished. In the process of restriction, TRIM5alpha itself is degraded by the proteasome. However, in the present study, we have shown that in the absence of a restriction-sensitive virus, TRIM5alpha is degraded by both proteasomal and autophagic degradation pathways. Notably, we observed that restriction of retroviruses by TRIM5alpha does not require autophagic machinery. These data indicate that the effector functions of TRIM5alpha can be separated from its degradation and may have further implications for understanding the mechanisms of other TRIM family members.
Journal Title: Journal of virology
Volume: 90
Issue: 7
ISSN: 1098-5514; 0022-538X
Publisher: American Society for Microbiology. All Rights Reserved  
Journal Place: United States
Date Published: 2016
Start Page: 3400
End Page: 3410
Language: eng
Notes: LR: 20160405; CI: Copyright (c) 2016; JID: 0113724; OID: NLM: PMC4794682 [Available on 09/11/16]; PMCR: 2016/09/11 00:00; 2015/12/01 [received]; 2016/01/06 [accepted]; 2016/01/13 [aheadofprint]; epublish