A non-canonical role for the autophagy machinery in anti-retroviral signaling mediated by TRIM5α.
TRIM5 is a key cross-species barrier to retroviral infection, with certain TRIM5 alleles conferring increased risk of HIV-1 infection in humans. TRIM5 is best known as a species-specific restriction factor that directly inhibits the viral life cycle. Additionally, it is also a pattern-recognition receptor (PRR) that activates inflammatory signaling. How TRIM5 carries out its multi-faceted actions in antiviral defense remains incompletely understood. Here, we show that proteins required for autophagy, a cellular self-digestion pathway, play an important role in TRIM5s function as a PRR. Genetic depletion of proteins involved in all stages of the autophagy pathway prevented TRIM5-driven expression of NF-{kappa}B and AP1 responsive genes. One of these genes is the preeminent antiviral cytokine interferon {beta} (IFN-{beta}), whose TRIM5-dependent expression was lost in cells lacking the autophagy proteins ATG7, BECN1, and ULK1. Moreover, we found that the ability of TRIM5 to stimulate IFN-{beta} expression in response to recognition of a TRIM5-restricted HIV-1 capsid mutant (P90A) was abrogated in cells lacking autophagy factors. Stimulation of human macrophage-like cells with the P90A virus protected them against subsequent infection with an otherwise resistant wild type HIV-1 in a manner requiring TRIM5, BECN1, and ULK1. Mechanistically, TRIM5 was attenuated in its ability to activate the kinase TAK1 in autophagy deficient cells, and both BECN1 and ATG7 contributed to the assembly of TRIM5-TAK1 complexes. These data demonstrate a non-canonical role for the autophagy machinery in assembling antiviral signaling complexes and demonstrate a role for autophagy in the establishment of a TRIM5-dependent antiviral state. SIGNIFICANCE STATEMENTTRIM5 is an antiretroviral protein that employs multiple mechanisms to protect cells against infection. Previous studies have linked TRIM5 to autophagy, a cytoplasmic quality control pathway with numerous roles in immunity, raising the possibility that TRIM5 engages autophagy in antiviral defense. This concept has been controversial, since TRIM5s best-known role as a directly acting antiretroviral effector is autophagy independent. However, retroviral restriction is only one aspect of TRIM5 function. We demonstrate that autophagy is crucial to another TRIM5 action: its role as a pattern-recognition receptor. We show that autophagy machinery is required for TRIM5 to transduce antiviral signaling and to establish an antiretroviral state. Our data indicate that autophagy provides TRIM5 with a platform upon which to activate antiviral responses.