Evidence for pleiotropic changes in lines of Chinese hamster ovary cells resistant to concanavalin A and phytohemagglutinin-P

Antagonism by dibutyryl adenosine cyclic 3',5'-monophosphate and testololactone of concanavalin A capping

Exposure of CHO-K1 cells in vitro to dibutyryl adenosine cyclic 3',5'-monophosphate (DBcAMP) plus testololactone produces a rapid, reversible antagonism of ligand-induced collection of initially dispersed concanavalin A (Con A) binding sites into a caplike mass. Morphologically, as Con A capping occurs, the cells become less spread and then round completely. With prolonged Con A exposure, cells cultured in either the absence or the presence of DBcAMP plus testololactone cap and round. Capping is blocked by cold treatment and respiratory inhibitors. Colcemid at concentrations greater than 1 muM promotes both Con A capping and cell rounding. Cytochalasin B at similar concentrations inhibits both capping and cell rounding. Treatment of cells with Con A has little effect on intracellular cAMP concentration. Possible mechanisms by which cAMP may modulate the movement of Con A binding sites are discussed.

Stable alterations at the cell membrane of Chinese hamster ovary cells resistant to the cytotoxicity of phytohemagglutinin

Chinese hamster ovary (CHO) cells selected for resistance to the cytotoxicity of phytohemagglutin (PHA) have been found to exhibit stable alterations at their plasma membranes. The PHA-resistant (PhaR) cells bind markedly less 125I-PHA than do sensitive CHO cells and also exhibit an increased sensitivity to the cytotoxicity of concanavalin A, a lectin of different receptor specificity. Mutagenesis with ethylmethanesulfonate increases the proportion of PhaR cells 20- to 100-fold. PHA-resistant cells maintained for up to 8 months in continuous culture in the absence of the selective agent have retained the PhaR phenotype. These and other characteristics of the experimental system suggest that CHO cells selected for PHA resistance are authentic somatic cell mutants. The Pha marker appears to behave recessively in hybrids formed between PhaR and PhaS cells.

Isolation of a clone of Chinese hamster ovary cells deficient in plant lectin-binding sites

Ricin, a galactose-binding lectin with potent cytotoxic activity, was used to select a clone of Chinese hamster ovary cells with altered plant lectin-binding properties. The clone (15B) is 80-fold less sensitive to the toxic action of ricin than the parent line. In the absence of ricin, it grows both in monolayer and suspension culture with a normal generation time. Plating efficiency, however, is significantly reduced. Relative to the parent cells, its binding of the Ricinus communis lectins, Phaseolus vulgaris erythroagglutinating phytohemagglutinin, Abrus precatorius phytohemagglutinin, and soybean phytohemagglutinin is less than 7%, while binding of lentil phytohemagglutinin, wheat-germ agglutinin, and mushroom phytohemagglutinin is 17%, 40%, and 109%, respectively. In contrast, its concanavalin A binding is increased by 70%. Consistent with these alterations, crude membrane preparations of the 15B cells were found to contain the same sugars as the parent-cell membranes but in different proportions. The 15B membranes have 28% less sialic acid, 38% less N-acetylglucosamine, 49% less galactose, the same amount of N-acetylgalactosamine, and 53% more mannose than the membranes of the parent cells.

Antagonism by dibutyryl adenosine cyclic 3',5'-monophosphate and testosterone of cell rounding reactions

In an attempt to understand further the mechanism of the morphological and functional "reverse transformation" of CHO-K1 cells induced by dibutyryl adenosine cyclic 3',5'-monophosphate (cAMP) and testosterone, the kinetics of variation in the susceptibility of cells to rounding after the addition or deletion of dibutyryl cAMP and testosterone have been investigated. Changes in susceptibility to cell rounding upon removal of divalent cations or pulse exposure to concanavalin A were complete within 0.5-1 h after addition or deletion of drug. In comparison, the gross conversion of CHO-K1 cells from epithelial- to fibroblast-like morphology after drug treatment or the converse change after drug removal required 8 or 4 h, respectively. The effects on cell rounding are not caused by an effect of dibutyryl cAMP upon cell growth rate. Inhibitor experiments indicate that the changes investigated do not require continued RNA or protein synthesis and are not prevented by agents which depolymerize microtubules.