ATPgammaS disrupts human immunodeficiency virus type 1 virion core integrity

Heat shock proteins and viral infection

Heat shock proteins (HSPs) are a kind of proteins which mostly found in bacterial, plant and animal cells, in which they are involved in the monitoring and regulation of cellular life activities. HSPs protect other proteins under environmental and cellular stress by regulating protein folding and supporting the correctly folded structure of proteins as chaperones. During viral infection, some HSPs can have an antiviral effect by inhibiting viral proliferation through interaction and activating immune pathways to protect the host cell. However, although the biological function of HSPs is to maintain the homeostasis of cells, some HSPs will also be hijacked by viruses to help their invasion, replication, and maturation, thereby increasing the chances of viral survival in unfavorable conditions inside the host cell. In this review, we summarize the roles of the heat shock protein family in various stages of viral infection and the potential uses of these proteins in antiviral therapy.

Stress proteins: the biological functions in virus infection, present and challenges for target-based antiviral drug development

Stress proteins (SPs) including heat-shock proteins (HSPs), RNA chaperones, and ER associated stress proteins are molecular chaperones essential for cellular homeostasis. The major functions of HSPs include chaperoning misfolded or unfolded polypeptides, protecting cells from toxic stress, and presenting immune and inflammatory cytokines. Regarded as a double-edged sword, HSPs also cooperate with numerous viruses and cancer cells to promote their survival. RNA chaperones are a group of heterogeneous nuclear ribonucleoproteins (hnRNPs), which are essential factors for manipulating both the functions and metabolisms of pre-mRNAs/hnRNAs transcribed by RNA polymerase II. hnRNPs involve in a large number of cellular processes, including chromatin remodelling, transcription regulation, RNP assembly and stabilization, RNA export, virus replication, histone-like nucleoid structuring, and even intracellular immunity. Dysregulation of stress proteins is associated with many human diseases including human cancer, cardiovascular diseases, neurodegenerative diseases (e.g., Parkinson’s diseases, Alzheimer disease), stroke and infectious diseases. In this review, we summarized the biologic function of stress proteins, and current progress on their mechanisms related to virus reproduction and diseases caused by virus infections. As SPs also attract a great interest as potential antiviral targets (e.g., COVID-19), we also discuss the present progress and challenges in this area of HSP-based drug development, as well as with compounds already under clinical evaluation.

ATeam technology for detecting early signs of viral cytopathic effect

Adenosine 5’-triphosphate (ATP), the major energy currency of the cell, is involved in many cellular processes, including the viral life cycle, and can be used as an indicator of early signs of cytopathic effect (CPE). In this study, we demonstrated that CPE can be analyzed using an FRET-based ATP probe named ATP indicator based on Epsilon subunit for Analytical Measurements (ATeam). The results revealed that as early as 3 hr, the virus infected cells showed a significantly different Venus/cyan fluorescent protein (CFP) ratio compared to the mock-infected cells. The ATeam technology is therefore useful to determine the early signs of ATP-based CPE as early as 3 hr without morphology-based CPE by light microscopy, and enables high throughput determination of the presence of microorganisms in neglected samples stored in laboratories.

The Host Heat Shock Protein MRJ/DNAJB6 Modulates Virus Infection

A variety of pathogens take advantage of cellular heat shock proteins (HSPs) to complete their life cycle and exert pathogenic effects. MRJ (DNAJB6), a member of the heat shock protein 40 family, acts as a molecular chaperone for a wide range of cellular processes. MRJ mutations are linked to human diseases, such as muscular dystrophy and neurodegenerative diseases. There are two MRJ isoforms generated by alternative use of terminal exons, which differ in their C-terminus. This mini-review summarizes how these two MRJ isoforms participate differentially in viral production and virulence, and the possibility for MRJ as a therapeutic target.

Hepatitis C Virus Replication

Viruses use synthetic mechanism and organelles of the host cells to facilitate their replication and make new viruses. Host's ATP provides necessary energy. Hepatitis C virus (HCV) is a major cause of liver disease. Like other positive-strand RNA viruses, the HCV genome is thought to be synthesized by the replication complex, which consists of viral- and host cell-derived factors, in tight association with structurally rearranged vesicle-like cytoplasmic membranes. The virus-induced remodeling of subcellular membranes, which protect the viral RNA from nucleases in the cytoplasm, promotes efficient replication of HCV genome. The assembly of HCV particle involves interactions between viral structural and nonstructural proteins and pathways related to lipid metabolisms in a concerted fashion. Association of viral core protein, which forms the capsid, with lipid droplets appears to be a prerequisite for early steps of the assembly, which are closely linked with the viral genome replication. This review presents the recent progress in understanding the mechanisms for replication and assembly of HCV through its interactions with organelles or distinct organelle-like structures.

Cucumber Necrosis Virus Recruits Cellular Heat Shock Protein 70 Homologs at Several Stages of Infection

RNA viruses often depend on host factors for multiplication inside cells due to the constraints of their small genome size and limited coding capacity. One such factor that has been exploited by several plant and animal viruses is heat shock protein 70 (HSP70) family homologs which have been shown to play roles for different viruses in viral RNA replication, viral assembly, disassembly, and cell-to-cell movement. Using next generation sequence analysis, we reveal that several isoforms of Hsp70 and Hsc70 transcripts are induced to very high levels during cucumber necrosis virus (CNV) infection of Nicotiana benthamiana and that HSP70 proteins are also induced by at least 10-fold. We show that HSP70 family protein homologs are co-opted by CNV at several stages of infection. We have found that overexpression of Hsp70 or Hsc70 leads to enhanced CNV genomic RNA, coat protein (CP), and virion accumulation, whereas downregulation leads to a corresponding decrease. Hsc70-2 was found to increase solubility of CNV CP in vitro and to increase accumulation of CNV CP independently of viral RNA replication during coagroinfiltration in N. benthamiana. In addition, virus particle assembly into virus-like particles in CP agroinfiltrated plants was increased in the presence of Hsc70-2. HSP70 was found to increase the targeting of CNV CP to chloroplasts during infection, reinforcing the role of HSP70 in chloroplast targeting of host proteins. Hence, our findings have led to the discovery of a highly induced host factor that has been co-opted to play multiple roles during several stages of the CNV infection cycle.

IMPORTANCE

Because of the small size of its RNA genome, CNV is dependent on interaction with host cellular components to successfully complete its multiplication cycle. We have found that CNV induces HSP70 family homologs to a high level during infection, possibly as a result of the host response to the high levels of CNV proteins that accumulate during infection. Moreover, we have found that CNV co-opts HSP70 family homologs to facilitate several aspects of the infection process such as viral RNA, coat protein and virus accumulation. Chloroplast targeting of the CNV CP is also facilitated, which may aid in CNV suppression of host defense responses. Several viruses have been shown to induce HSP70 during infection and others to utilize HSP70 for specific aspects of infection such as replication, assembly, and disassembly. We speculate that HSP70 may play multiple roles in the infection processes of many viruses.

M1 of Murine Gamma-Herpesvirus 68 Induces Endoplasmic Reticulum Chaperone Production

Viruses rely on host chaperone network to support their infection. In particular, the endoplasmic reticulum (ER) resident chaperones play key roles in synthesizing and processing viral proteins. Influx of a large amount of foreign proteins exhausts the folding capacity in ER and triggers the unfolded protein response (UPR). A fully-executed UPR comprises signaling pathways that induce ER folding chaperones, increase protein degradation, block new protein synthesis and may eventually activate apoptosis, presenting both opportunities and threats to the virus. Here, we define a role of the MHV-68M1 gene in differential modulation of UPR pathways to enhance ER chaperone production. Ectopic expression of M1 markedly induces ER chaperone genes and expansion of ER. The M1 protein accumulates in ER during infection and this localization is indispensable for its function, suggesting M1 acts from the ER. We found that M1 protein selectively induces the chaperon-producing pathways (IRE1, ATF6) while, interestingly, sparing the translation-blocking arm (PERK). We identified, for the first time, a viral factor capable of selectively intervening the initiation of ER stress signaling to induce chaperon production. This finding provides a unique opportunity of using viral protein as a tool to define the activation mechanisms of individual UPR pathways.

Gene expression deregulation in postnatal skeletal muscle of TK2 deficient mice reveals a lower pool of proliferating myogenic progenitor cells

Loss of thymidine kinase 2 (TK2) causes a heterogeneous myopathic form of mitochondrial DNA (mtDNA) depletion syndrome (MDS) in humans that predominantly affects skeletal muscle tissue. In mice, TK2 deficiency also affects several tissues in addition to skeletal muscle, including brain, heart, adipose tissue, kidneys and causes death about 3 weeks after birth. We analysed skeletal muscle and heart muscle tissues of Tk2 knockout mice at postnatal development phase and observed that TK2 deficient pups grew slower and their skeletal muscles appeared significantly underdeveloped, whereas heart was close to normal in size. Both tissues showed mtDNA depletion and mitochondria with altered ultrastructure, as revealed by transmission electron microscopy. Gene expression microarray analysis showed a strong down-regulation of genes involved in cell cycle and cell proliferation in both tissues, suggesting a lower pool of undifferentiated proliferating cells. Analysis of isolated primary myoblasts from Tk2 knockout mice showed slow proliferation, less ability to differentiate and signs of premature senescence, even in absence of mtDNA depletion. Our data demonstrate that TK2 deficiency disturbs myogenic progenitor cells function in postnatal skeletal muscle and we propose this as one of the causes of underdeveloped phenotype and myopathic characteristic of the TK2 deficient mice, in addition to the progressive mtDNA depletion, mitochondrial damage and respiratory chain deficiency in post-mitotic differentiated tissue.

Virus-producing cells determine the host protein profiles of HIV-1 virion cores

Background

Upon HIV entry into target cells, viral cores are released and rearranged into reverse transcription complexes (RTCs), which support reverse transcription and also protect and transport viral cDNA to the site of integration. RTCs are composed of viral and cellular proteins that originate from both target and producer cells, the latter entering the target cell within the viral core. However, the proteome of HIV-1 viral cores in the context of the type of producer cells has not yet been characterized.

Results

We examined the proteomic profiles of the cores purified from HIV-1 NL4-3 virions assembled in Sup-T1 cells (T lymphocytes), PMA and vitamin D₃ activated THP1 (model of macrophages, mMΦ), and non-activated THP1 cells (model of monocytes, mMN) and assessed potential involvement of identified proteins in the early stages of infection using gene ontology information and data from genome-wide screens on proteins important for HIV-1 replication. We identified 202 cellular proteins incorporated in the viral cores (T cells: 125, mMΦ: 110, mMN: 90) with the overlap between these sets limited to 42 proteins. The groups of RNA binding (29), DNA binding (17), cytoskeleton (15), cytoskeleton regulation (21), chaperone (18), vesicular trafficking-associated (12) and ubiquitin-proteasome pathway-associated proteins (9) were most numerous. Cores of the virions from SupT1 cells contained twice as many RNA binding proteins as cores of THP1-derived virus, whereas cores of virions from mMΦ and mMN were enriched in components of cytoskeleton and vesicular transport machinery, most probably due to differences in virion assembly pathways between these cells. Spectra of chaperones, cytoskeletal proteins and ubiquitin-proteasome pathway components were similar between viral cores from different cell types, whereas DNA-binding and especially RNA-binding proteins were highly diverse. Western blot analysis showed that within the group of overlapping proteins, the level of incorporation of some RNA binding (RHA and HELIC2) and DNA binding proteins (MCM5 and Ku80) in the viral cores from T cells was higher than in the cores from both mMΦ and mMN and did not correlate with the abundance of these proteins in virus producing cells.

Conclusions

Profiles of host proteins packaged in the cores of HIV-1 virions depend on the type of virus producing cell. The pool of proteins present in the cores of all virions is likely to contain factors important for viral functions. Incorporation ratio of certain RNA- and DNA-binding proteins suggests their more efficient, non-random packaging into virions in T cells than in mMΦ and mMN.

Visualization and measurement of ATP levels in living cells replicating hepatitis C virus genome RNA

Adenosine 5′-triphosphate (ATP) is the primary energy currency of all living organisms and participates in a variety of cellular processes. Although ATP requirements during viral lifecycles have been examined in a number of studies, a method by which ATP production can be monitored in real-time, and by which ATP can be quantified in individual cells and subcellular compartments, is lacking, thereby hindering studies aimed at elucidating the precise mechanisms by which viral replication energized by ATP is controlled. In this study, we investigated the fluctuation and distribution of ATP in cells during RNA replication of the hepatitis C virus (HCV), a member of the Flaviviridae family. We demonstrated that cells involved in viral RNA replication actively consumed ATP, thereby reducing cytoplasmic ATP levels. Subsequently, a method to measure ATP levels at putative subcellular sites of HCV RNA replication in living cells was developed by introducing a recently-established Förster resonance energy transfer (FRET)-based ATP indicator, called ATeam, into the NS5A coding region of the HCV replicon. Using this method, we were able to observe the formation of ATP-enriched dot-like structures, which co-localize with non-structural viral proteins, within the cytoplasm of HCV-replicating cells but not in non-replicating cells. The obtained FRET signals allowed us to estimate ATP concentrations within HCV replicating cells as ∼5 mM at possible replicating sites and ∼1 mM at peripheral sites that did not appear to be involved in HCV replication. In contrast, cytoplasmic ATP levels in non-replicating Huh-7 cells were estimated as ∼2 mM. To our knowledge, this is the first study to demonstrate changes in ATP concentration within cells during replication of the HCV genome and increased ATP levels at distinct sites within replicating cells. ATeam may be a powerful tool for the study of energy metabolism during replication of the viral genome.

ATP is the major energy currency of living cells. Replication of the virus genome is a physiological mechanism that is known to require energy for operations such as the synthesis of DNA or RNA and their unwinding. However, it has been difficult to comprehend how the ATP level is regulated inside single living cells where the virus replicates, since average ATP values in cell extracts have only been estimated using existing methods for ATP measurement. ATeam, which was established in 2009, is a genetically-encoded Förster resonance energy transfer (FRET)-based indicator for ATP that is composed of a small bacterial protein that specifically binds ATP sandwiched between two fluorescent proteins. In this study, by applying ATeam to the subgenomic replicon system, we have developed a method to monitor ATP at putative subcellular sites of RNA replication of the hepatitis C virus (HCV), a major human pathogen associated with liver disease, in living cells. We show here, for the first time, changes in ATP concentrations at distinct sites within cells undergoing HCV RNA replication. ATeam might open the door to understanding how regulation of ATP can affect the lifecycles of pathogens.

The Gag cleavage product, p12, is a functional constituent of the murine leukemia virus pre-integration complex

The p12 protein is a cleavage product of the Gag precursor of the murine leukemia virus (MLV). Specific mutations in p12 have been described that affect early stages of infection, rendering the virus replication-defective. Such mutants showed normal generation of genomic DNA but no formation of circular forms, which are markers of nuclear entry by the viral DNA. This suggested that p12 may function in early stages of infection but the precise mechanism of p12 action is not known. To address the function and follow the intracellular localization of the wt p12 protein, we generated tagged p12 proteins in the context of a replication-competent virus, which allowed for the detection of p12 at early stages of infection by immunofluorescence. p12 was found to be distributed to discrete puncta, indicative of macromolecular complexes. These complexes were localized to the cytoplasm early after infection, and thereafter accumulated adjacent to mitotic chromosomes. This chromosomal accumulation was impaired for p12 proteins with a mutation that rendered the virus integration-defective. Immunofluorescence demonstrated that intracellular p12 complexes co-localized with capsid, a known constituent of the MLV pre-integration complex (PIC), and immunofluorescence combined with fluorescent in situ hybridization (FISH) revealed co-localization of the p12 proteins with the incoming reverse transcribed viral DNA. Interactions of p12 with the capsid and with the viral DNA were also demonstrated by co-immunoprecipitation. These results imply that p12 proteins are components of the MLV PIC. Furthermore, a large excess of wt PICs did not rescue the defect in integration of PICs derived from mutant p12 particles, demonstrating that p12 exerts its function as part of this complex. Altogether, these results imply that p12 proteins are constituent of the MLV PIC and function in directing the PIC from the cytoplasm towards integration.

All retroviruses reverse transcribe their RNA genome to a DNA copy in the cytoplasm of the infected cell. To be expressed, the viral genomic DNA has to travel to the cell nucleus and to integrate into the cellular chromosomes. This trafficking is governed by cellular and viral proteins that associate with the viral genome to form a ‘pre-integration complex’ (PIC), yet the full composition of this complex is unknown. Former studies showed that for the murine leukemia virus (MLV), mutations in a viral protein named p12 abrogate MLV infection, after reverse transcription and prior to the integration step, suggesting a role for this protein in early stages of infection. However, the precise mechanism of p12 action is not known. We combined microscopic, genetic and biochemical techniques to provide evidence that the p12 protein is part of the MLV PIC and that it exerts its function from within this complex. These analyses also suggest a role for p12 in the trafficking of the PIC from the cytoplasm to the chromosomes of the infected cell. Altogether, these findings highlight an important ‘building block’ of a complex that is essential for MLV infection.

High affinity binding between Hsp70 and the C-terminal domain of the measles virus nucleoprotein requires an Hsp40 co-chaperone

The major inducible 70 kDa heat shock protein (hsp70) binds the measles virus (MeV) nucleocapsid with high affinity in an ATP-dependent manner, stimulating viral transcription and genome replication, and profoundly influencing virulence in mouse models of brain infection. Binding is mediated by two hydrophobic motifs (Box-2 and Box-3) located within the C-terminal domain (N(TAIL)) of the nucleocapsid protein, with N(TAIL) being an intrinsically disordered domain. The current work showed that high affinity hsp70 binding to N(TAIL) requires an hsp40 co-chaperone that interacts primarily with the hsp70 nucleotide binding domain (NBD) and displays no significant affinity for N(TAIL). Hsp40 directly enhanced hsp70 ATPase activity in an N(TAIL)-dependent manner, and formation of hsp40-hsp70-N(TAIL) intracellular complexes required the presence of N(TAIL) Box-2 and 3. Results are consistent with the functional interplay between hsp70 nucleotide and substrate binding domains (SBD), where ATP hydrolysis is rate limiting to high affinity binding to client proteins and is enhanced by hsp40. As such, hsp40 is an essential variable in understanding the outcome of MeV-hsp70 interactions.

Cyclosporine blocks incorporation of HIV-1 envelope glycoprotein into virions

Cyclosporine (CsA) decreases HIV-1 infectivity by blocking HIV-1 capsid (CA) interaction with target cell cyclophilin A (CypA). Yet, HIV-1 virions produced in the presence of CsA also exhibit decreased infectivity that was previously shown to be independent of the well-characterized HIV-1 CA-CypA interaction. Here, we demonstrate that CsA decreases gp120 and gp41 incorporation into HIV-1 virions and that the fusion of these virions with susceptible target cells is impaired. This effect was not observed with HIV-1 virions pseudotyped with the vesicular stomatitis virus glycoprotein or with the amphotropic envelope protein of murine leukemia virus. It was independent of calcineurin signaling, the endoplasmic reticulum luminal protein cyclophilin B, and the long cytoplasmic tail of gp41. Thus, cyclosporine blocks HIV-1 infectivity via two independent mechanisms, the first involving HIV-1 CA in target cells and the second involving HIV-1 Env in producer cells.

Inhibition of HIV-1 replication in human monocyte-derived macrophages by parasite Trypanosoma cruzi

BACKGROUND

Cells of monocyte/macrophage lineage are one of the major targets of HIV-1 infection and serve as reservoirs for viral persistence in vivo. These cells are also the target of the protozoa Trypanosoma cruzi, the causative agent of Chagas disease, being one of the most important endemic protozoonoses in Latin America. It has been demonstrated in vitro that co-infection with other pathogens can modulate HIV replication. However, no studies at cellular level have suggested an interaction between T. cruzi and HIV-1 to date.

METHODOLOGY/PRINCIPAL FINDINGS

By using a fully replicative wild-type virus, our study showed that T. cruzi inhibits HIV-1 antigen production by nearly 100% (p<0.001) in monocyte-derived macrophages (MDM). In different infection schemes with luciferase-reporter VSV-G or BaL pseudotyped HIV-1 and trypomastigotes, T. cruzi induced a significant reduction of luciferase level for both pseudotypes in all the infection schemes (p<0.001), T. cruzi-HIV (>99%) being stronger than HIV-T. cruzi (approximately 90% for BaL and approximately 85% for VSV-G) infection. In MDM with established HIV-1 infection, T. cruzi significantly inhibited luciferate activity (p<0.01). By quantifying R-U5 and U5-gag transcripts by real time PCR, our study showed the expression of both transcripts significantly diminished in the presence of trypomastigotes (p<0.05). Thus, T. cruzi inhibits viral post-integration steps, early post-entry steps and entry into MDM. Trypomastigotes also caused a approximately 60-70% decrease of surface CCR5 expression on MDM. Multiplication of T. cruzi inside the MDM does not seem to be required for inhibiting HIV-1 replication since soluble factors secreted by trypomastigotes have shown similar effects. Moreover, the major parasite antigen cruzipain, which is secreted by the trypomastigote form, was able to inhibit viral production in MDM over 90% (p<0.01).

CONCLUSIONS/SIGNIFICANCE

Our study showed that T. cruzi inhibits HIV-1 replication at several replication stages in macrophages, a major cell target for both pathogens.

Target cell type-dependent modulation of human immunodeficiency virus type 1 capsid disassembly by cyclophilin A

The binding of cyclophilin A (CypA) to the human immunodeficiency virus type 1 (HIV-1) capsid protein (CA protein) is required soon after virus entry into natural target cells. In Jurkat T lymphocytes, disrupting CypA-CA interaction either by cyclosporine (Cs) treatment or by alteration (e.g., P90A) of the CA inhibits HIV-1 infection. In HeLa cells, however, treatment with Cs or Cs analogues minimally inhibits the early phase of HIV-1 infection but selects for a Cs-dependent virus with a change (A92E) in CA. To understand these phenomena, we examined the effects of the P90A and A92E changes in the HIV-1 CA protein on the stability of capsid complexes assembled in vitro and on capsid disassembly in the cytosol of virus-exposed target cells. The A92E change impaired CA-CA interactions in vitro and decreased the amount of particulate capsids in the cytosol of HeLa target cells. Reducing the binding of CypA to the A92E mutant capsid, either by Cs treatment or by an additional P90A change in the CA protein, increased the amount of particulate capsids and viral infectivity in HeLa cells. In contrast, reduction of the binding of CypA to HIV-1 capsids in Jurkat T lymphocytes resulted in a decrease in the amount of particulate capsids and infectivity. Thus, depending on the capsid and the target cell, CypA-CA binding either stabilized or destabilized the capsid, indicating that CypA modulates HIV-1 capsid disassembly. In both cell types examined, decreased stability of the capsid was associated with a decrease in the efficiency of HIV-1 infection.

Molecular chaperones in pathogen virulence: emerging new targets for therapy

Infectious organisms have to cope with demanding and rapidly changing environments during establishment in the host. This is particularly relevant for pathogens that utilize different hosts to complete their life cycle. In addition to homeotic environmental challenges, other stressful factors, such as oxidative bursts, are often triggered in response to infection. It is not surprising that many successful pathogens have developed robust chaperone systems to conquer the stressful environments in the host. In addition to discussing ingenious ways by which pathogens have utilized chaperones, the potential of exploiting pathogen chaperones as drug targets is also discussed.

Combining human antisera to human leukocyte antigens, HIVgp120 and 70 kDa heat shock protein results in broadly neutralizing activity to HIV-1

OBJECTIVE

To elicit broadly neutralizing antibody activity by combining polyclonal human serum IgG antibodies with HIVgp120, human leukocyte antigen (HLA) class I or class II and 70 kDa heat shock protein.

DESIGN

: In addition to HIV antigens, HIV-1 virions express HLA class I, HLA class II and 70 kDa heat shock protein molecules, which have quantitative and functional significance. The complementary effect of combining human polyclonal IgG antibodies with these antigens may result in effective broad spectrum neutralizing activity.

METHODS

Polyclonal human sera with IgG antibodies and monoclonal antibody to HLA class I or class II, HIVgp120 and 70 kDa heat shock protein were selected and used in single, double or triple combinations. Dose-dependent inhibition studies of HIV-1 clades A, B, C and D were carried out using human CD4 T cells treated with the combinations of human sera and with monoclonal antibodies for clade B. The results are presented as half maximal (IC50) inhibitory concentration and maximum inhibition by these sera.

RESULTS

The half maximal (IC50) inhibitory concentration of clade B HIV-1 infection with single or a combination of two antisera was higher than those with three antisera, which also showed maximum inhibition of HIV-1. Further investigations of human sera with HIV-1 clades C and D also showed lower half maximal (IC50) inhibitory concentrations and higher maximum inhibition with combinations of the three antisera, but this was not seen with clade A.

CONCLUSION

A novel vaccination strategy eliciting broadly neutralizing antibody activity to the CCR5-using HIV-1 clades B, C and D has been demonstrated by the trimolecular complex of human antisera with HLA class II or class I, HIVgp120 and 70 kDa heat shock protein.

Trypanosoma cruzi (Chagas' disease agent) reduces HIV-1 replication in human placenta

Background

Several factors determine the risk of HIV mother-to-child transmission (MTCT), such as coinfections in placentas from HIV-1 positive mothers with other pathogens. Chagas' disease is one of the most endemic zoonoses in Latin America, caused by the protozoan Trypanosoma cruzi. The purpose of the study was to determine whether T. cruzi modifies HIV infection of the placenta at the tissue or cellular level.

Results

Simple and double infections were carried out on a placental histoculture system (chorionic villi isolated from term placentas from HIV and Chagas negative mothers) and on the choriocarcinoma BeWo cell line. Trypomastigotes of T. cruzi (VD lethal strain), either purified from mouse blood or from Vero cell cultures, 24 h-supernatants of blood and cellular trypomastigotes, and the VSV-G pseudotyped HIV-1 reporter virus were used for the coinfections. Viral transduction was evaluated by quantification of luciferase activity. Coinfection with whole trypomastigotes, either from mouse blood or from cell cultures, decreased viral pseudotype luciferase activity in placental histocultures. Similar results were obtained from BeWo cells. Supernatants of stimulated histocultures were used for the simultaneous determination of 29 cytokines and chemokines with the Luminex technology. In histocultures infected with trypomastigotes, as well as in coinfected tissues, IL-6, IL-8, IP-10 and MCP-1 production was significantly lower than in controls or HIV-1 transducted tissue. A similar decrease was observed in histocultures treated with 24 h-supernatants of blood trypomastigotes, but not in coinfected tissues.

Conclusion

Our results demonstrated that the presence of an intracellular pathogen, such as T. cruzi, is able to impair HIV-1 transduction in an in vitro system of human placental histoculture. Direct effects of the parasite on cellular structures as well as on cellular/viral proteins essential for HIV-1 replication might influence viral transduction in this model. Nonetheless, additional mechanisms including modulation of cytokines/chemokines at placental level could not be excluded in the inhibition observed. Further experiments need to be conducted in order to elucidate the mechanism(s) involved in this phenomenon. Therefore, coinfection with T. cruzi may have a deleterious effect on HIV-1 transduction and thus could play an important role in viral outcome at the placental level.

Cell factors stimulate human immunodeficiency virus type 1 reverse transcription in vitro

After fusion of the human immunodeficiency virus type 1 (HIV-1) envelope with the host cell membrane, the HIV-1 core enters the cell cytoplasm. Core components are then restructured to form the reverse transcription complex (RTC); the biochemical details of this process are currently unclear. To investigate early RTC formation, we characterized the endogenous reverse transcription activity of virions, which was less efficient than reverse transcription during cell infection and suggested a requirement for a cell factor. The addition of detergent to virions released reverse transcriptase and capsid, and reverse transcription products became susceptible to the action of exogenous nucleases, indicating virion disruption. Disruption was coincident with the loss of the endogenous reverse transcription activity of virions, particularly late reverse transcription products. Consistent with this observation, the use of a modified "spin thru" method, which uses brief detergent exposure, also disrupted virions. The addition of lysates made from mammalian cell lines (Jurkat, HEK293T, and NIH 3T3 cells) to virions delipidated by detergent stimulated late reverse transcription efficiency. A complex with reverse transcription activity that was slower sedimenting than virions on a velocity gradient was greatly stimulated to generate full-length reverse transcription products and was associated with only relatively small amounts of capsid. These experiments suggest that cell factors are required for efficient reverse transcription of HIV-1.

Hsp40 facilitates nuclear import of the human immunodeficiency virus type 2 Vpx-mediated preintegration complex

Human immunodeficiency virus type 2 (HIV-2) Vpx is required for nuclear translocation of the viral preintegration complex (PIC) in quiescent cells. In order to decipher the mechanism of action of Vpx, a cDNA library was screened with the yeast two-hybrid assay, resulting in the identification of heat shock protein 40, Hsp40/DnaJB6, as a Vpx-interactive protein. Interaction with Vpx was confirmed by glutathione S-transferase (GST) pull-down and coimmunoprecipitation assays. Overexpression of Hsp40/DnaJB6 enhanced Vpx nuclear import, whereas overexpression of a nuclear localization mutant of Hsp40/DnaJB6 (H31Q) or down-regulation of Hsp40/DnaJB6 by small interfering RNA (siRNA) reduced the nuclear import of Vpx. Hsp40/DnaJB6 competed with the Pr55(Gag) precursor protein for the binding of Vpx and incorporation into virus-like particles. Overexpression of Hsp40/DnaJB6 promoted viral PIC nuclear import, whereas siRNA down-regulation of Hsp40/DnaJB6 inhibited PIC nuclear import. These results demonstrate a role for Hsp40/DnaJB6 in the regulation of HIV-2 PIC nuclear transport.

Resistance of monocyte to HIV-1 infection is not due to uncoating defect

Freshly isolated blood monocytes show an early postentry block to in vitro HIV-1 infection. Differentiation into monocyte-derived macrophages (MDMs) is required to allow HIV replication in this cell type. In this study, we investigated whether the resistance of monocyte to HIV infection stemmed from uncoating defect. Monocyte and MDM lysates induced HIV-1 core uncoating to a comparable degree. This suggests that monocyte lacks a factor(s) essential for viral reverse transcription and/or contains a factor(s) interfering with this step.

Inhibition of human immunodeficiency virus type 1 infection of human CD4+ T cells by microbial HSP70 and the peptide epitope 407-426

Human immunodeficiency virus type 1 (HIV-1) virions contain heat shock proteins (HSP), but these proteins have received limited attention. The objectives of this study were to establish if the microbial 70-kDa HSP exerts an inhibitory effect on the HIV-1 infection of human CD4+ T cells, to identify an inhibitory peptide epitope within the sequence of HSP70, and to evaluate the kinetic features of any inhibitory activity. The results of these studies suggest that microbial HSP70 exerts dose-dependent inhibition on CCR5 (R5) strains of clades B, C, and D of HIV-1 infecting human CD4+ T cells. The site of the HIV-1-inhibitory function was identified within the C-terminal peptide binding domain of HSP70, and the function is expressed by the peptide epitope comprising amino acids 407 to 426. The mechanism of inhibition of HIV-1 infectivity by HSP70 is blocking of the CCR5 coreceptors directly and indirectly by inducing CC chemokines and APOBEC3G. The inhibitory effect of HSP70, its C-terminal fragment, or peptide 407-426 may make HSP70 useful as a microbicidal agent. A potentiating noncognate inhibition of HIV-1 infectivity by combined treatment with HSP70 and monoclonal or polyclonal antibody to CCR5 was demonstrated. This novel strategy may be utilized in therapeutic immunization against HIV-1 infection.

Specific recognition and accelerated uncoating of retroviral capsids by the TRIM5alpha restriction factor

The host restriction factor TRIM5alpha mediates species-specific, early blocks to retrovirus infection; susceptibility to these blocks is determined by viral capsid sequences. Here we demonstrate that TRIM5alpha variants from Old World monkeys specifically associate with the HIV type 1 (HIV-1) capsid and that this interaction depends on the TRIM5alpha B30.2 domain. Human and New World monkey TRIM5alpha proteins associated less efficiently with the HIV-1 capsid, accounting for the lack of restriction in cells of these species. After infection, the expression of a restricting TRIM5alpha in the target cells correlated with a decrease in the amount of particulate capsid in the cytosol. In some cases, this loss of particulate capsid was accompanied by a detectable increase in soluble capsid protein. Inhibiting the proteasome did not abrogate restriction. Thus, TRIM5alpha restricts retroviral infection by specifically recognizing the capsid and promoting its rapid, premature disassembly.

The retrovirus RNA trafficking granule: from birth to maturity

Post-transcriptional events in the life of an RNA including RNA processing, transport, translation and metabolism are characterized by the regulated assembly of multiple ribonucleoprotein (RNP) complexes. At each of these steps, there is the engagement and disengagement of RNA-binding proteins until the RNA reaches its final destination. For retroviral genomic RNA, the final destination is the capsid. Numerous studies have provided crucial information about these processes and serve as the basis for studies on the intracellular fate of retroviral RNA. Retroviral RNAs are like cellular mRNAs but their processing is more tightly regulated by multiple cis-acting sequences and the activities of many trans-acting proteins. This review describes the viral and cellular partners that retroviral RNA encounters during its maturation that begins in the nucleus, focusing on important events including splicing, 3' end-processing, RNA trafficking from the nucleus to the cytoplasm and finally, mechanisms that lead to its compartmentalization into progeny virions.