Loss of growth hormone secretagogue receptor 1a and overexpression of type 1b receptor transcripts in human adrenocortical tumors

Objective and Methods: Quantitative analysis of mRNA expression of ghrelin and its receptors GHS-R1a and -R1b in a large series of normal and neoplastic human adrenocortical tissues. Evaluation of the effects of ghrelin on GHS-R expression and proliferation of human adrenocortical carcinoma (ACC) cell lines. Results: Ghrelin and GHS-R transcripts are expressed in normal adrenal cortex, with GHS-R1b mRNA levels being 5- to 10-fold higher than GHS-R1a mRNA. A significant increase in ghrelin expression was observed in adrenocortical adenomas, but not in carcinomas. GHS-R1a was undetectable in about 60% of both benign and malignant tumor samples, except for cortisol-producing adenomas, which showed increased receptor expression. At variance, GHS-R1b was overexpressed in both benign and malignant adrenocortical tumors. In vitro studies in human ACC cell lines demonstrated that GHS-R1a is downregulated and GHS-R1b mRNA expression is upregulated by ghrelin, while inhibiting cell proliferation. Conclusion: Downregulation of GHS-R1a in adrenal tumors and the presence of high levels of GHS-R1b transcripts in adrenocortical tissue suggest a role for these receptors in adrenal function and growth. In this regard, ghrelin inhibits cell proliferation and modulates GHS-R expression in ACC cells in vitro. Copyright (C) 2005 S. Karger AG, Basel.