We have tried to identify carbohydrate structures involved in recognition and/or lysis of K562 target cells by human natural killer (NK) cells. Inhibition studies were performed with mono-, di- and trisaccharides, and with glycopeptides and glycoproteins of known carbohydrate composition. When tested with various monosaccharides, lysis of K562 cells was inhibited only by N-acetylneuraminic acid (NeuAc). Di- and trisaccharides and glycopeptides containing NeuAc or N-glycolylneuraminic acid (NeuGc) all inhibited NK cell-mediated lysis. Among the non-sialylated carbohydrates tested, only Gal beta(1----3)GalNAcol was effective. The inhibitory capacity of sialylated compounds appeared to be dependent on the linkage type of the sialic acid residue; carbohydrates containing alpha(2----6)-linked sialic acids were more potent inhibitors than their alpha(2----3) isomers. Also the sugar to which the sialic acid residue was attached was of importance, NeuAc alpha(2----6)GalNAcol being more effective than NeuAc alpha(2----6)Gal beta 1----R (where R = glucose or oligosaccharide-peptide). Sialylated compounds and free sialic acid had minor or no effects on cell-mediated cytotoxicity by allo-sensitized cytotoxic T lymphocytes. The conjugation of target cells and NK effector cells was not inhibited by carbohydrates that effectively blocked the cytolytic response. These results may indicate that cell-surface carbohydrates containing alpha(2----6)-linked sialic acid are crucial structures in a post-binding event in NK-cell-mediated lysis.

Invasion of malignant MO4 cells into embryonic chick heart fragments in an organ culture assay was arrested for at least 7 days when the temperature was lowered to 28 degrees C. Prolonged culturing of MO4 cells at 28 degrees C on tissue culture substrates showed no recuperation of fucose incorporation into cell surface glycopeptides. However, invasion was restored after 10 days of organ culture in confrontation with chick heart tissue at 28 degrees C. A histoautoradiographic study showed that the regained capability to invade was accompanied by an increase in fucose labeling of the MO4 cells in the invading areas. At 28 degrees C the incorporation of [3H]fucose into total cell protein was drastically reduced, whereas [3H]leucine incorporation as a measure for protein synthesis was less affected. Cell surface glycopeptides, metabolically labeled with either fucose or glucosamine at 28 degrees C, showed a time-dependent decrease in the incorporation of fucose but not of glucosamine and no changes in overall size distribution. Low temperature did not reduce fucosyltransferase activity but the relative accumulation of fucose-1-P suggested inhibited conversion towards GDP-fucose. Moreover, mouse L cells which were incapable of invading chick heart tissue appeared also deficient in fucose incorporation, owing to low levels of fucosyltransferase activity. According to the results, fucosylation of surface carbohydrates may be required for invasive capacity and restored in MO4 cells invading at 28 degrees C by metabolic cooperation with the host tissue.

The effect of time-controlled exposures to cholera toxin (CT) on intracellular levels of cyclic AMP (cAMP) and on the proliferative response of serum-stimulated 3T3 cells was investigated. Continuous exposure to CT caused up to 8-fold raises in cAMP content and inhibited DNA replication by delaying G1-S transition and by reducing the fraction of cells committed to DNA replication. In contrast, short exposures to CT during G0-G1 transition increased the fraction of cells responding to serum stimulation and potentiated the serum-induced morphological changes in the cell monolayer. A short exposure during late G1 phase, however, inhibited the onset of DNA synthesis but had little effect on ongoing DNA replication. The results indicate that cAMP has diverse and opposite effects on two defined restriction points in cell cycle control. Cyclic AMP was positively involved in the acquisition of the state of competence by quiescent cells (G0-G1 transition) but antagonistic on the onset of DNA replication (G1-S transition) in committed cells. The observations reconcile a number of controversial conclusions regarding the role of cAMP in cell cycle control.

Long-term mouse urothelial cell cultures were routinely established from explants of neonatal mouse bladders. Foci of proliferating cells could be observed one week after the initiation of the explant cultures. These persisted throughout the culture period and up to one year. Expression of keratin proteins confirmed the epithelial nature of the cultured cells. Morphologic analysis of nuclei sorted after DNA flow cytometry revealed a population of DNA-tetraploid and octoploid cells with large nuclei and prominent nucleoli in addition to a DNA-diploid cell population. Both cell populations showed DNA replicative activity as reflected by bromodeoxyuridine incorporation studies and mitotic activity. These long-term primary mouse urothelial cell cultures may prove useful for studies on urothelial cell kinetics and bladder carcinogenesis.

Invasion by MO4 mouse fibrosarcoma cells into fragments of embryonic chick heart or lung in organ culture was studied histologically and ultrastructurally at various temperatures between 12 and 40 degrees C. Invasion was absent for at least 7 days at or below temperatures of 29 degrees C. Invasion was invariably observed at or above 30.5 degrees C. Differences in invasion between 29 and 30.5 degrees C could not be ascribed to differences in growth, migration, or microtubule assembly/disassembly of MO4 cells. Neither could they be explained through differences in the attachment of MO4 cells to the heart fragments. Possible explanations for the absence of invasion at lower temperature are: altered resistance of the extracellular matrix in heart or lung fragments, and deficient expression of fucosylated glycoproteins at the surface of MO4 cells. A population of MO4 cells plated from the parent line and adapted to grow at 28 degrees C (MO(4)28 cell line) did not differ in invasiveness from the parent MO4 cells. We conclude that the temperature dependence of invasion in organ culture might indicate as yet unexplored aspects of the mechanisms of tumour invasion.