Proopiomelanocortin, glucocorticoid, and CRH receptor expression in human ACTH-secreting pituitary adenomas

Abstract

ACTH-secreting pituitary tumors are by definition partially autonomous, i.e., secrete ACTH independent of physiological control. However, only few, small-sized studies on proopiomelanocortin (POMC) and its regulation by corticotropin-releasing hormone (CRH) or glucocorticoids are available. Objective of the present study was to report on constitutive and CRH- and dexamethasone-regulated POMC, CRH (CRH-R1), and glucocorticoid receptor (NR3C1) gene expression in a large series of human corticotrope adenomas. Fifty-three ACTH-secreting adenomas were incubated with 10 nM CRH or 10 nM dexamethasone for 24 h. POMC, CRH-R1, NR3C1, and its alpha and beta isoforms were quantified and medium ACTH measured. Constitutive POMC expression proved extremely variable, with macroadenomas exhibiting higher levels than microadenomas. POMC increased during CRH in most specimens; conversely, changes induced by dexamethasone were varied, ranging from decrease to paradoxical increase. No correlation between POMC and ACTH was detected in any experimental condition. CRH-R1 expression was not linked to the response to CRH while NR3C1 was expressed at greater levels in specimens who failed to inhibit during dexamethasone; glucocorticoid receptor α was the more abundant isoform and subject to down-regulation by dexamethasone. Our results demonstrate a considerable variability in POMC expression among tumors and no correlation between POMC and ACTH, suggesting that POMC peptide processing/transport plays a major role in modulating ACTH secretion. Further, CRH-R1 and NR3C1 expression were not linked to the expected ligand-induced outcome, indicating that receptor signaling rather than abundance determines corticotrope responses. Our findings pave the way to new avenues of research into Cushing’s disease pathophysiology.Electronic supplementary materialThe online version of this article (doi:10.1007/s12020-016-0990-x) contains supplementary material, which is available to authorized users.

Sexual Dimorphism in Cellular and Molecular Features in Human ACTH-Secreting Pituitary Adenomas

“…As regards ACTH synthesis, we did not observe differences in POMC expression between maleand female-excised adenomas both in unchallenged wells and after CRH/dexamethasone incubation. This finding is in line with the lack of correlation between POMC and ACTH in corticotrope adenomas in vitro [53,54] and, in the present setting, suggests that sexual dimorphism affects POMC peptide processing and secretion rather than POMC transcription.…”

“…MIB-1 staining was <2% in all but one specimen; this adenoma presented MIB-1 index 9%, mitosis count 3 per 10 high power field and had been collected from a female patient in whom surgery proved successful. As per our previous publications [53,96,97], the presence of corticotrope cells in fresh adenoma specimens was assured by abundant ACTH secretion in culture medium [98]; as regards formalin-fixed specimens, abundant POMC and absent GH, PRL, PIT1, LHB, FSHB expression was documented by microarray analysis [13].…”

“…Taqman assay (Applied Biosystem) was used for POMC quantification (probe Hs00174947_m1). Basal expression data (2 −∆Ct ) was calculated and normalized to RPLP0 (probe Hs99999902_m1); expression after treatments was analysed as 2 −∆∆Ct and expressed in fold change from baseline [53].…”

Pituitary Hyperplasia, Hormonal Changes and Prolactinoma Development in Males Exposed to Estrogens—An Insight From Translational Studies

“…Regardless of the blood levels of glucocorticoids (variable in different studies with estradiol, as stated previously), reduced expression of GR in estrogen-induced pituitary tumors suggests generally weak glucocorticoid input in this context. Even ACTH-secreting pituitary tumors express a largely autonomous mode of ACTH secretion that is supposedly insensitive to physiological negative feedback and glucocorticoid levels [119]. On the other hand, glucocorticoids stimulate secretion of macrophage migration inhibitory factor (MIF) by folliculo-stellate cells, macrophages and T lymphocytes.…”

The Role of Single-Nucleotide Polymorphisms in Pituitary Adenomas Tumorigenesis

“…While the evidence described above supports corticotrophic adenomas as being monoclonal in nature, making somatic mutations a likely etiology, several studies have revealed increased incidence of somatic polymorphisms in patients with corticotrophic PAs, suggesting that these polymorphisms may promote the growth of these adenomas to sufficient size to cause clinically diagnosable Cushing's disease. For example, some studies have identified the importance of glucocorticoid receptor (GR) polymorphisms in tumorigenesis [61]. As corticotrophic adenomas are characterized by relative resistance to the negative feedback action of cortisol on ACTH secretion, it is reasonable to surmise that SNPs in GR genes may play some role in tumorigenesis, if not also tumor phenotype maintenance.…”