Accumulation of short DNA fragments in hydroxyurea treated mouse L-cells

Treatment of L-cells with hydroxyurea markedly inhibits the incorporation of [³H]thymidine into DNA. The ³H incorporation that persists during hydroxyurea inhibition is largely into 7S DNA chains. The labelled fragments can be chased into higher MW DNA, suggesting that they are intermediates in the replication process. This interpretation concurs with that of earlier reports which describe a similar effect of hydroxyurea on the replication of viral DNA.     

Murine glycosyltransferases responsible for the expression of globo-series glycolipids: cDNA structures, mRNA expression, and distribution of their products

Biological functions of globo-series glycosphingolipids are not well understood. In this study, murine cDNAs of two glycosyltransferases responsible for the synthesis of globo-series glycolipids and mRNA expression of those genes were analyzed. Distribution of their products was also analyzed. Murine cDNAs for Gb3/CD77 synthase and Gb4 synthase predicted that both of them are type II membrane proteins with 348 and 331 amino acids, respectively. In northern blotting, Gb3/CD77 synthase gene was mainly expressed in kidney and lung but also detected in many other tissues. Gb4 synthase was expressed in brain, heart, kidney, liver, skin, and testis. In the immunohistological analysis, Gb3/CD77 was mainly expressed in the proximal tubules as revealed with coincidental expression with angiotensin-converting enzyme (ACE). In spleen, it was detected in pre-B cells in the peripheral region of the white pulp, as suggested with coincidental expression with CD10. It was also expressed on the endothelia of the alveolar capillaries in lung and on the sebaceous ducts aside of the hair follicles. Gb4 was also detected mainly on the proximal tubules in kidney and on the endothelia of the alveolar capillaries in lung as Gb3/CD77. But it was also detected on the epithelium of the bronchus, seminiferous tubules and tails of spermatozoa in testis, blood vessels of choroids plexus and endothelial cells in brain, and central and hepatoportal veins in liver. The expression patterns of two genes and their products almost corresponded with some exception. The results would provide essential information for the functional studies of globo-series glycolipids.     

Binding of interleukin 2 to gangliosides

Exogenous gangliosides inhibit interleukin 2 (IL2)-dependent growth of a T cell line, AKIL -1.E8. IL2 activity is retained by columns of ganglioside covalently linked to poly(L-lysine)-agarose and is not eluted with ethylene glycol but is completely recovered by elution with 1% SDS. The ability of gangliosides to inhibit IL2 activity is directly related to the complexity of their carbohydrate portion, and related ceramide derivatives at similar concentrations do not inhibit IL2 activity. We conclude that IL2 bound to exogenous gangliosides is inactive and that the carbohydrate portion of the ganglioside is crucial to its interaction with IL2.     

Fucosyl-globoside and sialosyl-globoside are new glycolipids isolated from human teratocarcinoma cells

Several novel glycosphingolipids have been isolated from the human teratocarcinoma cell line HT-E (833K). These cells contain two neutral glycolipids which metabolically incorporate radio-labelled fucose. In addition, there are three new gangliosides present, which are all members of the globoside series of glycolipids. One of the fucose containing glycolipids forms globoside when treated with α-fucosidase, and one of the gangliosides forms globoside when treated with neuraminidase. On the basis of chromatographic behavior, exoglycosidase treatment and antibody reactivity, the tentative structures of these new glycolipids are:

$\text{Fuc}\text{(α1??)}\text{GalNAc}\text{(βl?3)}\text{Gal}\text{(α1?4)}\text{Gal}\text{(β1?4)}\text{Glc}\text{(β1-}\text{Cer}\text{)}$

$\text{and}$

$\text{NeuAc}\text{(α2?3)}\text{GalNAc}\text{(β1?3)}\text{Gal}\text{(α1?4)}\text{Gal}\text{(β7?4)}\text{Gle}\text{(β1?}\text{Cer}\text{)}$

     

Effect of puromycin and cycloheximide on glycosphingolipid biosynthesis by PHA stimulated human lymphocytes

The effect of puromycin and cycloheximide on the biosynthesis of neutral glycosphingolipids and gangliosides by PHA stimulated lymphocytes is studied. Under conditions of permanent inhibition of protein synthesis, and depending on the time of lymphocyte stimulation, inhibition of the biosynthesis of neutral glycosphingolipids was either restricted only to certain species or was very low for all glycosphingolipid species. The degree of inhibition of the various ganglioside species was affected by the time of incubation. After transient inhibition of protein synthesis and at times when protein biosynthesis had recovered, neutral glycosphingolipid and ganglioside biosynthesis inhibition was very prominent and did not recover. The possibility is discussed that glycosphingolipid biosynthesis does not depend directly on concurrent nascent peptide formation and it is proposed that inhibition of glycosphingolipid biosynthesis is related primarily to impairment of the endoplasmic reticulum and to inhibition of galactose transferases, secondary to the binding of the inhibitors.     

Incorporation of exogenous glycosphingolipids in plasma membranes of cultured hamster cells and concurrent change of growth behavior

Globoside added to culture medium was taken up by NIL cells and accumulated as a component of plasma membrane. This was evidenced by the recovery of ³H-labelled globoside from plasma membrane fractions and by the higher chemical quantity of globoside found in NIL cells cultured in medium containing globoside. Concomitantly the following changes in growth behavior were manifested: a reduction in growth rate due to an extended prereplicative phase and a reduced saturation density which may result from changed adhesive properties of cells.