Coinfections with opportunistic and pathogenic bacteria induce human immunodeficiency virus (HIV) replication through microbial antigen activation of NF-kappaB. Here, we assessed whether HIV type 1 protease inhibitors (PI) block microbial antigen activation of NF-kappaB. Human microvessel endothelial cells were transiently transfected with either endothelial cell-leukocyte adhesion molecule NF-kappaB luciferase or interleukin 6 (IL-6) promoter luciferase constructs by using FuGENE 6, and they were treated with PI (nelfinavir, ritonavir, or saquinavir) prior to stimulation with the Toll-like receptor 4 (TLR4) and TLR2 ligands, with lipopolysaccharide (LPS), soluble Mycobacterium tuberculosis factor, or Staphylococcus epidermidis phenol-soluble modulin, respectively, or with tumor necrosis factor alpha (TNF-alpha). Luciferase activity was measured by using a Promega luciferase kit. TNF-alpha release from the supernatant was measured by enzyme-linked immunosorbent assay. Cell death was assessed by lactate dehydrogenase assay. We observed that PI pretreatment blocked the TLR2- and TLR4- as well as the TNF-alpha-mediated NF-kappaB activation, in a dose-dependent manner. PI pretreatment also blocked the LPS-induced IL-6 promoter transactivation and TNF-alpha secretion. These data suggest that PI block HIV replication not only by inhibiting the HIV protease but also by blocking the TLR- and TNF-alpha-mediated NF-kappaB activation and proinflammatory cytokine production. These findings may help explain the immunomodulatory effects of PI, and they suggest an advantage for PI-containing drug regimens in the treatment of HIV-infected patients who are coinfected with opportunistic and pathogenic bacteria.
Opportunistic infections, common in HIV-1-infected patients, increase HIV replication; however, the intracellular signaling mechanisms involved are not clearly known. We have shown that Toll-like receptor 2 (TLR2), TLR4, and TLR9 mediate microbial Ag-induced HIV-long terminal repeat (HIV-LTR) trans-activation and HIV-1 replication, and that LPS-induced HIV-LTR trans-activation is mediated through myeloid differentiation adapter protein. Recently, Toll-IL-1R domain-containing adapter protein (TIRAP) has been identified as an adapter molecule that mediates responses to TLR2 and TLR4 ligands, and TIRAP was suggested to provide signaling specificity for different TLRs. Rac1, a small GTP-binding protein that is activated upon LPS stimulation of macrophages, activates phosphatidylinositol 3-kinase and Akt and leads to NF-kappaB activation. The roles of Rac1 and TIRAP in LPS activation of HIV replication is not known. In the present study we show that LPS stimulation of human microvessel endothelial cells leads to Rac1 activation. Constitutively active Rac1 (Rac1V12) simulated the effect of LPS to activate HIV-LTR, whereas the expression of dominant negative Rac1 (Rac1N17) partially blocked LPS-induced HIV-LTR trans-activation. Rac1V12-induced HIV-LTR activation was independent of myeloid differentiation adapter protein, and dominant negative TIRAP blocked Rac1V12-induced HIV-LTR trans-activation. In this study we show for the first time that activation of Rac1 leads to HIV-LTR trans-activation, and this is mediated through TIRAP. Together these results underscore the importance of Rac1 and TIRAP in TLR4 activation of HIV replication and help delineate the signaling pathways induced by TLRs to mediate microbial Ag-induced HIV replication and HIV pathogenesis.
Opportunistic infections are common in HIV-infected patients; they activate HIV replication and contribute to disease progression. In the present study we examined the role of Toll-like receptor 2 (TLR2) and TLR9 in HIV-long terminal repeat (HIV-LTR) trans-activation and assessed whether TLR4 synergized with TLR2 or TLR9 to induce HIV replication. Soluble Mycobacterium tuberculosis factor (STF) and phenol-soluble modulin from Staphylococcus epidermidis induced HIV-LTR trans-activation in human microvessel endothelial cells cotransfected with TLR2 cDNA. Stimulation of ex vivo spleen cells from HIV-1 transgenic mice with TLR4, TLR2, and TLR9 ligands (LPS, STF, and CpG DNA, respectively) induced p24 Ag production in a dose-dependent manner. Costimulation of HIV-1 transgenic mice spleen cells with LPS and STF or CpG DNA induced TNF-alpha and IFN-gamma production in a synergistic manner and p24 production in an additive fashion. In the THP-1 human monocytic cell line stably expressing the HIV-LTR-luciferase construct, LPS and STF also induced HIV-LTR trans-activation in an additive manner. This is the first time that TLR2 and TLR9 and costimulation of TLRs have been shown to induce HIV replication. Together these results underscore the importance of TLRs in bacterial Ag- and CpG DNA-induced HIV-LTR trans-activation and HIV replication. These observations may be important in understanding the role of the innate immune system and the molecular mechanisms involved in the increased HIV replication and HIV disease progression associated with multiple opportunistic infections.