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At least 487 records · Page 27Linked to original sources
PubMed2001

Mutated mtDNA distribution in exponentially growing cell cultures and how the segregation rate is increased by the mitochondrial compartments.

A cell contains many copies of mitochondrial DNA. The distribution of a mitochondrial gene mutation in a cell culture is governed by the way in which the mtDNA molecules of a cell are replicated and partitioned between the two daughter cells during mitosis. Assuming that this partition process is random, we describe the evolution of the mitochondrial genetic state of a cell culture. The mutated mtDNA is ultimately segregated and the rate of the trend to segregation is relatively slow. It is nevertheless greatly accelerated if the model takes into account the spatial mtDNA partition by the mitochondrial compartments.

Cell Division↗
PubMed1998

Macrophage cytoplasmic vesicle pH gradients and vacuolar H+-ATPase activities relative to virus infection.

A number of viruses replicate in macrophages, some having an obligate requirement for a macrophage host. This raised the question concerning the role of the macrophage endosomal/lysosomal compartment during such infections. Both lysosomotropic weak bases, amantadine and chloroquine, which interfere with endosomal/lysosomal pH gradients, and the macrolide antibiotic bafilomycin A1, which interferes with vacuolar H+-ATPase, inhibited African swine fever (ASF) virus replication in porcine macrophages. This inhibition was reversible: replenishment of bafilomycin, but not amantadine or chloroquine, maintained the inhibition. The characteristics of the inhibition, and the capacity of virus to escape and re-commence replication, related to the capacity of each drug to interfere with the endosomal/lysosomal proton pump. These results demonstrate that the virus actually requires macrophage endosomal/lysosomal activity for its replication. Therein, vacuolar H+-ATPase activity is particularly critical for successful virus replication, which is interesting considering the importance of this for endosomal/lysosomal activity and macrophage function.

Acridine Orange↗
PubMed2005

Lentiviral siRNAs targeting multiple highly conserved RNA sequences of human immunodeficiency virus type 1.

The high mutation rate of the human immunodeficiency virus (HIV) makes it difficult for any therapy employing a single anti-HIV targeting mechanism to sustain prolonged effect. In an attempt to explore novel therapy for AIDS, we developed and tested lentiviral small interfering RNA (siRNA) vectors targeting multiple highly conserved regions in the HIV type 1 (HIV-1) genome. The siRNA expression cassette was cloned into an extensively deleted HIV-1-derived lentiviral self-inactivating insulator (SIN) insulator [corrected] vector. Although some of the siRNAs targeting sites were also present in the helper construct of the vector system, the production of these lentiviral siRNA vectors were not significantly affected. When tested against different HIV-1 strains including pNL4-3 (subtype B), p89.6 (subtype B) and p90CF402.1.8 (subtype A/E recombinant), the siRNAs targeting conserved gag, pol, int and vpu, but not U3, nef or U5 regions, efficiently inhibited replication of all three viral strains. These lentiviral siRNA vectors also protected host cells from syncytium-forming macrophage- and T-cell-tropic HIV-1-induced cytotoxicity. Transduction of a long-term chronically infected human lymphoma cell line with lentiviral siRNAs resulted in stable inhibition of HIV-1 replication. Northern analysis showed that both genomic and subgenomic viral RNA species were downregulated. In addition, the viral RNA was inhibited in both the nuclear and cytoplasmic compartments of [corrected] chronically infected cells after prolonged passage, suggesting that [corrected] lentiviral siRNAs have a nuclear effect [corrected] Using these lentiviral siRNA [corrected] vectors, we further demonstrated reduced replication kinetics of HIV-1 in primary human peripheral blood lymphocytes. These results suggest that lentiviral siRNAs targeting multiple conserved HIV-1 sequences holds significant promise for the treatment of HIV-1 infections.

Base Sequence↗
PubMed1997

Anti-viral drug treatment: dynamics of resistance in free virus and infected cell populations.

Anti-viral drug treatment of infections with the human immunodeficiency virus type I (HIV-1) usually leads to a rapid decline in the abundance of plasma virus. The effect of single drug therapy, however, is often only short-lived as the virus readily develops drug-resistant mutants. In this paper we provide analytic approximations for the rate of emergence of resistant virus. We study the decline of wildtype virus and the rise of resistant mutant virus in different compartments of the virus population such as free plasma virus, cells infected with actively replicating virus, long-lived infected cells and cells carrying defective provirus. The model results are compared with data on the rise of drug-resistant virus in three HIV-1 infected patients treated with neverapine (NVP). We find that the half-life of latently infected cells is between 10 and 20 days, whereas the half-life of cells with defective provirus is about 80 days. We also provide a crude estimate for the basic reproductive ratio of HIV-1 during NVP therapy.

Antiviral Agents↗
PubMed1990

Cell kinetic disturbances induced by treatment of human diploid fibroblasts with 5-azacytidine indicate a major role for DNA methylation in the regulation of the chromosome cycle.

BrdU-Hoechst flow cytometry was used to investigate the effects of DNA hypomethylation, induced by treatment with 5-azacytidine (5AC), on cell proliferation. When human fibroblast-like cells derived from skin and amniotic fluid were exposed to 5AC during three successive cell cycles, their clone-forming ability was diminished after removal of the drug. Treated cells were rendered quiescent by culture with low serum in the absence of the drug. Upon serum stimulation, they showed a diminished fraction of proliferating cells, which exhibited a prolonged transit through the S and G2 phase of the cell cycle, and a permanent arrest within the G2 compartment. This pattern of disturbed cell proliferation may in part explain the changes in replication banding pattern reported in the literature. Cytogenetic analysis of 5AC-treated cells revealed numerous endomitoses and tetraploid metaphases indicating a disturbed chromosome cycle in association with these cell kinetic perturbations.

Azacitidine↗
PubMed2003

Regeneration of hepatocyte 'buds' in cirrhosis from intrabiliary stem cells.

BACKGROUND/AIMS: In massive hepatic necrosis, hepatic stem cells constitute a canal of Hering derived, cytokeratin 19 (CK19) positive 'ductular reaction' (DR). Whether DRs in cirrhosis are activated stem cells (so called 'buds') or biliary metaplasia of cholestatic, injured hepatocytes is still debated. We investigate derivation of intraseptal hepatocytes (ISHs) from DRs and from the biliary tree in cirrhosis. METHODS: Explants of hepatitis B and C, alcohol, primary biliary cirrhosis and primary sclerosing cholangitis-related cirrhosis were examined. ISHs were quantified and their associations with DRs and cholestasis recorded. 3D-reconstruction of ISHs and nearby bile ducts was performed in blocks from hepatitis C and primary sclerosing cholangitis cirrhosis. RESULTS: Seven hundred seventy five/830 (94%) ISHs were associated with CK19 positive DRs. ISHs without ductular reactions were more likely to show cholestatic features (P<0.0001). In 3D, ISHs were seen to bud directly from the biliary tree. In summary: ISHs: (1) are usually associated with stem cell-like DRs; (2) are rarely cholestatic, leaving the associated DRs unexplained; and (3) are linked to the biliary tree in 3D. Dynamic proliferation rates in hepatitis C over time suggest that hepatocyte replication diminishes in late stages, with an associated activation of the biliary stem cell compartment. CONCLUSIONS: We therefore suggest that the biliary tree, from at least its smaller branches up to the canals of Hering, are composed of or at least harbor facultative hepatic stem cells, and that ISH largely represent 'buds' of newly formed hepatocytes.

Biliary Tract↗
PubMed2002

The effects of the Fanconi anemia zinc finger (FAZF) on cell cycle, apoptosis, and proliferation are differentiation stage-specific.

FAZF, a member of the BTB/POZ family of transcriptional repressor proteins, has been shown to bind to FANCC, the protein defective in patients with the bone marrow failure syndrome Fanconi anemia complementation group C. Because bone marrow failure in Fanconi anemia has been attributed to a failure of the hematopoietic stem cell population to produce sufficient progeny, we documented the expression of FAZF in human CD34(+) hematopoietic progenitor cells. FAZF was expressed at high levels in early stages of differentiation but declined during subsequent differentiation into erythroid and myeloid lineages. Consistent with its presumed role as a transcriptional repressor, FAZF was found in the nuclear compartment, where it resides in distinct nuclear speckles at or near sites of DNA replication. Using a FAZF-inducible myeloid cell line, we found that enforced expression of FAZF was accompanied by accumulation in the G(1) phase of the cell cycle followed later by apoptosis. These results suggest an essential role for FAZF during the proliferative stages of primitive hematopoietic progenitors, possibly acting in concert with (a subset of) the Fanconi anemia proteins.

Antigens, CD34↗
PubMed2006

Autophagy in innate immunity against intracellular bacteria.

Many pathogenic bacteria can invade phagocytic and non-phagocytic cells and colonize them intracellularly, then become disseminated to other cells. The endocytic degradation pathway is thought to be the only prevention against such intracellular pathogens. Autophagy, a fundamental cellular homeostasis pathway that operates with the intracellular degradation/recycling system, causes the turnover of cellular components by delivering portions of the cytoplasm and organelles to lysosomes. Recently, we reported that autophagic degradation is a previously unrecognized effector of host innate immunity. Streptococcus pyogenes (Group A Streptococcus; GAS) successfully enters human epithelial cells via endocytosis. GAS immediately escapes from the endosomes to the cytoplasm and gains a replicative niche, after which GAS in the cytoplasm is trapped in autophagosome-like compartments and degraded upon fusion with lysosomes. This process indicates that autophagy plays a protective role in infectious diseases. We also found that autophagic degradation was induced against Staphylococcus aureus, while methicillin-resistant S. aureus were resistant to autophagic degradation. The present review focuses on the protective function of autophagy against bacterial invasion of cells.

Autophagy↗
PubMed2003

Inhibition of human immunodeficiency virus type 1 Env-mediated fusion by DC-SIGN.

DC-SIGN, a lectin expressed on dendritic cell and macrophage subsets, binds to human immunodeficiency virus Env glycoproteins, allowing capture of viral particles. Captured virions either infect target cells or are efficiently transmitted to lymphocytes. Cellular mechanisms underlying the effects of DC-SIGN remain poorly understood. Here we have analyzed the effects of DC-SIGN on viral entry and on syncytium formation induced by Env glycoproteins. The lectin enhanced susceptibility to viral infection and dramatically increased virion internalization. Captured virions accumulated in the vesicular pathway, and their access to the cytosol was altered. Strikingly, the presence of DC-SIGN on target cells inhibited their ability to form syncytia with Env-expressing cells. However, increasing CD4 surface levels on target cells alleviated this inhibitory effect of DC-SIGN. Moreover, the potency of the viral fusion inhibitor T-20 was not affected in DC-SIGN-expressing cells. Altogether, our results indicate that DC-SIGN exerts subtle and complex effects during early steps of HIV type 1 replication. DC-SIGN facilitates capture and accumulation of viral particles in a vesicular compartment and inhibits viral fusion. Competition between CD4 and DC-SIGN for Env binding likely affects virus access to the cytosol and syncytium formation.

CD4 Antigens↗
PubMed2006

Role of the forkhead protein FoxO1 in beta cell compensation to insulin resistance.

Diabetes is associated with defective beta cell function and altered beta cell mass. The mechanisms regulating beta cell mass and its adaptation to insulin resistance are unknown. It is unclear whether compensatory beta cell hyperplasia is achieved via proliferation of existing beta cells or neogenesis from progenitor cells embedded in duct epithelia. We have used transgenic mice expressing a mutant form of the forkhead-O1 transcription factor (FoxO1) in both pancreatic ductal and endocrine beta cells to assess the contribution of these 2 compartments to islet expansion. We show that the mutant FoxO1 transgene prevents beta cell replication in 2 models of beta cell hyperplasia, 1 due to peripheral insulin resistance (Insulin receptor transgenic knockouts) and 1 due to ectopic local expression of IGF2 (Elastase-IGF2 transgenics), without affecting insulin secretion. In contrast, we failed to detect a specific effect of the FoxO1 transgene on the number of periductal beta cells. We propose that beta cell compensation to insulin resistance is a proliferative response of existing beta cells to growth factor signaling and requires FoxO1 nuclear exclusion.

Animals↗
PubMed2006

A nucleolar localizing Rev binding element inhibits HIV replication.

The Rev protein of the human immunodeficiency virus (HIV) facilitates the nuclear export of intron containing viral mRNAs allowing formation of infectious virions. Rev traffics through the nucleolus and shuttles between the nucleus and cytoplasm. Rev multimerization and interaction with the export protein CRM1 takes place in the nucleolus. To test the importance of Rev nucleolar trafficking in the HIV-1 replication cycle, we created a nucleolar localizing Rev Response Element (RRE) decoy and tested this for its anti-HIV activity. The RRE decoy provided marked inhibition of HIV-1 replication in both the CEM T-cell line and in primary CD34+ derived monocytes. These results demonstrate that titration of Rev in the nucleolus impairs HIV-1 replication and supports a functional role for Rev trafficking in this sub-cellular compartment.

Journal Article↗
PubMed2001

Chemokine/CD4 receptor density ratios correlate with HIV replication in lymph node and peripheral blood of HIV-infected individuals.

OBJECTIVES: Lymphoid tissue is a major reservoir for virus replication in HIV-infected subjects. The relationship of CCR5 and CXCR4 coreceptor density and HIV replication in peripheral blood mononuclear cells (PBMC) and lymph node (LN) mononuclear cells (LNMC) of HIV-infected subjects was examined. METHODS: PBMC and cervical LNMC from 12 HIV-infected patients were examined for virological and immunological parameters including chemokine receptor density, HIV plasma and cellular viral load, coreceptor usage and CD38/HLA-DR expression. RESULTS: The number of CCR5 and CXCR4 molecules on CD4 lymphocytes in the LN were significantly higher than in PBMC. In contrast the number of CD4 molecules/CD4 T cell was higher in PBMC than in LNMC. The CXCR4/CD4 and CCR5/CD4 ratios in the LN were significantly higher than in the PBMC. This was associated with a cellular viral load in the LN that was approximately 110-fold higher than in PBMC. The absolute number of coreceptor molecules per cell did not correlate with the viral load. However, the CCR5/CD4 and CXCR4/CD4 ratios in the LN positively correlated with HIV cellular and plasma RNA. Characterization of the viral isolates suggested an association between clinical isolates using a distinct coreceptor and the upregulation of the corresponding chemokine receptor. CONCLUSIONS: The ratios of chemokine receptors to CD4 molecules in CD4 T cells from LN is higher than in PBMC and may account for the relative difference in cellular viral load in these compartments. Additionally, the coreceptor/CD4 ratios, particularly in the lymphoid tissue, were highly related to HIV replication.

Adult↗
PubMed1980

Divergent effects of long acting cyclic nucleotides and lysine vasopressin on the release of matrix sulfated proteoglycans into the medium of fetal rat chondrocytes in monolayer culture.

Release of sulfated proteoglycans into the medium of fetal rat chondrocytes in monolayer culture was studied by contrasting the effects of 10% calf serum, long-acting cyclic nucleotides (8 Br-cAMP or DBcAMP), and lysine vasopressin (LVP). Eight hours after initiation of the experiment, the monolayer was pulsed for 2 hours with Na2[35SO4=], the radioactivity was chased, and the monolayer was reincubated for 6 hours with conditioned medium from replicate cultures. Immediately after labelling, the amount of newly synthesized sulfated proteglycans was invariably higher in the insoluble matrix than in the medium compartment. Both additives selectively enhanced sulfate incorporation into chondroitin sulfate of the matrix when compared to serum controls, but only LVP stimulation caused increases in the medium. Remodeling (loss of cell layer and release into the medium at 6 hours) was suppressed by cAMP analogues and increased by LVP. This process was more active in cultures of lower cell density. Utilizing calibrated gel columns, no size difference of the glycosaminoglycans was found between the medium and cell layer compartments of the three treatment groups at the two time points. Because the cAMP analogues inhibit, while LVP stimulates cell division, our observations imply that the rate of degradation of the constraining matrix is increased when replication is favored, even when chondriotin sulfate synthesis is selectively stimulated.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1999

RANTES, IFN-gamma, CCR1, and CCR5 mRNA expression in peripheral blood, lymph node, and bronchoalveolar lavage mononuclear cells during primary simian immunodeficiency virus infection of macaques.

Primary infection of macaques with pathogenic isolates of simian immunodeficiency virus (SIV) (as a model of HIV infection in humans) represents a unique opportunity to study early lentivirus/host interactions. We sought to determine whether there is a temporal relationship linking SIV replication and dissemination and the expression of the chemokine RANTES (regulated upon activation normal T cell expressed and secreted) and the SIV/HIV coreceptor CCR5 in different tissues during acute SIV infection of macaques. Four cynomolgus macaques were inoculated intravenously with a pathogenic primary isolate of SIVmac251. RT-PCR was used to monitor the expression of RANTES and CCR5 mRNA in fresh isolated mononuclear cells from blood, lymph node, and bronchoalveolar lavages. These expressions were compared to those of IFN-gamma as an indicator of the development of the immune response and to another receptor for RANTES, CCR1, which is not described as a coreceptor for SIV/HIV-1 entry. An enhancement of CCR1/CCR5 mRNA expression was noticed during primary SIVmac251 infection of macaques, mainly in tissue. In the three different compartments investigated, IFN-gamma and RANTES overexpression was noticed by the time of systemic viral replication containment. Our results put CCR5 and RANTES mRNA expression back in the context of inflammatory and immune responses to SIV primary infection.

Animals↗
PubMed2002

Role of recycling endosomes and lysosomes in dynein-dependent entry of canine parvovirus.

Canine parvovirus (CPV) is a nonenveloped virus with a 5-kb single-stranded DNA genome. Lysosomotropic agents and low temperature are known to prevent CPV infection, indicating that the virus enters its host cells by endocytosis and requires an acidic intracellular compartment for penetration into the cytoplasm. After escape from the endocytotic vesicles, CPV is transported to the nucleus for replication. In the present study the intracellular entry pathway of the canine parvovirus in NLFK (Nordisk Laboratory feline kidney) cells was studied. After clustering in clathrin-coated pits and being taken up in coated vesicles, CPV colocalized with coendocytosed transferrin in endosomes resembling recycling endosomes. Later, CPV was found to enter, via late endosomes, a perinuclear vesicular compartment, where it colocalized with lysosomal markers. There was no indication of CPV entry into the trans-Golgi or the endoplasmic reticulum. Similar results were obtained both with full and with empty capsids. The data thus suggest that CPV or its DNA was released from the lysosomal compartment to the cytoplasm to be then transported to the nucleus. Electron microscopy analysis revealed endosomal vesicles containing CPV to be associated with microtubules. In the presence of nocodazole, a microtubule-disrupting drug, CPV entry was blocked and the virus was found in peripheral vesicles. Thus, some step(s) of the entry process were dependent on microtubules. Microinjection of antibodies to dynein caused CPV to remain in pericellular vesicles. This suggests an important role for the motor protein dynein in transporting vesicles containing CPV along the microtubule network.

Animals↗
PubMed1993

Chromosome bands--flavours to savour.

The mammalian chromosome is longitudinally heterogeneous in structure and function and this is the basis for the specific banding patterns produced by various chromosome staining techniques. The two most frequently used techniques are G, or Giemsa banding and R, or reverse banding. Each type of stained band is characterised by variations in gene density, time of replication, base composition, density of repeat sequences, and chromatin packaging. It is increasingly apparent that R and G bands, which are complementary to each other, represent separate compartments of the euchromatic human genome, with R bands containing the vast majority of genes. R bands are also more GC-rich, contain a higher density of Alu repeats, and replicate earlier in S phase, than G bands. These properties may be interdependent and may have coevolved.

Base Composition↗
PubMed2001

Signals for bidirectional nucleocytoplasmic transport in the duck hepatitis B virus capsid protein.

Hepadnavirus genome replication involves cytoplasmic and nuclear stages, requiring balanced targeting of cytoplasmic nucleocapsids to the nuclear compartment. In this study, we analyze the signals determining capsid compartmentalization in the duck hepatitis B virus (DHBV) animal model, as this system also allows us to study hepadnavirus infection of cultured primary hepatocytes. Using fusions to the green fluorescent protein as a functional assay, we have identified a nuclear localization signal (NLS) that mediates nuclear pore association of the DHBV nucleocapsid and nuclear import of DHBV core protein (DHBc)-derived polypeptides. The DHBc NLS mapped is unique. It bears homology to repetitive NLS elements previously identified near the carboxy terminus of the capsid protein of hepatitis B virus, the human prototype of the hepadnavirus family, but it maps to a more internal position. In further contrast to the hepatitis B virus core protein NLS, the DHBc NLS is not positioned near phosphorylation target sites that are generally assumed to modulate nucleocytoplasmic transport. In functional assays with a knockout mutant, the DHBc NLS was found to be essential for nuclear pore association of the nucleocapsid. The NLS was found to be also essential for virus production from the full-length DHBV genome in transfected cells and from hepatocytes infected with transcomplemented mutant virus. Finally, the DHBc additionally displayed activity indicative of a nuclear export signal, presumably counterbalancing NLS function in the productive state of the infected cell and thereby preventing nucleoplasmic accumulation of nucleocapsids.

Active Transport, Cell Nucleus↗
PubMed2006

Studies of HIV-associated immune responses in lymphoid compartments.

Acute HIV-1 infection results in profound depletion of CD4+ memory T cells in lymphoid tissue (LT) and subsequent persistent replication in activated CD4+ T cells despite induction of an HIV-specific cell-mediated immune response. Interferon-alpha, proinflammatory cytokines, and beta-chemokine production is present in LT. However, impaired expression of co-stimulatory molecules including CD80, CD86, and CD40L may contribute to low polyfunctional CD4+ T cell as well CD8+ T-cell activity. Accumulation of regulatory CD4+ T cells in LT may add to the lack of HIV-specific CD4+ T-cell proliferation and dysfunctional cytotoxic CD8+ T-cell response in LT.

CD4 Antigens↗