ucn-1028-c and Adrenal-Cortex-Neoplasms

The mechanisms and factors leading to enhanced aldosterone secretion and ultimately to neoplastic transformation of the adrenal cortex are poorly defined. Angiotensin-II (Ang-II) and endothelin-1 (ET-1) have emerged as likely candidates among potential aldosterone secretagogues and adrenocortical growth-promoting factors. We therefore compared the effects of Ang-II and ET-1 on steroid hormone secretion of Conn's adenomas.. Ten Conn's adenomas that showed responsiveness to Ang-II blockade in vivo were recruited. Fragments of the tumors were collected immediately after surgical excision, and dispersed cells were obtained by collagenase digestion and mechanical disaggregation. Steroid hormones secreted by dispersed Conn's adenoma cells were assayed by quantitative high-performance liquid chromatography or radioimmunoassay.. Both Ang-II and ET-1 (10(-9) mol/L) similarly enhanced the overall steroid hormone production. ET-1 raised the release of pregnenolone (as evaluated by blocking its further metabolism by cyanoketone), corticosterone, 18-hydroxycorticosterone, and aldosterone, without affecting that of 11-deoxycortisol, cortisol, and 11-deoxycorticosterone. The hormonal responses to ET-1 were partially reversed by 10(-7) mol/L of either the ETA-receptor antagonist BQ-123 or the ETB-receptor antagonist BQ-788 and were abolished when both antagonists were used together. The aldosterone response to the selective activation of ETA and ETB receptors was studied in three Conn's adenomas by exposing dispersed cells to ET-1 (10(-9) mol/L) plus BQ-788 (10(-7) mol/L) and to the ETB-receptor agonist BQ-3020 (10(-8) mol/L). Both treatments raised aldosterone output by about 2-fold. ETA receptor-mediated aldosterone response was abolished by the protein kinase (PK) C inhibitor calphostin C (10(-5) mol/L). ETB receptor-mediated secretory response was lowered by either calphostin C and the cyclooxygenase (COX) inhibitor indomethacin (10(-5) or 10(-4) mol/L) and was completely suppressed when these two were combined. The PKA inhibitor H-89 and the lipoxygenase inhibitor phenidone were ineffective.. Collectively, our findings indicate that Ang-II and ET-1 equipotently stimulate both early and late steps of aldosterone synthesis in Conn's adenoma cells. The secretagogue effect of ET-1 occurs via the activation of ETA and ETB receptors, which are coupled with the PKC-dependent and the PKC- and COX-dependent signaling pathways, respectively.

Topics: Adrenal Cortex Hormones; Adrenal Cortex Neoplasms; Adrenocortical Adenoma; Adult; Aged; Aldosterone; Angiotensin II; Endothelin-1; Endothelins; Female; Humans; Indomethacin; Isoquinolines; Male; Middle Aged; Naphthalenes; Oligopeptides; Peptide Fragments; Peptides, Cyclic; Piperidines; Prostaglandin-Endoperoxide Synthases; Protein Kinase C; Pyrazoles; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Signal Transduction; Sulfonamides; Tumor Cells, Cultured

The role of protein kinase C (PKC) in the regulation of basal steroidogenesis and steroid hydroxylase gene expression in Y1 adrenocortical cells was investigated. Treatment of Y1 cells with either staurosporine or calphostin C, inhibitors of PKC, increases steroid hormone production up to 7-fold. Induction of P450-cholesterol side chain cleavage enzyme (SCC) mRNA expression parallels induction of steroidogenesis by the PKC inhibitors. Staurosporine increases expression of a transiently transfected SCC promoter--human growth hormone construct in Y1 cells, indicating that PKC regulates expression of SCC mRNA at the level of transcription. Treatment with staurosporine increases expression of mRNA for two additional steroid synthetic enzymes, P450-11 beta-hydroxylase and 3 beta-hydroxysteroid dehydrogenase. These data indicate that PKC acts as a tonic negative regulator of basal steroidogenesis in Y1 cells by suppressing expression of mRNA encoding the steroid synthetic enzymes. Protein kinase A (PKA) and PKC have reciprocal effects on steroidogenesis and expression of the steroid synthetic enzymes in Y1 cells. However, the results of this study demonstrate that these signaling pathways are not interdependent. Steroid production by Y1 cells treated with (Bu)2cAMP and calphostin C together is equal to the sum of steroid production after treatment with either agent alone. Pretreatment of Y1 cells with Rp-8-Bromo-cAMP, a specific inhibitor of PKA, prevents induction of steroidogenesis by (Bu)2cAMP, but not by staurosporine, indicating that PKC is not dependent on PKA activity. In addition, induction of SCC mRNA expression by staurosporine, in Y1 cells which are defective in activation of PKA (Y1 kin-8), is equivalent to induction in Y1 cells. These data indicate that PKA and PKC regulate basal steroidogenesis through independent effects on expression of the steroid synthetic enzymes.

Topics: 3-Hydroxysteroid Dehydrogenases; Adenosine Monophosphate; Adrenal Cortex; Adrenal Cortex Hormones; Adrenal Cortex Neoplasms; Alkaloids; Animals; Bucladesine; Cholesterol Side-Chain Cleavage Enzyme; Cyclic AMP-Dependent Protein Kinases; Enzyme Induction; Mice; Naphthalenes; Neoplasm Proteins; Polycyclic Compounds; Promoter Regions, Genetic; Protein Kinase C; Recombinant Fusion Proteins; Signal Transduction; Staurosporine; Steroid 11-beta-Hydroxylase; Thionucleotides; Tumor Cells, Cultured