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Z Li

Publications and source records attributed to Z Li.

At least 1,225 records · Page 68Linked to original sources
PubMed1996

A 28-bp negative element with multiple factor-binding activity controls expression of the vimentin-encoding gene.

The promoter of the human vimentin-encoding gene (VIM) contains two enhancers separated by a negative region. The distal and proximal enhancers bind the transcription factors, AP-1 and NK-kappaB, respectively, which contribute to serum induction of Vim synthesis. We were interested in looking for particular regulatory elements that might be responsible for tissue-specific extinction and culture-dependent activation of human VIM. We have identified a 48-bp sequence in the distal enhancer which had not been reported before. This sequence includes a negative element, NE2, which confers transcriptional repression in transfection experiments and binds at least two factors in vitro. NE2 may participate in the differentiation-stage-specific control of VIM expression which involves multiple regulatory sequences and several positive and negative trans-acting factors.

Base Composition↗
PubMed1996

Characterization of the structure and function of a novel MAP kinase kinase (MKK6).

Mitogen-activated protein (MAP) kinases require dual phosphorylation on threonine and tyrosine residues in order to gain enzymatic activity. This activation is carried out by a family of enzymes known as MAP kinase kinases (MKKs or MEKs). It appears that there are at least four subgroups in this family; MEK1/MEK2 subgroup that activates ERK1/ERK2, MEK5 that activates ERK5/BMK1, MKK3 that activates p38, and MKK4 that activates p38 and Jun kinase. Here we describe the characteristics of a new MKK termed MKK6. The clones we isolated encode two splice isoforms of human MKK6 comprised of 278 and 334 amino acids, respectively, and one murine MKK6 with 237 amino acids. Sequence information derived from cDNA cloning indicated that MKK6 is most closely related to MKK3. The functional data revealed from co-transfection assays suggests that MKK6, like MKK3, selectively phosphorylates p38. Unlike the previously described MKKs (or MEKs), MKK6 exists in a variety of alternatively spliced isoforms with distinct patterns of tissue expression. This suggests novel mechanisms regulating activation and/or function of various forms of MKK6.

Amino Acid Sequence↗
PubMed1996

The role of individual cysteine residues in the activity of Escherichia coli RNase T.

Escherichia coli RNase T, which is responsible for the 3' processing and end-turnover of tRNA and the maturation of 5 S RNA, is extremely sensitive to sulfhydryl reagents and to oxidation, suggesting a role for cysteine residues in its activity. Titration of homogeneous RNase T with 5,5'-dithiobis-(2-nitrobenzoic acid) revealed that the 4 cysteine residues present in each of the two protein subunits are in a reduced form and that 1 or 2 of them are important for activity. To identify these residue(s), each of the cysteines in RNase T was changed individually to either serine or alanine. The serine mutant at position 168 is greatly reduced in RNase T activity both in vivo and in vitro; likewise, the serine mutant at position 112 and the alanine mutants at positions 112 and 168 also display decreased RNase T activity. Mutations at the other cysteine positions show little or no change. Kinetic analyses of the mutant enzymes showed that the Km values of C168S and C168A are increased considerably, whereas their Vmax values are reduced only slightly compared to the wild type enzyme. The other mutant enzymes are little changed. Additional amino acid replacements at position 168 showed that the in vivo and in vitro activities of RNase T are in the order Cys approximately Val > Ala >> Ser >> Asn approximately Asp, which closely follows the relative hydrophobicity of these amino acid residues. However, the affinity for tRNA, determined by fluorescence quenching, is not altered in C168S, suggesting that Cys-168 is not directly involved in substrate binding. Interestingly, proteins altered at position 168 showed increased temperature sensitivity as the residue at that position became less hydrophobic. These data indicate that Cys-168 contributes a hydrophobic group that influences the structure and ultimately the catalytic activity of RNase T.

Base Sequence↗
PubMed1996

Escherichia coli RNase T functions in vivo as a dimer dependent on cysteine 168.

It was shown that Cys-168 is required for RNase T function and thermostability and that its hydrophobic properties are important for this role (Li, Z., Zhan, L., and Deutscher, M. P. (1996) J. Biol Chem. 271, 1127-1132). To understand the molecular basis for these findings, further studies of Cys-168 and RNase T structure were carried out. Treatment of RNase T with the sulfhydryl-modifying agent 5,5'-dithiobis-(2-nitrobenzoic acid) leads not only to inactivation, but also to monomerization of the protein. Similarly, specifically converting Cys-168 to either serine or asparagine leads to loss of activity and to monomer formation at 37 degrees C. However, at 10 degrees C the serine mutant remains as a dimer and retains full RNase T activity, whereas the asparagine derivative shows only a low level of activity and of dimer formation. These data show a strong correlation between activity and the dimer form of RNase T. The importance of dimer formation was also shown in vivo using genetic studies. An inactive mutant of RNase T, termed HA2, which exists as a dimer at 37 degrees C in vitro, completely suppresses endogenous RNase T activity in vivo and in vitro when introduced into a RNase T+ cell on a multicopy phagemid, most likely as a consequence of inactive heterodimer formation. Introduction of the HA2 gene on a single-copy plasmid, as expected, leads to a proportionally smaller effect on endogenous activity. The dominant negative effect displayed by the HA2 protein can be relieved by an additional mutation in HA2 RNase T that abolishes its ability to dimerize. An inactive mutant asparagine derivative of Cys-168, which also does not dimerize, also shows little of the dominant negative phenotype. Thus, these data demonstrate that RNase T dimerizes in vivo, that the dimer form is required for RNase T activity, and that Cys-168 is needed for dimerization of the enzyme.

Cysteine↗
PubMed1996

Relationships between intermediate filaments and cell-specific functions in renal cell lines derived from transgenic mice harboring the temperature-sensitive T antigen.

Four renal cell lines were derived from glomeruli, proximal, distal, and cortical collecting tubules microdissected from the kidneys of transgenic mice carrying the temperature-sensitive mutant of the simian virus 40 large T antigen under the control of the vimentin promoter. All four cell lines contained large T antigen in their nuclei, grew rapidly, and contained vimentin filaments when grown in serum-enriched medium at the permissive temperature of 33 degrees C. The glomerular cell line formed multiple layers of cells and contained smooth muscle actin and desmin filaments, features of mesangial cells. The three tubule cell lines formed monolayers of polarized cuboid cells separated by tight junctions and having a patchy distribution of cytokeratins K8-K18. A shift from 33 degrees C to the restrictive temperature (39.5 degrees C) stopped cell growth in all cell lines and caused profound changes in the content of intermediate filaments. Vimentin was still present in mesangial-like cells, but the proximal, distal, and collecting tubule cells contained uniform networks of cytokeratins K8-K18 and desmoplakin I and II around the cell peripheries. Potassium transport, mediated by Na+-K+ ATPase pumps and specific cAMP hormonal sensitivities, significantly increased in proximal, distal, and collecting tubule cells when shifted from 33 degrees C to 39.5 degrees C. Thus, the temperature-dependent inactivation of large T antigen, responsible for the arrest of cell growth, did not affect the phenotype of mesangial-like glomerular cells but induced some changes in the expression of intermediate filaments and restored, at least partially, the main parental cell-specific functions in proximal, distal, and collecting tubule cultured cells.

Animals↗
PubMed1996

Random effects model for meta-analysis of multiple quantitative sibpair linkage studies.

The growing interest in detection of genetic effects for complex traits along with molecular revolution has stimulated many linkage studies. Multiple replication studies tend to produce different results. In such situations, rigorous meta-analysis methods can be useful for assessing the overall evidence for linkage. We propose here a random effects model for combining results from independent quantitative sibpair linkage studies. The model can be used to assess the aggregate evidence for linkage by combing the regression coefficients to the Haseman and Elston [(1972) Behav Genet 2:3-19] sibpair method as well as to assess heterogeneity among the multiple studies.

Genetic Linkage↗
PubMed1996

Insights into the local residual entropy of proteins provided by NMR relaxation.

A simple model is used to illustrate the relationship between the dynamics measured by NMR relaxation methods and the local residual entropy of proteins. The expected local dynamic behavior of well-packed extended amino acid side chains are described by employing a one-dimensional vibrator that encapsulates both the spatial and temporal character of the motion. This model is then related to entropy and to the generalized order parameter of the popular "model-free" treatment often used in the analysis of NMR relaxation data. Simulations indicate that order parameters observed for the methyl symmetry axes in, for example, human ubiquitin correspond to significant local entropies. These observations have obvious significance for the issue of the physical basis of protein structure, dynamics, and stability.

Entropy↗
PubMed1996

Neuromodulatory actions of dopamine on synaptically-evoked neostriatal responses in slices.

The present experiments were designed to further examine the hypothesis that receptor subtype determines the direction of dopamine's (DA) ability to modulate neostriatal neuronal responses. We have reported that DA potentiates responses mediated by activation of N-methyl-d-aspartate (NMDA) receptors, but attenuates responses mediated by activation of non-NMDA receptors in neocortex [Cepeda et al. (1992b) Synapse, 11:330-341] and neostriatum [Cepeda et al. (1993) Proc. Natl. Acad. Sci. U.S.A., 90:9576-9580]. In these studies, responses to excitatory amino acids (EAAs) were evoked by microphoretic application of agonists. The present studies examined whether this differential modulation also applies to components of synaptic responses evoked by electrical stimulation of neostriatal afferents and mediated by activation of specific subtypes of EAA receptors. Using brain slices, the actions of DA and its receptor specific agonists on components of neostriatal synaptic responses that were mediated either by NMDA or non-NMDA receptors were assessed. Responses mediated by NMDA receptors were potentiated by DA while those mediated by non-NMDA receptors were attenuated. These findings provide further support for the hypothesis that the direction of modulatory action of DA is determined by the specific subtype of EAA receptor activated. In addition, the enhancement of NMDA receptor-mediated responses was mimicked by application of SKF 38393, a D1 receptor agonist. Quinpirole, a D2 receptor agonist, consistently attenuated responses mediated by activation of non-NMDA receptors. Thus, the complex modulatory actions of DA are dependent upon combinations of co-activation of specific subtypes of EAA and DA receptors. These findings are of clinical relevance since the actions of DA and EAAs have been implicated in neurological and affective disorders.

Animals↗
PubMed1996

Association of murine splenocyte CD3 complex to the cytoskeleton: absence of modulation by exogenous fatty acids.

The cytoplasmic regions of the CD3 complex are presumably involved in signal transduction following ligand-receptor binding. We investigated the effects of incubating either stearic or oleic acid on the association of murine lymphocyte CD3 complex with the cytoskeleton. Both cytochalasin D, an inhibitor of microfilament formation, and W7, an inhibitor of calmodulin, inhibited capping of CD3. The association of CD3 with the cytoskeleton was confirmed by confocal laser scanning microscopy studies, which showed co-localization of the cross-linked CD3 receptors and the membrane attachment proteins ankyrin and fodrin. Although exogenous oleic acid increased plasma membrane fluidity, neither expression nor capping of CD3 receptors was increased. Nonetheless, oleic acid did increase uptake of tritiated thymidine after binding of anti-CD3 antibodies. Lymphoproliferation was progressively inhibited by both cytochalasin D and W7, confirming the importance of intact cytoskeleton for cellular activation.

Animals↗
PubMed1996

Role of calpain in spinal cord injury: increased calpain immunoreactivity in rat spinal cord after impact trauma.

Impact spinal cord injury (20 g-cm) was induced in rat by weight drop. The immunoreactivity of mcalpain was examined in the lesion and adjacent areas of the cord following trauma. Increased calpain immunoreactivity was evident in the lesion compared to control and the immunostaining intensity progressively increased after injury. The calpain immunoreactivity was also increased increased in tissue adjacent to the lesion. mCalpain immunoreactivity was significantly stronger in glial and endothelial cells, motor neurons and nerve fibers in the lesion. The calpain immunoreactivity also increased in astrocytes and microglial cells in the adjacent areas. Proliferation of microglia and astrocytes identified by GSA histochemical staining and GFAP immunostaining, respectively, was seen at one and three days after injury. Many motor neurons in the ventral horn showed increased calpain immunoreactivity and were shrunken in the lesion. These studies indicate a pivotal role for calpain and the involvement of glial cells in the tissue destruction in spinal cord injury.

Animals↗
PubMed1996

The value of perioperative echocardiography in percutaneous balloon mitral valvuloplasty.

In order to investigate the value of perioperative echocardiography in percutaneous balloon mitral valvuloplasty (PBMV), two-dimensional echocardiography (2-DE), Doppler echocardiography and color Doppler flow imaging (CDFI) were employed prior to PBMV in 52 patients and during or after PBMV in 15 patients. The results showed that TTE and TEE were helpful in the selection of candidates for 2-DE transseptal and balloon dilation procedures. Continuous monitoring of 2-DE, Doppler echocardiography and CDFI during PBMV could make this procedure safer and more effective, reduce X-ray exposure and avoid complications. Echocardiography was useful in fluoroscopy and could be used for evaluation of the effects of operation.

Adult↗
PubMed1996

Human desmin gene: cDNA sequence, regional localization and exclusion of the locus in a familial desmin-related myopathy.

Desmin is a muscle-specific intermediate filament that is encoded by a gene assigned to human chromosome 2q35. Desmin-related myopathies are inherited disorders characterized by an intrasarcoplasmic accumulation of desmin. Recently, the knockout of the desmin gene was shown to generate a myopathic syndrome in transgenic mice, suggesting that functional abnormality of desmin may generate similar clinical symptoms in mouse and human. To determine the potential role of the desmin gene in a well-defined desmin-related myopathy (autosomal dominant form of Fardeau), human desmin cDNAs obtained from affected and unaffected individuals were cloned, sequenced and compared. No obvious mutation was detected. A BssHII restriction fragment length polymorphism (RFLP) was identified in exon 6 of the desmin gene. This RFLP was associated with a previously identified EcoRV RFLP in exon 4 to generate a tetra-allelic system, which was tested for linkage to the desmin-related myopathy in three families. The human desmin gene was localized within an 11-cM interval on chromosome 2q using a panel of radiation hybrids. This 11-cM region was clearly excluded by linkage analysis in the three desmin-related myopathy families using a set of highly polymorphic microsatellite markers. These results suggest that the desmin gene is not primarily involved in this disease.

Alternative Splicing↗
PubMed1996

Hemodynamic effects of different pacing ratios in chronic dynamic double cardiomyoplasty.

BACKGROUND: Dynamic cardiomyoplasty is being used clinically worldwide, and evaluated by a clinical trial (phase III) in the United States. Some centers stimulate the skeletal muscle wrap with every heart beat (1:1 [muscle:heart]), whereas others use every other heart beat (1:2). Recent concern over the possible deleterious effects of too-frequent stimulation of the muscles motivated the attempt to evaluate, in a canine model of chronic, double cardiomyoplasty, the effects of two different pacing ratios on several hemodynamic parameters of interest. METHODS: Double cardiomyoplasty was performed using both latissimus dorsi muscles in 11 dogs. Fatigue resistance was achieved using the clinical transformation protocol. At a final experiment, acute cardiac failure was induced by administration of propranolol. Hemodynamic measurements of eight physiologic variables were averaged over complete pacing cycles, including the nonpaced beat at a 1:2 pacing ratio. RESULTS: The net effects of latissimus dorsi muscle stimulation at each of two pacing ratios were compared using nonparametric statistics. With the exception of left ventricular pressure (p = 0.0262) and its first derivative, dP/dt (p = 0.0099), there was no significant difference between hemodynamic performance at the two pacing ratios. CONCLUSIONS: In this canine model, pacing every other beat produces hemodynamic results that are statistically similar to pacing every beat. Less frequent stimulation of the latissimus dorsi muscle may preserve its function and improve clinical results without compromising hemodynamic benefit.

Acute Disease↗
PubMed1996

Modulation of acetylcholine receptor function in TE671 (rhabdomyosarcoma) cells by non-AChR ligands: possible relevance to seronegative myasthenia gravis.

The acetylcholine receptor (AChR) is the main target antigen in myasthenia gravis (MG), but about 15% of patients with typical immunologically mediated MG do not have detectable anti-AChR antibodies. Previous studies showed that plasma from these 'seronegative' patients (SNMG) reduced AChR function in the human AChR-expressing TE671 cell line, and it was proposed that SNMG plasmas may act indirectly via phosphorylation of AChR. We show here that substances such as the beta 2-adrenergic agonist, salbutamol, calcitonin-gene-related-peptide (CGRP), and cholera toxin, that increase intracellular cAMP via binding to specific cell-surface receptors, reduced AChR function in TE671 cells. Moreover, non-specific activation of cell surface proteins by lectins achieved similar results. These observations lead us to hypothesise that SNMG immunoglobulins act in TE671 cells by cross-linking of specific cell surface antigen(s) resulting in generation of intracellular cAMP and/or other second messengers. The role of such antibodies at the neuromuscular junction in vivo could be reduction in AChR function by desensitization and/or damage to the postsynaptic membrane following complement activation.

Adrenergic beta-Agonists↗
PubMed1996

Pneumonia in cats caused by Pneumocystis carinii purified from mouse lungs.

Fourteen mice trapped in or near houses were infected with Pneumocystis carinii and the establishment of pneumonia was helped by injecting with cortisone acetate for 6 weeks. Then 16 cats were infected with P. carinii by injection of lung homogenate from the mice which contained from 1.3 x 10(5) to 2.6 x 10(5) P. carinii cysts. The infection resulted in severe cough and tachypnea in Cats 1-8 injected with cortisone acetate, and a subclinical infection in Cats 9-16. In Cats 1-8, the main pathological finding was typical P. carinii pneumonia, but there only was slight swelling of the lungs in Cats 9-16.

Animals↗