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D Chen

Publications and source records attributed to D Chen.

At least 703 records · Page 39Linked to original sources
PubMed1994

A transcriptional regulatory element common to a large family of hepatic cytochrome P450 genes is a functional binding site of the orphan receptor HNF-4.

Hepatic cytochrome P450 (CYP) genes, including members of CYP1 to CYP4 families, comprise the majority of the CYP gene superfamily. Previous study has demonstrated that HepG2-specific transcriptional activation of two CYP2C genes was dependent on a common element that bound a HepG2 nuclear protein designated HPF-1 (Venepally, P., Chen, D., and Kemper, B. (1992) J. Biol. Chem. 267, 17333-17338). This cis-acting element is highly homologous to the hepatocyte nuclear factor 4 (HNF-4) binding motif and is present in the promoters of more than 20 other CYP2 genes. To investigate the relationship between HPF-1 and HNF-4, we have compared their tissue distribution, DNA binding, and immunochemical characteristics, as well as transcriptional activity of their recognition elements. DNase I footprint analyses and gel-shift assays indicated that HPF-1, like HNF-4, was present in liver and kidney, but not brain and spleen. Both factors bound to either the HPF-1 site in the CYP2C2 promoter or an HNF-4 site in the human apolipoprotein CIII promoter. These complexes could be "supershifted" by an antiserum specific for HNF-4. When the sequence of the HPF-1 site in the CYP2C2 promoter was changed to that of the apolipoprotein CIII HNF-4 site, comparable transcriptional activities were obtained with the wild-type promoter and the HNF-4 mutant in transfected HepG2 cells. Cotransfection of HNF-4 with CYP2C2 promoter-luciferase constructs in COS-1 cells indicated that HNF-4 could trans-activate the promoters containing the HPF-1 site. These results indicate that the HPF-1 motif is a functional HNF-4-binding site, and the common immunological properties indicate that HPF-1 and HNF-4 are closely related and possibly identical. HNF-4, therefore, may act as a common regulator for the liver-specific expression of many CYP2 genes.

Animals↗
PubMed1994

Plasma gastrin and cholecystokinin responses after pylorus-preserving pancreatoduodenectomy and defunctioned Roux loop pancreaticojejunostomy.

Several methods can be used to re-establish gastrointestinal continuity after the standard Whipple's Billroth II procedure or Longmire pylorus-preserving pancreatoduodenectomy (PPPD). Standard pancreatoduodenectomy abolishes the postprandial gastrin response whereas the response after Longmire PPPD is similar to that in controls. A novel reconstruction after PPPD has been designed to separate the biliary and pancreatic secretions by restoring continuity in the Billroth I manner, retaining the gastric antrum and with the pancreatic remnant anastomosed to a separate defunctioned Roux loop. Gastrin and cholecystokinin (CCK) responses were measured in the fasting state and after a standard liquid meal of 250 ml containing 15 per cent protein, 30 per cent fat and 55 per cent carbohydrate with an energy value of 525 kJ. Basal gastrin and CCK concentrations were similar in five healthy unoperated controls, and after standard pancreatoduodenectomy (five patients) and isolated Roux loop PPPD (six patients). In controls and after the new PPPD operation, but not after standard pancreatoduodenectomy, mean(s.e.m.) postprandial plasma gastrin values rose from 8.66(0.33) to 13.00(0.33) pmol l-1 at 10 min (controls) and from 7.66(1.56) to 15.00(1.36) pmol l-1 at 10 min (defunctioned Roux loop PPPD); the concentration remained raised for 20 min then fell transiently; a second peak was maintained for 40 min (controls) to 60 min (modified PPPD). In controls, mean(s.e.m.) postprandial plasma CCK concentrations rose from 0.43(0.12) basal to 10.50(1.03) pmol l-1 and returned to basal after 60 min. After standard pancreatoduodenectomy postprandial CCK concentrations rose at a similar rate and remained raised for 80 min. After isolated Roux loop PPPD plasma CCK concentrations remained low (mean(s.e.m.) 0.38(0.29) pmol l-1) after the test meal.

Aged↗
PubMed1994

Pharmacokinetics, acid-base balance and intraocular pressure effects of ethyloxaloylazolamide--a novel topically active carbonic anhydrase inhibitor.

Studies evaluated a novel series of biscarbonylamides of 2-amino-1,3,4-thiadiazole-5-sulfonamide (2-ATS) for topical use as ocular hypotensive carbonic anhydrase inhibitors (CAI). Transcorneal accession rate constants (k(in)) for ethyloxaloylazolamide (EtOxAz), ethylsuccinylazolamide (EtSuxAz) and ethyladipoylazolamide (EtAdipAz), and activity against carbonic anhydrase (CA) were determined in vitro by an enzymatic assay and High Performance Liquid Chromatography (HPLC). The ocular hypotensive effect was measured by pneumatonometry on conscious normotensive New Zealand White (NZW) rabbits, using masked, randomly assigned paired-eye design for treatment vs. control. At various time points following treatment, aqueous humor, ciliary processes and corneal buttons were collected and assayed for drug concentrations using enzymatic assay and HPLC. Transcorneal accession rates for the novel compounds were 1.5 to 18 times that of the parent compound, acetazolamide (Actz). The activity factor for EtOxAz was 72.8 x 10(3) hr-1 of 23 times that of Actz. The activity factors for EtSuxAz and EtAdipAz were 6.8 and 1.1 x 10(3) hr-1, respectively. Subcutaneous administration of EtOxAz. EtSuxAz, and EtAdipAz, in 225 mumol kg-1 concentrations, induced a significant decrease in the intraocular pressure (IOP) at 1 hr post injection of 4, 5.8 and 6 mmHg for EtOxAz, EtSuxAz and EtAdipAz, respectively (P < 0.05 for each). Topical application of 75 mM EtOxAz lowered the IOP by 3.0 mmHg (P < 0.05). This effect was maximal after 60 min and persisted for at least 5 hr. EtSuxAz and EtAdipAz did not alter the IOP significantly when given topically. Subcutaneous administration of the three compounds was associated with acidosis (pH as low as 7.21). Topical application did not cause any changes in the acid-base balance. There was a direct correlation between the amount of drug delivered to the ciliary process and the magnitude of ocular hypotensive effect. Following topical application EtOxAz reached the ciliary epithelium in concentrations sufficient to inhibit more than 99.95% of the ciliary carbonic anhydrase (> 8 microM), while plasma drug concentrations were below the limit of detection by the assay (< 0.2 microM). Within the first hour after topical application, half of the EtOxAz was eliminated from the anterior uvea. In summary, EtOxAz is a topically effective CAI. Structural modifications of thiadiazole sulfonamides, with the increase of both water and lipid solubilities, improved the transcorneal accession while preserving sufficient CA inhibitory activity, resulting in a significant IOP decrease following topical application of EtOxAz.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗
PubMed1994

Transfected MCF-7 cells as a model for breast-cancer progression.

The MCF-7 human breast carcinoma cell line has been used as a recipient for eukaryotic plasmid expression vectors to determine the effects of growth factor and growth factor receptor overexpression on the estrogen-dependent, antiestrogen sensitive and poorly metastatic phenotypes exhibited by this line. Overexpression of some members of the erbB family of ligands and receptors were found to have some effects on these phenotypes. However, only when two members of the fibroblast growth factor family, FGF-1 and FGF-4, were overexpressed was progressive in vivo growth observed is either ovariectomized nude mice without estrogen supplementation or in mice that received tamoxifen treatment. FGF transfected cells also exhibited an increased ability to form micrometastases. The implications of these results with regard to the possible role of the paracrine and autocrine effects of angiogenic growth factor production in breast cancer progression are discussed.

Adenocarcinoma↗
PubMed1994

Forty-two patients with acute ascaris pancreatitis in China.

Acute pancreatitis caused by Ascaris lumbricoides is more common in certain areas than is generally appreciated. We report a series of 42 patients, mostly young adult women, admitted to our hospital in Hunan Province, China, during the period January, 1983 to December, 1992. The diagnosis was based on the detection of worms by ultrasonography, and on the presence of severe upper abdominal pain and tenderness and raised serum amylase level without other apparent causes. Only 2 patients had necrotizing pancreatitis (4.8%). With our conservative policy, 40 patients recovered and 2 patients were operated. The mortality has remained at zero and we therefore believe that early surgical intervention is unwise. However, laparotomy should be performed if the patient fails to respond to conservative therapy, there is evidence of infection around the pancreas, bloody peritoneal fluid on aspiration, and dead worms remain within the biliary tree. We compare acute ascaris pancreatitis with acute pancreatitis caused by lithiasis.

Acute Disease↗
PubMed1994

Prevention of thromboembolism in spinal cord injury: role of low molecular weight heparin.

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are major causes of morbidity and mortality in patients with acute spinal cord injury. Our preliminary studies indicated that low molecular weight heparin (LMWH) was significantly more effective than standard heparin in preventing these complications. We have now extended these studies by screening an additional 122 patients and treating 60 who met predefined criteria with LMWH in a dose of 3,500 anti-Xa U given subcutaneously once daily for 8 weeks. All patients were examined daily at bedside and had regularly scheduled venous ultrasonography; those with abnormalities had confirmatory venography and lung scans. Postmortem examinations were conducted in those who died. Forty completed the trial without incident, 6 had DVT (4 proximal and 2 distal), 1 had a fatal PE, 1 had postoperative bleeding requiring discontinuation of the LMWH, 10 were transferred or discharged, and 2 died of respiratory failure. The percentage of patients free of thrombosis or bleeding after 8 weeks of treatment was 85.9 +/- 5.0% standard error of mean (SEM). Thirty-three patients entered a follow-up observation period of 4 weeks without thromboprophylaxis; 2 weeks into this period 1 had a proximal DVT and 1 had a fatal PE; the course of the remainder was uneventful. We conclude that LMWH compares favorably with standard heparin in preventing venous thromboembolism, and is associated with significantly less bleeding. Eight weeks of prophylaxis seems adequate for most patients.

Adult↗
PubMed1994

Acute responses of rat stomach enterochromaffinlike cells to gastrin: secretory activation and adaptation.

BACKGROUND/AIMS: Evidence for gastrin-induced histamine secretion from isolated rat enterochromaffinlike (ECL) cells was presented recently. We have investigated the gastrin-evoked secretory activation and adaptation of ECL cells in intact rats over a time span of a few minutes to several hours. METHODS: Fasted rats received a maximally effective dose of synthetic human Leu15-gastrin-17 by continuous intravenous infusion. ECL cell ultrastructure and ECL cell-related parameters (e.g., mucosal histamine and pancreastatin concentrations, histidine decarboxylase [HDC] activity, and messenger RNA [mRNA] concentration) were analyzed. RESULTS: Gastrin reduced the number of cytoplasmic vesicles in ECL cells while reducing the concentrations of histamine and pancreastatin in the oxyntic mucosa. The effects were maximal within a few hours after the start of gastrin infusion. The concentration of pancreastatin in serum was elevated for the duration of the study. The mucosal concentrations of histamine and pancreastatin returned to prestimulation values after 4-6 hours. The HDC activity and mRNA concentration increased progressively until after 6-8 hours of gastrin infusion. CONCLUSIONS: Gastrin promptly degranulates the ECL cells, releasing histamine and pancreastatin from the vesicles. Synthesis of histamine and pancreastatin is accelerated, a process associated with renewal of vesicles. The increase in HDC activity and mRNA concentration continues for several hours after restoration of the vesicles.

Adaptation, Physiological↗
PubMed1994

Polymorphism of a CAG trinucleotide repeat within Sry correlates with B6.YDom sex reversal.

Breeding the Y chromosome from certain Mus musculus domesticus strains onto the inbred laboratory mouse strain, C57BL/6J (B6), results in hermaphroditic progeny. This strain-dependent sex reversal suggests that there may be significant allelic variation in the murine sex determining gene, Sry. We have analysed the Sry genes from several domesticus-type Y chromosomes and show that they encode smaller proteins than the molossinus-type alleles SryB6 and Sry129. We have also identified a polymorphic stretch of trinucleotide repeats that is unique to strains causing sex reversal and show that specific changes in the predicted polyglutamine amino acid sequence at this site are associated with different degrees of sex reversal.

Amino Acid Sequence↗
PubMed1994

A classification scheme for cognitive strategies: implications for learning and teaching psychomotor skills.

The emphasis in cognitive psychology has been on the study of internal processes associated with processing information leading to task mastery. As one consequence, interest has been spurred in understanding and applying a variety of potential learning and performance strategies that might contribute to achievement in various tasks and situations. After many attempts to instruct people in the use of strategies, the results are far from conclusive. In addition, ambiguity has resulted in the way various strategies have been studied. Considering these circumstances, we propose a framework for classifying strategies that incorporates four criteria: (a) source (externally imposed or self-generated); (b) orientation (task or person); (c) purpose (learning or performance); and (d) scope (task specificity or generality). The purpose of this classification is to aid in interpreting research on strategies, to provide direction for future strategies research, and to communicate how results might be applied. Psychomotor skills are discussed with respect to maximizing the effectiveness of strategy training.

Adaptation, Psychological↗
PubMed1994

Contrasting IgA and IgG neutralization capacities and responses to HIV type 1 gp120 V3 loop in HIV-infected individuals.

Quantitative analysis for HIV-1-specific antibodies present in IgA and IgG preparations purified from the serum of HIV-seropositive individuals indicated that the proportion of HIV-specific antibodies present within the IgG isotype was seven times greater than the proportion of IgA HIV antibodies present within the IgA isotype. Dilution of IgA HIV-specific antibodies by nonspecific IgA was observed in patients with elevated serum IgA concentrations, whereas proportions of IgG HIV antibodies rose with increases in concentrations of serum IgG. Although proportions of IgA HIV antibodies were not observed to correlate with the CD4 counts of the individuals from whom immunoglobulins were purified, a significant association between the numbers of such cells and proportion of HIV antibodies present in the IgG isotype was found. Equivalent amounts of IgG were also more effective than IgA at inhibiting HIV-1IIIB infection of a susceptible T cell line. This may be due to the presence of higher proportions of IgG antibodies directed toward non-V3 determinants because reactivity against an HIV-1IIIB V3 peptide was low and did not differ significantly between these isotopes. IgA antibodies reacting against a V3 peptide containing the HIV consensus sequence could be detected in the majority of IgA samples purified from infected individuals. Proportions of IgG consensus V3-specific antibodies within the purified IgG samples were, however, much higher. The presence of accompanying increases in serum IgG concentration and proportions of IgG HIV antibodies, higher proportions of both HIV- and consensus V3-specific antibodies within this isotype, and more effective neutralization by IgG suggests that an HIV-driven response is dominated by B cells committed to production of this immunoglobulin isotype. The observed low proportions of HIV antigen-specific IgA antibodies with dilution in many individuals by elevations in non-HIV-specific IgA suggests that IgA B cells may be more susceptible to factors that mediate the polyclonal activation believed to be responsible for many of the B cell disorders characteristic of HIV infection.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Differential protein binding and transcriptional activities of HNF-4 elements in three closely related CYP2C genes.

A functional binding site for a liver-enriched transcription factor, hepatocyte nuclear factor-4 (HNF-4), has previously been identified around -100 in the CYP2C2 promoter and proposed to be a common regulatory motif for the hepatic expression of many CYP2 genes. The transcriptional activity of the proximal promoters of three closely related cytochrome P450 genes (CYP2C1, CYP2C2, and CYP2C3) have been compared in HepG2 cells and correlated with the relative binding affinities of the HNF-4 motifs in the genes for proteins in liver, kidney, and HepG2 extracts that react with antisera to HNF-4. Gel-shift assays suggested that these highly similar motifs bound HNF-4 with significantly different affinities. The relative binding affinities to the protein in liver extracts were estimated by competitive gel-shift binding, and the binding affinity of CYP2C2 was two-fold and eight-fold greater than that of CYP2C1 and CYP2C3, respectively. These affinity differences correlated well with the transcriptional activities of either the minimal hepatic promoters (117 to 135 bp of 5'-flanking region) of the genes in HepG2 cells or minimal CYP2C2 promoters containing the HNF-4 motif from each gene. Identification of the CYP2C3 site was somewhat indirect; the HNF-4 element in the CYP2C3 promoter could be converted to a motif with binding affinity and hepatic cell-specific transcriptional activity similar to that of CYP2C2 by a single nucleotide substitution. The activities of the minimal promoters did not correlate well with hepatic expression of each gene in vivo, as estimated previously by the concentration of mRNA in livers of untreated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Ketamine directly dilates bovine cerebral arteries by acting as a calcium entry blocker.

This in vitro study was performed to determine the role of calcium in ketamine-induced cerebral vasodilation. Isolated bovine middle cerebral arteries were cut into rings to measure isometric tension development or into strips to measure radioactive 45Calcium (45Ca) uptake. Ketamine produced direct relaxation of arterial rings; the relaxation was attenuated in Ca(2+)-deficient media. Ketamine produced dose-related relaxation of arteries preconstricted with potassium, a stable thromboxane A2 analogue, or endothelin. Endothelial stripping with Triton X-100 had no effect on subsequent ketamine-induced relaxation. In Ca(2+)-deficient media containing potassium or the stable thromboxane A2 analogue, ketamine produced competitive inhibition of subsequent Ca(2+)-induced constriction. Ketamine blocked potassium- and thromboxane A2-stimulated 45Ca uptake in a dose-dependent manner, but had no effect on basal 45Ca uptake, the externally bound 45Ca content, or the volume of the 3H-sorbitol space. These results indicate that ketamine can directly dilate cerebral arteries by acting as a calcium channel antagonist; ketamine inhibits 45Ca uptake through both potential-operated (potassium) and receptor-operated (thromboxane A2) channels in cerebrovascular smooth muscle.

Animals↗
PubMed1994

Topological promoter coupling in Escherichia coli: delta topA-dependent activation of the leu-500 promoter on a plasmid.

The leu-500 promoter of Salmonella typhimurium is activated in topA mutants. We have previously shown that this promoter can be activated on circular plasmids in a manner that depends on transcription and translation of the tetracycline resistance gene tetA and insertion of its product into the cell membrane. We have suggested that in the absence of enzymatic relaxation by topoisomerase I, the local domain of transcription-induced DNA supercoiling reaches a steady-state level that leads to the activation of the leu-500 promoter. In the present paper, we have shown that the leu-500 promoter may also be activated in Escherichia coli. Comparison of the closely related pair of E. coli strains DM800 (delta topA) and SD108 (topA+) shows that the activation is dependent on the presence of a null mutation in topA. We have also shown that activation of the plasmid-borne leu-500 promoter depends, as in S. typhimurium, on the function of an adjacent tetA gene, suggesting that membrane anchorage of the TetA peptide prevents dissipation of transcription-induced supercoiling by superhelical diffusion. The activity of the leu-500 promoter is boosted by placing a divergent tac promoter on the side opposite to tetA. The topoisomer distributions of these plasmids extracted from the cell have been analyzed. We find that when the parent plasmid pLEU500Tc, containing the leu-500 promoter upstream of the complete tetA gene, is extracted from E. coli DM800 (delta topA), the distribution of linking numbers is bimodal. There is a fraction with a lower level of supercoiling (mean linking difference approximately -0.05) that is constant for all plasmids extracted from either delta topA or topA+ cells. In addition, we observe a second fraction with highly negatively supercoiled DNA (mean linking difference approximately -0.09) only in DNA extracted from delta topA cells. The proportion of the oversupercoiled fraction correlates with the activity of the leu-500 promoter: it is strongly reduced when the tetA promoter is deleted or when translation of TetA is prematurely terminated, while it is increased when the strong tac promoter is present in cis. We suggest that this oversupercoiled fraction represents the proportion of plasmid molecules active in tetA transcription and that it is this supercoiling that activates the leu-500 promoter.

Antiporters↗
PubMed1994

Template-dependent, in vitro replication of rotavirus RNA.

A template-dependent, in vitro rotavirus RNA replication system was established. The system initiated and synthesized full-length double-stranded RNAs on rotavirus positive-sense template RNAs. Native rotavirus mRNAs or in vitro transcripts, with bona fide 3' and 5' termini, derived from rotavirus cDNAs functioned as templates. Replicase activity was associated with a subviral particle containing VP1, VP2, and VP3 and was derived from native virions or baculovirus coexpression of rotavirus genes. A cis-acting signal involved in replication was localized within the 26 3'-terminal nucleotides of a reporter template RNA. Various biochemical and biophysical parameters affecting the efficiency of replication were examined to optimize the replication system. A replication system capable of in vitro initiation has not been previously described for Reoviridae.

Animals↗
PubMed1994

Expression of the varicella-zoster virus origin-binding protein and analysis of its site-specific DNA-binding properties.

The varicella-zoster virus (VZV) genome contains homologs to each of the seven herpes simplex virus (HSV) genes that are required for viral DNA synthesis. VZV gene 51 is homologous to HSV UL9, which encodes an origin of DNA replication binding protein (OBP). It was previously shown, by using a protein A fusion protein, that the product of gene 51 is a site-specific DNA-binding protein which binds to sequences within the VZV origin (Stow et al., Virology 177:570-577, 1990). In this report, gene 51 was expressed in an in vitro translation system. Rabbit antiserum raised against the carboxyl-terminal 20 amino acids was used to confirm expression of the full-length gene 51 protein, and site-specific DNA-binding activity was demonstrated in a gel retardation assay. The origin-binding domain was located within a 263-amino-acid region of the carboxyl terminus by using a series of deletion mutants. The affinity of binding of the VZV OBP to the three binding sites in the VZV origin was found to be similar. In addition, as with UL9, a CGC triplet within a 10-bp consensus sequence is critical to the interaction between the OBP and the origin. The HSV and VZV OBPs, therefore, appear to have virtually identical recognition sequences despite only 33% identity and 44% similarity in the primary structure of their site-specific DNA-binding domains.

Amino Acid Sequence↗
PubMed1994

Interleukin-2 transcription is regulated in vivo at the level of coordinated binding of both constitutive and regulated factors.

Interleukin-2 (IL-2) transcription is developmentally restricted to T cells and physiologically dependent on specific stimuli such as antigen recognition. Prior studies have shown that this stringent two-tiered regulation is mediated through a transcriptional promoter/enhancer DNA segment which is composed of diverse recognition elements. Factors binding to some of these elements are present constitutively in many cell types, while others are signal dependent, T cell specific, or both. This raises several questions about the molecular mechanism by which IL-2 expression is regulated. Is the developmental commitment of T cells reflected molecularly by stable interaction between available factors and the IL-2 enhancer prior to signal-dependent induction? At which level, factor binding to DNA or factor activity once bound, are individual regulatory elements within the native enhancer regulated? By what mechanism is developmental and physiological specificity enforced, given the participation of many relatively nonspecific elements? To answer these questions, we have used in vivo footprinting to determine and compare patterns of protein-DNA interactions at the native IL-2 locus in cell environments, including EL4 T-lymphoma cells and 32D clone 5 premast cells, which express differing subsets of IL-2 DNA-binding factors. We also used the immunosuppressant cyclosporin A as a pharmacological agent to further dissect the roles played by cyclosporin A-sensitive factors in the assembly and maintenance of protein-DNA complexes. Occupancy of all site types was observed exclusively in T cells and then only upon excitation of signal transduction pathways. This was true even though partially overlapping subsets of IL-2-binding activities were shown to be present in 32D clone 5 premast cells. This observation was especially striking in 32D cells because, upon signal stimulation, they mobilized a substantial set of IL-2 DNA-binding activities, as measured by in vitro assays using nuclear extracts. We conclude that binding activities of all classes fail to stably occupy their cognate sites in IL-2, except following activation of T cells, and that specificity of IL-2 transcription is enforced at the level of chromosomal occupancy, which appears to be an all-or-nothing phenomenon.

Animals↗