Abstract
HIV-1 Tat protein contributes to HIV-neuropathogenesis in several ways including its ability to be taken up by uninfected bystander CNS cells and to activate inflammatory host genes causing synaptic injury. Here, we report that in the globally dominant HIV-1 clade C, Tat displays a naturally occurring polymorphism, R57S, in its basic domain, which mediates cellular uptake. We examined the effect of this polymorphism on Tat uptake and its consequences for cellular gene transactivation. In decapeptides corresponding to the basic domain, a R57S substitution caused up to a 70% reduction in uptake. We also used a transcellular Tat transactivation assay, where we expressed Tat proteins of HIV-1 clade B (Tat-B) or C (Tat-C) or their position 57 variants in HeLa cells. We quantified the secreted Tat proteins and measured their uptake by TZM-bl cells, which provide readout via an HIV-1 Tat-responsive luciferase gene. Transactivation by Tat-B was significantly reduced by R57S substitution, while that of Tat-C was enhanced by the reciprocal S57R substitution. Finally, we exposed microglia to Tat variants and found that R57 is required for maximal neuroinflammation. The R57S substitution dampened this response. Thus, genetic variations can modulate the ability of HIV-1 Tat to systemically disseminate neuroinflammation.
Highlights
HIV Tat protein can be detected in the CNS of patients receiving cART, even with well-controlled peripheral and CNS viral loads[9]
We describe the functional effects of a polymorphism at residue 57 in the HIV-1 Tat cell-penetrating peptide (CPP) motif, which has been shown to mediate the uptake of extracellular Tat by bystander/uninfected cells
We used TZM-bl cells, with a Tat-responsive LTR reporter to compare the relative uptake of Tat residue 57 variants with similar transactivation capabilities (i. e., Tat proteins of HIV-1 clade B (Tat-B)*/Tat-B*-R57S; Tat-C/Tat-C-S57R)
Summary
HIV Tat protein can be detected in the CNS of patients receiving cART, even with well-controlled peripheral and CNS viral loads[9]. To assess the biological impact of Tat-driven transactivation in the context of HIV neuropathogenesis, we exposed microglial cells to media from Tat-transfected cells, and observed a higher level of induction of proinflammatory cytokine genes – TNFα, IL-6, IL-8, IL-1β and CXCL1 - in response to the more efficient uptake of Tat-R57 when compared to Tat-S57.
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