Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this paper we show that hepatocytes that have been depleted of K+ secrete albumin, alpha-1-anti-trypsin and transferrin at a slower rate than cells to which K+ has been returned. K+ depletion has no effect on the intracellular nucleotide pools, and we provide evidence that the inhibitions of secretion caused by depletion of K+ and depletion of ATP are independent. Studies of the processing of alpha-1-anti-trypsin show that K+ depletion inhibits the formation of the mature form of the protein, but that immature forms are never secreted. In cells to which K+ was returned, secretion of the mature form was restored. This implies that transport is blocked at a point before the proteins reach the processing enzymes. Proteins delayed by K+ depletion are not removed from the secretory pathway, but are free to mix with protein synthesized subsequently. These data are supported by subcellular fractionation experiments, which show that the secretory proteins are delayed before reaching the Golgi complex, and by immunoelectron microscopic studies. These show that in K+-deficient cells the morphology of both the endoplasmic reticulum and the Golgi complex is normal. The secretory proteins are trapped in smooth vesicles that contain reaction product when incubated for glucose-6-phosphatase, a marker for the endoplasmic reticulum.
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PMID:Potassium depletion inhibits the intracellular transport of secretory proteins between the endoplasmic reticulum and the Golgi complex. 278 29

Cultured hepatocytes from adult Fischer 344 rats were transformed by virion or cloned simian virus 40 (SV40) DNA using the calcium phosphate method. Transformation by SV40 occurred in either serum-supplemented medium or chemically defined medium (CDM). The frequency was greatest in serum-supplemented medium but transformants did not remain differentiated. In contrast, SV40 transformants developed less frequently in CDM, but retained differentiated functions. The frequency of transformation was enhanced by treatments that stimulated cell proliferation, in particular supplementing CDM with epidermal growth factor. Hepatocytes transformed in CDM were epithelial in morphology, secreted albumin, transferrin, hemopexin, and expressed the enzyme glucose-6-phosphatase, all characteristics of normal liver. Transformants did not produce detectable levels of alpha-fetoprotein, a marker of fetal or abnormal liver. We conclude that (a) hepatocytes can be transformed by transfection with SV40 DNA; (b) the frequency of transformation is enhanced by stimulating DNA synthesis; and (c) the transformed cells retain specific functions of normal hepatocytes in situ. Using this system it will be possible to study transformation of hepatocytes by viral and cellular oncogenes and to determine their effects on hepatocellular differentiation.
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PMID:Transformation of rat hepatocytes by transfection with simian virus 40 DNA to yield proliferating differentiated cells. 301 81

A human hepatocyte line (HHY41) was established from normal human liver tissue. This cell line was derived from a primary culture of human hepatocytes maintained between two layers of collagen gel for 4 weeks. It differs from other human hepatocyte lines in that transfection with the simian virus 40 gene was not used for cellular transformation and nonhepatocellular coculture cells were not present. HHY41 cells have proliferated freely in serum and hormone-supplemented medium after more than 1 year in continuous culture, exhibiting typical morphological characteristics of hepatocytes. HHY41 cells retain glucose-6-phosphatase activity. They also retain the ability to secrete liver-specific proteins such as albumin, transferrin, and alpha-fetoprotein. Northern blot analysis confirmed the presence of albumin mRNA. Cytochromes P450 induced by polycyclic aromatic hydrocarbons are maintained in these cells. Detection of cell surface antigens revealed that HHY41 cells express alpha 1 beta 1-integrin, which is expressed by normal hepatocytes and not by bile duct epithelial cells. High-molecular-weight cytokeratin, a marker for bile duct cells, is also absent in HHY41. Cytogenetic analysis showed hyperdiploid karyotype with a consistent deletion in the short arm of chromosome 1. HHY41 can be considered a new human hepatocyte line which retains liver-specific functions of differentiated hepatocytes. Derived from normal liver tissue, not a hepatocellular carcinoma, it provides a new model system for studying the regulation of cell growth and differentiated functions in human hepatocytes.
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PMID:Establishment of a human hepatocyte line derived from primary culture in a collagen gel sandwich culture system. 749 48

Four separate continuous lines of human hepatocytes (HH01, HH02, HH09, HH25) were developed from normal liver tissue by subjecting cocultures of human hepatocytes with rat liver epithelial cells in a highly enriched medium to frequent subculturing. The addition of conditioned medium from either the human hepatoma line Hep G2 or one of these stable human hepatocyte lines (HH09) appeared to facilitate establishment of line HH25. These human hepatocyte lines have been in continuous culture for 2 to 5 yr and consist of approximately 95% human cells by analysis of cell surface antigens. Cytogenetic analysis also confirmed the human origin of these cells and showed clonal origin with abnormal ploidy. Cells in these human hepatocyte lines retain morphological features of hepatocytes by both light and electron microscopy. They also retain glucose-6-phosphatase activity and secrete proteins characteristic of hepatocytes, such as albumin, alpha-fetoprotein and transferrin. After incubation with 13 mumol/L dibenz(a,h) anthracene for 24 hr, each line had detectable activity of aryl hydrocarbon hydroxylase, ethoxyresorufin O-deethylase and methoxyresorufin O-demethylase. Thus, these human hepatocyte lines retain important differentiated characteristics of hepatocytes. Derived from normal liver tissue, they appear to be immortalized. They provide a new model system for studying human hepatocellular drug metabolism. These lines may also be useful for studying the regulation of synthesis of albumin, alpha-fetoprotein and other proteins in human hepatocytes, determining the effects of cytokines and growth factors and designing systems to effect gene transfer into human hepatocytes for the purpose of gene therapy.
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PMID:Characterization of human hepatocyte lines derived from normal liver tissue. 751 62

Transferrin receptor (TR) performs the major function of binding and internalizing its specific iron-loaded ligand, transferrin, and its expression is closely linked to the proliferation status of the cell. This study was undertaken to elucidate TR expression in the hyperplastic lesion of hepatocyte in chemically induced hepatic carcinogenesis. The resistant hepatocyte model was chosen for a rat model of carcinogenesis and Sprague-Dawley rats were divided into the following groups: the control groups of normal diet and iron-rich diet with or without hydroxyquinoline and the groups of carcinogen alone and carcinogen plus iron-rich diet with or without administration of hydroxyquinoline. Microscopic changes in the liver, expression of transferrin receptor and glucose-6-phosphatase were studied. The hepatocyte of the control group showed both cytoplasmic and membranous expression of TR. The liver of rats fed on high iron diet accumulated iron and the expression of TR was down regulated by intrahepatic iron accumulation. In the carcinogen administered group the resistant hepatocyte of hyperplastic lesion revealed strong membranous expression of TR and failed to accumulate iron in spite of high iron diet but in contrast the surrounding non-resistant hepatocyte expressed TR in both the membrane and cytoplasm and stored iron when fed on high iron diet. The strong membranous expression of TR is one of the characteristics of the resistant hepatocyte of hyperplastic lesion and it seems to be related to the inability to accumulate iron in spite of a high iron diet.
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PMID:Transferrin receptor expression of the hyperplastic lesions of hepatocyte in experimental hepatocarcinogenesis. 852 44

To establish the differentiation potential of progenitor cells, non-parenchymal epithelial cells from the F344 rat liver (FNRL cells) were studied. These cells reacted with the OV-6 antibody marker of oval cells, but were negative for hepatocyte markers (albumin, transferrin, glycogen, glucose-6-phosphatase, H4 antigen), biliary markers (gamma glutamyl transpeptidase, cytokeratin-19), and alpha-fetoprotein, although exposure to sodium butyrate induced nascent albumin and alpha-fetoprotein mRNA transcription. When stably transduced, FNRL cells expressed a retroviral promotor-driven lacZ reporter in vitro, similar to transgene expression in hepatocyte-derived HepG2 cells. However, lacZ expression in FNRL cells was rapidly extinguished in intact animals, whereas the reporter remained active in HepG2 cells. Transplanted FNRL cells showed copious glucose-6-phosphatase expression; however, the cell differentiation programme remained incomplete, despite two-thirds partial hepatectomy, D-galactosamine treatment or bile duct ligation. Interestingly, lacZ expression resumed in cultures of FNRL cells explanted from recipients. Moreover, lacZ expression was down-regulated by gamma-interferon in FNRL cells, without affecting lacZ activity in HepG2 cells. The data indicate that although subpopulations of oval cells may not fully differentiate into mature hepatocytes, these cells might serve critical functions, such as glucose utilization, and help survival after liver injury. Also, introduced genes may be regulated in progenitor cells at multiple levels, including by interactions between regulatory sequences, differentiation-specific cellular factors, and extracellular signals; in vivo studies are thus especially important for analysing gene regulation in progenitor cells.
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PMID:Differentiation-specific regulation of transgene expression in a diploid epithelial cell line derived from the normal F344 rat liver. 1039 93

Transdifferentiation of pancreas to liver is a well-recognized phenomenon and has been described in animal experiments and human pathology. We recently produced an in vitro model for the transdifferentiation (or conversion) of the pancreatic cell line AR42J-B13 to hepatocytes based on culture with dexamethasone (Dex). To determine whether the hepatocytes express markers of hepatic intermediary metabolism and detoxification, we investigated the patterns of expression of glucokinase, cytochrome P450s CYP3A1 and CYP2B1/2, testosterone/4-nitrophenol uridine diphosphate glucuronosyltransferase (UDPGT), and aryl sulfotransferase. All were expressed. We also determined the expression of 2 enzymes involved in ammonia detoxification: carbamoylphosphate synthetase I (CPS I) and glutamine synthetase (GS). These enzymes are normally strictly compartmentalized in liver in a wide periportal pattern and the last downstream perivenous hepatocytes, respectively. Following culture with Dex, CPS I and GS are expressed in 2 different cell populations, suggesting that both periportal and perivenous hepatocytes are induced. We also produced a reporter assay based on the activation of green fluorescent protein (GFP) by the transthyretin (TTR) promoter or glucose-6-phosphatase (G6Pase) promoter. After culture with Dex, transfected cells begin to express GFP, showing that hepatic promoters are activated in concert with the induction of the hepatocyte phenotype. Lastly, we examined the stability of the hepatic phenotype and found that some cells still express liver markers (transferrin or albumin) up to 14 days after removal of Dex. In conclusion, these results suggest that pancreatic hepatocytes produced by this method may offer an alternative model to primary cultures of hepatocytes for the study of liver function.
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PMID:Differentiated properties of hepatocytes induced from pancreatic cells. 1219 45

Proinsulin-transferrin (ProINS-Tf) fusion protein was evaluated for its in vivo pharmacokinetics, efficacy, and mechanism. Our previous studies have shown that ProINS-Tf was converted to active insulin-transferrin (INS-Tf) via the transferrin (Tf)-receptor-mediated pathway in hepatoma cells. We hypothesized that this fusion protein can be administered as a prodrug and be converted to a biologically active protein with specificity for the liver versus other insulin (INS)-sensitive tissues (muscle and adipose). Administration as an inactive prodrug with liver-specific action compared with other INS-sensitive tissues conceivably reduces negative side effects seen with other INS analogs. In this report, the data show that ProINS-Tf exhibited a slow, but sustained, in vivo hypoglycemic efficacy and long plasma half-life. The fusion protein showed activity in the liver, as evidenced by decreased expression of two key hepatic glucose production (HGP) enzymes, PEPCK and glucose-6-phosphatase, and increased glycogen levels under feeding conditions. Furthermore, the INS receptor (IR) phosphorylation (activation) in liver and muscle tissues was compared with postinjection of INS or ProINS-Tf. While INS activated IR in both the liver and muscle, ProINS-Tf only showed activation in the liver. Thus, ProINS-Tf fusion protein can potentially be administered as a prodrug with sustained Tf-mediated activation and selectivity in inhibiting HGP.
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PMID:Proinsulin-transferrin fusion protein as a novel long-acting insulin analog for the inhibition of hepatic glucose production. 2475 94