Deinduction of transcription of Xenopus 74-kDa albumin genes and destabilization of mRNA by estrogen in vivo and in hepatocyte cultures

Abstract

The goal of this study is to explain the molecular basis of the marked deinduction of Xenopus albumin synthesis and secretion accompanying the activation of vitellogenin genes by estrogen. We have characterized by restriction analysis, DNA sequencing and hybrid-selected translation of mRNA, a cloned cDNA specifying the two 74-kDa albumins which constitute the predominant circulating form of albumin in Xenopus luevis. Using this recombinant DNA plasmid as a hybridization probe, we have determined the steady-state levels of albumin mRNA, the rate of transcription of the two 74-kDa albumin genes and the stability of the mRNA in male and female Xenopus hepatocytes in vivo and in primary cell cultures following estrogen treatment.In both whole liver and cultured hepatocytes estradiol caused a rapid drop in the steady-state levels of 74-kDa albumin mRNAs, which was reversed spontaneously in the continued presence of the hormone. The concentration of albumin mRNA was substantially higher in male than in female hepatocytes, the hormonal effect being more marked in male than in female hepatocytes.The decrease in steady-state levels of mRNA was anticipated in male hepatocytes by a 70% inhibition of rate of transcription of albumin genes within 2 h of exposure to estradiol, as measured by run-off transcription in liver nuclei isolated from animals treated in vivo or by determining the absolute transcription rate in cell cultures. In the latter the diminished transcription rate returned to normal within 12 h in the continued presence of the hormone.Estradiol caused a threefold destabilization of albumin mRNA in both male and female hepatocyte cultures to tliz = 3 h and 2 h respectively. The combined effects on rate of transcription and mRNA stability largely explain the changes in the steady-state levels of mRNA caused by hormone administration.Comparison of the kinetics of transcription rates of vitellogenin and albumin genes in vivo and in vitro reveals a striking reciprocity in the selective activation of the inducible genes and deinduction of the constitutively expressed genes at the early stages of response of Xenopus hepatocytes to estrogen.

Transcriptional regulation of expression of the rainbow trout albumin gene by estrogen

“…Only E2 was able to modify Alb gene expression in trout, a large decrease in Alb mRNA level being observed after 5 days of treatment. Several studies performed in Xenopus (Wolffe et al 1985, Riegel et al 1986) and more recently in turtle (Selcer & Palmer 1995) showed a similar inhibition by E2 of Alb gene expression in oviparous liver. However, our results differ from those obtained in Xenopus with regard to the mechanisms involved in this inhibition.…”

“…Hybridization of the same RNA samples with a specific ER probe shows that regulation of ER gene expression by E2 occurs at both the transcriptional and post-transcriptional level, as previously demonstrated . Reduction of transcription of the Xenopus Alb gene has also been reported, but in this species the main mechanism involved in the downregulation of Alb gene expression is mRNA destabilization (Kazmaier et al 1985, Wolffe et al 1985, Riegel et al 1986, 1987. This Alb mRNA destabilization is mediated by a polysomal endoribonuclease which is under estrogenic control (Pastori et al 1991, Dompenciel et al 1995.…”

“…Although most examples concern E2 up-regulation, it is interesting to note that, in parallel, E2 downregulation occurs in the same organ. In Xenopus, several studies show that E2 is able to down-regulate the production of albumin (Alb), a serum protein synthesized in the liver (Wolffe et al 1985, Riegel et al 1986, Selcer & Palmer 1995. This downregulation in Xenopus is mediated by a decrease in gene transcriptional activity and destabilization of its mRNA.…”

Expression of the Estrogen and Progesterone Receptors and Insulin-like Growth Factor-I Genes in the Porcine Myometrium during Early Pregnancy.

“…Ligand-activated steroid hormone receptors may affect the steady state of mRNA levels by other mechanisms than alterations in transcriptional activity, for example stabilization and degradation of mRNA [33][34][35][36][37]. Steroid receptors may also be activated by ligand-independent phosphorylation [30,[38][39][40][41][42].…”

Estradiol and estrogen receptor-dependent stabilization of a minivitellogenin mRNA lacking 5,100 nucleotides of coding sequence.

“…The broad spectrum of estrogen effects on mRNA stability in Xenopus liver provides a striking example of the specificity and flexibility of this type of control. In hepatocytes, estrogen elicits a 30-fold increase in the stability of vitellogenin mRNA (6) and decreases the stability of albumin mRNA by 3-fold (30,41) without affecting the 16-h half-life (at 25°C) of total poly(A) mRNA (6).…”