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Biomedical subjects

V C Yu

Publications and source records attributed to V C Yu.

28 records · Page 2Linked to original sources
PubMed1988

Differentiation of human neuroblastoma cells: marked potentiation of prostaglandin E-stimulated accumulation of cyclic AMP by retinoic acid.

Neuroblastoma cells in culture contain low levels of cyclic AMP, a second messenger which plays a major role in neuronal maturation. In this study, human neuroblastoma cells, SK-N-SH-SY5Y, were induced to differentiate by treatment with either nerve growth factor (50 ng/ml), retinoic acid (10 microM), dibutyryl cyclic AMP (1 mM), or 12-O-tetradecanoylphorbol-13-acetate (0.1 microM), and the ability of several neurotransmitters or hormones to stimulate adenylyl cyclase was tested. Although all four differentiation factors caused morphological changes towards a neuronal phenotype, only retinoic acid dramatically enhanced cyclic AMP accumulation, specifically upon stimulation with prostaglandin E1 (PGE1). PGE2 was also active, but less potent, than PGE1, whereas the other cyclic AMP-stimulating agents tested were largely unaffected. Further, the rapid desensitization of the PGE1-cyclic AMP response observed in control cells after 20 min of PGE1 exposure did not occur in retinoic acid-treated cells, and the EC50 values for PGE1 were reduced from approximately 240 to 14 nM after retinoic acid treatment. The increased sensitivity to PGE was associated with an increase of high-affinity PGE1 binding sites, whereas the Gs coupling proteins and adenylyl cyclase were not measurably affected. A similar enhancement of the PGE1-cyclic AMP response by retinoic acid was also observed in two additional human neuroblastoma cell lines tested, Kelly and IMR-32, suggesting that up-regulation of the prostaglandin response by retinoic acid is common among neuroblastoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1988

Efficacy and tolerance of narcotic analgesics at the mu opioid receptor in differentiated human neuroblastoma cells.

Upon differentiation with retinoic acid of the human neuroblastoma cells SH-SY5Y into mature neurons, opioid drugs become highly effective in suppressing prostaglandin E1 (50% inhibition)- and forskolin (70% inhibition)-stimulated adenylate cyclase activity, which was assessed by measuring cyclic AMP accumulation in intact cells. Whereas the SH-SY5Y cells carry both mu and delta receptors in a ratio of mu/delta approximately equal to 5/1, the response is predominantly mediated by the mu receptor. Morphine acts as a strong agonist with an EC50 of 50 to 100 nM which falls into the therapeutic range expected for narcotic analgesic effects mediated by the mu receptor. Narcotic analgesic drugs with only partial agonism fail to evoke full response, which suggests that this cell model could provide a rapid screening assay for narcotic analgesic efficacy. Continued exposure of the cells to morphine resulted in partial tolerance within 12 hr with a 4-fold shift of morphine's EC50 to higher concentrations, whereas longer morphine exposure did not cause any further shift. Thus, the differentiated SH-SY5Y cells provide a suitable system for studying the molecular mechanisms of the narcotic analgesics.

Adenylyl Cyclases↗
PubMed1987

Differential expression of alpha-subunits of G-proteins in human neuroblastoma-derived cell clones.

The distribution of alpha- and beta-subunits of G-proteins was analyzed in membranes of three cell clones which are derived from the human neuroblastoma cell line SK-N-SH. The neuroblast-like clone SH-SY5Y shows a pattern of G-proteins very similar to that of human brain cortex with high levels of Gi alpha and Go alpha but low levels of G40 alpha. The intermediate clone SH-IN contains high levels of Go alpha and Gi alpha and moderate levels of G40 alpha. The non-neuronal clone SH-EP shows high levels of G40 alpha but lacks Go alpha. Differentiation of the neuroblast-like clone SH-SY5Y by retinoic acid or nerve growth factor does not change the amount of Gi alpha or Go alpha in the membrane.

Cell Differentiation↗
PubMed1987

Expression of neurotransmitter receptors and myc protooncogenes in subclones of a human neuroblastoma cell line.

Phenotypic variability of the human neuroblastoma cell line SK-N-SH was studied with the use of three subclones that interconvert at a slower rate than the parent cell line, i.e., a neuroblast-type subclone (SH-SY5Y), a nonneuronal, strongly substrate adherent subclone (SH-EP), and an intermediate type subclone (SH-IN). Rhodamine-phalloidin staining of actin fibers revealed differences in the cytoskeleton morphology of the three subclones, while the clathrin subunit proteins (heavy and light chains), components of coated vesicles, were invariant. Dramatic differences were observed for the expression of neurotransmitter systems, i.e., the mu and delta opioid receptor, the muscarinic cholinergic receptor and its effect on phosphatidylinositol turnover, and the uptake1 transporter for catecholamines. While these systems were strongly expressed in the parent line and the neuroblast-like clones SH-SY5Y and SH-IN, they were absent or barely detectable in the nonneuronal EP clone. Furthermore, the protooncogenes N- and c-myc were only expressed in the neuroblast containing lines, consistent with their growth characteristics of fully transformed cells. The strong c-myc expression in the absence of c- or N-myc amplification in SK-N-SH, adds a new form of high protooncogene activity in neuroblastoma cell lines. The remarkable differences of neurotransmitter systems and myc expression among the various phenotypes of human neuroblastoma cells should be considered in the therapy of neuroblastoma.

Actins↗
PubMed1986

Phosphatidylinositol turnover in neuroblastoma cells: regulation by bradykinin, acetylcholine, but not mu- and delta-opioid receptors.

The effect of opioids on phosphatidylinositol (PI) turnover to release inositol triphosphate (IP3) as second messenger was examined in mouse neuroblastoma X rat glioma hybrid cells NG108-15 (delta-receptors) and human neuroblastoma cells, SK-N-SH (predominantly mu-receptors). PI turnover can be stimulated in both NG108-15 and SK-N-SH cells by bradykinin and acetylcholine, respectively. In contrast, etorphine, DADL ([D-Ala2,D-Leu5]-enkephalin) and DAGO ([D-Ala2,MePhe4,Gly-ol5]-enkephalin), up to 1 microM concentrations failed to affect PI turnover in both cell lines. These results suggest that IP3 is not likely to serve as second messenger for both mu- and delta-opioid receptors.

Acetylcholine↗
PubMed1986

Delta opioid receptors in human neuroblastoma cell lines.

Opioid receptor sites were detectable in 4 out of 9 human neuroblastoma cell lines tested, in the human retinoblastoma line Y79 NHT C10 and in the mouse neuroblastoma line Neuro 2A. All of these cell lines expressed delta sites, while only one coexpressed mu sites (SK-N-SH). Together with delta sites previously found in rodent neuroblastoma lines, these results suggest that the expression of delta sites is under less stringent control than that of mu and chi sites. A large number of delta sites (greater than 10,000 sites per cell) is expressed in IMR-32 and NMB neuroblastoma lines. Agonist binding was sensitive to Na+ and guanine nucleotides. The delta sites in IMR-32 and NMB cells were further characterized with delta selective ligands and [3H]DADL tracer. Their delta binding affinities were identical to those of the mu and delta cell line SK-N-SH; therefore the presence of mu sites does not appear to affect the binding behavior of the delta sites by any potential interaction among the binding proteins. Further, close correlations were found when comparing ligand binding in the human neuroblastoma cell lines with those of mouse neuroblastoma cells and rodent brain, an indication that the delta receptor is highly preserved among different species.

Binding, Competitive↗
PubMed1986

A human neuroblastoma cell line expresses mu and delta opioid receptor sites.

A series of neuroblastoma cell lines were screened for the presence of opioid receptor sites with the tracers [3H]diprenorphine (mu, delta, kappa ligand) and [3H]naloxone (mu-selective ligand). One human neuroblastoma cell line, SK-N-SH, displayed avid binding for both tracers. Binding experiments with multiple tracers revealed the presence of both mu and delta sites. These sites were stereospecific, saturable, and proteinaceous in character. Saturation binding experiments provided an estimate of 50,000 mu and 10,000 delta sites/cell. NaCl (100 mM) and guanine nucleotide, guanylyl imidodiphosphate (50 microM), reduced opioid agonist but not antagonist binding to these sites. Etorphine at 1 nM inhibited prostaglandin E1-stimulated cyclic AMP production by approximately 20%, which was reversible by naloxone. The opioid-binding sites on SK-N-SH cells closely resemble the previously reported mu and delta sites in human and rodent brain. Therefore, the SK-N-SH neuroblastoma cell line represents a useful tool to study the molecular functions of opioid receptors.

Bone Neoplasms↗
PubMedDate not supplied

Dose-dependent kinetics of quinidine in the perfused rat liver preparation. Kinetics of formation of active metabolites.

The disposition of quinidine and the kinetics of metabolite formation were studied in the once-through perfused rat liver preparation by the stepwise increase in quinidine concentration. Dose-dependent kinetics of quinidine were observed; the steady-state hepatic extraction ratio decreased from 0.97 to 0.37 when input quinidine concentration varied from 1.34 to 33.9 micrograms/ml. Moreover, the formation of 3-hydroxyquinidine (detected only in perfusate as unconjugated 3-hydroxyquinidine) remained relatively linear while the formation of O-desmethylquinidine (present in bile and perfusate mostly as conjugates) apparently approached saturation kinetics within the quinidine concentrations used. The dose-dependent character of quinidine elimination cannot be attributed to changes in drug binding, as the blood/plasma ratio (4.07) and the degree of drug unbound in plasma (66.5%) remained unaltered for the quinidine concentrations used.

Animals↗