Thioredoxin (TRX), a disulfide-reducing intracellular dithiol enzyme,
is synthesized by both normal liver cells and the hepatocarcinoma cell
Line HepG2. Only the former, however, secrete abundant TRX extracellu
larly. When cultured in mild reducing conditions, HepG2 cells but not
normal hepatocytes increase the rate of TRY secretion and undergo grow
th inhibition accompanied by morphological changes. Also, recombinant
TRX inhibits proliferation of HepG2 cells. In contrast, exogenous thio
ls and TRX stimulate proliferation of a B-cell lymphoma line, indicati
ng that different cell. types respond differently to variations in the
extracellular redox potential.