Vpr protein of human immunodeficiency virus type 1 binds to 14-3-3 proteins and facilitates complex formation with Cdc25C: implications for cell cycle arrest

HIV-1 Vpr Functions in Primary CD4+ T Cells

HIV-1 encodes four accesory proteins in addition to its structural and regulatory genes. Uniquely amongst them, Vpr is abundantly present within virions, meaning it is poised to exert various biological effects on the host cell upon delivery. In this way, Vpr contributes towards the establishment of a successful infection, as evidenced by the extent to which HIV-1 depends on this factor to achieve full pathogenicity in vivo. Although HIV infects various cell types in the host organism, CD4+ T cells are preferentially targeted since they are highly permissive towards productive infection, concomitantly bringing about the hallmark immune dysfunction that accompanies HIV-1 spread. The last several decades have seen unprecedented progress in unraveling the activities Vpr possesses in the host cell at the molecular scale, increasingly underscoring the importance of this viral component. Nevertheless, it remains controversial whether some of these advances bear in vivo relevance, since commonly employed cellular models significantly differ from primary T lymphocytes. One prominent example is the "established" ability of Vpr to induce G2 cell cycle arrest, with enigmatic physiological relevance in infected primary T lymphocytes. The objective of this review is to present these discoveries in their biological context to illustrate the mechanisms whereby Vpr supports HIV-1 infection in CD4+ T cells, whilst identifying findings that require validation in physiologically relevant models.

BUD23-TRMT112 interacts with the L protein of Borna disease virus and mediates the chromosomal tethering of viral ribonucleoproteins

Persistent intranuclear infection is an uncommon infection strategy among RNA viruses. However, Borna disease virus 1 (BoDV-1), a nonsegmented, negative-strand RNA virus, maintains viral infection in the cell nucleus by forming structured aggregates of viral ribonucleoproteins (vRNPs), and by tethering these vRNPs onto the host chromosomes. To better understand the nuclear infection strategy of BoDV-1, we determined the host protein interactors of the BoDV-1 large (L) protein. By proximity-dependent biotinylation, we identified several nuclear host proteins interacting with BoDV-1 L, one of which is TRMT112, a partner of several RNA methyltransferases (MTase). TRMT112 binds with BoDV-1 L at the RNA-dependent RNA polymerase domain, together with BUD23, an 18S rRNA MTase and 40S ribosomal maturation factor. We then discovered that BUD23-TRMT112 mediates the chromosomal tethering of BoDV-1 vRNPs, and that the MTase activity is necessary in the tethering process. These findings provide us a better understanding on how nuclear host proteins assist the chromosomal tethering of BoDV-1, as well as new prospects of host-viral interactions for intranuclear infection strategy of orthobornaviruses. This article is protected by copyright. All rights reserved.

Centrosome amplification in cancer and cancer-associated human diseases

Accumulated evidence from genetically modified cell and animal models indicates that centrosome amplification (CA) can initiate tumorigenesis with metastatic potential and enhance cell invasion. Multiple human diseases are associated with CA and carcinogenesis as well as metastasis, including infection with oncogenic viruses, type 2 diabetes, toxicosis by environmental pollution and inflammatory disease. In this review, we summarize (1) the evidence for the roles of CA in tumorigenesis and tumor cell invasion; (2) the association between diseases and carcinogenesis as well as metastasis; (3) the current knowledge of CA in the diseases; and (4) the signaling pathways of CA. We then give our own thinking and discuss perspectives relevant to CA in carcinogenesis and cancer metastasis in human diseases. In conclusion, investigations in this area might not only identify CA as a biological link between these diseases and the development of cancer but also prove the causal role of CA in cancer and progression under pathophysiological conditions, potentially taking cancer research into a new era.

A novel PCV2 ORF5-interacting host factor YWHAB inhibits virus replication and alleviates PCV2-induced cellular response

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YWHAB is a PCV2 ORF5-interacting host factor.

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YWHAB expression is activated by PCV2 infection and ORF5 transfection.

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YWHAB inhibits PCV2 replication.

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YWHAB alleviates PCV2 infection induced ERS, autophagy, ROS production and apoptosis.

Porcine circovirus type 2 (PCV2) infection causes porcine circovirus associated diseases (PCVAD) worldwide. Identification of host factors that interact with viral proteins is a fundamental step to understand the pathogenesis of PCV2. Our previous study reported that ORF5, a newly identified PCV2 viral protein supports PCV2 replication and interacts with multiple host factors. Here, we showed that a host factor YWHAB is an ORF5-interacting protein and plays essential roles during PCV2 infection. By using protein-protein interaction assays, we confirmed that YWHAB directly interacts with PCV2-ORF5 protein. We further showed that YWHAB expression was potently induced upon ORF5 overexpression and PCV2 infection. Remarkably, we found that the YWHAB strongly inhibited PCV2 replication, suggesting its role in defending PCV2 infection. By using the ectopic overexpression and gene knockdown approaches, we revealed that YWHAB inhibits PCV2-induced endoplasmic reticulum stress (ERS), autophagy, reactive oxygen species (ROS) production and apoptosis, suggesting its vital role in alleviating PCV2-induced cellular damage. Together, this study demonstrated that an ORF5-interacting host factor YWHAB affects PCV2 infection and PCV2-induced cellular response, which expands the current understanding of YWHAB biological function and might serves as a new therapeutic target to manage PCV2 infection-associated diseases.

The tail domain of PRRSV NSP2 plays a key role in aggrephagy by interacting with 14-3-3ε

Porcine reproductive and respiratory syndrome (PRRS) caused by PRRS virus (PRRSV) is one of the most severe swine diseases that affects almost all swine-breeding countries. Nonstructural protein 2 (NSP2) is one of the most important viral proteins in the PRRSV life cycle. Our previous study showed that PRRSV NSP2 could induce the formation of aggresomes. In this study we explored the effects of aggresome formation on cells and found that NSP2 could induce autophagy, which depended on aggresome formation to activate aggrephagy. The transmembrane and tail domains of NSP2 contributed to aggrephagy and the cellular protein 14-3-3ε played an important role in NSP2-induced autophagy by binding the tail domain of NSP2. These findings provide information on the function of the C-terminal domain of NSP2, which will help uncover the function of NSP2 during PRRSV infection.

The Multifarious Role of 14-3-3 Family of Proteins in Viral Replication

The 14-3-3 proteins are a family of ubiquitous and exclusively eukaryotic proteins with an astoundingly significant number of binding partners. Their binding alters the activity, stability, localization, and phosphorylation state of a target protein. The association of 14-3-3 proteins with the regulation of a wide range of general and specific signaling pathways suggests their crucial role in health and disease. Recent studies have linked 14-3-3 to several RNA and DNA viruses that may contribute to the pathogenesis and progression of infections. Therefore, comprehensive knowledge of host-virus interactions is vital for understanding the viral life cycle and developing effective therapeutic strategies. Moreover, pharmaceutical research is already moving towards targeting host proteins in the control of virus pathogenesis. As such, targeting the right host protein to interrupt host-virus interactions could be an effective therapeutic strategy. In this review, we generated a 14-3-3 protein interactions roadmap in viruses, using the freely available Virusmentha network, an online virus-virus or virus-host interaction tool. Furthermore, we summarize the role of the 14-3-3 family in RNA and DNA viruses. The participation of 14-3-3 in viral infections underlines its significance as a key regulator for the expression of host and viral proteins.

HIV-1 Vpr inhibits autophagy during the early steps of infection of CD4 T cells

BACKGROUND INFORMATION

Autophagy is induced during HIV-1 entry into CD4 T cells by the fusion of the membranes triggered by the gp41 envelope glycoprotein. This anti-HIV-1 mechanism is inhibited by the viral infectivity factor (Vif) neosynthesized after HIV-1 integration to allow viral replication. However, autophagy is very rapidly controlled after HIV-1 entry by a still unknown mechanism. As HIV-1 viral protein R (Vpr) is the only auxiliary protein found within the virion in substantial amount, we studied its capability to control the early steps of HIV-1 envelope-mediated autophagy.

RESULTS

We demonstrated that ectopic Vpr inhibits autophagy in both the Jurkat CD4 T cell line and HEK.293T cells. Interestingly, Vpr coming from the virus also blocks autophagy in CD4 T cells, the main cell target of HIV-1. Furthermore, Vpr decreases the expression level of two essential autophagy proteins (ATG), LC3B and Beclin-1, and an important autophagy-related protein, BNIP3 as well as the level of their mRNA. We also demonstrated in HEK.293T cells that Vpr degrades the FOXO3a transcription factor through the ubiquitin proteasome system.

CONCLUSION

Vpr, the only well-expressed HIV-1 auxiliary protein incorporated into viruses, is able to negatively control autophagy induced during HIV-1 entry into CD4 T cells.

SIGNIFICANCE

We provide insights of how HIV-1 controls autophagy very early after its entry into CD4 T cells and discovered a new function of Vpr. These results open the route to a better understanding of the roles of Vpr during HIV-1 infection through FOXO3a degradation and could be important to consider additional therapies that counteract the role of Vpr on autophagy.

Breaking Bad: How Viruses Subvert the Cell Cycle

Interactions between the host and viruses during the course of their co-evolution have not only shaped cellular function and the immune system, but also the counter measures employed by viruses. Relatively small genomes and high replication rates allow viruses to accumulate mutations and continuously present the host with new challenges. It is therefore, no surprise that they either escape detection or modulate host physiology, often by redirecting normal cellular pathways to their own advantage. Viruses utilize a diverse array of strategies and molecular targets to subvert host cellular processes, while evading detection. These include cell-cycle regulation, major histocompatibility complex-restricted antigen presentation, intracellular protein transport, apoptosis, cytokine-mediated signaling, and humoral immune responses. Moreover, viruses routinely manipulate the host cell cycle to create a favorable environment for replication, largely by deregulating cell cycle checkpoints. This review focuses on our current understanding of the molecular aspects of cell cycle regulation that are often targeted by viruses. Further study of their interactions should provide fundamental insights into cell cycle regulation and improve our ability to exploit these viruses.

Comprehensive Proteomics Identification of IFN-λ3-regulated Antiviral Proteins in HBV-transfected Cells

Interferon lambda (IFN-λ) is a relatively unexplored, yet promising antiviral agent. IFN-λ has recently been tested in clinical trials of chronic hepatitis B virus infection (CHB), with the advantage that side effects may be limited compared with IFN-α, as IFN-λ receptors are found only in epithelial cells. To date, IFN-λ's downstream signaling pathway remains largely unelucidated, particularly via proteomics methods. Here, we report that IFN-λ3 inhibits HBV replication in HepG2.2.15 cells, reducing levels of both HBV transcripts and intracellular HBV DNA. Quantitative proteomic analysis of HBV-transfected cells was performed following 24-hour IFN-λ3 treatment, with parallel IFN-α2a and PBS treatments for comparison using a dimethyl labeling method. The depth of the study allowed us to map the induction of antiviral proteins to multiple points of the viral life cycle, as well as facilitating the identification of antiviral proteins not previously known to be elicited upon HBV infection (e.g. IFITM3, XRN2, and NT5C3A). This study also shows up-regulation of many effectors involved in antigen processing/presentation indicating that this cytokine exerted immunomodulatory effects through several essential molecules for these processes. Interestingly, the 2 subunits of the immunoproteasome cap (PSME1 and PSME2) were up-regulated whereas cap components of the constitutive proteasome were down-regulated upon both IFN treatments, suggesting coordinated modulation toward the antigen processing/presentation mode. Furthermore, in addition to confirming canonical activation of interferon-stimulated gene (ISG) transcription through the JAK-STAT pathway, we reveal that IFN-λ3 restored levels of RIG-I and RIG-G, proteins known to be suppressed by HBV. Enrichment analysis demonstrated that several biological processes including RNA metabolism, translation, and ER-targeting were differentially regulated upon treatment with IFN-λ3 versus IFN-α2a. Our proteomic data suggests that IFN-λ3 regulates an array of cellular processes to control HBV replication.

Molecular Mechanism of HIV-1 Vpr for Binding to Importin-α

Viral protein R (Vpr) is an accessory gene product of human immunodeficiency virus type 1 (HIV-1) that plays multiple important roles associated with viral replication. Structural studies using NMR have revealed that Vpr consists of three α-helices and contains flexible N- and C-termini. However, the molecular mechanisms associated with Vpr function have not been elucidated. To investigate Vpr multifunctionality, we performed an X-ray crystallographic study of Vpr complexes containing importin-α, a known Vpr binding partner present in host cells. Elucidation of the crystal structure revealed that the flexible C-terminus changes its conformation to a twisted β-turn via an induced-fit mechanism, enabling binding to a minor nuclear localization signal (NLS) site of importin-α. The Vpr C-terminus can also bind with major NLS sites of importin-α in an extended conformation in different ways. These results, which represent the first reported crystallographic analysis of Vpr, demonstrate the multifunctional aspects that enable Vpr interaction with a variety of cellular proteins.

HIV-1 Vpr protein activates the NF-κB pathway to promote G2/M cell cycle arrest

Viral protein R (Vpr) plays an important role in the replication and pathogenesis of Human immunodeficiency virus type 1 (HIV-1). Some of the various functions attributed to Vpr, including the induction of G2/M cell cycle arrest, activating the NF-κB pathway, and promoting viral reverse transcription, might be interrelated. To test this hypothesis, a panel of Vpr mutants were investigated for their ability to induce G2/M arrest and to activate the NF-κB pathway. The results showed that the Vpr mutants that failed to activate NF-κB also lost the activity to induce G2/M arrest, which suggests that inducing G2/M arrest via Vpr depends at least partially on the activation of NF-κB. This latter possibility is supported by data showing that knocking down the key factors in the NF-κB pathway-p65, RelB, IKKα, or IKKβ-partially rescued the G2/M arrest induced by Vpr. Our results suggest that the NF-κB pathway is probably involved in Vpr-induced G2/M cell cycle arrest.

Current topics in HIV-1 pathogenesis: The emergence of deregulated immuno-metabolism in HIV-infected subjects

HIV-1 infection results in long-lasting activation of the immune system including elevated production of pro-inflammatory cytokine/chemokines, and bacterial product release from gut into blood and tissue compartments, which are not fully restored by antiretroviral therapies. HIV-1 has also developed numerous strategies via viral regulatory proteins to hijack cell molecular mechanisms to enhance its own replication and dissemination. Here, we reviewed the relationship between viral proteins, immune activation/inflammation, and deregulated metabolism occurring in HIV-1-infected patients that ultimately dampens the protective innate and adaptive arms of immunity. Defining precisely the molecular mechanisms related to deregulated immuno-metabolism during HIV-1 infection could ultimately help in the development of novel clinical approaches to restore proper immune functions in these patients.

Aberrant upregulation of 14-3-3σ and EZH2 expression serves as an inferior prognostic biomarker for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common malignancy in the world. It is of important significance to find biomarkers for the prognostic monitoring of HCC. The 14-3-3σ and EZH2 proteins are involved in cell cycle regulation and epigenetic silencing. We herein examined the significance of 14-3-3 σ and EZH2 in HCC (n = 167) by immunohistochemistry, RT-PCR and qRT-PCR. The correlation between 14-3-3σ and EZH2 expression and patients' clinicopathologic features were examined, as was the correlation between 14-3-3σ and EZH2 expression and the prognosis of HCC patients. We found that 14-3-3σ and EZH2 were highly expressed in HCC (71% and 90%), the expression of EZH2, but not 14-3-3σ, is associated with vascular invasion and tumor differentiation (p<0.01). The coexistence of 14-3-3σ and EZH2 overexpression is associated with a relatively unfavorable prognosis (p<0.01), suggesting that aberrant upregulation of 14-3-3σ and EZH2 expression serves as an inferior prognostic biomarker for HCC.

Proteomic alteration of PK-15 cells after infection by porcine circovirus type 2

Porcine circovirus type 2 (PCV2) has been identified as the essential causal agent of post-weaning multisystemic wasting syndrome, which has spread worldwide. To discover cellular protein responses of PK-15 cells to PCV2 infection, two-dimensional liquid chromatography-tandem mass spectrometry (MS) coupled with isobaric tags for relative and absolute quantification (iTRAQ) labeling was employed to quantitatively identify the proteins that were differentially expressed in PK-15 from the PCV2-infected group compared to the uninfected control group. A total of 196 cellular proteins in PK-15 that were significantly altered at different time periods post-infection were identified. These differentially expressed proteins were related to the biological processes of binding, cell structure, signal transduction, cell adhesion, etc. and their interactions. Moreover, some of these proteins were further confirmed by Western blot. The high number of differentially expressed proteins identified should be very useful in elucidating the mechanism of replication and pathogenesis of PCV2 in the future.

HIV-1 Vpr-a still "enigmatic multitasker"

Like other HIV-1 auxiliary proteins, Vpr is conserved within all the human (HIV-1, HIV-2) and simian (SIV) immunodeficiency viruses. However, Vpr and homologous HIV-2, and SIV Vpx are the only viral auxiliary proteins specifically incorporated into virus particles through direct interaction with the Gag precursor, indicating that this presence in the core of the mature virions is mainly required for optimal establishment of the early steps of the virus life cycle in the newly infected cell. In spite of its small size, a plethora of effects and functions have been attributed to Vpr, including induction of cell cycle arrest and apoptosis, modulation of the fidelity of reverse transcription, nuclear import of viral DNA in macrophages and other non-dividing cells, and transcriptional modulation of viral and host cell genes. Even if some more recent studies identified a few cellular targets that HIV-1 Vpr may utilize in order to perform its different tasks, the real role and functions of Vpr during the course of natural infection are still enigmatic. In this review, we will summarize the main reported functions of HIV-1 Vpr and their significance in the context of the viral life cycle.

The DR6 protein from human herpesvirus-6B induces p53-independent cell cycle arrest in G2/M

HHV-6B infection inhibits cell proliferation in G2/M, but no protein has so far been recognized to exert this function. Here we identify the protein product of direct repeat 6, DR6, as an inhibitor of G2/M cell-cycle progression. Transfection of DR6 reduced the total number of cells compared with mock-transfected cells. Lentiviral transduction of DR6 inhibited host cell DNA synthesis in a p53-independent manner, and this inhibition was DR6 dose-dependent. A deletion of 66 amino acids from the N-terminal part of DR6 prevented efficient nuclear translocation and the ability to inhibit DNA synthesis. DR6-induced accumulation of cells in G2/M was accompanied by an enhanced expression of cyclin B1 that accumulated predominantly in the cytoplasm. Pull-down of cyclin B1 brought down pCdk1 with the inactivating phosphorylation at Tyr15. Together, DR6 delays cell cycle with an accumulation of cells in G2/M and thus might be involved in HHV-6B-induced cell-cycle arrest.

Scaffold functions of 14-3-3 adaptors in B cell immunoglobulin class switch DNA recombination

Class switch DNA recombination (CSR) of the immunoglobulin heavy chain (IgH) locus crucially diversifies antibody biological effector functions. CSR involves the induction of activation-induced cytidine deaminase (AID) expression and AID targeting to switch (S) regions by 14-3-3 adaptors. 14-3-3 adaptors specifically bind to 5'-AGCT-3' repeats, which make up for the core of all IgH locus S regions. They selectively target the upstream and downstream S regions that are set to undergo S-S DNA recombination. We hypothesized that 14-3-3 adaptors function as scaffolds to stabilize CSR enzymatic elements on S regions. Here we demonstrate that all seven 14-3-3β, 14-3-3ε, 14-3-3γ, 14-3-3η, 14-3-3σ, 14-3-3τ and 14-3-3ζ adaptors directly interacted with AID, PKA-Cα (catalytic subunit) and PKA-RIα (regulatory inhibitory subunit) and uracil DNA glycosylase (Ung). 14-3-3 adaptors, however, did not interact with AID C-terminal truncation mutant AIDΔ(180-198) or AIDF193A and AIDL196A point-mutants (which have been shown not to bind to S region DNA and fail to mediate CSR). 14-3-3 adaptors colocalized with AID and replication protein A (RPA) in B cells undergoing CSR. 14-3-3 and AID binding to S region DNA was disrupted by viral protein R (Vpr), an accessory protein of human immunodeficiency virus type-1 (HIV-1), which inhibited CSR without altering AID expression or germline IH-CH transcription. Accordingly, we demonstrated that 14-3-3 directly interact with Vpr, which in turn, also interact with AID, PKA-Cα and Ung. Altogether, our findings suggest that 14-3-3 adaptors play important scaffold functions and nucleate the assembly of multiple CSR factors on S regions. They also show that such assembly can be disrupted by a viral protein, thereby allowing us to hypothesize that small molecule compounds that specifically block 14-3-3 interactions with AID, PKA and/or Ung can be used to inhibit unwanted CSR.

YWHAE/14-3-3ε: a potential novel genetic risk factor and CSF biomarker for HIV neurocognitive impairment

YWHAE (14-3-3ε) protein levels are considered to be a reliable biomarker for neurodegeneration. The YWHAE protein interacts both directly and indirectly with human immunodeficiency virus (HIV) accessory proteins, leading to cell death. The purpose of this study was to examine the relationship between YWHAE polymorphisms and HIV-associated neurocognitive disorder (HAND) and the relationship between YWHAE protein levels and HAND. A cross-sectional study using random samples of HIV-seropositive (n = 20) and HIV-seronegative (controls) (n = 16) women from the Hispanic-Latino Longitudinal Cohort of Women was conducted. Individuals who are HIV-seropositive and heterozygous at the rs4790084/rs1204828 loci in the YWHAE gene were 3× more likely to display reduced cognitive functioning, to have received a HAND diagnosis, and to have less YHWAE protein expressed than homozygotes. Western blots from cerebral spinal fluid indicate that the HIV-seropositive women with HAND expressed 4.5× less YWHAE compared to HIV-seropositive cognitively normal women (94 % sensitivity, 84 % specificity; HIV-seropositive vs. controls). Therefore, polymorphism in YWHAE may be a genetic risk factor for HAND and levels of YWHAE protein are a likely biomarker for neurocognitive status in HIV-seropositive women.

14-3-3s are potential biomarkers for HIV-related neurodegeneration

Over the last decade, it has become evident that 14-3-3 proteins are essential for primary cell functions. These proteins are abundant throughout the body, including the central nervous system and interact with other proteins in both cell cycle and apoptotic pathways. Examination of cerebral spinal fluid in humans suggests that 14-3-3s including 14-3-3ε (YWHAE) are up-regulated in several neurological diseases, and loss or duplication of the YWHAE gene leads to Miller-Dieker syndrome. The goal of this review is to examine the utility of 14-3-3s as a marker of human immune deficiency virus (HIV)-dependent neurodegeneration and also as a tool to track disease progression. To that end, we describe mechanisms implicating 14-3-3s in neurological diseases and summarize evidence of its interactions with HIV accessory and co-receptor proteins.

Virus manipulation of cell cycle

Viruses depend on host cell resources for replication and access to those resources may be limited to a particular phase of the cell cycle. Thus manipulation of cell cycle is a commonly employed strategy of viruses for achieving a favorable cellular environment. For example, viruses capable of infecting nondividing cells induce S phase in order to activate the host DNA replication machinery and provide the nucleotide triphosphates necessary for viral DNA replication (Flemington in J Virol 75:4475-4481, 2001; Sullivan and Pipas in Microbiol Mol Biol Rev 66:179-202, 2002). Viruses have developed several strategies to subvert the cell cycle by association with cyclin and cyclin-dependent kinase complexes and molecules that regulate their activity. Viruses tend to act on cellular proteins involved in a network of interactions in a way that minimal protein-protein interactions lead to a major effect. The complex and interactive nature of intracellular signaling pathways controlling cell division affords many opportunities for virus manipulation strategies. Taking the maxim "Set a thief to catch a thief" as a counter strategy, however, provides us with the very same virus evasion strategies as "ready-made tools" for the development of novel antivirus therapeutics. The most obvious are attenuated virus vaccines with critical evasion genes deleted. Similarly, vaccines against viruses causing cancer are now being successfully developed. Finally, as viruses have been playing chess with our cell biology and immune responses for millions of years, the study of their evasion strategies will also undoubtedly reveal new control mechanisms and their corresponding cellular intracellular signaling pathways.

The human transcriptome during nontyphoid Salmonella and HIV coinfection reveals attenuated NFkappaB-mediated inflammation and persistent cell cycle disruption

Background. Invasive nontyphoid Salmonella (iNTS) disease is common and severe in adults with human immunodeficiency virus (HIV) infection in Africa. We previously observed that ex vivo macrophages from HIV-infected subjects challenged with Salmonella Typhimurium exhibit dysregulated proinflammatory cytokine responses.

Methods. We studied the transcriptional response in whole blood from HIV-positive patients during acute and convalescent iNTS disease compared to other invasive bacterial diseases, and to HIV-positive and -negative controls.

Results. During iNTS disease, there was a remarkable lack of a coordinated inflammatory or innate immune signaling response. Few interferon γ (IFNγ)--induced genes or Toll-like receptor/transcription factor nuclear factor κB (TLR/NFκB) gene pathways were upregulated in expression. Ex vivo lipopolysacharide (LPS) or flagellin stimulation of whole blood, however, showed that convalescent iNTS subjects and controls were competent to mount prominent TLR/NFκB-associated patterns of mRNA expression. In contrast, HIV-positive patients with other invasive bacterial infections (Escherichia coli and Streptococcus pneumoniae) displayed a pronounced proinflammatory innate immune transcriptional response. There was also upregulated mRNA expression in cell cycle, DNA replication, translation and repair, and viral replication pathways during iNTS. These patterns persisted for up to 2 months into convalescence.

Conclusions. Attenuation of NFκB-mediated inflammation and dysregulation of cell cycle and DNA-function gene pathway expression are key features of the interplay between iNTS and HIV.

Exposed hydrophobic residues in human immunodeficiency virus type 1 Vpr helix-1 are important for cell cycle arrest and cell death

The human immunodeficiency virus type 1 (HIV-1) accessory protein viral protein R (Vpr) is a major determinant for virus-induced G2/M cell cycle arrest and cytopathicity. Vpr is thought to perform these functions through the interaction with partner proteins. The NMR structure of Vpr revealed solvent exposed hydrophobic amino acids along helices 1 and 3 of Vpr, which could be putative protein binding domains. We previously showed that the hydrophobic patch along helix-3 was important for G2/M blockade and cytopathicity. Mutations of the exposed hydrophobic residues along helix-1 were found to reduce Vpr-induced cell cycle arrest and cell death as well. The levels of toxicity during virion delivery of Vpr correlated with G2/M arrest. Thus, the exposed hydrophobic amino acids in the amino-terminal helix-1 are important for the cell cycle arrest and cytopathicity functions of Vpr.

Human immunodeficiency virus type 1 Vif causes dysfunction of Cdk1 and CyclinB1: implications for cell cycle arrest

The two major cytopathic factors in human immunodeficiency virus type 1 (HIV-1), the accessory proteins viral infectivity factor (Vif) and viral protein R (Vpr), inhibit cell-cycle progression at the G2 phase of the cell cycle. Although Vpr-induced blockade and the associated T-cell death have been well studied, the molecular mechanism of G2 arrest by Vif remains undefined. To elucidate how Vif induces arrest, we infected synchronized Jurkat T-cells and examined the effect of Vif on the activation of Cdk1 and CyclinB1, the chief cell-cycle factors for the G2 to M phase transition. We found that the characteristic dephosphorylation of an inhibitory phosphate on Cdk1 did not occur in infected cells expressing Vif. In addition, the nuclear translocation of Cdk1 and CyclinB1 was disregulated. Finally, Vif-induced cell cycle arrest was correlated with proviral expression of Vif. Taken together, our results suggest that Vif impairs mitotic entry by interfering with Cdk1-CyclinB1 activation.

Human papillomavirus (HPV) E7 induces prolonged G2 following S phase reentry in differentiated human keratinocytes

The productive program of human papillomaviruses occurs in differentiated squamous keratinocytes. We have previously shown that HPV-18 DNA amplification initiates in spinous cells in organotypic cultures of primary human keratinocytes during prolonged G(2) phase, as signified by abundant cytoplasmic cyclin B1 (Wang, H. K., Duffy, A. A., Broker, T. R., and Chow, L. T. (2009) Genes Dev. 23, 181-194). In this study, we demonstrated that the E7 protein, which induces S phase reentry in suprabasal cells by destabilizing the p130 pocket protein (Genovese, N. J., Banerjee, N. S., Broker, T. R., and Chow, L. T. (2008) J. Virol. 82, 4862-4873), also elicited extensive G(2) responses. Western blots and indirect immunofluorescence assays were used to probe for host proteins known to control G(2)/M progression. E7 expression induced cytoplasmic accumulation of cyclin B1 and cdc2 in the suprabasal cells. The elevated cdc2 had inactivating phosphorylation on Thr(14) or Tyr(15), and possibly both, due to an increase in the responsible Wee1 and Myt1 kinases. In cells that harbored cytoplasmic cyclin B1 or cdc2, there was also an accumulation of the phosphatase-inactive cdc25C phosphorylated on Ser(216), unable to activate cdc2. Moreover, E7 expression induced elevated expression of phosphorylated ATM (Ser(1981)) and the downstream phosphorylated Chk1, Chk2, and JNKs, kinases known to inactivate cdc25C. Similar results were observed in primary human keratinocyte raft cultures in which the productive program of HPV-18 took place. Collectively, this study has revealed the mechanisms by which E7 induces prolonged G(2) phase in the differentiated cells following S phase induction.

Vpr-host interactions during HIV-1 viral life cycle

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) is a multifunctional viral protein that plays important role at multiple stages of the HIV-1 viral life cycle. Although the molecular mechanisms underlying these activities are subject of ongoing investigations, overall, these activities have been linked to promotion of viral replication and impairment of anti-HIV immunity. Importantly, functional defects of Vpr have been correlated with slow disease progression of HIV-infected patients. Vpr is required for efficient viral replication in non-dividing cells such as macrophages, and it promotes, to some extent, viral replication in proliferating CD4+ T cells. The specific activities of Vpr include modulation of fidelity of viral reverse transcription, nuclear import of the HIV-1 pre-integration complex, transactivation of the HIV-1 LTR promoter, induction of cell cycle G2 arrest and cell death via apoptosis. In this review, we focus on description of the cellular proteins that specifically interact with Vpr and discuss their significance with regard to the known Vpr activities at each step of the viral life cycle in proliferating and non-proliferating cells.

Parainfluenza virus 5 m protein interaction with host protein 14-3-3 negatively affects virus particle formation

Paramyxovirus matrix (M) proteins organize virus assembly, linking viral glycoproteins and viral ribonucleoproteins together at virus assembly sites on cellular membranes. Using a yeast two-hybrid screening approach, we identified 14-3-3 as a binding partner for the M protein of parainfluenza virus 5 (PIV5). Binding in both transfected and PIV5-infected cells was confirmed by coimmunoprecipitation and was mapped to a C-terminal region within the M protein, namely, 366-KTKSLP-371. This sequence resembles known 14-3-3 binding sites, in which the key residue for binding is a phosphorylated serine residue. Mutation of S369 within the PIV5 M protein disrupted 14-3-3 binding and improved the budding of both virus-like particles (VLPs) and recombinant viruses, suggesting that 14-3-3 binding impairs virus budding. 14-3-3 protein overexpression reduced the budding of VLPs. Using (33)P labeling, phosphorylated M protein was detected in PIV5-infected cells, and this phosphorylation was nearly absent in cells infected with a recombinant virus harboring an S369A mutation within the M protein. Assembly of the M protein into clusters and filaments at infected cell surfaces was enhanced in cells infected with a recombinant virus defective in 14-3-3 binding. These findings support a model in which a portion of M protein within PIV5-infected cells is phosphorylated at residue S369, binds the 14-3-3 protein, and is held away from sites of virus budding.

HIV-1 viral protein r: from structure to function

The viral protein r (Vpr) of HIV-1 binds several host proteins leading to pleiotropic functions, such as G2/M cell cycle arrest, apoptosis induction and gene transactivation. Vpr is encapsidated through the Gag C-terminus into the nascent viral particles, suggesting that Vpr plays several important functions in the early stages of the viral lifecycle. In this regard, Vpr interacts with nucleic acids and membranes to facilitate the preintegration complex migration and incorporation into the nucleus of nondividing cells. Thus, Vpr has to recruit several host and viral factors to promote its functions during HIV-1 pathogenesis. This article focuses on its interacting partners by giving an overview of the functional outcome of the different Vpr complexes, as well as the structural determinants of Vpr required for its binding properties.

Functional integrity of naturally occurring mutants of HIV-1 subtype C Vpr

HIV-1 Vpr, an accessory protein with multiple functions, is involved in the induction of apoptosis, cell cycle G2 arrest, and modulation of gene expression. Many functions of this protein have been documented for the wild-type subtype B Vpr, however the functionality of other subtypes has not sufficiently been addressed. In this study, the functionality of Subtype B Vpr, 6 subtype C mutant Vpr proteins and the consensus sequence of subtype C Vpr were compared with each other. All the subtype B and C Vpr proteins localized to the nucleus of human 293T cells. Subtype C Vpr proteins induced cell cycle G2 arrest in a lower proportion of human 293T cells compared to subtype B Vpr. Subtype B and the naturally mutant Vpr proteins induced apoptosis in a similar manner, ranging from 95.33% to 98.64%. However, an artificially designed Vpr protein containing the consensus sequences of subtype C Vpr indicated a reduced ability in induction of apoptosis. The study of mRNA profile of the transfected cells indicated that all Vpr proteins modulated the apoptotic genes triggering the intrinsic pathway of apoptosis. Our results indicate that subtype C Vpr is able to exert the same functions previously reported for subtype B Vpr. Most natural mutations in Vpr not only do not disturb the functions of the protein but also potentiate the protein for an increased functionality. The natural mutations of Vpr may thus not always be regarded as defective mutations. The study suggests the adaptive role of the natural mutations commonly found in subtype C Vpr.

Vpr and its interactions with cellular proteins

Like most viral regulatory proteins, HIV-1 Vpr and homologous proteins from primate lentiviruses are small and multifunctional. They are associated with a plethora of effects and functions, including induction of cell cycle arrest in the G(2) phase, induction of apoptosis, transactivation, enhancement of the fidelity of reverse transcription, and nuclear import of viral DNA in macrophages and other nondividing cells. This review focuses on the cellular proteins that have been reported to interact with Vpr and their significance with respect to the known functions and effects of Vpr on cells and on viral replication.

Aberrant methylation profile of 14-3-3 sigma and its reduced transcription/expression levels in Chinese sporadic female breast carcinogenesis

To study the relation of 14-3-3 sigma gene promoter hypermethylation and its transcription expression levels in sporadic breast carcinogenesis. Methylation of 14-3-3 sigma gene was detected by sensitive MSP assay in carcinous, non-cancerous, and normal tissue, and its mRNA was also detected by real time PCR based on SYBR Green 1 as well, and protein was detected by west blotting assay. The methylation frequencies of 14-3-3 sigma were 90% in 68 cases of sporadic breast cancer patients. Methylation was presented in portions (2/13, 18%) of hyperplastic samples, and no hypermethylation was presented in normal tissue. The methylation change of 14-3-3 sigma gene was markedly related with various types, grades, and lymph node metastases (P < 0.05), and no significant differences in methylation frequencies were seen between premenopause and postmenopause (P > 0.05). The methylation of 14-3-3 sigma shows reverse relation with its mRNA transcription and expression level (P < 0.05). Only was lymph node metastases strongly associated with poor outcome (P = 0.02). Whether 14-3-3 sigma promoter methylation or not did not affect the 5 years survival rate of sporadic breast cancer patients (P > 0.05). Epigenetics alterations of the 14-3-3 sigma can contribute to reducing or losing expression of 14-3-3 sigma protein, which play an important role in the development of sporadic breast carcinomas and involved in various types, grades, and lymph node metastases. Otherwise, node metastases of breast carcinogenesis patients are strongly associated with poor outcome.

Human immunodeficiency virus type 1 Vpr: functions and molecular interactions

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) is an accessory protein that interacts with a number of cellular and viral proteins. The functions of many of these interactions in the pathogenesis of HIV-1 have been identified. Deletion of the vpr gene reduces the virulence of HIV-1 dramatically, indicating the importance of this protein for the virus. This review describes the current findings on several established functions of HIV-1 Vpr and some possible roles proposed for this protein. Because Vpr exploits cellular proteins and pathways to influence the biology of HIV-1, understanding the functions of Vpr usually involves the study of cellular pathways. Several functions of Vpr are attributed to the virion-incorporated protein, but some of them are attributed to the expression of Vpr in HIV-1-infected cells. The structure of Vpr may be key to understanding the variety of its interactions. Due to the critical role of Vpr in HIV-1 pathogenicity, study of the interactions between Vpr and cellular proteins may help us to understand the mechanism(s) of HIV-1 pathogenicity.

cAMP signaling regulates histone H3 phosphorylation and mitotic entry through a disruption of G2 progression

cAMP signaling is known to have significant effects on cell growth, either inhibitory or stimulatory depending on the cell type. Study of cAMP-induced growth inhibition in mammalian somatic cells has focused mainly on the combined role of protein kinase A (PKA) and mitogen-activated protein (MAP) kinases in regulation of progression through the G1 phase of the cell cycle. Here we show that cAMP signaling regulates histone H3 phosphorylation in a cell cycle-dependent fashion, increasing it in quiescent cells but dramatically reducing it in cycling cells. The latter is due to a rapid and dramatic loss of mitotic histone H3 phosphorylation caused by a disruption in G2 progression, as evidenced by the inhibition of mitotic entry and decreased activity of the CyclinB/Cdk1 kinase. The inhibition of G2 progression induced through cAMP signaling is dependent on expression of the catalytic subunit of PKA and is highly sensitive to intracellular cAMP concentration. The mechanism by which G2 progression is inhibited is independent of both DNA damage and MAP kinase signaling. Our results suggest that cAMP signaling activates a G2 checkpoint by a unique mechanism and provide new insight into normal cellular regulation of G2 progression.

14-3-3 theta binding to cell cycle regulatory factors is enhanced by HIV-1 Vpr

Background

Despite continuing advances in our understanding of AIDS pathogenesis, the mechanism of CD4+ T cell depletion in HIV-1-infected individuals remains unclear. The HIV-1 Vpr accessory protein causes cell death, likely through a mechanism related to its ability to arrest cells in the G₂,M phase. Recent evidence implicated the scaffold protein, 14-3-3, in Vpr cell cycle blockade.

Results

We found that in human T cells, 14-3-3 plays an active role in mediating Vpr-induced cell cycle arrest and reveal a dramatic increase in the amount of Cdk1, Cdc25C, and CyclinB1 bound to 14-3-3 θ during Vpr_v-induced G₂,M arrest. By contrast, a cell-cycle-arrest-dead Vpr mutant failed to augment 14-3-3 θ association with Cdk1 and CyclinB1. Moreover, G₂,M arrest caused by HIV-1 infection strongly correlated with a disruption in 14-3-3 θ binding to centrosomal proteins, Plk1 and centrin. Finally, Vpr caused elevated levels of CyclinB1, Plk1, and Cdk1 in a complex with the nuclear transport and spindle assembly protein, importin β.

Conclusion

Thus, our data reveal a new facet of Vpr-induced cell cycle arrest involving previously unrecognized abnormal rearrangements of multiprotein assemblies containing key cell cycle regulatory proteins.

Reviewers

This article was reviewed by David Kaplan, Nathaniel R. Landau and Yan Zhou.

Human immunodeficiency virus type 1 Vpr induces cell cycle G2 arrest through Srk1/MK2-mediated phosphorylation of Cdc25

Human immunodeficiency virus type 1 (HIV-1) Vpr induces cell cycle G(2) arrest in fission yeast (Schizosaccharomyces pombe) and mammalian cells, suggesting the cellular pathway(s) targeted by Vpr is conserved among eukaryotes. Our previous studies in fission yeast demonstrated that Vpr induces G(2) arrest in part through inhibition of Cdc25, a Cdc2-specific phosphatase that promotes G(2)/M transition. The goal of this study was to further elucidate molecular mechanism underlying the inhibitory effect of Vpr on Cdc25. We show here that, similar to the DNA checkpoint controls, expression of vpr promotes subcellular relocalization of Cdc25 from nuclear to cytoplasm and thereby prevents activation of Cdc2 by Cdc25. Vpr-induced nuclear exclusion of Cdc25 appears to depend on the serine/threonine phosphorylation of Cdc25 and the presence of Rad24/14-3-3 protein, since amino acid substitutions of the nine possible phosphorylation sites of Cdc25 with Ala (9A) or deletion of the rad24 gene abolished nuclear exclusion induced by Vpr. Interestingly, Vpr is still able to promote Cdc25 nuclear export in mutants defective in the checkpoints (rad3 and chk1/cds1), the kinases that are normally required for Cdc25 phosphorylation and nuclear exclusion of Cdc25, suggesting that others kinase(s) might modulate phosphorylation of Cdc25 for the Vpr-induced G(2) arrest. We report here that this kinase is Srk1. Deletion of the srk1 gene blocks the nuclear exclusion of Cdc25 caused by Vpr. Overexpression of srk1 induces cell elongation, an indication of cell cycle G(2) delay, in a similar fashion to Vpr; however, no additive effect of cell elongation was observed when srk1 and vpr were coexpressed, indicating Srk1 and Vpr are likely affecting the cell cycle G(2)/M transition through the same cellular pathway. Immunoprecipitation further shows that Vpr and Srk1 are part of the same protein complex. Consistent with our findings in fission yeast, depletion of the MK2 gene, a human homologue of Srk1, either by small interfering RNA or an MK2 inhibitor suppresses Vpr-induced cell cycle G(2) arrest in mammalian cells. Collectively, our data suggest that Vpr induces cell cycle G(2) arrest at least in part through a Srk1/MK2-mediated mechanism.

Proteomic studies reveal coordinated changes in T-cell expression patterns upon infection with human immunodeficiency virus type 1

We performed an extensive two-dimensional differential in-gel electrophoresis proteomic analysis of the cellular changes in human T cells upon human immunodeficiency virus type 1 (HIV-1) infection. We detected 2,000 protein spots, 15% of which were differentially expressed at peak infection. A total of 93 proteins that changed in relative abundance were identified. Of these, 27 were found to be significantly downregulated and 66 were upregulated at peak HIV infection. Early in infection, only a small group of proteins was changed. A clear and consistent program of metabolic rerouting could be seen, in which glycolysis was downregulated and mitochondrial oxidation enhanced. Proteins that participate in apoptotic signaling were also significantly influenced. Apart from these changes, the virus also strongly influenced levels of proteins involved in intracellular transport. These and other results are discussed in light of previous microarray and proteomic studies regarding the impact of HIV-1 infection on cellular mRNA and protein content.

Activated glucocorticoid receptor interacts with the INHAT component Set/TAF-Ibeta and releases it from a glucocorticoid-responsive gene promoter, relieving repression: implications for the pathogenesis of glucocorticoid resistance in acute undifferentiated leukemia with Set-Can translocation

Set/template-activating factor (TAF)-Ibeta, part of the Set-Can oncogene product found in acute undifferentiated leukemia, is a component of the inhibitor of acetyltransferases (INHAT) complex. Set/TAF-Ibeta interacted with the DNA-binding domain of the glucocorticoid receptor (GR) in yeast two-hybrid screening, and repressed GR-induced transcriptional activity of a chromatin-integrated glucocorticoid-responsive and a natural promoter. Set/TAF-Ibeta was co-precipitated with glucocorticoid response elements (GREs) of these promoters in the absence of dexamethasone, while addition of the hormone caused dissociation of Set/TAF-Ibeta from and attraction of the p160-type coactivator GRIP1 to the promoter GREs. Set-Can fusion protein, on the other hand, did not interact with GR, was constitutively co-precipitated with GREs and suppressed GRIP1-induced enhancement of GR transcriptional activity and histone acetylation. Thus, Set/TAF-Ibeta acts as a ligand-activated GR-responsive transcriptional repressor, while Set-Can does not retain physiologic responsiveness to ligand-bound GR, possibly contributing to the poor responsiveness of Set-Can-harboring leukemic cells to glucocorticoids.

Lentiviral Vpr usurps Cul4-DDB1[VprBP] E3 ubiquitin ligase to modulate cell cycle

The replication of viruses depends on the cell cycle status of the infected cells. Viruses have evolved functions that alleviate restrictions imposed on their replication by the host. Vpr, an accessory factor of primate lentiviruses, arrests cells at the DNA damage checkpoint in G2 phase of the cell cycle, but the mechanism underlying this effect has remained elusive. Here we report that Vpr proteins of both the human (HIV-1) and the distantly related simian (SIVmac) immunodeficiency viruses specifically associate with a protein complex comprising subunits of E3 ubiquitin ligase assembled on Cullin-4 scaffold (Cul4-DDB1[VprBP]). We show that Vpr binding to Cul4-DDB1[VprBP] leads to increased neddylation and elevated intrinsic ubiquitin ligase activity of this E3. This effect is mediated through the VprBP subunit of the complex, which recently has been suggested to function as a substrate receptor for Cul4. We also demonstrate that VprBP regulates G1 phase and is essential for the completion of DNA replication in S phase. Furthermore, the ability of Vpr to arrest cells in G2 phase correlates with its ability to interact with Cul4-DDB1[VprBP] E3 complex. Our studies identify the Cul4-DDB1[VprBP] E3 ubiquitin ligase complex as the downstream effector of lentiviral Vpr for the induction of cell cycle arrest in G2 phase and suggest that Vpr may use this complex to perturb other aspects of the cell cycle and DNA metabolism in infected cells.

Evaluation of hepatitis B virus replication and proteomic analysis of HepG2.2.15 cell line after cyclosporine A treatment

AIM

The effect of cyclosporine A (CsA) on hepatitis B virus (HBV) replication was investigated, and proteomics expression differentiation after CsA treatment was studied in order to provide clues to explore the effect of CsA on HBV replication.

METHODS

Methyl thiazolyl tetrazolium (MTT) assay was used to evaluate the cytotoxicity of CsA. The HBV replication level in the HBV genomic DNA transfected HepG2.2.15 cell line was determined by an ELISA analysis of hepatitis B surface antigens (HBsAg) and Hepatitis B e antigens (HBeAg) in culture supernatant, while the intracellular HBV DNA replication level was analyzed by slot blot hybridization. Two-dimensional electrophoresis was used to investigate the alteration of protein expression in HepG2.2.15 after CsA treatment in vitro. The differentially-expressed proteins were identified by Matrix-assisted laser desorption/ionization-time of flight mass spectrometry combined with an online database search.

RESULTS

CsA was able to inhibit the expression of HBsAg, HBeAg, and HBV DNA replication in vitro in a dose-dependent manner. A proteomics analysis indicated that the expression of 17 proteins changed significantly in the CsA treatment group compared to the control group. Eleven of the 17 proteins were identified, including the overexpression of eukaryotic translation initiation factors (eIF) 3k, otubain 1, 14.3.3 protein, eIF2-1 alpha, eIF5A, and the tyrosine 3/tryptophan 5-mono-oxygenase activation protein in CsA-treated HepG2.2.15 cells. The downregulation of the ferritin light subunit, erythrocyte cytosolic protein of 51 kDa (ECP-51), stathmin 1/oncoprotein, adenine phosphoribosyl-transferase, and the position of a tumor protein, translationally controlled 1, was shifted, suggesting it had undergone posttranslational modifications.

CONCLUSION

Our study identified the inhibitory effect of CsA on HBV replication, and found that a group of proteins may be responsible for this inhibitory effect.

Vpr cytopathicity independent of G2/M cell cycle arrest in human immunodeficiency virus type 1-infected CD4+ T cells

The mechanism of CD4(+) T-cell depletion in human immunodeficiency virus type 1 (HIV-1)-infected individuals remains unknown, although mounting evidence suggests that direct viral cytopathicity contributes to this loss. The HIV-1 Vpr accessory protein causes cell death and arrests cells in the G(2)/M phase; however, the molecular mechanism underlying these properties is not clear. Mutation of hydrophobic residues on the surface of its third alpha-helix disrupted Vpr toxicity, G(2)/M arrest induction, nuclear localization, and self-association, implicating this region in multiple Vpr functions. Cytopathicity by virion-delivered mutant Vpr protein correlated with G(2)/M arrest induction but not nuclear localization or self-association. However, infection with whole virus encoding these Vpr mutants did not abrogate HIV-1-induced cell killing. Rather, mutant Vpr proteins that are impaired for G(2)/M block still prevented infected cell proliferation, and this property correlated with the death of infected cells. Chemical agents that inhibit infected cells from entering G(2)/M also did not reduce HIV-1 cytopathicity. Combined, these data implicate Vpr in HIV-1 killing through a mechanism involving inhibiting cell division but not necessarily in G(2)/M. Thus, the hydrophobic region of the third alpha-helix of Vpr is crucial for mediating G(2)/M arrest, nuclear localization, and self-association but dispensable for HIV-1 cytopathicity due to residual cell proliferation blockade mediated by a separate region of the protein.

Virus-mediated modulation of the host endocrine signaling systems: clinical implications

Viruses, which are among the simplest infective pathogens, can produce characteristic endocrine manifestations in infected patients. In addition to the classic modification of the host endocrine system by either direct or indirect destruction of the endocrine organs and/or effects exerted by systemic production of inflammatory and/or stress mediators, recent progress in molecular virology and endocrinology has revealed that virus-encoded molecules might alter the host endocrine-signaling systems by affecting extracellular and/or intracellular signal transduction and hormone sensitivity of host target tissues. Here, we provide a brief overview of such viral-mediated modulation of host endocrine signaling systems. We propose that virus-encoded molecules and the signaling systems they influence are potential therapeutic targets for the treatment of disorders that are associated with some viral infections.

Centrosome and retroviruses: the dangerous liaisons

Centrosomes are the major microtubule organizing structures in vertebrate cells. They localize in close proximity to the nucleus for the duration of interphase and play major roles in numerous cell functions. Consequently, any deficiency in centrosome function or number may lead to genetic instability. Several viruses including retroviruses such as, Foamy Virus, HIV-1, JSRV, M-PMV and HTLV-1 have been shown to hamper centrosome functions for their own profit, but the outcomes are very different. Foamy viruses, HIV-1, JSRV, M-PMV and HTLV-1 use the cellular machinery to traffic towards the centrosome during early and/or late stages of the infection. In addition HIV-1 Vpr protein alters the cell-cycle regulation by hijacking centrosome functions. Enthrallingly, HTLV-1 Tax expression also targets the functions of the centrosome, and this event is correlated with centrosome amplification, aneuploidy and transformation.

Molecular characterization of the HIV type 1 subtype C accessory genes vif, vpr, and vpu

HIV-1 Vif, Vpr, and Vpu proteins have a profound effect on efficient viral replication and pathogenesis. This study describes the genotypic characterisation of vif , vpr and vpu from 20 South African HIV-1 subtype C primary isolates, and extensive analysis and comparison of known motifs. All HIV-1 subtype C Vif, Vpr and Vpu proteins revealed the presence of highly conserved structural and functional motifs similar to other sub-types, for example, the Vif-APOBEC3G interaction domains. However, several differences were noted when these sequences were compared to subtype B, such as the presence of the LRLL motif which has been implicated in targeting subtype C Vpu predominantly to the cell surface, instead of the Golgi apparatus. A better understanding of the structure/function relationship of these proteins may lead to the development of new classes of antiviral drugs. These results indicate that antiviral drugs that target the conserved functional domains within Vif, Vpr or Vpu could be active against all circulating subtypes, including HIV-1 subtype C.

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

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

Latent protein LANA2 from Kaposi's sarcoma-associated herpesvirus interacts with 14-3-3 proteins and inhibits FOXO3a transcription factor

The Kaposi's sarcoma-associated herpesvirus latent protein LANA2 has been suggested to have an important role in the transforming activity of the virus based on its capacity to inhibit p53 and PKR-dependent apoptosis as well as the interferon-dependent response. Here, we describe a novel interaction between LANA2 and both the phosphoserine/phosphothreonine-binding 14-3-3 proteins and the transcription factor FOXO3a. In addition, our results indicate that LANA2 inhibits the transcriptional activity of FOXO3a and blocks the G2/M arrest induced by 14-3-3 protein overexpression. These results suggest a novel mechanism by which LANA2 may promote tumorigenesis.

Interactions between the RNA interference effector protein Ago1 and 14-3-3 proteins: consequences for cell cycle progression

The Argonaute family member Ago1 is required for formation of pericentric heterochromatin and small interfering RNA (siRNA)-mediated post-transcriptional gene silencing in the fission yeast Schizosaccharomyces pombe. In addition, we have recently demonstrated that Ago1 function is required for enactment of cell cycle checkpoints (Carmichael, J. B., Provost, P., Ekwall, K., and Hobman, T. C. (2004) Mol. Biol. Cell 15, 1425-1435). Here, we provide evidence that the amino terminus of Ago1 binds to proteins that function in cell cycle regulation including 14-3-3 proteins. Interestingly, the amino terminus of human Ago2, the endonuclease that cleaves siRNA-targeted mRNAs, was also demonstrated to bind 14-3-3 proteins. Overexpression of the Ago1 amino terminus in yeast resulted in cell cycle delay at the G(2)/M boundary. Further investigation revealed that nuclear import of the mitosis-inducing phosphatase Cdc25 is inhibited by overexpression of the Ago1 amino terminus. Under these conditions, we found that the cyclin-dependent kinase Cdc2 is constitutively phosphorylated on tyrosine 15, thereby reducing the activity of this kinase, a situation that delays entry into mitosis. We hypothesize that 14-3-3 proteins are required for Argonaute protein functions in cell cycle and/or gene-silencing pathways.

HIV-1 Vpr induces G2 cell cycle arrest in fission yeast associated with Rad24/14-3-3-dependent, Chk1/Cds1-independent Wee1 upregulation

Viral protein R (Vpr), an accessory protein of human immunodeficiency virus type 1 (HIV-1), induces the G2 cell cycle arrest in fission yeast for which host factors, such as Wee1 and Rad24, are required. Catalyzing the inhibitory phosphorylation of Cdc2, Wee1 is known to serve as a major regulator of G2/M transition in the eukaryotic cell cycle. It has been reported that the G2 checkpoint induced by DNA damage or incomplete DNA replication is associated with phosphorylation and upregulation of Wee1 for which Chk1 and Cds1 kinase is required. In this study, we demonstrate that the G2 arrest induced by HIV-1 Vpr in fission yeast is also associated with increase in the phosphorylation and amount of Wee1, but in a Chk1/Cds1-independent manner. Rad24 and human 14-3-3 appear to contribute to Vpr-induced G2 arrest by elevating the level of Wee1 expression. It appears that Vpr could cause the G2 arrest through a mechanism similar to, but distinct from, the physiological G2 checkpoint controls. The results may provide useful insights into the mechanism by which HIV-1 Vpr causes the G2 arrest in eukaryotic cells. Vpr may also serve as a useful molecular tool for exploring novel cell cycle control mechanisms.

Formation of nsP3-specific protein complexes during Sindbis virus replication

Alphaviruses are arthropod-borne viruses (arboviruses) that include a number of important human and animal pathogens. Their replication proceeds in the cytoplasm of infected cells and does not directly depend on nuclei. Alphaviruses encode only four nonstructural proteins that are required for the replication of viral genome and transcription of the subgenomic RNA. However, the replicative enzyme complexes (RCs) appear to include cellular proteins and assemble on cellular organelles. We have developed a set of recombinant Sindbis (SIN) viruses with green fluorescent protein (GFP) insertions in one of the nonstructural proteins, nsP3, to further understand the RCs' genesis and structure. We studied the assembly of nsP3/GFP-containing protein complexes at different stages of infection and isolated a combination of cellular proteins that are associated with SIN nsP3. We demonstrated the following. (i) SIN nsP3 can tolerate the insertion of GFP into different fragments of the coding sequence; the designed recombinant viruses are viable, and their replication leads to the assembly of nsP3/GFP chimeric proteins into gradually developing, higher-order structures differently organized at early and late times postinfection. (ii) At late times postinfection, nsP3 is assembled into complexes of similar sizes, which appear to be bound to cytoskeleton filaments and can aggregate into larger structures. (iii) Protein complexes that are associated with nsP3/GFP contain a high concentration of cytoskeleton proteins, chaperones, elongation factor 1A, heterogeneous nuclear ribonucleoproteins, 14-3-3 proteins, and some of the ribosomal proteins. These proteins are proposed to be essential for SIN RC formation and/or functioning.

Structural determinants of 14-3-3 binding specificities and regulation of subcellular localization of 14-3-3-ligand complexes: a comparison of the X-ray crystal structures of all human 14-3-3 isoforms

14-3-3 proteins are a ubiquitous class of regulatory proteins found in all eukaryotic cells and were the first class of molecules to be recognized as discrete phosphoserine/threonine binding modules. 14-3-3 proteins bind a large number of different substrates to regulate a wide array of cellular signaling events including cell cycle progression and DNA damage responses, programmed cell death, cytoskeletal dynamics, transcriptional control of gene expression, as well as processes directly related to cancer progression. In this review, the structural basis of phosphorylation-dependent binding of 14-3-3 to peptide and protein ligands is discussed along with mechanisms that govern how 14-3-3 regulates the function of its bound ligands. The X-ray crystal structures of all human 14-3-3 proteins bound to peptides have now been solved. Here, we use structural comparisons between isoforms as a framework for discussion of ligand binding by 14-3-3 as well as the mechanisms through which post-translational modification of the different isoforms alters their function.

Human immunodeficiency virus type 1 Vpr induces cell cycle arrest at the G(1) phase and apoptosis via disruption of mitochondrial function in rodent cells

Vpr of human immunodeficiency virus type 1 causes cell cycle arrest at the G(2)/M phase and induces apoptosis after G(2)/M arrest in primate cells. We have reported previously that Vpr also induces apoptosis independently of G(2)/M arrest in human HeLa cells. By contrast, Vpr does not induce G(2)/M arrest in rodent cells, but it retards cell growth. To clarify the relationship between cell cycle arrest and apoptosis, we expressed Vpr endogenously in rodent cells and investigated cell cycle profiles and apoptosis. We show here that Vpr induces cell cycle arrest at the G(1) phase and apoptosis in rodent cells. Vpr increased the activity of caspase-3 and caspase-9, but not of caspase-8. Moreover, Vpr-induced apoptosis could be inhibited by inhibitors of caspase-3 and caspase-9, but not by inhibitor of caspase-8. We also showed that Vpr induces the release of cytochrome c from mitochondria into the cytosol and disrupts the mitochondrial transmembrane potential. Finally, we showed that apoptosis occurred in HeLa cells through an identical pathway. These results suggest that disruption of mitochondrial functions by Vpr induces apoptosis via cell cycle arrest at G(1), but that apoptosis is independent of G(2)/M arrest. Furthermore, it appears that Vpr acts species-specifically with respect to induction of cell cycle arrest but not of apoptosis.