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PubMed1977

Effect of leukocyte hydrolases on bacteria. X. The role played by leukocyte factors, cationic polyelectrolytes, and by membrane-damaging agents in the lysis of Staphylococcus aureus: relation to chronic inflammatory processes.

A heat-stable factor present in extracts of human blood leukocytes is capable of lysing young Staphylococcus aureus at pH 5.0. Lysis is characterized by breakdown of cell-wall components as judged by electron microscopic and biochemical analysis. The leukocyte extracts can be replaced by a variety of agents known to injure cell membranes, e.g., leukocyte cationic protein histone, polymyxin B, colimycin, phospholipase A, and lysolecithin. The mechanisms by which all these agents bring about the degradation of the staphylococcal walls was studied. By using 14C-labeled cell walls devoid of cytoplasmic structures, it was demonstrated that none of the above-mentioned agents had a direct lytic effect on purified cell walls. On the other hand, when any of these agents first interacted with intact staphylococci, a factor (presumably an autolysin) was generated that directly lysed the cell walls. Lysis of cell walls in the presence of intact staphylococci used as a source of autolysin was strongly inhibited by a variety of anionic polyelectrolytes such as heparine and liquoid. The possible role played by bacterial autolysins in the generation of microbial cell-wall components capable of triggering chronic inflammation is discussed.

Bacteriolysis↗

PubMed2002

From single extracellular unit recording in experimental and human Parkinsonism to the development of a functional concept of the role played by the basal ganglia in motor control.

Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects the whole basal ganglia (BG). Various techniques have been used to study BG physiology and pathophysiology. Among these, extracellular single unit recording remains of particular importance. An impressive number of studies of BG electrophysiological activity have been carried out, both in non-human and in human primates, but the data collected show many omissions and disparities. BG activity has been well defined in the physiological situation, but remains far from clear in the Parkinsonian and virtually unexplored in the dopamine (DA)-replacement situation. This paper provides a brief synopsis of (i) recording techniques and (ii) BG electrophysiological activity in normal, Parkinsonian, and dopamine-replacement situations. We have restricted the data used to those obtained in BG structures of human and non-human primates. Only single unit recordings have been reported and four electrophysiological characteristics retained: mean firing frequency, firing pattern, periodic oscillation, and response to both passive and active movement. We have attempted to summarize (i) the commonly accepted characteristics of each BG structure in the three situations, (ii) discrepancies that exist, and (iii) missing elements. Then, the main successive theories aimed to explain the role played by BG in motor control are presented and discussed in the light of the most recently obtained results using the latest technological advances.

Animals↗

PubMed2005

Plexin-a4 mediates axon-repulsive activities of both secreted and transmembrane semaphorins and plays roles in nerve fiber guidance.

It has been proposed that four members of the plexin A subfamily (plexin-As; plexin-A1, -A2, -A3, and -A4) and two neuropilins (neuropilin-1 and neuropilin-2) form complexes and serve as receptors for class 3 secreted semaphorins (Semas), potent neural chemorepellents. The roles of given plexin-As in semaphorin signaling and axon guidance, however, are mostly unknown. Here, to elucidate functions of plexin-A4 in semaphorin signaling and axon guidance events in vivo, we generated plexin-A4 null mutant mice by targeted disruption of the plexin-A4 gene. Plexin-A4 mutant mice were defective in the trajectory and projection of peripheral sensory axons and sympathetic ganglion (SG) axons and the formation of the anterior commissure and the barrels. The defects in peripheral sensory and SG axons were fundamentally related to those of neuropilin-1 or Sema3A mutant embryos reported but were more moderate than the phenotype in these mutants. The growth cone collapse assay showed that dorsal root ganglion axons and SG axons of plexin-A4 mutant embryos partially lost their responsiveness to Sema3A. These results suggest that plexin-A4 plays roles in the propagation of Sema3A activities and regulation of axon guidance and that other members of the plexin-A subfamily are also involved in the propagation of Sema3A activities. Plexin-A4-deficient SG axons did not lose their responsiveness to Sema3F, suggesting that plexin-A4 serves as a Sema3A-specific receptor, at least in SG axons. In addition, the present study showed that plexin-A4 bound class 6 transmembrane semaphorins, Sema6A and Sema6B, and mediated their axon-repulsive activities, independently of neuropilin-1. Our results imply that plexin-A4 mediates multiple semaphorin signals and regulates axon guidance in vivo.

Animals↗

PubMed1998

Mechanisms of fatigue-induced activation of group IV muscle afferents: the roles played by lactic acid and inflammatory mediators.

We already showed that group IV muscle afferents are activated during electrically-induced fatigue. The purpose of this study is to identify the mechanisms of stimulation of these muscle afferents by electrically-induced fatigue at a high (100 Hz; high frequency fatigue, HFF) or a low rate (10 Hz; low frequency fatigue, LFF) of stimulation. In 23 paralyzed and anaesthetized rabbits, group IV afferent activity from the tibialis anterior muscle was recorded before and after 3-min HFF or 5-min LFF runs eliciting the same force failure. Plasma lactic acid concentration (LA) was also measured in leg venous blood. We tested the effects of dichloroacetate (DCA), which reduces lactic acid production, and of acetylsalicylic acid (ASA), a blocker of cyclooxygenase, on fatigue-induced activation of group IV muscle afferents after HFF and LFF trials. Pretreatment by ASA or DCA did not modify HFF-induced activation of muscle afferents. On the other hand, LFF-induced response was markedly depressed by each pharmacological agent (-44% after ASA and -75% after DCA). We verified that DCA markedly lowered LA production after LFF. The present results show that the activation of group IV muscle afferents by LFF or HFF results from different mechanisms and also demonstrate the major role played by lactic acid production and, to a lesser extent, the release of inflammatory mediators in LFF-induced activation of group IV muscle afferents.

Animals↗

PubMed2004

HMGN proteins play roles in DNA repair and gene expression in mammalian cells.

HMGN (high-mobility-group N) family members are vertebrate proteins that unfold chromatin and promote transcription and replication of chromatin templates in vitro. However, their precise roles in vivo have been elusive until recently. This paper summarizes recent advances from studies of Hmgn1 knockout mice and genetically engineered cell lines that are beginning to reveal the diverse roles that HMGN proteins play in DNA repair and transcription within mammalian cells.

Animals↗

PubMed1980

Role-playing with Paddy.

Explore the source record for details and available documents.

Child, Preschool↗

PubMed1993

Regulation of AP-1 expression and activity in antigen-stimulated mast cells: the role played by protein kinase C and the possible involvement of Fos interacting protein.

We have recently observed that protein kinase C (PKC) was involved in the regulation of the accumulation of mRNAs of the AP-1 components in cultured Abelson-transformed murine fetal-liver-derived mast cells stimulated by exocytotic stimuli. Here we analyzed the probable regulatory effect of PKC on the synthesis and DNA-binding activity of AP-1 complexes in immunologic stimulated mast cells. In this study we used the interleukin-3--dependent murine fetal-liver--derived mast cells that were not transformed by the Abelson oncogene. Study of PKC-depleted cells showed PKC dependency of c-fos mRNA accumulation and protein expression in IgE-Ag stimulated cells. In contrast, the c-jun mRNA accumulation was unaffected by PKC depletion, whereas its protein expression was dependent on this enzymatic activity. This suggests the involvement of PKC in the regulation of translation of c-Jun, a level of c-Jun regulation that was not previously described. The amount of AP-1 DNA-bound complex was also lowered in PKC-depleted cells. Therefore, PKC plays an important regulatory role in different stages of the signal transduction pathway because of IgE-Ag stimulation. Surprisingly, we have observed that although the amount of total synthesized c-Fos began to increase 15 minutes after immunologic stimulation, the amount of c-Fos associated with Juns did not increase, even after 45 minutes. This association was not affected by PKC. Using a Fos-interacting protein (FIP)-cDNA probe, an expression of 2.9 kb mRNA was detected in these cells. Furthermore, immunologic stimulation caused an increase in the amount of a Fos-containing protein complex that bound to an FIP-binding DNA oligonucleotide. Therefore, we propose that this protein complex that contains most of the immunologically induced c-Fos has an important role in IgE-Ag-stimulated signal transduction.

Animals↗

PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗

PubMed2002

Comparison of the catalytic roles played by the KMSKS motif in the human and Bacillus stearothermophilus trosyl-tRNA synthetases.

The Class I aminoacyl-tRNA synthetases are characterized by two signature sequence motifs, "HIGH" and "KMSKS." In Bacillus stearothermophilus tyrosyl-tRNA synthetase, the KMSKS motif (230KFGKT234) has been shown to stabilize the transition state for tyrosine activation through interactions with the pyrophosphate moiety of ATP. In most eukaryotic tyrosyl-tRNA synthetases, the second lysine in the KMSKS motif is replaced by a serine or an alanine residue. Recent kinetic studies indicate that potassium functionally compensates for the absence of the second lysine in the human tyrosyl-tRNA synthetase (222KKSSS226). In this paper, site-directed mutagenesis and pre-steady state kinetics are used to determine the roles that serines 224, 225, and 226 play in catalysis of the tyrosine activation reaction. In addition, the catalytic role played by a downstream lysine conserved in eukaryotic tyrosyl-tRNA synthetases, Lys-231, is investigated. Replacing Ser-224 and Ser-226 with alanine decreases the forward rate constant 7.5- and 60-fold, respectively. In contrast, replacing either Ser-225 or Lys-231 with alanine has no effect on the catalytic activity of the enzyme. These results are consistent with the hypothesis that the KMSSS sequence in human tyrosyl-tRNA synthetase stabilizes the transition state for the tyrosine activation reaction by interacting with the pyrophosphate moiety of ATP. In addition, although they play similar roles in catalysis, the overall contribution of the KMSKS motif to catalysis appears to be significantly less in human tyrosyl-tRNA synthetase than it is in the B. stearothermophilus enzyme.

Adenosine Triphosphate↗

PubMed1957