HIV-1 Tat Protein Activates both the MyD88 and TRIF Pathways To Induce Tumor Necrosis Factor Alpha and Interleukin-10 in Human Monocytes

Abstract

In this study, we show that the HIV-1 Tat protein interacts with rapid kinetics to engage the Toll-like receptor 4 (TLR4) pathway, leading to the production of proinflammatory and anti-inflammatory cytokines. The pretreatment of human monocytes with Tat protein for 10 to 30 min suffices to irreversibly engage the activation of the TLR4 pathway, leading to the production of tumor necrosis factor alpha (TNF-␣) and interleukin-10 (IL-10), two cytokines strongly implicated in the chronic activation and dysregulation of the immune system during HIV-1 infection. Therefore, this study analyzed whether the HIV-1 Tat protein is able to activate these two pathways separately or simultaneously. Using three complementary approaches, including mice deficient in the MyD88, TIRAP/MAL, or TRIF adaptor, biochemical analysis, and the use of specific small interfering RNAs (siRNAs), we demonstrated (i) that Tat was able to activate both the MyD88 and TRIF pathways, (ii) the capacity of Tat to induce TIRAP/MAL degradation, (iii) the crucial role of the MyD88 pathway in the production of Tat-induced TNF-␣ and IL-10, (iv) a reduction but not abrogation of IL-10 and TNF-␣ by Tat-stimulated macrophages from mice deficient in TIRAP/MAL, and (v) the crucial role of the TRIF pathway in Tat-induced IL-10 production. Further, we showed that downstream of the MyD88 and TRIF pathways, the Tat protein activated the protein kinase C (PKC) ␤II isoform, the mitogen-activated protein (MAP) kinases p38 and extracellular signal-regulated kinase 1/2 (ERK1/2), and NF-B in a TLR4-dependent manner. Collectively, our data show that by recruiting the TLR4 pathway with rapid kinetics, the HIV-1 Tat protein leads to the engagement of both the MyD88 and TRIF pathways and to the activation of PKC, MAP kinase, and NF-B signaling to induce the production of TNF-␣ and IL-10. IMPORTANCEIn this study, we demonstrate that by recruiting the TLR4 pathway with rapid kinetics, the HIV-1 Tat protein leads to the engagement of both the MyD88 and TRIF pathways and to the activation of PKC-␤II, MAP kinase, and NF-B signaling to induce the production of TNF-␣ and IL-10, two cytokines strongly implicated in the chronic activation and dysregulation of the immune system during HIV-1 infection. Thus, it may be interesting to target Tat as a pathogenic factor early after HIV-1 infection. This could be achieved either by vaccination approaches including Tat as an immunogen in potential candidate vaccines or by developing molecules capable of neutralizing the effect of the Tat protein.

Activated NK cells kill hepatic stellate cells via p38/PI3K signaling in a TRAIL-involved degranulation manner

“…IL‐18 signaling is MyD88 (Myeloid differentiation primary response gene 88) dependent, whereas poly I:C/TLR3 signaling is TIR‐domain‐containing adapter‐inducing interferon‐β (TRIF) dependent and MyD88 independent . Downstream of TRIF and MyD88, signaling as ERK, NF‐κB, IFN regulatory factor 5 (IRF5), and p38 could be the coordinates of these 2 pathways. IL‐12 plus IL‐18 stimulate greater IFN‐γ secretion by resting NK cells through stabilization of IFN‐γ mRNA via p38 MAPK, and highly augment human NK cell cytotoxicity and degranulation in vitro .…”

Targeting TNF and TNF Receptor Pathway in HIV-1 Infection: from Immune Activation to Viral Reservoirs

“…Both MyD88 and TIR-domain-containing adapter-inducing interferon-β (TRIF) axes recruit the TLR4 pathway, following stimulation by Tat, and lead to the activation of protein kinase C beta2 isoform, MAP kinase, and NF-κB, thus resulting in enhanced TNF production in monocytes [70]. …”

Conformational dynamics of cancer-associated MyD88-TIR domain mutant L252P (L265P) allosterically tilts the landscape toward homo-dimerization

“…MyD88 is a frequently altered gene in many studies (Xia et al, 2015;Cani et al, 2016), with potentially clinically relevant hot spot gain-of-function mutations identified in 71% of diffuse large B-cell lymphomas and 25% of marginal zone lymphomas (Cani et al, 2016). During an HIV-1 infection, the HIV-1 tat protein leads to the engagement of both MyD88 and TRIF pathways and to the activation of the cytokines which is strongly implicated in the chronic activation and dysregulation of the immune system (Planes et al, 2016).…”