The synthesis and secretion of albumin

Schreiber, Gerhard; Urban, Jörg

doi:10.1007/bfb0030497

Cited by 50 publications

(10 citation statements)

References 305 publications

(244 reference statements)

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“…Our reported triglyceride secretory rate is 10% higher than that reported by Patsch et al (39) for triglyceride secretion from perfused livers of carbohydrate-induced female rats. The rate of albumin secretion (405 jg/h per g wet liver weight) was similar to that in the intact rat (40). The use of fibronectin-coated dishes allowed hepatocytes to remain viable in culture without the requirement for insulin in the method as previously reported from this laboratory (25,26).…”

Section: Discussionsupporting

confidence: 69%

Effects of Insulin and Glucose on Very Low Density Lipoprotein Triglyceride Secretion by Cultured Rat Hepatocytes

Durrington¹,

Newton²,

Weinstein³

et al. 1982

J. Clin. Invest.

215

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A B S T R A C T The effect of insulin on hepatic triglyceride synthesis and secretion is controversial. Previously, we have described a cell culture system of adult rat hepatocytes that synthesize and secrete very low density lipoprotein (VLDL) triglycerides with small and irreproducible effects of insulin on triglyceride metabolism. To study the primary effects of insulin on hepatic triglyceride metabolism a method was developed utilizing fibronectin-coated culture dishes that allowed adhesion, spreading, and maintenance of hepatocytes for 2-3 d in the absence of serum and insulin. This culture system allowed mass measurements of both cellular and secreted VLDL triglycerides for long time periods after the addition of physiological concentrations of insulin to hormone-free culture medium. In the absence of insulin and after an initial 4 h in culture, the medium was replenished and triglyceride mass was measured at the end of 18-h incubations. VLDL triglyceride accumulated in the culture medium at a linear rate over this time-course with increasing accumulation as the medium glucose concentration was raised from 2.5 to 25 mM glucose (1.77±0.24 to 3.09±0.76 yg triglyceride/mg cell protein per h). There was no apparent significant lipolysis or hepatocellular reuptake of secreted VLDL triglycerides. In the absence of insulin cellular triglyceride levels were unchanged between 3 and 24 h in culture while insulin (50-500 gU/ml) significantly increased cellular triglyceride content at all glucose concentrations tested (0-25 mM). The addition of insulin to the culture medium progressively reduced the rate of VLDL triglyceride secretion accompanied by an increase in cellular triglyceride at insulin concentrations > 50 ,U/ml. Most or all of the observed increase in cell triglyceride content could in all experiments be accounted for by the insulin-induced inhibition of VLDL secretion. Incorporation of [2-3H]glycerol into cellular and VLDL triglycerides as a function of insulin concentration was also measured. Glycerol incorporation data at 20-22 h after plating of the cells closely paralleled the insulin-induced changes in cellular and VLDL triglyceride as determined by mass analysis. The observed effects of insulin occurred at concentrations close to the physiological range and suggest that the direct hepatic effect is to suppress VLDL secretion although the net effect in vivo will clearly reflect many additional accompanying changes.

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Section: Discussionsupporting

confidence: 69%

Effects of Insulin and Glucose on Very Low Density Lipoprotein Triglyceride Secretion by Cultured Rat Hepatocytes

Durrington¹,

Newton²,

Weinstein³

et al. 1982

J. Clin. Invest.

215

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“…As haptoglobin is among the most abundant glycoproteins secreted by the liver, it is reasonable to hypothesise that enhanced hepatic synthesis of the protein will occur due to an acute phase response in ovarian cancer patients resulting in elevated serum haptoglobin precursor concentration. As most secreted proteins are initially synthesised as larger precursor with an extended NH 2 -terminal sequence that is cleaved at the late-stage secretory process either within the Golgi complex or related vesicles (Schreiber and Urban, 1978), one can assume that the elevation of the HAP1 in cancer patients serum may result due to a disease-specific defective intracellular processing.…”

Section: Discussionmentioning

confidence: 99%

Proteomic-based identification of haptoglobin-1 precursor as a novel circulating biomarker of ovarian cancer

et al. 2004

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Screening for specific biomarkers of early-stage detection of ovarian cancer is a major health priority due to the asymptomatic nature and poor survival characteristic of the disease. We utilised two-dimensional gel electrophoresis (2DE) to identify differentially expressed proteins in the serum of ovarian cancer patients that may be useful as biomarkers of this disease. In this study, 38 ovarian cancer patients at different pathological grades (grade 1 (n ¼ 6), grade 2 (n ¼ 8) and grade 3 (n ¼ 24)) were compared to a control group of eight healthy women. Serum samples were treated with a mixture of Affigel-Blue and protein A (5 : 1) for 1 h to remove high abundance protein (e.g. immunoglobulin and albumin) and were displayed using 11 cm, pH 4 -7 isoelectric focusing strips for the first dimension and 10% acrylamide gel electrophoresis for the second dimension. Protein spots were visualised by SYPRO-Ruby staining, imaged by FX-imager and compared and analysed by PDQuest software. A total of 24 serum proteins were differentially expressed in grade 1 (Po0.05), 31 in grade 2 (Po0.05) and 25 in grade 3 (Po0.05) ovarian cancer patients. Six of the protein spots that were significantly upregulated in all groups of ovarian cancer patients were identified by nano-electrospray quadrupole quadrupole time-of-flight mass spectrometry (n-ESIQ(q)TOFMS) and matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOFMS) as isoforms of haptoglobin-1 precursor (HAP1), a liver glycoprotein present in human serum. Further identification of the spots at different pathological grades was confirmed by Western blotting using monoclonal antibody against a haptoglobin epitope contained within HAP1. Immunohistochemical localisation of HAP1-like activity was present in malignant ovarian epithelium and stroma but strong immunostaining was present in blood vessels, areas with myxomatous stroma and vascular spaces. No tissue localisation of HAP1-like immunoreactivity was observed in normal ovarian surface epithelium. These data highlight the need to assess circulating concentration of HAP1 in the serum of ovarian cancer patients and evaluate its potential as a biomarker in the early diagnosis of ovarian cancer.

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“…All of these investigations involved immunocytochemical localization of albumin-containing cells in fixed, histologic sections of liver. Although the reasons for the discrepancies in the results are not clear, several points should be noted : in two cases (5,40), the authors themselves warned of technical problems encountered in tissue and section processing that could markedly affect results; in a review, Schreiber et al (41) albumin is soluble in the acid-alcohol fixative employed in almost all these studies ; and, finally, in no case were serial sections examined, which, given the intracellular localization of albumin, would probably be required to obtain an accurate count of the albumin containing cells. In our investigation, albumin was identified in isolated rat hepatocytes .…”

Section: Discussionmentioning

confidence: 99%

Immunocytochemical identification of phenylalanine hydroxylase and albumin in cultured hepatoma cells and isolated rat hepatocytes.

Baker

Jefferson²,

Shiman

1981

The Journal of Cell Biology

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Rhodamine-conjugated antibodies specific for phenylalanine hydroxylase and serum albumin were employed as cytochemical probes to identify these two proteins in H4 hepatoma cells and in isolated rat hepatocytes . Each fluorescent antibody stained the cells specifically and in a distinctive manner . In both cell types, albumin staining was discretely localized in cytoplasmic "bundles," whereas, phenylalanine hydroxylase staining was diffuse and cytoplasmic and in H4 cultures varied somewhat from cell to cell. Evidence from cultures of REB15 cells, a strain derived by cloning H4 cells in tyrosine-free medium, suggested that the staining variability of H4 cells could reflect a variability in phenylalanine hydroxylase content. Hydrocortisone-treated H4 and REB15 cultures contain increased amounts of phenylalanine hydroxylase ; and all cells in the culture appear to be induced by the hormone .Evidence was presented to show that the albumin visualized within the isolated hepatocytes had been synthesized by these cells, and, furthermore, that quantitatively nearly all intracellular albumin in the isolated rat hepatocytes appeared to be entrained in the secretion pathway (analogous data already exist for H4 cells [Baker, R. E ., and R. Shiman . 1979 . J . Biol . Chem. 254: [9633][9634][9635][9636][9637][9638][9639]) . By scoring specific fluorescence, 86 and 98% of the H4 cells and 89 and 98% of the isolated hepatocytes were found to contain phenylalanine hydroxylase and albumin, respectively . Therefore, almost all cells in each population appeared to synthesize both proteins . An implication of these findings is that in rat virtually all liver parenchymal cells must synthesize both phenylalanine hydroxylase and albumin .Serum albumin synthesis and phenylalanine hydroxylase expression are differentiated functions of normal mammalian liver . Both functions are also expressed by the Reuber hepatoma (rat) cell line H4 (1) . Recently, we developed a new method for measuring protein turnover and used it to determine the half-life of phenylalanine hydroxylase in H4 cultures (2). Because the method, which we hoped also to apply in studies with perfused rat liver, involved the use of albumin as a reference protein, the question immediately arose as to whether or not albumin and phenylalanine hydroxylase were simultaneously synthesized within the same cells. Several studies (3-7) indicate that only a minority of liver parenchymal cells contain and, by implication, synthesize albumin. To our knowledge, there is no existing information regarding the distribution of phenylalanine hydroxylase among hepatic cells either in vivo or in culture. To answer the cosynthesis question, THE JOURNAL Of CELL BIOLOGY " VOLUME 90 JULY 1981 145-152 ©The Rockefeller University Press " 0021-9525/81/07/0145/OB $1 .00 we employed immunocytochemical methods to identify albumin and phenylalanine hydroxylase in H4 cultures and also in freshly isolated rat hepatocytes. Our results, reported here, are of quite general interest, because they supply...

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The synthesis and secretion of albumin

Cited by 50 publications

References 305 publications

Effects of Insulin and Glucose on Very Low Density Lipoprotein Triglyceride Secretion by Cultured Rat Hepatocytes

Effects of Insulin and Glucose on Very Low Density Lipoprotein Triglyceride Secretion by Cultured Rat Hepatocytes

Proteomic-based identification of haptoglobin-1 precursor as a novel circulating biomarker of ovarian cancer

Immunocytochemical identification of phenylalanine hydroxylase and albumin in cultured hepatoma cells and isolated rat hepatocytes.

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