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Biomedical subjects

W Zhong

Publications and source records attributed to W Zhong.

At least 127 records · Page 7Linked to original sources
PubMed1995

VH3-21 B cells escape from a state of tolerance in rheumatoid arthritis and secrete rheumatoid factor.

BACKGROUND: Rheumatoid factor (RF) is a characteristic but not pathognomic feature in patients with rheumatoid arthritis (RA). It is unknown whether the repertoire of immunoglobulin genes utilized by RF+ B cells of RA patients is unique and whether RF+ B cells in normal individuals are silenced or deleted. MATERIALS AND METHODS: Clonal B cell populations were established from the peripheral blood of normal donors (127 B cell clones), RA patients (113 RF- and 60 RF+ B cell clones) and patients with primary Sjögren's syndrome (82 RF- and 47 RF+ B cell clones) by coculturing with anti-CD3-stimulated T helper cell clones. The cross-reactivity pattern of antibodies secreted by the B cell clones was determined by ELISA on a panel of antigens. The molecular structure of the IgM heavy chains was characterized by VH family-specific RT-PCR and sequencing. VH elements which correlated with RF specificity were identified. The responsiveness of B cells expressing these VH elements to T helper cell signals was compared in normal individuals and RA patients. RESULTS: The majority of RF+ B cells were monospecific when specificity was tested on five antigens. RF+ B cells expressed a significantly different repertoire of VH gene segments than RF- B cells. In particular, the VH3 gene segment V3-21 was not detected in B cell clones from normals but was the most frequent VH element in RF+ B cell clones from RA patients. Most of the V3-21 sequences were in germline configuration. The correlation between RF specificity and V3-21 gene segment usage was maintained in patients with Sjögren's syndrome. V3-21 transcripts were present in peripheral blood B cells from normal individuals. VH3-21+ B cells from RA patients but not from normal donors were responsive to preactivated T helper cells. Stimulation with a bacterial superantigen could overcome the nonresponsiveness of V3-21+ B cells in normal donors and induce the secretion of RF. CONCLUSIONS: RF production is correlated with the usage of the V3-21 gene segment in two distinct RF+ diseases. In patients with these diseases, V3-21+ B cells secrete antibodies with RF activity in response to activated T helper cells. V3-21+ B cells remain in a state of nonresponsiveness in normal individuals that can be broken by superantigen stimulation. The germline configuration of VH3-21+ RF+ immunoglobulins in RA patients suggests that the loss of tolerance is not an antigen-driven process.

Antibody Specificity↗
PubMed1994

Ciliary neurotrophic factor (CNTF) enhances the effects of nerve growth factor on PC12 cells.

The rat pheochromocytoma cell line PC12 responds readily to nerve growth factor (NGF) but poorly to ciliary neurotrophic factor (CNTF). However, in a selected line derived from PC12 that normally responded weakly to NGF, CNTF potentiated the effect of NGF with respect to inhibition of proliferation, neurite outgrowth, and choline acetyltransferase (ChAT) induction. ChAT activity was assayed enzymatically, and an increase in the mRNA of ChAT was also detected by means of reverse transcription-polymerase chain reaction (RT-PCR). The PCR product was verified by sequencing and by Southern hybridization using a specific oligonucleotide probe. The presence of CNTF receptor in PC12 cells was confirmed by RT-PCR for its mRNA. The results indicate that PC12 responds to CNTF mainly when used in combination with NGF, and suggest an interaction between the two growth factors.

Adrenal Gland Neoplasms↗
PubMed1994

Sequencing of chromosome I of Saccharomyces cerevisiae: analysis of the 42 kbp SPO7-CENI-CDC15 region.

Determination of the DNA sequence and preliminary functional analysis of a 42 kbp centromeric section of chromosome I have been completed. The section spans the SPO7-CEN1-CDC15 loci and contains 19 open reading frames (ORFs). They include an apparently inactive Ty1 retrotransposon and eight new ORFs with no known homologs or function. The remaining ten genes have been previously characterized since this part of the yeast genome has been studied in an unusually intensive manner. Our directed sequencing allows a complete ordering of the region.

Chromosome Mapping↗
PubMed1994

LTE1 of Saccharomyces cerevisiae is a 1435 codon open reading frame that has sequence similarities to guanine nucleotide releasing factors.

The DNA sequence of the LTE1 gene on the left arm of chromosome I of Saccharomyces cerevisiae has been determined. The LTE1 open reading frame comprises 4305 bp that can be translated into 1435 amino acid residues. The position of this open reading frame corresponds well to that of a 4.7 kb transcript that has been mapped to this position. The derived amino acid sequence has significant similarities to the amino acid sequence of the guanine nucleotide releasing factor isolated from a rat brain library. The carboxy-terminus of the LTE1 protein also shows similarities to other guanine nucleotide exchange factors of the S. cerevisiae CDC25 family.

Amino Acid Sequence↗
PubMed1994

Tissue-specific regulation of mouse hepatocyte nuclear factor 4 expression.

Hepatocyte nuclear factor 4 (HNF-4) is a liver-enriched transcription factor and a member of the steroid hormone receptor superfamily. HNF-4 is required for the hepatoma-specific expression of HNF-1 alpha, another liver-enriched transcription factor, suggesting the early participation of HNF-4 in development. To prepare for further study of HNF-4 in development, the tissue-specific expression of the mouse HNF-4 gene was studied by analyzing the promoter region for required DNA elements. DNase-hypersensitive sites in the gene in liver and kidney tissues were found in regions both distal and proximal to the RNA start that were absent in tissues in which HNF-4 expression did not occur. By use of reporter constructs in transient-transfection assays and with transgenic mice, a region sufficient to drive liver-specific expression of HNF-4 was identified. While an HNF-1 binding site between bp -98 and -68 played an important role in the hepatoma-specific promoter activity of HNF-4 in transient-transfection assays, it was not sufficient for the liver-specific expression of a reporter gene in transgenic mice. Distal enhancer elements indicated by the presence of DNase I-hypersensitive sites at kb -5.5 and -6.5, while not functional in transient-transfection assays, were required for the correct expression of the mouse HNF-4 gene in animals.

Amino Acid Sequence↗
PubMed1993

The expression pattern of a Drosophila homolog to the mouse transcription factor HNF-4 suggests a determinative role in gut formation.

A Drosophila gene, HNF-4(D), was selected by cross-hybridization with a probe to rat HNF-4 (hepatocyte nuclear factor 4), a steroid hormone receptor super-family member that plays an important role in liver-specific gene expression. The Drosophila gene matched the mouse gene in 60 out of 66 amino acids in the zinc finger DNA binding domain and in 140 out of 206 amino acids in the domain that specifies dimerization and ligand binding. HNF-4(D) is expressed in developing Drosophila embryos in mid-gut, fat bodies and malpighian tubules, a striking similarity to its limited expression in the adult intestine, liver and kidney of the mouse. Furthermore, Drosophila mutant that has a chromosome deletion spanning the HNF-4(D) locus fails to develop tissues where HNF-4(D) is expressed during late embryogenesis. These findings together with the earlier realization that the rat hepatocyte nuclear factor 3 (HNF-3) and forkhead, a Drosophila gene required for anterior and posterior gut formation, had virtually the identical DNA binding domain, lead us to speculate that a group of genes that participate in gut formation of invertebrates has survived in evolution to perform similar functions in mammals.

Amino Acid Sequence↗
PubMed1993

Physical localization of yeast CYS3, a gene whose product resembles the rat gamma-cystathionase and Escherichia coli cystathionine gamma-synthase enzymes.

We have cloned, sequenced and physically mapped the CYS3 gene of Saccharomyces cerevisiae. This gene can complement the cys3-1 allele, and disruptions at this locus lead to cysteine auxotrophy. The predicted CYS3 product is closely related (46% identical) to the rat cystathionine gamma-lyase (Erickson et al., 1990), but differs in lacking cysteine residues. These results provide further evidence that the S288C strain of yeast resembles mammals in synthesizing cysteine solely via a trans-sulfuration pathway. The CYS3 product was found to have strong homology to three other enzymes involved in cysteine metabolism: the Escherichia coli metB and metC products and the S. cerevisiae MET25 gene product. The trans-sulfuration enzymes appear to form a diverged family and carry out related functions from bacteria to mammals.

Amino Acid Sequence↗
PubMed1993

Flock house virus: down-regulation of subgenomic RNA3 synthesis does not involve coat protein and is targeted to synthesis of its positive strand.

Flock house virus is a small insect virus with a bipartite RNA genome consisting of RNA1 and RNA2. RNA3 is a subgenomic element encoded by RNA1, the genomic segment required for viral RNA synthesis (T. M. Gallagher, P. D. Friesen, and R. R. Rueckert, J. Virol. 46:481-489, 1983). Synthesis of RNA3 is strongly inhibited by RNA2, the gene for viral coat protein. Evidence that coat protein is not the regulatory element was obtained by using a defective interfering RNA2 which was messenger inactive. It was also found that RNA2 selectively down-regulated synthesis of positive-strand RNA3 but not of its complementary negative strand. cDNA-generated RNA2 transcripts, carrying four extra nonviral bases at the 3' end, failed to repress synthesis of RNA3 but recovered this activity after a single passage in Drosophila cells in the presence of RNA1, suggesting that down-regulation of RNA3 synthesis is controlled by competition with RNA2 for viral replicase.

Animals↗
PubMed1993

Sequencing of chromosome I from Saccharomyces cerevisiae: analysis of a 32 kb region between the LTE1 and SPO7 genes.

The DNA sequencing and preliminary functional analysis of a 32 kb section of yeast chromosome I has been completed. This region lies on the left arm of the chromosome between the LTE1 and SPO7 genes and contains 14 open reading frames (ORFs) positioned closely together, with an average spacing of approximately 350 nucleotides between coding regions. Three of these ORFs correspond to previously identified genes, a further three show significant homology with other proteins, while the remaining eight ORFs share no significant homology to genes in the databases.

Amino Acid Sequence↗
PubMed1992

Evidence that the packaging signal for nodaviral RNA2 is a bulged stem-loop.

Flock house virus is an insect virus belonging to the family Nodaviridae; members of this family are characterized by a small bipartite positive-stranded RNA genome. The larger genomic segment, RNA1, encodes viral replication proteins, whereas the smaller one, RNA2, encodes coat protein. Both RNAs are packaged in a single particle. A defective-interfering RNA (DI-634), isolated from a line of Drosophila cells persistently infected with Flock house virus, was used to show that a 32-base region of RNA2 (bases 186-217) is required for packaging into virions. RNA folding analysis predicted that this region forms a stem-loop structure with a 5-base loop and a 13-base-pair bulged stem.

Base Sequence↗
PubMed1992

Murine chromosomal location of four hepatocyte-enriched transcription factors: HNF-3 alpha, HNF-3 beta, HNF-3 gamma, and HNF-4.

The genes for rat hepatocyte nuclear factors 3 and 4 (HNF-3 alpha, HNF-3 beta, HNF-3 gamma, and HNF-4) have been mapped in mouse by analysis of restriction fragment length polymorphisms in interspecific backcross mice. These hepatocyte-enriched transcription factors are positive-acting transcription factors with binding sites in regulatory regions of many genes expressed in hepatocytes. Both HNF-3 alpha, beta, and gamma and HNF-4 are also expressed in intestine. They have recently been implicated as potential participants in endodermal development from early gut cells because of their close homology to Drosophila genes, which themselves are expressed in the developing gut. Despite having similar functional roles and highly conserved DNA binding domains, the three loci from the Hnf-3 family of genes mapped to three different mouse chromosomes, suggesting that the Hnf-3 family has become widely dispersed during evolution and implying the necessity for independent activation of each member of the HNF-3 family.

Animals↗
PubMed1992

Maturation cleavage required for infectivity of a nodavirus.

Nodaviral morphogenesis involves formation of labile precursor particles, called provirions, which mature by autocatalytic cleavage of the 407-residue coat precursor protein between asparagine residue 363 and alanine residue 364. It has previously been demonstrated that maturation results in increased physicochemical stability of the virion. We show here that cleavage of coat protein in purified provirions of Flock House virus was accompanied by a five- to eightfold increase in specific infectivity. Cleavage-negative provirions, produced by site-directed mutagenesis of asparagine residue 363 to aspartate, threonine, or alanine, displayed no infectivity above revertant frequencies as measured by plaque assay. All viable revertants (nine of nine) restored asparagine to the mutated position, suggesting high specificity for asparagine at the cleavage site.

Animals↗