HIV-1 establishes latent reservoirs, which rapidly release new infectious viruses after therapy interruption and lead to HIV persistence. Macrophages are an important HIV reservoir. They are primary targets for HIV-1 infection and infiltrated in almost all organs, which can spread HIV throughout the body. Unfortunately, current HIV-1 drugs do not work in macrophages as effectively as in T cells, and they cannot cross tissue barriers for delivery to the tissue-sanctuary sites such as brain macrophages. Thus, new anti-HIV mechanism is expected for development of innovative methods to treat HIV-infected macrophages. Vpr is a HIV-1 auxiliary protein, which is also produced by HIV-2 and SIV, and conserved in these viruses. Vpr enhances viral replication in terminally differentiated (non-dividing) myeloid cells, but this mechanism remains unclear. Recently, we uncovered that Vpr could increase HIV-1 Env expression and promote viral replication in monocyte-derived dendritic cells (MDDC). When Vpr was not expressed, Env was rapidly degraded via ER-associated protein degradation (ERAD) pathway, resulting in inhibition of viral replication; when Vpr was expressed, the Env stability was restored, resulting in enhancement of viral replication. These results demonstrate that Vpr blocks Env degradation via ERAD. HIV-1 Env glycoproteins are produced through the classical secretory pathway, which are folded into natural conformation in the ER via the oxidative folding process. The ER protein folding process is error-prone, so eukaryotes have evolved the ERAD quality control pathway to specifically degrade misfolded glycoproteins. HIV-1 Env glycoproteins have a large number of cysteine residues that must be cross-linked into 10 disulfide bonds, so the Env folding efficiency is extremely lower: over 80% Env proteins are misfolded and retained in the ER for degradation. Notably, Vpr has been found to activate the oxidative stress pathway. Here, we propose to study the molecular mechanisms of how Vpr protects Env from the ERAD pathway and how ERAD targets Env for degradation in macrophages. Our general hypothesis is that Vpr promotes Env oxidative folding to increase Env expression in macrophages. We will have three specific aims to elucidate: 1) The role of redox signaling pathway in Env expression in macrophages; 2) The role of Vpr in Env expression in macrophages; 3) The mechanism of Env degradation in macrophages. We believe that by elucidating this newly discovered HIV-host arm race, we will identify new drug targets to specifically block the release of infectious HIV-1 particles from macrophages, resulting in disruption of this HIV reservoir.
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