Induction of tyrosine aminotransferase activity by concanavalin A in cultured rat hepatoma cells.

Concanavalin (Con A) induced tyrosine aminotransferase activity in cultured rat hepatoma cells (R117-21B). The highest level of the induced enzyme activity was observed at 6 to 8 hr of incubation with Con A, and the activity returned to the control level after 24 hr. This enzyme induction was dose-dependent in the range of 0.5 to 5 micrograms Con A per ml, while at higher concentrations (more than 50 micrograms/ml) the induction was very small or absent. The addition of alpha-methyl-D-mannoside abolished the effect of Con A. A 4 hr incubation of the cells with Con A and a subsequent 2 hr incubation was necessary to yield the maximal induction of tyrosine aminotransferase activity. Simultaneous incubation of the cells with Con A (5 micrograms/ml) and insulin or dexamethasone, induced tyrosine aminotransferase activity to levels higher than each activator alone, and the effect of Con A on the induction of tyrosine aminotransferase activity by dexamethasone was almost an additive. It was concluded that Con A at low concentrations mimics insulin in the induction of tyrosine aminotransferase activity in R117-21B cells, and that the effect of Con A and insulin on the induction of the enzyme is different from the effect of dexamethasone on this process.