Biomedical subjects

K Guo

Publications and source records attributed to K Guo.

At least 55 records · Page 3Linked to original sources

PubMed1997

Rb functions to inhibit apoptosis during myocyte differentiation.

During in vitro myogenesis, a portion of myoblasts undergo apoptosis, whereas others continue with their differentiation program and form myotubes that are resistant to cell death. Previous work has shown that the expression of the Cdk inhibitor p21 correlates with enhanced resistance to apoptosis and that forced expression of p21 will confer this phenotype on differentiating myocytes. Here we examine the role of the retinoblastoma gene (Rb) in myocyte survival. Compared with wild-type myocytes, CC42 (Rb-/-) myocytes undergo higher frequencies of apoptosis during mitogen deprivation-induced myogenesis. Despite these features, Rb-/- myocytes display normal up-regulation of p21 and down-regulation of Cdk activities upon differentiation. Adenoviral constructs expressing the Cdk inhibitors p21 or p16 inhibit apoptosis in wild-type but not Rb-/- myocyte cultures. On the other hand, a Rb-expressing adenoviral construct inhibited apoptosis in both cell types. These data demonstrate that Rb functions downstream from the Cdk inhibitors to coordinate cell cycle withdrawal with programmed cell death during myocyte differentiation.

Animals↗

PubMed1997

Inhibition of myogenesis by multiple cyclin-Cdk complexes. Coordinate regulation of myogenesis and cell cycle activity at the level of E2F.

During skeletal myogenesis, cell cycle withdrawal accompanies the expression of the contractile phenotype. Here we show that ectopic expression of each D-type cyclin is sufficient to inhibit the transcriptional activation of the muscle-specific creatine kinase (MCK) gene. In contrast, ectopic expression of cyclin A or cyclin E inhibits MCK expression only when they are co-expressed with their catalytic partner cyclin-dependent kinase 2 (Cdk2). For each of these conditions, myogenic transcriptional inhibition is reversed by the ectopic co-expression of the general Cdk inhibitor p21. Inhibition of MCK expression by cyclins or cyclin-Cdk combinations correlates with E2F activation, suggesting that the inhibition is mediated by the overall Rb-kinase activities of the Cdk complexes. In support of this hypothesis, a hyperactive mutant of Rb was found to partially reverse the inhibition of MCK expression by cyclin D1 and by the combination of cyclin A and Cdk2. These data demonstrate that the inhibition of myogenic transcriptional activity is a general feature of overall Cdk activity which is mediated, at least in part, by an pocket protein/E2F-dependent pathway. MCK promoter activity is also inhibited by ectopic E2F1 expression, but this inhibition is not reversed by the co-expression of p21. Analyses of a series of E2F1 mutants revealed that the transcriptional activation, leucine zipper, basic, and cyclin A/Cdk2-binding domains are dispensable, but the helix-loop-helix region is essential for myogenic inhibition. These data demonstrate that myocyte proliferation and differentiation are coordinated at the level of E2F and that these opposing activities are regulated by different E2F domains.

Animals↗

PubMed1997

Isolation of myelin basic protein from whole tissue extracts by selective pH-dependent solubilization.

A previous study of the selective solubility of myelin basic protein (MBP) of tissue extracts at pH 9.0 has raised issues of its quantitative recovery, and the differential solubility of its charge isomers. The pH-dependent solubility of proteins of acid extracts of delipidated tissue of bovine spinal cord was therefore reexamined. MBP of whole extracts was completely soluble up to pH 8.0 only, and less so by 25% at pH 9.0, and 43% at pH 10.0. The proteins other than MBP were virtually insoluble between pH 5.0 to 6.0, and 9.0 to 10.0. The solubility of the main charge isomers I to III of MBP of 18.5 kDa was found not to be affected by pH. Either pH 5.0 or 9.0 is therefore suitable for the selective isolation of MBP from whole tissue extracts, only pH 5.0 providing for the complete recovery of MBP. The pH-dependent solution behaviour was also examined following the separation of proteins of whole extracts by anion exchange chromatography at pH 10.4. Purified MBP and several related minor cationic components of lower molecular weight were soluble throughout. In contrast, the anionic proteins were only partly soluble between pH 4.0 to 10.0, i.e. by 4 to 20%. The results are consistent with specific protein-protein interactions of the proteins of whole extracts, either enhancing the solubility of non-MBP proteins, e.g. at pH 7.0, or impairing that of MBP between pH 8.0 to 10.0.

Animals↗

PubMed1997

[Expression of hepatitis C viral structure protein by recombinant vaccinia virus].

The hepatitis C viral (HCV) DNA fragment coding for the core and two glycoproteins E1 + E2/NS1 were inserted into vaccinia virus vector pJSA1175, under the control of the promoter 7.5K. 143TK- cells transfected with the HCV recombinant plasmid pJSA1175CE in the presence of infectious TK+ vaccinia virus (Tiantan stain) yielded recombinant vaccinia virus and expressed an approximately 90 kDa polyprotein. Southern blot hybridization showed that the inserted HCV cDNA was located at the vaccinia virus TK+ gene, J fragment. One polypeptide band between 106 and 80 kDa was revealed in SDS-PAGE which reacted with anti-core murine serum. The polypeptide could be secreted into the medium, the total amount was about the same as in the cells.

Gene Expression↗

PubMed1997

[Comparison of the Chinese LJ strain structural gene with HM175, MBB, LA strains and the expression of hepatitis A virus antigen by LJ/HM175 recombinant vaccinia virus].

The nucleotide and amino acid sequences of a Chinese hepatitis A virus Long-Jia (LJ) strain were compared with that of HM175, MBB and LA strains in structural genes (nt 630-3049). The most extensive nucleotide homology was identified between LJ and MBB strains. The identity rates of nucleotide were 95.4%, 96.7% and 91.4%, respectively. Variation rates of amino acid were 0.91%, 0.91% and 2.98%, respectively. A total of 23 amino acid differences located in whole capsid region between LJ and LA strain, especially in VP1. Only 7 amino acid differences located in VP2 and VP3 between LJ and HM175/MBB strain. Restriction enzyme sites increased 10, 13 and 30 sites in 56 restriction enzymes tested, and decreases 15, 1 and 27 sites, respectively. BstE II (nt 2810) and Pvu I (nt 2013) were the peculiar sites of LJ strain. Hind III, Pst I and Sac I sites were identical among the four strains. After structural gene (nt 745-2993) of HM175 strain was replaced by LJ strain, the complete hepatitis A virus cDNA open reading frame was inserted into pJSA1175 (vaccinia virus expression vector) downstream of promoter 7.5 k. Hepatitis A virus antigen expressed was 1:16 in titer by sandwich ELISA. Band-patterns of anti-VP0, anti-VP1 and anti-VP1, 2, 3, were as same as that of HM175 strain and natural hepatitis A virus antigen by Western blot analysis.

Hepatitis A Antigens↗

PubMed1997

[Gaze-position-dependent activities of striate cortex (V1) neurones of awake macaque monkeys].

We recorded the activities of single neurons of the primary visual cortex in awake, behaving monkeys to test the influence of the position of gaze on cellular activity. Two monkeys (Macaca mulatta) were trained to fixate a small spot positioned sequentially at 25 locations on a viewing screen. About half (52%) of the neurons recorded showed a selective gaze field (GF), when monkey fixated at this field of view, the cell activities increased significantly. For the majority of the neurons, GF located at the contralateral field of view with respect to the hemisphere from which responses were recorded. The GF was usually found a few degrees peripheral to the related RF. Gaze-position-dependent neurons were found at different depths of the cortex, but mostly in the superficial and the deepest layers. The results indicate that the striate cortex neurons may code information about gaze position.

Animals↗

PubMed1997

[Influence of visual stimuli on eye-position related activities of neurons in primary visual cortex (V1) of awake monkeys].

Extracellular recordings were made in the primary visual cortex (V1) in two awake monkeys to test the influence of visual stimuli on the eye-position related activites of the neurons. While the monkeys gazed on a fixation point (FP) positioned sequentially at different locations on a TV screen, two types of visual stimuli were presented on the same screen: (1) A small light ring flashed repeatedly around the FP or (2) A prefered light bar shifted continuously across the cell's receptive field (RF). Both stimuli significantly enhanced the eye-position related activities and correspondingly increased the incidence of the eye-position dependent neurons. The results show that the integration of information on vision and on eye position may take place at quite the earliest stage of the visual cortices.

Animals↗

PubMed1996

Expression of hyaluronidase by tumor cells induces angiogenesis in vivo.

Hyaluronic acid is a proteoglycan present in the extracellular matrix and is important for the maintenance of tissue architecture. Depolymerization of hyaluronic acid may facilitate tumor invasion. In addition, oligosaccharides of hyaluronic acid have been reported to induce angiogenesis. We report here that a hyaluronidase similar to the one on human sperm is expressed by metastatic human melanoma, colon carcinoma, and glioblastoma cell lines and by tumor biopsies from patients with colorectal carcinomas, but not by tissues from normal colon. Moreover, angiogenesis is induced by hyaluronidase+ tumor cells but not hyaluronidase- tumor cells and can be blocked by an inhibitor of hyaluronidase. Tumor cells thus use hyaluronidase as one of the "molecular saboteurs" to depolymerize hyaluronic acid to facilitate invasion. As a consequence, breakdown products of hyaluronic acid can further promote tumor establishment by inducing angiogenesis. Hyaluronidase on tumor cells may provide a target for anti-neoplastic drugs.

Animals↗

PubMed1996

Regulation of a physiological apoptosis: mouse mammary involution.

Continuous milk production during lactation is dependent on a complex interplay of lactogenic hormones and the suckling stimulus exerted by the young. Involution can be initiated in the mouse mammary gland at any stage of lactation by removing the pups; involution then remains reversible for about 30 to 36 h. Involution in the mouse mammary gland is characterized by a massive loss of secretory epithelial cells from programmed cell death. The nuclear activation of protein kinase A and transcription factor activator protein 1 precede the irreversible phase of involution that is characterized by internucleosomal DNA fragmentation. Activation of activator protein 1 and fragmentation of chromosomal DNA can be prevented by lactogenic hormone treatment in explant cultures derived from mammary tissue at lactation. The elevation in activator protein 1 coincides with the epithelial expression of sulfated glycoprotein 2, a potential target gene of activator protein 1. Programmed cell death in the mammary gland is associated with the expression of the growth arrest gene, gas-1, and the integrin-associated protein gene, IAP, which codes for a putative Ca2+ channel that is dependent on integrin. Their potential roles during involution are discussed.

Animals↗

PubMed1996

[Selective training of the vastus medialis muscle using electrical stimulator for chondromalacia patella].

Chondromalacia patella is closely related with subluxation and tilt of patella, as well as with muscular atrophy of quadriceps, especially in vastus medialis muscle. 364 cases of chondromalacia patella were treated with selective training of the vastus medialis muscle using electrical stimulator in our hospital. 211 cases were followed up after treatment from 6 months to 3 years. Among them excellent and good results were seen in 130 cases (62%), fair results were seen in 69 cases (33%) and no change was seen in 12 cases (5%). Significant reduction of CA (P < 0.01) and LPA (P < 0.001) were observed in all these patients in comparison with their primary angle. We believe that the selective training of the vastus medialis muscle using electrical stimulator is one of the effective methods for the treatment of chondromalacia patella.

Adult↗

PubMed1996

[Modified duodenum-preserving resection of the head of the pancreas].

A modified procedure of duodenum-preserving resection of the head of the pancreas was used in treating three patients with benign lesions in the head of the pancreas. Compared with Beger's procedure, the modified procedure was simpler, and pancreaticojejunostomy on duodenal side was not necessary because of less remaining pancreas attached to the conjunction of the pancreatobiliary duct. The patients, recovered and ate food from 4 to 6 days after operation without symptoms of duodenal obstruction. The patient's digestive function was normal, and the pre- and postoperative pancreatic endocrine function was almost identical. This procedure can be used as the first-choice surgical procedure for benign lesions in the head of the pancreas. Problems in how to protect blood supply of the duodenum were also discussed.

Adult↗

PubMed1995

Cloning, chromosomal localization and expression analysis of the mouse Akt2 oncogene.

We isolated mouse cDNA clones containing the entire coding region of the putative oncogene Akt2. Sequence analysis revealed that, like its human homolog, Akt2 encodes a protein-serine/threonine kinase containing a pleckstrin homology domain at its amino terminus. Fluorescence in situ hybridization of the mouse cDNA to rodent metaphase spreads demonstrated that the Akt2 gene maps to mouse chromosome band 7B1 and rat chromosome 1q22. Expression levels of mouse Akt2 mRNA and Akt2 protein varied among tissues, with the highest levels in skeletal muscle. Akt2 expression was low in a multipotent fibroblast cell line, but it was upregulated when these cells were transformed with Myod and induced to differentiate into myocytes. These data demonstrate that Akt2 expression is activated during cellular differentiation and suggest that it functions in the signaling pathways of some adult tissues.

Amino Acid Sequence↗

PubMed1995

Prokaryotic expression and analysis of the antibody response to a Newcastle isolate of the core gene of hepatitis C.

The full length hepatitis C virus (HCV) core gene was isolated from a Newcastle strain and expressed in E. coli. A truncated HCV core gene which lacks the hydrophobic carboxyl-terminal sequence was also expressed. The truncated HCV core was expressed at higher levels with fewer cleavage products. Antibody reactivity to the recombinant HCV core antigen was analysed by ELISA and Western blotting in 60 HCV antibody-positive patients with a broad spectrum of liver disease. There was no significant difference between the presence of IgG to recombinant HCV core and reactivity to the core antigen in the RIBA-2 test. There was also no significant difference between the presence of IgG to recombinant core and diagnostic PCR as a marker for active liver inflammation.

Antigens, Viral↗

PubMed1995

Measurements of geometric illusions, illusory contours and stereo-depth at luminance and colour contrast.

We investigated four geometric optical illusions (Zöllner, Müller-Lyer, Ponzo and Delboeuf), plus illusory contour/border induction (Kanizsa) and depth in random-dot stereograms (Julesz). Two different display conditions were compared: equiluminance with chromaticity contrast and heteroluminance without chromaticity contrast. The main results are as follows. (1) The strength of the four geometric optical illusions is the same under both display conditions. The Zöllner illusion reaches its maximum and levels off at a luminance contrast of about 80%; it disappears at luminance contrasts of less than 15%. (2) No illusory contours are perceived in equiluminant Kanizsa figures. The minimum luminance contrast for illusory contour induction in the Kanizsa square is on average 1.8%, for illusory border induction in the abutting grating illusion it is 5.3%. (3) Random-dot stereograms were found to induce depth equally well in both display modes. The disparity threshold for perceiving depth in isochromatic random-dot stereograms levels off at a luminance contrast of 30%. With larger disparities, depth is perceived down to about 10% contrast. The findings suggest that geometric optical illusions of parallelness (orientation), length and size are mediated by the parvocellular system; furthermore, that stereoscopic depth is mediated both by the magnocellular and the parvocellular systems; and that illusory contours are mediated by the magnocellular system.

Color Perception↗

PubMed1995

Serum induction of MEF2/RSRF expression in vascular myocytes is mediated at the level of translation.

Vascular smooth muscle cells (VSMCs) reversibly coordinate the expression of VSMC-specific genes and the genes required for cell cycle progression. Here we demonstrate that isoforms of the MEF2/RSRF transcription factor are expressed in VSMCs and in vascular tissue. The MEF2A DNA-binding activity was upregulated when quiescent VSMCs were stimulated to proliferate with serum mitogens. The serum-induction of MEF2A DNA-binding activity occurred approximately 4 h following serum activation, and this correlated with an increase in the level of MEF2A protein without changes in the level of MEF2A mRNA or protein stability. These results indicate that MEF2A induction by serum is regulated at the level of translation.

Animals↗

PubMed1995

MyoD-induced expression of p21 inhibits cyclin-dependent kinase activity upon myocyte terminal differentiation.

The terminal differentiation of C2C12 skeletal muscle cells involves the activation of unique sets of genes and an irreversible withdrawal from the cell cycle. This process is associated with a decrease in cdk2 activity in cell extracts. The decrease in cdk2 activity correlates with diminished levels of cdk2 and cyclin A and with a marked induction of the p21 cyclin-dependent kinase (cdk) inhibitor. The upregulation of p21 occurred at the levels of mRNA and protein, and p21 formed a complex with the cyclin kinases in myotubes. Further, the immunodepletion of p21 from myotube extracts neutralized the heat-stable cdk2 inhibitory activity that was induced upon myogenic differentiation. The levels of p21 mRNA, protein, and activity remained constant in myotubes when they were reexposed to mitogen-rich growth medium, indicating that permanent changes in the cell's genetic program contribute to its sustained expression following terminal differentiation. Indeed, 10T1/2 fibroblasts transformed with the myogenic factor MyoD, but not the parental multipotent cells, upregulated p21 transcript levels when induced to differentiate by serum withdrawal, demonstrating that the upregulation is an integral feature of myogenic commitment and differentiation. The functional consequences of this upregulation were indicated by ectopically expressing p21 in myoblasts; this was sufficient for cell cycle arrest in mitogen-rich growth medium. The induction and sustained expression of p21 appears to be a contributory mechanism by which myocytes irreversibly exit the cell cycle upon terminal differentiation.

Base Sequence↗

PubMed1995

Defective repair of O6-methylguanine-DNA in primary Sjögren's syndrome patients predisposed to lymphoma.

OBJECTIVE: To investigate a role for mutation in the aetiogenesis of autoimmune disease by examining levels of repairing enzyme for the promutagenic DNA base lesion, O6-methylguanine, in lymphocyte extracts from patients with autoimmune diseases. We included primary Sjögrens syndrome (PSS) patients because of the additional relevance of their being at increased risk (> 40-fold) of developing lymphoma. METHODS: Lymphocytes were prepared from patients with PSS (n = 22) (12 with parotid gland enlargement, an indicator of extensive lymphoproliferation), rheumatoid arthritis (n = 12), primary biliary cirrhosis (n = 11), osteoarthritis (n = 12), and healthy individuals (n = 11). MGMT amounts were determined in lymphocyte extracts by direct enzyme assay and expressed in relation to total extract DNA, protein, or cell number. RESULTS: We found no defect in the repairing methyltransferase enzyme between any of the groups, except in PSS patients at increased risk of developing lymphoma (those with enlarged parotid glands): p < 0.0001 and p = 0.0056, compared with healthy controls and PSS patients without parotid gland swelling, respectively. CONCLUSIONS: Our findings implicate persistence of O6-methylguanine-DNA in the aetiology of lymphoma associated with PSS, and raise the possibility that an alternative repair process for O6-methylguanine-DNA, nucleotide excision repair, might be defective in autoimmune disease.

Aged↗

PubMed1995

Intratracheal administration of endotoxin and cytokines. VI. Antiserum to CINC inhibits acute inflammation.

Cytokine-induced neutrophil chemoattractant (CINC), a chemotactic molecule of the interleukin (IL)-8 family, is known to be induced in the rat in response to tumor necrosis factor (TNF), IL-1, and lipopolysaccharide (LPS). Intratracheal injection of endotoxin (LPS) is shown to cause CINC mRNA expression in pulmonary tissue, peaking after 2 h, and CINC protein expression in bronchoalveolar lavage (BAL) fluid, peaking after 2-4 h. Intratracheal injection of synthetic CINC causes acute inflammation that is abrogated by coinjection of antiserum to purified natural rat CINC. Intratracheal injection of antiserum to CINC inhibits intratracheal LPS- and IL-1-induced neutrophil emigration into BAL fluid by approximately 60-70%. Despite the anti-inflammatory activity of anti-CINC antiserum, TNF is elevated in the lavage fluid of rats receiving anti-CINC, suggesting that CINC may act in a negative feedback loop to downregulate TNF expression. Intratracheal injection of antiserum to CINC combined with intravenous injection of anti-E-selectin antibody inhibits intratracheal LPS- and IL-1-induced neutrophil emigration into BAL fluid by approximately 75-85%. CINC-mediated chemotactic activity and E-selectin-mediated adherence of neutrophils to endothelium contribute significantly to the pathogenesis of LPS-initiated acute inflammation.

Acute Disease↗