Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Using a combination of immunoblotting, double immunoprecipitation, immunoglobulin-affinity chromatography, and isoelectrofocusing, we have been able to identify a group of proteins that display CDP-reductase activity and contain antigenic epitopes recognized by anti-ribonucleotide reductase M1 subunit and anti-ubiquitin antibodies. In the cytoplasm of rat liver cells, we could detect a total of five proteins with molecular masses of 92, 89, 56, 45, and 37 kilodaltons which reacted with the anti-M1 subunit serum. All of them, except the 89-kilodalton protein (the nascent unmodified M1), were also recognized by the anti-ubiquitin antibody. In normal liver cells, all of the apparently ubiquitinated species of the M1 protein were found in the cytoplasm, but not in the nuclear envelope associated pool of the enzyme. However, we did not detect ubiquitinated M1 protein fragments in the cytoplasm of Morris hepatoma 5123tc. The level of the apparently ubiquitinated fragments of the M1 subunit increased in parallel to the DNA-synthetic activity of normal liver cells, suggesting that ubiquitination plays a key role in the regulation of the activity of the enzyme during the cell cycle.
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PMID:The M1 subunit of rat liver ribonucleotide reductase appears to be modified by ubiquitination. 132 59

To gain insight into the activity of cytosolic proteases in tumors, the ATP-dependent proteolysis of cell sap and the ATP- and ubiquitin-dependent proteolysis of Fraction II (a cytosolic subfraction freed of endogenous ubiquitin) were measured in the anaplastic Yoshida ascites hepatoma AH 130. Hepatoma cell sap showed only low, although significant, ATP-stimulated proteolysis, as best seen by comparisons with rat liver made on the basis of wet weight. Much of the basal proteolytic activity of cell sap and of its subfraction enriched in high Mr complexes (Fraction X) peaked near 18S in sucrose gradients. In contrast with cell sap, Fraction II from hepatoma degraded [14C]methylcasein more efficiently than Fraction II from normal liver, but the activities for liver and tumor did not differ on a wet weight basis. Altered polypeptide patterns shown by SDS-PAGE in the Yoshida hepatoma suggested that some abundant hepatoma-specific cytosolic protein might interfere with degradation of the [14C]methylcasein by hepatoma.
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PMID:ATP- and ATP+ ubiquitin-stimulated proteolysis in rat liver and Yoshida ascites hepatoma. 165 48

A clone of about 1 kb has been isolated from a human brain cDNA library. The clone possesses a 151 amino acid open reading frame that exhibits 72% amino acid identity with the E2 ubiquitin-conjugating enzyme encoded by the RAD6 gene of Saccharomyces cerevisiae. A 90% amino acid identity was observed in a central sequence surrounding a cysteine, which most likely contributes the sulfhydryl group involved in the formation of the ubiquitin-E2 thiolester linkage. Northern hybridization analyses have identified a poly(A)-containing mRNA of about 1 kb encoding the E2-like sequence in human CEM lymphoblastoid and HeLa cells, Novikoff rat hepatoma cells and S49 mouse leukemia cells. Southern hybridization analyses indicate the presence of a single gene encoding this sequence in both human cell lines, but of two or more related genes in the rodent cell lines.
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PMID:Mammalian mRNAs encoding protein closely related to ubiquitin-conjugating enzyme encoded by yeast DNA repair gene RAD6. 188 45

Ubiquitin, a 76 amino acid protein, is covalently attached to abnormal and short-lived proteins, thus marking them for ATP-dependent proteolysis in eukaryotic cells. Free (unconjugated) ubiquitin was localized in hepatoma cells using affinity purified anti-ubiquitin antibodies and colloidal gold immunoelectron microscopy. The anti-ubiquitin antibodies recognize only unconjugated ubiquitin. Ubiquitin is found within the cytoplasm, nucleus, the microvilli, autophagic vacuoles and lysosomes.
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PMID:Immunoelectron microscopic localization of ubiquitin in hepatoma cells. 284 72

Radioiodinated, native and denatured bovine serum albumin (albumin) beta-lactoglobulin and cytochrome c were introduced into hepatoma tissue culture cells by erythrocyte-ghost-mediated microinjection, and their rates of degradation were compared. Denatured albumin was degraded at 20% of the rate of undenatured albumin, denatured beta-lactoglobulin was degraded three times faster than undenatured beta-lactoglobulin, while denatured and undenatured cytochrome c were degraded at the same rate. Thus, denaturation does not affect the rates of intracellular breakdown of microinjected proteins in a simple predictable way. Exhaustive methylation did not inhibit the degradation of denatured beta-lactoglobulin or albumin, indicating that, like their undenatured counterparts, they are not degraded via the ubiquitin pathway. In reticulocyte lysates, in the presence of ATP, denatured albumin and beta-lactoglobulin were broken down at slightly slower rates than the parent proteins. Exhaustive methylation of both denatured and undenatured proteins completely abolished their ATP-dependent breakdown. This inhibition is consistent with the hypothesis that free -NH2 groups are required for the attachment of ubiquitin prior to degradation in this system. Removal of an ammonium sulfate fraction from reticulocyte lysates produces a proteolytic system markedly different from the whole lysate [Speiser, S. & Etlinger, J. D. (1983) Proc. Natl Acad. Sci. USA 80, 3577-3580]. In this system both denatured and undenatured albumin and beta-lactoglobulin were degraded essentially independently of ATP. Methylation only slightly decreased the breakdown of denatured proteins, suggesting that they are not degraded via the ubiquitin pathway. A possible explanation of these results is that removal of the ammonium sulfate fraction unmasks an ATP-independent proteolytic system unrelated to the ubiquitin pathway.
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PMID:Effects of denaturation and methylation on the degradation of proteins in cultured hepatoma cells and in reticulocyte cell-free systems. 298 89

[125I]Ubiquitin introduced into permeabilized hepatoma tissue culture (HTC) cells rapidly forms conjugates with endogenous proteins. A characteristic pattern of low mol. wt conjugates is obtained which includes the ubiquitinated histone, uH2A, and unknown molecular species with MrS of 14, 23, 26 (two bands) and 29 kd. A broad spectrum of higher mol. wt conjugates is also produced. The formation of all conjugates is absolutely dependent on ATP, and upon depletion of ATP they are rapidly broken down. The 14, 23 and 29 kd species are found in all subcellular fractions examined. uH2A is located exclusively in the nuclear fraction. The pair of 26 kd bands is specifically associated with the ribosome fraction. A considerable percentage of the higher mol. wt conjugates sediments with the small particle (100,000 g) fraction in the ultracentrifuge but is solubilized with deoxycholate, indicating that there are many membrane-associated conjugates. The pattern of ubiquitin conjugation in interphase and metaphase cells was compared. The incorporation of ubiquitin into uH2A was markedly reduced in metaphase cells whereas its incorporation into other low mol. wt conjugates and into high mol. wt conjugates was affected slightly, if at all. This shows that the known decrease of uH2A levels in metaphase is due to a specific effect on histone ubiquitination and not to a general decrease in ubiquitination activity or increase of isopeptidase activity. Changes in the levels of uH2A during mitosis measured by immunoblotting were similar to those estimated in permeabilized cells. These experiments indicate that permeabilized cells provide a useful approach to the study of rapidly turning over ubiquitin conjugates in mammalian cells.
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PMID:Conjugation of [125I]ubiquitin to cellular proteins in permeabilized mammalian cells: comparison of mitotic and interphase cells. 301 20

Exposure of cultured rat hepatoma (HTC) cells to a 43 degrees C heat shock transiently accelerates the degradation of the long-lived fraction of cellular proteins. The rapid phase of proteolysis which lasts approximately 2 h after temperature step-up is followed by a slower phase of proteolysis. During the first 2 h after temperature step-up there is a wave of ubiquitin conjugation to cellular proteins which is accompanied by a fall in ubiquitin and ubiquitinated histone 2A (uH2A) levels. Upon continued incubation at 43 degrees C the levels of ubiquitin conjugates fall with a corresponding increase of ubiquitin and uH2A to initial levels. The burst of protein degradation and ubiquitin conjugation after temperature step-up is not affected by the inhibition of heat shock protein synthesis. Cells of the FM3A ts85 mutant, which have a thermolabile ubiquitin activating enzyme (E1), do not accelerate protein degradation in response to a 43 degrees C heat shock, whereas wild-type FM3A mouse cells do. This observation indicates that the ubiquitin system is involved in the degradation of heat-denatured proteins. Sequential temperature jump experiments show that the extent of proteolysis at temperatures up to 43 degrees C is related to the final temperature and not to the number of steps taken to attain it. Temperature step-up to 45 degrees C causes the inhibition of intracellular proteolysis. We propose the following explanation of the above observations. Heat shock causes the conformational change or denaturation of a subset of proteins stable at normal temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of heat shock on protein degradation in mammalian cells: involvement of the ubiquitin system. 303 79

Radioiodinated proteins were introduced into hepatoma tissue culture (HTC) cells by erythrocyte ghost-mediated microinjection, and their degradation was studied. 125I-bovine serum albumin and 125I-lysozyme were degraded with half-lives of about 7 and 11 h, respectively. The process was ATP-dependent. The breakdown of these proteins was not inhibited by the following inhibitors of lysosomal proteolysis: NH4Cl, methylamine, chloroquine, leupeptin, or antipain. Methylation of 94% of the amino groups of bovine serum albumin or 99% of the amino groups of lysozyme had little effect on the rates of their degradation in HTC cells. In contrast, methylation almost completely inhibited the ATP-dependent proteolysis of both proteins in reticulocyte lysates. Methylated bovine serum albumin was not detectably demethylated in HTC cells. It is concluded that in HTC cells, bovine serum albumin and lysozyme are degraded by a nonlysosomal pathway which differs from the ubiquitin-dependent proteolysis system of reticulocytes in that it does not require free amino groups.
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PMID:Degradation of microinjected methylated and unmethylated proteins in hepatoma tissue culture cells. 688 59

Rats implanted with Yoshida ascites hepatoma (YAH) show a rapid and selective loss of muscle protein due mainly to a marked increase (63-95%) in the rate of protein degradation (compared with rates in muscles of pair-fed controls). To define which proteolytic pathways contribute to this increase, epitrochlearis muscles from YAH-bearing and control rats were incubated under conditions that modify different proteolytic systems. Overall proteolysis in either group of rats was not affected by removal of Ca2+ or by blocking the Ca(2+)-dependent proteolytic system. Inhibition of lysosomal function with methylamine reduced proteolysis (-12%) in muscles from YAH-bearing rats, but not in muscles of pair-fed rats. When ATP production was also inhibited, the remaining accelerated proteolysis in muscles of tumor-bearing rats fell to control levels. Muscles of YAH-bearing rats showed increased levels of ubiquitin-conjugated proteins and a 27-kDa proteasome subunit in Western blot analysis. Levels of mRNA encoding components of proteolytic systems were quantitated using Northern hybridization analysis. Although their total RNA content decreased 20-38%, pale muscles of YAH-bearing rats showed increased levels of ubiquitin mRNA (590-880%) and mRNA for multiple subunits of the proteasome (100-215%). Liver, kidney, heart, and brain showed no weight loss and no change in these mRNA species. Muscles of YAH-bearing rats also showed small increases (30-40%) in mRNA for cathepsins B and D, but not for calpain I or heat shock protein 70. Our findings suggest that accelerated muscle proteolysis and muscle wasting in tumor-bearing rats result primarily from activation of the ATP-dependent pathway involving ubiquitin and the proteasome.
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PMID:Activation of the ATP-ubiquitin-proteasome pathway in skeletal muscle of cachectic rats bearing a hepatoma. 753 18

Rats bearing the Yoshida AH-130 ascites hepatoma for 7 days showed an important decrease in muscle mass--over 30% in gastrocnemius and extensor digitorum longus (EDL)--in relation to non-tumour-bearing controls, which is associated with an increased proteolytic rate in in vitro incubation. In order to identify the precise biochemical process which was involved, we measured different proteolytic systems in incubated EDL muscles. The capacity for intralysosomal proteolysis, as measured by sensitivity to methylamine, was not increased in tumour-bearing rats, suggesting that the mechanism involved in the increased proteolytic rate was extralysosomal. Incubations using the Ca2+ ionophore A23187 revealed no change in the activity of calcium-dependent proteases as a consequence of tumour growth. Finally, muscle incubation in an ATP-depleted medium allowed us to conclude that energy-dependent proteases were involved in the activation of muscle proteolysis in tumour-bearing rats. In particular, the ubiquitin-dependent proteolytic system is involved, since there is an important increase in ubiquitin conjugates in the skeletal muscle of tumour-bearing rats. It may thus be suggested that extralysosomal ATP- and ubiquitin-dependent proteases underlie the biochemical mechanism of muscle wastage associated with cancer cachexia.
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PMID:Muscle wasting associated with cancer cachexia is linked to an important activation of the ATP-dependent ubiquitin-mediated proteolysis. 770 27


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