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Biomedical subjects

H Y Yang

Publications and source records attributed to H Y Yang.

At least 37 records · Page 2Linked to original sources
PubMed2000

Oncogenic signals of HER-2/neu in regulating the stability of the cyclin-dependent kinase inhibitor p27.

Overexpression and activation of HER-2/neu, a proto-oncogene, play a pivotal role in cancer formation. Strong expression of HER-2/neu in cancers has been associated with poor prognosis. Reduced expression of p27(Kip1), a cyclin-dependent kinase inhibitor, correlates with poor clinical outcome in many types of carcinomas. Because many cancers with the overexpression of HER-2/neu overlap with those affected by reduced p27 expression, we studied the link between HER-2/neu oncogenic signals and p27 regulation. We found that down-regulation of p27 correlates with HER-2/neu overexpression. To address the molecular mechanism of this inverse correlation, we found that reduction of p27 is caused by enhanced ubiquitin-mediated degradation, and the HER-2/Grb2/MAPK pathway is involved in the decrease of p27 stability. Also, HER-2/neu activity causes mislocation of p27 and Jun activation domain-binding protein 1 (JAB1), an exporter of p27, into the cytoplasm, thereby facilitating p27 degradation. These results reveal that HER-2/neu signals reduce p27 stability and thus present potential points for therapeutic intervention in HER-2/neu-associated cancers.

3T3 Cells↗
PubMed2000

Association of the cyclin-dependent kinases and 14-3-3 sigma negatively regulates cell cycle progression.

14-3-3 sigma, implicated in cell cycle arrest by p53, was cloned by expression cloning through cyclin-dependent kinase 2 (CDK2) association. 14-3-3 sigma shares cyclin-CDK2 binding motifs with different cell cycle regulators, including p107, p130, p21(CIP1), p27(KIP1), and p57(KIP2), and is associated with cyclin.CDK complexes in vitro and in vivo. Overexpression of 14-3-3 sigma obstructs cell cycle entry by inhibiting cyclin-CDK activity in many breast cancer cell lines. Overexpression of 14-3-3 sigma can also inhibit cell proliferation and prevent anchorage-independent growth of these cell lines. These findings define 14-3-3 sigma as a negative regulator of the cell cycle progression and suggest that it has an important function in preventing breast tumor cell growth.

14-3-3 Proteins↗
PubMed2000

Pharmacogenomics and metabolite measurement for 6-mercaptopurine therapy in inflammatory bowel disease.

BACKGROUND & AIMS: The effects of 6-mercaptopurine (6-MP) are mediated via its intracellular conversion to 6-thioguanine (6-TG) and 6-methylmercaptopurine (6-MMP) nucleotide metabolites, the latter genetically controlled by thiopurine methyltransferase (TPMT). We sought to determine optimal therapeutic 6-MP metabolite levels and their correlation with medication-induced toxicity and TPMT genotype. METHODS: Therapeutic response was determined in 92 pediatric patients with inflammatory bowel disease coincidentally with hematologic, pancreatic, and hepatic laboratory parameters, and compared with erythrocyte metabolite levels and TPMT genotype. RESULTS: Clinical response was highly correlated with 6-TG levels (P < 0.0001) but not with any other variable, including 6-MMP levels, drug dose, gender, and concurrent medications. The frequency of therapeutic response increased at 6-TG levels > 235 pmol/8 x 10(8) erythrocytes (P < 0.001). Hepatotoxicity correlated with elevated 6-MMP levels (>5700 pmol/8 x 10(8) erythrocytes; P < 0.05). Although leukopenia was associated with higher 6-TG levels (P < 0.03), it was observed in only 8% of responders. Patients heterozygous for TPMT (8/92) had higher 6-TG levels (P < 0.0001), and all responded to therapy. CONCLUSIONS: 6-MP metabolite levels and TPMT genotyping may assist clinicians in optimizing therapeutic response to 6-MP and identifying individuals at increased risk for drug-induced toxicity.

Adolescent↗
PubMed2000

[Studies on quantitative chromatographic retention-structure relationships].

Using quantum and molecular mechanics methods, 48 structural descriptors of alkylbenzene compounds such as atomic partial charge, dipole moment, molecular area, molecular volume etc. were calculated. GFA regression methods were applied to build a quantitative chromatographic retention-structure relationships equation. The equation have good fitness and strong predictivity. Principle structural factors that effect chromatographic retention of alkylbenzenes were discussed.

Alkylation↗
PubMed2000

[A study on the mechanism of reductive alkylation for preparing 3-(beta-hydroxy-ethyl-sulfonyl) N-ethyl aniline with HPLC/MS].

Hydrogenating 3-(beta-hydroxy-ethyl-sulfonyl)-aniline and acetaldehyde in the presence of Raney Nickel as a catalyst, 3-(beta-hydroxy-ethyl-sulfonyl)-N-ethyl-aniline was obtained with 98% conversion and 95% monoalkylation selectivity under optimum conditions. By using high performance liquid chromatography/mass selective detection technique to characterize the structures of the products, the mechanism of reductive alkylation is proposed. From the intermediates determined, it is shown that the reaction mechanism would go via an unstable N-alpha-hydroxyethylaniline derivative and Schiff base stage. After hydrogenation of Schiff base, finally the product 3-(beta-hydroxyethyl-sulfonyl)-N-ethyl aniline was formed.

English Abstract↗
PubMed1999

Wild-type p53 protein potentiates phototoxicity of 2-BA-2-DMHA in HT29 cells expressing endogenous mutant p53.

To better understand the effects of p53 on the process of photodynamic therapy (PDT)-induced cell death, we introduced a wild-type p53 gene into the HT29 colorectal carcinoma cell line, which bears an endogenous mutant p53, using a lipofectin system. The influence of p53 status on the sensitivity induced by 2-butylamino-2-demethoxy-hypocrellin A (2-BA-2-DMHA) photosensitization was then examined. The results indicate that infection with wild-type p53 induces a growth arrest but does not induce cell death, and sensitizes the cells to PDT. At a concentration of 5 microM 2-BA-2-DMHA with a red light of 18 J/cm2 (lambda = 600-700 nm), the survival is reduced from 58.72% in HT29 cells to 13.49% in wild-type p53-infected HT29 cells. Apoptosis following PDT appears earlier in HT29 cells infected with wild-type p53 than in parent HT29 cells and empty vector-infected HT29 cells. These findings suggest that although wild-type p53 is, by itself, insufficient to induce apoptosis in cells with p53 mutation, it enhances the photosensitivity of 2-BA-2-DMHA by strongly potentiating the induction of apoptosis.

Apoptosis↗
PubMed1999

Chronic exposure to antibodies directed against anti-opiate peptides alter delta-opioid receptor levels.

The development of addictive states in response to chronic opioid use may be regulated partially by the release of endogenous peptides. These anti-opiate peptides (AOP) are secreted or released into the CNS and produce diverse actions that counterbalance the effects of prolonged opiate exposure. Though the mechanism(s) by which these peptides exert their physiological properties remain largely unknown, there is some indication that AOP's modulate opioid receptor levels. In this study, we investigated the effects of chronically infused alpha-melanocyte stimulating hormone (alpha-MSH), dynorphin(1-8) (DYN(1-8)), dynorphin A (DYNA), and NPFF antibodies on delta-opioid receptor expression in rat brains. Quantitative autoradiographic experiments revealed that antibodies directed against alpha-MSH and DYNA produced significant increases in delta receptor levels in the caudate, claustrum, and cingulate cortex of the rat brain. Conversely, NPFF monoclonal antibodies caused significant decreases in the caudate, nucleus accumbens, olfactory tubercle, and cingulate cortex. These results suggest that the density of delta-opioid receptors is affected by changes in the levels of the anti-opioid peptides in the extracelluar fluid in the rat brain.

Animals↗
PubMed1999

GC/MS analysis of anandamide and quantification of N-arachidonoylphosphatidylethanolamides in various brain regions, spinal cord, testis, and spleen of the rat.

Anandamide [N-arachidonoylethanolamide (NAE)] was initially isolated from porcine brain and proposed as an endogenous ligand for cannabinoid receptors in 1992. Accumulating evidence has now suggested that, in the tissue, NAE is generated from N-arachidonoylphosphatidylethanolamides (N-ArPEs) by phosphodiesterase. In this study a sensitive and specific procedure was developed to quantify NAE and N-ArPE, including organic solvent extraction, reverse-phase C-18 cartridge separation, derivatization, and gas chromatography/mass spectrometry (GC/MS) analysis. NAE is converted by a two-step derivatization procedure to a pentafluorobenzoyl ester followed by pentafluoropropionyl acylation. Quantification was performed by isotope dilution GC/MS using deuterium-labeled NAE (NAE-2H8) as an internal standard. The same chemical derivatization was applicable to N-ArPE quantification. The separated N-ArPE fractions were converted by a two-step cleavage/derivatization procedure into the pentafluorobenzoyl ester of NAE and then to its pentafluoropropionyl amide. The derivative was quantified by GC/MS using deuterium-labeled 1,2-[2H8]dioleoyl-sn-glycero-3-phospho(arachidonoyl)ethanolamid e as an internal standard. Using these methods, we have found that endogenous NAE levels in rat brain, spleen, testis, liver, lung, and heart were below the level of quantification achievable (0.1 pmol/mg of protein) but that N-ArPE is readily quantifiable and is widely distributed in the rat CNS with the highest level in the spinal cord. The striatum, hippocampus, and accumbens contain intermediate concentrations of N-ArPE, whereas the value is lowest in the cerebellum.

Animals↗
PubMed1999

Synthesis of glucose oxidase and catalase by Aspergillus niger in resting cell culture system.

The synthesis of glucose oxidase and catalase by Aspergillus niger was investigated using a resting cell culture system without growth being established. Calcium carbonate induced the synthesis of both enzymes and calcium chloride inhibited it. The optimal pH for the biosynthesis of glucose oxidase and catalase was 6.0 and 5.7, respectively. The effects of other bivalent cations, reductive compounds and metabolic products on enzyme synthesis were also tested. The biosynthesis of glucose oxidase and catalase was promoted by MnCO3, thioglycolic acid, pyroracemic acid and gluconic acid.

Aspergillus niger↗
PubMed1999

Bcl-2 overexpression prevents apoptosis-induced Madin-Darby canine kidney simple epithelial cyst formation.

BACKGROUND: Madin-Darby canine kidney (MDCK) cells develop into simple epithelial cell cysts when cultured in type I collagen gel. We found that MDCK cells initially grow into multilayer cell aggregates and subsequently develop central lumen that contain apoptotic cells. We hypothesized that apoptosis might be essential for the formation of MDCK cysts. METHODS: Using MDCK cells cultured in collagen gel as the experimental model, we investigated how renal cells organize to form cysts. To delineate the role of apoptosis in the process of cyst formation, MDCK cells were transfected with the bcl-2 gene. Characterization of apoptosis was studied by morphological and biochemical methods. RESULTS: Bcl-2 overexpression conferred resistance to apoptosis. Cultured in collagen gel, Bcl-2 transfectants rarely formed a simple epithelial cyst, but instead remained as a multilayer cell aggregate containing central or multiple lumens, or even developing into branching structures. CONCLUSIONS: Because Bcl-2 overexpression averts cyst cavitation, these data clearly indicate that apoptosis is an essential initial event for renal cyst formation.

Animals↗
PubMed1999

Identification and characterization of the inward K+ channel in the plasma membrane of Brassica pollen protoplasts.

Patch clamp techniques have been used to identify and characterize the whole-cell currents carried by inward K+ channels in isolated matured pollen protoplasts of Brassica chinensis var. chinensis. The whole-cell inward currents in the isolated pollen protoplasts were activated at hyperpolarized membrane potentials more negative than -100 mV. The magnitudes of the whole-cell inward currents were strongly dependent on the external K+ concentration, and were highly selective for K+ over other monovalent cations. The inward currents were not observed when external K+ was replaced with the same concentration of Cs+ or Na+. The addition of 1 mM or 10 mM Ba2+ in external solutions resulted in 30% or 80% inhibition of the inward currents at -180 mV, respectively. These results demonstrated that the inward K+ currents mainly account for the recorded whole-cell inward currents in Brassica pollen protoplasts. Increase of cytoplasmic Ca2+ concentrations from 10 nM to 30 microM or even 5 mM did not affect the inward K+ currents. Decrease of external Ca2+ concentrations from 10 mM to 1 mM inhibited the inward K+ currents by 25%, while the increase of external Ca2+ from 10 mM to 50 mM almost completely blocked the inward K+ currents. Physiological importance of K+ transport into pollen and its possible regulatory mechanisms are also discussed.

Brassica↗
PubMed1999

Dry eye after haematopoietic stem cell transplantation.

AIMS: To determine the incidence, natural course, and severity of dry eye occurring or worsening after haematopoietic stem cell transplantation (SCT). METHODS: At a tertiary care hospital, 53 patients undergoing allogeneic or autologous SCT followed by at least 180 days of follow up were studied prospectively. Examination included grading of symptoms of dry eye, evaluation of ocular surface, tear break up time, and Schirmer tests with and without nasal stimulation. Meibomian gland secretion was also examined using a slit lamp while applying steady digital pressure. RESULTS: Of the 53 patients, 44 received allografts. Half of these patients (22) developed dry eye or their pre-existing dry eye worsened after SCT, while none of nine autograft recipients did. Onset of dry eye was 171 (SD 59) days after SCT. Two types of dry eye occurred. One (n=10) was severe with ocular surface findings resembling Sjögren's syndrome and reduction of reflex tearing soon after onset. A mild type (n=12) had unimpaired reflex tearing. Meibomian gland dysfunction (MGD) was more frequent and severe in patients with dry eye and chronic graft versus host disease (GVHD), and overall severity of dry eye was greater in patients with MGD and chronic GVHD. CONCLUSIONS: Dry eye after SCT occurred only in allograft recipients, and was not evident in autograft recipients. The severe form of dry eye had a tendency to develop rapidly. Further study on the prediction and treatment of severe dry eye after SCT is necessary.

Adult↗
PubMed1998

Activation of neuropeptide FF neurons in the brainstem nucleus tractus solitarius following cardiovascular challenge and opiate withdrawal.

Neuropeptide FF (NPFF), a morphine modulatory peptide, is localized within discrete autonomic regions including the brainstem nucleus tractus solitarius (NTS) and the parabrachial nucleus (PBN). We investigated the activation of NPFF neurons in the NTS of rats induced by cardiovascular challenge and centrally generated opiate withdrawal. For hypotensive stimulation, we used systemic infusions of sodium nitroprusside (NP) or hemorrhage (HEM), and hypertension was achieved by intravenous phenylephrine (PHENYL) or angiotensin II (AII). In rats that received continuous intracerebroventricular injections of morphine, intraperitoneal injections of naloxone precipitated behavioural signs of opioid withdrawal. Activated NTS neurons were identified by using a combined immunohistochemistry for Fos and NPFF, and neurons projecting to the PBN were determined with a retrograde tracer. HEM, administration of vasoactive drugs, and opiate withdrawal produced a very robust activation of NTS neurons. In NP and HEM groups, 25.6+/-3.2% and 7.6+/-1.3% of NPFF neurons were activated, respectively. Lesser numbers of NPFF neurons were activated in the PHENYL (4.6+/-1.6%) and AII (2.4+/-0.8%) groups. However, following opiate withdrawal, virtually no Fos expression was observed in NPFF neurons. NPFF neurons activated during NP infusion constituted the largest number of cells projecting to the PBN. This study shows that NPFF neurons in NTS that project to the PBN respond selectively to NP as opposed to other cardiovascular challenges or opiate withdrawal. These data support an emerging and important role for NPFF in the context of central cardiovascular regulation.

Angiotensin II↗
PubMed1998

A novel photosensitizer, 2-butylamino-2-demethoxy-hypocrellin A (2-BA-2-DMHA). 1. Synthesis of 2-BA-2-DMHA and its phototoxicity to MGC803 cells.

The reaction of hypocrellin A (HA) with n-butylamine in pyridine under reflux leads to the formation of 2-butylamino-2-demethoxy-hypocrellin A (2-BA-2-DMHA), which is illustrated by ultraviolet-visible absorption spectra, proton nuclear magnetic resonance spectra, infrared spectra and mass spectra. The product exhibits stronger red-light absorption and has a much higher photopotentiation factor than HA (i.e., more than 200 versus four at a dose of 4 J cm-2 of red light on human gastric adenocarcinoma MGC803 cells). The mechanism of phototoxicity of 2-BA-2-DMHA on MGC803 cells irradiated with red light (lamada = 600-700 nm) has also been studied. An examination of extracted cellular DNA by agarose gel electrophoresis shows that the DNA has degraded into fragments with lengths which are multiples of approximately 180-190 base pairs (i.e., oligonucleosome size), a biochemical marker of apoptosis. Transmission electron microscopy reveals chromatin condensation around the periphery of the nucleus, which is also characteristic of apoptosis. This study suggests that 2-BA-2-DMHA is a potential photosensitizer and that its photoxicity to MGC803 cells proceeds via apoptosis.

Adenocarcinoma↗
PubMed1998

Lipocortin 1 co-associates with cytokeratins 8 and 18 in A549 cells via the N-terminal domain.

An affinity chromatography strategy was used to search for proteins in A549 cells which interact with the N-terminus of lipocortin 1 (annexin 1). Using the biologically active fragment Lc13-25 as the affinity ligand, two proteins of molecular weight (m.w.) 52 and 48kDa were extracted. Affinity blots of these proteins bound iodinated Lc13-25. Partial tryptic digests of these proteins were analysed by matrix assisted laser desorption mass spectrometry and found to display fragmentation patterns with a strong similarity to those of cytokeratin 8 and 18 respectively. Subsequent blotting with a panel of specific cytokeratin antibodies strongly supported the idea that the two proteins were cytokeratin 8 and cytokeratin 18. Cytokeratin 8 was isolated from A549 cells in intermediate filament (IF) preparations which were also found to contain lipocortin 1 as a potential intermediate filament associated protein (IFAP). This association persisted throughout cycles of IF assembly and disassembly. Dual-labelling immuno-histochemistry in A549 cells showed strong co-localization of lipocortin 1 and cytokeratin 8. The implications of this finding are discussed in the light of the biological activity and possible function of lipocortin 1.

Annexin A1↗
PubMed1998

Allergic conjunctivitis as a risk factor for regression and haze after photorefractive keratectomy.

PURPOSE: To analyze the relation between allergic conjunctivitis and the results of photorefractive keratectomy performed with an excimer laser in myopic eyes. METHODS: Fifty-seven myopic eyes in 57 Japanese patients were classified into three groups: a normal group (30 eyes of 30 patients), a treatment group composed of eyes with allergic conjunctivitis that were treated with fluorometholone and cromolyn sodium eyedrops from month 3 until the end of the 12- to 18-month follow-up period (16 eyes of 16 patients), and a no-treatment group composed of eyes with allergic conjunctivitis that received no allergic treatment until the end of the follow-up period (11 eyes of 11 patients). Preoperative and postoperative examinations included evaluation of corrected and uncorrected visual acuity and grading of corneal haze. RESULTS: In the no-treatment group, the mean corneal haze score +/- SD of 0.8 +/- 0.98 was significantly greater than the normal group score of 0.38 +/- 0.49 (P = .02). There was no significant difference in the haze score between the treated and normal groups. A refractive outcome of +/- 1 diopter was obtained in 30 (100%) of the 30 patients in the normal group, 15 (93.8%) of 16 patients in the treatment group, and four (36.4%) of the 11 patients in the no-treatment group. Visual acuity was 20/40 or better after photorefractive keratectomy in 30 patients (100%) in the normal group, 15 patients (93.8%) in the treatment group, and six patients (54.5%) in the no-treatment group. CONCLUSION: These findings suggest that untreated allergic conjunctivitis is a significant risk factor for haze and myopic regression after photorefractive keratectomy.

Adult↗
PubMed1998

Antiserum against neuropeptide FF augments vasopressin release in conscious rats.

We previously reported that centrally administered neuropeptide FF (NPFF) inhibited arginine vasopressin (AVP) release. In this study, immunoneutralization of central NPFF was performed to evaluate the role of endogenous NPFF in the regulation of AVP release. Intracerebroventricular (ICV) injection of antiserum against NPFF (Anti-NPFF) significantly augmented the plasma AVP increase induced by hyperosmolality [intraperitoneal injection of hypertonic saline (600 mOsm/kg, 2% BW)] at 60 min after ICV injection compared with normal rabbit serum (NRS) (NRS: 4.20+/-0.30 pg/ml, Anti-NPFF: 5.83+/-0.46 pg/ml, p < 0.01). Anti-NPFF did not cause significant change in plasma osmolality, plasma volume or arterial blood pressure. This evidence indicates that endogenous NPFF might be physiologically involved in osmoregulation of the plasma AVP level through its inhibitory action.

Amino Acid Sequence↗