Creating "hotels" for cells by electrospinning honeycomb-like polymeric structures

It is well established that three-dimensional honeycomb-like nanofibrous structures enhance cell activity. In this work, we report that electrospun polymer nanofibres self-assemble into three-dimensional honeycomb-like structures. The underlying mechanism is studied by varying the polymer solution concentration, collecting substrates and working distance. The polymer solution concentration has a significant effect on the size of the electrospun nanofibres. The collection substrate and working distance affect the electric field strength, the evaporation of solvent and the discharging of nanofibres and consequently these two had a significant influence on the self-assembly of nanofibres.

Subcellular distribution of the human putative nucleolar GTPase GNL1 is regulated by a novel arginine/lysine-rich domain and a GTP binding domain in a cell cycle-dependent manner

GNL1, a putative nucleolar GTPase, belongs to the MMR1-HSR1 family of large GTPases that are emerging as crucial coordinators of signaling cascades in different cellular compartments. Members of this family share very closely related G-domains, but the signals and pathways regulating their subcellular localization with respect to cell growth remain unknown. To understand the nuclear transport mechanism of GNL1, we have identified a novel arginine/lysine-rich nucleolar localization signal in the NH(2)-terminus that is shown to translocate GNL1 and a heterologous protein to the nucleus/nucleolus in a pathway that is independent of importin-α and importin-β. In addition, the present investigation provided evidence that GNL1 localized to the nucleus and the nucleolus only in G2 stage, in contrast to its cytoplasmic localization in the G1 and S phases of the cell cycle. Using heterokaryon assay, we have demonstrated that GNL1 shuttles between the nucleus and the cytoplasm and that the motif between amino acids 201 and 225 is essential for its export from the nucleus by a signal-mediated CRM1-independent pathway. Alanine-scanning mutagenesis of conserved residues within G-domains suggests that the G2 motif is critical for guanine nucleotide triphosphate (GTP) binding of GNL1 and further showed that nucleolar retention of GNL1 is regulated by a GTP-gating-mediated mechanism. Expression of wild-type GNL1 promotes G2/M transition, in contrast to the G-domain mutant (G2m), which fails to localize to the nucleolus. These data suggest that nucleolar translocation during G2 phase may be critical for faster M-phase transition during cell proliferation. Replacement of conserved residues within the G5 motif alters the stability of GNL1 without changing GTP binding activity. Finally, our data suggest that ongoing transcription is essential for the efficient localization of GNL1 to the nucleolus. Overall, the results reported here demonstrate that multiple mechanisms are involved in the translocation of GNL1 to the nucleolus in a cell cycle-dependent manner to regulate cell growth and proliferation.

Duration of Ross River viraemia in a mouse model--implications for transfusion transmission

BACKGROUND AND OBJECTIVES

There is little data on the duration of viraemia following infection with Ross River virus (RRV), the most common cause of arbovirus disease in Australia. In particular, no accurate estimate exists for the duration of pre-symptomatic RRV infection, which is important in assessing the potential for transfusion transmission.

MATERIALS AND METHODS

We used an established mouse model of RRV infection involving adult Swiss outbred mice to measure viraemia following infection. Applying our experimental data to a published probabilistic model for estimating the risk of dengue transmission by transfused blood, we derived comparable risk estimates for RRV.

RESULTS

Ross River virus RNA was measured using highly sensitive real-time PCR in serum samples to determine the duration of asymptomatic viraemia, which typically lasted 5 days, but extended to 9 days in some mice. Assuming the potential for transfusion transmission is proven, the risk of RRV transmission by blood during a 2004 outbreak in Cairns, Australia was retrospectively estimated as 1 in 13,542 (range from 1 in 4765 to 47,563).

CONCLUSION

This study provides updated epidemiological data useful to underpin modelling to assess the potential risk of transfusion-transmitted RRV. Using an established model for dengue, the risk estimate for RRV transmission is comparable in the same geographical region. Should transfusion be proven as a route of transmission, this supports consideration of appropriate mitigation strategies to safeguard blood recipients.

Mechanism of host cell MAPK/ERK-2 incorporation into lentivirus particles: characterization of the interaction between MAPK/ERK-2 and proline-rich-domain containing capsid region of structural protein Gag

The characteristic event that follows infection of a cell by retroviruses Including human immunodeficiency virus (HIV)/ simian immunodeficiency virus (SIV) is the formation of a reverse transcription complex in which viral nucleic acids are synthesized. Nuclear transport of newly synthesized viral DNA requires phosphorylation of proteins in the reverse transcription complex by virion-associated cellular kinases. Recently, we demonstrated that disruption of cellular mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 2 (ERK-2) incorporation into SIV virions inhibits virus replication in nonproliferating target cells, indicating that MAPK/ERK-2 plays an important role in HIV /SIV replication. The mechanism of incorporation of MAPK/ERK-2 into virus particles is not defined. In this regard, we hypothesized that a likely interaction of MAPK/ERK-2 with Gag(p55) may enable its packaging into virus particles. In the present investigation, we provided evidence for the first time that MAPK/ERK-2 interacts with the structural Gag polyprotein p55 using a combination of mutagenesis and protein-protein interaction analysis. We further show that MAPK/ERK-2 interacts specifically with the poly-proline motif present in the capsid region of Gag(p55). Utilizing virus-like particles directed by Gag, we have shown that the exchange of conserved proline residues within capsid of Gag(p55) resulted in impaired incorporation of MAPK/ERK-2. In addition, the deletion of a domain comprising amino acids 201 to 255 within host cell MAPK/ERK-2 abrogates its interaction with Gag(p55). The relevance of the poly-proline motif is further evident by its conservation in diverse retroviruses, as noted from the sequence analysis and structural modeling studies of predicted amino acid sequences of the corresponding Gag proteins. Collectively, these data suggest that the interaction of MAPK/ERK-2 with Gag polyprotein results in its incorporation into virus particles and may be essential for retroviral replication.

Extracellular signal-regulated kinase 2 (ERK-2) mediated phosphorylation regulates nucleo-cytoplasmic shuttling and cell growth control of Ras-associated tumor suppressor protein, RASSF2

Ras GTPase controls the normal cell growth through binding with an array of effector molecules, such as Raf and PI3-kinase in a GTP-dependent manner. RASSF2, a member of the Ras association domain family, is known to be involved in the suppression of cell growth and is frequently down-regulated in various tumor tissues by promoter hypermethylation. In the present study, we demonstrate that RASSF2 shuttles between nucleus and cytoplasm by a signal-mediated process and its export from the nucleus is sensitive to leptomycin B. Amino acids between 240 to 260 in the C-terminus of RASSF2 harbor a functional nuclear export signal (NES), which is necessary and sufficient for efficient export of RASSF2 from the nucleus. Substitution of conserved Ile254, Val257 and Leu259 within the minimal NES impaired RASSF2 export from the nucleus. In addition, wild type but not the nuclear export defective RASSF2 mutant interacts with export receptor, CRM-1 and exported from the nucleus. Surprisingly, we observed nucleolar localization for the nuclear export defective mutant suggesting the possibility that RASSF2 may localize in different cellular compartments transiently in a cell cycle dependent manner and the observed nuclear localization for wild type protein may be due to faster export kinetics from the nucleolus. Furthermore, our data suggest that RASSF2 is specifically phosphorylated by MAPK/ERK-2 and the inhibitors of MAPK pathway impair the phosphorylation and subsequently block the export of RASSF2 from the nucleus. These data clearly suggest that ERK-2 mediated phosphorylation plays an important role in regulating the nucleo-cytoplasmic shuttling of RASSF2. Interestingly, nuclear import defective mutant of RASSF2 failed to induce cell cycle arrest at G1/S phase and apoptosis suggesting that RASSF2 regulates cell growth in a nuclear localization dependent manner. Collectively, these data provided evidence for the first time that MAPK/ERK-2 mediated phosphorylation regulates nucleo-cytoplasmic transport and cell growth arrest activity of RASSF2. Taken together, the present study suggests that active transport between nucleus and cytoplasm may constitute an important regulatory mechanism for RASSF2 function.

Interleukin-15 mediates potent antiviral responses via an interferon-dependent mechanism

Interleukin-15 (IL-15) is a potent growth factor for activated T and natural killer (NK) cells, stimulator of memory T cells and plays an important role in viral immunity. To investigate mechanisms underlying the antiviral activity of IL-15, a recombinant vaccinia virus (rVV) encoding murine IL-15 (VV-IL-15) was constructed. Following infection of mice with VV-IL-15, virus titres in the ovaries were significantly reduced compared to mice infected with control VV. Growth of VV-IL-15 was also reduced in nude athymic mice, indicating the antiviral activity of IL-15 does not require T cells. Additionally, VV-IL-15 augmented the cytolytic activity of natural NK cells in the spleen and enhanced interferon (IFN) mRNA expression and transcription factors associated with IFN induction. Using knockout mice and antibody depletion studies, we showed for the first time that the control of VV-IL-15 replication in mice is dependent on NK cells and IFNs and, in their absence, the protective role of IL-15 is abolished.

Mechanism of interleukin-25 (IL-17E)-induced pulmonary inflammation and airways hyper-reactivity

BACKGROUND

IL-25, a novel member of the IL-17 cytokine family, promotes CD4+ T-helper 2 lymphocyte-like (Th type-2) inflammatory responses in the lung. Although IL-25 up-regulates IL-13 in the lung, the contribution of this and other type 2 cytokine signalling pathways to the induction and persistence of airways hyper-reactivity (AHR) and allergic inflammation are unclear.

OBJECTIVE

To determine the downstream factors employed by IL-25 to induce Th type-2 pulmonary inflammation and AHR.

METHODS

IL-25 was delivered to the airways of BALB/c mice by intra-tracheal (i.t.) instillation and AHR and Th type-2 inflammatory responses were characterized in wild type (WT) and Th type-2-cytokine and -signalling pathway-deficient (-/-) mice.

RESULTS

IL-25 treatment resulted in AHR, eosinophilic inflammation, mucus hypersecretion and a progressive increase in the production of Th type-2 cytokines in the lungs. Levels of arginase-I (arg-I) and eotaxin were also elevated by IL-25 treatment. A significant reduction in AHR, and attenuation of mucus production was observed in IL-25-treated IL-13-/-, IL-4 receptor alpha (IL-4Ralpha-/-)- and signal-transducer-and-activator-of-transcription-factor-6 (STAT6-/-)-deficient mice. AHR was also inhibited in IL-4(-/-)- and IL-5/eotaxin(1)(-/-)- deficient mice treated with IL-25, however, mucus hypersecretion was not completely ablated. IL-25 promoted Th type-2 responses by directly acting on naïve T cells.

CONCLUSION

IL-25 potently (single dose) induces sustained AHR and acute pulmonary inflammation with eosinophilia. IL-25-induced AHR is dependent on the production of Th type-2 cytokines, and removal of IL-13 and its signal transduction pathway prevents IL-25-induced airways inflammation and AHR. IL-25 potently induces inflammatory cascades that may exacerbate allergic airways inflammation by promoting Th type-2 cytokine responses in conjunction with the up-regulation of factors (eotaxin and arg-I) that can amplify inflammation associated with allergic disorders. Dysregulation in IL-25 production may predispose to features of allergic airways disease.

Nuclear transport of Ras-associated tumor suppressor proteins: different transport receptor binding specificities for arginine-rich nuclear targeting signals

Ras proteins regulate a wide range of biological processes by interacting with a variety of effector proteins. In addition to the known role in tumorigensis, the activated form of Ras exhibits growth-inhibitory effects by unknown mechanisms. Several Ras effector proteins identified as mediators of apoptosis and cell-cycle arrest also exhibit properties normally associated with tumor suppressor proteins. Here, we show that Ras effector RASSF5/NORE-1 binds strongly to K-Ras but weakly to both N-Ras and H-Ras. RASSF5 was found to localize both in the nucleus and the nucleolus in contrast to other Ras effector proteins, RASSF1C and RASSF2, which are localized in the nucleus and excluded from nucleolus. A 50 amino acid residue transferable arginine-rich nucleolar localization signal (NoLS) identified in RASSF5 is capable of interacting with importin-beta and transporting the cargo into the nucleolus. Surprisingly, similar arginine-rich signals identified in RASSF1C and RASSF2 interact with importin-alpha and transport the heterologous cytoplasmic proteins to the nucleus. Interestingly, mutation of arginine residues within these nuclear targeting signals prevented interaction of Ras effector proteins with respective transport receptors and abolished their nuclear translocation. These results provide evidence for the first time that arginine-rich signals are able to recognize different nuclear import receptors and transport the RASSF proteins into distinct sub-cellular compartments. In addition, our data suggest that the nuclear localization of RASSF5 is critical for its cell growth control activity. Together, these data suggest that the transport of Ras effector superfamily proteins into the nucleus/nucleolus may play a vital role in modulating Ras-mediated cell proliferation during tumorigenesis.

A novel lysine-rich domain and GTP binding motifs regulate the nucleolar retention of human guanine nucleotide binding protein, GNL3L

A variety of G-proteins and GTPases are known to be involved in nucleolar function. We describe here a new evolutionarily conserved putative human GTPase, guanine nucleotide binding protein-like 3-like (GNL3L). Genes encoding proteins related to GNL3L are present in bacteria and yeast to metazoa and suggests its critical role in development. Conserved domain search analysis revealed that the GNL3L contains a circularly permuted G-motif described by a G5-G4-G1-G2-G3 pattern similar to the HSR1/MMR1 GTP-binding protein subfamily. Highly conserved and critical residues were identified from a three-dimensional structural model obtained for GNL3L using the crystal structure of an Ylqf GTPase from Bacillus subtilis. We demonstrate here that GNL3L is transported into the nucleolus by a novel lysine-rich nucleolar localization signal (NoLS) residing within 1-50 amino acid residues. NoLS identified here is necessary and sufficient to target the heterologous proteins to the nucleolus. We show for the first time that the lysine-rich targeting signal interacts with the nuclear transport receptor, importin-beta and transports GNL3L into the nucleolus. Interestingly, depletion of intracellular GTP blocks GNL3L accumulation into the nucleolar compartment. Furthermore, mutations within the G-domains alter the GTP binding ability of GNL3L and abrogate wild-type nucleolar retention even in the presence of functional NoLS, suggesting that the efficient nucleolar retention of GNL3L involves activities of both basic NoLS and GTP-binding domains. Collectively, these data suggest that GNL3L is composed of distinct modules, each of which plays a specific role in molecular interactions for its nucleolar retention and subsequent function(s) within the nucleolus.

A recombinant vaccinia virus encoding the interferon-inducible T-cell alpha chemoattractant is attenuated in vivo

Murine interferon-inducible T-cell alpha chemoattractant (I-TAC) is a potent non-ELR CXC chemokine that predominantly attracts activated T lymphocytes, binds to the receptor CXCR3 and is induced by interferon-gamma (IFN-gamma). We analysed I-TAC expression by reverse transcriptase-polymerase chain reaction during three different virus-infection models in mice, respiratory syncytial virus (RSV), influenza A and vaccinia virus western reserve (VV-WR). In the lungs from mice infected with RSV or influenza A viruses, peak expression of I-TAC coincided with peak viraemia. Surprisingly, there was no expression in the lungs of mice infected with vaccinia, unlike the elevated expression shown previously for other interferon-regulated chemokines, such as Crg2 and Mig. To further investigate the importance of this difference during vaccinia infection in mice, a recombinant virus encoding I-TAC (rVV I-TAC) was generated. Studies in C57BL/6 and Swiss nude mice showed that I-TAC expression caused increased mononuclear cell infiltration and significantly attenuated the VV. Infection of the footpads of naïve or already immune (with VV-WR) mice with either rVV I-TAC or VV-WR demonstrated that I-TAC expression reduced overall inflammation during infection and that this reduction was more pronounced in already immune mice. The data presented here show that I-TAC can have an important role during virus infections and that vaccinia has evolved ways to avoid inducing I-TAC expression.

A non-canonical transferable signal mediates nuclear import of simian immunodeficiency virus Vpx protein

Protein transport into the nucleus is generally considered to involve specific nuclear localization signals (NLS) though it is becoming increasingly evident that efficient and well controlled import of proteins which lack a canonical NLS also occurs in cells. Vpx, a 112 amino acid protein from human immunodeficiency virus type 2 (HIV-2) and the closely related simian immunodeficiency virus (SIV) is one such protein, which does not have an identifiable canonical NLS and is yet efficiently imported to the nuclear compartment. Here we report that Vpx protein is imported to the nucleus independently of virus-encoded cofactors. When fusions of truncated versions of Vpx with full-length beta-galactosidase (beta-Gal) were tested, the region from Vpx 61 to 80 was found to be sufficient to mediate the import of the heterologous cytoplasmic protein to the nucleus. Inactivation of Vpx NLS precluded nuclear import of Vpx and reduced virus replication in non-dividing macrophage cultures, even when functional integrase and Gag matrix proteins implicated in viral nuclear import were present. Importantly, we identified and characterized a novel type of 20 amino acid transferable nuclear import signal in Vpx that is distinct from other import signals described. In addition, we show that the minimal nuclear targeting domain identified here overlaps with helical domain III (amino acid (aa) 64-82) and the structural integrity of this helical motif is critical for the nuclear import of Vpx. Taken together, these data suggest that Vpx is imported to the nucleus via a novel import pathway that is dependent on its 20 amino acid unique nuclear targeting signal, and that the nuclear import property of Vpx is critical for the optimal virus replication in non-dividing cells such as macrophages.

IFN-gamma regulates murine interferon-inducible T cell alpha chemokine (I-TAC) expression in dendritic cell lines and during experimental autoimmune encephalomyelitis (EAE)

Murine interferon-inducible T cell alpha chemokine (I-TAC) is a potent non-ELR Cys-X-Cys (CXC) chemokine that predominantly attracts activated T lymphocytes and binds to the receptor CXCR3. Using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) we analysed murine I-TAC expression in two different progenitor dendritic cell (DC) lines, MTHC-D2 and JAWS II which were exposed to various cytokines, and Con A-activated splenocytes from a panel of knockout mice. Analysis of the progenitor DC lines and Con A cultures demonstrated that murine I-TAC is primarily regulated by interferon (IFN)-gamma via interferon regulatory factor (IRF)-1. It has been proposed that I-TAC may have a role in autoimmune diseases such as multiple sclerosis (MS). Because I-TAC appears to be secreted from antigen-presenting cells (APCs) and attracts activated T cells, we examined the level of murine I-TAC mRNA in the central nervous system (CNS) of wild-type and IFN-gamma-receptor knockout (IFN-gammaR-/-) mice with myelin oligodendrocyte glycoprotein (MOG)35-55 peptide-induced experimental autoimmune encephalomyelitis (EAE). Peak I-TAC expression was detected in wild-type mice on day 14 when the mice begin to recover, whereas very low levels of I-TAC were detected in the CNS of IFN-gammaR-/- mice which develop severe EAE and die. The expression characteristics of murine I-TAC suggest an important mediator of immune cell communication that could augment vaccines and autoimmune therapies.

HIV-1 Vpr transactivates LTR-directed expression through sequences present within -278 to -176 and increases virus replication in vitro

Human immunodeficiency virus type 1 (HIV-1) Vpr, a 14-kDa virion-associated protein, plays an important role in the viral life cycle. Using a panel of truncated HIV-1 LTR-CAT constructs and Vpr expression plasmid, we have identified sequences from nucleotide -278 to -176 in LTR as Vpr-mediated transactivation domain. This region includes the glucocorticoid response element (GRE) in HIV-1 LTR. Transactivation by Vpr was noted with the HIV-1 LTR reporter constructs containing CAT or luciferase. A similar effect was also observed with a construct in which the GRE motif was linked to CAT. Studies involving Vpr mutants identified that helical domains I and III, and amino acid residues at G75 and C76, are responsible for GRE-mediated LTR transactivation. The transactivation function of Vpr is independent of its cell cycle arrest activity. Further, viral replication studies indicated that Vpr-mediated increase in viral replication is directly correlated with the ability of Vpr to transactivate HIV-1 LTR. The results presented here demonstrate that Vpr activates HIV-1 LTR through the host GR pathway and suggest that an intact GRE in the LTR is critical for Vpr activity.