The regulation of the ACTH-receptor gene is unique in that it is up-regulated by its own ligand, ACTH. Ligand-induced up-regulation of ACTH-receptor expression may be an important adaptive process directed towards optimizing adrenal responsiveness to ACTH in the context of physiological stress and the maintenance of metabolic homeostasis in which the adrenals play a pivotal role. Whereas enhancement by ligand-induced up-regulation permits a more efficient and rapid glucocorticoid response, negative feedback regulation of glucocorticoids in the hypothalamus and pituitary inhibits ACTH secretion and allows a balanced adrenal response to stress. Since the cloning of the promoter region of the ACTH receptor, considerable progress in the understanding of the regulatory processes has been made. The effects of ACTH on ACTH-receptor expression is dependent on cAMP, probably mediated through AP-1.The profound effect of three SF-1-binding sites in the ACTH-receptor promoter was demonstrated by deletion experiments. Conversely, ACTH-receptor expression can be suppressed by adrenal-specific transcription factors,like DAX-1.Despite an extensive search, no activating ACTH-receptor mutations have been found in adrenal tumors,excluding the ACTH receptor as a relevant oncogene in adrenal tumorigenesis. However, the ACTH receptor may act as a differentiation factor as suggested by LOH in adrenal carcinomas with an undifferentiated tumor type.In benign adrenal tumors, a strong correlation between ACTH-receptor expression and expression of P450 steroidogenic enzymes is evident. This close regulative relationship is lost in adrenal carcinoma, probably as a result of tumor dedifferentiation. Down-regulation of ACTH-receptor expression in normal and neoplastic tissue can be achieved by adrenostatic compounds such as aminoglutethimide and metyrapone.

We have isolated a gene, PKX1, by virtue of its position within the candidate region for chondrodysplasia punctata in Xp22.3. Although data from one patient render it unlikely that PKX1 is the CDPX gene, this gene shows several interesting features. First, PKX1 appears to encode a novel type of human protein kinase that is related to the catalytic subunit of cAMP-dependent protein kinases and has striking homology to the DC2 protein kinase from Drosophila melanogaster. Second, PKX1 is part of a family of at least four genes or pseudogenes, of which three map to the human sex chromosomes. In contrast to all other genes from the X-specific region of Xp22.3, PKX1 has a homologue on Yp rather than Yq. This is intriguing as it indicates that the single pericentric inversion event hypothesized to have occurred during primate evolution is not sufficient to explain the present X/Y-homology pattern of Xp22.3. Third, we have characterized patients with different chromosomal rearrangements in Xp22.3 or Yp and show that a high proportion of these have occurred within the PKX1 locus. This suggests that the PKX1 gene, besides harbouring a previously described hot-spot for illegitimate Xp/Yp-recombination, contains additional sequences predisposing to chromosomal breakage events.

RNA-binding motif (RBM) genes are found on all mammalian Y chromosomes and are implicated in spermatogenesis. Within human germ cells, RBM protein shows a similar nuclear distribution to components of the pre-mRNA splicing machinery. To address the function of RBM, we have used protein-protein interaction assays to test for possible physical interactions between these proteins. We find that RBM protein directly interacts with members of the SR family of splicing factors and, in addition, strongly interacts with itself. We have mapped the protein domains responsible for mediating these interactions and expressed the mouse RBM interaction region as a bacterial fusion protein. This fusion protein can pull-down several functionally active SR protein species from cell extracts. Depletion and add-back experiments indicate that these SR proteins are the only splicing factors bound by RBM which are required for the splicing of a panel of pre-mRNAs. Our results suggest that RBM protein is an evolutionarily conserved mammalian splicing regulator which operates as a germ cellspecific cofactor for more ubiquitously expressed pre-mRNA splicing activators. T he azoospermia factor was originally postulated as a gene on the long arm of the human Y chromosome deleted in some infertile men. Subsequently, candidate genes have been identified on the Y chromosome by positional cloning. One of these genes, RBM (an acronym for RNA-binding motif), encodes a germ cell-restricted nuclear protein (1, 2). Y chromosome RBM genes are found in all mammals and are related to the X chromosome gene which encodes hnRNP G (3, 4), a member of the hnRNP family of proteins (heterogeneous nuclear ribonucleoproteins, reviewed in ref. 5). The functions of RBM and hnRNP G are unknown.Within germ cell nuclei, RNA-binding motif protein (RBMp) is found distributed throughout the nucleoplasm and within discrete punctate nuclear structures (6) which also contain pre-mRNA splicing factors. The latter include the SR proteins, which have been shown to play a crucial role in constitutive and alternative splicing (for reviews, see refs. 7 and 8). A strong prediction of these results is that RBMp might interact with components of the splicing machinery, and that these interactions may contribute to mediating the observed subnuclear distributions. Moreover, through such interactions RBMp might operationally affect pre-mRNA splice site choices in germ cells. To test these predictions, we carried out a series of proteinprotein interaction and in vitro splicing assays. Our results show that RBMp interacts strongly with members of the SR family of pre-mRNA splicing factors and that this interaction can have functional consequences for splicing. These results suggest that RBM is a prototypical mammalian example of a cell-specific splicing factor that functions in conjunction with SR proteins to direct splicing in germ cell nuclei. Materials and MethodsPlasmid Constructions. Constructs encoding amino acids 85-330 of mouse RBMp in pACTII and pAS1-CYH2 vectors (Clontech) we...

The ACTH receptor has a pivotal role in the regulation of adrenal cortisol secretion. Here, we describe a polymorphism within the transcription initiation site of the ACTH receptor promoter altering the consensus sequence from CTC to CCC. The prevalence of the polymorphism in 1266 unrelated healthy men was 80.2% for CTC/CTC, 19.0% for CTC/CCC, and 0.8% for CCC/CCC, respectively. In vitro studies using luciferase assays demonstrated a lower basal (CCC, 73 +/- 4%; CTC, 100 +/- 5%; P = 0.02) and forskolin-stimulated (CCC, 143 +/- 13%; CTC, 194 +/- 15%; P = 0.0008) promoter activity in the CCC construct compared with CTC. The clinical significance of the in vitro findings was investigated by a 6-h ACTH stimulation test with increasing ACTH(1-24) doses in normal subjects, demonstrating a blunted cortisol response in CCC/CCC subjects compared with CTC/CTC individuals (area under the curve, 12176 +/- 966; 16334 +/- 1051 nmol/liter.min; P < 0.03). Accordingly, after CRH stimulation, subjects with CCC/CCC showed a higher ACTH/cortisol ratio (P < 0.05) suggesting a decreased adrenal responsiveness to endogenous ACTH. In conclusion, we describe an ACTH receptor promoter polymorphism that results in a lower promoter activity in vitro and is associated with a lower cortisol secretion to prolonged ACTH stimulation in vivo. This polymorphism might influence cortisol homeostasis under stress conditions.

Our data demonstrate that adrenostatic compounds not only act by suppression of steroidogenic enzymes but can also influence both ACTH-R expression and cell proliferation in adrenal cells. As these effects occur in vitro at concentrations that are reached during treatment with these drugs in patients, they are probably also of clinical relevance. Particularly the antiproliferative activity of ETO may be useful in Cushing's syndrome due to adrenocortical cancer. The interaction of steroidogenesis, ACTH-R and glucocorticoid receptor expression as well as cell proliferation provides a new concept of the intra-adrenal response to stress in humans.