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K K Cheung

Publications and source records attributed to K K Cheung.

29 records · Page 2Linked to original sources
PubMed2000

Bcl-2 and p53 protein expression, apoptosis, and p53 mutation in human epithelial ovarian cancers.

Bcl-2 and p53 gene products have been both linked to cell death by apoptosis. In the present study, we examined the relationship of Bcl-2 and p53 protein expression, p53 mutation and apoptosis in normal human ovaries and different types of human ovarian epithelial tumors by immunohistochemical localization, in situ terminal transferase-mediated dUTP nick end labeling and polymerase chain reaction-single strand conformation polymorphism. It was found that Bcl-2 expressed strongly in the surface epithelium of normal ovaries and benign and borderline ovarian tumors but weakly in the malignant tumors. On the contrary, strong protein expression of p53 was found in 54% (25/46) of the malignant epithelial tumors examined but similar expression of p53 was not observed in borderline and benign tumors and normal ovarian surface epithelium. A significant inverse correlation between Bcl-2 and p53 expression was found in the malignant ovarian tumors examined. p53 gene mutation at exons 5-11 was however not a pre-requisite for p53 expression in both borderline and malignant tumors. Apoptotic activities, as reflected by apoptotic indices, were low in normal ovarian surface epithelium and benign tumors but were increased in borderline and malignant tumors, with the highest average apoptotic index found in grade III malignant tumors. Statistical analyses showed a positive correlation between apoptosis and p53 expression, but similar correlation was not found between apoptosis and Bcl-2 expression. Our results also indicate that although expression of Bcl-2 is important during ovarian carcinogenesis, the Bcl-2 protein may have other roles to play apart from being a modulator of apoptosis in human ovarian epithelial cancers.

Apoptosis↗
PubMed2000

A new trinortriterpenoid from Cleome chrysantha.

A new trinortriterpenoid, 1-epibrachyacarpone, was isolated from aerial parts of Cleome chrysantha. Its structure was elucidated as 1 by NMR investigations and X-ray crystallographic studies.

Crystallography, X-Ray↗
PubMed1998

DOC-2, a candidate tumor suppressor gene in human epithelial ovarian cancer.

Using RNA fingerprinting (RAP) strategy and Northern blot analysis, we identified a differentially expressed sequence DOC-2 which is detectable in all normal human ovarian surface epithelial (HOSE) cell cultures but not in ovarian cancer cell lines and tissues. Subsequent cloning of DOC-2 from a cDNA library generated from the HOSE cells was carried out using the 3' and 5' RACE approach. A 3268 base pair full length cDNA of DOC-2 was isolated and sequenced. The predicted protein has a length of 770 amino acids. Homology search of all NCBI sequences indicated that the amino acid sequence of DOC-2 shares 93% homology with the mouse p96/mDab2 phosphoprotein and has a phosphotyrosine interacting domain (PID) and multiple SH3 binding motifs. Chromosomal localization by FISH showed that the DOC-2 gene is located on 5p13. Western blot analysis showed that the 105 kDa DOC-2 protein was down-regulated in all the carcinoma cell lines. In-situ immunohistochemistry performed on normal ovaries, and benign, borderline and invasive ovarian tumor tissues showed down regulation of DOC-2 protein particularly in serous ovarian tumor tissues. When DOC-2 was transfected into the ovarian carcinoma cell line SKOV3, the stable transfectants showed significantly reduced growth rate and ability to form tumors in nude mice. These data suggest that down-regulation of DOC-2 may play an important role in ovarian carcinogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed1998

The saturation characteristics of glucose transport in bovine retinal pigment epithelium.

PURPOSE: To study the saturation characteristics of the glucose transport across the bovine retinal pigment epithelium(RPE). METHODS: The bovine RPE preparations were munted with a modified Ussing chamber. The L-[3H]-glucose and 3-O-methyl-D-[14C]-glucose fluxes across the RPE from the choroid to retina were studied at different glucose concentrations. RESULTS: The glucose transport was found to be stereospecific, with 3-O-methyl-D-glucose (MDG) being transported about three times faster than L-glucose. The glucose transport showed typical saturation characteristics in Michaelis-Menten fashion. The Vmax and the Km of corrected MDG were 2452 nmol cm-2h-1 and 30.8 mM respectively. It was shown that the glucose transport system was saturated at 61.6 mM. CONCLUSIONS: The saturation characteristics of the corrected MDG flux suggested that the capacity of glucose transport through the bovine RPE is immense.

3-O-Methylglucose↗
PubMed1997

Endothelium-dependent rhythmic contractions induced by cyclopiazonic acid in rat mesenteric artery.

The action of cyclopiazonic acid, the putative inhibitor of the Ca(2+)-ATPase of endoplasmic reticulum, on phenylephrine-evoked-isometric contractions in rat isolated mesenteric arteries were investigated. Cyclopiazonic acid (3 microM) induced an initial relaxation followed by rhythmic contractions of the phenylephrine-precontracted arteries with intact endothelium. Removal of endothelium abolished the effect of cyclopiazonic acid. Pretreatment of tissues with NG-nitro-L-arginine (100 microM) abolished the initial relaxation but not the rhythmic contractions. Indomethacin and glibenclamide did not affect the cyclopiazonic acid-induced response. Charybdotoxin (100 nM) converted the cyclopiazonic acid-induced rhythmic contractions to the sustained tension in the absence or presence of NG-nitro-L-arginine (100 microM). Pretreatment of charybdotoxin (100 nM) abolished cyclopiazonic acid-induced rhythmic activity but not the initial relaxation. Nifedipine (10 nM) abolished the effect of cyclopiazonic acid. Moderate increase of extracellular K+ (20 mM) reduced the initial relaxation but completely abolished rhythmic contractions induced by cyclopiazonic acid. The remaining relaxation was reversed or prevented by NG-nitro-L-arginine (100 microM). The results of the present investigation indicate that cyclopiazonic acid caused endothelium-dependent response in rat isolated mesenteric arteries probably by releasing nitric oxide responsible for the initial relaxation, and probably by releasing endothelium-derived hyperpolarizing factors primarily responsible for activation of charybdotoxin-sensitive K+ channels and induction of rhythmic contractile activity.

Animals↗
PubMed1996

Choledocholithiasis in anomalous biliary system.

Although congenital biliary abnormalities are common, preduodenal portal vein is very rare, not to mention preduodenal common bile duct (CBD) which has not been described before in the literature. A case with both anomalies complicated by biliary tract stones is reported. A brief review of embryonic development is also presented to explain the unusual biliary anatomy of this patient.

Adult↗
PubMed1978

Polyadenylic acid synthesis activity of purified DNA-dependent RNA polymerase from Caulobacter.

Characterization of purified DNA-dependent RNA polymerase (EC 2.7.7.6) of Caulobacter crescentus, strain CB15 has led to the conclusion that this enzyme catalyzes poly(A) synthesis in the absence of template. Poly(A) synthetase activity co-purifies with both holoenzyme and core polymerase on DNA-cellulose columns, and core polymerase purified to 98% homogeneity by glycerol gradient centrifugation is still capable of catalyzing poly(A) polymerization. Both RNA synthesis and poly(A) polymerization activities are sensitive to rifampicin. In addition, RNA polymerase purified from partially rifampicin-sensitive mutants exhibits the same partial sensitivity in vitro to the drug in the synthesis of RNA and poly(A). The enzyme used in these studies was prepared by a simple method which allows a high yield of pure RNA polymerase from large batches of exponential cells. The procedure includes high speed centrifugation of cell extracts, DEAE-cellulose column, DNA-affinity chromatography, and low salt glycerol gradient centrifugation. Holoenzyme can be resolved into core and sigma subunit by either DNA-cellulose chromatography or glycerol gradient centrifugation, and the latter step allows recovery of pure sigma factor.

Bacteria↗
PubMedDate not supplied

Elfin is expressed during early heart development.

Elfin (previously named CLIM1) is a protein that possesses an N-terminal PDZ domain and a C-terminal LIM domain. It belongs to the family of Enigma proteins. Enigma proteins are a family of cytoplasmic proteins that contain an N-terminal PDZ domain and a series of C-terminal LIM domains. By virtue of these two protein interacting domains, Enigma proteins are capable of protein-protein interactions. It has been proposed that Enigma proteins may act as adapters between kinases and the cytoskeleton. We have previously shown that Elfin is most abundantly expressed in the heart and it colocalizes with alpha-actinin 2 at the Z-disks of the myocardium. In this report, Elfin was shown to localize at the actin stress fibers of myoblasts, as revealed by green fluorescent protein (GFP) tagging. In situ hybridization and immunostaining showed that Elfin expression begins at an early stage in mouse development and is present throughout the developing heart. Taken together, our experimental results suggest that Elfin may play an important role in myofibrillogenesis and heart development.

Actinin↗