Suppression of HIV-1 viral replication and cellular pathogenesis by a novel p38/JNK kinase inhibitor

Integrated analysis to study the interplay between post-translational modifications (PTM) in hepatitis C virus proteins and hepatocellular carcinoma (HCC) development

Many PTMs dysregulation is known to be the major cause of many cancers including HCV induced HCC. PTMs of hepatitis C virus (HCV) regions NS3/4A, NS5A and NS5B are crucial for proper protein functions and replication that directly affect the generation of infectious virus particles and completion of its life cycle. In this study, we have performed comprehensive analysis of PTMs within HCV non-structural proteins (NS3/4A, NS5A and NS5B) through bioinformatics analysis to examine post-translational crosstalk between phosphorylation, palmitoylation, methylation, acetylation and ubiquitination sites in selected viral proteins. Our analysis has revealed many highly putative PTMs sites that are also conserved among major genotypes conferring the importance of these sites. We have also analysed viral 3D structures in their modified and unmodified forms to address extent and signatures of structural changes upon PTM. This study provides evidence that PTMs induce significant conformational changes and make viral proteins more stable. To find the potential role of PTMs in HCV induced HCC, docking analysis between selected viral proteins and p38-MAPK has been performed which also confirms their strong association with HCV induced HCC. The major findings proposed that PTMs at specific sites of HCV viral proteins could dysregulate specific pathways that cause the development of HCC.

p38 activation and viral infection

Viruses completely rely on the energy and metabolic systems of host cells for life activities. Viral infections usually lead to cytopathic effects and host diseases. To date, there are still no specific clinical vaccines or drugs against most viral infections. Therefore, understanding the molecular and cellular mechanisms of viral infections is of great significance to prevent and treat viral diseases. A variety of viral infections are related to the p38 MAPK signalling pathway, and p38 is an important host factor in virus-infected cells. Here, we introduce the different signalling pathways of p38 activation and then summarise how different viruses induce p38 phosphorylation. Finally, we provide a general summary of the effect of p38 activation on virus replication. Our review provides integrated data on p38 activation and viral infections and describes the potential application of targeting p38 as an antiviral strategy.

Inhibition of apoptosis signal-regulating kinase 1 mitigates the pathogenesis of human immunodeficiency virus-associated nephropathy

BACKGROUND

Chronic kidney disease (CKD) is a common cause of morbidity and mortality in human immunodeficiency virus (HIV)-positive individuals. Among the HIV-related kidney diseases, HIV-associated nephropathy (HIVAN) is a rapidly progressive renal disease characterized by collapsing focal glomerulosclerosis (GS), microcystic tubular dilation, interstitial inflammation and fibrosis. Although the incidence of end-stage renal disease due to HIVAN has dramatically decreased with the widespread use of antiretroviral therapy, the prevalence of CKD continues to increase in HIV-positive individuals. Recent studies have highlighted the role of apoptosis signal-regulating kinase 1 (ASK1) in driving kidney disease progression through the activation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase and selective ASK-1 inhibitor GS-444217 was recently shown to reduce kidney injury and disease progression in various experimental models. Therefore we examined the efficacy of ASK1 antagonism by GS-444217 in the attenuation of HIVAN in Tg26 mice.

METHODS

GS-444217-supplemented rodent chow was administered in Tg26 mice at 4 weeks of age when mild GS and proteinuria were already established. After 6 weeks of treatment, the kidney function assessment and histological analyses were performed and compared between age- and gender-matched control Tg26 and GS-444217-treated Tg26 mice.

RESULTS

GS-444217 attenuated the development of GS, podocyte loss, tubular injury, interstitial inflammation and renal fibrosis in Tg26 mice. These improvements were accompanied by a marked reduction in albuminuria and improved renal function. Taken together, GS-4442217 attenuated the full spectrum of HIVAN pathology in Tg26 mice.

CONCLUSIONS

ASK1 signaling cascade is central to the development of HIVAN in Tg26 mice. Our results suggest that the select inhibition of ASK1 could be a potential adjunctive therapy for the treatment of HIVAN.

Different Patterns of HIV-1 Replication in MACROPHAGES is Led by Co-Receptor Usage

Background and objectives: To enter the target cell, HIV-1 binds not only CD4 but also a co-receptor β-chemokine receptor 5 (CCR5) or α chemokine receptor 4 (CXCR4). Limited information is available on the impact of co-receptor usage on HIV-1 replication in monocyte-derived macrophages (MDM) and on the homeostasis of this important cellular reservoir. Materials and Methods: Replication (measured by p24 production) of the CCR5-tropic 81A strain increased up to 10 days post-infection and then reached a plateau. Conversely, the replication of the CXCR4-tropic NL4.3 strain (after an initial increase up to day 7) underwent a drastic decrease becoming almost undetectable after 10 days post-infection. The ability of CCR5-tropic and CXCR4-tropic strains to induce cell death in MDM was then evaluated. While for CCR5-tropic 81A the rate of apoptosis in MDM was comparable to uninfected MDM, the infection of CXCR4-tropic NL4.3 in MDM was associated with a rate of 14.3% of apoptotic cells at day 6 reaching a peak of 43.5% at day 10 post-infection. Results: This suggests that the decrease in CXCR4-tropic strain replication in MDM can be due to their ability to induce cell death in MDM. The increase in apoptosis was paralleled with a 2-fold increase in the phosphorylated form of p38 compared to WT. Furthermore, microarray analysis showed modulation of proapoptotic and cancer-related genes induced by CXCR4-tropic strains starting from 24 h after infection, whereas CCR5 viruses modulated the expression of genes not correlated with apoptotic-pathways. Conclusions: In conclusion, CXCR4-tropic strains can induce a remarkable depletion of MDM. Conversely, MDM can represent an important cellular reservoir for CCR5-tropic strains supporting the role of CCR5-usage in HIV-1 pathogenesis and as a pharmacological target to contribute to an HIV-1 cure.

Different involvement of the MAPK family in inflammatory regulation in human pulmonary microvascular endothelial cells stimulated with LPS and IFN-γ

Pulmonary endothelial injury is central in the pathogenesis of acute lung injury (ALI). The MAPK signaling cascades are generally thought to be involved in the molecular mechanism underlying the ALI development, but their roles in pulmonary endothelial injury is poorly understood. We thus examined the involvement of the MAPK family member in inflammatory responses of human pulmonary microvascular endothelial cells (HPMVECs) stimulated with LPS and IFN-γ. HPMVECs were found to exhibit the upregulation of expression of Toll-like receptor 4 by IFN-γ, resulting in potentiation of inflammatory cytokine release by LPS stimulation. All MAPKs, ERK1/2, JNK, and p38, were activated by simultaneous stimulation with LPS/IFN-γ. JNK activation in cells stimulated with LPS/IFN-γ was significantly potentiated by the two different p38 inhibitors, SB203580 and RWJ67657, suggesting the negative regulation of JNK activation by p38 in HPMVECs. The mRNA and protein expression levels of ICAM-1 were eliminated by the JNK inhibitor, suggesting that ICAM-1 expression is positively regulated by JNK. The p38 inhibitor significantly enhanced ICAM-1 expression. ERK1/2 activation was not responsible for the LPS/IFN-γ-induced ICAM-1 upregulation in HPMVECs. THP-1 monocyte adhesion to HPMVECs under LPS/IFN-γ stimulation was inhibited by the JNK inhibitor and enhanced by the p38 inhibitor. We conclude that, in HPMVECs stimulated with LPS/IFN-γ, JNK mediates ICAM-1 expression that can facilitate leukocyte adherence and transmigration, while p38 MAPK negatively regulates the upregulation of ICAM-1 through inhibition of JNK activation.

Hsa-let-7c-5p augments enterovirus 71 replication through viral subversion of cell signaling in rhabdomyosarcoma cells

Background

Human enterovirus 71 (EV71) causes severe hand, foot and mouse disease, accompanied by neurological complications. During the interaction between EV71 and the host, the virus subverts host cell machinery for its own replication. However, the roles of microRNAs (miRNAs) in this process remain obscure.

Results

In this study, we found that the miRNA hsa-let-7c-5p was significantly upregulated in EV71-infected rhabdomyosarcoma cells. The overexpression of hsa-let-7c-5p promoted replication of the virus, and the hsa-let-7c-5p inhibitor suppressed viral replication. Furthermore, hsa-let-7c-5p targeted mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4) and inhibited its expression. Interestingly, downregulation of MAP4K4 expression led to an increase in EV71 replication. In addition, MAP4K4 knockdown or transfection with the hsa-let-7c-5p mimic led to activation of the c-Jun NH2-terminal kinase (JNK) signaling pathway, whereas the hsa-let-7c-5p inhibitor inhibited activation of this pathway. Moreover, EV71 infection promoted JNK pathway activation to facilitate viral replication.

Conclusions

Our data suggested that hsa-let-7c-5p facilitated EV71 replication by inhibiting MAP4K4 expression, which might be related to subversion of the JNK pathway by the virus. These results may shed light on a novel mechanism underlying the defense of EV71 against cellular responses. In addition, these findings may facilitate the development of new antiviral strategies for use in future therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-017-0135-9) contains supplementary material, which is available to authorized users.

Cocaine Enhances HIV-1 Transcription in Macrophages by Inducing p38 MAPK Phosphorylation

Cocaine is a commonly used illicit drug among HIV-1 infected individuals and is known to increase HIV-1 replication in permissive cells including PBMCs, CD4(+) T cells, and macrophages. Cocaine's potentiating effects on HIV-1 replication in macrophages- the primary targets of the virus in the central nervous system, has been suggested to play an important role in HIV-1 neuro-pathogenesis. However, the mechanism by which cocaine enhances HIV-1 replication in macrophages remain poorly understood. Here, we report the identification of cocaine-induced signaling events that lead to enhanced HIV-1 transcription in macrophages. Treatment of physiologically relevant concentrations of cocaine enhanced HIV-1 transcription in a dose-dependent manner in infected THP-1 monocyte-derived macrophages (THP-1macs) and primary monocyte-derived macrophages (MDMs). Toward decoding the underlying mechanism, results presented in this report demonstrate that cocaine induces the phosphorylation of p38 mitogen activated protein kinase (p38 MAPK), a known activator of HIV-1 transcription. We also present data suggesting that the p38 MAPK-driven HIV-1 transcription is dependent on the induction of mitogen- and stress-activated protein kinase 1 (MSK1). Consequently, MSK1 mediates the phosphorylation of serine 10 residue of histone 3 (H3 Ser10), which is known to activate transcription of genes including that of HIV-1 in macrophages. Importantly, our results show that inhibition of p38 MAPK/MSK1 signaling by specific pharmacological inhibitors abrogated the positive effect of cocaine on HIV-1 transcription. These results validate the functional link between cocaine and p38 MAPK/MSK1 pathways. Together, our results demonstrate for the first time that the p38 MAPK/MSK1 signaling pathway plays a critical role in the cocaine-induced potentiating effects on HIV-1 infection, thus providing new insights into the interplay between cocaine abuse and HIV-1 neuro-pathogenesis.

JNK1 Derived from Orange-Spotted Grouper, Epinephelus coioides, Involving in the Evasion and Infection of Singapore Grouper Iridovirus (SGIV)

c-Jun N-terminal kinase (JNK) regulates cellular responses to various extracellular stimuli, environmental stresses, pathogen infections, and apoptotic agents. Here, a JNK1, Ec-JNK1, was identified from orange-spotted grouper, Epinephelus coioides. Ec-JNK1 has been found involving in the immune response to pathogen challenges in vivo, and the infection of Singapore grouper iridovirus (SGIV) and SGIV-induced apoptosis in vitro. SGIV infection activated Ec-JNK1, of which phosphorylation of motif TPY is crucial for its activity. Over-expressing Ec-JNK1 phosphorylated transcription factors c-Jun and promoted the infection and replication of SGIV, while partial inhibition of the phosphorylation of Ec-JNK1 showed the opposite effects by over-expressing the dominant-negative EcJNK1-Δ183-185 mutant. Interestingly, SGIV enhanced the viral infectivity by activating Ec-JNK1 which in turn drastically inhibited the antiviral responses of type 1 IFN, indicating that Ec-JNK1 could be involved in blocking IFN signaling during SGIV infection. In addition, Ec-JNK1 enhanced the activation of AP-1, p53, and NF-κB, and resulted in increasing the levels of SGIV-induced cell death. The caspase 3-dependent activation correlated with the phosphorylation of Ec-JNK1 and contributed to SGIV-induced apoptosis. Taken together, SGIV modulated the phosphorylation of Ec-JNK1 to inactivate the antiviral signaling, enhance the SGIV-induced apoptosis and activate transcription factors for efficient infection and replication. The “positive cooperativity” molecular mechanism mediated by Ec-JNK1 contributes to the successful evasion and infection of iridovirus pathogenesis.

Impaired IL-2 expression in latent HIV-1 infection

Regarding the T cell function in HIV-1 infection, activation of T cells is enhanced in acutely HIV-1-infected T cells upon stimuli. However, T cell immune responses underlying the activation of T cell receptor (TCR) signaling molecules and interleukin (IL)-2 production in latently HIV-1-infected cells are poorly understood. The expression and activation of TCR components and its downstream molecules in acutely and latently HIV-1-infected T cells were compared using quantitative reverse transcription polymerase chain reaction (RT-PCR) for mRNA expression and enzyme-linked immunosorbent assay (ELISA) for levels of IL-2 in phytohemagglutinin M (PHA-M). The levels of T cell surface molecules and TCR signaling molecules in latently HIV-1-infected cells were greatly decreased without changes in their mRNA levels. In addition, downstream TCR-signaling molecules in latently HIV-1-infected cells were not activated even in the presence of PHA-M. The phosphorylation of mitogen-activated protein kinases (MAPKs) in the presence of PHA-M was weakly induced in latently HIV-1-infected cells but was greater in acutely HIVNL4-3-infected cells. Finally, the production of IL-2 was significantly decreased in latently HIV-1-infected cells compared with uninfected parent cells. Thus, IL-2-related immunological functions in latently HIV-1-infected T cells were markedly impaired even in the presence of stimuli.

Type I Interferon at the Interface of Antiviral Immunity and Immune Regulation: The Curious Case of HIV-1

Type I interferon (IFN-I) play a critical role in the innate immune response against viral infections. They actively participate in antiviral immunity by inducing molecular mechanisms of viral restriction and by limiting the spread of the infection, but they also orchestrate the initial phases of the adaptive immune response and influence the quality of T cell immunity. During infection with the human immunodeficiency virus type 1 (HIV-1), the production of and response to IFN-I may be severely altered by the lymphotropic nature of the virus. In this review I consider the different aspects of virus sensing, IFN-I production, signalling, and effects on target cells, with a particular focus on the alterations observed following HIV-1 infection.

Contrasting roles of mitogen-activated protein kinases in cellular entry and replication of hepatitis C virus: MKNK1 facilitates cell entry

The human kinome comprises over 800 individual kinases. These contribute in multiple ways to regulation of cellular metabolism and may have direct and indirect effects on virus replication. Kinases are tempting therapeutic targets for drug development, but achieving sufficient specificity is often a challenge for chemical inhibitors. While using inhibitors to assess whether c-Jun N-terminal (JNK) kinases regulate hepatitis C virus (HCV) replication, we encountered unexpected off-target effects that led us to discover a role for a mitogen-activated protein kinase (MAPK)-related kinase, MAPK interacting serine/threonine kinase 1 (MKNK1), in viral entry. Two JNK inhibitors, AS601245 and SP600125, as well as RNA interference (RNAi)-mediated knockdown of JNK1 and JNK2, enhanced replication of HCV replicon RNAs as well as infectious genome-length RNA transfected into Huh-7 cells. JNK knockdown also enhanced replication following infection with cell-free virus, suggesting that JNK actively restricts HCV replication. Despite this, AS601245 and SP600125 both inhibited viral entry. Screening of a panel of inhibitors targeting kinases that may be modulated by off-target effects of AS601245 and SP600125 led us to identify MKNK1 as a host factor involved in HCV entry. Chemical inhibition or siRNA knockdown of MKNK1 significantly impaired entry of genotype 1a HCV and HCV-pseudotyped lentiviral particles (HCVpp) in Huh-7 cells but had only minimal impact on viral RNA replication or cell proliferation and viability. We propose a model by which MKNK1 acts to facilitate viral entry downstream of the epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase (ERK), both of which have been implicated in the entry process.

Interplay between Hepatitis C Virus and Redox Cell Signaling

Hepatitis C virus (HCV) infects approximately 3% of the world’s population. Currently licensed treatment of HCV chronic infection with pegylated-interferon-α and ribavirin, is not fully effective against all HCV genotypes and is associated to severe side effects. Thus, development of novel therapeutics and identification of new targets for treatment of HCV infection is necessary. Current opinion is orienting to target antiviral drug discovery to the host cell pathways on which the virus relies, instead of against viral structures. Many intracellular signaling pathways manipulated by HCV for its own replication are finely regulated by the oxido-reductive (redox) state of the host cell. At the same time, HCV induces oxidative stress that has been found to affect both virus replication as well as progression and severity of HCV infection. A dual role, positive or negative, for the host cell oxidized conditions on HCV replication has been reported so far. This review examines current information about the effect of oxidative stress on HCV life cycle and the main redox-regulated intracellular pathways activated during HCV infection and involved in its replication.

Inhibition of p38-MAPK alters SRC coactivation and estrogen receptor phosphorylation

The p38 mitogen activated protein kinase pathway (MAPK) is known to promote cell survival, endocrine therapy resistance and hormone independent breast cancer cell proliferation. Therefore, we utilized the novel p38 inhibitor RWJ67657 to investigate the relevance of targeting this pathway in the ER (+) breast cancer cell line MCF-7. Our results show that RWJ67657 inhibits both basal and estrogen stimulated phosphorylation of p38α, resulting in decreased activation of the downstream p38α targets hsp27 and MAPAPK. Furthermore, inhibition of p38α by RWJ67657 blocks clonogenic survival of MCF-7 cells with little effect on non-cancerous breast epithelial cells. Even though p38α is known to phosphorylate ERα at residue within ER's hinge region at Thr311, resulting in increased ERα transcriptional activation, our results suggest RWJ67657 inhibits the p38α-induced activation of ER by targeting both the AF-1 and AF-2 activation domains within ERα. We further show that RWJ67657 decreases the transcriptional activity of the ER coactivators SRC-1, SRC-2 and SRC-3. Taken together, our results strongly suggest that in addition to phosphorylating Thr311 within ERα, p38α indirectly activates the ER by phosphorylation and stimulation of the known ERα coactivators, SRC-1, -2 and-3. Overall, our data underscore the therapeutic potential of targeting the p38 MAPK pathway in the treatment of ER (+) breast cancer.

Signaling through the P38 and ERK pathways: a common link between HIV replication and the immune response

One of the defining characteristics of HIV is its ability to manipulate the human immune response to promote its own replication. Since the beginning of the epidemic, there has been controversy whether a robust immune response to the virus is beneficial or detrimental for the host. Therefore, the effects of HIV on signaling pathways and cytokine production need to be characterized in order to distinguish between protective immune responses and inappropriate immune activation. Cytokine and biomarker expression during HIV infection results from the combined effects of intracellular signaling pathways orchestrated by kinases like P38 and ERK. The P38 and ERK Mitogen-Activated Protein Kinase (MAPK) pathways govern the regulation of cytokines (IL-2, IL-10, and TNF-α) as well biomarkers (PD-1, Fas/FasL, among others) that are skewed in chronic HIV infection. HIV utilizes the P38 and ERK pathways to produce new virions and to deplete CD4+ T cells from the host's immune system. Understanding the interplay between HIV and the cytokines induced by activation of the P38 and ERK pathways may provide insights into HIV immunopathogenesis and the development of a protective vaccine.

JNK1 is required for lentivirus entry and gene transfer

Although a lot of progress has been made in development of lentiviral vectors for gene therapy, the interactions of these vectors with cellular factors have not been explored adequately. Here we show that lentivirus infection phosphorylates JNK and that blocking the kinase activity of JNK decreases gene transfer in a dose-dependent manner, regardless of the viral envelope glycoprotein. Knockdown by small interfering RNA (siRNA) revealed that JNK1 but not JNK2 was required for productive gene transfer. The effect of JNK on gene transfer was not due to changes in the cell cycle, as JNK knockdown did not affect the cell cycle profile of target cells and even increased cell proliferation. In addition, confluent cell monolayers also exhibited JNK phosphorylation upon lentivirus infection and a dose-dependent decrease in gene transfer efficiency upon JNK inhibition. On the other hand, JNK activation was necessary for lentivirus internalization into the cell cytoplasm, while inhibition of JNK activity decreased virus entry without affecting binding to the cell surface. These experiments suggest that JNK is required for lentivirus entry into target cells and may have implications for gene transfer or for development of antiviral agents.

Mitogen-activated protein kinase p38 in HIV infection and associated brain injury

Infection with human immunodeficiency virus-1 (HIV-1) often leads to HIV-associated neurocognitive disorders (HAND) prior to the progression to acquired immunodeficiency syndrome (AIDS). At the cellular level, mitogen-activated protein kinases (MAPK) provide a family of signal transducers that regulate many processes in response to extracellular stimuli and environmental stress, such as viral infection. Recently, evidence has accumulated suggesting that p38 MAPK plays crucial roles in various pathological processes associated with HIV infection, ranging from macrophage activation to neurotoxicity and impairment of neurogenesis to lymphocyte apoptosis. Thus, p38 MAPK, which has generally been linked to stress-related signal transduction, may be an important mediator in the development of AIDS and HAND.

Proteomic analyses of the effects of drugs of abuse on monocyte-derived mature dendritic cells

Drug abuse has become a global health concern. Understanding how drug abuse modulates the immune system and how the immune system responds to pathogens associated with drug abuse, such hepatitis C virus (HCV) and human immunodeficiency virus (HIV-1), can be assessed by an integrated approach comparing proteomic analyses and quantitation of gene expression. Two-dimensional (2D) difference gel electrophoresis was used to determine the molecular mechanisms underlying the proteomic changes that alter normal biological processes when monocyte-derived mature dendritic cells were treated with cocaine or methamphetamine. Both drugs differentially regulated the expression of several functional classes of proteins including those that modulate apoptosis, protein folding, protein kinase activity, and metabolism and proteins that function as intracellular signal transduction molecules. Proteomic data were validated using a combination of quantitative, real-time PCR and Western blot analyses. These studies will help to identify the molecular mechanisms, including the expression of several functionally important classes of proteins that have emerged as potential mediators of pathogenesis. These proteins may predispose immunocompetent cells, including dendritic cells, to infection with viruses such as HCV and HIV-1, which are associated with drug abuse.

Role of mitogen-activated protein kinases, nuclear factor-kappaB, and interferon regulatory factor 3 in Toll-like receptor 4-mediated activation of HIV long terminal repeat

Monocytes/macrophages are known to represent a potential reservoir of human immunodeficiency virus type 1 (HIV-1), which ensures continuous replication of the virus in patients on highly active antiretroviral therapy (HAART). Infected macrophages are a highly productive source of HIV-1 during infections with common opportunistic pathogens. Previous studies report that toll like receptors (TLR)s play a role in HIV-1 replication in macrophages. Here, we investigate the three main pathways activated through TLR4 and the interactions with the HIV-1 long terminal repeat (LTR), using human embryonic kidney (HEK) 293 cells expressing TLR4 and transfected with a luciferase reporter under the control of the HIV-1 LTR. Here, we demonstrate, that TLR4-mediated activation of HIV-LTR is largely governed by the nuclear factor-kappaB pathway. Neither of the mitogen-activated protein kinases ERK1/2, JNK, or p38 nor the transcription factor interferon regulatory factor 3 were involved in the direct transactivation of HIV-LTR through stimulation of TLR4.

HIV-1 activates macrophages independent of Toll-like receptors

Background

Macrophages provide an interface between innate and adaptive immunity and are important long-lived reservoirs for Human Immunodeficiency Virus Type-1 (HIV-1). Multiple genetic networks involved in regulating signal transduction cascades and immune responses in macrophages are coordinately modulated by HIV-1 infection.

Methodology/Principal Findings

To evaluate complex interrelated processes and to assemble an integrated view of activated signaling networks, a systems biology strategy was applied to genomic and proteomic responses by primary human macrophages over the course of HIV-1 infection. Macrophage responses, including cell cycle, calcium, apoptosis, mitogen-activated protein kinases (MAPK), and cytokines/chemokines, to HIV-1 were temporally regulated, in the absence of cell proliferation. In contrast, Toll-like receptor (TLR) pathways remained unaltered by HIV-1, although TLRs 3, 4, 7, and 8 were expressed and responded to ligand stimulation in macrophages. HIV-1 failed to activate phosphorylation of IRAK-1 or IRF-3, modulate intracellular protein levels of Mx1, an interferon-stimulated gene, or stimulate secretion of TNF, IL-1β, or IL-6. Activation of pathways other than TLR was inadequate to stimulate, via cross-talk mechanisms through molecular hubs, the production of proinflammatory cytokines typical of a TLR response. HIV-1 sensitized macrophage responses to TLR ligands, and the magnitude of viral priming was related to virus replication.

Conclusions/Significance

HIV-1 induced a primed, proinflammatory state, M1_HIV, which increased the responsiveness of macrophages to TLR ligands. HIV-1 might passively evade pattern recognition, actively inhibit or suppress recognition and signaling, or require dynamic interactions between macrophages and other cells, such as lymphocytes or endothelial cells. HIV-1 evasion of TLR recognition and simultaneous priming of macrophages may represent a strategy for viral survival, contribute to immune pathogenesis, and provide important targets for therapeutic approaches.

Erythromycin derivatives inhibit HIV-1 replication in macrophages through modulation of MAPK activity to induce small isoforms of C/EBPbeta

Macrophages (MPhis) are a major source of HIV-1 especially in patients with tuberculosis. There are MPhis that are permissive and those that restrict HIV-1. Regulation of hematopoietic cell kinase (Hck) activity and selective expression of CCAAT enhancer binding protein beta (C/EBPbeta) isoforms greatly contribute to determine distinct susceptibility of MPhis to HIV-1. Resistance is attributable to reduced expression of Hck and augmented expression of an inhibitory small isoform of C/EBPbeta. Derivatives of erythromycin A (EMA) EM201 and EM703 inhibit the replication of HIV-1 in tissue MPhis, at posttranscriptional and translational levels. We demonstrate that EM201 and EM703 convert tissue MPhis from HIV-1 susceptible to HIV-1 resistant through down-regulation of Hck and induction of small isoforms of C/EBPbeta. These drugs inhibit p38MAPK activation which is expressed only in susceptible tissue MPhis. Activated CD4(+)T cells stimulate the viral replication in HIV-1 resistant MPhis through down-regulation of small isoforms of C/EBPbeta via activation of ERK1/2. EM201 and EM703 can inhibit the MAPK activation and inhibit the burst of viral replication produced when CD4(+)T cells and MPhis interact. These EM derivatives may be highly beneficial for repression of residual HIV-1 in the lymphoreticular system of HIV-1-infected patients and offer great promise for the creation of new anti-HIV drugs for the future treatment of AIDS patients.

Compartmentalised MAPK pathways

The mitogen-activated protein kinase (MAPK) pathway provides cells with the means to interpret external signal cues or conditions, and respond accordingly. This cascade regulates many cell functions such as differentiation, proliferation and migration. Through modulation of both the amplitude and duration of MAPK signalling, cells can control their responses to the multiple activators of the pathway. In addition, recent work has highlighted the importance of the cellular compartment from which the signalling occurs. Cells have developed intricate systems that enable them to localise MAPK components to specific subcellular domains in response to a particular stimulus. Consequently, different factors can activate the same kinase in separate locations. Crucial to this ability are molecular scaffolds, which act as signalling modules for MAPKs, confining them to the desired compartment. The participation of the MAPK network in fundamental physiological processes, such as cell proliferation and inflammation, and the derangement of the homeostasis that occurs in disease processes, renders MAPK a highly desirable target for therapeutic intervention. As we enhance our comprehension of scaffolds and other regulatory molecules, novel targets for drug design may be discovered that will afford selective and specific MAPK modulation.

Implication of p38 mitogen-activated protein kinase isoforms (alpha, beta, gamma and delta) in CD4+ T-cell infection with human immunodeficiency virus type I

The CD4(+) T-cell reduction characteristic of human immunodeficiency virus type 1 (HIV-1) infection is thought to result, in addition to infected T-cell death, mainly from uninfected bystander T-cell apoptosis. Nevertheless, the immunological and virological mechanisms leading to T-cell death during HIV-1 infection are not yet fully understood. In the present study, we analysed the individual implication of the p38 mitogen-activated protein kinase (MAPK) isoforms (p38alpha, p38beta, p38gamma and p38delta) during apoptosis induced by HIV-1, taking into account that HIV-1 replication is known to be blocked by p38 inhibitors. For this purpose, we used the SupT1 cell line, where death induced by HIV-1 mainly occurs by uninfected bystander cell apoptosis. A variety of SupT1-based cell lines were constructed constitutively expressing, under the control of cytomegalovirus promoter (PCMV), each dominant-negative (dn) p38 isoform and each wild-type p38 isoform as a control. An enhanced green fluorescent protein marker gene, under the control of the HIV-1 promoter, was inserted in all of them. These cell lines were infected with HIV-1 and analysed by flow cytometry. We found that survival in SupT1-based cell lines infected by HIV-1 was increased by the p38alphadn, p38gammadn and p38deltadn isoforms, but not by the p38betadn isoform. HIV-1 replication was delayed most by p38deltadn and to a lesser extent by p38alphadn and p38gammadn. Moreover, these three isoforms, p38alphadn, p38gammadn and p38deltadn, reduced apoptosis induced by HIV-1. These results suggest that, in SupT1-based cell lines, p38alpha, p38gamma and p38delta, but not p38beta, are implicated in both HIV-1 induced replication and apoptosis in infected and uninfected bystander cells.

Five years of progress on cyclin-dependent kinases and other cellular proteins as potential targets for antiviral drugs

In 1997-1998, the pharmacological cyclin-dependent kinase (CDK) inhibitors (PCIs) were independently discovered to inhibit replication of human cytomegalovirus, herpes simplex virus type 1 and HIV-1. The results from small clinical trials against cancer were then suggesting that PCIs could be safe enough to be used clinically. It was thus hypothesized that PCIs could have the potential to be developed as novel antivirals targeting cellular proteins. Consequently, Antiviral Chemistry & Chemotherapy published in 2001 the first review on the potential of CDKs, and cellular proteins in general, as potential targets for antivirals. The viral functions inhibited by PCIs, or their cellular targets, were then just starting to be characterized. The antiviral spectrum of PCIs and their effects on viral disease were still mostly untested. Even their actual specificity was not yet completely characterized. In addition, cellular proteins were not accepted as valid targets for antivirals. Significant progress has been made in the last 5 years in understanding the antiviral activities of PCIs and the potential roles of cellular proteins in general as targets for antivirals. The first clinical trials of the antiviral activities of PCIs and other inhibitors of cellular protein kinases have now been scheduled. Herein, we review the progress made since the publication of the first review on PCIs as potential antiviral drugs and on CDKs, and cellular proteins in general, as potential targets for antiviral drugs. We also highlight the major issues that still need to be addressed before PCIs or other drugs targeting cellular proteins can be developed as clinical antivirals.

"UnPAKing" human immunodeficiency virus (HIV) replication: using small interfering RNA screening to identify novel cofactors and elucidate the role of group I PAKs in HIV infection

In order to identify novel proviral host factors involved in human immunodeficiency virus (HIV) infection, we performed a screen of a small interfering RNA (siRNA) library targeting 5,000 genes with the highest potential for being targets for therapeutics. Many siRNAs in the library against known host factors, such as TSG101, furin, and CXCR4, were identified as inhibitors by the screen and thus served as internal validation. In addition, many novel factors whose knockdown inhibited infection were identified, including Pak3, a member of the serine/threonine group I PAK kinases. The HIV accessory factor Nef has been shown to associate with a PAK kinase, leading to enhanced viral production; however, the exact identity of the kinase has remained controversial. Prompted by the Pak3 screen hit, we further investigated the involvement of group I PAK kinases in HIV using siRNA. Contrary to the current literature, Pak1 depletion strongly inhibited HIV infection in multiple cell systems and decreased levels of integrated provirus, while Pak2 depletion showed no effect. Overexpression of a constitutively active Pak1 mutant also enhanced HIV infection, further supporting its role as the dominant PAK involved.

Activation of JNK-dependent pathway is required for HIV viral protein R-induced apoptosis in human monocytic cells: involvement of antiapoptotic BCL2 and c-IAP1 genes

Human immunodeficiency virus (HIV) accessory protein viral protein R (Vpr) plays a key role in virus replication and induces cell cycle arrest and apoptosis in various cell types including T cells and neuronal and tumor cells following infection with Vpr-expressing HIV isolates or exposure to the extracellular Vpr protein. The C-terminal Vpr peptide encompassing amino acids 52-96 (Vpr-(52-96)) is required for exerting the apoptotic effects, whereas the N-terminal Vpr-(1-45) peptide is responsible for virus transcription. We demonstrate that Vpr-(52-96) induced apoptosis in human promonocytic THP-1 cells and primary monocytes through the mitochondrial pathway in a caspase-dependent manner. To understand the regulation of Vpr-induced apoptosis, we investigated the signaling pathways, particularly the MAPKs, and the transcription factors involved. Although both Vpr-(52-96) and Vpr-(1-45) peptides induced phosphorylation of all the three members of the MAPKs, Vpr-(52-96)-activated JNK selectively induced apoptosis in monocytic cells through the mitochondrial pathway as determined by using JNK inhibitors SP60025, dexamethasone, curcumin, and JNK-specific small interfering RNAs. Furthermore Vpr-(52-96)-induced apoptosis was mediated by inhibition of downstream antiapoptotic Bcl2 and c-IAP1 genes whose expression could be restored following pretreatment with JNK-specific inhibitors. Overall the results suggest that Vpr-(52-96)-activated JNK plays a key role in inducing apoptosis through the down-regulation of antiapoptotic Bcl2 and c-IAP1 genes.

Recent status of HIV-1 gene expression inhibitors

Human immunodeficiency virus type 1 (HIV-1) gene expression and transcription is a crucial step in the viral replication cycle, which is considered to be a potential target for inhibition of HIV-1. Among the factors involved in this step, the cellular protein nuclear factor (NF)-kappaB is the most powerful inducer of HIV-1 gene expression. On the other hand, the viral protein Tat plays a central role in sustaining a high level of HIV-1 replication. Several compounds have been reported to selectively inhibit the functions of Tat and NF-kappaB. Tat inhibitors target either the Tat/TAR RNA interaction or the Tat cofactor cyclin-dependent kinase 9/cyclin T1. Antioxidants, protein kinase C inhibitors, and IkappaB kinase inhibitors are known to suppress the activation of NF-kappaB. Although some of the compounds inhibit HIV-1 replication in cell cultures at low concentrations, they also have considerable toxicity to the host cells. Considering the increase of treatment failure cases in highly active antiretroviral therapy due to the emergence of multidrug resistance, HIV-1 gene expression inhibitors should be extensively studied as alternative approach to effective anti-HIV-1 chemotherapy.

Mechanisms of apoptosis induction by the HIV-1 envelope

The envelope glycoprotein complex (Env) of human immunodeficiency virus-1 (HIV-1) can induce apoptosis by a cornucopia of distinct mechanisms. A soluble Env derivative, gp120, can kill cells through signals that are transmitted by chemokine receptors such as CXCR4. Cell surface-bound Env (gp120/gp41), as present on the plasma membrane of HIV-1-infected cells, can kill uninfected bystander cells expressing CD4 and CXCR4 (or similar chemokine receptors, depending on the Env variant) by at least three different mechanisms. First, a transient interaction involving the exchange of lipids between the two interacting cells ('the kiss of death') may lead to the selective death of single CD4-expressing target cells. Second, fusion of the interacting cells may lead to the formation of syncytia which then succumb to apoptosis in a complex pathway involving the activation of several kinases (cyclin-dependent kinase-1, Cdk1; checkpoint kinase-2, Chk2; mammalian target of rapamycin, mTOR; p38 mitogen-activated protein kinase, p38 MAPK; inhibitor of NF-kappaB kinase, IKK), as well as the activation of several transcription factors (NF-kappaB, p53), finally resulting in the activation of the mitochondrial pathway of apoptosis. Third, if the Env-expressing cell is at an early stage of imminent apoptosis, its fusion with a CD4-expressing target cell can precipitate the death of both cells, through a process that may be considered as contagious apoptosis and which does not involve Cdk1, mTOR, p38 nor p53, yet does involve mitochondria. Activation of some of the above- mentioned lethal signal transducers have been detected in patients' tissues, suggesting that HIV-1 may indeed trigger apoptosis through molecules whose implication in Env-induced killing has initially been discovered in vitro.

CDK9/cyclin T1: a host cell target for antiretroviral therapy

Hijacking of the host cell’s signal transduction machinery has been increasingly regarded as an important strategy for facilitating virus propagation. The positive-transcription elongation factor (P-TEFb) complex, cyclin-dependent kinase (CDK)9/cyclin T1, is an example of such an attack by HIV. Upon infection of cells, the HIV protein transactivator of transcription (Tat) forms a highly specific complex with the two host cell proteins CDK9 and cyclin T1. This complex ensures phosphorylation of the native CDK9 substrate, RNA polymerase II, leading to productive elongation of viral RNA in the host cell. Although challenging, inhibition of CDK9 activity with small molecules is a therapeutically valid strategy to inhibit HIV replication. Other than direct antiviral agents, that inhibit HIV replication through a direct interaction with viral proteins, CDK9 inhibitors might not suffer from the emergence of resistant virus strains. This review outlines the advantages and prospects of selective CDK9 inhibitors in the management of HIV infections.

Rhinoviral infections activate p38MAP-kinases via membrane rafts and RhoA

Rhinoviral infections belong to the most frequent human infections characterized by common cold, chronic bronchitis, exacerbations of asthma, otitis media and sinusitis. Here, we define molecular mechanisms that mediate infections of human epithelial cells with human rhinovirus strain 14 (RV14). We demonstrate that RV14 activates p38-MAPKinase (p38-K) in a biphasic time course. Early stimulation of p38-K by RV14 was observed a few minutes after initiation of the infection, while the late increase of p38-K activity occurred 7-12 hrs upon infection. The stimulation of p38-K was mediated by the small G-protein RhoA,which was activated by RV14. Transfection of a genetic construct preventing RhoA activation blocked RV14-induced p38-K activation. Further, integrity of cholesterol and sphingolipid-enriched membrane domains was required for RV14-mediated p38-K activation, which was inhibited by destruction of membrane rafts. The data indicate that RV employs a signaling cascade from membrane rafts via the small G-protein RhoA to p38-K to infect human cells.

R5 and X4 HIV envelopes induce distinct gene expression profiles in primary peripheral blood mononuclear cells

HIV envelope binds to and signals through its primary cellular receptor, CD4, and through a coreceptor, either CC chemokine receptor 5 (CCR5) or CXC chemokine receptor 4 (CXCR4). Here, we evaluate the response of peripheral blood mononuclear cells to a panel of genetically diverse R5 and X4 envelope proteins. Modulation of gene expression was evaluated by using oligonucleotide microarrays. Activation of transcription factors was evaluated by using an array of oligonucleotides encoding transcription factor binding sites. Responses were strongly influenced by coreceptor specificity. Treatment of cells from CCR5delta32 homozygous donors with glycoprotein (gp)120 derived from an R5 virus demonstrated that the majority of responses elicited by R5 envelopes required engagement of CCR5. R5 envelopes, to a greater extent than X4 envelopes, induced the expression of genes belonging to mitogen-activated protein kinase signal transduction pathways and genes regulating the cell cycle. A number of genes induced by R5, but not X4, envelopes were also up-regulated in the resting CD4+ T cell population of HIV-infected individuals. These results suggest that R5 envelope facilitates replication of HIV in the pool of resting CD4+ T cells. Additionally, signaling by R5 gp120 may facilitate the transmission of R5 viruses by inducing a permissive environment for HIV replication.

p38 mitogen-activated protein kinase-dependent hyperinduction of tumor necrosis factor alpha expression in response to avian influenza virus H5N1

Avian influenza A virus subtype H5N1 can infect humans to cause a severe viral pneumonia with mortality rates of more than 30%. The biological basis for this unusual disease severity is not fully understood. We previously demonstrated that in contrast to human influenza A virus subtypes including H1N1 or H3N2, the H5N1 virus associated with the "bird flu" outbreak in Hong Kong in 1997 (H5N1/97) hyperinduces proinflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), in primary human macrophages in vitro. To delineate the molecular mechanisms involved, we analyzed the role of transcription factor NF-kappaB and cellular kinases in TNF-alpha dysregulation. H5N1 and H1N1 viruses did not differ in the activation of NF-kappaB or degradation of IkappaB-alpha in human macrophages. However, we demonstrated that unlike H1N1 virus, H5N1/97 strongly activates mitogen-activated protein kinase (MAPK), including p38 MAPK and extracellular signal-regulated kinases 1 and 2. Specific inhibitors of p38 MAPK significantly reduced the H5N1/97-induced TNF-alpha expression in macrophages. Taken together, our findings suggest that H5N1/97-mediated hyperinduction of cytokines involves the p38 MAPK signaling pathway. These results may provide insights into the pathogenesis of H5N1 disease and rationales for the development of novel therapeutic strategies.

HIV-1 Nef-induced FasL induction and bystander killing requires p38 MAPK activation

The human immunodeficiency virus (HIV) has been reported to target noninfected CD4 and CD8 cells for destruction. This effect is manifested in part through up-regulation of the death receptor Fas ligand (FasL) by HIV-1 negative factor (Nef), leading to bystander damage. However, the signal transduction and transcriptional regulation of this process remains elusive. Here, we provide evidence that p38 mitogen-activated protein kinase (MAPK) is required for this process. Loss-of-function experiments through dominant-negative p38 isoform, p38 siRNA, and chemical inhibitors of p38 activation suggest that p38 is necessary for Nef-induced activator protein-1 (AP-1) activation, as inhibition leads to an attenuation of AP-1-dependent transcription. Furthermore, mutagenesis of the FasL promoter reveals that its AP-1 enhancer element is required for Nef-mediated transcriptional activation. Therefore, a linear pathway for Nef-induced FasL expression that encompasses p38 and AP-1 has been elucidated. Furthermore, chemical inhibition of the p38 pathway attenuates HIV-1-mediated bystander killing of CD8 cells in vitro.

Essential role of p53 phosphorylation by p38 MAPK in apoptosis induction by the HIV-1 envelope

The proapoptotic activity of the transcription factor p53 critically depends on the phosphorylation of serine 46 (p53S46P). Here, we show that syncytia containing p53S46P could be detected in lymph node biopsies from human immunodeficiency virus (HIV)-1 carriers, in the brain of patients with HIV-1–associated dementia and in cocultures of HeLa expressing the HIV-1 envelope glycoprotein complex (Env) with HeLa cells expressing CD4. In this latter model, cell death was the result of a sequential process involving cell fusion, nuclear fusion (karyogamy), phosphorylation of serine 15 (p53S15P), later on serine 46 (p53S46P), and transcription of p53 target genes. Cytoplasmic p38 mitogen-activated protein kinase (MAPK) was found to undergo an activating phosphorylation (p38T180/Y182P [p38 with phosphorylated threonine 180 and tyrosine 182]) before karyogamy and to translocate into karyogamic nuclei. p38T180/Y182P colocalized and coimmunoprecipitated with p53S46P. Recombinant p38 phosphorylated recombinant p53 on serine 46 in vitro. Inhibition of p38 MAPK by pharmacological inhibitors, dominant-negative p38, or small interfering RNA, suppressed p53S46P (but not p53S15P), the expression of p53-inducible genes, the conformational activation of proapoptotic Bax and Bak, the release of cytochrome c from mitochondria, and consequent apoptosis. p38T180/Y182P was also detected in HIV-1–induced syncytia, in vivo, in patients' lymph nodes and brains. Dominant-negative MKK3 or MKK6 inhibited syncytial activation of p38, p53S46P, and apoptosis. Altogether, these findings indicate that p38 MAPK-mediated p53 phosphorylation constitutes a critical step of Env-induced apoptosis.

Interactions among human immunodeficiency virus (HIV)-1, interferon-gamma and receptor of activated NF-kappa B ligand (RANKL): implications for HIV pathogenesis

We reported recently that exposure of human T cells to soluble HIV-1 envelope glycoprotein gp120 induced biologically active tumour necrosis factor (TNF)-alpha-related cytokine receptor of activated NF-kappaB ligand (RANKL), the primary drive to osteoclast differentiation and bone resorption. Furthermore, certain anti-HIV protease inhibitors linked clinically to accelerated bone loss in HIV disease blocked the physiological control of RANKL activity by interferon (IFN)-gamma through inhibition of degradation of the RANKL nuclear adapter signalling protein, TNF receptor associated protein 6 (TRAF6). We now report a series of reciprocal interactions among HIV-1, RANKL and IFN-gamma. RANKL augmented HIV replication in acutely and chronically infected cells of T lymphocyte and monocyte lineage, effects which occurred at a transcriptional level in conjunction with activation of NF-kappaB. TNF-alpha and RANKL were markedly synergistic in induction of HIV. Low pharmacological levels of IFN-gamma (0.75-3 ng/ml) suppressed RANKL-driven enhancement of HIV replication, as did L-T6DP-1, a cell-permeable peptide inhibitor of TRAF6. In contrast, HIV replication induced by TNF-alpha and phorbol ester were not inhibited, and in some cases augmented, by IFN-gamma. We conclude that a positive feedback loop exists between RANKL production and HIV replication, which may be relevant to both the pathophysiology of HIV-linked osteopenia and control of HIV growth. This pathway appears distinct from those of other cytokine activators of HIV, with respect to its utilization of TRAF6 and its suppression by IFN-gamma. These data raise the possibility that TRAF-specific inhibitory peptides, alone or in conjunction with IFN-gamma, could be used to regulate HIV activation in vivo.