Role of concanavalin A as an endocytic modulator in Chinese hamster ovary cells

The effect of the lectin, concanavalin A (Con A), on pinocytic uptake and pinosome-lysosome fusion in Chinese hamster ovary (CHO) cells, a fibroblast line, was investigated. The glycosylated protein, horseradish peroxidase (HRPase), and the non-glycosylated protein, 125I-labelled bovine serum albumin ([125I]BSA), was used as endocytic tracers. Con A at high concentrations (greater than or equal to 50 micrograms/ml) promoted the uptake of HRPase and inhibited the degradation of ingested HRPase. Con A inhibited the degradation of HRPase whether the two were added simultaneously or at different times to the cultures. Fusion of HRPase-positive pinosomes with secondary lysosomes was observed by electron microscopy in Con A-treated CHO cells. Con A at 200 micrograms/ml had no effect on either the uptake or degradation of [125I]BSA. Together these observations strongly suggest that the effects of high Con A concentrations on the uptake and degradation of HRPase are a consequence of direct complex formation between lectin and glycoprotein. Con A does not appear to have a general modulating effect on the dynamics of endocytic membrane in CHO cells.