Effect of thyroid hormones on the level of the hepatic mRNA for α 2u globulin

329

Thyroid and glucocorticoid hormones stimulate growth hormone synthesis in cultured rat pituitary cells (GC). We have compared changes in growth hormone production and mRNA in these cells. Triiodothyronine (10 nM) and dexamethasone (1 MtM) stimulated increases in growth hormone production by 2.5-and 3.8-fold, respectively. There were corresponding increases in the capacity of RNA from hormone-treated cells to direct synthesis of pregrowth hormone in a wheat germ cell-free translation system, suggesting hormone-regulated increases in growth hormone mRNA. Hormone-induced changes in mRNA were also demonstrated by determining the kinetics of hybridization of a cDNA probe prepared from RNA enriched (about 70%) for growth hormone translational activity with RNA from control and hormone-treated cells. These results suggest that thyroid and glucocorticoid hormones can regulate growth hormone production by influencing the levels of its mRNA. Thyroid and glucocorticoid hormones profoundly influence development, differentiation, and metabolism (1-3). Although little is known about the mechanism of thyroid hormone action, the discovery of nuclear receptors (4, 5) that are DNA-binding proteins (6) and Tata's report (7) of changes in total RNA synthesis in response to thyroid hormone have directed attention to chromatin as one possible site of hormonal control. Further, recent cell-free translational data have shown that hepatic a2u globulin mRNA is increased in thyroid hormone-treated animals (8,9). This system is somewhat complicated because at least four hormones are required, the kinetics are slow, and the stimulations have been performed in animals in which primary hormone influences have not been differentiated from secondary influences. Nevertheless, these data may indicate that thyroid hormones regulate specific mRNAs. In a few cases, the idea that glucocorticoids influence specific mRNAs has been supported directly by experiments in which cell-free translation assays of mRNA, such as that for tryptophan oxygenase (10), were used, but cDNA-RNA hybridization assays have not yet been performed except in the case of viral RNA production (11,12).Thyroid and glucocorticoid hormones stimulate growth hormone production in cultured rat pituitary cells (refs. 13-16;

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

See 1 more Smart Citation

Regulation of growth hormone messenger RNA by thyroid and glucocorticoid hormones.

Martial¹,

Baxter²,

Goodman³

et al. 1977

329

“…Thyroid hormone and androgenic steroids appear to act in a concerted fashion to influence the in vivo synthesis of rat liver a2u-globulin. The induction of a2u-globulin by thyroid hormone and androgenic steroids parallels the change in the hepatic levels of a2u globulin mRNA (25). Whether the multihormonal regulation of specific mRNA levels by thyroid and steroid hormones reflects a common control mechanism that applies to other thyroid and steroid hormone responsive systems will require further study.…”

Section: Discussionmentioning

confidence: 97%

Thyroid and glucocorticoid hormones synergistically control growth hormone mRNA in cultured GH1 cells.

Shapiro¹,

Samuels²,

Yaffe³

1978

160

We have previously demonstrated that thyroid hormone controls growth hormone synthesis in GH1 cells and that the induction of the growth hormone response by glucocorticoid appears to be highly dependent on thyroid hormone action. Thyroid hormone induces growth hormone synthesis approximately 5-to 20-fold and cortisol increases this response 2-to 6-fold further. Long-term kinetics of the growth hormone response show that, without added thyroid hormone, cortisol can induce a small-growth hormone response after 48 hr of incubation. Sodium dodecyl sulfate/polyacrvlamide gel electrophoresis of proteins synthesized in intact celis demonstrates that the cortisol enhancement of growth hormone synthesis in cells incubated with thyroid hormone is a relatively selective process. Quantitation of growth hormone mRNA levels by cell-free protein synthesis demonstrates that the regulation of growth hormone synthesis by thyroid and glucocorticoid hormones is explained by a synergistic pretranslational control mechanism, presumably at the level of the growth hormone gene.

“…Later, DeGroot et al and Dilman et al showed increase in the poly(A)-rich fraction of RNA (2,3). Demonstrations of stimulation of a specific mRNA by thyroid hormones were recently provided by Kurtz et al (4) and by Roy et al (5) for a2u-globulin in the rat. However, because a number of hormones are known to stimulate the synthesis of this protein (6) and because thyroid hormone profoundly alters the level of such hormones (7), experiments done in the whole animal do not provide sufficient evidence for the direct induction of -d2u-globulin mRNA by thyroid hormone.…”

mentioning

confidence: 91%

Triiodothyronine stimulates specifically growth hormone mRNA in rat pituitary tumor cells.

Seo¹,

Vassart²,

Brocas³

et al. 1977

147

In a cell-free protein-synthesizing system from a rabbit reticulocyte lysate, total RNA extracted from cultured rat pituitary tumor (GH3) cells directed, in a dose-related manner, the synthesis of proteins that were precipitated by antisera specific to rat growth hormone (somatotropin) and rat prolactin. A marked decrease in growth hormone secretion and growth hormone mRNA activity was observed when cells were grown in a medium deficient in thyroid hormone. Addition of triiodothyronine in physiologic amounts both prevented and completely reversed this effect within 48 hr. Thyroid hormone had no effect on prolactin secretion or prolactin mRNA activity. These data suggest that thyroid hormone may stimulate synthesis of growth hormone throug induction of transcriptional activity. The possibility of an additional effect at the posttranscriptional level has not been excluded. Although thyroid hormone is believed to have a general effect on a variety of metabolic processes, some effects, at the molecular level, may be quite selective, as indicated by the observed changes in growth hormone but not prolactin mRNA activity. The GH3 cell model is useful in the study of triiodothyronine action because of independence from secondary hormonal effects caused by hypothyroidism and because simultaneous measurement of prolactin mRNA activity serves as a unique internal control. The demonstration of triiodothyronine (T3) binding to nuclear proteins raises the possibility that thyroid hormone may regulate gene expression. Earlier work from Tata's laboratory showed that thyroid hormone-induced protein synthesis was preceded by formation of new RNA (1). Later, DeGroot et al. and Dilman et al. showed increase in the poly(A)-rich fraction of RNA (2, 3). Demonstrations of stimulation of a specific mRNA by thyroid hormones were recently provided by Kurtz et al. (4) and by Roy et al. (5) for a2u-globulin in the rat. However, because a number of hormones are known to stimulate the synthesis of this protein (6) and because thyroid hormone profoundly alters the level of such hormones (7), experiments done in the whole animal do not provide sufficient evidence for the direct induction of -d2u-globulin mRNA by thyroid hormone. Samuels et al. have reported a quantitative correlation between nuclear T3 receptor occupancy and stimulation of growth hormone (GH, somatotropin) synthesis in cultured rat pituitary cells (8). We have adopted a similar experimental model to study more directly the action of thyroid hormone on the induction of a specific mRNA. In a recent report, we have shown that GH and prolactin mRNA activities in the total RNA extracted from a rat pituitary cell line (GH3) that actively synthesizes both hormones can be quantitated using a rabbit reticulocyte lysate cell-free system (9). In this report, we show that in the normal rat serum were 5.4 ,ug/100 ml and 60 ng/100 ml, respectively, and in the Tx rat serum were 0.6 ,g/100 ml and less than 20 ng/100 ml, respectively. RNA Extraction. Each RNA preparation was obta...