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At least 1,333 records · Page 74Linked to original sources
PubMed2003

Ribosomal crystallography: peptide bond formation and its inhibition.

Ribosomes, the universal cellular organelles catalyzing the translation of genetic code into proteins, are protein/RNA assemblies, of a molecular weight 2.5 mega Daltons or higher. They are built of two subunits that associate for performing protein biosynthesis. The large subunit creates the peptide bond and provides the path for emerging proteins. The small has key roles in initiating the process and controlling its fidelity. Crystallographic studies on complexes of the small and the large eubacterial ribosomal subunits with substrate analogs, antibiotics, and inhibitors confirmed that the ribosomal RNA governs most of its activities, and indicated that the main catalytic contribution of the ribosome is the precise positioning and alignment of its substrates, the tRNA molecules. A symmetry-related region of a significant size, containing about two hundred nucleotides, was revealed in all known structures of the large ribosomal subunit, despite the asymmetric nature of the ribosome. The symmetry rotation axis, identified in the middle of the peptide-bond formation site, coincides with the bond connecting the tRNA double-helical features with its single-stranded 3' end, which is the moiety carrying the amino acids. This thus implies sovereign movements of tRNA features and suggests that tRNA translocation involves a rotatory motion within the ribosomal active site. This motion is guided and anchored by ribosomal nucleotides belonging to the active site walls, and results in geometry suitable for peptide-bond formation with no significant rearrangements. The sole geometrical requirement for this proposed mechanism is that the initial P-site tRNA adopts the flipped orientation. The rotatory motion is the major component of unified machinery for peptide-bond formation, translocation, and nascent protein progression, since its spiral nature ensures the entrance of the nascent peptide into the ribosomal exit tunnel. This tunnel, assumed to be a passive path for the growing chains, was found to be involved dynamically in gating and discrimination.

Anti-Bacterial Agents↗
PubMed2002

A new method (GOREC) for directed mutagenesis and gene repair by homologous recombination.

Directed mutagenesis in mammalian cells has been the focus of intense research because of its promising application for gene correction and engineering. Both natural and modified oligonucleotides (ODN), RNA-DNA chimeric oligonucleotide (RDO) and small fragment DNA (SFHR), as well as vector DNA were used for promoting homologous replacement with varying success. It was recently shown that a triple helix-forming oligonucleotide (TFO) tethered to an oligonucleotide (donor DNA) can enhance mutagenesis by homologous recombination in cells. The basic idea is to accelerate homology search by oligonucleotide-directed triple helix formation in the vicinity of the target site for donor DNA. Here we describe a new method named GOREC (guided homologous recombination) which shares similar gene targeting, but has notable difference in the concept with the previous method. It is made of a homing device (TFO) and a donor DNA for effecting distinct functions. They are linked together by non-covalent or covalent interaction. This modular concept allows guidance of either an oligonucleotide (ODN, RDO) or a small DNA fragment to the target site for homologous replacement. Therefore, the triple helix site can be hundreds of base pairs away from the target site. An episomal assay for proof-of-principle study will be presented and discussed.

Animals↗
PubMed2002

Guidelines for using antiretroviral agents among HIV-infected adults and adolescents.

The availability of an increasing number of antiretroviral agents and the rapid evolution of new information have introduced substantial complexity into treatment regimens for persons infected with human immunodeficiency virus (HIV). In 1996, the Department of Health and Human Services and the Henry J. Kaiser Family Foundation convened the Panel on Clinical Practices for the Treatment of HIV to develop guidelines for clinical management of HIV-infected adults and adolescents (CDC. Report of the NIH Panel To Define Principles of Therapy of HIV Infection and Guidelines for the use of antiretroviral agents in HIV-infected adults and adolescents. MMWR. 1998;47[RR-5]:1-41). This report, which updates the 1998 guidelines, addresses 1) using testing for plasma HIV ribonucleic acid levels (i.e., viral load) and CD4+ T cell count; 2) using testing for antiretroviral drug resistance; 3) considerations for when to initiate therapy; 4) adherence to antiretroviral therapy; 5) considerations for therapy among patients with advanced disease; 6) therapy-related adverse events; 7) interruption of therapy; 8) considerations for changing therapy and available therapeutic options; 9) treatment for acute HIV infection; 10) considerations for antiretroviral therapy among adolescents; 11) considerations for antiretroviral therapy among pregnant women; and 12) concerns related to transmission of HIV to others. Antiretroviral regimens are complex, have serious side effects, pose difficulty with adherence, and carry serious potential consequences from the development of viral resistance because of nonadherence to the drug regimen or suboptimal levels of antiretroviral agents. Patient education and involvement in therapeutic decisions are critical. Treatment should usually be offered to all patients with symptoms ascribed to HIV infection. Recommendations for offering antiretroviral therapy among asymptomatic patients require analysis of real and potential risks and benefits. In general, treatment should be offered to persons who have <350 CD4+ T cells/mm3 or plasma HIV ribonucleic acid (RNA) levels of >55,000 copies/mL (by b-deoxyribonucleic acid [bDNA] or reverse transcriptase-polymerase chain reaction [RT-PCR] assays). The recommendation to treat asymptomatic patients should be based on the willingness and readiness of the person to begin therapy; the degree of existing immunodeficiency as determined by the CD4+ T cell count; the risk for disease progression as determined by the CD4+ T cell count and level of plasma HIV RNA; the potential benefits and risks of initiating therapy in an asymptomatic person; and the likelihood, after counseling and education, of adherence to the prescribed treatment regimen. Treatment goals should be maximal and durable suppression of viral load, restoration and preservation of immunologic function, improvement of quality of life, and reduction of HIV-related morbidity and mortality. Results of therapy are evaluated through plasma HIV RNA levels, which are expected to indicate a 1.0 log10 decrease at 2-8 weeks and no detectable virus (<50 copies/mL) at 4-6 months after treatment initiation. Failure of therapy at 4-6 months might be ascribed to nonadherence, inadequate potency of drugs or suboptimal levels of antiretroviral agents, viral resistance, and other factors that are poorly understood. Patients whose therapy fails in spite of a high level of adherence to the regimen should have their regimen changed; this change should be guided by a thorough drug treatment history and the results of drug-resistance testing. Because of limitations in the available alternative antiretroviral regimens that have documented efficacy, optimal changes in therapy might be difficult to achieve for patients in whom the preferred regimen has failed. These decisions are further confounded by problems with adherence, toxicity, and resistance. For certain patients, participating in a clinical trial with or without access to new drugs or using a regimen that might not achieve complete suppression of viral replicatioing a regimen that might not achieve complete suppression of viral replication might be preferable. Because concepts regarding HIV management are evolving rapidly, readers should check regularly for additional information and updates at the HIV/AIDS Treatment Information Service website ( http://www.hivatis.org ).

Adolescent↗
PubMed2002

Guidelines for using antiretroviral agents among HIV-infected adults and adolescents. Recommendations of the Panel on Clinical Practices for Treatment of HIV.

The availability of an increasing number of antiretroviral agents and the rapid evolution of new information has introduced substantial complexity into treatment regimens for persons infected with human immunodeficiency virus (HIV). In 1996, the Department of Health and Human Services and the Henry J. Kaiser Family Foundation convened the Panel on Clinical Practices for the Treatment of HIV to develop guidelines for clinical management of HIV-infected adults and adolescents (CDC. Report of the NIH Panel To Define Principles of Therapy of HIV Infection and Guidelines for the use of antiretroviral agents in HIV-infected adults and adolescents. MMWR 1998;47[RR-5]:1-41). This report, which updates the 1998 guidelines, addresses 1) using testing for plasma HIV ribonucleic acid levels (i.e., viral load) and CD4+ T cell count; 2) using testing for antiretroviral drug resistance; 3) considerations for when to initiate therapy; 4) adherence to antiretroviral therapy; 5) considerations for therapy among patients with advanced disease; 6) therapy-related adverse events; 7) interruption of therapy; 8) considerations for changing therapy and available therapeutic options; 9) treatment for acute HIV infection; 10) considerations for antiretroviral therapy among adolescents; 11) considerations for antiretroviral therapy among pregnant women; and 12) concerns related to transmission of HIV to others. Antiretroviral regimens are complex, have serious side effects, pose difficulty with adherence, and carry serious potential consequences from the development of viral resistance because of nonadherence to the drug regimen or suboptimal levels of antiretroviral agents. Patient education and involvement in therapeutic decisions is critical. Treatment should usually be offered to all patients with symptoms ascribed to HIV infection. Recommendations for offering antiretroviral therapy among asymptomatic patients require analysis of real and potential risks and benefits. Treatment should be offered to persons who have <350 CD4+ T cells/mm3 or plasma HIV ribonucleic acid (RNA) levels of >55,000 copies/mL (by b-deoxyribonucleic acid [bDNA] or reverse transcriptase-polymerase chain reaction [RT-PCR] assays). The recommendation to treat asymptomatic patients should be based on the willingness and readiness of the person to begin therapy; the degree of existing immunodeficiency as determined by the CD4+ T cell count; the risk for disease progression as determined by the CD4+ T cell count and level of plasma HIV RNA; the potential benefits and risks of initiating therapy in an asymptomatic person; and the likelihood, after counseling and education, of adherence to the prescribed treatment regimen. Treatment goals should be maximal and durable suppression of viral load, restoration and preservation of immunologic function, improvement of quality of life, and reduction of HIV-related morbidity and mortality. Results of therapy are evaluated through plasma HIV RNA levels, which are expected to indicate a 1.0 log10 decrease at 2-8 weeks and no detectable virus (<50 copies/mL) at 4-6 months after treatment initiation. Failure of therapy at 4-6 months might be ascribed to nonadherence, inadequate potency of drugs or suboptimal levels of antiretroviral agents, viral resistance, and other factors that are poorly understood. Patients whose therapy fails in spite of a high level of adherence to the regimen should have their regimen changed; this change should be guided by a thorough drug treatment history and the results of drug-resistance testing. Because of limitations in the available alternative antiretroviral regimens that have documented efficacy, optimal changes in therapy might be difficult to achieve for patients in whom the preferred regimen has failed. These decisions are further confounded by problems with adherence, toxicity, and resistance. For certain patients, participating in a clinical trial with or without access to new drugs or using a regimen that might not achieve complete suppression of viral replication might be preferable. Because concepts regarding HIV management are evolving rapidly, readers should check regularly for additional information and updates at the HIV/AIDS Treatment Information Service website (http://www.hivatis.org).

Adolescent↗
PubMed2026

Reducing haystacks to needles - ViralClust: A Nextflow pipeline to cluster viral sequences.

BACKGROUND: The rapid accumulation of viral genome sequences presents major challenges for downstream analysis tools, including tools for multiple sequence alignments, phylogeny, and genome/alignment visualization, due to computational constraints and sampling biases caused by outbreak-driven over-representation. Selecting representative genomes through clustering offers a principled alternative to random subsampling, yet choosing appropriate clustering strategies remains non-trivial and context-dependent. RESULTS: Here, we present ViralClust, a modular Nextflow pipeline for bias-aware representative selection from large viral genome datasets. ViralClust integrates five distinct clustering algorithms (CD-HIT-EST, SUMACLUST, VSEARCH, MMSeqs2, and HDBSCAN) within a unified workflow, enabling direct comparison of clustering outcomes and flexible adaptation to diverse biological questions, considering a balanced phylogenetic distribution of the selected sequences. We evaluated ViralClust on six RNA and DNA virus datasets ranging from 632 to 156,586 sequences and spanning genome lengths from 890 to 197,185 nucleotides. Across all datasets, clustering reduced dataset size by ~95&#xa0;% or more while preserving genetic diversity across species, genera, and families, and effectively mitigating biases introduced by outbreaks, partial genomes, and sequence orientation artifacts. CONCLUSIONS: By supporting whole-genome clustering and scalable representative selection, ViralClust enables efficient and reproducible downstream analyses that would otherwise be computationally infeasible. Rather than offering a prescriptive, guided analysis engine, our framework functions as a flexible comparative collection of complementary strategies, allowing users to empirically evaluate trade-offs and choose the ideal method tailored to their specific analytical endpoints.

Bioinformatics↗
PubMed1999

The kissing-loop motif is a preferred site of 5' leader recombination during replication of SL3-3 murine leukemia viruses in mice.

A panel of mouse T-cell lymphomas induced by SL3-3 murine leukemia virus (MLV) and three primer binding site mutants thereof (A. H. Lund, J. Schmidt, A. Luz, A. B. Sorensen, M. Duch, and F. S. Pedersen, J. Virol. 73:6117-6122, 1999) were analyzed for the occurrence of recombination between the exogenous input virus and endogenous MLV-like sequences within the 5' leader region. Evidence of recombination within the region studied was found in 14 of 52 tumors analyzed. Sequence analysis of a approximately 330-bp fragment of 44 chimeric proviruses, encompassing the U5, the primer binding site, and the upstream part of the 5' untranslated region, enabled us to map recombination sites, guided by distinct scattered nucleotide differences. In 30 of 44 analyzed sequences, recombination was mapped to a 33-nucleotide similarity window coinciding with the kissing-loop stem-loop motif implicated in dimerization of the diploid genome. Interestingly, the recombination pattern preference found in replication-competent viruses from T-cell tumors is very similar to the pattern previously reported for retroviral vectors in cell culture experiments. The data therefore sustain the hypothesis that the kissing loop, presumably via a role in RNA dimer formation, constitutes a hot spot for reverse transcriptase-mediated recombination in MLV.

5' Untranslated Regions↗
PubMed2006

Upregulation of chondroitin 6-sulphotransferase-1 facilitates Schwann cell migration during axonal growth.

Cell migration is central to development and post-traumatic regeneration. The differential increase in 6-sulphated chondroitins during axonal growth in both crushed sciatic nerves and brain development suggests that chondroitin 6-sulphotransferase-1 (C6ST-1) is a key enzyme that mediates cell migration in the process. We have cloned the cDNA of the C6ST-1 gene (C6st1) (GenBank accession number AF178689) from crushed sciatic nerves of adult rats and produced ribonucleotide probes accordingly to track signs of 6-sulphated chondroitins at the site of injury. We found C6st1 mRNA expression in Schwann cells emigrating from explants of both sciatic nerve segments and embryonic dorsal root ganglia. Immunocytochemistry indicated pericellular 6-sulphated chondroitin products around C6ST-1-expressing frontier cells. Motility analysis of frontier cells in cultures subjected to staged treatment with chondroitinase ABC indicated that freshly produced 6-sulphated chondroitin moieties facilitated Schwann cell motility, unlike restrictions resulting from proteoglycan interaction with matrix components. Sciatic nerve crush provided further evidence of in vivo upregulation of the C6ST-1 gene in mobile Schwann cells that guided axonal regrowth 1-14 days post crush; downregulation then accompanied declining mobility of Schwann cells as they engaged in the myelination of re-growing axons. These findings are the first to identify upregulated C6st1 gene expression correlating with the motility of Schwann cells that guide growing axons through both developmental and injured environments.

Animals↗
PubMedDate not supplied

Intratumoral gene therapy for non-small cell lung cancer: current status and future directions.

Major advances in the field of molecular genetics and cancer biology have allowed for the development of rationally designed anti-cancer strategies. When genetic material (DNA or RNA) is used for this purpose, this approach is called gene therapy. Cancer cells are remarkably sensitive to the inhibition of activated oncogenes or replacement of lost tumor suppressor gene (TSG) function. Replacement of lost TSG p53 function has been achieved by the use of recombinant adenoviral vectors (rAdp53) that carry an expression cassette for this gene. Non-small cell lung cancer has been the subject of early clinical trials in which intratumoral injection of rAdp53 has been performed by transthoracic CT-guided injection or bronchoscopy. Gene transfer and p53 transgene expression have been documented in injected tumors as well as the safety and feasibility of this type of gene therapy. Tumor regression has been reported in rAdp53-injected lesions, either alone or in combination with systemic chemotherapy. Randomized controlled studies as well as clear demonstrations of clinical benefit are missing at present. The results of ongoing studies will allow a verdict on the future of first generation rAdp53 gene therapy. For the whole of the field of gene therapy the advent of more efficient and safe gene transfer technology will determine the speed by which this innovative therapeutic modality will meet with clinical success.

Carcinoma, Non-Small-Cell Lung↗
PubMed1998

Differential regulation of chemokine receptors during dendritic cell maturation: a model for their trafficking properties.

Upon exposure to immune or inflammatory stimuli, dendritic cells (DC) migrate from peripheral tissues to lymphoid organs, where they present Ag. CC chemokines induce chemotactic and transendothelial migration of immature DC, in vitro. Maturation of DC by CD40L, or by LPS, IL-1, and TNF, induces down-regulation of the two main CC chemokine receptors expressed by these cells, CCR1 and CCRS, and abrogates chemotaxis to their ligands. Inhibition was rapid (<1 h) and included the unrelated agent FMLP. Concomitantly, the expression of CCR7 and the migration to its ligand EBI1 ligand chemokine (ELC)/macrophage inflammatory protein (MIP)-3beta, a chemokine expressed in lymphoid organs, were strongly up-regulated, though with slower kinetics (24-48 h). Rapid inhibition of responsiveness to chemoattractants present at sites of inflammation and immune reaction may be permissive for leaving peripheral tissues. Conversely, the slower acquisition of responsiveness to ELC/MIP-3beta may guide subsequent localization of DC in lymphoid organs.

CD40 Antigens↗
PubMed2005

Dose reduction for the management of indinavir-related toxicity in human immunodeficiency virus type 1-infected patients in Taiwan: clinical and pharmacokinetic assessment.

This study evaluated the feasibility of reducing the indinavir (IDV) dosage in Taiwanese patients receiving the standard IDV/ritonavir (RTV) dosage of 800/100 mg twice a day who had undetectable plasma human immunodeficiency virus type 1 (HIV-1) RNA but had developed IDV-related toxicities. After dosage reduction to IDV/RTV 600/100 mg twice a day, the dose-related toxicity decreased and plasma HIV RNA remained undetectable at 24 weeks post-switch in all patients. The maximal plasma concentration (Cmax) and area under the plasma concentration-time curve of IDV decreased significantly (median, 6.3 vs 4.3 microg/mL and 1892 vs 1292 microg.min/mL, p=0.01 and 0.001, respectively) but the minimal plasma concentration remained at a similar level (median, 1.0 vs 0.8 microg/mL, p=0.12). This study found that the reduction in the dosage of IDV in HIV-1 infected patients receiving the standard IDV/RTV regimen guided by therapeutic drug monitoring decreased the Cmax, dose-related toxicity and medical cost without compromising viral control.

Acquired Immunodeficiency Syndrome↗
PubMed2003

Induction of neuropilins-1 and -2 and their ligands, Sema3A, Sema3F, and VEGF, during Wallerian degeneration in the peripheral nervous system.

The neuropilins, NP-1 and NP-2, are coreceptors for Sema3A and Sema3F, respectively, both of which are repulsive axonal guidance molecules. NP-1 and NP-2 are also coreceptors for vascular endothelial growth factor (VEGF). The neuropilins and their ligands are known to play prominent roles in axonal pathfinding, fasciculation, and blood vessel formation during peripheral nervous system (PNS) development. We confirmed a prior report (Exp. Neurol. 172 (2001) 398) that VEGF mRNA levels rise during Wallerian degeneration in the PNS and herein demonstrate that NP-1, NP-2, Sema3A, and Sema3F mRNA levels increase in peripheral nerves distal to a transection or crush injury. In a sciatic nerve crush model, in which axonal regeneration is robust, the highest levels of Sema3F mRNA below the injury site are in the epi- and perineurium. Our results suggest the possibility that the neuropilins and their semaphorin ligands serve to guide, rather than to impede, regenerating axons in the adult PNS.

Animals↗
PubMed2004

Isoprenoids control germ cell migration downstream of HMGCoA reductase.

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoAr) provides attractive cues to Drosophila germ cells, guiding them toward the embryonic gonad. However, it remains unclear how HMGCoAr mediates this attraction. In a genomic analysis of the HMGCoAr pathway, we found that the fly genome lacks several enzymes required for cholesterol biosynthesis, ruling out cholesterol and cholesterol-derived proteins as mediators of PGC migration. Genetic analysis of the pathway revealed that two enzymes, farnesyl-diphosphate synthase and geranylgeranyl-diphosphate synthase, required for the production of isoprenoids, act downstream of HMGCoAr in germ cell migration. Consistent with a role in geranylgeranylation, embryos deficient in geranylgeranyl transferase type I show germ cell migration defects. Our data, together with similar findings in zebrafish, implicate an isoprenylated protein in germ cell attraction. The specificity and evolutionary conservation of the HMGCoAr pathway for germ cells suggest that an attractant common to invertebrates and vertebrates guides germ cells in early embryos.

Alkyl and Aryl Transferases↗
PubMed2002

Gene transcript quantitation by real-time RT-PCR in cells selected by immunohistochemistry-laser capture microdissection.

Studying tissue-based gene expression in different cell populations often requires immunohistochemistry-guided microdissection. However, mRNA degradation occurs during long staining procedures. We combined a novel rapid immunoperoxidase technique with laser capture microdissection (LCM) and real-time quantitative RT-PCR to compare p27 mRNA expression in prostatic basal/secretory cells. Eight frozen prostate sections were immunostained with antibody 34betaE12 (high-molecular-weight keratin). Secretory and basal cells were separately collected by LCM. p27 transcripts from each cell group were quantitated by real-time RT-PCR, with GAPDH as standard. Immunostaining took 22 minutes, with RNA extraction from approximately 40 dissected cells from each compartment initiated within 40 minutes. Qualitative RT-PCR gave a product of the expected size from each sample. Quantitative RT-PCR gave basal/secretory p27/GAPDH ratios of 0.99-16.24 (mean 5.53 +/- 0.643). Immunostaining for keratin 34betaE12 can be done on frozen sections in approximately 20 minutes, and mRNA from pure cell populations can be quantitated by RT-PCR. We used this technique to show that p27 transcript levels are greater in basal than in secretory prostate cells, suggesting, when combined with prior studies, that regulation of p27 occurs at the protein level in normal cells. This technique may have wide applicability to studies of gene expression in distinct cell populations in heterogeneous tissues.

Dissection↗
PubMed2006

High-content screening of functional genomic libraries.

Recent advances in functional genomics have enabled genome-wide genetic studies in mammalian cells. These include the establishment of high-throughput transfection and viral propagation methodologies, the production of large-scale cDNA and siRNA libraries, and the development of sensitive assay detection processes and instrumentation. The latter has been significantly facilitated by the implementation of automated microscopy and quantitative image analysis, collectively referred to as high-content screening (HCS), toward cell-based functional genomics application. This technology can be applied to whole genome analysis of discrete molecular and phenotypic events at the level of individual cells and promises to significantly expand the scope of functional genomic analyses in mammalian cells. This chapter provides a comprehensive guide for curating and preparing function genomics libraries and performing HCS at the level of the genome.

Animals↗
PubMed2002

Differential expression of human equilibrative nucleoside transporter 1 (hENT1) protein in the Reed-Sternberg cells of Hodgkin's disease.

Gemcitabine is a cytotoxic nucleoside analog with activity in relapsing/refractory Hodgkin's disease (HD). Because gemcitabine is hydrophilic, it requires plasma membrane nucleoside transporter proteins to access intracellular targets. The most abundant and widely distributed transporter in human cells is human equilibrative nucleoside transporter 1 (hENT1). Because our prior studies showed that a deficiency in hENT1 confers high-level resistance to gemcitabine toxicity in vitro, we developed an immunohistochemical method to assess the hENT1 abundance of cells in tumor tissue. We now report the application of this method for visualizing the hENT1 protein abundance in the plasma membranes of Reed-Sternberg cells in lymph nodes of HD patients. Frozen sections of 30 lymph nodes were stained with monoclonal antibodies (mAb 10D7G2) raised against a synthetic peptide comprised of residues 254-271 from the large intracellular loop of hENT1 and staining intensity was scored on a 0-4 + scale. hENT1-staining intensity varied among HD lymph node samples (score/n; 0/8; 1/10; 2/9; 3/3; 4/0) and suggested that at least 60% of the tumors appeared hENT1 deficient. Because Epstein-Barr virus (EBV) is often associated with HD, staining for Epstein-Barr early RNA was also examined. Although 9/30 patients tested positive for EBV, there was no correlation with hENT1 staining. hENT1-staining intensities were positively correlated with age of the patient but were independent of other clinical, laboratory or pathology features (tumor stage, histologic subtype, presence of B symptoms, staining for CD15 or CD30, serum biochemistry, disease free survival, and overall survival). We conclude that, because hENT1 deficiency has been previously related to nucleoside-drug resistance, immunohistochemical staining for hENT1 warrants evaluation as a predictive tool for guiding the appropriate use of gemcitabine in the treatment of HD.

Adolescent↗
PubMed1998

Trophoblast class I major histocompatibility complex (MHC) products are resistant to rapid degradation imposed by the human cytomegalovirus (HCMV) gene products US2 and US11.

US11 and US2 encode gene products expressed early in the replicative cycle of human cytomegalovirus (HCMV), which cause dislocation of human and murine major histocompatibility complex (MHC) class I molecules from the lumen of the endoplasmic reticulum to the cytosol, where the class I heavy chains are rapidly degraded. Human histocompatibility leukocyte antigens (HLA)-C and HLA-G are uniquely resistant to the effects of both US11 and US2 in a human trophoblast cell line as well as in porcine endothelial cells stably transfected with human class I genes. Dislocation and degradation of MHC class I heavy chains do not appear to involve cell type-specific factors, as US11 and US2 are fully active in this xenogeneic model. Importantly, trophoblasts HLA-G and HLA-C possess unique characteristics that allow their escape from HCMV-associated MHC class I degradation. Trophoblast class I molecules could serve not only to block recognition by natural killer cells, but also to guide virus-specific HLA-C- and possibly HLA-G-restricted cytotoxic T-lymphocytes to their targets.

Animals↗
PubMed2005

Schwann cell behavior after nerve repair by means of tissue-engineered muscle-vein combined guides.

Schwann cells play a critical role in peripheral nerve regeneration. When a non-nervous conduit is used to bridge a nerve defect, the conduit is soon colonized by a number of Schwann cells that make a pathway for regrowing axons. By using electron microscopy, immunohistochemistry, and reverse transcriptase-polymerase chain reaction analysis, we have investigated the behavior of migratory glial cells along a particular type of autologous tissue-engineered conduit made of a vein filled with fresh skeletal muscle, using the rat sciatic nerve model. With this particular type of autograft, our data show that many Schwann cells soon take up a close relationship with grafted muscle fibers, and especially with their basal lamina, which appears to serve as a migration pathway for them. The early and massive colonization of the conduit is sustained by both Schwann cell migration and proliferation, as demonstrated by PCNA immunostaining. Later, as they meet regenerating axons, Schwann cells become closely associated with them and eventually lose their connections with grafted muscle fibers because of the formation of perineurial envelopes. Because previous studies showed that alpha(2a-2b) NRG1 is overexpressed at early stages along the muscle-vein combined tubes, we have also investigated mRNA expression of its two receptors, erbB2 and erbB3. Both messengers are overexpressed, although with different time courses. Overall, our results provide some morphological and biochemical bases for explaining the effectiveness of fresh muscle-vein combined nerve guides and throw an interesting light on the possible role of alpha(2a-2b) NRG1 through the erbB2/erbB3 heterodimer receptor for nerve regeneration inside non-nervous conduits.

Animals↗