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L Shapiro

Publications and source records attributed to L Shapiro.

At least 55 records · Page 3Linked to original sources
PubMed1999

Chromosome segregation during the prokaryotic cell division cycle.

Recent work has dramatically changed our view of chromosome segregation in bacteria. Rather than being a passive process, it involves rapid movement of parts of the circular chromosome. Several genes involved in chromosome segregation have been identified, and the analysis of their functions and intracellular localization are beginning to shed light on the mechanisms that ensure efficient chromosome segregation.

Bacillus subtilis↗
PubMed1999

Differential localization of two histidine kinases controlling bacterial cell differentiation.

The bacterium C. crescentus coordinates cellular differentiation and cell cycle progression via a network of signal transduction proteins. Here, we demonstrate that the antagonistic DivJ and PleC histidine kinases that regulate polar differentiation are differentially localized as a function of the cell cycle. The DivJ kinase localizes to the stalked pole in response to a signal at the G1-to-S transition, while the PleC kinase is localized to the flagellar pole in swarmer and predivisional cells but is dispersed throughout the cell in the stalked cell. PleC, which is required for DivJ localization, may provide the cue at the G1-to-S transition that directs the polar positioning of DivJ. The dynamic positioning of signal transduction proteins may contribute to the regulation of polar differentiation at specific times during the bacterial cell cycle.

Bacterial Proteins↗
PubMed1999

The CtrA response regulator mediates temporal control of gene expression during the Caulobacter cell cycle.

In its role as a global response regulator, CtrA controls the transcription of a diverse group of genes at different times in the Caulobacter crescentus cell cycle. To understand the differential regulation of CtrA-controlled genes, we compared the expression of two of these genes, the fliQ flagellar gene and the ccrM DNA methyltransferase gene. Despite their similar promoter architecture, these genes are transcribed at different times in the cell cycle. PfliQ is activated earlier than PccrM. Phosphorylated CtrA (CtrA approximately P) bound to the CtrA recognition sequence in both promoters but had a 10- to 20-fold greater affinity for PfliQ. This difference in affinity correlates with temporal changes in the cellular levels of CtrA. Disrupting a unique inverted repeat element in PccrM significantly reduced promoter activity but not the timing of transcription initiation, suggesting that the inverted repeat does not play a major role in the temporal control of ccrM expression. Our data indicate that differences in the affinity of CtrA approximately P for PfliQ and PccrM regulate, in part, the temporal expression of these genes. However, the timing of fliQ transcription but not of ccrM transcription was altered in cells expressing a stable CtrA derivative, indicating that changes in CtrA approximately P levels alone cannot govern the cell cycle transcription of these genes. We propose that changes in the cellular concentration of CtrA approximately P and its interaction with accessory proteins influence the temporal expression of fliQ, ccrM, and other key cell cycle genes and ultimately the regulation of the cell cycle.

Bacterial Proteins↗
PubMed1999

Loving openness as a meta-world hypothesis: expanding our vision of mind and medicine.

In 1942, Stephen C. Pepper published a seminal book, World Hypothesis, that sought to explain how people create hypotheses about the world. Pepper proposed that there were four basic world hypotheses: (1) formistic (the hypothesis that nature exists as categories); (2) mechanistic (the hypothesis that nature obeys cause-effect relationships); (3) contextual (the hypothesis that processes in nature are relative and context dependent); and (4) organismic (the hypothesis that processes in nature reflect interactive relationships in systems). Most classical and modern theories of science and medicine implicitly adopt one or more of these foundational hypotheses. In 1997, Schwartz and Russek proposed that there were four additional world hypotheses: (5) implicit process (the hypothesis that nature consists of invisible forces and information, such as energy and consciousness); (6) circular causality (the hypothesis that nature consists of circulating interactions that inherently change over time); (7) creative unfolding (the hypothesis that processes in nature reflect flexible designs or plans that have adaptive function); and (8) integrative diversity (the hypothesis that phenomena in nature reflect complex integrations of diverse processes). Theories in postmodern and integrative science implicitly adopt hypotheses 5 through 8. However, underlying the creation of the eight world hypotheses is an implicit meta-world hypothesis which we term loving openness (the hypothesis that phenomena in nature reflect levels of openness and caring). This paper briefly explains the origin and implications of the loving openness meta-world hypothesis for understanding mind-body healing in medicine, the reordering of values in integrative medicine (with a primary focus on caring with humility), and the fostering of a new vision for twenty-first century frontier science, spirituality, and medicine.

Attitude↗
PubMed1998

Interleukin 18 stimulates HIV type 1 in monocytic cells.

The cytokine interleukin (IL) 18 (formerly interferon gamma-inducing factor) induces the T helper type 1 response. In the present studies, IL-18 increased HIV type 1 (HIV-1) production from 5- to 30-fold in the chronically infected U1 monocytic cell line. Inhibition of tumor necrosis factor (TNF) activity by the addition of TNF-binding protein reduced IL-18-stimulated HIV-1 production by 48%. In the same cultures, IL-18-induced IL-8 was inhibited by 96%. Also, a neutralizing anti-IL-6 mAb reduced IL-18-induced HIV-1 by 63%. Stimulation of U1 cells with IL-18 resulted in increased production of IL-6, and exogenous IL-6 added to U1 cells increased HIV-1 production 4-fold over control. A specific inhibitor of the p38 mitogen-activated protein kinase reduced IL-18-induced HIV-1 by 73%, and a 50% inhibition was observed at 0.05 microM. In the same cultures, IL-8 was inhibited by 87%. By gel-shift and supershift analyses, increased binding activity of the transcription factor NF-kappaB was measured in nuclear extracts from U1 cells 1 h after exposure to IL-18. These results demonstrate induction of HIV-1 by IL-18 in a monocyte target associated with an intermediate role for TNF and IL-6, activation of p38 mitogen-activated protein kinase, and nuclear translocation of NF-kappaB.

Base Sequence↗
PubMed1998

Role of p38 mitogen-activated protein kinase in HIV type 1 production in vitro.

The proinflammatory cytokines interleukin (IL)-1 and tumor necrosis factor (TNF) promote HIV type 1 viral replication in vitro. In the present studies, HIV production was increased in the macrophagic U1 cell line expressing the HIV genome after exposure to IL-1beta, osmotic stress, or surface adhesion, suggesting a confluence of signaling pathways for proinflammatory cytokines and cell stressors. The p38 mitogen-activated protein kinase (MAPK) mediates both cytokine and stress responses; thus the role of this kinase in HIV production was investigated. HIV production as measured by p24 antigen correlated with changes in the expression of a specific (non-alpha) isoform of p38 MAPK. In the presence of a specific p38 MAPK inhibitor (p38 inh), IL-1beta-induced HIV production was suppressed by more than 90% and IL-1beta-induced IL-8 production was suppressed completely, both with IC50 of 0.01 microM. p38 inhibition blocked cell-associated p24 antigen and secreted virus to a similar extent. The p38 inh also decreased constitutive HIV production in freshly infected peripheral blood mononuclear cells by up to 50% (P < 0.05). Interruption of p38 MAPK activity represents a viable target for inhibition of HIV.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1998

Interleukin-1beta-induced rat pancreatic islet nitric oxide synthesis requires both the p38 and extracellular signal-regulated kinase 1/2 mitogen-activated protein kinases.

Interleukin-1beta (IL-1beta) is cytotoxic to rat pancreatic beta-cells by inhibiting glucose oxidation, causing DNA damage and inducing apoptosis. Nitric oxide (NO) is a necessary but not sufficient mediator of these effects. IL-1beta induced kinase activity toward Elk-1, activation transcription factor 2, c-Jun, and heat shock protein 25 in rat islets. By Western blotting with phosphospecific antibodies and by immunocomplex kinase assay, IL-1beta was shown to activate extracellular signal-regulated kinase (ERK) 1/2 and p38 mitogen-activated protein kinase (p38) in islets and rat insulinoma cells. Specific ERK1/2 and p38 inhibitors individually reduced but in combination blocked IL-1beta-mediated islet NO synthesis, and reverse transcription-polymerase chain reaction of inducible NO synthase mRNA showed that ERK1/2 and p38 controlled IL-1beta-induced islet inducible NO synthase expression at the transcriptional level. Hyperosmolarity caused phosphorylation of Elk-1, activation transcription factor 2, and heat shock protein 25 and activation of ERK1/2 and p38 in islets comparable to that induced by IL-1beta but did not lead to NO synthesis. Inhibition of p38 but not of ERK1/2 attenuated IL-1beta-mediated inhibition of glucose-stimulated insulin release. We conclude that ERK1/2 and p38 activation is necessary but not sufficient for IL-1beta-mediated beta-cell NO synthesis and that p38 is involved in signaling of NO-independent effects of IL-1beta in beta-cells.

Animals↗
PubMed1998

A cell cycle-regulated adenine DNA methyltransferase from Caulobacter crescentus processively methylates GANTC sites on hemimethylated DNA.

The kinetic properties of an adenine DNA methyltransferase involved in cell cycle regulation of Caulobacter crescentus have been elucidated by using defined unmethylated or hemimethylated DNA (DNAHM) substrates. Catalytic efficiency is significantly enhanced with a DNAHM substrate. Biphasic kinetic behavior during methyl incorporation is observed when unmethylated or DNAHM substrates are used, indicating that a step after chemistry limits enzyme turnover and is most likely the release of enzyme from methylated DNA product. The enzyme is thermally inactivated at 30 degrees C within 20 min; this process is substantially decreased in the presence of saturating concentrations of DNAHM, suggesting that the enzyme preferentially binds DNA before S-adenosylmethionine. The activity of the enzyme shows an unusual sensitivity to salt levels, apparently dissociating more rapidly from methylated DNA product as the salt level is decreased. The enzyme acts processively during methylation of specific DNA sequences, indicating a preferred order of product release in which S-adenosylhomocysteine is released from enzyme before fully methylated DNA. The kinetic behavior and activity of the enzyme are consistent with the temporal constraints during the cell cycle-regulated methylation of newly replicated chromosomal DNA.

Caulobacter crescentus↗
PubMed1998

The crystal structure of a complement-1q family protein suggests an evolutionary link to tumor necrosis factor.

ACRP30--adipocyte complement-related protein of 30 kDa or AdipoQ--is an abundant serum protein, secreted exclusively from fat cells, which is implicated in energy homeostasis and obesity [1,2]. ACRP30 is a close homologue of the complement protein C1q, which is involved in the recognition of microbial surfaces [3-5] and antibody-antigen complexes [6,7] in the classical pathway of complement. We have determined the crystal structure of a homotrimeric fragment from ACRP30 at 2.1 A resolution. The structure reveals an unexpected homology to the tumor necrosis factor (TNF) family. Identical folding topologies, key residue conservations, and similarity of trimer interfaces and intron positions firmly establish an evolutionary link between the TNF and C1q families. We suggest that TNFs--which control many aspects of inflammation, adaptive immunity, apoptosis and energy homeostasis--arose by divergence from a primordial recognition molecule of the innate immune system. The evolutionary connection between C1q-like proteins and TNFs illuminates the shared functions of these two important groups of proteins.

Complement C1q↗
PubMed1998

Negative control of bacterial DNA replication by a cell cycle regulatory protein that binds at the chromosome origin.

Caulobacter crescentus divides asymmetrically generating two distinct cell types at each cell division: a stalked cell competent for DNA replication, and a swarmer cell that is unable to initiate DNA replication until it differentiates into a stalked cell later in the cell cycle. The CtrA protein, a member of the response regulator family of the two-component signal transduction system, controls multiple cell cycle processes in Caulobacter and is present in swarmer cells but absent from stalked cells. We report that CtrA binds five sites within the chromosome replication origin in vitro. These sites overlap an essential DnaA box and a promoter in the origin that is essential for replication initiation. Analysis of mutant alleles of ctrA and point mutations in one of the CtrA binding sites in the origin demonstrate that CtrA represses replication in vivo. CtrA-mediated repression at the origin thus restricts replication to the stalked cell type. Thus, the direct coupling of chromosome replication with the cell cycle is mediated by the ubiquitous two-component signaling proteins.

Alleles↗
PubMed1998

Structure-function analysis of cell adhesion by neural (N-) cadherin.

To investigate the possible biological function of the lateral "strand dimer" observed in crystal structures of a D1 domain extracellular fragment from N-cadherin, we have undertaken site-directed mutagenesis studies of this molecule. Mutation of most residues important in the strand dimer interface abolish the ability of N-cadherin to mediate cell adhesion. Mutation of an analogous central residue (Trp-2) in E-cadherin also abrogates the adhesive capacity of that molecule. We also determined the crystal structure of a Ca2+-complexed two-domain fragment from N-cadherin. This structure, like its E-cadherin counterpart, does not adopt the strand dimer conformation. This suggests the possibility that classical cadherins might stably exist in both dimeric and monomeric forms. Data from several laboratories imply that lateral dimerization or clustering of cadherins may increase their adhesivity. We suggest the possibility that the strand dimer may play a role in this activation.

Animals↗
PubMed1998

Sinus bradycardia and asystole during spinal and epidural anesthesia: a report of 13 cases.

STUDY OBJECTIVE: To characterize the clinical features that predispose to sinus bradycardia and cardiac arrest during spinal and epidural anesthesia. DESIGN: Retrospective clinical review. SETTING: University affiliated medical center. PATIENTS: 13 patients, aged 26 to 76 years, who suffered severe sinus bradycardia or asystole over a 5-year period, during which approximately 4,000 regional anesthetics were administered. MEASUREMENTS AND MAIN RESULTS: Case histories of 13 patients who developed severe sinus bradycardia or asystole during spinal or epidural anesthesia are summarized. Twelve cases occurred during spinal anesthesia, and the thirteenth, during epidural anesthesia. In all but one case, the acute event occurred 15 minutes or longer from the time of the anesthetic injection. Resuscitation was successful in all cases, with no postoperative sequelae. CONCLUSION: The clinical picture suggests a reflex cause, possibly associated with low right-sided cardiac filling pressure. No common precipitating cause or high-risk patient profile was noted.

Adult↗