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Biomedical subjects

W Zhou

Publications and source records attributed to W Zhou.

At least 361 records · Page 20Linked to original sources
PubMed1994

A fumagillin derivative angiogenesis inhibitor, AGM-1470, inhibits activation of cyclin-dependent kinases and phosphorylation of retinoblastoma gene product but not protein tyrosyl phosphorylation or protooncogene expression in vascular endothelial cells.

Fumagillin analogue AGM-1470 potently inhibits angiogenesis with a minimal toxicity in vivo and is expected to be of therapeutic use as a powerful antitumor agent (Ingber et al., Nature, 348:555-557, 1990). In the present study, we have investigated the effects and the mechanism of action of AGM-1470 on cultured human umbilical vein endothelial cells. AGM-1470 acts directly on endothelial cells to inhibit growth factor-induced DNA synthesis, with half maximal and maximal effects obtained at approximately 2 x 10(-10) and 5 x 10(-9) M, respectively. AGM-1470 does not inhibit early G1 mitogenic events, such as cellular protein tyrosyl phosphorylation or the expression of immediate early genes c-fos and c-myc, but potently inhibits phosphorylation of RB protein, a tumor suppressor retinoblastoma gene product. The later addition of AGM-1470 up to 3 h after the growth factor stimulation still exerts full inhibitory effects on both DNA synthesis and RB phosphorylation, suggesting that the major site of action of AGM-1470 is located relatively late in the G1 phase. AGM-1470 inhibits growth factor-induced activation of candidate RB kinases cdc2 and cdk2 but fails to inhibit them directly in vitro. AGM-1470 completely abolishes the growth factor-induced mRNA expression of cdc2 and cyclin A and partially inhibits that of cyclin E but has little effect on the mRNA level of cdk2, cdk4, or cyclin D1. These results indicate that angioinhibitory action of AGM-1470 involves suppression of mRNA expression of specific members of cdks and cyclins and of activation of both cdc2 and cdk2 kinases in endothelial cells.

CDC2 Protein Kinase↗
PubMed1994

Characterization of al-2, the phytoene synthase gene of Neurospora crassa. Cloning, sequence analysis, and photoregulation.

We have cloned the al-2 gene of Neurospora crassa and have analyzed its structure and regulation. The gene encodes a 603-residue polypeptide with a segment homologous to prokaryotic and other eukaryotic phytoene synthases. RNA measurements showed that the level of al-2 mRNA increased over 30-fold in photoinduced mycelia compared with dark-grown mycelia. This observation is consistent with the fact that carotenoid biosynthesis is induced by blue light during growth of N. crassa mycelia. The photoinduced increase in al-2 mRNA levels was not observed in two Neurospora mutants, wc-1 and wc-2, that are defective in all physiological photoresponses.

Alkyl and Aryl Transferases↗
PubMed1994

E2F1, B-myb and selective members of cyclin/cdk subunits are targets for protein kinase C-mediated bimodal growth regulation in vascular endothelial cells.

In human umbilical vein endothelial cells, the protein kinase C (PKC) stimulation during the early G1 phase leads to potentiations in growth factor-stimulated DNA synthesis, the activation of cdc2 and cdk2 cyclin-dependent kinases, and the mRNA expression of cdc2, cyclins A, D1 and E, but not cdk2 or cdk4. Conversely, the PKC stimulation in the late G1 phase completely inhibits DNA synthesis, the activation of cyclin-dependent kinases, and the mRNA expression of the same set of molecules except cyclin D1. Further, we found that the PKC stimulation bimodally regulates the message levels of E2F1 and B-myb, which are transcription factors implicated in the control of the mammalian cell cycle progression. These results indicate that the PKC signal transduction pathway, depending on the timing of activation in the G1 phase, either positively or negatively regulates the message level of growth-regulating genes that are crucial for the G1 to S phase progression.

CDC2-CDC28 Kinases↗
PubMed1994

Impaired surface expression of PAF receptors on human neutrophils is dependent upon cell activation.

The capacity of human neutrophils to bind PAF was rapidly diminished upon cell stimulation with both physiological agonists (N-formylmethionylleucylphenylalanine (FMLP), leukotriene B4 (LTB4)) and pharmacologic agonists (phorbol 12-myristate 13-acetate (PMA), A23187). As a consequence, PAF responses in neutrophils were blunted, as monitored by an inhibition of intracellular Ca2+ mobilization. Downregulation of the PAF receptor in neutrophils by diverse agonists was temperature-sensitive and required intact cells. Scatchard analysis of binding data revealed that PAF binding sites were lost without an appreciable change in the affinity of the ligand for the receptor. The binding of the PAF receptor antagonist WEB2086 to neutrophils decreased in parallel with PAF binding. PMA-induced PAF receptor downregulation was staurosporine-sensitive while PAF receptor downregulation by A23187, FMLP, or LTB4 was staurosporine-resistant. Both neutrophil aggregation (a form of intercellular adhesion) and PAF receptor downregulation occurred only at high concentrations of agonists while other signaling processes such as the increase in [Ca2+]i, PKC activation, and PAF synthesis were stimulated at low concentrations of agonists. Furthermore, agonist-induced PAF receptor downregulation was observed only under conditions in which the activated neutrophils were stirred (or shaken) and were allowed to aggregate. Additionally, chelation of extracellular Ca2+ with EGTA minimized cell aggregation and also inhibited PAF receptor downregulation. While the nature of the biochemical signal or the physical changes in the plasma membrane associated with aggregation or that follow aggregation remain to be elucidated it is clear that full expression of cell activation (i.e., neutrophil aggregation) is required for PAF receptor downregulation.

Calcimycin↗
PubMed1994

Suppression of neointimal smooth muscle cell accumulation in vivo by antisense cdc2 and cdk2 oligonucleotides in rat carotid artery.

Deendothelializing balloon injury of rat carotid artery results in progressive intimal smooth muscle cell accumulation and luminal stenosis over 14 days after injury. We have found transient rises (approximately 3-fold maximal increases over the uninjured control value) of the kinase activities of both cdc2 and cdk2, key molecules for cell cycle progression, in the injured carotid artery along with the development of intimal proliferation. The topical application of the antisense, but not the sense, cdc2 and cdk2 phosphorothioate oligodeoxynucleotides dissolved in F127 pluronic gel around the freshly injured artery resulted in reductions of the intimal smooth muscle cell accumulation by 47% and 55% respectively, as estimated by an intimal to medial cross-sectional area ratio, with concomitant decreases in cdc2 and cdk2 kinase activities. These results indicate that both cdc2 and cdk2 kinases are involved in intimal smooth muscle cell accumulation after balloon angioplasty and suggest a potential usefulness of the antisense cdc2 and cdk2 oligonucleotide therapy for arterial stenosis.

Angioplasty, Balloon↗
PubMed1994

Lipid mediator production in acute and chronic pancreatitis in the rat.

Pancreatic production of lipid mediators of inflammation, including eicosanoids and platelet-activating factor (PAF), was examined in two models of pancreatitis in the rat. Chronic pancreatitis was induced by ligation of the pancreatic duct and acute pancreatitis by infusion of sodium taurocholate into the pancreatic duct. In the model of chronic pancreatitis, prostaglandin E2 (PGE2), PGD2, 6-keto PGF1 alpha, thromboxane B2 (TXB2), and PAF increased significantly in the pancreas in a similar fashion, whereas leukotriene B4 (LTB4) remained unchanged. BN52021, a PAF antagonist, reduced the accumulation of pancreatic TXB2, 6-keto PGF1 alpha, and PGD2, and did not affect PGE2. In the model of acute pancreatitis, LTB4 increased, whereas PGE2, TXB2, and 6-keto PGF1 alpha decreased significantly; PGD2 changed slightly; and PAF was undetectable. The present results indicate that mild chronic pancreatitis is accompanied by the production and accumulation of a wide spectrum of lipid mediators while LTB4 was the only lipid mediator detected at biologically active concentrations in the model of severe acute pancreatitis. It is suggested that various mediators are involved in establishing a balance between inflammation and the repair of the inflamed pancreatic tissue observed in mild chronic pancreatitis. While both eicosanoids and PAF are involved in such self-limiting responses to inflammatory challenge, PAF seems to play a central role in instigating the production of the various other mediators detected in the model of chronic pancreatitis. In the model of acute pancreatitis while the deficiency of various lipid mediators may render the pancreatic tissue more susceptible to acute damage, enhanced LTB4 appears to contribute to the destructive pathology observed.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗
PubMed1994

Expert systems in the control of animal cell culture processes: potentials, functions, and perspectives.

In recent years, the development of advanced systems for bioprocess monitoring and control has become an area of intensive research. Along with traditional techniques, there are several new approaches which are increasingly being applied to bioprocess operations. Among these, of special note is expert system technology, which provides possibilities for the design of efficient bioprocess control systems with new functional capabilities. This technology has been successfully applied to variety of microbial processes at laboratory and industrial scale. The present paper analyzes the possibility for application of expert systems to animal cell cultures processes whose high complexity is well suited to expert control. The discussion focuses on the organization and the functionality of the intelligent control systems, and covers some practical aspects of their design.

Animals↗
PubMed1994

Redox effects on the bacteriochlorophyll a-containing Fenna-Matthews-Olson protein from Chlorobium tepidum.

The BChl a-containing Fenna-Matthews-Olson (FMO) protein from the green sulfur bacterium Chlorobium tepidum was purified and characterized. Fluorescence spectra indicate that efficient excited state quenching occurs at neutral or oxidizing redox potentials. The major fluorescence lifetime at room temperature is approximately 60 ps in samples that are in neutral or oxidizing conditions, and approximately 2 ns in samples where the strong reductant sodium dithionite has been added. A similar change is observed in pump-probe picosecond absorbance difference experiments, where the long life time component increases after dithionite addition. A 16 Gauss wide EPR signal with g factor = 2.005 is observed in samples without dithionite. This signal largely disappears upon addition of dithionite. Dithionite induces large reversible changes in the 77 K absorbance spectra of the purified FMO protein and in whole cells. These results indicate that the FMO protein contains redox active groups, which may be involved in the regulation of energy transfer. Room temperature circular dichroism and low temperature absorption spectra show that dithionite also induces conformational or structural changes of the FMO protein complex.

Bacterial Proteins↗
PubMed1994

Novel expression of gastrin (CCK-B) receptors in pancreatic carcinomas and dysplastic pancreas from transgenic mice.

Transgenic mice bearing the elastase I promoter--SV40 T-antigen fusion gene (ELSV) develop pancreatic acinar cell carcinomas by 3 to 6 months of age. The purpose of the study was to determine if pancreatic carcinomas and dysplastic pancreas from the Tg (Ela-1, SV40E + Ela-1, neo) Bri19 strain of ELSV transgenic mice express gastrin (CCK-B) receptors. To accomplish this, we utilized iodine 125 (125I)-gastrin binding studies, reverse transcription-polymerase chain reaction (RT-PCR), and Southern blot analysis to examine pancreatic carcinomas from 26-week-old male ELSV transgenic mice, dysplastic pancreas from 8-week-old male ELSV transgenic mice, and normal pancreas from 30-week-old nontransgenic male mice (SJL/J) and from 8-week-old nontransgenic male mice (B6SJLF1/J). No saturable gastrin binding to normal nontransgenic mouse pancreas was found. In contrast, saturable gastrin binding was detected at pH 6.5, 22 degrees C, in 9 of 13 pancreatic carcinomas and all 5 dysplastic pancreata. Competitive inhibition 125I-gastrin binding assays showed gastrin bound to a single class of high-affinity receptors (receptor binding affinity [Kd] 0.11 +/- 0.02 nM, binding capacities ranging from 1 to 60 fmol/mg protein for pancreatic carcinomas; Kd: 0.15 +/- 0.04 nM, binding capacities ranging from 1 to 9 fmol/mg protein for dysplastic pancreas). RT-PCR and Southern blot analysis confirmed 125I-gastrin binding studies by demonstrating gastrin (CCK-B) receptor mRNA expression in pancreatic carcinomas and dysplastic pancreas but an absence of mRNA expression in normal nontransgenic mouse pancreas. In conclusion, pancreatic carcinomas and dysplastic pancreas in ELSV transgenic mice novelly express gastrin (CCK-B) receptors. This expression may provide a growth advantage to acinar cells as part of the multistage process of carcinogenesis.

Animals↗
PubMed1994

Stimulation of in vivo pancreatic growth in the rat is mediated specifically by way of cholecystokinin-A receptors.

BACKGROUND/AIMS: Cholecystokinin (CCK) and gastrin stimulate growth of rodent pancreas in vivo. However, it remains unclear whether these growth effects are mediated specifically by CCK-A receptors, CCK-B receptors, or both. To clarify this issue, the present study examined the effect of highly selective and biologically active CCK agonists on pancreatic growth. METHODS: Rats were subcutaneously injected with either (1) CCK-8, a nonselective CCK agonist (2.50 micrograms/kg body wt); (2) A-71623, a selective CCK-A agonist, tert-butyl-oxycarbonyl-Trp-Lys (epsilon-N-2-methylphenylaminocarbonyl)-Asp-(N-methyl)-Phe-NH2 (1.84 micrograms/kg body wt); (3) SNF-8815; a selective CCK-B agonist, [(2R,3S)-beta-MePhe28, N-MeNle31]CCK26-33 (2.40 micrograms/kg body wt); or (4) saline (control) for 21 days. Rats were killed, and pancreatic weight, protein content, RNA content, DNA content, protein-DNA ratio, RNA-DNA ratio, pancreatic area per nucleus, and number of mitoses per 10,000 acinar cells were determined. RESULTS: Nonselective CCK agonist significantly increased pancreatic weight, protein, RNA, and DNA contents, and number of mitoses per 10,000 acinar cells. Likewise, selective CCK-A agonist significantly increased pancreatic weight, protein, RNA, and DNA contents, protein-DNA ratio, RNA-DNA ratio, pancreatic area per nucleus, and number of mitoses per 10,000 acinar cells. In contrast, selective and biologically active CCK-B agonist had no effect. CONCLUSION: These findings indicate that pancreatic growth is mediated specifically by CCK-A receptors in the rat in vivo.

Animals↗
PubMed1994

Femtosecond energy transfer and spectral equilibration in bacteriochlorophyll a--protein antenna trimers from the green bacterium Chlorobium tepidum.

Femtosecond energy transfer processes in a bacteriochlorophyll a-protein antenna complex from the green sulfur bacterium Chlorobium tepidum have been studied by one-color, two-color, and broadband absorption difference spectroscopy. Much of the spectral excitation equilibration in this antenna occurs with 350 to 450 fs kinetics. The anisotropy decay functions r(t) exhibit two major lifetime components, 100 to 130 fs and 1.7 to 2.0 ps. The short component lifetimes may represent single-step energy transfer kinetics in this antenna; the long component is similar to the anisotropy decay observed in earlier picosecond pump-probe experiments.

Bacteria↗
PubMed1994

Structure of the mouse gonadotropin-releasing hormone receptor gene: variant transcripts generated by alternative processing.

The mouse gonadotropin-releasing hormone receptor (GnRHR) is unique among G-protein-coupled receptors in its lack of a putative intracellular carboxy-terminal domain. A gonadotrope cell line cDNA library was screened in a search for alternative forms of the receptor transcript and 42 clones were obtained, representing a number of variant cDNAs. To determine the origin of these transcripts, the structure of the mouse gene was mapped from 11 distinct genomic clones. The gene contains three exons, spanning more than 22 kb. Exons 1, 2, and 3 encode, respectively, nucleotides +1 to +522, +523 to +739, and +740 to +981 of the open reading frame of the cDNA for the functional mouse GnRHR. Southern blot analysis with genomic DNA is consistent with the presence of a single gene. By comparison with the genomic sequence, the origins of the variant cDNAs isolated can be clarified. All the cDNAs contain the first exon and the majority (71%) encode the functional 327-amino-acid receptor previously reported. One group of clones (14%), which contains exons 1 and 2, continues 700 bp past the exon 2 splice donor of the wild-type receptor. These clones terminate after a polyadenylation signal and have an open reading frame encoding a protein of only 261 amino acids. In a different group of transcripts (5%), exon 2 is absent, resulting in a shift in the reading frame and encoding a protein of 177 amino acids. These data support alternative processing of the mouse GnRHR gene.

Alternative Splicing↗
PubMed1994

A 60-bp core promoter sequence of murine lactate dehydrogenase C is sufficient to direct testis-specific transcription in vitro.

A clone containing the 5' flanking region of the testis-specific murine lactate dehydrogenase C (Ldhc) gene was isolated from a mouse genomic library. Promoter activity was demonstrated within a 720-bp fragment in testis nuclear extract (TN). Interestingly, the addition of liver nuclear extract (LN) significantly repressed Ldhc promoter activity in the transcription assay system. Sequence analysis of this promoter region revealed several ubiquitous cis-regulatory elements, including one TATA box, one GC box, and two putative CCAAT elements. Analysis of a series of deletion mutants revealed that a 60-bp core promoter sequence was sufficient to direct basal, testis-specific transcription in an in vitro transcription system. A 103-kDa protein in TN and a 65-kDa protein in LN bind to the same palindromic sequences within the 60-bp core promoter region.

Animals↗
PubMed1994

Photodegradation of sulfamethoxazole: a chemical system capable of monitoring seasonal changes in UVB intensity.

Sulfamethoxazole (SMX) in its nonionized form in aqueous solution has ultraviolet (UV) absorption that is maximal at 268 nm but extends through the ultraviolet-B (UVB) region. It was found to be extremely susceptible to photodegradation when exposed to artificial UV radiation through a Pyrex filter or to unfiltered natural sunlight. The SMX anion was more stable. The quantum yields of the photodegradation of both forms were determined by use of monochromatic light and ferrioxalate chemical actinometry, the values of 0.47 (pH 3.0) and 0.084 (pH 9.0) at the maximum absorption wavelengths (268 and 257 nm, respectively) being obtained. Using literature data on sunlight intensity, the photochemical shelf-life of SMX solutions exposed to direct sunlight was calculated for Sydney (latitude 33.5 degrees S) as a function of season of the year and verified experimentally. A fixed correlation was established between the rate constant for SMX degradation and UVB intensity measured by a radiometer, suggesting the capacity of this chemical system to monitor changes in the UVB region of sunlight.

Humans↗
PubMed1994

Characterization of a Marek's disease virus BamHI-L-specific cDNA clone obtained from a Marek's disease lymphoblastoid cell line.

Two Marek's disease (MD) virus BamHI-L-specific cDNA clones were isolated from a cDNA library constructed from poly(A)+ RNA fractions of an MD lymphoblastoid cell line, MDCC-CU41 (CU41). These clones were mapped to the region corresponding to the BamHI-Q2 and L-regions. These clones hybridized with 2.5-, 0.8-, and 0.6-kb transcripts prepared from CU41. The transcriptional unit of the 0.6-kb transcript was determined by RNase protection assays. An open reading frame encoding a 107-amino-acid polypeptide was identified in the 0.6-kb transcript. Reverse transcriptase-PCR demonstrated the presence of this transcript in both CU41 and a reticuloendotheliosis virus-transformed cell line latently infected with MD virus.

Animals↗
PubMed1994

Identification of a membrane-binding domain within the amino-terminal region of human immunodeficiency virus type 1 Gag protein which interacts with acidic phospholipids.

Retroviral Gag proteins are targeted to the plasma membrane, where they play the central role in virion formation. Several studies have suggested that the membrane-binding signal is contained within the amino-terminal matrix sequence; however, the precise location has never been determined for the Gag protein of any retrovirus. In this report, we show that the first 31 residues of human immunodeficiency virus type 1 Gag protein can function independently as a membrane-targeting domain when fused to heterologous proteins. A bipartite membrane-targeting motif was identified, consisting of the myristylated N-terminal 14 amino acids and a highly basic region that binds acidic phospholipids. Replacement of the N-terminal membrane-targeting domain of pp60v-src with that of human immunodeficiency virus type 1 Gag elicits efficient membrane binding and a transforming phenotype. Removal of myristate or the basic region results in decreased membrane binding of Gag-Src chimeras in vitro and impaired virion formation by Pr55gag in vivo. We propose that the N-terminal Gag sequence functions as a targeting signal to direct interaction with acidic phospholipids on the cytoplasmic leaflet of the plasma membrane.

Acids↗