Glycoprotein synthesis: activity of collagen-galactosyl and collagen-glucosyl transferases in synchronized nouse leukemic cells L5178Y

Perturbing cell surface beta-(1,4)-galactosyltransferase on F9 embryonal carcinoma cells arrests cell growth and induces laminin synthesis

Cell growth and differentiation are influenced by intercellular contact, suggesting that cell adhesion molecules may be instrumental in triggering these events. F9 embryonal carcinoma cells are an ideal system in which to examine the function of cell adhesion molecules in growth and differentiation, since the relevant cell adhesion molecules and differentiation markers are well defined. Intercellular adhesion in F9 cells is mediated by uvomorulin, or E-cadherin, and cell surface beta-(1,4)-galactosyltransferase. Since previous studies suggested that neither F9 cell growth nor differentiation is directly dependent on uvomorulin function, in this study we examined whether cell surface galactosyltransferase plays any role in F9 cell growth or differentiation. A variety of galactosyltransferase perturbants, including anti-galactosyltransferase antibodies, UDPgalactose, and the substrate modifier protein alpha-lactalbumin, inhibited the growth of F9 cells, whereas control reagents did not. To examine this in more detail, we analyzed the effects of perturbing surface galactosyltransferase on progression through the F9 cell cycle. Anti-galactosyltransferase IgG treatment inhibited ornithine decarboxylase activity and lengthened the F9 cell cycle during G1 and G2, the latter mimicking the effects of retinoic acid, a reagent known to prolong the F9 cell cycle and induce differentiation. In contrast, anti-uvomorulin antibodies had no effect on F9 cell growth, ornithine decarboxylase activity, or progression through the cell cycle. Furthermore, perturbation of surface galactosyltransferase adhesions in F9 cell aggregates induced precocious F9 cell differentiation, as assayed by increased laminin synthesis, whereas control reagents had no effect. Thus, perturbing surface galactosyltransferase adhesions in F9 cells both decreases growth and stimulates synthesis of laminin. These results imply that interactions between surface galactosyltransferase and its oligosaccharide ligand during cell adhesion may affect the normal growth-regulatory and differentiation-inducing signals, as is seen, in part, during treatment with retinoic acid.

Uroporphyrin I stimulation of collagen biosynthesis in human skin fibroblasts. A unique dark effect of porphyrin

Porphyria cutanea tarda and erythropoietic porphyria are disorders of heme synthesis that originate in the liver and bone marrow, respectively. Each is characterized by increased accumulation of uroporphyrin, I, by cutaneous photosensitivity, and in some patients by indurated plaques and scarring that resemble scleroderma. These scleroderma-like lesions occur in light-exposed and light-protected body areas. In these studies we evaluated the role of uroporphyrin I and of light in evoking the scleroderma-like cutaneous changes. Normal human skin fibroblasts were exposed to uroporphyrin I and to 400 nm radiation and the effect of these agents on collagen accumulation by the cells was determined. Radioactive tracer studies showed that uroporphyrin I caused a specific increase in the accumulation of newly synthesized collagen by fibroblast monolayer cultures, as verified by [(3)H]hydroxyproline and collagenase digestion assays. Collagen accumulation was stimulated 1.5- to 2.7-fold by uroporphyrin I, whereas noncollagenous protein accumulation was unchanged. The increased collagen accumulation was time and uroporphyrin I-concentration-dependent, and occurred both in the presence or absence of ultraviolet light exposure. Further studies demonstrated that the increased accumulation was not the result of decreased rates of collagen degradation nor was it due to changes in cell population growth parameters (generation times and saturation densities). No changes in morphology of the treated cells occurred. These studies indicate that porphyrins possess previously undemonstrated biological effects that are independent of their photosensitizing properties. This novel dark effect of uroporphyrin I may account for the sclerodermatous lesions seen in the skin of patients with porphyria cutanea tarda and erythropoietic porphyria.

The use of zonal centrifugation to study membrane formation during the life cycle of mammalian cells. Synthesis of 'marker' enzymes and other components of cellular organelles

1. The activity of enzymes characteristic of microsomes (NADPH-cytochrome c reductase and uridine diphosphatase) and of inner mitochondrial membranes (cytochrome c oxidase and succinate-cytochrome c reductase) increases during the cell cycle of P815Y neoplastic mast cells in concert with total protein. The activity of glutamate dehydrogenase, an enzyme of the mitochondrial matrix, increases in a somewhat different manner. 2. The specific activity of mitochondrial structures involved in energy-coupling measured with a fluorescent probe remains constant during the cell cycle. 3. Mitochondrial and microsomal protein increases during the cycle at the same time as total protein; nuclear protein increases rather more sharply. 4. The rate of incorporation of labelled choline or inositol into nuclear, mitochondrial or microsomal phospholipid during the cell cycle follows the rate of incorporation into total phospholipid. 5. It is concluded that the major components of cellular membranes are synthesized, like total protein or phospholipid, throughout most of the intermitotic period.