PubMed Health⌕ Search

Biomedical subjects

S L Zeichner

Publications and source records attributed to S L Zeichner.

At least 19 recordsLinked to original sources
PubMed1999

Rapid telomere shortening in children.

Telomere shortening may reflect the total number of divisions experienced by a somatic cell and is associated with replicative senescence. We found that the average rate of telomere shortening in peripheral blood mononuclear cells (PBMCs) obtained longitudinally from nine different infants during the first 3 years of life (270 bp per year) is more than fourfold higher than in adults and does not correlate with telomerase activity. These results show that the rate of telomere loss changes during ontogeny, suggesting the existence of periods of accelerated cell division. Because human immunodeficiency virus (HIV) preferentially infects actively dividing cells, our observation suggesting accelerated cell division in children may provide an explanation for some of the distinctive pathogenic features of the HIV disease in infants, including higher viral loads and more rapid progression to acquired immunodeficiency syndrome (AIDS).

Adult↗
PubMed1999

Telomere dynamics in monkeys: increased cell turnover in macaques infected with chimeric simian-human immunodeficiency viruses.

To address the question of how cell turnover is affected by retroviral infections, we used the telomeric terminal restriction fragments (TRFs) as markers of cell replicative history and measured their length in macaques infected with chimeric simian-human immunodeficiency viruses (SHIVs). The TRF lengths of mononuclear cells in 104 samples, including longitudinal samples from nine cynomolgus and ten pig-tailed macaques infected with SHIV, and in samples from 26 uninfected macaques, were quantitated by an improved method, based on two-dimensional calibration of DNA sizes, pulsed field electrophoresis, and high-resolution Southern blot images. The average TRF lengths of peripheral blood mononuclear cells (PBMCs) from uninfected pig-tailed (14.9+/-1.6 kbp) and cynomolgus (14.1+/-1.8 kbp) macaques were about 3 and 5 kbp longer than those of human infants and 30-year-old adults, respectively. The rate of TRF length shortening in infected pig-tailed macaques was significantly (P = 0.035) higher (2.2-fold) than in uninfected monkeys. The TRFs in SHIV-infected cynomolgus monkeys, which, in general, had lower viral loads than pig-tailed macaques, shortened on average more rapidly (1.6-fold) than in uninfected animals, but the difference was not statistically significant. The TRFs of mononuclear cells from the lymph nodes of two rapidly progressing SHIV-infected macaques that developed AIDS and died also shortened in parallel but somewhat more rapidly than in the PBMCs. These results suggest that the rate of PBMC turnover in macaques could be increased several-fold during infections by immunodeficiency viruses, likely due to immune activation by SHIV antigens.

Animals↗
PubMed1999

Long-term telomere dynamics: modest increase of cell turnover in HIV-infected individuals followed for up to 14 years.

To quantify the long-term dynamics of telomere lengths and the effect of HIV infection on lymphocyte turnover rates, we measured in a blinded study longitudinal samples from 6 individuals using a highly accurate method based on two-dimensional calibration of DNA sizes. For two uninfected controls followed 8 and 10 years the average telomeric terminal restriction fragment (TRF) shortening rate in peripheral blood mononuclear cells (PBMCs) was 50 and 60 bp/year, respectively, in agreement with previous measurements of cross-sectional samples. The TRF lengths of PBMCs from two slow progressors followed for 14 years declined by a rate of 120 +/-10 bp/year, i.e. 2-fold higher than the rate of TRF shortening for uninfected individuals. The rate of TRF shortening was higher in CD8 (140 +/-10 bp/year) than in CD4 (100 +/-10 bp/year) cells. The CD8 cell TRFs of the two fast progressors shortened faster (240 +/-10 bp/year) and the rate of CD4 cell TRF shortening in one of the fast progressors was 160 bp/year. These data suggest that HIV infection causes only a modest increase in the lymphocyte turnover which we speculate could be due to chronic activation of the immune system, and may not result in the exhaustion of its regenerative capacity and immunopathogenesis.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Individual prognoses of long-term responses to antiretroviral treatment based on virological, immunological and pharmacological parameters measured during the first week under therapy.

OBJECTIVE: To predict long-term (12 weeks or longer) virological responses to antiretroviral treatment from measurements made during the first few days on therapy. METHODS: Forty-one HIV-1-infected children were treated with ritonavir for 12 weeks followed by triple drug combination treatment, and the kinetics of virus decay in plasma, ritonavir concentration and CD4 cell counts were measured. A robust multivariate pattern recognition method was used for prediction of the longterm virological responses. RESULTS: The virus decay rate constants calculated from measurements of plasma viral RNA concentrations on the first, second, third, fourth and seventh day on therapy, the drug concentrations in the plasma on day seven, and the pretreatment levels of viral RNA and CD4 cell counts, correlated with long-term levels of plasma HIV-1 RNA. The combination of these parameters contained sufficient information for correct and robust prediction of the long-term response in 88% of the treated children. The predictions of individual responses were stable as demonstrated by a cross-validation analysis, which was highly statistically significant (r=0.87) and specific. CONCLUSION: These results demonstrate that multiple parameters determine the response to antiretroviral therapy and offer a very early measure of individual long-term responses, suggesting that treatment could be optimized after few days of therapy.

Adolescent↗
PubMed1998

The expression of the essential nuclear splicing factor SC35 is altered by human immunodeficiency virus infection.

In order to identify cellular genes differentially expressed during human immunodeficiency virus 1 (HIV-1) infection, we conducted a screen using differential display. The sequence of one of the clones, 0085, was identical to a sequence present in the RNA splicing factor SC35. Since splicing is an essential point of control during HIV gene expression, we carried out additional experiments to examine SC35 expression during HIV infection. RNA blots confirmed that SC35 RNA was induced following HIV infection; a 2-3-fold increase in expression of SC35 RNA was detected by day 2 of HIV infection. Fluorescence-activated cell-sorting revealed concomitant increases in SC35 protein and double staining studies demonstrated that increases in SC35 protein occurred specifically in the HIV-infected cells. Laser scanning confocal microscopy revealed SC35 was associated with 2 microm 'nuclear speckles' in both infected and uninfected cells, suggesting that increases in SC35 accumulated in these nuclear structures and that HIV infection did not alter the intracellular distribution of SC35. These findings indicate that an essential splicing factor is induced after HIV infection, suggesting that the consequences of HIV infection include alterations in relative levels of a splicing factor.

Anti-HIV Agents↗
PubMed1998

Telomere dynamics in HIV-1 infected and uninfected chimpanzees measured by an improved method based on high-resolution two-dimensional calibration of DNA sizes.

We developed an improved method for accurately measuring telomere lengths based on two-dimensional calibration of DNA sizes combined with pulsed field electrophoresis and quantitative analysis of high-resolution gel images. This method was used to quantify the length of telomeres in longitudinal samples of peripheral blood mononuclear cells (PBMCs) from five chimpanzees infected with human immunodeficiency virus type 1 (HIV-1) and three uninfected animals, 14 to 27 years of age. The average length of the telomere restriction fragments (TRF) of infected and uninfected chimpanzees were 11.7 +/- 0.25 kbp, and 11.6 +/- 0.61 kbp, respectively, and were about 1 kbp and 3 kbp longer than those of human infants and 30 year old adults, respectively. There was a trend of a slight decrease (30-60 bp per year) in the TRF of two HIV infected chimpanzees over 30-35 months, while the TRF of one naive chimpanzee slightly increased over 20 months. Although the number of chimpanzees in this study is small and no statistically significant linear dependencies on time were observed, it appears that in chimpanzees, rates of shortening of the TRF are comparable or smaller than in adult humans and are not significantly affected by HIV-1 infection, which may be related to the inability of HIV-1 to cause disease in these animals.

Age Factors↗
PubMed1998

Foscarnet.

Explore the source record for details and available documents.

Antiviral Agents↗
PubMed1997

HIV-1 infection and the developing nervous system: lineage-specific regulation of viral gene expression and replication in distinct neuronal precursors.

Neurologic abnormalities are common in HIV-1 infected patients and often represent the dominant clinical manifestation of pediatric AIDS. Although the neurological dysfunction has been directly related to CNS invasion by HIV-1, the pathogenesis of neurologic disorders remains unclear. Microglia and macrophages are major HIV-1 targets in the brain, whereas HIV-1 infected neurons or glial cells have been rarely reported. This suggests that indirect mechanisms may account for the severe neuronal damage observed in these patients. Nevertheless, immature, mitotically active neuronal and glial cells, which are present during fetal development, are susceptible to HIV-1 infection and replication in vitro, suggesting that HIV-1 infection during organ development may present unique features. To better characterize virus-host cells interactions in the developing CNS, we have examined the susceptibility of embryologically and biochemically distinct neuronal cell lines to HIV-1 infection. Here we show that mitotically active, immature neurons of distinct lineages, have different susceptibilities to HIV-1 infection and replication and different abilities to support viral gene expression. Mutational analysis of HIV-1 LTR reveals that a region of the viral promoter between nucleotide -255 to -166 is responsible for most quantitative and qualitative differences in viral transactivation among different neuroblasts. This suggests that specific regions of the viral promoter and cellular factors, either lineage- or differentiation-dependent, which bind to those regions, may contribute to control the levels of virus replication and possibly restrict the viral tropism in the developing brain. This may contribute to the establishment of a virus reservoir in the immature CNS and participate by either direct or indirect mechanisms to the severity of the AIDS-related pediatric neurological dysfunction.

Cell Line↗
PubMed1996

Human immunodeficiency virus type 1 infection of H9 cells induces increased glucose transporter expression.

A clone obtained from a differential display screen for cellular genes with altered expression during human immunodeficiency virus (HIV) infection matched the sequence for the human GLUT3 facilitative glucose transporter, a high-velocity-high-affinity facilitative transporter commonly expressed in neurons of the central nervous system. Northern (RNA) analysis showed that GLUT3 expression increased during infection. Flow cytometry showed that GLUT3 protein expression increased specifically in the HIV-infected cells; this increase correlated with increased 2-deoxyglucose transport in the HIV-infected culture. HIV infection therefore leads to increased expression of a glucose transporter normally expressed at high levels in other cell types and a corresponding increase in glucose transport activity. If HIV infection places increased metabolic demands on the host cell, changes in the expression of a cellular gene that plays an important role in cellular metabolism might provide a more favorable environment for viral replication.

Biological Transport↗
PubMed1996

Kinetics of HIV-1 RNA concentration changes in pediatric patients.

Recent studies have used potent antiviral agents to investigate the kinetics of HIV infection in vivo. They provided estimates for important kinetic parameters, including the decay constants for circulating virus and infected CD4+cells. However, since all of these studies fundamentally rely on the use of antiviral agents, it would be useful to develop other approaches capable of independently verifying the values of the kinetic parameters through other means. Since CD4+ cells are known to exhibit diurnal variations and since there have been suggestions that circulating virus concentrations also vary in a diurnal fashion, as well as nonperiodically, we developed a mathematical model to describe those natural variations. The model predicted variations in viral RNA concentrations and produced estimates of the values of viral kinetic parameters without the use of antiviral agents. To compare the model with experimental data we measured the temporal dependence of the concentration of plasma viral RNA obtained from pediatric HIV-1 patients. The data analysis led to finding diurnal variation in the viral RNA and an estimate of the circulating virus half-life in the order of few hours, in reasonable agreement with the estimates obtained using antiviral agents. These results are the first demonstration of diurnal variations in AIDS patients and confirm the order of magnitude of the virus half-life found by using antiviral drugs. These findings may have implications for understanding HIV-1 pathogenesis and the development of therapeutic protocols.

Adolescent↗
PubMed1994

The molecular biology of HIV. Insights into pathogenesis and targets for therapy.

In the past 10 years, a large number of investigators have produced an enormous amount of information concerning the molecular biology of HIV. These studies at the most basic biological level have provided essential insights into the pathogenesis of the disease. They have supplied the information necessary for the creation of the antiviral therapies now available and have indicated the direction for the development of new therapies now in clinical trials and under investigation. Although the relatively ineffective therapies currently available serve as a constant source of disappointment for those practitioners who care for HIV-infected patients, there is some comfort to be gained from the rapid pace of investigation into the basic biology of the virus and the certainty that any more effective therapy must build upon the basic biological knowledge already obtained. A detailed study of some of the unique features observed during pediatric and perinatal HIV infection, particularly the relatively shortened time from infection to symptoms and the relative importance of CNS disease, may suggest new therapeutic approaches that will benefit both adult and pediatric patients. Finally, a comprehensive knowledge of HIV biology is an essential requirement for therapeutic maneuvers designed to interrupt the transmission of HIV from mother to child.

DNA, Viral↗
PubMed1993

Replication of type 1 human immunodeficiency viruses containing linker substitution mutations in the -201 to -130 region of the long terminal repeat.

In previous transfection analyses using the chloramphenicol acetyltransferase reporter gene system, we determined that linker substitution (LS) mutations between -201 and -130 (relative to the transcription start site) of the human immunodeficiency virus type 1 long terminal repeat (LTR) caused moderate decreases in LTR transcriptional activity in a T-cell line (S. L. Zeichner, J. Y. H. Kim, and J. C. Alwine, J. Virol. 65:2436-2444, 1991). In order to confirm the significance of this region in the context of viral replication, we constructed several of these LS mutations (-201 to -184, -183 to -166, -165 to -148, and -148 to -130) in proviruses and prepared viral stocks by cocultivation of transfected RD cells with CEMx174 cells. In addition, two mutations between -93 and -76 and between -75 and -58 were utilized, since they affect the nuclear factor kappa B (NF-kappa B)- and Sp1-binding sites and were expected to diminish viral replication. Our results suggest that while transfection analyses offer an adequate approximation of the effects of the LS mutations, the analysis of viral replication using a mutant viral stock presents a more accurate picture, which is sometimes at variance with the transfection results. Three mutants (-201/-184 NXS, -165/-148 NXS, and -147/-130 NXS) had effects on viral replication that were much more severe than the effects predicted from their performance in transfection analyses, and the effects of two LS mutations (-201/-184 NXS and -183/-166 NXS) were not predicted by their effects in transfection. In addition, we observed cell type-specific permissiveness to replication of some mutant viruses. In the cell types tested, the LS mutations indicated an apparent requirement not only for the intact NF-kappa B and SP1-binding sites but also for several regions between -201 and -130 not previously associated with viral infectivity.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Differentiation-dependent human immunodeficiency virus long terminal repeat regulatory elements active in human teratocarcinoma cells.

We have examined the transcriptional utilization of the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) under differentiating conditions by using the embryonal carcinoma cell line NTERA-2. NTERA-2 cells undergo two distinct pathways of terminal differentiation, to a neuronal phenotype in response to retinoic acid and to a nonneuronal phenotype in response to hexamethylene bisacetamide. To identify LTR regulatory elements active in each cell type we used a set of HIV LTR linker substitution mutants, which contain mutations that progressively replace adjacent 18-bp segments across the U3 region and into the R region (between nucleotides -453 and +15 relative to the transcription start site). Although each differentiating cell type showed utilization of expected key elements (e.g., NF-kappa B, SP1, TATA) in the 3' portion of the LTR (+1 to -112), the data indicated differentiation-dependent differences in the utilization of these elements. In addition, regions showing dramatic differentiation-dependent effects were detected in the 5' portion of the LTR (-112 to -453), in positions where transcription control elements have not been described previously. The marked differences in the sets of LTR regulatory elements required by each cell type indicate that the LTR can function under a variety of differentiation conditions. Together with previous findings, the data suggest that the complexity of the HIV LTR for transcriptional control is much greater than was previously thought and that the LTR maintains elements which facilitate transcription in many cell types.

Base Sequence↗
PubMed1991

Linker-scanning mutational analysis of the transcriptional activity of the human immunodeficiency virus type 1 long terminal repeat.

We have compared the relative importance of transcription regulatory regions in the U3 and R regions of the human immunodeficiency virus type 1 long terminal repeat (LTR) by using linker-scanning mutational analysis. Twenty-six mutant LTR-chloramphenicol acetyltransferase (CAT) transient expression plasmids were prepared in which consecutive 18-bp regions of wild-type LTR were replaced with an NdeI-XhoI-SalI (NXS) polylinker. The mutant LTR-CAT plasmids were transfected into unstimulated Jurkat cells, Jurkat cells stimulated with phytohemagglutinin and tetradecanoylphorbol acetate, and Jurkat cells which constitutively express the human immunodeficiency virus type 1 trans-activator protein, Tat. Transcriptional activity was measured by analysis of CAT activity. The activities of these mutants identified one major and several minor transcription control elements in addition to previously identified elements. In addition, this fine-structure analysis identified differences in utilization of regulatory regions between unstimulated, stimulated, and Tat-expressing Jurkat cells. A significant regulatory region was indicated by linker-scanning mutations between nucleotides -183 and -130 (relative to the transcription start site, +1). These mutations caused marked decreases in activity of the LTR in unstimulated and especially in stimulated Jurkat cells but had no effect in Tat-expressing Jurkat cells. DNA mobility shift studies comparing probes of wild-type and mutant sequences in the -183 to -130 region indicated that alterations in specific DNA binding correspond to the altered transcriptional activity of the mutants. The effects of mutations in several regulatory regions, in addition to the -183 to -130 region described above, differ between Tat-expressing and -nonexpressing Jurkat cells. For example, the NF-kB sites are necessary for transcription in both Tat-expressing and -nonexpressing cells. However, Tat-expressing Jurkat cells primarily require only the 3'-proximal site, while both stimulated and unstimulated Jurkat cells appear to require both sites. Mutants downstream of the TATA element cause a more significant decrease in activity in Tat-expressing Jurkat cells than in the others. Finally, several mutations in the 5' half of the LTR (-453 to -184) show modest increases in transcription (1.5-fold or less) in unstimulated Jurkat cells only, suggesting possible negative regulatory sites. In summary, our studies have identified a control region (-183 to -130) upstream of the NF-kB sites and have more precisely defined significant differences in the utilization of regulatory regions between unstimulated, stimulated, and Tat-expressing Jurkat cells.

Base Sequence↗
PubMed1991

Analysis of the human immunodeficiency virus long terminal repeat by in vitro transcription competition and linker scanning mutagenesis.

Previous studies designed to map the transcriptional regulatory sequences of the human immunodeficiency virus (HIV) long terminal repeat (LTR) have shown disparate results depending on the method of analysis. Experiments have shown that deletions 5' to -104 (relative to the transcription start site, +1) are not required for transcription in vitro, while other experiments have shown that various mutations in this 5' region of the HIV-1 LTR affect both reporter gene activity in transient expression systems and viral growth. To correlate in vitro and in vivo findings, we performed in vitro transcription competition studies to define minimal sequences necessary for competitive factor binding or competitive transcription complex formation. Using normal HeLa cell nuclear extracts, we found that transcription of a reporter gene run by the U3-R region was efficiently competed only by intact LTR DNA fragments representing virtually the entire U3-R region (-453 to +80). Smaller subfragments of the LTR were less effective competitors; these included fragments from -453 to -159, which had a modest competitive ability at higher competitor concentrations, -159 to +80, and -402 to -34, which were both relatively poor competitors. These findings indicate that although the U3-R region truncated to -104 is able to promote in vitro transcription, a more stable transcription complex appears to form on the entire U3-R region. Hence sequences between -453 and -104 appear to be significant in transcription complex formation. In vivo transfection competition studies confirmed these findings. Specific sequences between -453 and -104 which may affect expression or transcription complex formation were mapped using a set of linker-scanning mutants spanning the LTR.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1988

Mechanisms and pathways of congenital infections.

Fetal and neonatal infections can occur at different times during pregnancy, from conception to birth. Infections that take place near the time of conception often destroy the zygote or embryo and only rarely leave definitive evidence. The mother can transmit the infection to her fetus through several routes, but the most likely routes are through ascending infections and through the blood. The inability of most agents to infect the early embryo probably depends largely on local barriers to the infectious agent, such as the zona pellucida. Some viruses, however, because of their systems for gene regulation of expression, can infect only embryos of certain developmental stages. Certain retroviruses can infect embryos, integrate into cellular DNA, and become part of the germline. After implantation, most infectious agents reach the fetus hematogenously. Organisms circulating in the mother reach and infect the placenta. They then may breach the placenta, gain access to the fetal circulation, and disseminate through the fetal body. Agents with particular tropisms infect particular organs and cause particular symptom complexes. The damage done by the organisms depends largely on the gestational age of the fetus at the time of the infection. The ability of the agent to infect or damage the fetus at all often depends on whether the mother is experiencing a primary infection or has previously mounted an effective immune response. Agents harm the fetus through direct destruction of parenchymal cells, through destruction of blood vessels and resulting infarction, through continued replication in fetal and neonatal tissues, through altering the growth parameters of various fetal tissues, and through provoking autoimmune responses. Infections that begin in the perinatal period usually infect the fetus by direct inoculation from infected foci in the birth canal or through direct contact with large amounts of infected maternal body fluids. Direct tissue destruction of the immediate sequelae of invasive infections usually causes the fetal damage from these perinatally acquired agents. The clinical features of the disease that begin in this period provide an opportunity for effective therapeutic intervention. Understanding the routes of fetal infection and the mechanisms underlying fetal damage from infection will help in devising strategies for preventing and treating congenital infections.

Bacterial Infections↗
PubMed1983

Isolation and characterization of macrophage phagosomes containing infectious and heat-inactivated Chlamydia psittaci: two phagosomes with different intracellular behaviors.

Infectious Chlamydia psittaci enters macrophages via a cytochalasin B-insensitive pathway in which chlamydia-containing phagosomes do not fuse with lysosomes; heat-inactivated C. psittaci enters macrophages via a route in which phagosomes do fuse with lysosomes. In an attempt to explain these differences, phagosomes containing infectious and heated chlamydiae were isolated from mouse macrophages by a procedure developed to isolate L-cell chlamydial phagosomes by rate zonal centrifugation. Macrophage phagosomes acted similarly to L-cell phagosomes on dextran and discontinuous sucrose gradients and exhibited similar detergent sensitivities. Total proteins of the two phagosomes were compared with each other, L-cell proteins, and surface-labeled proteins from macrophages. Both macrophage phagosome membranes had at least nine proteins with equal sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobilities; some were the same as L-cell phagosome proteins. Each phagosome had at least one protein not seen in the other. Only two phagosome proteins had mobilities equal to macrophage plasma membrane proteins. Macrophage phagosomes containing infectious and heat-inactivated C. psittaci, although created by different entry mechanisms and destined for different intracellular fates, exhibited only a few differences in their proteins.

Animals↗