To elucidate the molecular mechanism of the pathogenesis of benign functioning
adrenocortical adenomas causing
Cushing's syndrome, we employed suppression 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/Dwarf1 (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 hybridization 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 examined the expression pattern of hDiminuto
mRNA in normal human adrenal cortex. 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, adjacent 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 in the normal adrenal cortex where hDiminuto expression was abundant. These results are compatible with a recent report that hDiminuto acts as an antiapoptotic factor in neurons. The expression of hDiminuto in the normal adrenal cortex was most abundant in the zona fasciculata, suggesting its possible regulation by
ACTH/cAMP. Indeed,
forskolin treatment of H295R human adrenocortical cells resulted in a significant induction of the
mRNA in a time- and dose-dependent manner. To further demonstrate the physiological regulation, an in vivo experiment was carried out in
dexamethasone-treated rats.
ACTH administration to these rats increased the
mRNA expression. These results 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 synthesis and cell growth.