Cell cycle arrest in G2/M promotes early steps of infection by human immunodeficiency virus

Cell cycle regulation of the psoriasis associated gene CCHCR1 by transcription factor E2F1

The coiled-coil alpha-helical rod protein 1 (CCHCR1) was first identified as a candidate gene in psoriasis and has lately been found to be associated with a wide range of clinical conditions including COVID-19. CCHCR1 is located within P-bodies and centrosomes, but its exact role in these two subcellular structures and its transcriptional control remain largely unknown. Here, we showed that CCHCR1 shares a bidirectional promoter with its neighboring gene, TCF19. This bidirectional promoter is activated by the G1/S-regulatory transcription factor E2F1, and both genes are co-induced during the G1/S transition of the cell cycle. A luciferase reporter assay suggests that the short intergenic sequence, only 287 bp in length, is sufficient for the G1/S induction of both genes, but the expression of CCHCR1 is further enhanced by the presence of exon 1 from both TCF19 and CCHCR1. This research uncovers the transcriptional regulation of the CCHCR1 gene, offering new perspectives on its function. These findings contribute to the broader understanding of diseases associated with CCHCR1 and may serve as a foundational benchmark for future research in these vital medical fields.

Topoisomerase Inhibitors Increase Episomal DNA Expression by Inducing the Integration of Episomal DNA in Hepatic Cells

Gene therapy is a promising strategy to treat and cure most inherited metabolic liver disorders. Viral vectors such as those based on adeno-associated viruses (AAVs) and lentiviruses (LVs) are used as vehicles to deliver functional genes to affected hepatocytes. Adverse events associated with the use of high vector doses have motivated the use of small molecules as adjuvants to reduce the dose. In this study, we showed that a one-hour treatment with topoisomerase inhibitors (camptothecin and etoposide) prior to viral transduction is enough to increase AAV and LV reporter expression in non-dividing hepatic cells in culture. Topoisomerase inhibitors increased both integration-competent (ICLV) and integration-deficient (IDLV) LV-derived expression, with a much stronger increase in the IDLV transduction system. In agreement with that, topoisomerase inhibitors increased viral genome integration in both strains, with a greater impact on the IDLV strain, supporting the idea that topoisomerase inhibitors increased episomal DNA integration, especially when viral integrase activity is abolished. These effects correlated with an increase in the DNA damage response produced by the treatments. Our study highlights the need to monitor DNA damage and undesired integration of viral episomal DNAs into the host genome when studying chemical compounds that increase viral transduction.

HUSH-mediated HIV silencing is independent of TASOR phosphorylation on threonine 819

BACKGROUND

TASOR, a component of the HUSH repressor epigenetic complex, and SAMHD1, a cellular triphosphohydrolase (dNTPase), are both anti-HIV proteins antagonized by HIV-2/SIVsmm Viral protein X. As a result, the same viral protein is able to relieve two different blocks along the viral life cell cycle, one at the level of reverse transcription, by degrading SAMHD1, the other one at the level of proviral expression, by degrading TASOR. Phosphorylation of SAMHD1 at T592 has been shown to downregulate its antiviral activity. The discovery that T819 in TASOR was lying within a SAMHD1 T592-like motif led us to ask whether TASOR is phosphorylated on this residue and whether this post-translational modification could regulate its repressive activity.

RESULTS

Using a specific anti-phospho-antibody, we found that TASOR is phosphorylated at T819, especially in cells arrested in early mitosis by nocodazole. We provide evidence that the phosphorylation is conducted by a Cyclin/CDK1 complex, like that of SAMHD1 at T592. While we could not detect TASOR in quiescent CD4 + T cells, TASOR and its phosphorylated form are present in activated primary CD4 + T lymphocytes. In addition, TASOR phosphorylation appears to be independent from TASOR repressive activity. Indeed, on the one hand, nocodazole barely reactivates HIV-1 in the J-Lat A1 HIV-1 latency model despite TASOR T819 phosphorylation. On the other hand, etoposide, a second cell cycle arresting drug, reactivates latent HIV-1, without concomitant TASOR phosphorylation. Furthermore, overexpression of wt TASOR or T819A or T819E similarly represses gene expression driven by an HIV-1-derived LTR promoter. Finally, while TASOR is degraded by HIV-2 Vpx, TASOR phosphorylation is prevented by HIV-1 Vpr, likely as a consequence of HIV-1 Vpr-mediated-G2 arrest.

CONCLUSIONS

Altogether, we show that TASOR phosphorylation occurs in vivo on T819. This event does not appear to correlate with TASOR-mediated HIV-1 silencing. We speculate that TASOR phosphorylation is related to a role of TASOR during cell cycle progression.

Role of IFNLR1 gene in PRRSV infection of PAM cells

Background

Interferon lambda receptor 1 (IFNLR1) is a type II cytokine receptor that clings to interleukins IL-28A, IL29B, and IL-29 referred to as type III IFNs (IFN-λs). IFN-λs act through the JAK-STAT signaling pathway to exert antiviral effects related to preventing and curing an infection. Although the immune function of IFN-λs in virus invasion has been described, the molecular mechanism of IFNLR1 in that process is unclear.

Objectives

The purpose of this study was to elucidate the role of IFNLR1 in the pathogenesis and treatment of porcine reproductive and respiratory syndrome virus (PRRSV).

Methods

The effects of IFNLR1 on the proliferation of porcine alveolar macrophages (PAMs) during PRRSV infection were investigated using interference and overexpression methods.

Results

In this study, the expressions of the IFNLR1 gene in the liver, large intestine, small intestine, kidney, and lung tissues of Dapulian pigs were significantly higher than those in Landrace pigs. It was determined that porcine IFNLR1 overexpression suppresses PRRSV replication. The qRT-PCR results revealed that overexpression of IFNLR1 upregulated antiviral and IFN-stimulated genes. IFNLR1 overexpression inhibits the proliferation of PAMs and upregulation of p-STAT1. By contrast, knockdown of IFNLR1 expression promotes PAMs proliferation. The G0/G1 phase proportion in IFNLR1-overexpressing cells increased, and the opposite change was observed in IFNLR1-underexpressing cells. After inhibition of the JAK/STAT signaling pathway, the G2/M phase proportion in the IFNLR1-overexpressing cells showed a significant increasing trend. In conclusion, overexpression of IFNLR1 induces activation of the JAK/STAT pathway, thereby inhibiting the proliferation of PAMs infected with PRRSV.

Conclusion

Expression of the IFNLR1 gene has an important regulatory role in PRRSV-infected PAMs, indicating it has potential as a molecular target in developing a new strategy for the treatment of PRRSV.

The Interaction of Viruses with the Cellular Senescence Response

Cellular senescence is viewed as a mechanism to prevent malignant transformation, but when it is chronic, as occurs in age-related diseases, it may have adverse effects on cancer. Therefore, targeting senescent cells is a novel therapeutic strategy against senescence-associated diseases. In addition to its role in cancer protection, cellular senescence is also considered a mechanism to control virus replication. Both interferon treatment and some viral infections can trigger cellular senescence as a way to restrict virus replication. However, activation of the cellular senescence program is linked to the alteration of different pathways, which can be exploited by some viruses to improve their replication. It is, therefore, important to understand the potential impact of senolytic agents on viral propagation. Here we focus on the relationship between virus and cellular senescence and the reported effects of senolytic compounds on virus replication.

Materials promoting viral gene delivery

Therapeutic viral gene delivery is an emerging technology which aims to correct genetic mutations by introducing new genetic information to cells either to correct a faulty gene or to initiate cell death in oncolytic treatments. In recent years, significant scientific progress has led to several clinical trials resulting in the approval of gene therapies for human treatment. However, successful therapies remain limited due to a number of challenges such as inefficient cell uptake, low transduction efficiency (TE), limited tropism, liver toxicity and immune response. To adress these issues and increase the number of available therapies, additives from a broad range of materials like polymers, peptides, lipids, nanoparticles, and small molecules have been applied so far. The scope of this review is to highlight these selected delivery systems from a materials perspective.

Cell Cycle Regulation in Macrophages and Susceptibility to HIV-1

Macrophages are the first line of defence against invading pathogens. They play a crucial role in immunity but also in regeneration and homeostasis. Their remarkable plasticity in their phenotypes and function provides them with the ability to quickly respond to environmental changes and infection. Recent work shows that macrophages undergo cell cycle transition from a G0/terminally differentiated state to a G1 state. This G0-to-G1 transition presents a window of opportunity for HIV-1 infection. Macrophages are an important target for HIV-1 but express high levels of the deoxynucleotide-triphosphate hydrolase SAMHD1, which restricts viral DNA synthesis by decreasing levels of dNTPs. While the G0 state is non-permissive to HIV-1 infection, a G1 state is very permissive to HIV-1 infection. This is because macrophages in a G1 state switch off the antiviral restriction factor SAMHD1 by phosphorylation, thereby allowing productive HIV-1 infection. Here, we explore the macrophage cell cycle and the interplay between its regulation and permissivity to HIV-1 infection.

Insights into the Gene Expression Profiles of Active and Restricted Red/Green-HIV+ Human Astrocytes: Implications for Shock or Lock Therapies in the Brain

A significant number of people living with human immunodeficiency virus type 1 (HIV-1) suffer from HIV-associated neurocognitive disorders (HAND). Many previous studies investigating HIV in astrocytes as a heterogenous population have established the relevance of astrocytes to HIV-associated neuropathogenesis. However, these studies were unable to differentiate the state of infection, i.e., active or latent, or to evaluate how this affects astrocyte biology. In this study, the pseudotyped doubly labeled fluorescent reporter red/green (R/G)-HIV-1 was used to identify and enrich restricted and active populations of HIV⁺ astrocytes based on the viral promoter activity. Here, we report that the majority of human astrocytes restricted R/G-HIV-1 gene expression early during infection and were resistant to reactivation by vorinostat and interleukin 1β. However, actively infected astrocytes were inducible, leading to increased expression of viral proteins upon reactivation. R/G-HIV-1 infection also significantly decreased the cell proliferation and glutamate clearance ability of astrocytes, which may contribute to excitotoxicity. Moreover, transcriptome analyses to compare gene expression patterns of astrocyte harboring active versus restricted long terminal repeats (LTRs) revealed that the gene expression patterns were similar and that the active population demonstrated more widespread and robust changes. Our data suggest that harboring the HIV genome profoundly alters astrocyte biology and that strategies that keep the virus latent (e.g., block and lock) or those that reactivate the latent virus (e.g., shock and kill) would be detrimental to astrocyte function and possibly augment their contributions to HAND.IMPORTANCE More than 36 million people are living with HIV-1 worldwide, and despite antiretroviral therapy, 30 to 50% of the people living with HIV-1 suffer from mild to moderate neurocognitive disorders. HIV-1 reservoirs in the central nervous system (CNS) are challenging to address due to low penetration of antiretroviral drugs, lack of resident T cells, and permanent integration of provirus into neural cells such as microglia and astrocytes. Several studies have shown astrocyte dysfunction during HIV-1 infection. However, little is known about how HIV-1 latency affects their function. The significance of our research is in identifying that the majority of HIV⁺ astrocytes restrict HIV expression and were resistant to reactivation. Further, simply harboring the HIV genome profoundly altered astrocyte biology, resulting in a proinflammatory phenotype and functional changes. In this context, therapeutic strategies to reactivate or silence astrocyte HIV reservoirs, without excising proviral DNA, will likely lead to detrimental neuropathological outcomes during HIV CNS infection.

Viral protein X unlocks the nuclear pore complex through a human Nup153-dependent pathway to promote nuclear translocation of the lentiviral genome

Simian immunodeficiency virus (SIV) and human immunodeficiency virus 2 (HIV-2) display unique ability to infect nondividing target cells. Viral protein X (Vpx) of HIV-2/SIV is known to be involved in the nuclear import of viral genome in nondividing cells, but the mechanism remains poorly understood. In the present investigation for the first time we provide evidence that Vpx of SIV_smPBj1.9 physically interacts with human nucleoporin 153 (Nup153), which is known to provide a docking site for protein-cargo complexes at the nuclear pore complex (NPC). Results from superresolution-structured illumination microscopy studies reveal that Vpx interaction with NPC-associated Nup153 is critical for its efficient nuclear translocation. Virion-associated MAPK/ERK-2-mediated phosphorylation of Vpx plays a critical role in its interaction with human Nup153 and this interaction was found to be evolutionarily conserved in various SIV isolates and HIV-2. Interestingly, MAPK/ERK-2 packaging defective SIV failed to promote the efficient nuclear import of viral genome and suggests that MAPK/ERK-2-mediated Vpx phosphorylation is important for its interaction with Nup153, which is critical for lentiviruses to establish infection in nondividing target cells. Together, our data elucidate the mechanism by which Vpx orchestrates the challenging task of nuclear translocation of HIV-2/SIV genome in nondividing target cells.

Akt inhibition at the initial stage of CAR-T preparation enhances the CAR-positive expression rate, memory phenotype and in vivo efficacy

The adoptive transfer of chimeric antigen receptor-modified T (CAR-T) cells is a novel cancer treatment that has led to encouraging breakthroughs in the treatment of haematological malignancies. The efficacy of infused CAR-T cells is associated with a high CAR-positive expression rate, a strong proliferative response and the persistence of CAR-T cells in vivo. Manufacturing CAR-T cells is a process usually associated with the decreased CAR-positive expression rate and terminal differentiation of the infused CAR-T cells, which causes decreased proliferation and persistence of CAR-T cells in vivo. Therefore, the preparation of a high CAR-positive expression rate and few differentiated CAR-T cells is particularly important for clinical cancer treatment. In this study, we transduced and expanded CAR-T cells targeting the epithelial cell adhesion molecule (EpCAM) in the presence of an Akt inhibitor (MK2206) during the initial stage of CAR-T cell preparation. We show that the Akt inhibitor did not suppress the proliferation or effector function of the EpCAM-CAR-T cells but increased the CAR-positive expression rate and decreased the number of terminally differentiated EpCAM-CAR-T cells. Furthermore, EpCAM-CAR-T cells prepared using this protocol appeared to have enhanced antitumor activity in vivo. Taken together, these findings suggest that Akt inhibition during the initial stage of CAR-T cell preparation could improve the performance of CAR-T cells.

Proteasomal Degradation Machinery: Favorite Target of HIV-1 Proteins

Proteasomal degradation pathways play a central role in regulating a variety of protein functions by controlling not only their turnover but also the physiological behavior of the cell. This makes it an attractive target for the pathogens, especially viruses which rely on the host cellular machinery for their propagation and pathogenesis. Viruses have evolutionarily developed various strategies to manipulate the host proteasomal machinery thereby creating a cellular environment favorable for their own survival and replication. Human immunodeficiency virus-1 (HIV-1) is one of the most dreadful viruses which has rapidly spread throughout the world and caused high mortality due to its high evolution rate. Here, we review the various mechanisms adopted by HIV-1 to exploit the cellular proteasomal machinery in order to escape the host restriction factors and components of host immune system for supporting its own multiplication, and successfully created an infection.

Porcine reproductive and respiratory syndrome virus inhibits MARC-145 proliferation via inducing apoptosis and G2/M arrest by activation of Chk/Cdc25C and p53/p21 pathway

Porcine reproductive and respiratory syndrome virus(PRRSV) is an important immunosuppressive virus which can suppresses infected cells proliferation. In this work, we examined PRRSV ability to manipulate cell cycle progression of MARC-145 cells and explored the potential molecular mechanisms. The results showed that PRRSV infection imposed a growth-inhibitory effect on MARC-145 cells by inducing cell cycle arrest at G2/M phase. This arrest was due to the significant decrease of Cdc2-cyclinB1 complex activity in PRRSV-infected cells and the activity reduction was a result of Cdc2 Tyr15 phosphorylation and the accumulation of Cdc2 and cyclinB1 in the nucleus. Not only elevated Wee1 and Myt1 expression and inactivated Cdc25C, but also increase of p21 and 14–3-3σ in a p53-dependent manner caused the inhibitory Tyr15 phosphorylation of Cdc2. PRRSV infection also activated Chk1. Our data suggest PRRSV infection induces G2/M arrest via various molecular regulatory mechanisms. These results provide a new insights for PRRSV pathogenesis.

Orthosiphon stamineus Extracts Inhibits Proliferation and Induces Apoptosis in Uterine Fibroid Cells

Objectives: The effects of water and 50% ethanolic-water extracts of Orthosiphon stamineus Benth (OS) on cell proliferation and apoptotic activity against uterine leiomyosarcoma (SK-UT-1) cells were investigated. Methods: Anti-proliferation effect was evaluated through cell cycle analysis whereas apoptotic activity was determined via screening and quantifying using fluorescence microscopy and flow cytometric analysis, respectively. The effect of extracts on molecular mechanism was studied using real-time reverse transcription polymerase chain reaction and Western blotting. Results: Cell cycle flow cytometric analysis showed the induction of cell cycle arrests were behaves in a p53-independent manner. The examination using fluorescence microscopy and Annexin V flow cytometry revealed the presence of morphological features of apoptotic bodies. Downregulation of anti-apoptotic gene (Bcl-2) supports the apoptotic activity of OS extracts although poorly induce PARP-1 cleavage in Western blot analysis. The extracts also inhibit the SK-UT-1 growth by suppressing VEGF-A, TGF-β1 and PCNA genes, which involved in angiogenesis and cell proliferation. Conclusion: This study demonstrates that O. stamineus extracts are able to inhibit proliferation and induced apoptosis of uterine fibroid cells and is worth further investigation.

Structural alteration of DNA induced by viral protein R of HIV-1 triggers the DNA damage response

Background

Viral protein R (Vpr) is an accessory protein of HIV-1, which is potentially involved in the infection of macrophages and the induction of the ataxia-telangiectasia and Rad3-related protein (ATR)-mediated DNA damage response (DDR). It was recently proposed that the SLX4 complex of structure-specific endonuclease is involved in Vpr-induced DDR, which implies that aberrant DNA structures are responsible for this phenomenon. However, the mechanism by which Vpr alters the DNA structures remains unclear.

Results

We found that Vpr unwinds double-stranded DNA (dsDNA) and invokes the loading of RPA70, which is a single-stranded DNA-binding subunit of RPA that activates the ATR-dependent DDR. We demonstrated that Vpr influenced RPA70 to accumulate in the corresponding region utilizing the LacO/LacR system, in which Vpr can be tethered to the LacO locus. Interestingly, RPA70 recruitment required chromatin remodelling via Vpr-mediated ubiquitination of histone H2B. On the contrary, Q65R mutant of Vpr, which lacks ubiquitination activity, was deficient in both chromatin remodelling and RPA70 loading on to the chromatin. Moreover, Vpr-induced unwinding of dsDNA coincidently resulted in the accumulation of negatively supercoiled DNA and covalent complexes of topoisomerase 1 and DNA, which caused DNA double-strand breaks (DSBs) and DSB-directed integration of proviral DNA. Lastly, we noted the dependence of Vpr-promoted HIV-1 infection in resting macrophages on topoisomerase 1.

Conclusions

The findings of this study indicate that Vpr-induced structural alteration of DNA is a primary event that triggers both DDR and DSB, which ultimately contributes to HIV-1 infection.

Electronic supplementary material

The online version of this article (10.1186/s12977-018-0391-8) contains supplementary material, which is available to authorized users.

BIRC2/cIAP1 Is a Negative Regulator of HIV-1 Transcription and Can Be Targeted by Smac Mimetics to Promote Reversal of Viral Latency

Combination antiretroviral therapy (ART) is able to suppress HIV-1 replication to undetectable levels. However, the persistence of latent viral reservoirs allows for a rebound of viral load upon cessation of therapy. Thus, therapeutic strategies to eradicate the viral latent reservoir are critically needed. Employing a targeted RNAi screen, we identified the ubiquitin ligase BIRC2 (cIAP1), a repressor of the noncanonical NF-κB pathway, as a potent negative regulator of LTR-dependent HIV-1 transcription. Depletion of BIRC2 through treatment with small molecule antagonists known as Smac mimetics enhanced HIV-1 transcription, leading to a reversal of latency in a JLat latency model system. Critically, treatment of resting CD4+ T cells isolated from ART-suppressed patients with the histone deacetylase inhibitor (HDACi) panobinostat together with Smac mimetics resulted in synergistic activation of the latent reservoir. These data implicate Smac mimetics as useful agents for shock-and-kill strategies to eliminate the latent HIV reservoir.

Activation of the DNA Damage Response by RNA Viruses

RNA viruses are a genetically diverse group of pathogens that are responsible for some of the most prevalent and lethal human diseases. Numerous viruses introduce DNA damage and genetic instability in host cells during their lifecycles and some species also manipulate components of the DNA damage response (DDR), a complex and sophisticated series of cellular pathways that have evolved to detect and repair DNA lesions. Activation and manipulation of the DDR by DNA viruses has been extensively studied. It is apparent, however, that many RNA viruses can also induce significant DNA damage, even in cases where viral replication takes place exclusively in the cytoplasm. DNA damage can contribute to the pathogenesis of RNA viruses through the triggering of apoptosis, stimulation of inflammatory immune responses and the introduction of deleterious mutations that can increase the risk of tumorigenesis. In addition, activation of DDR pathways can contribute positively to replication of viral RNA genomes. Elucidation of the interactions between RNA viruses and the DDR has provided important insights into modulation of host cell functions by these pathogens. This review summarises the current literature regarding activation and manipulation of the DDR by several medically important RNA viruses.

Comparative Analysis of Tat-Dependent and Tat-Deficient Natural Lentiviruses

The emergence of human immunodeficiency virus (HIV) causing acquired immunodeficiency syndrome (AIDS) in infected humans has resulted in a global pandemic that has killed millions. HIV-1 and HIV-2 belong to the lentivirus genus of the Retroviridae family. This genus also includes viruses that infect other vertebrate animals, among them caprine arthritis-encephalitis virus (CAEV) and Maedi-Visna virus (MVV), the prototypes of a heterogeneous group of viruses known as small ruminant lentiviruses (SRLVs), affecting both goat and sheep worldwide. Despite their long host-SRLV natural history, SRLVs were never found to be responsible for immunodeficiency in contrast to primate lentiviruses. SRLVs only replicate productively in monocytes/macrophages in infected animals but not in CD4+ T cells. The focus of this review is to examine and compare the biological and pathological properties of SRLVs as prototypic Tat-independent lentiviruses with HIV-1 as prototypic Tat-dependent lentiviruses. Results from this analysis will help to improve the understanding of why and how these two prototypic lentiviruses evolved in opposite directions in term of virulence and pathogenicity. Results may also help develop new strategies based on the attenuation of SRLVs to control the highly pathogenic HIV-1 in humans.

Canonical Wnt signaling pathway contributes to the proliferation and survival in porcine pancreatic stem cells (PSCs)

Pancreatic stem cells (PSCs) transplantation is a potential therapeutic approach to type 1 diabetes mellitus (D1M). However, before clinical use, there are some major hurdles to be faced that need to be comprehensively considered and given some potential solutions in vitro. Human PSCs are difficult to obtain and have a short replicative senescence. As an alternative, we instead established porcine PSCs; as insulin is highly conserved and physiological glucose levels are similar between human and porcine. In order to solve the problems during transplantation therapy, such as the need for an enormous amount of PSCs and good cell survival in overactive autoimmunity induced by reactive oxygen cpecies (ROS) in D1M patients, we utilized Wnt3a overexpression to activate the canonical Wnt signaling pathway in PSCs. We found that the expression of proliferation genes, such as c-Myc, was up-regulated as the downstream of β-catenin, which promoted the PSCs proliferation and made cell numbers to meet the transplantation needs. We also showed that activation of the Wnt pathway made cells more readily tolerate ROS-caused mitochondria injury and cell apoptosis, thus making cells survive in autoimmune patients. The present study provides a theoretical basis for cell transplantation therapy of diabetes.

Mono-guanidine heterolipid based SMEDDS: A promising tool for cytosolic delivery of antineoplastics

In the present work, we designed and synthesized a novel mono-guanidine heterolipid (MGH) and confirmed its structure by NMR and ESI-MS. The MGH was used as cationic lipid in developing etoposide loaded cationic self-microemulsifying drug delivery system (ECS) intended to be delivered by intratumoral route. The ECS exhibited size <50 nm and zeta potential +32.6 mV on dilution with various isotonic vehicles with no phase separation or drug precipitation. The ECS could be easily sterilized by membrane filtration method and showed excellent stability for 6 months. The ECS demonstrated excellent in vitro antiproliferative activity against B16F10 cells which is attributed to its high transfection efficiency and capability to cause prolonged drug release in cytosolic space. In vivo antitumor activity of ECS was conducted in B16F10 induced melanoma tumor model. ECS at 12 mg/kg dose showed superior tumor suppression ability and exhibited 100% survival compared to other formulations. Mice treated with ECS by intratumoral route, showed neither systemic side effect nor any evidences of hepatotoxicity and nephrotoxicity. In contrast, etoposide administered by intravenous route showed remarkable systemic toxicity, hepatotoxicity and nephrotoxicity.

High-throughput screening identifies compounds that enhance lentiviral transduction

A difficulty in the field of gene therapy is the need to increase the susceptibility of hematopoietic stem cells (HSCs) to ex vivo genetic manipulation. To overcome this obstacle a high-throughput screen was performed to identify compounds that could enhance the transduction of target cells by lentiviral vectors. Of the 1280 compounds initially screened using the myeloid-erythroid-leukemic K562 cell line, 30 were identified as possible enhancers of viral transduction. Among the positive hits were known enhancers of transduction (camptothecin, etoposide and taxol), as well as the previously unidentified phorbol 12-myristate 13-acetate (PMA). The percentage of green fluorescent protein (GFP)-positive-expressing K562 cells was increased more than fourfold in the presence of PMA. In addition, the transduction of K562 cells with a lentiviral vector encoding fVIII was four times greater in the presence of PMA as determined by an increase in the levels of provirus in genetically modified cells. PMA did not enhance viral transduction of all cell types (for example, sca-1(+) mouse hematopoietic cells) but did enhance viral transduction of human bone marrow-derived CD34(+) cells. Notably, the percentage of GFP-positive CD34(+) cells was increased from 7% in the absence of PMA to greater than 22% in the presence of 1 nM PMA. PMA did not affect colony formation of CD34(+) cells or the expression of the hematopoietic markers CD34 and CD45. These data demonstrate that high-throughput screening can be used to identify compounds that increase the transduction efficiency of lentiviral vectors, identifying PMA as a potential enhancer of lentiviral HSC transduction.

HIV-1 Vpr redirects host ubiquitination pathway

HIV-1 modulates key host cellular pathways for successful replication and pathogenesis through viral proteins. By evaluating the hijacking of the host ubiquitination pathway by HIV-1 at the whole-cell level, we now show major perturbations in the ubiquitinated pool of the host proteins post-HIV-1 infection. Our overexpression- and infection-based studies of T cells with wild-type and mutant HIV-1 proviral constructs showed that Vpr is necessary and sufficient for reducing whole-cell ubiquitination. Mutagenic analysis revealed that the three leucine-rich helical regions of Vpr are critical for this novel function of Vpr, which was independent of its other known cellular functions. We also validated that this effect of Vpr was conserved among different subtypes (subtypes B and C) and circulating recombinants from Northern India. Finally, we establish that this phenomenon is involved in HIV-1-mediated diversion of host ubiquitination machinery specifically toward the degradation of various restriction factors during viral pathogenesis.

IMPORTANCE

HIV-1 is known to rely heavily on modulation of the host ubiquitin pathway, particularly for counteraction of antiretroviral restriction factors, i.e., APOBEC3G, UNG2, and BST-2, etc.; viral assembly; and release. Reports to date have focused on the molecular hijacking of the ubiquitin machinery by HIV-1 at the level of E3 ligases. Interaction of a viral protein with an E3 ligase alters its specificity to bring about selective protein ubiquitination. However, in the case of infection, multiple viral proteins can interact with this multienzyme pathway at various levels, making it much more complicated. Here, we have addressed the manipulation of ubiquitination at the whole-cell level post-HIV-1 infection. Our results show that HIV-1 Vpr is necessary and sufficient to bring about the redirection of the host ubiquitin pathway toward HIV-1-specific outcomes. We also show that the three leucine-rich helical regions of Vpr are critical for this effect and that this ability of Vpr is conserved across circulating recombinants. Our work, the first of its kind, provides novel insight into the regulation of the ubiquitin system at the whole-cell level by HIV-1.

DNA damage repair machinery and HIV escape from innate immune sensing

Viruses have been long known to perturb cell cycle regulators and key players of the DNA damage response to benefit their life cycles. In the case of the human immunodeficiency virus (HIV), the viral auxiliary protein Vpr activates the structure-specific endonuclease SLX4 complex to promote escape from innate immune sensing and, as a side effect, induces replication stress in cycling cells and subsequent cell cycle arrest at the G2/M transition. This novel pathway subverted by HIV to prevent accumulation of viral reverse transcription by-products adds up to facilitating effects of major cellular exonucleases that degrade pathological DNA species. Within this review we discuss the impact of this finding on our understanding of the interplay between HIV replication and nucleic acid metabolism and its implications for cancer-related chronic inflammation.

Functional evidence for the involvement of microtubules and dynein motor complexes in TRIM5α-mediated restriction of retroviruses

The tripartite motif (TRIM) family of proteins includes the TRIM5α antiretroviral restriction factor. TRIM5α from many Old World and some New World monkeys can restrict the human immunodeficiency virus type 1 (HIV-1), while human TRIM5α restricts N-tropic murine leukemia virus (N-MLV). TRIM5α forms highly dynamic cytoplasmic bodies (CBs) that associate with and translocate on microtubules. However, the functional involvement of microtubules or other cytoskeleton-associated factors in the viral restriction process had not been shown. Here, we demonstrate the dependency of TRIM5α-mediated restriction on microtubule-mediated transport. Pharmacological disruption of the microtubule network using nocodazole or disabling it using paclitaxel (originally named taxol) decreased the restriction of N-MLV and HIV-1 by human or simian alleles of TRIM5α, respectively. In addition, pharmacological inhibition of dynein motor complexes using erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and small interfering RNA-mediated depletion of the dynein heavy chain (DHC) similarly decreased TRIM5α-mediated restriction. The loss in restriction resulting from either the disassembly of microtubules or the disruption of dynein motor activity was seen for both endogenous and overexpressed TRIM5α and was not due to differences in protein stability or cell viability. Both nocodazole treatment and DHC depletion interfered with the dynamics of TRIM5α CBs, increasing their size and altering their intracellular localization. In addition, nocodazole, paclitaxel, and DHC depletion were all found to increase the stability of HIV-1 cores in infected cells, providing an alternative explanation for the decreased restriction. In conclusion, association with microtubules and the translocation activity of dynein motor complexes are required to achieve efficient restriction by TRIM5α.

IMPORTANCE

The primate innate cellular defenses against infection by retroviruses include a protein named TRIM5α, belonging to the family of restriction factors. TRIM5α is present in the cytoplasm, where it can intercept incoming retroviruses shortly after their entry. How TRIM5α manages to be present at the appropriate subcytoplasmic location to interact with its target is unknown. We hypothesized that TRIM5α, either as a soluble protein or a high-molecular-weight complex (the cytoplasmic body), is transported within the cytoplasm by a molecular motor called the dynein complex, which is known to interact with and move along microtubules. Our results show that destructuring microtubules or crippling their function decreased the capacity of human or simian TRIM5α to restrict their retroviral targets. Inhibiting dynein motor activity, or reducing the expression of a key component of this complex, similarly affected TRIM5α-mediated restriction. Thus, we have identified specific cytoskeleton structures involved in innate antiretroviral defenses.

Rapamycin inhibits acrolein-induced apoptosis by alleviating ROS-driven mitochondrial dysfunction in male germ cells

OBJECTIVES

Acrolein (Acr) is a highly reactive α, β-unsaturated aldehyde, which can induce reactive oxygen species (ROS) generation. Several factors, including lipid peroxidation, clinical use of cyclophosphamide, fried foods, automobile exhausts, smoking and aging can increase its concentration in blood serum. Mounting evidence has suggested that Acr-induced ROS might reduce quality of sperm. Thus, the aim of this study was to examine reproductive toxicity of Acr-caused ROS in vitro and find a means to alleviate it.

MATERIALS AND METHODS

We investigated the effects of Acr on male germ cell (MGC)-derived GC-1 cells in vitro. Dihydroethidium and DCFH-DA fluorescent dyes were used to determine generation of intracellular ROS.

RESULTS

We found that Acr induced ROS generation, which was accompanied by reduced Bcl2/Bax ratio, substantial decline in mitochondrial membrane potential, and further promoted apoptosis of MGCs. Furthermore, Rapamycin was capable of alleviating Acr-induced ROS, reducing ROS-induced apoptosis by increasing ratio of Bcl2/Bax mRNA and proteins, and protecting MGC mitochondrial membranes.

CONCLUSION

Rapamycin inhibited Acr-induced apoptosis by alleviating ROS-driven mitochondrial dysfunction in MGCs.

The natural organosulfur compound dipropyltetrasulfide prevents HOCl-induced systemic sclerosis in the mouse

Introduction

The aim of this study was to test the naturally occurring organosulfur compound dipropyltetrasulfide (DPTTS), found in plants, which has antibiotic and anticancer properties, as a treatment for HOCl-induced systemic sclerosis in the mouse.

Methods

The prooxidative, antiproliferative, and cytotoxic effects of DPTTS were evaluated ex vivo on fibroblasts from normal and HOCl mice. In vivo, the antifibrotic and immunomodulating properties of DPTTS were evaluated in the skin and lungs of HOCl mice.

Results

H₂O₂ production was higher in fibroblasts derived from HOCl mice than in normal fibroblasts (P < 0.05). DPTTS did not increase H₂O₂ production in normal fibroblasts, but DPTTS dose-dependently increased H₂O₂ production in HOCl fibroblasts (P < 0.001 with 40 μM DPTTS). Because H₂O₂ reached a lethal threshold in cells from HOCl mice, the antiproliferative, cytotoxic, and proapoptotic effects of DPTTS were significantly higher in HOCl fibroblasts than for normal fibroblasts. In vivo, DPTTS decreased dermal thickness (P < 0.001), collagen content in skin (P < 0.01) and lungs (P < 0.05), αSMA (P < 0.01) and pSMAD2/3 (P < 0.01) expression in skin, formation of advanced oxidation protein products and anti-DNA topoisomerase-1 antibodies in serum (P < 0.05) versus untreated HOCl mice. Moreover, in HOCl mice, DPTTS reduced splenic B-cell counts (P < 0.01), the proliferative rates of B-splenocytes stimulated by lipopolysaccharide (P < 0.05), and T-splenocytes stimulated by anti-CD3/CD28 mAb (P < 0.001). Ex vivo, it also reduced the production of IL-4 and IL-13 by activated T cells (P < 0.05 in both cases).

Conclusions

The natural organosulfur compound DPTTS prevents skin and lung fibrosis in the mouse through the selective killing of diseased fibroblasts and its immunomodulating properties. DPTTS may be a potential treatment for systemic sclerosis.

Transmissible gastroenteritis virus infection induces cell cycle arrest at S and G2/M phases via p53-dependent pathway

•

TGEV induced cell cycle arrest at S and G2/M phase in PK-15 and ST cells.

•

p53 might play key roles in mediation of TGEV-induced cell cycle arrest.

•

The host cells staying at S or G2/M phase is beneficial for TGEV replication.

p53 signaling pathway plays an important role in the regulation of cell cycle. Our previous studies have demonstrated that TGEV infection induces the activation of p53 signaling pathway. In this study we investigated the effects of TGEV infection on the cell cycle of host cells and the roles of p53 activation in this process. The results showed that TGEV infection induced cell cycle arrest at S and G2/M phases in both asynchronous and synchronized PK-15 and ST cells, while UV-inactivated TGEV lost the ability of induction of cell cycle arrest. TGEV infection promoted p21 accumulation, down-regulated cell cycle-regulatory proteins cyclins B1, cdc2, cdk2 and PCNA. Further studies showed that inhibition of p53 signaling could attenuate the TGEV-induced S- and G2/M-phase arrest by reversing the expression of p21 and corresponding cyclin/cdk. In addition, TGEV infection of the cells synchronized in various stages of cell cycle showed that viral genomic RNA and subgenomic RNA, and virus titer were higher in the cells released from S-phase- or G2/M phase-synchronized cells than that in the cells released from the G0/G1 phase-synchronized or asynchronous cells after 18 h p.i. Taken together, our data suggested that TGEV infection induced S and G2/M phase arrest in host cells, which might provide a favorable condition for viral replication.

An HIV-1 replication pathway utilizing reverse transcription products that fail to integrate

Integration is a central event in the replication of retroviruses, yet ≥ 90% of HIV-1 reverse transcripts fail to integrate, resulting in accumulation of unintegrated viral DNA in cells. However, understanding what role, if any, unintegrated viral DNA plays in the natural history of HIV-1 has remained elusive. Unintegrated HIV-1 DNA is reported to possess a limited capacity for gene expression restricted to early gene products and is considered a replicative dead end. Although the majority of peripheral blood CD4(+) T cells are refractory to infection, nonactivated CD4 T cells present in lymphoid and mucosal tissues are major targets for infection. Treatment with cytokine interleukin-2 (IL-2), IL-4, IL-7, or IL-15 renders CD4(+) T cells permissive to HIV-1 infection in the absence of cell activation and proliferation and provides a useful model for infection of resting CD4(+) T cells. We found that infection of cytokine-treated resting CD4(+) T cells in the presence of raltegravir or with integrase active-site mutant HIV-1 yielded de novo virus production following subsequent T cell activation. Infection with integration-competent HIV-1 naturally generated a population of cells generating virus from unintegrated DNA. Latent infection persisted for several weeks and could be activated to virus production by a combination of a histone deacetylase inhibitor and a protein kinase C activator or by T cell activation. HIV-1 Vpr was essential for unintegrated HIV-1 gene expression and de novo virus production in this system. Bypassing integration by this mechanism may allow the preservation of genetic information that otherwise would be lost.

Cell cycle perturbations induced by human herpesvirus 6 infection and their effect on virus replication

In this study, we demonstrate that infection of HSB-2 cells with human herpesvirus 6 (HHV-6) resulted in the accumulation of infected cells in the G2/M phase of the cell cycle. Analysis of various cell-cycle-regulatory proteins indicated that the levels of cyclins A2, B1, and E1 were increased in HHV-6-infected cells, but there was no difference in cyclin D1 levels between mock-infected and HHV-6-infected cells. Our data also showed that inducing G2/M phase arrest in cells infected by HHV-6 provided favorable conditions for viral replication.

Topoisomerases facilitate transcription of long genes linked to autism

Topoisomerases are expressed throughout the developing and adult brain and are mutated in some individuals with autism spectrum disorder (ASD). However, how topoisomerases are mechanistically connected to ASD is unknown. Here we found that topotecan, a Topoisomerase 1 (TOP1) inhibitor, dose-dependently reduced the expression of extremely long genes in mouse and human neurons, including nearly all genes >200 kb. Expression of long genes was also reduced following knockdown of Top1 or Top2b in neurons, highlighting that each enzyme was required for full expression of long genes. By mapping RNA polymerase II density genome-wide in neurons, we found that this length-dependent effect on gene expression was due to impaired transcription elongation. Interestingly, many high confidence ASD candidate genes are exceptionally long and were reduced in expression following TOP1 inhibition. Our findings suggest that chemicals and genetic mutations that impair topoisomerases could commonly contribute to ASD and other neurodevelopmental disorders.

Polyploidization without mitosis improves in vivo liver transduction with lentiviral vectors

Lentiviral vectors are efficient gene delivery vehicles for therapeutic and research applications. In contrast to oncoretroviral vectors, they are able to infect most nonproliferating cells. In the liver, induction of cell proliferation dramatically improved hepatocyte transduction using all types of retroviral vectors. However, the precise relationship between hepatocyte division and transduction efficiency has not been determined yet. Here we compared gene transfer efficiency in the liver after in vivo injection of recombinant lentiviral or Moloney murine leukemia viral (MoMuLV) vectors in hepatectomized rats treated or not with retrorsine, an alkaloid that blocks hepatocyte division and induces megalocytosis. Partial hepatectomy alone resulted in a similar increase in hepatocyte transduction using either vector. In retrorsine-treated and partially hepatectomized rats, transduction with MoMuLV vectors dropped dramatically. In contrast, we observed that retrorsine treatment combined with partial hepatectomy increased lentiviral transduction to higher levels than hepatectomy alone. Analysis of nuclear ploidy in single cells showed that a high level of transduction was associated with polyploidization. In conclusion, endoreplication could be exploited to improve the efficiency of liver-directed lentiviral gene therapy.

Enhanced autointegration in hyperstable simian immunodeficiency virus capsid mutants blocked after reverse transcription

After entering a host cell, retroviruses such as simian immunodeficiency virus (SIV) uncoat, disassembling the viral capsid. Rates of uncoating that are too high and too low can be detrimental to the efficiency of infection. Rapid uncoating typically leads to blocks in reverse transcription, but the basis for replication defects associated with slow uncoating is less clear. Here we characterize the phenotypes of two SIVmac239 mutants with changes, A87E and A87D, in the helix 4/5 loop of the capsid protein. These mutant viruses exhibited normal capsid morphology but were significantly attenuated for infectivity. The infectivity of wild-type and mutant SIVmac239 was not decreased by aphidicolin-induced growth arrest of the target cells. In the cytosol of infected cells, the A87E and A87D capsids remained in particulate form longer than the wild-type SIVmac239 capsid, suggesting that the mutants uncoat more slowly than the wild-type capsid. Both mutants exhibited much higher levels of autointegrated DNA forms than wild-type SIVmac239. Thus, some changes in the helix 4/5 loop of the SIVmac239 capsid protein result in capsid hyperstability and an increase in autointegration.

Toward system-level understanding of baculovirus-host cell interactions: from molecular fundamental studies to large-scale proteomics approaches

Baculoviruses are insect viruses extensively exploited as eukaryotic protein expression vectors. Molecular biology studies have provided exciting discoveries on virus-host interactions, but the application of omic high-throughput techniques on the baculovirus-insect cell system has been hampered by the lack of host genome sequencing. While a broader, systems-level analysis of biological responses to infection is urgently needed, recent advances on proteomic studies have yielded new insights on the impact of infection on the host cell. These works are reviewed and critically assessed in the light of current biological knowledge of the molecular biology of baculoviruses and insect cells.

High content image based analysis identifies cell cycle inhibitors as regulators of Ebola virus infection

Viruses modulate a number of host biological responses including the cell cycle to favor their replication. In this study, we developed a high-content imaging (HCI) assay to measure DNA content and identify different phases of the cell cycle. We then investigated the potential effects of cell cycle arrest on Ebola virus (EBOV) infection. Cells arrested in G1 phase by serum starvation or G1/S phase using aphidicolin or G2/M phase using nocodazole showed much reduced EBOV infection compared to the untreated control. Release of cells from serum starvation or aphidicolin block resulted in a time-dependent increase in the percentage of EBOV infected cells. The effect of EBOV infection on cell cycle progression was found to be cell-type dependent. Infection of asynchronous MCF-10A cells with EBOV resulted in a reduced number of cells in G2/M phase with concomitant increase of cells in G1 phase. However, these effects were not observed in HeLa or A549 cells. Together, our studies suggest that EBOV requires actively proliferating cells for efficient replication. Furthermore, multiplexing of HCI based assays to detect viral infection, cell cycle status and other phenotypic changes in a single cell population will provide useful information during screening campaigns using siRNA and small molecule therapeutics.

Characterization of the interaction between human respiratory syncytial virus and the cell cycle in continuous cell culture and primary human airway epithelial cells

Viruses can modify conditions inside cells to make them more favorable for replication and progeny virus production. One way of doing this is through manipulation of the cell cycle, a process that describes the ordered growth and division of cells. Analysis of model cell lines, such as A549 cells and primary airway epithelial cells, infected with human respiratory syncytial virus (HRSV) has shown alteration of the cell cycle during infection, although the signaling events were not clearly understood. In this study, targeted transcriptomic analysis of HRSV-infected primary airway epithelial cells revealed alterations in the abundances of many mRNAs encoding cell cycle-regulatory molecules, including decreases in the D-type cyclins and corresponding cyclin-dependent kinases (CDK4 and CDK6 [CDK4/6]). These alterations were reflected in changes in protein abundance and/or relocalization in HRSV-infected cells; taken together, they were predicted to result in G(0)/G(1) phase arrest. In contrast, there was no change in the abundances of D-type cyclins in A549 cells infected with HRSV. However, the abundance of the G(1)/S phase progression inhibitor p21(WAF1/CIP1) was increased over that in mock-treated cells, and this, again, was predicted to result in G(0)/G(1) phase arrest. The G(0)/G(1) phase arrest in both HRSV-infected primary cells and A549 cells was confirmed using dual-label flow cytometry that accurately measured the different stages of the cell cycle. Comparison of progeny virus production in primary and A549 cells enriched in G(0)/G(1) using a specific CDK4/6 kinase inhibitor with asynchronously replicating cells indicated that this phase of the cell cycle was more efficient for virus production.

AAV exploits subcellular stress associated with inflammation, endoplasmic reticulum expansion, and misfolded proteins in models of cystic fibrosis

Barriers to infection act at multiple levels to prevent viruses, bacteria, and parasites from commandeering host cells for their own purposes. An intriguing hypothesis is that if a cell experiences stress, such as that elicited by inflammation, endoplasmic reticulum (ER) expansion, or misfolded proteins, then subcellular barriers will be less effective at preventing viral infection. Here we have used models of cystic fibrosis (CF) to test whether subcellular stress increases susceptibility to adeno-associated virus (AAV) infection. In human airway epithelium cultured at an air/liquid interface, physiological conditions of subcellular stress and ER expansion were mimicked using supernatant from mucopurulent material derived from CF lungs. Using this inflammatory stimulus to recapitulate stress found in diseased airways, we demonstrated that AAV infection was significantly enhanced. Since over 90% of CF cases are associated with a misfolded variant of Cystic Fibrosis Transmembrane Conductance Regulator (ΔF508-CFTR), we then explored whether the presence of misfolded proteins could independently increase susceptibility to AAV infection. In these models, AAV was an order of magnitude more efficient at transducing cells expressing ΔF508-CFTR than in cells expressing wild-type CFTR. Rescue of misfolded ΔF508-CFTR under low temperature conditions restored viral transduction efficiency to that demonstrated in controls, suggesting effects related to protein misfolding were responsible for increasing susceptibility to infection. By testing other CFTR mutants, G551D, D572N, and 1410X, we have shown this phenomenon is common to other misfolded proteins and not related to loss of CFTR activity. The presence of misfolded proteins did not affect cell surface attachment of virus or influence expression levels from promoter transgene cassettes in plasmid transfection studies, indicating exploitation occurs at the level of virion trafficking or processing. Thus, we surmised that factors enlisted to process misfolded proteins such as ΔF508-CFTR in the secretory pathway also act to restrict viral infection. In line with this hypothesis, we found that AAV trafficked to the microtubule organizing center and localized near Golgi/ER transport proteins. Moreover, AAV infection efficiency could be modulated with siRNA-mediated knockdown of proteins involved in processing ΔF508-CFTR or sorting retrograde cargo from the Golgi and ER (calnexin, KDEL-R, β-COP, and PSMB3). In summary, our data support a model where AAV exploits a compromised secretory system and, importantly, underscore the gravity with which a stressed subcellular environment, under internal or external insults, can impact infection efficiency.

Misfolded proteins have been associated with a variety of disorders such as cystic fibrosis, diabetes insipidus, alpha-antitrypsin deficiency, Parkinson's disease, and cancer. In this study, by using cellular models of events in cystic fibrosis lung disease we have revealed an effect of misfolded proteins on increasing susceptibility to infection with a parvovirus. Infection efficiency was an order of magnitude higher in cells expressing misfolded Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) mutant proteins than in cells expressing the correctly folded protein. During infection, virus capsids accumulated near cellular factors that normally process misfolded proteins and are involved in retrograde trafficking from the Golgi to endoplasmic reticulum. Furthermore, we have demonstrated that infection efficiency can be attenuated by restoring correct protein folding or augmented by siRNA-mediated knockdown of secretory pathway components. Taken together our results indicate that converging cellular systems operate to clear misfolded proteins and virus capsids from an infected cell. We raise the possibility that parvoviruses and perhaps other viruses exploit congested cellular secretory pathways during entry, and that viral infection could be a contributing factor in the progression of diseases associated with misfolded proteins.

Cellometer vision as an alternative to flow cytometry for cell cycle analysis, mitochondrial potential, and immunophenotyping

Cell phenotyping and cell cycle analysis are two commonly used assays in both clinical diagnosis and biomedical research. Cell phenotyping by identifying different biomarkers is essential for the diagnosis of hematologic malignancy, sub-classifying diseases, monitoring response to treatment, predicting prognosis, detecting rare cell populations and residual malignant cells. Cell cycle analysis distinguishes cells in different phases of cell cycle and is often used to determine the cellular response to drugs and biological stimulations. These assays have been traditionally carried out by sensitive fluorescence detection methods such as flow cytometry and laser scanning cytometry for fluorescence-based cell population analysis. However, these instruments remain relatively expensive, large in size, and require a considerable amount of maintenance, which may not be feasible for smaller research groups that do not have access to these equipments or field clinics that require quick diagnostic results on site. Recently, a small portable imaging cytometry system (Cellometer Vision) has been developed by Nexcelom Bioscience LLC (Lawrence, MA) for automated cell concentration and viability measurement using bright-field and fluorescent imaging methods. Here we report new applications of the Cellometer imaging cytometry for fluorescence-based cell population analysis and compared them with conventional flow cytometry. Cell population analysis assays such as immunophenotyping, cell cycle, and mitochondrial membrane potential detection methods have not yet been reported for the Cellometer Vision system. Using this imaging cytometry method for fluorescence-based assays that are typically done by flow cytometry offers a quick, simple, and inexpensive alternative method for biomedical research, which may be beneficial for smaller research laboratories and clinics.

Human herpesvirus 6 suppresses T cell proliferation through induction of cell cycle arrest in infected cells in the G2/M phase

Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus that primarily infects immune cells and strongly suppresses the proliferation of infected cells. However, the mechanisms responsible for the regulation and suppression mediated by HHV-6 are still unknown. In this study, we examined the ability of HHV-6A to manipulate cell cycle progression in infected cells and explored the potential molecular mechanisms. We demonstrated that infection with HHV-6A imposed a growth-inhibitory effect on HSB-2 cells by inducing cell cycle arrest at the G(2)/M phase. We then showed that the activity of the Cdc2-cyclin B1 complex was significantly decreased in HHV-6A-infected HSB-2 cells. Furthermore, we found that inactivation of Cdc2-cyclin B1 in HHV-6A-infected cells occurred through the inhibitory Tyr15 phosphorylation resulting from elevated Wee1 expression and inactivated Cdc25C. The reduction of Cdc2-cyclin B1 activity in HHV-6-infected cells was also partly due to the increased expression of the cell cycle-regulatory molecule p21 in a p53-dependent manner. In addition, HHV-6A infection activated the DNA damage checkpoint kinases Chk2 and Chk1. Our data suggest that HHV-6A infection induces G(2)/M arrest in infected T cells via various molecular regulatory mechanisms. These results further demonstrate the potential mechanisms involved in immune suppression and modulation mediated by HHV-6 infection, and they provide new insights relevant to the development of novel vaccines and immunotherapeutic approaches.

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.

Patients on HAART often have an excess of unintegrated HIV DNA: implications for monitoring reservoirs

HIV establishes a latent reservoir early in infection that is resistant to anti-retroviral therapy and has a slow rate of decay. It is thought that the majority of HIV DNA in treated patients is integrated since unintegrated HIV DNA appears to be unstable. Thus, to monitor the HIV latent reservoir, total HIV DNA is commonly measured in PBMC from infected individuals. We investigated how often total approaches integrated HIV DNA in treated patients. To do this, we first assessed how accurate our integration assay is and determined the error in our measurements of total and integrated HIV DNA. We demonstrated an excess of total over integrated HIV DNA was present in a subset of patients, suggesting that measurements of total HIV DNA do not always correlate to the level of integration. Determining the cause of this excess and its frequency may have important implications for understanding HIV latent reservoir maintenance.

XPB mediated retroviral cDNA degradation coincides with entry to the nucleus

Retroviruses must integrate their cDNA to a host chromosome, but a significant fraction of retroviral cDNA is degraded before integration. XPB and XPD are part of the TFIIH complex which mediates basal transcription and DNA nucleotide excision repair. Retroviral infection increases when XPB or XPD are mutant. Here we show that inhibition of mRNA or protein synthesis does not affect HIV cDNA accumulation suggesting that TFIIH transcription activity is not required for degradation. Other host factors implicated in the stability of cDNA are not components of the XPB and XPD degradation pathway. Although an increase of retroviral cDNA in XPB or XPD mutant cells correlates with an increase of integrated provirus, the integration efficiency of pre-integration complexes is unaffected. Finally, HIV and MMLV cDNA degradation appears to coincide with nuclear import. These results suggest that TFIIH mediated cDNA degradation is a nuclear host defense against retroviral infection.

Up-regulation of HIV-1 transduction in nondividing cells by double-strand DNA break-inducing agents

Efficient HIV-1 transduction depends on a number of cellular co-factors. Cellular double-strand DNA break (DSB) repair proteins have been proposed, by ourselves and others, to be required for efficient HIV-1 transduction. Expression and/or activity of these DNA repair proteins can be induced by the introduction of DSBs into the host cell genome. HIV-1 transduction was up-regulated by treatment with DSB-inducing agents in both drug-arrested cells and differentiated neuronal cells. The presented data support the hypothesis that DSB repair proteins are involved in the early steps of the retroviral life-cycle.

Centriole age underlies asynchronous primary cilium growth in mammalian cells

Primary cilia are microtubule-based sensory organelles that play important roles in development and disease . They are required for Sonic hedgehog (Shh) and platelet-derived growth factor (PDGF) signaling. Primary cilia grow from the older of the two centrioles of the centrosome, referred to as the mother centriole. In cycling cells, the cilium typically grows in G1 and is lost before mitosis, but the regulation of its growth is poorly understood. Centriole duplication at G1/S results in two centrosomes, one with an older mother centriole and one with a new mother centriole, that are segregated in mitosis. Here we report that primary cilia grow asynchronously in sister cells resulting from a mitotic division and that the sister cell receiving the older mother centriole usually grows a primary cilium first. We also show that the signaling proteins inversin and PDGFRalpha localize asynchronously to sister cell primary cilia and that sister cells respond asymmetrically to Shh. These results suggest that the segregation of differently aged mother centrioles, an asymmetry inherent to every animal cell division, can influence the ability of sister cells to respond to environmental signals, potentially altering the behavior or fate of one or both sister cells.

Characterization of the behavior of functional viral genomes during the early steps of human immunodeficiency virus type 1 infection

Infectious viral DNA constitutes only a small fraction of the total viral DNA produced during retroviral infection, and as such its exact behavior is largely unknown. In the present study, we characterized in detail functional viral DNA produced during the early steps of human immunodeficiency virus type 1 infection by analyzing systematically their kinetics of synthesis and integration in different target cells. In addition, we have compared the functional stability of viral nucleoprotein complexes arrested at their pre-reverse transcription state, and we have attempted to measure the kinetics of loss of capsid proteins from viral complexes through the susceptibility of the early phases of infection to cyclosporine, a known inhibitor of the interaction between viral capsid and cyclophilin A. Overall, our data suggest a model in which loss of capsid proteins from viral complexes and reverse transcription occur concomitantly and in which the susceptibility of target cells to infection results from a competition between the ability of the cellular environment to quickly destabilize viral nucleoprotein complexes and the capability of the virus to escape such targeting by engaging the reverse transcription reaction.

HIV-1 exploits importin 7 to maximize nuclear import of its DNA genome

BACKGROUND

Nuclear import of the HIV-1 reverse transcription complex (RTC) is critical for infection of non dividing cells, and importin 7 (imp7) has been implicated in this process. To further characterize the function of imp7 in HIV-1 replication we generated cell lines stably depleted for imp7 and used them in conjunction with infection, cellular fractionation and pull-down assays.

RESULTS

Imp7 depletion impaired HIV-1 infection but did not significantly affect HIV-2, simian immunodeficiency virus (SIVmac), or equine infectious anemia virus (EIAV). The lentiviral dependence on imp7 closely correlated with binding of the respective integrase proteins to imp7. HIV-1 RTC associated with nuclei of infected cells with remarkable speed and knock down of imp7 reduced HIV-1 DNA nuclear accumulation, delaying infection. Using an HIV-1 mutant deficient for reverse transcription, we found that viral RNA accumulated within nuclei of infected cells, indicating that reverse transcription is not absolutely required for nuclear import. Depletion of imp7 impacted on HIV-1 DNA but not RNA nuclear import and also inhibited DNA transfection efficiency.

CONCLUSION

Although imp7 may not be essential for HIV-1 infection, our results suggest that imp7 facilitates nuclear trafficking of DNA and that HIV-1 exploits imp7 to maximize nuclear import of its DNA genome. Lentiviruses other than HIV-1 may have evolved to use alternative nuclear import receptors to the same end.

Lentiviral vector gene transfer is limited by the proteasome at postentry steps in various types of stem cells

The isolation of human embryonic and somatic stem cells of different types has made it possible to design novel gene and cell replacement therapies. Vectors derived from retro/lentiviruses are used to stably introduce genes into stem cells and their progeny. However, the permissivity to retroviral infection varies among cell types. We previously showed that hematopoietic stem cells are poorly permissive to human immunodeficiency virus (HIV)-derived vectors and that pharmacological inhibition of the proteasome strongly enhances gene transfer. Here we report that the proteasome limits lentiviral gene transfer in all stem cell types tested, including embryonic, mesenchymal, and neural, of both human and mouse origin. Remarkably, this inhibitory activity was sharply reduced upon differentiation of the stem cells, suggesting that it represents a novel feature of the stem cell/immature progenitor phenotype. Proteasome-mediated inhibition was specific for lentiviral vectors and occurred at a postentry infection step. It was not mediated by activation of nuclear factor-kappaB, a major signaling pathway modulated by the proteasome, and did not correlate with high proteasome activity. Interaction of the virion core with cyclophilin A was required to maximize the effect of proteasome inhibitor on the infection pathway. These findings are relevant to uncover new mediators of HIV gene transfer and help in designing more effective protocols for the genetic modification of stem cells. Disclosure of potential conflicts of interest is found at the end of this article.

Primate lentiviral Vpx commandeers DDB1 to counteract a macrophage restriction

Primate lentiviruses encode four "accessory proteins" including Vif, Vpu, Nef, and Vpr/Vpx. Vif and Vpu counteract the antiviral effects of cellular restrictions to early and late steps in the viral replication cycle. We present evidence that the Vpx proteins of HIV-2/SIV(SM) promote virus infection by antagonizing an antiviral restriction in macrophages. Fusion of macrophages in which Vpx was essential for virus infection, with COS cells in which Vpx was dispensable for virus infection, generated heterokaryons that supported infection by wild-type SIV but not Vpx-deleted SIV. The restriction potently antagonized infection of macrophages by HIV-1, and expression of Vpx in macrophages in trans overcame the restriction to HIV-1 and SIV infection. Vpx was ubiquitylated and both ubiquitylation and the proteasome regulated the activity of Vpx. The ability of Vpx to counteract the restriction to HIV-1 and SIV infection was dependent upon the HIV-1 Vpr interacting protein, damaged DNA binding protein 1 (DDB1), and DDB1 partially substituted for Vpx when fused to Vpr. Our results indicate that macrophage harbor a potent antiviral restriction and that primate lentiviruses have evolved Vpx to counteract this restriction.

G2/M cell cycle arrest in the life cycle of viruses

There is increasing evidence that viral infection, expression of viral protein or the presence of viral DNA causes the host cell cycle to arrest during G2/M. The mechanisms used by viruses to cause arrest vary widely; some involve the activation of the cellular pathways that induce arrest in response to DNA damage, while others use completely novel means. The analysis of virus-mediated arrest has not been proven easy, and in most cases the consequences of arrest for the virus life cycle are not well defined. However, a number of effects of arrest are being investigated and it will be interesting to see to what extent perturbation of the G2/M transition is involved in viral infections.