Persistent estrogen induction of hepatic Xenopus laevis serum retinol binding protein mRNA

Administration of estradiol-17β to male Xenopus laevis induces the hepatic mRNA coding for the serum retinol binding protein (RBP) approximately 10-fold, both in vivo and in primary liver cultures. Estrogen induction of RBP mRNA is completely blocked by the anti-estrogen, hydroxytamoxifen. Testosterone administration reduces the elevated level of RBP mRNA observed in livers of female X. laevis to the constitutive level seen in livers of control male animals, and partially blocks the estrogen induction of RBP mRNA. Intracellular RBP mRNA levels therefore represent a balance between the opposing effects of estradiol-17β and testosterone. In marked contrast to the estrogen induction of vitellogenin mRNA, which requires the continuous presence of exogenous estrogen, induction of RBP mRNA persists for at least 4 months after a single injection of estrogen. Runoff transcription measurements demonstrate that persistent induction of RBP mRNA is due to an increased rate of RBP gene transcription. Administration of hydroxytamoxifen abolishes persistent induction of RBP mRNA, suggesting that residual hormone receptor complex plays a role in the persistent induction of RBP gene transcription. The persistent estrogen induction of RBP mRNA provides the first demonstration of long-term activation of the transcription of a hormone-responsive gene in response to a transient dose of a steroid hormone.