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Y K Fung

Publications and source records attributed to Y K Fung.

At least 73 records · Page 4Linked to original sources
PubMed1987

Structural evidence for the authenticity of the human retinoblastoma gene.

The retinoblastoma (Rb) gene is the prototype for a class of recessive human cancer genes in which loss of activity of both normal alleles is thought to be associated with tumorigenesis. Sixteen of 40 retinoblastomas examined with a complementary DNA probe shown to be the Rb gene had identifiable structural changes of the Rb gene including in some cases homozygous internal deletions with corresponding truncated transcripts. An osteosarcoma also had a homozygous internal deletion with a truncated transcript. In addition, possible hot spots for deletion were identified within the Rb genomic locus. Among those tumors with no identifiable structural changes there was either absence of an Rb transcript or abnormal expression of the Rb transcript. Comparison of the structural changes in the tumor cells and fibroblasts of certain patients provided support for Knudson's two-hit hypothesis for the development of retinoblastoma at the molecular level. The ability to detect germline structural deletions in fibroblasts from some patients with bilateral retinoblastoma also indicates that the isolated gene is useful for diagnostic purposes.

Alleles↗
PubMed1987

Identification of protein products encoded by the proto-oncogene int-1.

The proto-oncogene int-1 is activated by adjacent insertions of proviral DNA in mouse mammary tumor virus-induced tumors and has transforming activity in certain mammary epithelial cell lines. The gene is normally expressed in the central nervous system of mid-gestational embryos and in the adult testis. We raised antibodies against synthetic int-1 peptides and used these to identify protein products of the gene in cells transfected or infected with retroviral vectors expressing int-1. Four protein species of 36,000, 38,000, 40,000, and 42,000 Mr were immunoprecipitated by antibodies against two different int-1 peptides and were not present in control cells. Partial degradation with V8 protease showed the four species to be structurally related to each other and to int-1 polypeptide synthesized in vitro. Treatment of the cells with tunicamycin prevented the appearance of all but the 36,000-Mr species, suggesting that the slower-migrating forms are glycosylated derivatives. The unglycosylated 36,000-Mr species migrated faster in polyacrylamide gels than the in vitro translation product of int-1 and has probably undergone cleavage of an amino-terminal signal peptide.

Animals↗
PubMed1986

Pharmacological effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on striatal dopamine receptor system.

In mice, chronic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces an increase in the maximum number of [3H]spiperone binding sites in the striatum. The sensitivity of striatal protein phosphorylation to calcium plus calmodulin is also potentiated in MPTP-treated mice. These observations are associated with an enhancement of apomorphine-induced climbing behavior in the drug-treated animals. The results of this study suggest that in an animal model for Parkinson's disease, MPTP interrupts the dopamine (DA) transmission by chemically denervating the nigrostriatal neurons and through a compensatory mechanism, it increases the number of DA receptors as well as the sensitivity of protein phosphorylation to calcium plus calmodulin in mouse striatum. The latter two events may contribute to the development of DA receptor supersensitivity.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

Modulation of apomorphine-induced climbing behavior by estradiol.

The acute and chronic effects of estradiol benzoate were studied on apomorphine-induced climbing behavior in intact female mice. Climbing behavior was measured by determining the maximum climbing time and climbing index. Mice pretreated with estradiol benzoate (0.1 or 0.3 mg/kg, SC) for 3.5 or 24 hours prior to apomorphine administration showed no significant difference in climbing behavior when compared to corn oil-treated controls. However, mice pretreated with estradiol benzoate (0.1 mg/kg, SC) for 3 consecutive days showed an attenuation in apomorphine-induced climbing at 24 or 72 hours after the last steroid injection. This study shows that the mouse climbing behavioral model provides a simple and quantitative procedure for studying the antidopaminergic effects of estrogen.

Animals↗
PubMed1986

Stereoselective syntheses of the trans-decahydroquinoline-5-carboxylic acid epimers. Diastereomeric zwitterionic probes of gamma-aminobutyric acid related biological properties in vitro and in vivo.

The syntheses of the 5 beta and 5 alpha epimers of trans-(4a alpha,8a beta)-decahydroquinoline-5-carboxylic acids (3 and 4) from vinylogous bicyclic imide 10 are described. The reduction of trans-5-(1,3-dithian-2-ylidene)octahydro-2(1H)-quinolinone (13) to afford the 5 alpha-(1,3-dithian-2-yl) compound 16 was a key step in the synthesis of trans-4 while hydroboration-H2O2 treatment of phenylmethyl trans-octahydro-5-methylene-1(2H)-quinolinecarboxylate (21) to afford the 5 beta-hydroxymethyl compound 22 was a key step in the synthesis of 3. These trans diastereomers 3 and 4 and the previously prepared cis analogues 1 and 2 were investigated for their ability to interact with GABAA and GABAB receptors and picrotoxin binding sites as well as with neuronal GABA transport systems in brain tissue. Like 1 and 2, tonic-clonic seizures were induced when trans-3 or -4 were administered to mice intracerebroventricularly. Only trans-4 weakly inhibited [3H]GABA binding to GABAA and GABAB receptors in vitro. Large doses (10 mg/kg) of diazepam reversed the convulsant activity of both trans-3 and trans-4. Although trans-3 is the more potent convulsant, trans-4 may have GABA antagonist activity in vivo. However, none of the decahydroquinoline diastereomers have a pronounced effect on GABA receptors that can currently be studied in vitro. Results obtained in vivo lead us to propose that these diastereoisomers may serve as unique conformational probes relating certain zwitterionic topographies to stimulatory activity in the central nervous system.

Animals↗
PubMed1986

Acute effect of nicotine on the striatal dopaminergic system in the rat.

The acute effects of nicotine (1.5 mg kg-1 day-1) on the striatal dopaminergic system have been examined in the rat. Twenty-four hours after nicotine treatment, spontaneous locomotor activity in response to apomorphine or (+)-amphetamine and the binding of [3H]spiperone to striatal particulates were determined. Pretreatment of nicotine did not alter the characteristics of [3H]spiperone binding to striatal dopamine receptors. The nicotine treatment did not affect the apomorphine-induced locomotor activity, however, the (+)-amphetamine-stimulated locomotor activity was attenuated. These results suggest that nicotine acutely alters the presynaptic dopaminergic activity without significantly affecting the postsynaptic dopaminergic function.

Animals↗
PubMed1985

Amphetamine-induced circling behaviour in MPTP-lesioned mice.

This study was designed to examine the effect of intrastriatal administration of MPTP on (+)-amphetamine-induced circling behaviour in mice. The results demonstrate that (+)-amphetamine elicits circling behaviour in MPTP-lesioned animals. MPTP produced a 70% depletion of striatal dopamine concentration.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1985

Nucleotide sequence and expression in vitro of cDNA derived from mRNA of int-1, a provirally activated mouse mammary oncogene.

The mouse int-1 gene is a putative mammary oncogene discovered as a target for transcriptionally activating proviral insertion mutations in mammary carcinomas induced by the mouse mammary tumor virus in C3H mice. We have isolated molecular clones of full- or nearly full-length cDNA transcribed from int-1 RNA (2.6 kilobases) in a virus-induced mammary tumor. Comparison of the nucleotide sequence of the cDNA clones with that of the int-1 gene (A. van Ooyen and R. Nusse, Cell 39:233-240, 1984) shows the following. The coding region of the int-1 gene is composed of four exons. The splice donor and acceptor sites conform to consensus; however, at least two closely spaced polyadenylation sites are used, and the transcriptional initiation site remains ambiguous. The major open reading frame is preceded by an open frame 10 codons in length. The mRNA encodes a 41-kilodalton protein with several striking features--a strongly hydrophobic amino terminus, a cysteine-rich carboxy terminus, and four potential glycosylation sites. There are no differences in nucleotide sequence between the known exons of the normal and a provirally activated allele. The length of the deduced open reading frame was further confirmed by in vitro translation of RNA transcribed from the cDNA clones with SP6 RNA polymerase.

Animals↗
PubMed1983

An in-vivo method for testing drugs that influence striatal dopaminergic functions.

A procedure is described for evaluating the effects of drugs on dopaminergic function in the striatum of mice. Mice, anesthetized with chloral hydrate are injected with 6-hydroxydopamine into one striatum to destroy dopamine nerve terminals at this site. Several days later, the mice are anesthetized with halothane, and test drugs or saline are injected into the intact striatum either before or after the systemic administration of amphetamine. The effect of these drugs on amphetamine-induced circling behavior is evaluated. Using this model, we have found that pilocarpine and muscimol can inhibit amphetamine-induced circling and their effects are blocked by the systemic administration of scopolamine and picrotoxin, respectively. In addition, ethyleneglycol-bis-(beta-amino-ethyl ether) N,N'-tetraacetic acid (EGTA), a calcium chelating agent, inhibited amphetamine-induced circling behavior and this effect is prevented by adding calcium to the EGTA solution. Finally, the intrastriatal administration of prostaglandin E2 but not its metabolite, 13,14-dihydro-15-keto-prostaglandin E2 inhibited amphetamine-induced circling suggesting a selective effect of the active prostaglandin. These results suggest that this procedure could be used for evaluating both the mechanism of action of drugs in the striatum as well as screening drugs for their therapeutic potential.

Animals↗
PubMed1983

An automated method for measurement of circling behavior in the mouse.

Circling behavior in animals lesioned unilaterally in one striatum with 6-hydroxydopamine is widely used to test pharmacological compounds with dopaminergic activity. Although automated techniques employed to record this behavior have previously been reported, most of these methods either limit the movement of the animal or are less reliable for various reasons. This paper describes a new method which allows the free movement of the animal in addition to recording the circling behavior automatically. Furthermore, this device provides new and unique data on the diameter and total area of the circles that are circumscribed by the animal. Consequently, the present device may prove to be a better and more reliable tool to assess the pharmacological effect of drugs on the striatal dopaminergic system.

Amphetamine↗
PubMed1983

Activation of the cellular oncogene c-erbB by LTR insertion: molecular basis for induction of erythroblastosis by avian leukosis virus.

Avian leukosis virus (ALV), a slowly oncogenic retrovirus, induces in chickens a variety of neoplasms, including lymphoid leukosis and erythroblastosis. In lymphoid leukosis, a cellular oncogene, c-myc, is activated by the insertion of ALV LTR. We provide evidence that ALV utilizes a similar mechanism in erythroblastosis induction by activating a different cellular oncogene, c-erbB. We report the isolation, from leukemic erythroblast DNA, of a clone that represents the viral-cell junction fragment and carried the ALV LTR and part of the c-erbB locus. Restriction and sequence analyses reveal that the LTR is located upstream from the erbB coding region and is oriented in the same transcriptional direction; such a structure would be compatible with the promoter-insertion type of activation. Our findings provide a molecular explanation for the multipotency of slowly oncogenic retroviruses.

Animals↗
PubMed1983

Tumor induction by direct injection of cloned v-src DNA into chickens.

The in vitro transforming potential of Rous sarcoma viruses has been shown to reside in a gene segment, v-src. To provide direct proof that the isolated v-src sequence contains all the information necessary for sarcoma induction in vivo, we have injected subgenomic and genomic cloned DNA carrying v-src directly into chickens. We report that v-src, without the complements of other viral genes, can effectively induce sarcomas in the host within weeks after injection. The sarcoma tumors generated by subgenomic v-src DNA are of mono- or oligoclonal origin. They have acquired v-src sequences in the genome and expressed high levels of src messages. Intact long terminal repeats do not seem to be essential in the tumorigenic process.

Animals↗
PubMed1983

Stereostructure-activity relationships of the GABA-containing cis-decahydroquinoline-5-carboxylic acids; intracerebroventricular studies in mice.

Two cis-decahydroquinoline-5-carboxylic acids, cis-1 and 2 were investigated for their pharmacological activities in vivo. Intracerebroventricular administration of either agent elicited convulsant activity in mice. This convulsant effect can be antagonized by pretreating the mice with n-dipropylacetate (valproate). Our results suggest that cis-1 may act indirectly as a partial gamma-aminobutyric acid (GABA) agonist in vivo. On the other hand, both cis-1 and 2, at higher concentrations, exhibit properties of a GABA-antagonist, but this effect seems not to be due to GABA receptor binding.

Animals↗
PubMed1982

BehavioraL and biochemical changes caused by muscimol in mice withdrawN from haloperidol administration.

This study was designed to determine the behavioral and biochemical effects of the gamma-aminobutyric acid (GABA) agonist, muscimol, in mice withdrawn from chronic haloperidol administration. Mice received either haloperidol or vehicle In their drinking water for 35 days, after which the haloperidol was replaced with vehicle. Seven days after withdrawal from chronic treatment with haloperidol, the effect of apomorphine on the climbing behavior of haloperidol-withdrawn mice was markedly enhanced as compared to control mice that received only vehicle. Muscimol produced a dose-related reduction in the intensity of climbing behavior induced by apomorphine in both control and haloperidol-withdrawn mice. However, the inhibition of climbing behavior induced by muscimol was significantly greater in haloperidol-withdrawn animals. In addition, in haloperidol-withdrawn mice, muscimol produced a significant reduction in striatal homovanillic (HVA) levels with no change in striatal dopamine (DA) levels, suggesting a decrease in DA turnover. In support of this conclusion, muscimol decreased the disappearance of dopamine in haloperidol-withdrawn mice that were injected with alpha-methyl-p-tyrosine. Both the behavioral and biochemical effects of muscimol were blocked by the GABA antagonist, picrotoxin. These results indicate that after chronic haloperidol administration there is not only an enhanced response to dopaminergic agonists but also to GABAergic agonists.

Animals↗
PubMed1982

An in vivo method for testing GABAergic compounds.

This report describes an intracerebroventricular technique of drug injection which enables compounds with GABAergic properties to be rapidly identified in vivo. In addition, this method allows for the testing of compounds that poorly penetrate the blood brain barrier for GABAergic activities. Subcutaneous administration of apomorphine (1.5 mg/kg, SC) elicits climbing behavior in mice. The apomorphine-induced climbing behavior is inhibited by the intracerebroventricular or intraperitoneal administration of known GABA (gamma aminobutyric acid) agonists including muscimol (10-50 ng) and GABA (2-10 micrograms). This inhibitory effect of GABA or muscimol on apomorphine-induced climbing behavior can be reversed by picrotoxin (2 mg/kg, IP), a known GABA-receptor antagonist.

Animals↗
PubMed1982

Orientation and position of avian leukosis virus DNA relative to the cellular oncogene c-myc in B-lymphoma tumors of highly susceptible 15I5 X 7(2) chickens.

We previously reported our characterizations of the B-lymphoma tumors induced in a highly susceptible line of chickens (15I5 X 7(2)) by the avian leukosis virus RAV-1 (Proc. Natl. Acad. Sci. 78:3418-3422, 1981). We demonstrated that in greater than 90% of the tumors, the RAV-1 provirus is integrated near a cellular oncogene, c-myc. In the present study, we devised a simple approach, relying on SalI digestion, for further defining the locations and orientations of the proviruses with respect to the c-myc gene. We report here that in the great majority of cases the provirus is situated upstream from and in the same transcriptional direction as the c-myc gene--a configuration compatible with the promoter-insertion model proposed by Hayward et al. (Nature [London] 290:475-480, 1981).

Animals↗