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71.
Senescence-specific increase in cytosolic glutamine synthetase and its mRNA in radish cotyledons 总被引:11,自引:4,他引:7
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Changes in the levels of cytosolic and chloroplastic isoforms of glutamine synthetase were examined in senescing radish (Raphanus sativus L. cv Comet) cotyledons by immunoblotting analysis using antibodies raised separately against maize glutamine synthetase isoforms. Translatable mRNAs for these isoforms were also examined by analyzing translation products from poly(A)+ RNA in a wheat germ system with the antibodies. The relative content of cytosolic isoform (GS1) increased twofold in the cotyledons that were placed in the dark for 72 hours to accelerate senescence, while that of chloroplastic isoform (GS2) declined to half of its initial level. The dark-treatment also increased the relative level of translatable mRNA for GS1 sevenfold after 72 hours, and decreased rapidly that for GS2 and for other nuclear-coded chloroplast proteins as well. Cotyledons also accumulated GS1 mRNA when they became senescent after a lengthy growth period under continuous light. These observations suggested that GS1 genes were activated, while those for GS2 were repressed, and eventually the population of the enzyme was altered in senescent cotyledonary cells. The role of increased cytosolic enzyme is discussed in relation to the nitrogen metabolism in senescent leaves. 相似文献
72.
Characterization of a renal tubular epithelial cell line which secretes the autologous target antigen of autoimmune experimental interstitial nephritis 总被引:19,自引:0,他引:19
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T P Haverty C J Kelly W H Hines P S Amenta M Watanabe R A Harper N A Kefalides E G Neilson 《The Journal of cell biology》1988,107(4):1359-1368
Proximal tubular epithelial cells from mice which develop autoimmune interstitial nephritis were found to express the nephritogenic target antigen, 3M-1. Anti-3M-1 mAbs (alpha 3M-1-Ab) were used to positively select for 3M-1-secreting tubular epithelium and, after stabilization in culture, this new cell line (MCT) was examined for the production of several moieties important to either immune interactions or to the development of extracellular matrix. Alkaline phosphatase-staining MCT cells also express epithelial growth factor receptors with a Kd of 0.87 nM and an epithelial growth factor receptor constant (Ro) of 2.1 X 10(4) receptors/cell. MCT culture supernatants contain greater amounts of laminin, and types IV and V procollagens compared to types I and III procollagens, and growing MCT cells on type I collagen matrix causes them to preferentially secrete even more type IV and V procollagen. The 30,000-Mr 3M-1 antigen could be immunoprecipitated from biosynthetically labeled MCT cell supernatants with alpha 3M-1-Ab. An identical-sized moiety was isolated by immunoaffinity chromatography from collagenase-solubilized mouse kidney tubular basement membranes. The 3M-1 antigen can be found on the MCT cell surface by radioimmunoassay, or deposited in a linear array in the extracellular matrix surrounding the MCT cells in culture by immunofluorescence. Mature messenger RNA species for both class I and class II major histocompatibility complex (MHC) molecules were detected by Northern hybridization, and their corresponding cell surface gene products were detected by cytofluorography of MCT cells stained with haplotype-specific antibodies. Both the cell surface 3M-1 and the small amounts of detected class II MHC molecules appear to be biologically functional, as MCT cells can support the proliferation of 3M-1-specific, class II MHC-restricted helper T cells in culture. These findings suggest that MCT cells provide all the necessary biological parameters for interfacing both as the target of a nephritogenic immune response, and as a potential source for new extracellular matrix which develops as a fibrogenic response to interstitial nephritis. 相似文献
73.
To determine whether hepatic sinusoidal cells contain glucagon receptors and, if so, to study the significance of the receptors in the cells, binding of [125I]-glucagon to nonparenchymal cells (mainly endothelial cells and Kupffer cells) isolated from mouse liver was examined by quantitative autoradiography and biochemical methods. Furthermore, the pathway of intracellular transport of colloidal gold-labeled glucagon (AuG) was examined in vivo. Autoradiographic and biochemical results demonstrated many glucagon receptors in both endothelial cells and Kupffer cells, and more receptors being present in endothelial cells than in Kupffer cells. In vivo, endothelial cells internalized AuG particles into coated vesicles via coated pits and transported the particles to endosomes, lysosomes, and abluminal plasma membrane. Therefore, receptor-mediated transcytosis of AuG occurs in endothelial cells. The number of particles present on the abluminal plasma membrane was constant if the amount of injected AuG increased. Therefore, the magnitude of receptor-mediated transcytosis of AuG appears to be regulated by endothelial cells. Kupffer cells internalized the ligand into cytoplasmic tubular structures via plasma membrane invaginations and transported the ligand exclusively to endosomes and lysosomes, suggesting that the ligand is degraded by Kupffer cells. 相似文献
74.
M Watanabe T Watanabe Y Ishii H Matsuba S Kimura T Fujita E Kominami N Katunuma Y Uchiyama 《The journal of histochemistry and cytochemistry》1988,36(7):783-791
To determine the characteristics of lysosomes in rat islet endocrine cells, we examined the precise localization of cathepsins B, H, and L and their specific inhibitors, cystatins alpha and beta, using immunocytochemical techniques. By use of serial semi-thin sections, we detected immunoreactivity for cathepsin B in insulin-, glucagon-, somatostatin-, and pancreatic polypeptide-positive (PP) cells. Strong immunoreactivity for cathepsin H was seen in A-cells and weak immunoreactivity in PP cells, but none in others. Immunodeposits for cystatin beta were demonstrated in B-cells. Brief dipping of thin sections in 1% sodium methoxide before the following immunocytochemical reaction enhanced specific deposits of immunogold particles on the target organelles. Use of a double-immunostaining technique showed co-localization of insulin with cystatin beta in many secretory granules. This suggests that cystatin beta may regulate converting enzymes participating in the maturation process of insulin. By use of an immunogold technique, heterogeneous localization of cathepsins B and H in lysosomes was also found among islet cells at the light microscopic level. This may be due to the difference in peptides degraded in lysosomes among the cells. 相似文献
75.
Preventive effect of MCI-186 on 15-HPETE induced vascular endothelial cell injury in vitro 总被引:8,自引:0,他引:8
T Watanabe I Morita H Nishi S Murota 《Prostaglandins, leukotrienes, and essential fatty acids》1988,33(1):81-87
Using cultured bovine aortic endothelial cells, the effects of MCI-186, a radical scavenger, were studied on arachidonic acid metabolism and on the cell injury caused by 15-HPETE. MCI-186 at 3 X 10(-5) M enhanced prostacyclin production in the intact endothelial cells without affecting phospholipase A2. When endothelial cell homogenates were used as an enzyme source, it was found that MCI-186 stimulated the conversion of arachidonic acid to prostacyclin like phenol, perhaps by trapping OH radicals produced in the process of the conversion of PGG2 to PGH2. On the other hand, MCI-186 was found to inhibit lipoxygenase metabolism of arachidonic acid in cell free homogenates of rat basophilic leukemia cells. The lipoxygenase inhibition caused by 3 X 10(-5) M MCI-186 was almost equivalent to that caused by 3 X 10(-6) M BW 755C. MCI-186 remarkably protected against endothelial cell damage caused by 15-HPETE. 3 X 10(-5) M of 15-HPETE caused endothelial cell death in about 60% of the population: however, pretreatment of the cells with 10(-5) M of MCI-186 or concomitant addition of 10(-5) M of MCI-186 with 15-HPETE to the cultures prevented the cell death completely. These results suggest that MCI-186 may become an unique anti-ischemic drug. 相似文献
76.
77.
The ''second-codon rule'' and autophosphorylation govern the stability and activity of Mos during the meiotic cell cycle in Xenopus oocytes. 总被引:13,自引:4,他引:9
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The c-mos proto-oncogene product, Mos, functions in both early (germinal vesicle breakdown) and late (metaphase II arrest) steps during meiotic maturation in Xenopus oocytes. In the early step, Mos is only partially phosphorylated and metabolically unstable, while in the late step it is fully phosphorylated and highly stable. Using a number of Mos mutants expressed in oocytes, we show here that the instability of Mos in the early step is determined primarily by its penultimate N-terminal residue, or by a rule referred to here as the 'second-codon rule'. We demonstrate that unstable Mos is degraded by the ubiquitin-dependent pathway. In the late step, on the other hand, Mos is stabilized by autophosphorylation at Ser3, which probably acts to prevent the N-terminus of Mos from being recognized by a ubiquitin-protein ligase. Moreover, we show that Ser3 phosphorylation is essential for Mos to exert its full cytostatic factor (CSF) activity in fully mature oocytes. Thus, a few N-terminal amino acids are primary determinants of both the metabolic stability and physiological activity of Mos during the meiotic cell cycle. 相似文献
78.
79.
Effect of dietary alpha-linolenate/linoleate balance on lipopolysaccharide-induced tumor necrosis factor production in mouse macrophages 总被引:1,自引:0,他引:1
We examined the effect of dietary alpha-linolenate (18:3n-3)/linoleate (18:2n-6) balance on lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF) production in mouse macrophages. Resident and casein-induced peritoneal macrophages from mice fed a high alpha-linolenate diet produced a higher amount of TNF than in the high linoleate diet group. However, TNF production was not affected by the dietary alpha-linolenate/linoleate balance when thioglycollate- and complete Freund's adjuvant-induced macrophages were stimulated with LPS. Serum TNF levels of mice intraperitoneally injected with LPS was also higher in the high alpha-linolenate group than in the high linoleate group. These diets affected the n-3/n-6 ratios of 20 and 22 carbon highly unsaturated fatty acids in macrophage lipids. Thus, the dietary enrichment with alpha-linolenate was found to enhance TNF production of macrophages isolated under limited conditions. 相似文献
80.
Mutagenicity of 30 chemicals in Salmonella typhimurium strains possessing different nitroreductase or O-acetyltransferase activities 总被引:2,自引:0,他引:2
Salmonella typhimurium YG1021, YG1024, YG1026 and YG1029 are new derivatives of the Ames tester strains TA98 and TA100, with elevated 'classical' nitroreductase or acetyl-CoA:N-hydroxyarylamine O-acetyltransferase level. Thirty mutagens with different structures were tested using these strains and the sensitivities were compared with those of the conventional strains and of the enzyme-deficient strains. Elevated O-acetyltransferase activity of the indicator strains specifically increased their ability to detect the mutagenicity of aromatic nitro, amino and hydroxylamino compounds, whereas the strains with high nitroreductase activity were very sensitive to some nitroaromatics. The combined use of the isogenic tester strains with different metabolic capacities was quite useful to assess the intracellular metabolic activation and detoxification mechanisms of chemical mutagens. 相似文献