Adrenocorticotropin-dependent changes in SF-1/DAX-1 ratio influence steroidogenic genes expression in a novel model of glucocorticoid-producing adrenocortical cell lines derived from targeted tumorigenesis.

We established the first adrenocortical tumor cell lines with complete zona fasciculata (ZF) cell phenotype from tumors induced in transgenic mice by large T-antigen of simian virus 40 under the control of the aldose reductase-like akr1b7 gene promoter. Adrenocortical tumor cell lines produced high amounts of corticosterone and were responsive to ACTH. All genes that are supportive for glucocorticoid synthesis including cyp21a1 and cyp11b1 were expressed, and most of them were transiently up-regulated by ACTH at transcriptional level: stimulation culminated after 3-6 h and returned to basal levels after 24 h. Taking advantage of these cells, we have examined the effect of ACTH on DAX-1 (dosage-sensitive sex reversal-adrenal hypoplasia congenita critical region on X-chromosome, gene 1) and SF-1 (steroidogenic factor 1), two transcription factors known to respectively repress and activate adrenocortical steroidogenesis by acting on common target genes. According to their antagonistic activities, DAX-1 mRNA and protein levels were transiently down-regulated by ACTH, whereas those of SF-1 were stimulated, with kinetics paralleling those of steroidogenic genes expression, notably of two known SF-1 target genes, star and akr1b7. This suggests an essential role of SF-1/DAX-1 proteins ratio to achieve proper ACTH control of steroidogenic gene expression in cells derived from ZF. This was confirmed in mice adrenals, where repression of dax-1 gene and concomitant up-regulation of sf-1, star, and akr1b7 genes were observed in response to ACTH stimulation. In conclusion, using both unique differentiated cell lines and in vivo approaches, we provide the first evidence that hormonally induced changes in SF-1/DAX-1 ratio are part of the molecular arsenal of ZF cells to fine tune ACTH responsiveness.

Do sex steroids regulate glutamine synthesis with age?

Glutamine synthetase, a key enzyme in the production of glutamine, is known to be induced by glucocorticoids and preserved in skeletal muscle during aging, but the effect of other steroids, such as sex steroids (progesterone, estradiol), is unknown in vivo. The aim of this study was to determine whether progesterone or estradiol plays a role in the regulation of glutamine synthetase (GS) with aging. The effects of glucocorticoids and sex steroids on muscle GS activity and mRNA expression were measured in adult (6-8 mo; n = 7 in each group) and aged (26 mo; n = 10 in each group) female Wistar rats after adrenalectomy (ADX), ovariectomy (OV), or both (ADXOV) and were compared with those in sham-operated (Sham) control rats. In tibialis anterior muscle, ADX noticeably decreased both GS activity and expression irrespective of age (50-60%; P < 0.05), whereas OV had no effect at either age. Progesterone and estradiol replacement had no effect on the recovery of muscle GS response in either ADX or OV rats, regardless of age. In contrast, heart GS activity was decreased by ADX in aged animals only. These results suggest that the reproductive endocrine status of female rats does not affect muscle GS activity either in muscle or in heart, in young or aged animals, and that the heart GS response to steroids may be differently regulated in aged rats.