Blockade of BFA-mediated apoptosis in macrophages by the HIV-1 Nef protein

JC virus small tumor antigen promotes S phase entry and cell cycle progression

The early coding region of JC virus (JCV) encodes several regulatory proteins including large T antigen (LT-Ag), small t antigen (Sm t-Ag) and T' proteins because of the alternative splicing of the pre-mRNA. LT-Ag plays a critical role in cell transformation by targeting the key cell cycle regulatory proteins including p53 and pRb, however, the role of Sm t-Ag in this process remains elusive. Here, we investigated the effect of Sm t-Ag on the cell cycle progression and demonstrated that it facilitates S phase entry and exit when cells are released from G0/G1 growth arrest. Examination of the cell cycle stage specific expression profiles of the selected cyclins and cyclin-dependent kinases, including those active at the G1/S and G2/M transition state, demonstrated a higher level of early expression of these regulators such as cyclin B, cycling E, and Cdk2. In addition, analysis of the effect of Sm t-Ag on the growth promoting pathways including those active in the PI3K/Akt/mTOR axis showed substantially higher levels of the phosphorylated-Akt, -Gsk3-β and -S6K1 in Sm t-Ag-positive cells. Collectively, our results demonstrate that Sm t-Ag promotes cell cycle progression by activating the growth promoting pathways through which it may contribute to LT-Ag-mediated cell transformation.

XPOT Disruption Suppresses TNBC Growth through Inhibition of Specific tRNA Nuclear Exportation and TTC19 Expression to Induce Cytokinesis Failure

Transfer RNAs (tRNAs) impact the development and progression of various cancers, but how individual tRNAs are modulated during triple-negative breast cancer (TNBC) progression remains poorly understood. Here, we found that XPOT (Exportin-T), a nuclear export protein receptor of tRNAs, is associated with poor prognosis in breast cancer and directly orchestrates the nuclear export of a subset of tRNAs, subsequently promoting protein synthesis and proliferation of human TNBC cells. XPOT knockdown inhibited TNBC cell proliferation in vitro, and RNA-seq indicated that XPOT is involved in the completion of cytokinesis in TNBC cells. High-throughput sequencing of tRNA revealed that XPOT specifically influenced a subset of tRNA isodecoders involved in nucleocytoplasmic trafficking, including tRNA-Ala-AGC-10-1. Through codon preferential analysis and protein mass spectrometry, we found that XPOT preferentially transported nuclear tRNA-Ala-AGC-10-1 to the cytoplasm, driving the translation of TPR Repeat Protein 19 (TTC19). TTC19 is also indispensable for cytokinesis and proliferation of TNBC cells. Altogether, these findings provide a novel regulatory translation mechanism for preferential tRNA isodecoder nucleocytoplasmic transport through XPOT, which coordinates the spatial location of specific tRNA and the translation of mRNA to facilitate TNBC proliferation and progression. Targeting XPOT may be a novel therapeutic strategy for treating TNBC.

Enhancing HIV-1 Neutralization by Increasing the Local Concentration of Membrane-Proximal External Region-Directed Broadly Neutralizing Antibodies

Broadly neutralizing antibodies (bNAbs) against the membrane-proximal external region (MPER) of the gp41 component of the human immunodeficiency virus type 1 (HIV-1) envelope (Env) are characterized by long, hydrophobic, heavy chain complementarity-determining region 3s (HCDR3s) that interact with the MPER and some viral membrane lipids to achieve increased local concentrations. Here, we show that increasing the local concentration of MPER-directed bNAbs at the cell surface via binding to the high-affinity Fc receptor FcγRI potentiates their ability to prevent viral entry in a manner analogous to the previously reported observation wherein the lipid-binding activity of MPER bNAbs increases their concentration at the viral surface membrane. However, binding of MPER-directed bNAb 10E8 to FcγRI abolishes the neutralization synergy that is seen with the N-heptad repeat (NHR)-targeting antibody D5_AR and NHR-targeting small molecule enfuvirtide (T20), possibly due to decreased accessibility of the NHR in the FcγRI-10E8-MPER complex. Taken together, our results suggest that lipid-binding activity and FcγRI-mediated potentiation function in concert to improve the potency of MPER-directed bNAbs by increasing their local concentration near the site of viral fusion. Therefore, lipid binding may not be a strict requirement for potent neutralization by MPER-targeting bNAbs, as alternative methods can achieve similar increases in local concentrations while avoiding potential liabilities associated with immunologic host tolerance. IMPORTANCE The trimeric glycoprotein Env, the only viral protein expressed on the surface of HIV-1, is the target of broadly neutralizing antibodies and the focus of most vaccine development efforts. Broadly neutralizing antibodies targeting the membrane proximal external region (MPER) of Env show lipid-binding characteristics, and modulating this interaction affects neutralization. In this study, we tested the neutralization potencies of variants of the MPER-targeting antibody 10E8 with different viral-membrane-binding and host FcγRI-binding capabilities. Our results suggest that binding to both lipid and FcγRI improves the neutralization potency of MPER-directed antibodies by concentrating the antibodies at sites of viral fusion. As such, lipid binding may not be uniquely required for MPER-targeting broadly neutralizing antibodies, as alternative methods to increase local concentration can achieve similar improvements in potency.

Aberrant protein synthesis and cancer development: The role of canonical eukaryotic initiation, elongation and termination factors in tumorigenesis

In tumourigenesis, oncogenes or dysregulated tumour suppressor genes alter the canonical translation machinery leading to a reprogramming of the translatome that, in turn, promotes the translation of selected mRNAs encoding proteins involved in proliferation and metastasis. It is therefore unsurprising that abnormal expression levels and activities of eukaryotic initiation factors (eIFs), elongation factors (eEFs) or termination factors (eRFs) are associated with poor outcome for patients with a wide range of cancers. In this review we discuss how RNA binding proteins (RBPs) within the canonical translation factor machinery are dysregulated in cancers and how targeting such proteins is leading to new therapeutic avenues.

CD9 and ITGA3 are regulated during HIV-1 infection in macrophages to support viral replication

Monocytes/macrophages are important target cells for HIV-1. Here, we investigated whether HIV-1 induces changes in the macrophage gene expression profile to support viral replication. We observed that the macrophage gene expression profiles dramatically changed upon HIV-1 infection. The majority of the HIV-1 regulated genes were also differentially expressed in M2a macrophages. The biological functions associated with the HIV-1 induced gene expression profile in macrophages were mainly related to inflammatory responses. CD9 and ITGA3 were among the top genes upregulated upon HIV-1 infection. We showed that these genes support viral replication and that downregulation of these genes decreased HIV-1 replication in macrophages. Here we showed that HIV-1 infection of macrophages induces a gene expression profile that may dampen inflammatory responses. CD9 and ITGA3 were among the top genes regulated by HIV-1 and were shown to support viral production most likely at the level of viral budding and release.

Hepatitis B Virus DNA Polymerase Displays an Anti-Apoptotic Effect by Interacting with Elongation Factor-1 Alpha-2 in Hepatoma Cells

Hepatitis B virus (HBV) genome P-encoded protein HBV DNA polymerase (Pol) has long been known as a reverse transcriptase during HBV replication. In this study, we investigated the impact of HBV Pol on host cellular processes, mainly apoptosis, and the underlying mechanisms. We showed a marked reduction in apoptotic rates in the HBV Pol-expressed HepG2 cells compared to controls. Moreover, a series of assays, i.e., yeast two-hybrid, GST pull-down, co-immunoprecipitation, and confocal laser scanning microscopy, identified the host factor eEF1A2 to be associated with HBV Pol. Furthermore, knockdown of eEF1A2 gene by siRNA abrogated the HBV Pol-mediated anti-apoptotic effect with apoptosis induced by endoplasmatic reticulum (ER) stress-inducer thapsigargin (TG), thus suggesting that the host factor eEF1A2 is essential for HBV Pol's anti-apoptosis properties. Our findings have revealed a novel role for HBV Pol in its modulation of apoptosis through integrating with eEF1A2.

The Role of Macrophages in HIV-1 Persistence and Pathogenesis

Current antiretroviral therapy (ART) effectively suppresses Human Immunodeficiency Virus type 1 (HIV-1) in infected individuals. However, even long term ART does not eradicate HIV-1 infected cells and the virus persists in cellular reservoirs. Beside memory CD4⁺ T cells, cells of the myeloid lineage, especially macrophages, are believed to be an important sanctuary for HIV-1. Monocytes and macrophages are key players in the innate immune response to pathogens and are recruited to sites of infection and inflammation. Due to their long life span and ability to reside in virtually every tissue, macrophages have been proposed to play a critical role in the establishment and persistence of the HIV-1 reservoir. Current HIV-1 cure strategies mainly focus on the concept of “shock and kill” to purge the viral reservoir. This approach aims to reactivate viral protein production in latently infected cells, which subsequently are eliminated as a consequence of viral replication, or recognized and killed by the immune system. Macrophage susceptibility to HIV-1 infection is dependent on the local microenvironment, suggesting that molecular pathways directing differentiation and polarization are involved. Current latency reversing agents (LRA) are mainly designed to reactivate the HIV-1 provirus in CD4+ T cells, while their ability to abolish viral latency in macrophages is largely unknown. Moreover, the resistance of macrophages to HIV-1 mediated kill and the presence of infected macrophages in immune privileged regions including the central nervous system (CNS), may pose a barrier to elimination of infected cells by current “shock and kill” strategies. This review focusses on the role of monocytes/macrophages in HIV-1 persistence. We will discuss mechanisms of viral latency and persistence in monocytes/macrophages. Furthermore, the role of these cells in HIV-1 tissue distribution and pathogenesis will be discussed.

TREM-1 Protects HIV-1-Infected Macrophages from Apoptosis through Maintenance of Mitochondrial Function

The major challenge to human immunodeficiency virus (HIV) treatment is the development of strategies that lead to viral eradication. A roadblock to accomplishing this goal is the lack of an approach that would safely eliminate HIV from all resting/latent reservoirs, including macrophages. Macrophages are a key part of the innate immune system and are responsible for recognizing invading microbes and sending appropriate signals to other immune cells. Here, we found that HIV induces the upregulation of the protein TREM1 (triggering receptor expressed on myeloid cells 1), which signals an increase in the expression of antiapoptotic proteins, thus promoting survival of HIV-infected macrophages.

Macrophages are a reservoir for latent human immunodeficiency type 1 (HIV) infection and a barrier to HIV eradication. In contrast to CD4⁺ T cells, macrophages are resistant to the cytopathic effects of acute HIV infection. Emerging data suggest a role for TREM1 (triggering receptor expressed on myeloid cells 1) in this resistance to HIV-mediated cytopathogenesis. Here, we show that upon HIV infection, macrophages increase the expression of BCL2, BCLXL, TREM1, mitofusin 1 (MFN1), and MFN2 and the translocation of BCL2L11 (BIM) to the mitochondria and decrease the expression of BCL2-associated agonist of cell death (BAD) and BAX while maintaining a 95% survival rate over 28 days. The HIV proteins Tat and gp120 and the GU-rich single-stranded RNA (ssRNA) (RNA40) from the HIV long terminal repeat region (and a natural Toll-like receptor 8 [TLR8] agonist) induced similar effects. TREM1 silencing in HIV-infected macrophages led to decreased expression of BCL2, BCLXL, MFN1, and MFN2 and increased expression of BAD and BAX. This correlated with a significant increase in apoptosis mediated by a disruption of the mitochondrial membrane potential (Δψm), leading to the release of cytochrome c and caspase 9 cleavage. Exposure of TREM1-silenced macrophages to Tat, gp120, or RNA40 similarly resulted in the disruption of Δψm, cytochrome c release, caspase 9 cleavage, and apoptosis. Thus, our findings identify a mechanism whereby HIV promotes macrophage survival through TREM1-dependent upregulation of BCL2 family proteins and mitofusins that inhibits BCL2L11-mediated disruption of Δψm and subsequent apoptosis. These findings indicate that TREM1 can be a useful target for elimination of the HIV reservoir in macrophages.

Oxazole-Benzenesulfonamide Derivatives Inhibit HIV-1 Reverse Transcriptase Interaction with Cellular eEF1A and Reduce Viral Replication

HIV-1 replication requires direct interaction between HIV-1 reverse transcriptase (RT) and cellular eukaryotic translation elongation factor 1A (eEF1A). Our previous work showed that disrupting this interaction inhibited HIV-1 uncoating, reverse transcription, and replication, indicating its potential as an anti-HIV-1 target. In this study, we developed a sensitive, live-cell split-luciferase complementation assay (NanoBiT) to quantitatively measure inhibition of HIV-1 RT interaction with eEF1A. We used this to screen a small molecule library and discovered small-molecule oxazole-benzenesulfonamides (C7, C8, and C9), which dose dependently and specifically inhibited the HIV-1 RT interaction with eEF1A. These compounds directly bound to HIV-1 RT in a dose-dependent manner, as assessed by a biolayer interferometry (BLI) assay, but did not bind to eEF1A. These oxazole-benzenesulfonamides did not inhibit enzymatic activity of recombinant HIV-1 RT in a homopolymer assay but did inhibit reverse transcription and infection of both wild-type (WT) and nonnucleoside reverse transcriptase inhibitor (NNRTI)-resistant HIV-1 in a dose-dependent manner in HEK293T cells. Infection of HeLa cells was significantly inhibited by the oxazole-benzenesulfonamides, and the antiviral activity was most potent against replication stages before 8 h postinfection. In human primary activated CD4+ T cells, C7 inhibited HIV-1 infectivity and replication up to 6 days postinfection. The data suggest a novel mechanism of HIV-1 inhibition and further elucidate how the RT-eEF1A interaction is important for HIV-1 replication. These compounds provide potential to develop a new class of anti-HIV-1 drugs to treat WT and NNRTI-resistant strains in people infected with HIV.IMPORTANCE Antiretroviral drugs protect many HIV-positive people, but their success can be compromised by drug-resistant strains. To combat these strains, the development of new classes of HIV-1 inhibitors is essential and a priority in the field. In this study, we identified small molecules that bind directly to HIV-1 reverse transcriptase (RT) and inhibit its interaction with cellular eEF1A, an interaction which we have previously identified as crucial for HIV-1 replication. These compounds inhibit intracellular HIV-1 reverse transcription and replication of WT HIV-1, as well as HIV-1 mutants that are resistant to current RT inhibitors. A novel mechanism of action involving inhibition of the HIV-1 RT-eEF1A interaction is an important finding and a potential new way to combat drug-resistant HIV-1 strains in infected people.

The Role of Macrophages in HIV-1 Persistence and Pathogenesis

Current antiretroviral therapy (ART) effectively suppresses Human Immunodeficiency Virus type 1 (HIV-1) in infected individuals. However, even long term ART does not eradicate HIV-1 infected cells and the virus persists in cellular reservoirs. Beside memory CD4⁺ T cells, cells of the myeloid lineage, especially macrophages, are believed to be an important sanctuary for HIV-1. Monocytes and macrophages are key players in the innate immune response to pathogens and are recruited to sites of infection and inflammation. Due to their long life span and ability to reside in virtually every tissue, macrophages have been proposed to play a critical role in the establishment and persistence of the HIV-1 reservoir. Current HIV-1 cure strategies mainly focus on the concept of "shock and kill" to purge the viral reservoir. This approach aims to reactivate viral protein production in latently infected cells, which subsequently are eliminated as a consequence of viral replication, or recognized and killed by the immune system. Macrophage susceptibility to HIV-1 infection is dependent on the local microenvironment, suggesting that molecular pathways directing differentiation and polarization are involved. Current latency reversing agents (LRA) are mainly designed to reactivate the HIV-1 provirus in CD4+ T cells, while their ability to abolish viral latency in macrophages is largely unknown. Moreover, the resistance of macrophages to HIV-1 mediated kill and the presence of infected macrophages in immune privileged regions including the central nervous system (CNS), may pose a barrier to elimination of infected cells by current "shock and kill" strategies. This review focusses on the role of monocytes/macrophages in HIV-1 persistence. We will discuss mechanisms of viral latency and persistence in monocytes/macrophages. Furthermore, the role of these cells in HIV-1 tissue distribution and pathogenesis will be discussed.

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

Several cellular functions such as apoptosis, cellular proliferation, inflammation, and immune regulation involve the tumor necrosis factor-α (TNF)/TNF receptor (TNFR) pathway. Human immunodeficiency virus 1 (HIV-1) interacts with the TNF/TNFR pathway. The activation of the TNF/TNFR pathway impacts HIV-1 replication, and the TNF/TNFR pathway is the target of HIV-1 proteins. A hallmark of HIV-1 infection is immune activation and inflammation with increased levels of TNF in the plasma and the tissues. Therefore, the control of the TNF/TNFR pathway by new therapeutic approaches could participate in the control of immune activation and impact both viral replication and viral persistence. In this review, we will describe the intricate interplay between HIV-1 proteins and TNF/TNFR signaling and how TNF/TNFR activation modulates HIV-1 replication and discuss new therapeutic approaches, especially anti-TNF therapy, that could control this pathway and ultimately favor the clearance of infected cells to cure HIV-infected patients.

The Potyviral P3 Protein Targets Eukaryotic Elongation Factor 1A to Promote the Unfolded Protein Response and Viral Pathogenesis

The biochemical function of the potyviral P3 protein is not known, although it is known to regulate virus replication, movement, and pathogenesis. We show that P3, the putative virulence determinant of soybean mosaic virus (SMV), targets a component of the translation elongation complex in soybean. Eukaryotic elongation factor 1A (eEF1A), a well-known host factor in viral pathogenesis, is essential for SMV virulence and the associated unfolded protein response (UPR). Silencing GmEF1A inhibits accumulation of SMV and another ER-associated virus in soybean. Conversely, endoplasmic reticulum (ER) stress-inducing chemicals promote SMV accumulation in wild-type, but not GmEF1A-knockdown, plants. Knockdown of genes encoding the eEF1B isoform, which is important for eEF1A function in translation elongation, has similar effects on UPR and SMV resistance, suggesting a link to translation elongation. P3 and GmEF1A promote each other's nuclear localization, similar to the nuclear-cytoplasmic transport of eEF1A by the Human immunodeficiency virus 1 Nef protein. Our results suggest that P3 targets host elongation factors resulting in UPR, which in turn facilitates SMV replication and place eEF1A upstream of BiP in the ER stress response during pathogen infection.

Role of hexokinase-1 in the survival of HIV-1-infected macrophages

Viruses have developed various strategies to protect infected cells from apoptosis. HIV-1 infected macrophages are long-lived and considered reservoirs for HIV-1. One significant deciding factor between cell survival and cell death is glucose metabolism. We hypothesized that HIV-1 protects infected macrophages from apoptosis in part by modulating the host glycolytic pathway specifically by regulating hexokinase-1 (HK-1) an enzyme that converts glucose to glucose-6-phosphate. Therefore, we analyzed the regulation of HK-1 in HIV-1 infected PBMCs, and in a chronically HIV-1 infected monocyte-like cell line, U1. Our results demonstrate that HIV-1 induces a robust increase in HK-1 expression. Surprisingly, hexokinase enzymatic activity was significantly inhibited in HIV-1 infected PBMCs and in PMA differentiated U1 cells. Interestingly, we observed increased levels of mitochondria-bound HK-1 in PMA induced U1 cells and in the HIV-1 accessory protein, viral protein R (Vpr) transduced U937 cell derived macrophages. Dissociation of HK-1 from mitochondria in U1 cells using a pharmacological agent, clotrimazole (CTZ) induced mitochondrial membrane depolarization and caspase-3/7 mediated apoptosis. Dissociation of HK-1 from mitochondria in Vpr transduced U937 also activated caspase-3/7 activity. These observations indicate that HK-1 plays a non-metabolic role in HIV-1 infected macrophages by binding to mitochondria thereby maintaining mitochondrial integrity. These results suggest that targeting the interaction of HK-1 with the mitochondria to induce apoptosis in persistently infected macrophages may prove beneficial in purging the macrophage HIV reservoir.

Mycobacterium tuberculosis and Human Immunodeficiency Virus Type 1 Cooperatively Modulate Macrophage Apoptosis via Toll Like Receptor 2 and Calcium Homeostasis

The emergence of drug resistant strains of Mycobacterium tuberculosis (M. tuberculosis) together with reports of co-infections with the human immunodeficiency virus (HIV) has renewed interest to better understand the intricate mechanisms prevalent during co-infections. In this study we report a synergistic effect of M. tuberculosis and HIV-1, and their antigens Rv3416 and Nef, respectively, in inhibiting apoptosis of macrophages. This inhibition involves the TLR2 pathway and second messengers that play complementing and contrasting roles in regulating apoptosis. Interestingly, the route of calcium influx into cells differentially regulates apoptosis during antigenic co-stimulation. While calcium released from intracellular stores was anti-apoptotic, calcium influx from the external milieu was pro-apoptotic. Further, molecular sensors of intracellular calcium release aid in antigen mediated inhibition of apoptosis. A cross-regulation between oxidative burst and differential routing of calcium influx governed apoptosis. Interestingly, the HIV-1 Nef supported anti-apoptotic responses in macrophages whereas Vpu had no significant effect. These results point to a synergistic liaison between M. tuberculosis and HIV-1 in regulating macrophage apoptosis.

The eEF1A Proteins: At the Crossroads of Oncogenesis, Apoptosis, and Viral Infections

Eukaryotic translation elongation factors 1 alpha, eEF1A1 and eEF1A2, are not only translation factors but also pleiotropic proteins that are highly expressed in human tumors, including breast cancer, ovarian cancer, and lung cancer. eEF1A1 modulates cytoskeleton, exhibits chaperone-like activity and also controls cell proliferation and cell death. In contrast, eEF1A2 protein favors oncogenesis as shown by the fact that overexpression of eEF1A2 leads to cellular transformation and gives rise to tumors in nude mice. The eEF1A2 protein stimulates the phospholipid signaling and activates the Akt-dependent cell migration and actin remodeling that ultimately favors tumorigenesis. In contrast, inactivation of eEF1A proteins leads to immunodeficiency, neural and muscular defects, and favors apoptosis. Finally, eEF1A proteins interact with several viral proteins resulting in enhanced viral replication, decreased apoptosis, and increased cellular transformation. This review summarizes the recent findings on eEF1A proteins indicating that eEF1A proteins play a critical role in numerous human diseases through enhancement of oncogenesis, blockade of apoptosis, and increased viral pathogenesis.

Human immunodeficiency virus-1 (HIV-1)-mediated apoptosis: new therapeutic targets

HIV has posed a significant challenge due to the ability of the virus to both impair and evade the host’s immune system. One of the most important mechanisms it has employed to do so is the modulation of the host’s native apoptotic pathways and mechanisms. Viral proteins alter normal apoptotic signaling resulting in increased viral load and the formation of viral reservoirs which ultimately increase infectivity. Both the host’s pro- and anti-apoptotic responses are regulated by the interactions of viral proteins with cell surface receptors or apoptotic pathway components. This dynamic has led to the development of therapies aimed at altering the ability of the virus to modulate apoptotic pathways. These therapies are aimed at preventing or inhibiting viral infection, or treating viral associated pathologies. These drugs target both the viral proteins and the apoptotic pathways of the host. This review will examine the cell types targeted by HIV, the surface receptors exploited by the virus and the mechanisms whereby HIV encoded proteins influence the apoptotic pathways. The viral manipulation of the hosts’ cell type to evade the immune system, establish viral reservoirs and enhance viral proliferation will be reviewed. The pathologies associated with the ability of HIV to alter apoptotic signaling and the drugs and therapies currently under development that target the ability of apoptotic signaling within HIV infection will also be discussed.

HIV-1 Nef is transferred from expressing T cells to hepatocytic cells through conduits and enhances HCV replication

HIV-1 infection enhances HCV replication and as a consequence accelerates HCV-mediated hepatocellular carcinoma (HCC). However, the precise molecular mechanism by which this takes place is currently unknown. Our data showed that infectious HIV-1 failed to replicate in human hepatocytic cell lines. No discernible virus replication was observed, even when the cell lines transfected with HIV-1 proviral DNA were co-cultured with Jurkat T cells, indicating that the problem of liver deterioration in the co-infected patient is not due to the replication of HIV-1 in the hepatocytes of the HCV infected host. Instead, HIV-1 Nef protein was transferred from nef-expressing T cells to hepatocytic cells through conduits, wherein up to 16% (average 10%) of the cells harbored the transferred Nef, when the hepatocytic cells were co-cultured with nef-expressing Jurkat cells for 24 h. Further, Nef altered the size and numbers of lipid droplets (LD), and consistently up-regulated HCV replication by 1.5∼2.5 fold in the target subgenomic replicon cells, which is remarkable in relation to the initially indolent viral replication. Nef also dramatically augmented reactive oxygen species (ROS) production and enhanced ethanol-mediated up-regulation of HCV replication so as to accelerate HCC. Taken together, these data indicate that HIV-1 Nef is a critical element in accelerating progression of liver pathogenesis via enhancing HCV replication and coordinating modulation of key intra- and extra-cellular molecules for liver decay.

HIV-1 latency in monocytes/macrophages

Human immunodeficiency virus type 1 (HIV-1) targets CD4⁺ T cells and cells of the monocyte/macrophage lineage. HIV pathogenesis is characterized by the depletion of T lymphocytes and by the presence of a population of cells in which latency has been established called the HIV-1 reservoir. Highly active antiretroviral therapy (HAART) has significantly improved the life of HIV-1 infected patients. However, complete eradication of HIV-1 from infected individuals is not possible without targeting latent sources of infection. HIV-1 establishes latent infection in resting CD4⁺ T cells and findings indicate that latency can also be established in the cells of monocyte/macrophage lineage. Monocyte/macrophage lineage includes among others, monocytes, macrophages and brain resident macrophages. These cells are relatively more resistant to apoptosis induced by HIV-1, thus are important stable hideouts of the virus. Much effort has been made in the direction of eliminating HIV-1 resting CD4⁺ T-cell reservoirs. However, it is impossible to achieve a cure for HIV-1 without considering these neglected latent reservoirs, the cells of monocyte/macrophage lineage. In this review we will describe our current understanding of the mechanism of latency in monocyte/macrophage lineage and how such cells can be specifically eliminated from the infected host.