The human homolog of Diminuto/Dwarf1 gene (hDiminuto): A novel ACTH-responsive gene overexpressed in benign cortisol-producing adrenocortical adenomas

To elucidate the molecular mechanism of the pathogenesis of benign function ing adrenocortical adenomas causing Cushing's syndrome, we employed suppres sion PCR-based cDNA subtractive hybridization to identify novel genes that are differentially expressed in the adenoma. In this report we describe the adenoma-specific overexpression of the human homolog of the Diminuto/Dwarf 1 (hDiminuto) gene. Northern blot analysis revealed that hDiminuto mRNA was overexpressed in the adenoma tissue of 14 patients with Cushing's syndrome in comparison to the adjacent nontumorous adrenal gland. In situ hybridiza tion using hDiminuto cRNA probe showed its abundant expression in the tumor cells, whereas the nontumorous cells showed a low level of expression. As the atrophic adjacent gland may not represent the normal architecture, we e xamined the expression pattern of hDiminuto mRNA in normal human adrenal co rtex. In situ hybridization revealed that it was expressed in all layers of the normal adrenal cortex. In situ apoptosis detection by the TUNEL method revealed that a low level of hDiminuto expression in the atrophic, adjacen t gland was associated with numerous TUNEL-positive cells in all layers of cortex. In contrast almost no apoptotic cell was detected in the tumor or i n the normal adrenal cortex where hDiminuto expression was abundant. These results are compatible with a recent report that hDiminuto acts as an antia poptotic factor in neurons. The expression of hDiminuto in the normal adren al cortex was most abundant in the zona fasciculata, suggesting its possibl e regulation by ACTH/cAMP. Indeed, forskolin treatment of H295R human adren ocortical cells resulted in a significant induction of the mRNA in a time- and dose-dependent manner. To further demonstrate the physiological regulat ion, an in vivo experiment was carried out in dexamethasone-treated rats. A CTH administration to these rats increased the mRNA expression. These resul ts led us to speculate that the overexpression of hDiminuto in the adenoma could be due to the abundant expression of ACTH receptor, as we previously described. Diminuto is involved in steroid synthesis and cell elongation in plants. We, therefore, hypothesize that hDiminuto might be involved in the molecular events of adrenocortical tumorigenesis by facilitating steroid s ynthesis and cell growth.