Thyroid hormone receptors and stimulation of angiotensinogen production in HepG2 cells

Binding characteristics and effects of 3,5,-3'-triiodo-L-thyronine (T3) on angiotensinogen production in HepG2 were studied in serum-free medium. Binding was performed on intact cells and on partially purified isolated nuclei using [125I]T3. Scatchard plots revealed one class of high affinity binding sites with a Kd of approximately 80 pmol/liter. Calculation of maximum binding showed that HepG2 possess approximately 1000 binding sites per cell. Unlabeled T3 and T4 competed for binding sites on intact HepG2 with 50% inhibition of [125I] T3 binding at approximately 3.0 and 38.0 pmol/liter, respectively. The HepG2 showed a dose-dependent increase in angiotensinogen production in serum-free medium which was maximal at 10(-5) mol/liter (two-fold increase/10(6) cells/24 h) and had an EC50 of approximately 5.0 x 10(-8) mol/liter. T3 also produced after 24 h a dose-dependent increase in DNA highly correlated with T3 applied (r = 0.88, P less than 0.01). In conclusion, this study shows that HepG2 possess specific high affinity binding sites for T3 and that T3 stimulates angiotensinogen production and DNA synthesis in these cells.