Multiple Hormones Regulate Angiotensinogen Messenger Ribonucleic Acid Levels in a Rat Hepatoma Cell Line

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Abstract
Angiotensinogen is regulated by both hormones and changes in cardiovascular and electrolyte status. We have used the Reuber (H4IIE) rat hepatoma cell line to study the regulation of angiotensinogen mRNA levels by dexamethasone, aldosterone, L-T3, and 17 .beta.-estradiol. Using the AccI (1097 basepairs) fragment of our angiotensinogen cDNA clone, we have studied, by Northern and slot blot analysis, the accumulation of angiotensinogen mRNA in this cell culture system. Angiotensinogen mRNA of approximately 1800 bases was identified in these cells. It was identical in size to angiotensinogen mRNA from rat liver. Cells grown in medium containing serum depleted of thyroid and steroid hormones for up to 72 h showed a progressive decrease in angiotensinogen mRNA. Dexamethasone treatment resulted in a time- and dose-dependent increase in angiotensinogen mRNA. The half-maximal response occurred at 10-9 M dexamethasone, with a maximal response of approximately 4-fold (serum-free conditions). Aldosterone induced a dose-dependent increase in mRNA. Half-maximal levels were obtained at 5 .times. 10-8 M. Competition studies using the glucocorticoid antagonist RU38486 (Roussel-UCLAF) confirmed that dexamethasone was acting through the glucocorticoid receptor and suggested that aldosterone was acting through the same receptor. L-T3 treatment caused a dose and time-dependent increase in angiotensinogen mRNA levels. The half-maximal response occurred at 5 .times. 10-8 M, and the maximal response was a 2-fold increase. Combined treatment with dexamethasone and L-T3 triiodothyronine resulted in a synergistic increase in angiotensinogen mRNA levels. 17.beta.-Estradiol failed to elicit a change in angiotensinogen mRNA levels consistent with the observation that these cells lack estrogen receptors. Our results indicate that hepatic angiotensinogen mRNA levels are regulated in a complex fashion by several hormones. These cells provide a useful system for studying the hormonal regulation of the angiotensinogen gene.