How do animal DNA viruses get to the nucleus?

Polymer translocation: effects of periodically driven confinement

We study the influence of confinement on the dynamics of translocation of a linear polymer chain in a good solvent through a cone-shaped pore. Using the Langevin dynamics simulations, we calculate both the first attempt time and translocation time as a function of the position of the back wall and apex angle α. As the in vivo confining environment is inherently dynamic, we extended the present study to explore the consequences of a periodically driven back wall and apex angles on the translocation dynamics. Our findings reveal that the translocation time initially decreases as the driving frequency increases, but increases after a certain frequency. The frequency at which the translocation time is found to be minimum is referred to as the resonance activation. Analyzing the distribution of translocation times around this frequency renders interesting information about the translocation process. We further explore the translocation dynamics by calculating the residence time of individual monomers, shedding light on the microscopic aspects of the process.

Survivin-targeted nanomedicine for increased potency of abiraterone and enzalutamide against prostate cancer

Prostate cancer is the leading and most aggressive cancer around the world, several therapeutic approaches have emerged but none have achieved the satisfactory result. However, these therapeutic approaches face many challenges related to their delivery to target cells, including their in vivo decay, the limited uptake by target cells, the requirements for nuclear penetration (in some cases), and the damage caused to healthy cells. These barriers can be avoided by effective, targeted, combinatorial approaches, with minimal side effects, which are being investigated for the treatment of cancer. Here, we developed a combinatorial nanomedicine comprising abiraterone and enzalutamide bioconjugated survivin-encapsulated gold nanoparticles (AbEzSvGNPs) for targeted therapy of prostate cancer. AbEzSvGNPs were characterized by different biophysical techniques such as UV visible spectroscopy, dynamic light scattering, zeta potential, transmission electron microscope, and Fourier transform infrared spectroscopy. Interestingly, the effect of abiraterone, enzalutamide and surviving encapsulated gold nanoparticles was found to be synergistic in nature in AbEzSvGNPs against DU 145 (IC50 = 4.21 µM) and PC-3 (IC50 = 5.58 µM) cells and their potential was observed to be greatly enhanced as compared with the combined effect of the drugs (abiraterone and enzalutamide) in their free form. Furthermore, AbEzSvGNPs were found to be highly safe and did not exhibit significant cytotoxicity against normal rat kidney cells. The observed effects of AbEzSvGNPs involved the modulation of different signaling pathways in prostate cancer cells. This delivery system employed non-androgen receptor-dependent delivery of abiraterone and enzalutamide. The anionic AbEzSvGNPs delivered abiraterone and enzalutamide unaltered into the nucleus through caveolae mediated internalization to act nonspecifically on DNA; internalization of the anionic nanoparticles into the cytoplasm was also observed via other routes. AbEzSvGNPs synthesized and evaluated in this study are promising candidates for prostate cancer therapy.

Novel Bioengineered Antibacterial and Anticancer ZnO Nanoparticles

Transition metal oxide NPs have delivered wide applications in various fields. Therefore, in this study, a novel fungus, Alternaria sp. (NCBI Accession No: MT982648) was isolated and characterized from the vicinity of medicinal plants. Eventually, in this method extracted proteins from isolated fungus were utilized to synthesize highly biocompatible zinc nanoparticles (ZnO NPs). The various physical techniques including UV-visible spectroscopy, TEM, HR-TEM, XRD, DLS, zeta potential, and FTIR were used to characterize particles. The UV-visible absorption (λ_Max) and binding energy for the as-synthesized particles were found to be 329 nm and 3.91 eV, respectively. Further, the polydispersed particles were revealed to have regular crystallinity with hexagonal wurtzite phase of ZnO with the spacing of ~2.46 Å under XRD and HR-TEM. The average size of a particle under TEM was found to be ~18 nm. The evaluation of various surface functional groups of particles was done by FTIR. The average hydrodynamic diameter of particles was found to be ~57 d. nm with 0.44 particle distribution index whereas the nanoemulsion stability was explained by Zeta potential (-9.47 mV). These particles were found to exhibit potential antibacterial and anticancer activities. They were found to be bactericidal against S. abony (MIC 5.73 μg/mL); B. pumilis (MIC 6.64 μg/mL); K. pneumonia (MIC 14.4 μg/mL); E. coli (MIC 8.7 μg/mL); B. subtilis (MIC 5.63 μg/mL) and S. aureus (MIC 12.04 μg/mL). Further, they are also found to be concentration-dependent anticancer and inhibited the growth of A549 cells (IC₅₀-65.3 μg/mL) whereas they were found to demonstrate no any cytotoxicity against NRK normal kidney cell line. The internalization of particles into the nucleus (i.e., nuclear fragmentation and DNA damage) was confirmed by DAPI staining. The intracellular particles were found to generate excessive ROS. Further, the anticancer potential was also estimated by noticing a hike in oxidative stress parameters, cell viability, cell morphology, and change in mitochondrial membrane potential. We effectively synthesized potentially potent antibacterial and anticancer novel bioengineered ZnO NPs.

Nucleolar protein NPM1 is essential for circovirus replication by binding to viral capsid

Entry of circovirus into the host cell nucleus is essential for viral replication during the early stage of infection. However, the mechanisms by which nucleolar shuttle proteins are used during viral replication is still not well understood. Here, we report a previously unidentified nucleolar localization signal in circovirus capsid protein (Cap), and that circovirus hijacks the nucleolar phosphoprotein nucleophosmin-1 (NPM1) to facilitate its replication. Colocalization analysis showed that NPM1 translocates from the nucleolus to the nucleoplasm and cytoplasm during viral infection. Coimmunoprecipitation and glutathione S-transferase pull-down assays showed that Cap interacts directly with NPM1. Binding domain mapping showed that the arginine-rich N-terminal motif ¹MTYPRRRYRRRRHRPRSHLG²⁰ of Cap, and residue serine-48 of the N-terminal oligomerization domain of NPM1, are essential for the interaction. Virus rescue experiments showed that all arginine to alanine substitution in the N-terminal arginine-rich motif of Cap resulted in diminished viral replication. Knockdown of NPM1 and substitution of serine-48 in NPM1 to glutamic acid also decreased viral replication. In addition, binding assays showed that the arginine-rich motif of Cap is a nucleolar localization signal. Taken together, our findings demonstrate that circovirus protein Cap is a nucleolus-located, and regulates viral replication by directly binding to NPM1.

Papain Mediated Synthesized Gold Nanoparticles Encore the Potency of Bioconjugated Flutamide

BACKGROUND

Prostate cancer is the second most common cause of male cancer death after lung cancer in the US. Therefore, there is an urgent need for a highly effective therapeutic drug at substantially low doses.

OBJECTIVE

Anti-androgen drug flutamide was delivered to the prostate cancer cells using Papain Mediated Synthesized Gold Nanoparticles (PGNPs) as the drug delivery system. PGNPs and flutamide worked synergistically against cancer cells.

METHODS

Flutamide was used to bioconjugate with PGNPs to improve its efficacy against prostate cancer. The synthesis and bioconjugation of flutamide with PGNPs (F-PGNPs) were characterized by various characterization techniques such as UV-vis spectroscopy, Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), and zeta potential to ensure the synthesis, size, shape, size distribution, and stability. The drug loading efficiency of flutamide in F-PGNPs was confirmed and validated by UV-vis spectroscopy. Eventually, in vitro studies were performed to determine the potency of F-PGNPs, changes in nuclear morphology, and generation of Reactive Oxygen Species (ROS).

RESULTS

The efficacy of F-PGNPs (IC₅₀ is 46.54 μg/mL) was found to be improved significantly over pure flutamide (IC50 is 64.63 μg/mL) against human prostate cancer PC-3 cell line whereas F-PGNPs did not show any significant toxicity up to a fairly high concentration toward normal mouse macrophage J774A.1 cells. The apoptotic effects and ROS generation of F-PGNPs were analyzed by increased permeability of the cell membrane and condensed chromatin with deep blue and green fluorescent nucleus, respectively.

DISCUSSION

The results clearly showed that F-PGNPs significantly improved the potency of flutamide by delivering it directly into the nucleus of cancer cells through caveolae-dependent endocytosis.

CONCLUSION

Thus, the greater inhibitory effect of F-PGNPs over the pure drug would be of great advantage during prostate cancer treatment.

Nanotechnology: A Promising Approach for Delivery of Neuroprotective Drugs

Central nervous system (CNS) disorders especially neurodegenerative disorders are the major challenge for public health and demand the great attention of researchers to protect people against them. In past few decades, different treatment strategies have been adopted, but their therapeutic efficacy are not enough and have only shown partial mitigation of symptoms. Blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BSCFB) guard the CNS from harmful substances and pose as the major challenges in delivering drugs into CNS for treatment of CNS complications such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), stroke, epilepsy, brain tumors, multiple sclerosis (MS), and encephalitis, etc. Nanotechnology has come out as an exciting and promising new platform of treating neurological disorders and has shown great potential to overcome problems related to the conventional treatment approaches. Molecules can be nanoengineered to carry out multiple specific functions such as to cross the BBB, target specific cell or signaling pathway, respond to endogenous stimuli, and act as a vehicle for gene delivery, support nerve regeneration and cell survival. In present review, the role of nanocarrier systems such as liposomes, micelles, solid lipid nanoparticles (SLNPs), dendrimers, and nanoemulsions for delivery of various neurotherapeutic agents has been discussed, besides this, their mechanism of action, and nanoformulation of different neuroprotective agents like curcumin, edaravone, nerve growth factors in CNS disorders like Alzheimer’s, Parkinsonism, epilepsy, stroke, and brain tumors has been reviewed.

Cellular p32 Is a Critical Regulator of Porcine Circovirus Type 2 Nuclear Egress

Circoviruses are the smallest DNA viruses known to infect mammalian and avian species. Although circoviruses are known to be associated with a range of clinical diseases, the details of circovirus DNA release still remain unknown. Here, we identified p32 as a key regulator for porcine circoviral nuclear egress. Upon porcine circovirus type 2 (PCV2) infection, p32 was recruited into the nucleus by the viral capsid (Cap) protein; simultaneously, protein kinase C isoform δ (PKC-δ) was phosphorylated at threonine 505 by phospholipase C (PLC)-mediated signaling at the early stage of infection, which was further amplified by Jun N-terminal protein kinase (JNK) and extracellular signal-regulated kinase (ERK) signaling at the late infection phase. p32 functioned as an adaptor to recruit phosphorylated PKC-δ and Cap to the nuclear membrane to phosphorylate lamin A/C, resulting in a rearrangement of nuclear lamina and thus facilitating viral nuclear egress. Consistent with these findings, knockout (KO) of p32 in PCV2-infected cells markedly reduced the phosphorylation of PKC-δ and impeded the recruitment of p-PKC-δ and Cap to the nuclear membrane, hence abolishing the phosphorylation of lamin A/C and the rearrangement of nuclear lamina. As a result, p32 depletion profoundly impaired the production of cell-free viruses during PCV2 infection. We further identified the N-terminal 24RRR26 of Cap to be crucial for binding to p32, and mutation of these three arginine residues significantly weakened the replication and pathogenesis of PCV2 in vivo In summary, our findings highlight a critical role of p32 in the activation and recruitment of PKC-δ to phosphorylate lamin A/C and facilitate porcine circoviral nuclear egress, and they certainly help understanding of the mechanism of PCV2 replication.IMPORTANCE Circovirus infections are highly prevalent in mammalian and avian species. Circoviral capsid protein is the only structural protein of the virion that plays an essential role in viral assembly. However, the machinery of circovirus nuclear egress is currently unknown. In this work, we identified p32 as a key regulator of porcine circovirus type 2 (PCV2) nuclear egress that forms a complex with the viral capsid (Cap) protein to enhance protein kinase C isoform δ (PKC-δ) activity; this resulted in a recruitment of phosphorylated PKC-δ to the nuclear membrane, which further phosphorylates lamin A/C to promote the rearrangement of nuclear lamina and facilitate viral nuclear egress. Notably, we found that the N-terminal 24RRR26 of Cap, a highly conserved motif among circovirus species, was required for interacting with p32, and that mutation of this motif markedly impeded PCV2 nuclear egress. These data indicate that p32 is a critical regulator of PCV2 nuclear egress and reveal the importance of this finding in circovirus replication.

Development of a novel DsRed-NLS vector with a monopartite classical nuclear localization signal

The nuclear localization signal (NLS) marks proteins for transport to the nucleus and is used in various applications in many fields. NLSs are used to achieve efficient and stable transport of biomolecules. Previously, commercial vectors used in NLS studies contained three iterations of the NLS sequence, but these sequences can affect experimental results and alter protein function. Here, we investigated a new vector using a single classical NLS sequence with a mutation in pDsRed2-C1-wt to reduce experimental artifacts. In the newly constructed pDsRed2-C1-1NLS vector, the NLS sequence is placed near the multiple cloning sites of pDsRed2-C1-wt, and the multiple cloning site region was designed to facilitate insertion of the desired gene by site-directed mutagenesis. Fluorescent protein expression in the nucleus can be visually confirmed. The results show that the fluorescent protein was bound to the transport protein. The constructed vector had a cell survival rate of 89-95% and a transfection efficiency of 39-56% when introduced into animal cells, which are similar to those of other NLS vectors. Additionally, the constructed NLS vector can be used to demonstrate complementary binding between target proteins, and that the target protein is transported by the NLS transport system. Especially, we show that the vector can be useful for experiments involving the S100A10 gene. In addition, the constructed vector is useful for studies of genes and proteins that show potential for gene therapy or drug delivery applications.

Biogenic pentagonal silver nanoparticles for safer and more effective antibacterial therapeutics

Background

Biological synthesis of nanomaterials possesses unprecedented potential in the production of nanomaterials due to their ability to produce nanomaterials with improved biocompatibility in addition to eco-friendly synthetic procedures.

Methods

This article reports the isolation of an air-borne fungus from the campus of Integral University, Lucknow, with an exceptional ability to withstand very high concentrations of silver salt. The fungus was found to produce pentagonal silver nanoparticles (AgPgNps) when silver ions were reduced from silver nitrate. Molecular analysis and biochemical characterization techniques based on 18-seconds rRNA identified the fungus to belong to the Aspergillus sp. with the NCBI accession no KF913249. Material characterization techniques including ultraviolet (UV)–visible spectroscopy, transmission electron microscopy, and zeta potential analysis were used to satisfactorily characterize the as-synthesized AgPgNps.

Results

The AgPgNps synthesized by the fungus Aspergillus sp. exhibit an absorption that is maximum centered at about 416 nm, with a standard particle size of 23.22±2 nm. These AgPgNps exhibited broad-spectrum antimicrobial activities against an array of bacterial pathogens with remarkable minimum inhibitory concentration (MIC₅₀) values: Staphylococcus aureus (ATCC 25923) – 9.230 µg/mL, Bacillus sp. (ATCC 14593) – 12.781 µg/mL, Escherichia coli (ATCC 25922) – 5.063 µg/mL, and Klebsiella pneumoniae (ATCC 13883) – 5.426 µg/mL. In vitro cytotoxicity analysis of biosynthesized AgPgNps showed a dose–response activity against human cervical cancer cell line (HeLa) and adenocarcinoma cells (A549) with MIC₅₀ values of 0.038 µg/mL and 0.044 µg/mL, respectively.

Conclusion

These findings are very crucial to evaluate the biosynthetic process for the synthesis of nanoparticles (NPs) with unique properties. These NPs may find potential applications in sensing, medicine, and antimicrobial and anticancer therapies.

Gold nanoconjugates reinforce the potency of conjugated cisplatin and doxorubicin

Osteosarcoma or osteogenic sarcoma is the most common and prevalent cancerous tumor of bone and occurs especially in children and teens. Recent treatment strategy includes a combination of both chemotherapy and surgeries. Although, the use of single drug-based chemotherapy treatment remains unsatisfactory. Therefore, combinatorial therapy has emerged as a potential strategy for treatment with limited side- effects. Here, we evaluated the combinatorial anticancerous effect of cisplatin (CIS) and doxorubicin (DOX) bioconjugated bromelain encapsulated gold nanoparticles (B-AuNPs conjugated CIS and DOX) in the treatment of osteosarcoma. The synthesized B-AuNPs conjugated CIS and DOX were characterized by various characterization techniques like UV-vis spectroscopy, TEM, DLS and zeta potential to ensure the synthesis, size, shape, size distribution and stability. Drug loading efficiency bioconjugation of CIS and DOX was ensured by UV-vis spectroscopy. Bioconjugation of CIS and DOX was further confirmed using UV-vis spectroscopy, TEM, DLS, Zeta potential and FT-IR analysis. The combinatorial effect of CIS and DOX in B-AuNPs conjugated CIS and DOX showed highly improved potency against MG-63 and Saos-2 cells at a very low concentration where primary osteoblasts didn't show any cytotoxic effect. The apoptotic effect of B-AuNPs conjugated CIS and DOX on osteosarcoma and primary osteoblasts cells were analyzed by increased permeability of the cell membrane, condensed chromatin and deep blue fluorescent condensed nucleus. The results clearly showed that B-AuNPs conjugated CIS and DOX significantly improved the potency of both the chemotherapeutic drugs by delivering them specifically into the nucleus of cancer cells through caveolae-dependent endocytosis. Thus, the greater inhibitory effect of combinatorial drugs (B-AuNPs conjugated CIS and DOX) over single drug based chemotherapy would be of great advantage during osteosarcoma treatment.

Entry, infection, replication, and egress of human polyomaviruses: an update

Polyomaviruses (PyVs), belonging to the family Polyomaviridae, are a group of small, nonenveloped, double-stranded, circular DNA viruses widely distributed in the vertebrates. PyVs cause no apparent disease in adult laboratory mice but cause a wide variety of tumors when artificially inoculated into neonates or semipermissive animals. A few human PyVs, such as BK, JC, and Merkel cell PyVs, have been unequivocally linked to pathogenesis under conditions of immunosuppression. Infection is thought to occur early in life and persists for the lifespan of the host. Over evolutionary time scales, it appears that PyVs have slowly co-evolved with specific host animal lineages. Host cell surface glycoproteins and glycolipids seem to play a decisive role in the entry stage of viral infection and in channeling the virions to specific intracellular membrane-bound compartments and ultimately to the nucleus, where the genomes are replicated and packaged for release. Therefore the transport of the infecting virion or viral genome to this site of multiplication is an essential process in productive viral infection as well as in latent infection and transformation. This review summarizes the major findings related to the characterization of the nature of the interactions between PyV and host protein and their impact in host cell invasion.

Replication

This chapter provides an overview of the key stages in virus replication, including the historic experiments which resulted in our present understanding. It describes, step by step, how replication unfolds, starting with the initial interaction between the virus and a host cell and finishing with the release of infectious virus particles which can go on and infect new cells. Since these processes are essential in the replication cycle, understanding how they can be blocked specifically without damaging the host cell is the key to understanding how antiviral drugs work.

On completing this chapter you should be able to:

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Explain the phases of virus replication.

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Describe the key experiments which allowed us to understand what happens during replication.

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Discuss how drugs which block these processes can be used to combat virus infections.

Retroviral microRNAs

Eukaryotic cells and several DNA viruses encode miRNAs to regulate the expression of specific target genes. It has been controversial whether RNA viruses can encode such miRNAs as miRNA excision may lead to cleavage of the viral RNA genome. We will focus on the retrovirus family, HIV-1 in particular, and discuss the production of virus-encoded miRNAs and their putative function in the viral replication cycle. An intricate scenario of multi-layer virus-host interactions becomes apparent with small RNAs as the regulatory molecules.

BK and JC virus: a review

Polyomaviruses are ubiquitous, species-specific viruses belonging to the family Papovaviridae. The two most commonly known human polyomaviruses, BK virus and JC virus were first described in the 1970s. Newer human polyomaviruses, namely KI polyoma virus, WU polyoma virus and Merkel cell polyoma virus were identified in the last five years. Most humans encounter BK and JC virus during childhood, causing mild illness. However, when reactivated or acquired in the immunocompromised host, BK and JC virus have been implicated in a number of human clinical disease states. BK is most commonly associated with renal involvement, such as ureteral stenosis, hemorrhagic cystitis and nephropathy. Less commonly, it is associated with pneumonitis, retinitis, liver disease and meningoencephalitis. JC virus is most well known for its association with progressive multifocal leukoencephalopathy, and is possibly implicated in the development of various human neoplasms. The following chapter will outline the basic virology, epidemiology and clinical manifestations of BK and JC virus and discuss relevant diagnostic and treatment options.

Molecular biology, epidemiology, and pathogenesis of progressive multifocal leukoencephalopathy, the JC virus-induced demyelinating disease of the human brain

Progressive multifocal leukoencephalopathy (PML) is a debilitating and frequently fatal central nervous system (CNS) demyelinating disease caused by JC virus (JCV), for which there is currently no effective treatment. Lytic infection of oligodendrocytes in the brain leads to their eventual destruction and progressive demyelination, resulting in multiple foci of lesions in the white matter of the brain. Before the mid-1980s, PML was a relatively rare disease, reported to occur primarily in those with underlying neoplastic conditions affecting immune function and, more rarely, in allograft recipients receiving immunosuppressive drugs. However, with the onset of the AIDS pandemic, the incidence of PML has increased dramatically. Approximately 3 to 5% of HIV-infected individuals will develop PML, which is classified as an AIDS-defining illness. In addition, the recent advent of humanized monoclonal antibody therapy for the treatment of autoimmune inflammatory diseases such as multiple sclerosis (MS) and Crohn's disease has also led to an increased risk of PML as a side effect of immunotherapy. Thus, the study of JCV and the elucidation of the underlying causes of PML are important and active areas of research that may lead to new insights into immune function and host antiviral defense, as well as to potential new therapies.

Viral polymerases

Viral polymerases play a central role in viral genome replication and transcription. Based on the genome type and the specific needs of particular virus, RNA-dependent RNA polymerase, RNA-dependent DNA polymerase, DNA-dependent RNA polymerase, and DNA-dependent RNA polymerases are found in various viruses. Viral polymerases are generally active as a single protein capable of carrying out multiple functions related to viral genome synthesis. Specifically, viral polymerases use variety of mechanisms to recognize initial binding sites, ensure processive elongation, terminate replication at the end of the genome, and also coordinate the chemical steps of nucleic acid synthesis with other enzymatic activities. This review focuses on different viral genome replication and transcription strategies, and the polymerase interactions with various viral proteins that are necessary to complete genome synthesis.

Replication

This chapter begins with an overview of virus replication, and explains how studying bacteriophages has helped understand more complex viruses that are harder to work with, and then explains the processes involved in virus replication step by step. The virus replication involves three broad essential stages carried out by all types of viruses: the initiation of infection, replication and expression of the genome, and the release of mature virions from the infected cell. At a detailed level, there are many differences in the replication processes of different viruses that are imposed by the biology of the host cell and the nature of the virus genome. The other stages that have been discussed are: attachment, penetration, uncoating, genome replication, gene expression, assembly, maturation, and release. The chapter illustrates similarities in the pattern of replication of different viruses. Regardless of their hosts, all viruses must undergo each of these stages in some form to successfully complete their replication cycles.

What's in this chapter?

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We start with an overview of virus replication, then move on to look at how studying bacteriophages has helped us understand more complex viruses that are harder to work with.

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Then we go through the processes involved in virus replication step by step.

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Along the way, we start to consider whether knowledge of these processes can be used to combat virus infections.

Potential for the Anopheles gambiae densonucleosis virus to act as an "evolution-proof" biopesticide

"Evolution-proof" or "late-life-acting" insecticides (LLAIs) preferentially kill older adult mosquitoes and are of extreme interest to control vector-borne diseases such as malaria. We used quantitative PCR to assess whether the Anopheles gambiae densonucleosis virus (AgDNV) had potential as an LLAI. After infection, AgDNV titers increased modestly during larval development but replicated slower than the host cells, resulting in a significant decrease in the normalized virus titer during larval and pupal development. Normalized virus titers dramatically increased after adult emergence, peaking in 7- to 10-day-old adults. Unlike other DNVs, AgDNV does not significantly replicate in preadult mosquitoes but rather preferentially replicates in older adults. The natural dynamics of AgDNV make it ideal for expression of insect-specific toxin genes as a biological LLAI.

Transportin mediates nuclear entry of DNA in vertebrate systems

Delivery of DNA to the cell nucleus is an essential step in many types of viral infection, transfection, gene transfer by the plant pathogen Agrobacterium tumefaciens and in strategies for gene therapy. Thus, the mechanism by which DNA crosses the nuclear pore complex (NPC) is of great interest. Using nuclei reconstituted in vitro in Xenopus egg extracts, we previously studied DNA passage through the nuclear pores using a single-molecule approach based on optical tweezers. Fluorescently labeled DNA molecules were also seen to accumulate within nuclei. Here we find that this import of DNA relies on a soluble protein receptor of the importin family. To identify this receptor, we used different pathway-specific cargoes in competition studies as well as pathway-specific dominant negative inhibitors derived from the nucleoporin Nup153. We found that inhibition of the receptor transportin suppresses DNA import. In contrast, inhibition of importin beta has little effect on the nuclear accumulation of DNA. The dependence on transportin was fully confirmed in assays using permeabilized HeLa cells and a mammalian cell extract. We conclude that the nuclear import of DNA observed in these different vertebrate systems is largely mediated by the receptor transportin. We further report that histones, a known cargo of transportin, can act as an adaptor for the binding of transportin to DNA.

Human polyoma viruses and disease with emphasis on clinical BK and JC

Polyoma viruses are ubiquitous infecting many different mammalian species including humans. There are five known human polyoma viruses. JC virus and BK virus are two polyoma viruses identified nearly three decades ago. Recently WU, KI and Merkel cell polyoma viruses have been isolated from humans. The exact role of these three newly discovered viruses in human disease is not known. Most human polyoma disease is caused by BK and JC viruses which are usually acquired in childhood. Approximately 50-80% of humans have seropositivity to these viruses. Clinically apparent diseases in immunocompetent hosts are extremely rare. These viruses remain latent possibly in the lymphoid organs, neuronal tissue, and kidney and under the circumstances of severe immunosuppression both these viruses reactivate. Neurotropic JC virus reaches the brain and causes progressive multifocal leukoencephalopathy, a demyelinating disease of the central nervous system with a high mortality rate. BK virus is urotheliotropic and its reactivation causes a form of interstitial nephritis, known as BK or polyoma virus associated nephropathy which is associated with high graft loss if not recognized early. There are no known effective antiviral agents for any of the polyoma viruses.

DNA-tumor virus entry--from plasma membrane to the nucleus

DNA-tumor viruses comprise enveloped and non-enveloped agents that cause malignancies in a large variety of cell types and tissues by interfering with cell cycle control and immortalization. Those DNA-tumor viruses that replicate in the nucleus use cellular mechanisms to transport their genome and newly synthesized viral proteins into the nucleus. This requires cytoplasmic transport and nuclear import of their genome. Agents that employ this strategy include adenoviruses, hepadnaviruses, herpesviruses, and likely also papillomaviruses, and polyomaviruses, but not poxviruses which replicate in the cytoplasm. Here, we discuss how DNA-tumor viruses enter cells, take advantage of cytoplasmic transport, and import their DNA genome through the nuclear pore complex into the nucleus. Remarkably, nuclear import of incoming genomes does not necessarily follow the same pathways used by the structural proteins of the viruses during the replication and assembly phases of the viral life cycle. Understanding the mechanisms of DNA nuclear import can identify new pathways of cell regulation and anti-viral therapies.

The Polyomaviridae: Contributions of virus structure to our understanding of virus receptors and infectious entry

This review summarizes the field's major findings related to the characterization of polyomavirus structures and to the characterization of virus receptors and mechanisms of host cell invasion. The four members of the family that have received the most attention in this regard are the mouse polyomavirus (mPyV), the monkey polyomavirus SV40, and the two human polyomaviruses, JCV and BKV. The structures of both the mPyV and SV40 alone and in complex with receptor fragments have been solved to high resolution. The majority of polyomaviruses recognize terminal sialic acid in either an α2,3 linkage or an α2,6 linkage to the underlying galactose. Studies on virus structure, receptor utilization and mechanisms of entry have led to new insights into how these viruses interact in an active way with cells to ensure the nuclear delivery and expression of their genomes. Critical work on virus entry has led to the discovery of a pH neutral endocytic compartment that accepts cargo from caveolae and to novel roles for endoplasmic reticulum (ER) associated factors in virus uncoating and penetration of ER membranes. This review will summarize the major findings and compare and contrast the mechanisms used by these viruses to infect cells.

Development of lipid particles targeted via sugar-lipid conjugates as novel nuclear gene delivery system

Efficient nuclear gene delivery is essential for successful gene therapy. This study developed a novel system that mimics the mechanism of nuclear entry of adenovirus (Ad) by means of a Multifunctional Envelope-type Nano Device (MEND). In this system, plasmid DNA (pDNA) was condensed with polycation, followed by encapsulation in a lipid membrane. To target MEND to the nuclear pore complex (NPC), sugar served as a NPC-mediated nuclear targeting device was modified on the surface of the lipid envelope. This was accomplished via synthesis of a sugar-cholesterol conjugate. After binding of the MEND to the NPC, the pDNA core was transferred into the nucleus in conjunction with a breakdown of the lipid envelope. Sugar-modified MEND showed higher transfection efficiency compared with unmodified MEND, in non-dividing and dividing cells. Confocal microscopy confirmed that nuclear transfer of pDNA was improved by sugar modification of MEND. Furthermore, destabilization of the lipid envelope significantly enhanced transfection activity: therefore, nuclear-delivery efficiency was closely related to lipid envelope stability. Moreover, quantitative evaluation of cellular uptake and nuclear transfer processes by real-time PCR confirmed that the surface sugars affected nuclear transfer, but not cellular uptake. In summary, a novel system for the nuclear delivery of pDNA was successfully developed by using a sugar-modified MEND and by optimizing the lipid envelope stability.

"Alternative" endocytic mechanisms exploited by pathogens: new avenues for therapeutic delivery?

Some pathogens utilize unique routes to enter cells that may evade the intracellular barriers encountered by the typical clathrin-mediated endocytic pathway. Retrograde transport and caveolar uptake are among the better characterized pathways, as alternatives to clathrin-mediated endocytosis, that are known to facilitate entry of pathogens and potential delivery agents. Recent characterization of the trafficking mechanisms of prion proteins and certain bacteria may present new paradigms for strategizing improvements in therapeutic spread and retention of therapy. This review will provide an overview of such endocytic pathways, and discuss current and future possibilities in using these routes as a means to improve therapeutic delivery.

[Serological response to herpes simplex virus type 1 and 2 infection among women of reproductive age]

INTRODUCTION

Herpes simplex viruses type 1 and 2 (HSV-1 and HSV-2) are alpha herpes viruses. Humans are the only natural host and they can be transmitted through oral or genital secretions. These viruses are ubiquitous all over the world, with different percentage rates. The aims of this paper were to determine the serological response to HSV-1 and HSV-2 infection among pregnant women and women of reproductive age and seroprevalence of HSV-1 and HSV-2 antibodies among pregnant women and women of reproductive age.

MATERIAL AND METHODS

A total of 81 serum samples were analyzed. 32 sera were collected from pregnant women, and 49 sera were from non-pregnant women of reproductive age. Serum samples were tested for IgM antibodies to both herpes simplex viruses by use of immunoenzymatic assay (Bioelisa HSV IgM Immunocapture; Biokit, Spain)). Sero-type specific ELISA tests: Bioelisa HSV-1 IgG and Bioelisa HSV-2 IgG (Biokit, Spain) were used for detection of IgG antibodies to HSV-1 and HSV-2, respectively.

RESULTS

Type-common IgM antibodies were found in 6.25% of pregnant women, and in 4.08% of women of reproductive age. Type-specific IgG antibodies to HSV-1 were detected in 68.75% of pregnant women, and in 81.63% of non-pregnant women. The seroprevalence of HSV-1 in our sample was 76.5%. Type-specific IgG antibodies to HSV-2 were detected in 12.5% of pregnant women, and in 12.24% of non-pregnant women of reproductive age. The seroprevalence of HSV-2 in the whole sample was 12.35%.

CONCLUSION

Most women have antibodies to HSV-1, which is partially protective against HSV-2 infection. The seroprevalence of HSV-2 in our sample is relatively low, and similar to seroprevalence in developed European countries. However, there is a high risk of acquiring primary genital HSV infection during pregnancy. Our sample was small, therefore further investigations are required for valid evaluation of seroprevalence of HSV-1 and HSV-2 in Serbia.

Modulation of adenoviral transduction in vitro and in vivo by hyaluronan and its receptor CD44

Adenovirus infection is a significant cause of ocular, respiratory, and gastrointestinal illness and can spread rapidly. Morbidity is considerable in immune-suppressed individuals and there is significant mortality. There are no effective therapies. During preclinical studies of adenoviral-mediated gene therapy for ocular disorders, we noticed a significant increase in transduction when the target cells were exposed to adenovirus in the presence of ocular vitreous. The vitreous is mainly comprised of water, collagen, and the large polysaccharide hyaluronan. In this paper, we report data that implicate hyaluronan in the adenoviral infectious process and show that interference with the interaction between hyaluronan and its cellular receptor CD44 can block adenovirus transduction in vitro and in vivo.

Molecular dissection of nuclear entry-competent SV40 during infection

To establish viral infection, SV40 must expose nuclear localization signals (NLSs) that are internal in the virion architecture in order to enter the nucleus via interaction with the host's nuclear import machinery, which includes importin alpha and importin beta. The time course for SV40 association with the importins in infected cells was examined. The viral DNA associated with importin alpha by 1.5h post infection, before associating with the importin beta nuclear import receptor, by 3h post infection. Only a small fraction of cell-internalized SV40 that contained viral DNA was bound by the two importins. This fraction, termed "nuclear entry-competent SV40," was slightly smaller than the virion but, importantly, was larger than the viral chromatin and contained both Vp1 and Vp3. Furthermore, the internalized viral DNA in either anti-importin or anti-Vp3 immune complexes was sensitive to DNase I, whereas the viral DNA in mature virions was resistant. All these results suggest that once SV40 enters the cytoplasm, it undergoes an architectural modification that exposes the virion's NLSs for nuclear entry.

Simian virus 40 late proteins possess lytic properties that render them capable of permeabilizing cellular membranes

Many nonenveloped viruses have evolved an infectious cycle that culminates in the lysis or permeabilization of the host to enable viral release. How these viruses initiate the lytic event is largely unknown. Here, we demonstrated that the simian virus 40 progeny accumulated at the nuclear envelope prior to the permeabilization of the nuclear, endoplasmic reticulum, and plasma membranes at a time which corresponded with the release of the progeny. The permeabilization of these cellular membranes temporally correlated with late protein expression and was not observed upon the inhibition of their synthesis. To address whether one or more of the late proteins possessed an inherent capacity to induce membrane permeabilization, we examined the permeability of Escherichia coli that separately expressed the late proteins. VP2 and VP3, but not VP1, caused the permeabilization of bacterial membranes. Additionally, VP3 expression resulted in bacterial cell lysis. These findings demonstrate that VP3 possesses an inherent lytic property that is independent of eukaryotic signaling or cell death pathways.

Adeno-associated virus vectors: potential applications for cancer gene therapy

Augmenting cancer treatment by protein and gene delivery continues to gain momentum based on success in animal models. The primary hurdle of fully exploiting the arsenal of molecular targets and therapeutic transgenes continues to be efficient delivery. Vectors based on adeno-associated virus (AAV) are of particular interest as they are capable of inducing transgene expression in a broad range of tissues for a relatively long time without stimulation of a cell-mediated immune response. Perhaps the most important attribute of AAV vectors is their safety profile in phase I clinical trials ranging from CF to Parkinson's disease. The utility of AAV vectors as a gene delivery agent in cancer therapy is showing promise in preclinical studies. In this review, we will focus on the basic biology of AAV as well as recent progress in the use of this vector in cancer gene therapy.

Intracellular trafficking of nucleic acids

Until recently, the attention of most researchers has focused on the first and last steps of gene transfer, namely delivery to the cell and transcription, in order to optimise transfection and gene therapy. However, over the past few years, researchers have realised that the intracellular trafficking of plasmids is more than just a "black box" and is actually one of the major barriers to effective gene delivery. After entering the cytoplasm, following direct delivery or endocytosis, plasmids or other vectors must travel relatively long distances through the mesh of cytoskeletal networks before reaching the nuclear envelope. Once at the nuclear envelope, the DNA must either wait until cell division, or be specifically transported through the nuclear pore complex, in order to reach the nucleoplasm where it can be transcribed. This review focuses on recent developments in the understanding of these intracellular trafficking events as they relate to gene delivery. Hopefully, by continuing to unravel the mechanisms by which plasmids and other gene delivery vectors move throughout the cell, and by understanding the cell biology of gene transfer, superior methods of transfection and gene therapy can be developed.

Nuclear import in viral infections

The separation of transcription in the nucleus and translation in the cytoplasm requires nucleo-cytoplasmic exchange of proteins and RNAs. Viruses have evolved strategies to capitalize on the nucleo-cytoplasmic trafficking machinery of the cell. Here, we first discuss the principal mechanisms of receptor-mediated nuclear import of proteinaceous cargo through the nuclear pore complex, the gate keeper of the cell nucleus. We then focus on viral strategies leading to nuclear import of genomes and subgenomic particles. Nucleo-cytoplasmic transport is directly important for those viruses that are replicating in the nucleus, such as DNA tumor viruses and RNA viruses, including parvoviruses, the DNA retroviruses hepadnaviruses, RNA-retrotransposons and retroviruses, adenoviruses, herpesviruses, papovaviruses, and particular negative-sense RNA viruses, such as the orthomyxovirus influenza virus. The viral strategies of nuclear import turn out to be surprisingly diverse. Their investigation continues to give insight into how nucleic acids pass in and out of the nucleus.

A conformational change in the adeno-associated virus type 2 capsid leads to the exposure of hidden VP1 N termini

The complex infection process of parvoviruses is not well understood so far. An important role has been attributed to a phospholipase A2 domain which is located within the unique N terminus of the capsid protein VP1. Based on the structural difference between adeno-associated virus type 2 wild-type capsids and capsids lacking VP1 or VP2, we show via electron cryomicroscopy that the N termini of VP1 and VP2 are involved in forming globules inside the capsids of empty and full particles. Upon limited heat shock, VP1 and possibly VP2 become exposed on the outsides of full but not empty capsids, which is correlated with the disappearance of the globules in the inner surfaces of the capsids. Using molecular modeling, we discuss the constraints on the release of the globularly organized VP1-unique N termini through the channels at the fivefold symmetry axes outside of the capsid.

Further Characterization of Human DNA Polymerase δ Interacting Protein 38

Polymerase delta interacting protein 38 (PDIP38) was identified as a human DNA polymerase (pol) delta interacting protein through a direct interaction with p50, the small subunit of human pol delta. PDIP38 was also found to interact with proliferating cell nuclear antigen, which suggested that it might play a role in vivo in the processes of DNA replication and DNA repair in the nucleus. In order to characterize further this novel protein, we have examined its subcellular localization by the use of immunochemical and cellular fractionation techniques. These studies show that PDIP38 is a novel mitochondrial protein and is localized mainly to the mitochondria. PDIP38 was shown to possess a functional mitochondrial targeting sequence that is located within the first 35 N-terminal amino acid residues. The mature PDIP38 protein is about 50 amino acid residues smaller than the full-length precursor PDIP38 protein, consistent with it being processed by cleavage of the mitochondrial targeting sequence during entry into the mitochondria. His-tagged mature PDIP38 inhibited pol delta activity in vitro and interacted with human papillomavirus 16 E7 oncoprotein, suggesting that PDIP38 might play a role in the pol delta-mediated viral DNA replication. Although the localization of PDIP38 to the mitochondria suggests that it serves functions within the mitochondria, we cannot eliminate the possibility that it may be involved in pol delta-mediated DNA replication or DNA repair under certain conditions such as viral infection.

Clathrin- and caveolin-1-independent endocytosis: entry of simian virus 40 into cells devoid of caveolae

Simian Virus 40 (SV40) has been shown to enter host cells by caveolar endocytosis followed by transport via caveosomes to the endoplasmic reticulum (ER). Using a caveolin-1 (cav-1)-deficient cell line (human hepatoma 7) and embryonic fibroblasts from a cav-1 knockout mouse, we found that in the absence of caveolae, but also in wild-type embryonic fibroblasts, the virus exploits an alternative, cav-1-independent pathway. Internalization was rapid (t1/2 = 20 min) and cholesterol and tyrosine kinase dependent but independent of clathrin, dynamin II, and ARF6. The viruses were internalized in small, tight-fitting vesicles and transported to membrane-bounded, pH-neutral organelles similar to caveosomes but devoid of cav-1 and -2. The viruses were next transferred by microtubule-dependent vesicular transport to the ER, a step that was required for infectivity. Our results revealed the existence of a virus-activated endocytic pathway from the plasma membrane to the ER that involves neither clathrin nor caveolae and that can be activated also in the presence of cav-1.

Viral entry, lipid rafts and caveosomes

Lipid rafts and caveolae are detergent-insoluble plasma membrane microdomains, involved in cellular endocytic processes and signalling. Several viruses, including a human pathogen, echovirus 1, and an extensively studied simian virus 40 utilize these domains for internalization into the host cells. Interaction of viruses with receptors on the cell surface triggers specific conformational changes of the virus particle and can give rise to signalling events, which determine the mechanisms of virus entry. After internalization via cell surface lipid rafts or caveolae, virus-containing vesicles can fuse with caveosomes, pre-existing cytoplasmic organelles, or dock on other intracellular organelles. These pathways may deliver viruses further to different cellular destinations, where the viral replication cycle then takes place. The information concerning the viral entry processes is important for understanding the details of the infections, for finding new targets for antiviral therapy and for elucidating the cellular internalization pathways in general.

Characterization of a nuclear localization signal in the C-terminus of the adeno-associated virus Rep68/78 proteins

Adeno-associated virus (AAV) replicates in the nucleus of infected cells, and therefore multiple nuclear import events are required for productive infection. We analyzed nuclear import of the viral Rep proteins and characterized a nuclear localization signal (NLS) in the C-terminus. We demonstrate that basic residues in this region constitute an NLS that is transferable and mediates interaction with the nuclear import receptor importin alpha in vitro. Mutant Rep proteins are predominantly cytoplasmic and are severely compromised for interactions with importin alpha, but retain their enzymatic functions in vitro. Interestingly, mutations of the NLS had significantly less effect on importin alpha interaction and replication in the context of Rep78 than when incorporated into the Rep68 protein. Together, our results demonstrate that a bipartite NLS exists in the shared part of Rep68 and Rep78, and suggest that an alternate entry mechanism may also contribute to nuclear localization of the Rep78 protein.

How viruses enter animal cells

Viruses replicate within living cells and use the cellular machinery for the synthesis of their genome and other components. To gain access, they have evolved a variety of elegant mechanisms to deliver their genes and accessory proteins into the host cell. Many animal viruses take advantage of endocytic pathways and rely on the cell to guide them through a complex entry and uncoating program. In the dialogue between the cell and the intruder, the cell provides critical cues that allow the virus to undergo molecular transformations that lead to successful internalization, intra-cellular transport, and uncoating.

Expression of the telomeric retrotransposon HeT-A in Drosophila melanogaster is correlated with cell proliferation

Drosophila melanogaster extends its telomeres by transposition of two non-LTR retrotransposons, HeT-A and TART, to chromosome ends. We have determined the tissue-specific expression of these two elements by whole-mount in situ hybridization with digoxigenin-labeled RNA sense and antisense probes in the germ line and in a variety of larval tissues during normal development in the wild type and in tissues of mutants that cause overproliferation. Our results indicate that transcript levels, which are a key component in the process of telomere elongation in D. melanogaster, are correlated with cell proliferation in normal tissues and that RNA levels are elevated in growth-stimulated tissues.

Intracellular trafficking of HIV-1 cores: journey to the center of the cell

After entry into the cytoplasm, many diverse viruses, including both RNA and DNA viruses, require import into the nucleus and access to the cellular nuclear machinery for productive replication to proceed. Because diffusion through the crowded cytoplasmic environment is greatly restricted, most (if not all) of these viruses must first be actively transported from the site of cytoplasmic entry to the nuclear periphery (Luby-Phelps 2000; Lukacs et al. 2000; Sodeik 2000). Having reached the nucleus, viruses have evolved assorted methods to overcome the formidable physical barrier that is presented by the nuclear envelope. This review examines how these issues relate to human immunodeficiency virus type-1 (HIV-1) infection. Specifically, HIV-1 uncoating, cytoplasmic transport, and nuclear entry are addressed.

Herpes simplex virion entry into and intracellular transport within mammalian cells

Alphaherpesviruses, membrane-enveloped DNA viruses that are responsible for a host of human ailments, bind to, enter and are directly targeted to specific intracellular domains within their mammalian host cells. This review emphasizes recent work on the best studied of the alphaherpesviruses, Herpes simplex virus type 1 (HSV1). One area of focus is on recent work that has identified viral glycoproteins that are important in binding and internalization of the virus to the host cell. Complementary work on the receptors for those viral glycoproteins that reside on the host cell surface is also presented, with some discussion of how receptor variety might lead to the tissue tropism demonstrated by alphaherpes viruses. An additional area of focus in this review is how HSV uses the host cell transport systems to achieve intracellular targeting of the incoming virion toward the cell nucleus, and, after production of newly synthesized and assembled viral progeny, targeting them toward the plasma membrane for release.

Insider information: what viruses tell us about endocytosis

Viruses have long served as tools in molecular and cellular biology to study a variety of complex cellular processes. Currently, there is a revived interest in virus entry into animal cells because it is evident that incoming viruses make use of numerous endocytic pathways that are otherwise difficult to study. Besides the classical clathrin-mediated uptake route, viruses use caveolae-mediated endocytosis, lipid-raft-mediated endocytic pathways, and macropinocytosis. Some of these are subject to regulation, involve novel endocytic organelles, and some of them connect organelles that were previously not known to communicate by membrane traffic.