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Biomedical subjects

Y K Fung

Publications and source records attributed to Y K Fung.

At least 37 records · Page 2Linked to original sources
PubMed1995

Regulation of retinoblastoma gene expression in hormone-dependent breast cancer.

Studies have shown an increased risk for breast cancer in the mothers of children suffering from retinoblastoma and osteosarcoma, suggesting a role for the retinoblastoma susceptibility (Rb) gene product in breast cancer. We now show that estradiol decreases the expression of Rb at the level of protein and messenger RNA (mRNA) in estrogen-dependent breast cancer cell lines. Treatment of MCF-7 cells with 10(-9) M estradiol for 48 h resulted in a 70% decrease in the level of Rb protein. Ribonuclease protection assays showed a 50% decrease in the steady state levels of Rb mRNA by 12 h and a 70% decrease in Rb mRNA by 24 h. Treatment with estradiol had no effect on the rate of Rb gene transcription or on Rb mRNA stability, but resulted in an increase in the steady state level of Rb mRNA in the nucleus. The effect of estradiol was inhibited by 10(-7) M 4-hydroxytamoxifen. In the absence of estradiol, the antiestrogens 4-hydroxytamoxifen and ICI 164,384 increased Rb mRNA by 50% over that in estrogen-depleted conditions. Estradiol regulation of Rb mRNA also occurred in other estrogen-dependent breast cancer cell lines. Insulin-like growth factor I, insulin, progestins, and epidermal growth factor had no effect on Rb expression. In summary, these results show that estradiol specifically regulates the expression of the Rb susceptibility gene product in hormone-dependent breast cancer by a posttranscriptional mechanism that occurs in the nucleus. The results from this study suggest that the negative regulation of Rb expression by estradiol, rather than Rb loss or mutation, may play an important role in breast carcinogenesis.

Breast Neoplasms↗
PubMed1995

Determination of blood mercury concentrations in Alzheimer's patients.

Trace element neurotoxicity can be an etiologic factor for Alzheimer's disease. This cross sectional clinical study determined blood mercury in patients with diagnosed Alzheimer's disease as compared to control subjects without known central nervous system and renal disorders. Unique within the confines of a nursing home, all subjects were exposed to the same environment and consumed a diet without fish and seafood for a period of three months prior to the study. The results of this study show that blood mercury concentrations detected in subjects with Alzheimer's disease were not statistically different than that of control subjects. Ratios of blood mercury to blood selenium were also determined and no statistical difference was found between these two groups.

Aged↗
PubMed1994

Behavioural consequences of cocaine withdrawal in rats.

This study was designed to examine the impact of cocaine withdrawal on several behavioural parameters in rats. After 1 and 3 day withdrawal from continuous cocaine administration (50 mg kg-1 for 28 days, subcutaneous infusion via osmotic minipumps), rats showed significant changes in spontaneous locomotor activity, conditioned avoidance response and increased levels of anxiety. However, cocaine withdrawal did not alter the motor co-ordination, body weight, food and water consumption of these animals. The neurochemical effects of cocaine on central dopaminergic neuronal systems may account for locomotor deficit observed in these cocaine-withdrawal animals.

Animals↗
PubMed1993

Cell cycle regulation of nuclear localization of hepatitis B virus core protein.

The hepatitis B virus (HBV) core protein has been found in the nucleus, the cytoplasm, or both of HBV-infected hepatocytes. However, the mechanism that regulates the subcellular localization of the HBV core protein is still unclear. In this report, we demonstrate that nuclear localization of the HBV core protein is cell cycle-regulated in two different cell lines. The amount of the core protein in the nucleus was increased during the G1 phase, reduced to an undetectable level during the S phase, and increased again when the cells were confluent and ceased to grow. Thus, the nuclear localization of the core protein during HBV infection can be at least partially attributed to liver injury and regeneration, which cause the hepatocytes to enter cell cycles. Based on the observation that the cytoplasmic core protein was phosphorylated and the nuclear core protein was not, we speculate that nuclear localization of the HBV core protein is negatively regulated by phosphorylation during the cell cycle.

3T3 Cells↗
PubMed1993

Effects of systemic and topical nicotine on pulpal blood flow in dogs.

It has been suggested that nicotine exerts cardiovascular effects which are similar to stimulation of the sympathoadrenal system. If this observation is true, nicotine administration would decrease pulpal blood flow and possible alter the pulpal response to injury. The purpose of this study was to measure pulpal blood flow in dogs using the radiolabelled microsphere method following topical or systemic administration of nicotine for 28 days. Thirteen dogs were divided into three groups. Group one received topical nicotine (8 mg nicotine/kg/day) combined with orabase which was applied in two equal doses to the mandibular anterior gingiva. Group two received systemic nicotine (2.5 mg/kg/day) delivered by osmotic pumps implanted subcutaneously in the back of each animals' neck. Group three were controls, and these animals received either topical orabase twice daily applied to the mandibular anterior gingiva or saline via osmotic pumps. Results indicated pulpal blood flow increased from Day 0 to Day 28 in both nicotine treated groups. Group one (topical nicotine) exhibited a mean increase in blood flow of 21.8 ml/min/100 g, while group two exhibited a mean increase of 50.1 ml/min/100 g. Group three, the control animals, exhibited a mean decrease in pulpal blood flow of 22.1 ml/min/100 g over the 28-day interval. These changes were not statistically significant (p > 0.05).

Analysis of Variance↗
PubMed1993

The Rb gene suppresses the growth of normal cells.

The suppression of tumor formation, first demonstrated by somatic cell hybrid and microcell fusion experiments, suggests the existence of a class of genes that selectively suppress the growth of tumor cells but not normal cells. The reintroduction of these genes into tumor cells presumably renders the cells responsive to in vivo growth inhibitory environment. As the inheritance of a defective retinoblastoma gene (Rb-1) allele results in a predisposition to the development of various cancers, and since inactivation of both alleles are observed in tumor cells, the Rb gene has been suspected to have the ability to suppress tumor growth. Data presented here demonstrated that different types of normal cells, which have a limited life span, were also growth arrested by a transfected Rb gene. Cell lines which are resistant to the growth suppression effect of the Rb gene in vitro, retain the ability to form tumors in nude mice even in the presence of a stable and highly expressed wild type Rb protein. We conclude that while the Rb gene can suppress the growth of many tumor cell lines, its growth suppression effect is not tumor specific.

3T3 Cells↗
PubMed1992

The role of the retinoblastoma gene in breast cancer development.

The observation that the human retinoblastoma gene is inactivated in about 20% of breast carcinomas indicates that it may be important in the development of these tumors. The fact that the loss of RB1 expression correlates with the progression of the disease, and especially with the inability of the cells to differentiate, is consistent with the clinical observation that retinoblastoma does not occur in children in whom the target cells have already fully differentiated. This suggests that the normal function of RB1 is to promote differentiation. It is possible that the loss of the ability of a cell to differentiate contributes to its ability to grow in a foreign environment (metastasis), but this hypothesis remains to be tested. Our observation that the overexpression of RB1 suppresses the growth of these tumor cells in vitro is consistent with this hypotheses.

Breast Neoplasms↗
PubMed1992

Chronic effects of nicotine on mesolimbic dopaminergic system in rats.

Rats were pretreated with saline or nicotine (1.5 mg/kg/day) by subcutaneously implanting each animal with an Alzet osmotic minipump which continuously released saline or nicotine (1.5 mg/kg/day) for 14 days. The behavioral and biochemical effects of nicotine on the dopaminergic neuronal system in rat nucleus accumbens were examined. It was found that chronic nicotine treatment increased the affinity of L-[3H]nicotine binding site in the nucleus accumbens. This treatment also potentiated the ability of (+)-amphetamine, but not high potassium, to stimulate formation and release of [3H]dopamine in tissue slices from rat nucleus accumbens. Chronic nicotine treatment did not alter the characteristics of [3H]spiperone binding site, the rate of dopamine turnover and the concentrations of gamma-aminobutyric acid in the nucleus accumbens.

Animals↗
PubMed1992

Detection of retinoblastoma gene copy number in metaphase chromosomes and interphase nuclei by fluorescence in situ hybridization.

Fluorescence in situ hybridization (FISH) was applied to detect the copy number of the retinoblastoma (RB1) tumor suppressor gene in metaphase chromosomes and interphase nuclei. We used 14 lambda phage clones spanning the whole RB1 gene region as a probe and obtained a specific hybridization signal in normal metaphase chromosomes at 13q14. Normal interphase nuclei showed two RB1 signals in about 90% of cases, whereas two cell lines with cytogenetically defined deletions involving the RB1 gene showed only one hybridization signal in about 80% of the nuclei. Analogous changes were detected in metaphase chromosomes. Multicolor FISH with subsets of the phage clones allowed visualization of subregions within the 200-kb gene in interphase nuclei. Analysis of clinical breast cancer samples showed that most of the cells contained two copies of the RB1 gene, even when restriction fragment length polymorphism analysis showed loss of heterozygosity (LOH) at the RB1 locus. This indicates that LOH at the RB1 locus in breast cancer cells probably involves mechanisms other than physical deletion.

Breast Neoplasms↗
PubMed1992

Nicotine enhances interleukin production of rat splenic T lymphocytes.

Very little is known regarding the effects of nicotine, the most pharmacologically active component of tobacco products, on T lymphocyte activity or interleukin production. Therefore, rats were implanted subcutaneously with osmotic mini-pumps containing either physiological saline, nicotine (1.5 mg/kg/day) or a high dose of nicotine (4.5 mg/kg/day) for a period of 14 days. The ability of the splenic T lymphocytes to respond to the polyclonal T lymphocyte mitogens, Concanavalin A (ConA) or phytohemagglutinin (PHA), and the ability of mitogen stimulated splenic T lymphocytes to produce interleukin 2 (IL2) were determined. Treatment with nicotine suppressed, in a dose dependent fashion, the ability of splenic T lymphocytes to respond to mitogen, but dramatically enhanced the ability of mitogen stimulated lymphocytes to generate IL2.

Animals↗
PubMed1992

Coupled down-regulation of the RB retinoblastoma and c-myc genes antecedes cell differentiation: possible role of RB as a "status quo" gene.

The ability of the well known morphogen, retinoic acid (RA), as well as 1,25-dihydroxy-vitamin D3 (VD), whose receptor complex binds a DNA consensus sequence related to that of the retinoic acid receptor, to regulate expression of the retinoblastoma (RB) tumor suppressor gene in a context of induced cell differentiation was characterized. HL-60 human promyelocytic leukemia cells were induced to undergo myeloid or monocytic terminal cell differentiation by these agents. To investigate the potential coupling between down-regulation of RB and c-myc oncogene expression with cell differentiation, dose response relationships for the induced down-regulation of RB and c-myc expression were compared with each other and with induced cell differentiation. The total amount of RB protein per cell increased as cells advanced through the cell cycle, but the amount of RB protein relative to the total cell mass remained approximately constant. Treated with RA or VD, an early progressive decrease in cellular content of the RB protein occurred in all cell cycle phases well before any cell cycle modulation or phenotypic differentiation. For a differentiation-defective variant HL-60 cell line, failure to differentiate was preceded by a failure to down-regulate cellular levels of the RB protein. In dose response experiments, progressively increasing RA or VD concentrations caused progressively greater reductions in RB as well as c-myc expression with an increasing fraction of cells terminally differentiating. For both RA and VD, the dose response relationships for reductions in RB and c-myc expression were similar suggesting that their down-regulation may be coupled. These observations are consistent with a model whereby RB expression acts as a cellular brake to sustain a developmentally ordained state of differentiation (i.e., preserve the "status quo"); and the down-regulation of heterogeneously distributed RB protein per cell below a threshold is part of the metabolic cascade culminating in terminal cell differentiation. Thus, RB may have a role in this developmental context.

Calcitriol↗
PubMed1991

Characterization of the cytoplasmic proline-directed protein kinase in proliferative cells and tissues as a heterodimer comprised of p34cdc2 and p58cyclin A.

Site-specific analysis of tyrosine hydroxylase phosphorylation in rat pheochromocytoma led previously to the identification of a novel growth factor-sensitive serine/threonine protein kinase, designated proline-directed protein kinase (PDPK). In this article we describe further the activation, purification, subunit configuration, and biochemical characteristics of this cytoplasmic enzyme system. In human A431 epidermoid carcinoma cells PDPK activity was found to be stimulated by epidermal growth factor in a dose-dependent, time-dependent manner. The PDPK purified from the cytosol of mouse FM3A mammary carcinoma cells exhibited the same chromatographic behavior and biochemical properties as the tyrosine hydroxylase-associated enzyme purified originally from rat pheochromocytoma. The presence of p34cdc2 was ultimately detected in all active fractions of highly purified PDPK by Western blotting and immunoprecipitation; however, it was determined that this catalytic subunit is complexed with a 58-kDa regulatory subunit that is clearly distinct from that of the "growth-associated" M phase-specific histone H1 kinase (i.e. cyclin B). The 58 kDa regulatory subunit of PDPK was identified by direct immunoblotting as a mammalian A-type cyclin. Furthermore, the p58cyclin A subunit of PDPK was found to be phosphorylated on tyrosine residues in vivo and in vitro, the latter of which resulted in a significant increase in PDPK activity. Additional distinctions between this growth factor-sensitive PDPK (p34cdc2-p58cyclin A) and the M phase-specific histone H1 kinase (p34cdc2-p62cyclin B-p13suc1) are identified on the basis of chromatographic behavior, enzyme kinetics, and physicochemical properties. Based on these findings, it is proposed that PDPK represents a unique complex of the p34cdc2 protein kinase which is active in the cytoplasm of proliferative cells, is regulated differently from the M phase-specific histone H1 kinase by phosphorylation reactions, and is modulated selectively by growth factors.

Amino Acid Sequence↗
PubMed1991

Chronic administration of nicotine fails to alter the MPTP-induced neurotoxicity in mice.

1. The effects of chronic (14 day) administration of nicotine on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (15 mg/kg, s.c.)-induced neurotoxicity in C57BL/6 mice were examined. 2. Nicotine pretreatment failed to alter the deficit in locomotor activity and the reduction in striatal levels of dopamine produced by MPTP. 3. Our results do not support a therapeutic action of nicotine in a Parkinsonian animal model.

Animals↗
PubMed1991

Effect of chronic administration of nicotine or cocaine on steroidogenesis in rat adrenocortical cells.

Rats were implanted subcutaneously with osmotic mini-pumps containing either 0.9% NaCl, nicotine (1.5 or 4.5 mg kg-1 day-1), or cocaine (30 mg kg-1 day-1), for 14 days. Neither nicotine nor cocaine treatment significantly altered the maximal rate of steroidogenesis in adrenocortical cell preparations from the animals. However, pretreatment with cocaine increased the sensitivity of the preparation to stimulation by ACTH, the ED50 was 5 pM compared with 10 pM from control animals. Addition of nicotine or cocaine at concentrations up to 100 microM to adrenal cell suspensions from naive rats did not stimulate steroidogenesis or increase the sensitivity of cells to ACTH stimulation. These results suggest that the primary chronic effect of nicotine on steroidogenesis is exerted at the level of the hypothalamus and/or pituitary and not directly on adrenocortical cells. On the contrary, pretreatment with cocaine causes persistent changes in adrenocortical cells.

Adrenal Cortex↗
PubMed1991

Effects of topical and systemic nicotine on gingival blood flow in dogs.

It has been suggested that due to its vasoconstrictive action, nicotine may have a deleterious effect on the periodontium. This study examined the effects of topical and systemic nicotine administration on gingival blood flow. Eighteen young adult dogs were divided into three groups receiving the following treatments for 28 days; topical nicotine in orabase, systemic nicotine via osmotic mini-pumps, and topical orabase or systemic saline via osmotic mini-pumps. Blood flow to the gingiva was measured (at days 0 and 28) by the radiolabeled microsphere method. Blood flow was consistently increased from day 0 to day 28 in the nicotine-treated animals. Comparison of days 0 and 28 blood-flow values demonstrated a statistically significant change (p less than 0.05) in the anterior regions of the topical-nicotine group as compared with the control group. The increased flow may be a reflection of the mode of nicotine delivery and timing of the blood-flow determination procedures.

Administration, Topical↗
PubMed1991

Analysis of viral and cellular gene expression during progression and suppression of the transformed phenotype in type 5 adenovirus-transformed rat embryo cells.

Transformation of secondary Sprague-Dawley rat embryo (RE) cells with type 5 adenovirus (Ad5) results in morphologically transformed cells which can undergo a series of sequential changes resulting in enhanced expression of the transformed phenotype, a process termed progression. Selection for a progressed phenotype often occurs after growth in agar or tumor formation in nude mice, and this process is reversible following treatment of cells with 5-azacytidine. In the present study we have analyzed a series of clonal populations of Ad5-transformed RE cells representing different stages in a defined progression lineage. Progression was not associated with alterations in the steady-state levels of mRNA produced by the viral transforming genes, E1A and E1B, or the cellular gene, c-myc. In addition, the tumor-promoting agent 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which induces expression of a progressed phenotype in Ad5-transformed RE cells, did not significantly alter the RNA transcription rates of the Ad5 E1A or E1B genes, the TPA-inducible gene TPA-S1 or the TPA-responsive genes Pro1 or protein kinase C. TPA did, however, increase by 1 h the steady-state level of c-fos mRNA, but this effect was similar in both progressed and unprogressed cells. Progression also did not involve a change in the RNA transcription rate of a number of cellular and viral genes, including actin, c-Ha-ras, c-myc, v-fos, erbB, TGF-alpha, TGF-beta, Pro-2, transin, TPA-R1, v-myb and c-mos, or other adenovirus genes in addition to E1A and E1B, including E2A and E4. Immunoblotting analysis using E1B polyclonal antiserum further indicated that progression was not associated with changes in the levels of an Mr 21,000 polypeptide encoded by E1B. Similarly, immunoprecipitation analysis with an Ad2 E1A monoclonal antibody indicated similar levels of the Mr 55,000 and 48,000 E1A polypeptides, as well as coprecipitated proteins of Mr 300,000, 107,000 and 105,000 [which is the retinoblastoma (Rb) protein], in E11 and E11-NMT cells. Immunoprecipitation of cell lysates with a monoclonal antibody specific for the Mr 105,000 Rb protein further demonstrated that progression also was not associated with a change in the level or state of phosphorylation of the Rb protein. However, transfection of a human Rb gene (also containing a neomycin resistance gene) into Ad5-transformed RE cells was more inhibitory, with respect to formation of G418-resistant colonies, in unprogressed than in progressed Ad5-transformed RE cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenoviruses, Human↗