Gangliosides of plasma membranes from normal rat liver and Morris hepatoma.

Plasma membranes were isolated from normal rat liver and Morris hepatoma 5123tc by discontinuous sucrose gradient centrifugation. There was an average two and one-halffold enrichment of gangliosides in plasma membranes from normal liver and hepatoma as compared with their respective whole cells. The amount of total gangliosides in plasma membranes from hepatoma was eight times greater than that found in normal liver. This increase resulted from a fivefold increase in hematosides, an eightfold increase in monosialogangliosides and a twenty-twofold increase in disialogangliosides. Trisialogangliosides were present in normal liver but not in hepatoma.     

Comparative proteomics of rat liver and Morris hepatoma 7777 plasma membranes

Plasma membranes from normal rat liver and hepatocellular carcinoma Morris hepatoma 7777 were selectively solubilized by use of different reagents. After selective solubilization, proteins were identified by nano-HPLC-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS). Using simple software, the patterns of proteins identified in membrane solubilizates from liver and hepatoma were compared. Proteins identified in Morris hepatoma 7777 and not in the corresponding membrane solubilizate from liver, mostly members of the annexin and heat shock protein families, are discussed as potential candidate markers for hepatocellular carcinomas.     

Phospholipid composition of nuclear membranes and cell nuclei of rat liver and hepatoma 27]

Phospholipid composition of nuclei and nuclear membranes from rat liver and hepatoma-27 were investigated. Hepatoma nuclei and nuclear membranes were found to contain cardiolipin which was absent in the same fractions of rat liver. In the nuclei and nuclear membranes of hepatoma the content of sphingomyelin was higher and that of lecithin is lower than in the corresponding subcellular fractions of rat liver. The content of acid phospholipids was much higher in hepatoma nuclear membranes than those of the normal liver. The data obtained show that the general trend of lipid dedifferentiation which earlier was demonstrated for various membranes of different tumor cells is observed also in the case of nuclear membranes.     

Studies on histones and nuclear phosphoproteins of rat liver and Morris hepatoma.

1. The chemical composition of chromatins obtained from Buffalo rat liver and Morris hepatoma strain 5123 was investigated. 2. The presence of an additional subfraction within the very lysine-rich histone (fl) was states in both kinds of tissues. It amounted to about 8% and 5% of fl in rat liver and Morris hepatoma, respectively. 3. Nuclear phosphoproteins (phenol-soluble) from normal and tumour tissues in polyacrylamide gel in SDS showed some qualitative differences in the range of molecular weights of about 40 000 - 70 000 and over 100 000 daltons.     

Lipid peroxidation and fluidity of plasma membranes from rat liver and Morris hepatoma 3924A

Plasma membranes isolated from the fast-growing, maximal-deviation, Morris hepatoma 3924A exhibit remarkable changes in lipid composition, lipid peroxidation and to some extent in the physical state with respect to rat liver plasmalemmas. A correlation appears to exit between the lower phospholipid: protein ratio, higher cholesterol: phospholipid ratio, lower rate of lipid peroxidation and decrease in fluidity in tumor plasma membranes.     

Different turnover of fucose residues in plasma membranes of rat liver and Morris hepatoma 7777.

Half-lives and rate constants of degradation of protein-bound fucose have been determined in plasma membranes and total cell homogenates of rat liver and Morris hepatoma 7777. The existence of at least two dynamically different classes of fucose-containing glycoproteins could be demonstrated in both liver and hepatoma plasma membranes. The apparent half-lives were 8.4 and 24.5 h (host liver) and 11.5 and 33.9 h (Morris hepatoma). Since this biphasic loss of fucose residues was not observed for sialic acid [Harms & Reutter (1974) Cancer Res. 34, 3165--3172], the differences are possibly related to specific functions of fucosylated glycoproteins of the plasma membrane.     

Lipid composition and turnover of rough and smooth microsomal membranes in rat liver

Subfractions of rat liver microsomes (rough, smooth I, and smooth II), isolated in a cation-containing sucrose gradient system, were analyzed. After removal of adsorbed and luminal protein, these subfractions had the same phospholipid/protein ratio, about 0.40. Both the classes and the relative amounts of phospholipids were similar in the three subfractions, but the relative amounts of neutral lipids (predominantly free cholesterol and triglycerides) were higher in smooth I and especially in smooth II than in rough microsomes. Various pieces of evidence indicate that the neutral lipids are tightly bound to the membranes. Glycerol-(3)H was incorporated into the phospholipids of the rough and smooth I microsomes significantly faster than into those of the smooth II membranes; (32)P incorporation followed a similar but less pronounced pattern. Acetate-(3)H was incorporated into the free cholesterol of smooth I microsomes only half as fast as into the other two subfractions. Injection of phenobarbital increased the cellular phospholipid and neutral lipid content in the rough and smooth I, but not in the smooth II microsomes. Consequently, the neutral lipid/phospholipid ratio of all three subfractions remained unchanged after phenobarbital treatment. It is concluded that the membranes of the rough and the two smooth microsomal subfractions from rat liver have a similar phospholipid composition, but are dissimilar in their neutral lipid content and in the incorporation rate of precursors into membrane lipids.     

Pyruvate kinase isoenzymes in chromatin extracts of Ehrlich ascites tumour, Morris hepatoma 7777 and normal mouse and rat livers

A pyruvate kinase (EC 2.7.1.40) variant inhibited by L-cysteine has been found in Ehrlich ascites tumour and Morris hepatoma 7777, but not in normal mouse and rat livers used for comparison. Chromatin extracts of all materials studied contained three pyruvate kinase isoenzymes (alpha, beta, gamma) which showed the greatest electrophoretic mobility in normal mouse and rat livers. The isoenzyme mobility diminished in both tumour chromatin extracts, and the slow migrating gamma isoenzyme exhibited sensitivity to L-cysteine inhibition. This gamma isoenzyme sensitive to L-cysteine might be considered as a tumour marker. All tumour pyruvate kinase isoenzymes were insensitive to normal signal molecules, i.e., to ATP and fructose 1,6-diphosphate, which regulate liver pyruvate kinase activity. It was, however, noted that the binding of pyruvate kinase isoenzymes to DNA is connected with a diminution in their catalytic activity.     

Induction of peroxisomal beta-oxidation in 7800 C1 Morris hepatoma cells in steady state by fatty acids and fatty acid analogues

(1) The activities of peroxisomal beta-oxidation and palmitoyl-CoA hydrolase in Morris hepatoma 7800 C1 cells were studied. The cells were grown until they reached steady state (constant DNA content per dish) and then were cultured in the presence of fatty acids or alkylthioacetic acids, i.e., S-substituted fatty acid analogues. (2) The fatty acid analogues increased the activity of the cyanide-insensitive palmitoyl-CoA oxidase several-fold. The effect was dose-dependent; 5 microM tetradecylthioacetic acid (TTA) was sufficient to give a significant induction. With 20 microM TTA, the increase in enzyme activity was discernable after 3 h and reached a maximum after 3 days. The inducing effect of the alkylthioacetic acids increased with the length of the hydrophobic alkyl end of the analogue. The inducing ability disappeared when the fatty acid analogue was omega-oxidized to the corresponding dicarboxylic acid. Oxidation of the sulfur atom resulted in inhibited cellular uptake and abolished enzyme induction. (3) At higher concentrations (0.5-1 mM), normal fatty acids also induced cyanide-insensitive palmitoyl-CoA oxidation. Myristic acid was the most potent inducer, whereas fatty acids with shorter as well as longer carbon chains were less efficient. The inducing effect increased with the number of double bounds in the fatty acid. (4) The normal fatty acids as well as the fatty acid analogues also induced palmitoyl-CoA hydrolase, but the relative changes were much less pronounced than with the palmitoyl-CoA oxidase.