PubMed Health⌕ Search

Biomedical subjects

W Gevers

Publications and source records attributed to W Gevers.

At least 37 records · Page 2Linked to original sources
PubMed1987

The surface distribution of low density lipoprotein receptors on cultured fibroblasts and endothelial cells. Ultrastructural evidence for dispersed receptors.

The distribution of low density lipoprotein (LDL) receptors marked with colloidal gold-conjugated low density lipoproteins has been mapped on the surfaces of cultured human skin fibroblasts and bovine aortic endothelial cells viewed whole in the transmission electron microscope. A dispersed or scattered population of LDL receptors, in addition to and clearly distinct from clustered receptors was detected on the surfaces of both fibroblasts and dividing endothelial cells. No LDL receptors could be detected on contact-inhibited endothelial cells. Clustered receptors imaged in whole-mount preparations were often arranged in rings with an approximate diameter of 250 nm. In ultra-thin sections of marked cells, clustered receptors were localised in coated pits while the few dispersed receptors seen were restricted to non-coated membrane regions. Clustered receptors often appeared localised on the rims of coated pits whose central areas were not marked. The dispersed population of receptors was usually distributed diffusely amongst the clusters on dividing endothelial cells and normal fibroblasts. Only the dispersed population appeared on LDL receptor internalisation-defective mutant fibroblasts. The marginal zones of both fibroblasts and dividing endothelial cells were populated by dispersed receptors. Clusters appeared further "inland" and were rarely seen near the cell margins. These results indicate that LDL receptors on dividing endothelial cells and fibroblasts may be dispersed on the cell surface upon or soon after their insertion during recycling.

Animals↗
PubMed1986

DNA hypermethylation in sodium butyrate-treated WI-38 fibroblasts.

Sodium butyrate is very often used to alter gene expression in cultured cells. In this study, we examined the effects of this compound on various cellular events in WI-38 human embryonic lung fibroblasts in culture. During a 16-20-h treatment at sodium butyrate concentrations of between 5 and 20 mM, no adverse effects on cell morphology were observed. However, cell division and DNA synthesis were reversibly inhibited, the latter by 85, 80, and 70% at sodium butyrate concentrations of 5, 10, and 20 mM, respectively. Although overall protein synthetic activity was not significantly affected, RNA synthesis decreased to 76% of the control values at a sodium butyrate concentration of 5 mM. Butyrate treatment also caused hypermethylation of DNA cytosines as determined by differential digestion by MspI/HpaII restriction endonucleases and by high performance liquid chromatography analysis of the DNA. The 5-methylcytosine content of the DNA in untreated WI-38 fibroblasts was 2.94 +/- 0.46% of total cytosine residues, while in cultures treated with 5, 10, and 20 mM sodium butyrate, these values were 5.76 +/- 0.28, 5.91 +/- 0.37, and 6.8 +/- 0.44%, respectively. An interesting feature is that this hypermethylation occurred in DNA which was synthesized in the presence of sodium butyrate (newly synthesized) as well as in DNA which had been synthesized before butyrate administration (pre-existing DNA). The hypermethylated state was conserved only in the former situation, since the methylcytosines were rapidly lost in the subsequent generation in the latter case. It would therefore appear that methylcytosines are maintained after cell replication only if they are generated on newly synthesized DNA.

Butyrates↗
PubMed1986

Effects of sodium butyrate on the synthesis and methylation of DNA in normal cells and their transformed counterparts.

The effects of various concentrations of sodium butyrate were examined on a normal embryonic lung fibroblast cell line (WI-38) and its two transformed counterparts, a simian virus 40-transformed line (SVWI-38) and a cell line transformed by gamma-irradiation (CT-1). The rate of thymidine incorporation into DNA was inhibited by 60-80% in the WI-38 cells, even at butyrate concentrations as low as 5 mM. The two transformed cell lines showed no inhibition of DNA synthesis, even at concentrations of 75 mM butyrate. Analysis of RNA and protein synthesis revealed that the former was inhibited by +/- 20% at 5-10 mM butyrate in the normal WI-38 cell line, while protein synthesis was not inhibited at these concentrations. The inhibition of RNA synthesis was not dose dependent up to butyrate concentrations of 20 mM, and protein synthesis was inhibited less than 15% at this concentration. None of these inhibitory effects was observed in the case of the SVWI-38 or CT-1 cell lines. Analysis of the 5-methylcytosine content of DNA that was labeled either prior to or during treatment with butyrate revealed an increased content of methylcytosine when compared with control cells. Both preexisting and newly synthesized DNAs were thus subject to hypermethylation. Although all three cell lines showed a dose-dependent hypermethylation of DNA, the extent of this methylation differed in the normal and transformed lines, as preexisting DNA was more methylated in WI-38 cells compared with SVWI-38 and CT-1 cells, while methylation of newly synthesized DNA occurred to a greater extent in the SVWI-38 cells. These studies show that sodium butyrate affects major macromolecular synthetic processes as well as DNA methylation quite differently in normal and transformed cells.

Butyrates↗
PubMed1985

The interaction between calcium and the activation of Na+, K+-ATPase by noradrenaline.

The interaction of noradrenaline, various cation chelators and calcium on Na+, K+-ATPase from rat cerebral cortex plasma membranes was studied. It was shown that chelation of inhibitory cations by EGTA, EDTA and dipyridyl activated Na+, K+-ATPase to the same extent as noradrenaline but at higher concentrations; increasing concentrations of EGTA depressed the activation by noradrenaline; calcium in the form of a calcium-EGTA buffer depressed Na+, K+-ATPase at physiological concentrations; the inhibition of Na+, K+-ATPase by calcium is dependent on the magnesium concentration in the assay and the inhibition by calcium was partially reversed by noradrenaline.

Animals↗
PubMed1985

Modulating influence of D,L-propranolol on triiodothyronine-induced skeletal muscle protein degradation.

There is evidence suggesting that thyrotoxicosis increases beta-adrenoreceptor density on some target tissues. We have studied the in vivo effect of D,L-propranolol (a nonselective beta-adrenoreceptor blocking agent) on T3-induced enhancement of in situ proteolysis in fast twitch muscle fibers of the rat. Chronic treatment with T3 as opposed to saline resulted in a 76% enhancement of the rate of in situ muscle proteolysis [0.79 +/- 0.04 (n = 8) compared with 0.45 +/- 0.01 (n = 8) nmol tyrosine/mg muscle . 2 h]. Treatment of rats with both T3 and 2 mg propranolol resulted in a 62% reduction in the T3-induced increment in situ muscle proteolysis [0.58 +/- 0.02 (n = 8) vs. 0.79 +/- 0.04]. This significant inhibition by propranolol of T3-induced enhanced proteolytic rates in vitro suggests that this may comprise one component of the observed beneficial clinical effects of beta-blockade in thyrotoxic myopathy.

Animals↗
PubMed1985

Lysosomal acid hydrolase alterations in gastric mucosa from an experimental peptic ulcer model.

Ligation of the common bile duct in pigs causes esophagogastric ulceration in 100 per cent of instances within seven days postoperatively. The results of previous studies have suggested a peptic cause for these ulcers. The possible role of lysosomal acid hydrolases in the primary pathogenesis was investigated herein. The total activities of two lysosomal acid hydrolases in mucosal specimens taken at biopsy from ulcerated pars esophagea and one in ulcerated gastric cardia were significantly lower in pigs undergoing ligation of the bile duct postoperatively, than in comparable pigs undergoing sham operations while there was evidence of increased extracellular activity. Mucosal deoxythymidine kinase activity was increased in gastric cardia suggesting attempted repair. Pigs with parakeratosis of the pars esophagea and edema of the gastric cardia, consistent with the preulcerative state also showed lowered enzyme activity. These results in intact pigs suggest that release of lysosomal acid hydrolases occurs with and may precede peptic ulceration.

Acetylglucosaminidase↗
PubMed1984

Demethylation of the type I procollagen genes in transformed fibroblasts treated with 5-azacytidine.

Transformation of the human embryonic lung fibroblast line, WI-38, with simian virus 40 (SV40) results in inactivation of the type I procollagen genes. No type I collagen or procollagen mRNA is detected in these transformed cells, as determined by polyacrylamide gel electrophoresis. Analysis of the methylation patterns of these genes showed the type I procollagen genes to be hypermethylated at certain cytosine residues in the transformed cells. However, several of the cytosine residues were methylated in the normal cells where these genes are expressed. These methylation patterns can be altered by treatment of the cells with 5-azacytidine or 5-azadeoxycytidine, but without a resultant activation of the type I procollagen genes. These results show that demethylation alone is not sufficient for gene activation, but that other signals are also required.

Azacitidine↗
PubMed1984

Comparison of muscle and fat wasting in patients suffering from breast and other cancers: an anthropometric study.

An anthropometric study was undertaken to determine muscle and fat areas in 50 cancer patients and 258 control patients suffering from minor conditions, to assess the degree of cachexia in patients with breast cancer, and in patients with other types of cancer. Patients suffering from cancers other than those of the breast showed muscle and fat wasting when compared with matched standard values and when the muscle and fat area measurements were expressed as a percentage of the appropriate mean standard value. Breast cancer patients showed increased muscle and fat area values, irrespective of whether they were in remission, or had progressive disease. This is interesting in view of the strong association between dietary fat intake and breast cancer incidence, and correlates well with present ideas on nutrition and the incidence of breast cancer.

Adipose Tissue↗
PubMed1984

Protein metabolism of the heart.

The heart contains many cell types; mechanical work is done by cardiomyocytes which do not divide but are terminally differentiated and capable of continuous protein synthesis and degradation. The steps in protein synthesis are (1) transport of amino acids into heart cells by a variety of cell-membrane carriers, (2) ATP-dependent activation of the amino acids by specific enzymes, forming aminoacyl-transfer RNA molecules, (3) initiation of protein synthesis on ribosomes to which messenger-RNA molecules are bound at the initiation 'code word', (4) elongation of the polypeptide chains by the repetitive operation of a ribosomal enzyme acting on incoming aminoacyl-transfer RNAs selected by their ability to bind to the messenger-RNA code words in place at any one time, and (5) completion of chain growth when the appropriate termination code word appears in the messenger RNA on the ribosome. Certain genes are available in differentiated heart cells for transcription by RNA polymerase into pre-messenger RNA molecules. These RNA molecules are chemically modified, complexed with proteins and shortened by means of specific excisions before they leave the nuclei as messenger-ribonucleoprotein complexes which can be used for protein synthesis. Regulation of protein synthesis involves both 'quantity' and 'quality' control and is exerted mainly, but not exclusively, at the two levels of initiation, namely that of RNA synthesis in the nucleus, and protein synthesis in the cytoplasm. Protein degradation to the level of amino acids is a process which probably requires disassembly of protein complexes or organelles, and is catalyzed by proteinases present in the cytoplasm or by others occurring in lysosomes, or possibly by both. Basal degradation occurs continuously, and may be supplemented by a separate process, called autophagy, which is under hormonal or nutritional control. The complex processes of biosynthesis and degradation are finely balanced and do not interfere with function despite their occurrence at a rate which means that most of the cardiac protein is replaced every 7 to 14 days. Nutritional and hormonal factors, and especially workload, are determinants that influence the 'set' of the protein turnover mechanism and therefore the size of the organ as a whole.

Adenosine Triphosphate↗
PubMed1983

Increased sulphation level and altered composition of glycosaminoglycans synthesized by cultured smooth muscle cells in the presence of beta-D-xylosides.

Cultured rat and bovine smooth muscle cells incorporated more 35SO4 into macromolecular glycosaminoglycans in the presence of beta-D-xylosides than in their absence. More than 90% of the xyloside-initiated glycosaminoglycans were secreted rapidly into the culture medium and were more highly sulphated than glycosaminoglycans polymerized on core protein. The increased extents of sulphation were associated with increased synthesis of dermatan sulphate and a decrease in that of nitrous acid-sensitive glycosaminoglycans.

Animals↗
PubMed1983

A high-molecular-weight cysteine endopeptidase from rat skeletal muscle.

A cytosolic enzyme of high molecular weight (about 500 000), which attacks native or denatured proteins (inter alia, casein, globin and hexokinase) was purified about 1000-fold from mixed rat skeletal muscles, including muscles freed of mast cells by prior treatment of the animals with the degranulator, compound 48/80. Peptides of varying size were generated from radioactively labelled globin, but no free amino acids were formed; free tyrosine was also not released from azocasein. The pH optimum was 7.5 and the presence of an essential cysteine group was suggested because dithiothreitol (1 mM) stimulated the activity and N-ethylmaleimide (5 mM) and p-chloromercuriphenylsulphonic acid (1 mM) were inhibitors. The activity was markedly inhibited by Zn2+ but not by leupeptin, chymostatin or pepstatin. The enzyme was stabilized by ATP, at concentrations as low as 0.1 mM, against inactivation at 42 degrees C. The endopeptidase was clearly separated on gel chromatography from another large protease, also sensitive to Zn2+, but with marked aminopeptidase activity and the properties of hydrolase H. The activity levels of the protease, assayed after chromatography on Sepharose 6B of high-speed supernatant fractions, did not vary significantly in skeletal muscle samples which were derived from denervated, starved, diabetic or hyperthyroid animals, in all of which the abnormal physiological states expressed themselves as enhanced rates of tyrosine released by incubated soleus and extensor digitorum longus muscles. Nevertheless, the enzyme described here may be part of an ATP-dependent, multi-component proteolytic system similar to that already known to be present in reticulocytes.

Adenosine Triphosphate↗
PubMed1983

Serum amino acids in weight-losing patients with cancer and tuberculosis.

A study of arterial and arterio-venous amino acid concentration differences across the forearm was performed in 19 weight-losing cancer (CWL) patients (9 with lung cancer and 10 with other types of cancer), 8 weight-losing patients with active pulmonary tuberculosis (TWL) and 10 normal controls. Arterial concentrations of many of the amino acids measured were found to be lower in CWL than in TWL patients. In addition, the data suggested a venous excess of amino acids in the CWL patients compared with TWL patients and controls. The increased release of alanine from forearm muscles in the CWL group, together with the low arterial glycogenic amino acid levels, supports the concept of enhanced gluconeogenesis in CWL patients. Low arterial amino acid levels and possible increased release of amino acids from forearm muscle in CWL patients implies enhanced proteolysis with increased central clearance or tumour sequestration of these amino acids, though decreased proteogenesis cannot be excluded in accounting for the venous excesses in this group. Hypocitrullinemia in lung cancer patients was marked, and possible mechanisms to account for this are discussed.

Adult↗
PubMed1983

Soluble and particulate forms of muscle alkaline proteinase show differential sensitivity to endogenous inhibitor(s).

Membrane-free washed myofibrils derived from rat skeletal muscle homogenates contained a chymostatin-sensitive protease(s) which acted on associated myofibrillar proteins, at an optimum pH of 8.5, much less rapidly at low ionic strength (insoluble myofilaments) than at high salt concentrations (solubilized proteins). When the myofibrillar fraction was added to the particle-free cytosol prepared from the muscle extracts, proteins of the cytosol were also degraded, but the activity in this case was much more pronounced at low ionic strength. This was because inhibitor(s) of the proteinase present in the cytosol fraction were only effective at high ionic strength when all the myofibrillar (and associated) proteins were in solution. The protease was separated from the bulk of the myofibrillar proteins by gel chromatography at high ionic strength. On dialysis against a low-salt buffer, part of the enzyme was precipitated. The putative cytosolic inhibitor(s) were again only effective on the soluble enzyme at high ionic strength.

Animals↗
PubMed1983

Sulphate turnover of surface proteoglycans in cultured rat smooth muscle cells.

Turnover of radioactive sulphate-labelled proteoglycans in cultured rat smooth muscle cells was detected by pulse chase techniques. The degradation appeared to take the form of desulphation of sulphated macromolecules, with a loss in total sulphate of approximately 50% in 5 days. The desulphation process occurred in the pericellular/matrix compartment of the culture system and was unaffected by inhibition of matrix formation by beta-aminopropionitrile, or by incubation of cells with lysomotropic inhibitors. There was no evidence for further degradation of desulphated species even when exogenous, radio-labelled proteoglycans were added to fresh cultures and incubated for four days. Labelled macromolecules initiated on xyloside acceptors were desulphated by rat smooth muscle cell cultures more slowly than intact proteoglycans.

Animals↗