Visualization of a proteasome-independent intermediate during restriction of HIV-1 by rhesus TRIM5alpha.

TRIM5 proteins constitute a class of restriction factors that prevent host cell infection by retroviruses from different species. TRIM5alpha restricts retroviral infection early after viral entry, before the generation of viral reverse transcription products. However, the underlying restriction mechanism remains unclear. In this study, we show that during rhesus macaque TRIM5alpha (rhTRIM5alpha)-mediated restriction of HIV-1 infection, cytoplasmic HIV-1 viral complexes can associate with concentrations of TRIM5alpha protein termed cytoplasmic bodies. We observe a dynamic interaction between rhTRIM5alpha and cytoplasmic HIV-1 viral complexes, including the de novo formation of rhTRIM5alpha cytoplasmic body-like structures around viral complexes. We observe that proteasome inhibition allows HIV-1 to remain stably sequestered into large rhTRIM5alpha cytoplasmic bodies, preventing the clearance of HIV-1 viral complexes from the cytoplasm and revealing an intermediate in the restriction process. Furthermore, we can measure no loss of capsid protein from viral complexes arrested at this intermediate step in restriction, suggesting that any rhTRIM5alpha-mediated loss of capsid protein requires proteasome activity.