Qualitative and quantitative interactions of lectins with untreated and neuraminidase-treated normal, wild-type, and...

The lectin receptors of confluently grown hamster BHK, wild type polyoma virus transformed PyBHK, and temperature-sensitive polyoma transformed ts3-PyBHK fibroblasts were investigated using cell agglutination, quantitative (125I)lectin binding, and ferritin-lectin labeling. PyBHK and permissively grown ts3-PyBHK cells agglutinated more strongly with Ricinus communis I agglutinin (RCA-I)compared to BHK and nonpermissively grown ts3-PyBHK, although saturation binding of (125I)RCA-I to these cells at 4 degrees resulted in a twofold difference in lectin-binding sites on BHK and nonpermissively grown ts3-PyBHK cells (1.0-1.3 x 10 7 sites/cell) compared to PyBHK and permissively grown ts3-PyBHK (0.4-0.6 x 10 7 sites/cell). These cells bound equivalent amounts of (125I)concanavalin A (0.8-1 x 10 7 sites/cell) and (125I)wheat germ agglutinin (1-2.2 x 10 7 sites/cell). Under these binding conditions little endocytosis occurred, as judged by the subsequent release of greater than 90% cell-bound (125I)RCA-I by the RCA-I inhibitor lactose and localization of ferritin-RCA-I exclusively to the extracellular plasma membrane surface. However, if the binding is performed at 22 degrees, only 50% of the bound lectin can be removed by lactose, and ferritin-RCA-I is localized inside the cell within endocytotic vesicles. The relative mobility of RCA-I receptors was examined on ts3-PyBHK cells by the ability of ferritin-RCA-I to induce clustering of its receptors at 22 degrees. RCA-I receptors on permissively grown ts3-PyBHK cells appeared to be more mobile than on nonpermissively grown cells. BHK and PyBHK cells were treated with neuraminidase, and the resulting enzyme-treated cells were assayed for lectin agglutinability and quantitative binding of RCA-I, concanavalin A, and wheat germ agglutinin. Neuraminidase treatment resulted in decreased concanavalin A and wheat germ agglutinability and a slight increase in RCA-I agglutinability. The enzyme-treated BHK and PyBHK cells bound less (125I)wheat germ agglutinin (2.8 x 10 6 and 2.2 x 10 6 sites/cell, respectively) and 2.5 and 6.2 times more (125I)RCA-I (2.5-3 x 10 7) and 3.5-4 x 10 7 sites/per cell, respectively). There was no change in the number of concanavalin A binding sites after neuraminidase treatment. The increase in RCA-I binding sites approximated the decrease in wheat germ agglutinin binding sites indicating that the predominant penultimate oligosaccharide residue to sialic acid on these cells is D-Gal.