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Glucocorticoids enhance corticotropin receptor mRNA levels in ovine adrenocortical cells

N Picard-Hagen, A Penhoat, D Hue, C Jaillard, and P Durand

ABSTRACT

We have shown previously that chronic treatment with glucocorticoids enhances both ACTH-induced cAMP production and ACTH- or 8Br-cAMP-induced steroidogenesis of cultured ovine adrenocortical cells. This treatment has been shown to involve an increase in the number of ACTH receptors. The present study aimed to explore the mechanism of this effect of glucocorticoids on ACTH receptors. Ovine adrenocortical cells expressed one major ACTH receptor transcript of 3·6 kb and three minor ones of 4·2, 1·8 and 1·3 kb. Dexamethasone treatment of cultured cells increased the levels of all these transcripts in a time- and dose-dependent manner, with an EC50 of (1·5±0·6) × 10−8 m. The mean increase over control with 10−6 m dexamethasone was 144 ± 11% (n=14). This enhancing effect was specific for glucocorticosteroids. The antiglucocorticoid Ru38486 blocked the effect of dexamethasone. Testosterone did not modify, while high concentrations of 17β-estradiol decreased, ACTH receptor mRNA levels. Treatment of cells with aminoglutethimide (an inhibitor of steroidogenesis) resulted in a dose-dependent decrease in ACTH receptor mRNA levels, which was prevented by concomitant treatment with dexamethasone. Treatment with ACTH also increased ACTH receptor mRNA levels more than twofold. Addition of aminoglutethimide together with ACTH resulted in a smaller increase than that achieved with ACTH alone. Neither dexamethasone nor ACTH modified ACTH receptor mRNA half-lives. However, these two hormones enhanced the levels of both newly synthesized and total ACTH receptor mRNAs. These results indicate that the positive trophic effect of glucocorticoids on ovine adrenocortical cells involves an enhancement of the transcription rate of the ACTH receptor gene. In addition, they suggest that part of the trophic action of ACTH on ACTH receptors may be mediated by ACTH-induced steroidogenesis.

DOI:
https://doi.org/10.1677/jme.0.0190029
Volume 19: Issue 1,
Pages:
29–36 (8 total)
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ACTH and angiotensin II regulation of insulin-like growth factor-I and its binding proteins in cultured bovine adrenal cells

A. Penhoat, P. Leduque, C. Jaillard, P. G. Chatelain, P. M. Dubois, and J. M. Saez

ABSTRACT

Insulin-like growth factor-I (IGF-I) is required for the maintenance of differentiated functions of bovine adrenal fasciculata cells in culture. We have investigated, by immunocytochemistry, the presence of IGF-I in cells cultured in the absence or presence of ACTH and angiotensin II (AII), as well as the secretion of IGF-I and its binding proteins (IGFBPs). In control cultures, very few cells were specifically stained with the anti-IGF-I serum. Following 2 days of treatment with AII (1μm) or ACTH (10 nm) the number of stained cells increased by 5- and 14-fold respectively. In all cases the staining was specific, since it was abolished when non-immune rabbit serum replaced the anti-IGF serum or when the anti-IGF-I serum was preincubated with saturating concentrations of the peptide. Under the same experimental conditions the secretion of IGF-I into the medium, evaluated by a specific radioimmunoassay, was increased two- and sevenfold by AII and ACTH respectively. Using the method of Western ligand blotting, the major form of IGFBP secreted by control adrenal cells was found to be a 38–42kDa doublet protein. Two minor forms with apparent molecular weights of 28–31 kDa and 24kDa have also been identified. Following acid—ethanol extraction of the conditioned medium, all the IGFBPs were recovered in the pellet, whereas most of the IGF-I was in the supernatant. ACTH and, to a lesser extent, AII pretreatment increased the 38–42kDa IGFBP by several fold, decreased the 28–31 kDa IGFBP and had no effect on the 24kDa IGFBP. In conclusion, these results demonstrate (i) that bovine adrenal cells contain IGF-I-like immunoreactive material, (ii) that the stimulatory effects of ACTH and AII on IGF-I secretion by bovine adrenal cells are due mainly to an increase in the number of IGF-I-producing cells and (iii) that ACTH and AII modulate the secretion of IGFBP by adrenal cells. Although the roles of IGFBPs have not been defined in adrenal cells, they are capable of modulating the biological action of IGFs in other cell cultures. Regulation of both IGF-I and its binding proteins by the two specific hormones ACTH and AII suggests important roles for these binding proteins in modulating the action of IGF-I in bovine adrenal cell function.

DOI:
https://doi.org/10.1677/jme.0.0070223
Volume 7: Issue 3,
Pages:
223–232 (10 total)