HIV and the multifaceted deregulation of interleukin-12 through Vpr-GR, CD14, TLR4 expression and SAPK signalling

Abstract

Infection with HIV is characterized by a progressive loss of cell mediated immunity and altered cytokine production. The decreased production of the cytokine IL-12 is pivotal in the multi-faceted immune pathogenesis of HIV infection. The objective of this study was to understand the mechanisms of IL-12 production and HIV-mediated inhibition of IL-12 in primary human monocytes. The HIV-mediated effect on LPS-induced IL-12 p40 was investigated through the evaluation of 1) the stress activated protein kinase (SAPK) pathway, 2) HIV-Vpr interactions with the glucocorticoid receptor (GR), and 3) the expression of LPS receptors CD14 and TLR4. Our results indicate that HIV may utilize the SAPK pathway through p38 and JNK to inhibit LPS-induced IL-12 p40 nuclear factors Sp-1, Ets-2, NFkappaB, and AP-1 binding to the promoter, leading to decreased promoter activity, mRNA expression and IL-12 p40 protein production. HIV viral tropism, extracellular Vpr, and intracellular Vpr expressed through a retroviral system were further evaluated for their effects on upstream CDI4, TLR4 and GR expression in the presence and absence of LPS stimulation. In vitro HIV infection resulted in an increase in CD14 expression and a decrease in TLR4 expression both with and without LPS stimulation, while there was no effect on GR expression. The C-terminal Vpr peptide containing the GR binding motif inhibited LPS-induced IL-12 p40 in a GR dependent manner. Vpr further enhanced the GR ligand, dexamethasone, mediated inhibition of IL-12 p40 production. The addition of extracellular Vpr resulted in increased CD14 and GR expression and decreased TLR4 expression following LPS stimulation. Intracellular expression of Vpr inhibited LPS-induced IL-12 p40 and TLR4 receptor expression in a GR dependent mechanism. Furthermore, intracellular expression of Vpr inhibited the CD14 receptor response to LPS while having no effect on GR. The receptor expression and response to intracellular Vpr expression were different in monocytes cultured within PBMC and monocytes cultured in isolation. Overall this study furthers our understanding of HIV-mediated inhibition of IL-12 p40 and highlights a new potential therapeutic target for development to restore IL-12 p40 by targeting the GR binding motif of Vpr.