ß-Catenin activation and illicit receptor expression in adrenocortical cells.

Adrenal cortisol-producing tumors can express illicit membrane receptors such as luteinizing hormone (LH), glucose-dependent insulinotropic peptide (GIP) or type 4 and 7 serotonin (5-HT4/7) receptors. Abnormal expression of the LH receptor (LH-R) has been ascribed to the activation of the Wnt/ß-catenin signaling pathway in adrenocortical cells. In the present study, we have investigated whether ß-catenin activation may also trigger the illegitimate expression of GIP and 5-HT receptors. Three models of ß-catenin activation in adrenocortical cells were used: an APC-mutated adrenocortical tumor, human-transfected adrenocortical cells and genetically modified mouse adrenal glands. The methods employed include quantitative reverse transcription PCR, immunohistochemistry and measurement of cortisol secretion by cultured tumor cells. Abnormal expression of the GIP, 5-HT7and LH receptors was observed in the APC-mutated adrenocortical tumor tissue. In addition, GIP, 5-HT and human chorionic gonadotropin stimulated cortisol production from tumor cells in primary culture. Conversely, only the LHCGR was upregulated in human and mouse adrenocortical cells harboring the activation of ß-catenin. Moreover, LH-R immunoreactivity was detected in clusters of zona fasciculata cells in the ß-catenin-activated mouse model. Our data indicate that activation of the ß-catenin signaling pathway can promote the illicit expression of functional LH-Rs in adrenal zona fasciculata cells but does not favor the abnormal expression of GIP and 5-HT receptors.

Illicit Upregulation of Serotonin Signaling Pathway in Adrenals of Patients With High Plasma or Intra-Adrenal ACTH Levels.

CONTEXT: In the human adrenal, serotonin (5-HT), released by mast cells stimulates corticosteroid secretion through activation of type 4 serotonin receptors (5-HT4R). In primary pigmented nodular adrenocortical disease cells, activation of the cAMP/protein kinase A (PKA) pathway by PRKAR1A mutations triggers upregulation of the 5-HT synthesizing enzyme tryptophan hydroxylase (TPH) and the 5-HT4, 5-HT6, and 5-HT7 receptors. Because ACTH stimulates cortisol secretion through activation of PKA, adrenocortical tissues exposed to sustained stimulation by ACTH may harbor increased expression of TPH and 5-HT4/6/7 receptors. OBJECTIVE: To investigate the effects of long-term ACTH stimulation on the serotonergic pathway in adrenals of patients with high plasma or intra-adrenal ACTH levels. METHODS: Adrenal tissues were obtained from patients with Cushing disease, ectopic secretion of ACTH [paraneoplastic Cushing syndrome; (paraCS)], 21-hydroxylase deficiency (21-OHD), primary bilateral macronodular adrenal hyperplasia with intra-adrenal ACTH presence, or cortisol-producing adenomas. TPH and 5-HT4/6/7 receptor expression was investigated using RT-PCR and immunochemistry in comparison with normal adrenals. Primary cultured adrenocortical cells originating from a patient with paraCS were incubated with 5-HT and 5-HTR agonists/antagonists. RESULTS: TPH and/or 5-HT4/6/7 receptors were overexpressed in the different types of tissues. In paraCS cultured cells, the cortisol response to 5-HT was exaggerated compared with normal adrenal cells and the stimulatory action of 5-HT was reduced by 5-HT4R antagonist. CONCLUSION: Our results indicate that prolonged activation of the cAMP/PKA pathway by ACTH induces an aberrant serotonergic stimulatory loop in the adrenal cortex that likely participates in the pathogenesis of corticosteroid hypersecretion.