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.
D000818:Animals; D002478:Cells, Cultured; D003208:Concanavalin A / Q000494:pharmacology*; D003907:Dexamethasone / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D008766:Methylmannosides / Q000494:pharmacology; D051381:Rats; D014444:Tyrosine Transaminase / Q000096:biosynthesis*
D007328:Insulin; D008766:Methylmannosides; D003208:Concanavalin A; C008466:methylmannoside; D003907:Dexamethasone; D014444:Tyrosine Transaminase