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E F Walborg

Publications and source records attributed to E F Walborg.

At least 37 records · Page 2Linked to original sources
PubMed1995

Induction of short-term biomarkers of tumor promotion in skin of CD-1 mice by petroleum middle distillates: preliminary observations.

The induction of sustained epidermal hyperplasia in mouse skin has been shown to be a reliable predictor of tumor promoting activity for chemicals as diverse as phorbol esters, anthralins, n-dodecane and organic peroxides (DiGiovanni, 1992). The results contained herein demonstrate that API 81-07 and API 81-10, petroleum middle distillates that exhibit tumor promoting activity in mouse skin, induce epidermal hyperplasia and ODC activity. Other petroleum middle distillates (odorless light petroleum hydrocarbons, a light vacuum distillate, and a mineral seal oil) were also shown to share these activities. It should be emphasized that the relevance of these observations to human skin remains unresolved; however, the availability of these short-term biomarkers offers the opportunity to address the issue by performing comparative investigations on the effects of petroleum middle distillates on human skin xenografted to athymic (nude) mice. Such studies are being initiated.

Alkanes↗
PubMed1985

Identification of dipeptidyl peptidase IV as a protein shared by the plasma membrane of hepatocytes and liver biomatrix.

The histotypic organization of liver parenchyma involves specific intercellular contacts and interaction of hepatocytes with supporting biomatrix. Evidence from this laboratory identified a peptide (Hep105, apparent Mr 105 000) that is shared by the plasma membrane of rat hepatocytes and rat liver biomatrix. This report identifies Hep105 as a peptide component of dipeptidyl peptidase IV (DPPIV; EC 3.4.14.-). A monoclonal antibody (MAb 236.3) was shown to immunoprecipitate DPPIV from non-ionic detergent extracts of surface-labeled 125I hepatocytes. The immunoprecipitate contained two 125I-labeled peptides: Hep105 and a peptide of apparent Mr 150000 (Hep150). Proteolysis of 125I-labeled Hep105 and Hep150 by Staphylococcus aureus V8 protease yielded essentially identical patterns of 125I-labeled peptide degradation products, indicating that Hep105 and Hep150 are structurally related. Only Hep150 exhibited DPPIV activity on transblot analysis, an observation that is consistent with the interpretation that it is the monomeric form of the enzyme. Heating (100 degrees C, 5 min) of purified Hep150 in the presence of sodium dodecylsulfate (SDS) resulted in its conversion to Hep105 and the disappearance of any demonstrable enzymatic activity. 3H-labeled diisopropyl fluorophosphate was incorporated into Hep105, indicating that Hep105 contains the active site for DPPIV. Purified rat liver biomatrix was shown to possess significant DPPIV activity. Taken together, these data indicate that Hep105 s a peptide component of DPPIV.

Animals↗
PubMed1984

Cell surface expression by adult rat hepatocytes of a non-collagen glycoprotein present in rat liver biomatrix.

A rabbit antiserum raised against ACI rat liver biomatrix was used to identify components common to biomatrix and plasma membranes of adult hepatocytes. Biomatrix was isolated from intact rat livers by reverse perfusion via the inferior vena cava with sodium deoxycholate, nucleases and lipid extracting solvents. Immunoprecipitation analysis of detergent extracts of hepatocytes surface-labeled with 125I indicated that antibodies, purified from anti- biomatrix antiserum by adsorption and desorption from intact hepatocytes, showed reactivity with a single MW 105 kD component, designated Hep 105. Indirect immunofluorescence analysis showed that Hep 105 was expressed in some regions of the perisinusoidal space and in all three domains of the hepatocyte plasma membrane and was present on some but not all of the fibrous elements in frozen sections of biomatrix . The presence of Hep 105 on biomatrix was confirmed by immunoprecipitation analysis which showed that Hep 105 was present in components solubilized from biomatrix by sequential treatment with 0.5 M acetic acid, 0.05% collagenase and 4 M urea. Further characterization using immunoprecipitation analysis in combination with immobilized lectins and two-dimensional polyacrylamide gel electrophoresis (PAGE) indicated that Hep 105 was a non-collagen glycoprotein which showed charge heterogeneity and existed on the cell surface as a disulfide-linked heterodimer of apparent MW 125 kD. Two hybridomas, constructed by fusing P3 X 63Ag8 myeloma cells with spleen cells from mice immunized with intact hepatocytes, were shown by immunodepletion and two-dimensional gel electrophoretic analysis to be secreting monoclonal antibodies (Mab) against Hep 105. Examination of frozen sections of rat liver stained by indirect immunofluorescence showed that reactivity of both Mabs was concentrated in the bile canalicular domain of the hepatocyte plasma membrane, suggesting that the reactive epitopes were not accessible in the sinusoidal and intercellular membrane domains. Taken together, these results suggest that Hep 105 may play a role in the interactions between hepatocytes and extracellular matrix.

Animals↗
PubMed1984

Structural differences in envelope glycoproteins associated with rat leukaemia virus produced by Novikoff hepatocellular carcinoma and spontaneously transformed Wistar rat embryo cells.

Immunochemical and immunocytochemical techniques have been used to characterize viral glycoproteins and endogenous rat leukaemia viruses (RaLV) produced both by Novikoff hepatocellular carcinoma cells and spontaneously transformed Wistar rat embryo cells (WRC). Results from immunocytochemical analysis demonstrated that RaLV produced by Novikoff and WRC cells could be distinguished by their unique patterns of reactivity with xenoantisera raised against virus particles or viral glycoproteins. This differential labelling was unexpected since all the antisera tested had been shown by immunoprecipitation and immunodepletion analysis to be reactive with viral glycoproteins expressed on the cell surface. Since no significant differences in cell surface-associated viral glycoproteins and those shed from the cell surface were detected by pulse iodination analysis, it was concluded that the apparent discrepancy between immunoferritin labelling and immunoprecipitation analysis resulted from differences in antigen accessibility on intact virions caused by structural differences in the viral glycoproteins expressed on Novikoff and WRC cells. This conclusion was supported by results from ferritin-lectin labelling, affinity chromatography and neuraminidase digestion studies which demonstrated differences in the saccharide moieties on both virion and cell surface-associated viral glycoproteins. Further evidence of structural differences was provided by limited digestion with trypsin and V8 protease of the Mr 64 000 (Nov gp64) and Mr 68 000 (WRC gp68) viral glycoproteins immunoprecipitated from Novikoff and WRC cells, respectively, with either monospecific anti-Rauscher murine leukaemia virus anti-gp70 serum or monospecific antiserum against Nov gp64 (anti-gp64). Results from digestion studies showed that all the major cleavage fragments from WRC gp68 were of higher molecular weight than their Nov gp64-derived counterparts. Evidence that Nov gp64 and WRC gp68 both share structural homology with other murine viral gp70s was suggested by results from immunoprecipitation analysis with anti-gp70 and anti-gp64 sera under reducing and non-reducing conditions which demonstrated the presence of an interchain disulphide bond in both glycoproteins and showed that at least some of these molecules exist on the cell surface as disulphide-linked heterodimers of Mr 78 000 and 82 000.

Animals↗
PubMed1983

Characterization of a family of glycoproteins associated with the bile canalicular membrane of normal hepatocytes but not expressed by two transplantable rat hepatocellular carcinomas.

Xenoantisera were used to investigate the expression of normal cell-surface components on transplantable rat hepatocellular carcinoma (253 and 311c) cells. Cell-surface components, immunoprecipitated from non-ionic detergent extracts of 125I-labeled hepatocytes by xenoantisera raised against rat hepatocytes, 253 cells, or 311c cells, were analyzed by 2-dimensional polyacrylamide gel electrophoresis. Comparison of the gel patterns revealed that anti-hepatocyte antiserum was reactive with a component having an apparent molecular weight of 105,000 (gp105) that was not recognized by xenoantisera against 253 or 311c cells. This component was isolated by affinity adsorption to Sepharose-conjugated wheat germ agglutinin, reconstituted in liposomes, and used to immunize a rabbit. The resulting antiserum, anti-gp105, was reactive with a family of glycoproteins that had an apparent molecular weight of 105,000 but differed in isoelectric points. Immunohistochemical techniques revealed that gp105 was localized in the bile canalicular domain of the hepatocyte plasma membrane. Immunodepletion analysis, blocking of immunoprecipitation by extracts of tumor cells, and labeling of cells by immunohistochemical techniques indicated that gp105 was not expressed at the surface of 253 or 311c cells. These studies suggest that the altered expression of gp105 on 253 and 311c hepatocellular carcinoma cells may be associated with the abnormal tissue architecture and growth patterns exhibited by these transplantable tumors.

Animals↗
PubMed1981

Evaluation of periodate/lysine/paraformaldehyde fixation as a method for cross-linking plasma membrane glycoproteins.

Fixation by periodate/lysine/paraformaldehyde, a method purported to cross-link specifically plasma membrane glycoproteins, was evaluated using Novikoff rat ascites hepatocellular carcinoma cells. Cells were treated with periodate/lysine, periodate/glycine, and periodate/lysine/paraformaldehyde and subsequently reduced with NaB3H4. The glycoproteins labeled with 3H were resolved by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and visualized by fluorography. The effects of reactant concentrations on 3H-labeling of cellular components, cell viability, and cross-linkage of 3H-labeled proteins were examined. The effect of increasing the localized density of plasma membrane glycoproteins on the extent of cross-linkage by periodate and lysine was investigated using cells in which patching of the plasma membrane glycoproteins had been induced by ferritin-conjugated concanavalin A/rabbit antiferritin antiserum. Also investigated was the periodate-independent to mixtures of periodate and lysine or glycine. Results of these studies did not support a mechanism of cross-linking involving reaction between the free base lysin and aldehyde groups on periodate oxidized carbohydrate residues but suggested a complex interaction between periodate oxidized plasma membrane glycoproteins and polymeric complexes of lysine and formaldehyde.U

Animals↗
PubMed1980

Accessibility of plasma membrane sialoglycoconjugates of Novikoff tumor cells to exogenous neuraminidase and proteases.

Plasma membrane glycoconjugates of Novikoff tumor cells were radioactively labeled by oxidation with NaIO4 followed by reduction with NaB3H4 Submission of the radioactively labeled glycoconjugates to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate followed by fluorography revealed the presence of at least ten major glycoproteins and a glycolipid fraction. The glycolipid fraction contained 34% of the cell-surface radioactive label. Pretreatment of cells with neuraminidase from Vibrio cholerae reduced radioactive labeling of the glycoproteins by 71% and that of the glycolipids by 39%. Sequential treatment of cells with papain and neuraminidase further reduced radioactive labeling of the glycolipid fraction, indicating that resistance of this fraction to the hydrolytic action of neuraminidase was determined, at least in part, by steric factors. Incubation of cells with papain resulted in extensive degradation of most of the radioactively labeled glycoproteins with the exception of a subset of glycoproteins having apparent molecular weights of 48 000 +/- 5000. Trypsin was more selective, degrading three glycoproteins having apparent molecular weights of 200 000, 140 000 and 37 000.

Animals↗
PubMed1980

Role of cell surface receptor mobility in concanavalin A-induced agglutination of Novikoff hepatoma and normal rat liver cells.

The relationshio between Con A-receptor mobility and Con A-induced agglutination of Novikoff hepatoma and normal rat liver cells was investigated. Novikoff cells, incubated with fluorescein-labelled Con A at 3 degrees C displayed uniform, ring-like surface fluorescence. Increasing the temperature of the cells to 37 degrees C caused capping of Con A receptors in approximately 65% of the cells, a phenomenon that could be prevented by prefixing the cells with glutaraldehyde. In spite of these variations in Con A-receptor distribution, Con A-induced agglutination was remarkably constant over a temperature range from 3 to 37 degrees C. In contrast to Novikoff cells, normal hepatocytes displayed a uniform, ringlike surface fluorescence at both 3 and 37 degrees C. No capping was observed. However, hepatocytes, similar to Novikoff cells, were agglutinable by low concentrations of Con A. These findings indicate that, in this model system, Con A-induced cytoagglutination is not dependent upon long-range lateral mobility of Con A receptors. The qualitative differences in the lateral mobility of cell-surface Con A receptors of normal and malignant rat liver cells may represent a marker for neoplastioc transformation during hepatocarcinogenesis, adaptation to growth in ascitic form, or progression of a tumour to a more malignant state.

Animals↗
PubMed1979

Concanavalin A and wheat germ agglutinin receptors in the ascitic fluid of rat hepatomas.

The presence of glycopeptide lectin receptors in the ascitic fluid of rats bearing Novikoff or AS-30D hepatoma was investigated. Macrosialoglycopeptides, resistant to pronase digestion, were partially purified from the ascitic fluid of hepatoma-bearing rats by gel filtration on Sephadex G-50. A macrosialoglycopeptide fraction, isolated from the ascitic fluid of rats bearing the Novikoff hepatoma, possessed potent concanavalin A (Con A) receptor activity. This fraction possessed higher Con A receptor activity than did the comparable macrosialoglycopeptide fraction from the ascitic fluid of rats bearing the AS-30D hepatoma; this obeservation is in agreement with the Con A-induced agglutination properties of these 2 hepatoma cell lines and with the Con A receptor activities of the glycopeptides released from the surface of the hepatoma cells by papain digestion. Rat blood serum contained a comparable macrosialoglycopeptide fraction, which possessed weak Con A receptor activity. The macrosialoglycopeptide fractions from the ascitic fluid of hepatoma-bearing rats possessed wheat germ agglutinin receptor activity. However, this activity was also present in normal rat serum. These results suggest that glycopeptides present on the surface of Novikoff hepatoma cells are shed into the ascitic fluid and may be distinguished from components in normal serum by their Con A receptor activity.

Animals↗
PubMed1979

Lectin affinity chromatography of cell surface proteins of Novikoff tumor cells.

Novikoff hepatocellular carcinoma cells were radioiodinated by a cell surface-specific method using lactoperoxidase/125I. The iodinated proteins were solubilized in 0.5% Nonidet P-40 and subjected to affinity chromatography on Sepharose-conjugated lectins (Ricinus communis agglutinins I or II, soybean agglutinin, concanavalin A, or wheat germ agglutinin) and analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Almost all the iodinated proteins bound to one or more of the Sepharose-conjugated lectins, presumptive evidence that these peptides are glycosylated. Lectin affinity chromatography resolved defined subsets of iodinated glycoproteins and suggested that certain glycoproteins could be fractionated on the basis of heterogeneity of their heterosaccharide moieties. Incubation of the iodinated cells with neuraminidase resulted in increased binding of iodinated proteins to Sepharose-conjugated Ricinus communis agglutinins I and II and soybean agglutinin and decreased binding to Sepharose-conjugated wheat germ agglutinin. Binding of iodinated proteins to concanavalin A was unaffected by neuraminidase treatment of the cells. These studies demonstrate the utility of lectins for the multicomponent analysis of plasma membrane proteins.

Animals↗
PubMed1979

A statistical evaluation of the binding of ferritin-conjugated lectins to the surface of rat cells. Topographical variations as a function of lectin concentration and cell type.

Statistical procedures were utilized to evaluate the concentration dependence of labeling by ferritin-conjugated lectins on four different rat cells: hepatocytes, normal thymocytes, Friend virus-induced rat tumor cells and feline sarcoma virus-induced rat sarcoma cells. Labeling by ferritin conjugates of concanavalin A, wheat germ agglutinin and Ricinus communis agglutinins I and II was quantitated by counting the number of ferritin granules on 600 Angstrom membrane segments. Relationships between the arithmetic means and variances for sample populations from each cell and ferritin-lectin combination were used to define four types of topographical distributions: uniform/ordered, uniform/random, random and clustered. It was found that the distribution and/or density of surface-bound lectin was concentration-dependent for all four ferritin-lectins. The nature of this dependency was complex and varied with both lectin and cell type.

Animals↗