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S Chen

Publications and source records attributed to S Chen.

At least 847 records · Page 47Linked to original sources
PubMed1997

p53-dependent response in UV-induced transformation.

Cells carrying different numbers of copies of wild-type p53 were transformed by UV irradiation. Putative dense foci were analyzed for their growth behavior in low serum and for anchorage-independence. A correlation was found between number of copies of wild-type p53 gene and transformation frequency: cells with more copies of p53 gene were more resistant to transformation by UV. The p53 in the transformed clones was shown to be wild-type at the protein level. A single DNA base change was detected between GenBank data and our normal and transformed cells; this pre-existing single base difference is probably due to the differences between the strains of mice from which the cells were derived.

Animals↗
PubMed1997

Genotypic variation in drought tolerance of poplar in relation to abscisic acid.

We investigated effects of water stress and external abscisic acid (ABA) supply on shoot growth, stomatal conductance and water status in 1-year-old cuttings of a drought-sensitive poplar genotype Populus x euramericana cv. I-214 (Italica) and a drought-tolerant genotype P. 'popularis 35-44' (popularis). Populus popularis was more productive and maintained higher leaf water potentials throughout the drought treatment than cv. Italica. Supply of ABA to the xylem sap caused a greater decline in growth and more leaf abscission in shoots of cv. Italica than in shoots of P. popularis. Immediately after initiation of the drought treatment in P. popularis, the ABA concentration ([ABA]) of the xylem increased rapidly and stomatal conductance declined; however, stomatal conductance had returned to control values by the third day of the drought treatment, coincident with a gradual decline in xylem [ABA]. In contrast, xylem [ABA] of cv. Italica initially increased more slowly than that of P. popularis in response to the drought treatment, but the increase continued for 3 days at which time a tenfold increase in xylem [ABA] was observed that was followed by abscission of more than 40% of the leaves. We conclude that sensitivity of poplar roots to variation in soil water content varies by clone and that a rapid short-term accumulation of ABA in shoots in response to water stress may contribute to drought tolerance.

Journal Article↗
PubMed1997

Photodynamic treatment of red blood cell concentrates for virus inactivation enhances red blood cell aggregation: protection with antioxidants.

Photodynamic treatment (PDT) using phthalocyanines and red light appears to be a promising procedure for decontamination of red blood cell (RBC) concentrates for transfusion. A possible complication of this treatment may be induced aggregation of RBC. The production of RBC aggregates was measured with a novel computerized cell flow properties analyzer (CFA). The PDT of RBC concentrates with sulfonated aluminum phthalocyanine (AIPcS4) and the silicon phthalocyanine Pc 4 under virucidal conditions markedly enhanced RBC aggregation and higher shear stress was required to disperse these aggregates. The clusters of cells were huge and abnormally shaped, unlike the rouleaux formed by untreated RBC. This aggregation was prevented when a mixture of antioxidants was included during PDT. Addition of the antioxidants after PDT reduced aggregation only partially. It is concluded that inclusion of antioxidants during PDT of RBC concentrates prior to transfusion may reduce or eliminate the hemodynamic risk that the virucidal treatment may present to the recipient.

Antioxidants↗
PubMed1997

Construction and characterization of Escherichia coli genetically engineered for bioremediation of Hg(2+)-contaminated environments.

Escherichia coli strains were genetically engineered to express an Hg2+ transport system and metallothionein. Overexpression of a glutathione S-transferase fusion protein of Saccharomyces cerevisiae or pea metallothionein significantly increased the bioaccumulation of Hg2+ transported by MerT and MerP and protected the cells from the accumulated Hg2+. The recombinant strains have excellent properties for bioremediation of Hg(2+)-contaminated environments.

Bacterial Proteins↗
PubMed1997

Molecular characterization of murine humoral immune response to botulinum neurotoxin type A binding domain as assessed by using phage antibody libraries.

To produce antibodies capable of neutralizing botulinum neurotoxin type A (BoNT/A), the murine humoral immune response to BoNT/A binding domain (H(C)) was characterized at the molecular level by using phage antibody libraries. Mice were immunized with BoNT/A H(C), the spleens were harvested, and single-chain Fv (scFv) phage antibody libraries were constructed from the immunoglobulin heavy and light chain variable region genes. Phage expressing BoNT/A binding scFv were isolated by selection on immobilized BoNT/A and BoNT/A H(C). Twenty-eight unique BoNT/A H(C) binding scFv were identified by enzyme-linked immunosorbent assay and DNA sequencing. Epitope mapping using surface plasmon resonance in a BIAcore revealed that the 28 scFv bound to only 4 nonoverlapping epitopes with equilibrium constants (Kd) ranging from 7.3 x 10(-8) to 1.1 x 10(-9) M. In a mouse hemidiaphragm assay, scFv binding epitopes 1 and 2 significantly prolonged the time to neuroparalysis, 1.5- and 2.7-fold, respectively, compared to toxin control. scFv binding to epitopes 3 and 4 showed no protection against neuroparalysis. A combination of scFv binding epitopes 1 and 2 had an additive effect on time to neuroparalysis, which increased to 3.9-fold compared to the control. The results suggest that there are two "productive" receptor binding sites on H(C) which lead to toxin internalization and toxicity. Blockade of these two epitopes with monoclonal antibodies may provide effective immunoprophylaxis or therapy against BoNT/A intoxication.

Amino Acid Sequence↗
PubMed1997

Role of NifS in maturation of glutamine phosphoribosylpyrophosphate amidotransferase.

Glutamine phosphoribosylpyrophosphate amidotransferase from Bacillus subtilis is synthesized as an inactive precursor that requires two maturation steps: incorporation of a [4Fe-4S] center and cleavage of an 11-residue NH2-terminal propeptide. Overproduction from a multicopy plasmid in Escherichia coli leads to the formation of soluble proenzyme and mature enzyme forms as well as a small fraction of insoluble proenzyme. Heterologous expression of Azotobacter vinelandii nifS from a compatible plasmid increased the maturation of the soluble proenzyme three- to fourfold without influencing the content of the insoluble fraction. These results support a role for NifS in heterologous Fe-S cluster assembly and enzyme maturation.

Amidophosphoribosyltransferase↗
PubMed1997

The Myc negative autoregulation mechanism requires Myc-Max association and involves the c-myc P2 minimal promoter.

Increasing evidence supports an important biological role for Myc in the downregulation of specific gene transcription. Recent studies suggest that c-Myc may suppress promoter activity through proteins of the basal transcription machinery. We have previously reported that Myc protein, in combination with additional cellular factors, suppresses transcription initiation from the c-myc promoter. To characterize the cis components of this Myc negative autoregulation pathway, fragments of the human c-myc promoter were inserted upstream of luciferase reporter genes and assayed for responsiveness to inducible MycER activation in Rat-1 fibroblasts. We found four- to fivefold suppression of a c-myc P2 minimal promoter fragment upon induction of wild-type MycER protein activity, while induction of a mutant MycER protein lacking amino acids 106 to 143 required for Myc autosuppression failed to elicit this response. This assay is physiologically significant, as it reflects Myc autosuppression of the endogenous c-myc gene with regard to kinetics, dose dependency, cell type specificity, and c-Myc functional domains. Analysis of mutations within the P2 minimal promoter indicated that the cis components of Myc autosuppression could not be ascribed to any known protein-binding motifs. In addition, to address the trans factors required for Myc negative autoregulation, we expressed MycEG and MaxEG leucine zipper dimerization mutants in Rat-1 cells and found that Myc-Max heterodimerization is obligatory for Myc autosuppression. Two models for the Myc autosuppression mechanism are discussed.

3T3 Cells↗
PubMed1997

Molecular cloning of human FKBP51 and comparisons of immunophilin interactions with Hsp90 and progesterone receptor.

A cDNA for human FKBP51 has been cloned and sequenced, and protein products have been expressed in both in vitro and bacterial systems. The deduced amino acid sequence for human FKBP51 is 90% identical to sequences of recently described murine proteins and is 55% identical to the sequence of human FKBP52. Human FKBP51 mRNA is expressed in a wide range of tissues, and the protein has peptidylprolyl isomerase activity that is inhibited by FK506 but not cyclosporine. FKBP51 is the same as a previously described progesterone receptor-associated immunophilin that, similar to FKBP52 and cyclophilin 40, is an Hsp90-binding protein and appears in functionally mature steroid receptor complexes along with Hsp90 and p23. Each of the three receptor-associated immunophilins displays interactions with progesterone receptor that are more dynamic than Hsp90-receptor interactions. Whereas FKBP52 and FKBP51 compete about equally well for binding to Hsp90 in a purified system, FKBP51 accumulates preferentially in progesterone receptor complexes assembled in a cell-free system. This observation provides a precedent for differential interactions between Hsp90-associated immunophilins and target proteins such as steroid receptors.

Amino Acid Isomerases↗
PubMed1997

Cerebellar nitric oxide synthase is expressed within granule cell patches innervated by specific mossy fiber terminals: a developmental profile.

The nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) staining technique was utilized as a marker of nitric oxide synthase (NOS) to map NOS expression in developing and adult rat cerebellum. NADPH-d-positive cells were first visualized in the cerebellar cortex at postnatal day 5 (PND5) which increased to peak levels by PND30 when they began to exhibit a patch-like organization. In order to determine the relationship of the NADPH-d staining pattern with mossy fiber innervation, mossy fiber projections were traced using cholera toxin B subunit or biocytin injected into the lateral reticular nuclei (LRtN) or pontine nuclei (PtN), respectively. Double staining revealed that the clustered mossy fiber terminals projecting from the ventrorostral LRtN and caudal PtN were well matched with NADPH-d-stained patches. This patch-like localization of NOS matched with specific mossy fiber terminals in adult cerebellum implicates these NOS patches as defining distinct anatomical zones.

Afferent Pathways↗
PubMed1997

I. Adrenal cortex and steroid 21-hydroxylase autoantibodies in adult patients with organ-specific autoimmune diseases: markers of low progression to clinical Addison's disease.

Adrenal cortex antibodies (ACA) were measured by immunofluorescence in 8840 adult patients with organ-specific autoimmune diseases without overt hypoadrenalism. Sixty-seven (0.8%) patients were ACA-positive, with the highest prevalence in those with premature ovarian failure (8.9%). Forty-eight ACA-positive and 20 ACA-negative individuals were enrolled into a prospective study. Antibodies to steroid 21-hydroxylases (21-OH), steroid 17 alpha-hydroxylase (17 alpha-OH) and cytochrome P450 side chain cleavage enzyme (P450scc) were measured by immunoprecipitation assay. Human leucocyte antigens D-related (HLA-DR) genotyping was also carried out and adrenal function assessed by ACTH test. On enrollment, 75% of ACA-positive patients had a normal adrenal function, while 25% revealed a subclinical hypoadrenalism. 21-OH antibodies were positive in 91% of ACA-positive sera. Eleven patients were positive for steroid-cell antibodies by immunofluorescence, and 9 revealed a positivity for antibodies to 17 alpha-OH and/or P450scc. During the prospective study, overt Addison's disease developed in 21% and subclinical hypoadrenalism in 29% of ACA-positive patients, while 50% maintained normal adrenal function. Progression to Addison's disease was more frequent in patients with subclinical hypoadrenalism, high titers of ACA and higher levels of 21-OH antibodies, complement-fixing ACA and HLA-DR3 status. All 20 persistently ACA-negative patients were also negative for antibodies to 21-OH, 17 alpha-OH, and P450scc, and all maintained normal adrenal function during follow-up. In conclusion, the detection of ACA/21-OH antibodies in adults is a marker of low progression toward clinical Addison's disease.

Addison Disease↗
PubMed1997

II. Adrenal cortex and steroid 21-hydroxylase autoantibodies in children with organ-specific autoimmune diseases: markers of high progression to clinical Addison's disease.

Adrenal cortex autoantibodies (ACA) were measured by immunofluorescence in 808 children with organ-specific autoimmune diseases without adrenal insufficiency. ACA were found in 14 children (1.7%), mostly in hypoparathyroidism (48%). Ten ACA-positive and 12 ACA-negative children were followed up for a maximum of 10 yr by evaluation of adrenocortical function (ACTH test) and autoantibody status. In all patients steroid-producing cell autoantibodies were assessed by immunofluorescence and autoantibodies to steroid 21-hydroxylase, 17 alpha-hydroxylase, and cytochrome P450 side-chain cleavage enzyme by immunoprecipitation assay. All 10 ACA-positive patients were positive for 21-hydroxylase autoantibodies. Six were positive for steroid-producing cell autoantibodies and 5 also for autoantibodies to 17 alpha-hydroxylase and/or P450 side-chain cleavage enzyme. Overt Addison's disease developed in 9 (90%) ACA/21-OH-antibody-positive children after 3-121 months, and 1 remaining child had subclinical hypoadrenalism. By contrast, all ACA/21-OH antibody-negative children maintained normal adrenal function. Adrenal failure was not related to ACA titres, sex, adrenal function, type of preexisting autoimmune disorder, or human leucocyte antigens D-related status. In conclusion, in children with autoimmune endocrine diseases, ACA/21-hydroxylase autoantibodies are important predictive markers for the development of Addison's disease.

Addison Disease↗
PubMed1997

Steroid 21-hydroxylase autoantibodies: measurements with a new immunoprecipitation assay.

Autoantibodies (Abs) to steroid 21-hydroxylase (21-OH) are a major component of adrenal cortex Abs and are characteristic of autoimmune Addison's disease. We have developed a new method for measuring Abs to 21-OH based on 125I-labeled recombinant human 21-OH produced in yeast. With this assay, 21-OH Abs were detected in 43 of 60 (72%) sera from patients with isolated Addison's disease, 11 of 12 (92%) autoimmune polyglandular syndrome type I sera, 27 of 27 (100%) autoimmune polyglandular syndrome type II sera, and 24 of 30 (80%) sera from patients who were positive for adrenal cortex antibodies by immunofluorescence but had no overt Addison's disease. 21-OH Abs were found by 125I assay in 4 of 150 (2.7%) sera from patients with insulin-dependent diabetes mellitus, 1 of 77 (1.3%) Graves' sera, 1 of 67 (1.5%) Hashimoto's sera, and 6 of 243 (2.5%) sera from healthy blood donors. 21-OH Abs were not detected in 9 sera from patients with Addison's disease due to tuberculosis, 32 sera from patients with noninsulin-dependent diabetes mellitus, 35 sera from patients with myasthenia gravis, or 17 sera from patients with premature ovarian failure. There was good agreement between the 125I-labeled 21-OH assay and an assay based on 35S-labeled 21-OH produced in an in vitro transcription/translation system (r = 0.86; n = 129; P < 0.001). In the case of sera from patients with Addison's disease, insulin-dependent diabetes mellitus, Graves' disease, and Hashimoto's disease and from healthy blood donors that were low positive in the 125I assay, neutralization studies with unlabeled 21-OH confirmed the presence of specific 21-OH Abs. Overall, the 21-OH Ab assay based on 125I-labeled 21-OH showed good sensitivity, precision, and disease group specificity. This, combined with a simple assay protocol and the convenience of 125I handling and counting, make it attractive for routine use. Further investigations with the new assay should allow wider assessment of the prevalence and pattern of inheritance of adrenal autoimmunity. In addition, studies of the effect of treatment or possible preventative measures on 21-OH Ab levels in individuals without overt adrenal failure may suggest ways of delaying the onset of autoimmune Addison's disease.

Addison Disease↗
PubMed1997

Functional role of a conformationally flexible homopurine/homopyrimidine domain of the androgen receptor gene promoter interacting with Sp1 and a pyrimidine single strand DNA-binding protein.

The androgen receptor (AR) gene promoter does not contain the TATA or CAAT box, but it contains a long (approximately 90-bp) homopurine/homopyrimidine (pur/ pyr) stretch immediately upstream of the Sp1-binding GC box site. This pur-pyr stretch is conserved at the same proximal position in the rat, mouse, and human AR gene promoters. Mutation of this region results in a 3-fold decline in promoter activity, indicating an important regulatory function. Examination of the conformational state of the AR pur/pyr region with the single-strand-specific S1 nuclease showed that it is capable of forming a non-B DNA structure involving unpaired single strands. Fine mapping of the S1-sensitive site revealed an unsymmetric cleavage pattern indicative of an intramolecular triple helical H-form DNA conformation. Electrophoretic mobility shift analyses showed that the pur/pyr region of the AR promoter can bind a novel pyrimidine single-strand-specific protein (ssPyrBF) and also a double-strand DNA-binding protein. Both oligonucleotide cross-competition and antibody supershift experiments established that the double-strand binding protein is equivalent to Sp1. Deoxyribonuclease I (DNase I) footprinting analysis showed multiple Sp1-binding to the pur/pyr site and a weaker Sp1 interaction to this region compared with the adjacently located GC box, where Sp1 functions to recruit the TFIID complex. These results suggest that the pur/pyr domain of the AR gene can serve to attract additional Sp1 molecules when it exists in the double-stranded B-DNA conformation. However, binding of ssPyrBF and the resultant stabilization of the non-B DNA structure is expected to prevent its interaction with Sp1. We speculate that in the TATA-less AR gene promoter, multiple weak Sp1 sites at the pur/pyr region adjacent to the GC box can provide a readily available source of this transcription factor to the functional GC box, thereby facilitating the assembly of the initiation complex.

Animals↗
PubMed1997

Autoantibody binding to steroid 21-hydroxylase--effect of five mutations.

Steroid 21-hydroxylase (21-OH) is a key haem containing steroidogenic enzyme and a major adrenal specific autoantigen. Cys 428 in 21-OH is thought to have an important role in haem binding and we now describe the effects of mutations at Cys 428 (to Ser, Arg and Phe) on 21-OH autoantibody binding. Expression of wild type and mutated 21-OH was carried out using an in vitro transcription/translation (TnT) system and reactivity of 21-OH autoantibodies with mutated 21-OH analysed by western blotting (in the case of unlabelled proteins) or immunoprecipitation assay (IPA) (in the case of 35S-labelled proteins). All 3 substitutions at Cys 428 had similar effects on 21-OH autoantibody binding and each one caused a reduction in autoantibody binding to about 50% of wild type in the case of IPA and to about 70% of wild type in the case of western blotting analysis. In addition to mutations at Cys 428, we studied 2 naturally occurring mutations at Pro 30 to Leu and Ile 172 to Asn which are associated with diminished 21-OH enzyme activity. The Pro 30 mutation had no effect, but the Ile 172 mutation caused a reduction in 21-OH autoantibody binding in the IPA to about 80% of wild type. Overall, our studies emphasise the close relationship between the 21-OH aminoacid sequences important for 21-OH enzyme activity and 21-OH autoantibody binding.

Addison Disease↗
PubMed1997

The melanoma epidemic: more apparent than real?

To examine inconsistencies between the growth in incidence of melanoma and more modest changes in melanoma-related mortality, we reviewed the medical literature on the incidence of melanoma diagnosis and associated mortality and on the changes in diagnosis and mortality over time. Increases in melanoma surveillance activity have been associated with increases in the diagnosis of thin melanomas, but the incidence of advanced tumors has changed minimally. The large increases in diagnosis of melanoma without commensurate increases in advanced tumors and mortality are not compatible with presumed malignant behavior of thin melanomas. Increased intensity of melanoma surveillance may artificially increase the incidence of melanoma by harvesting histologically "malignant" but biologically benign tumors. Little available evidence suggests the presence of an actual increase in the frequency of biologically malignant tumors. Attempts to increase screening intensity for melanoma may result in further increases in diagnosis of melanomas. Nevertheless, limitations in histopathologic diagnostic techniques will continue to hinder efforts at early identification of those at risk for death from melanoma without diagnosing melanoma in large numbers of patients with biologically benign pigmented skin tumors.

Disease Outbreaks↗
PubMed1997

[Expression of CerbB-2 and EGFR mRNA in human nasopharyngeal carcinomas and pericarcinomatous tissues].

Using the digoxin labelled probes and DNA-RNA in-situ hybridization technique, the expression of C-erbB-2 and EGFR mRNA in routine paraffin sections of 30 human nasopharyngeal carcinomas (NPC), 20 pericarcinomatous tissues (PCT) and 16 chronic inflammatory mucosae. The results showed the positive rates of C-erbB-2 and EGFR mRNA expression were 86.7%, 83.3% respectively in NPC and 80.0%, 70.0% in PCT, while those in chronic inflammatory mucosae were no detected. Co-expression of these two genes occurred in 83.3% of NPC and 70.0% of PCT. In the PCT, the positive rates of C-erbB-2 and EGFR mRNA in the atypic hyperplasia were higher than that in the simple hyperplasia, the amount of the positive cells of these two genes increased steadily in the mild, moderate and severe dysplasia and diffused from basal lamina of epithelium to the whole epithelium. The results suggest that the activation of C-erbB-2 and EGFR genes is an early event and play a synergic role in the carcinogenesis of NPC and examination of their expression is helpful in early diagnosis.

Carcinoma↗