Endocrine Abstracts

Corticotrophinomas represent >10% of all surgically removed pituitary adenomas, which are the most commonly encountered intracranial neoplasms that are identified in >25% of unselected autopsies and approximately 20% of the population undergoing intracranial imaging. Corticotrophinomas are associated with hypersecretion of adrenocorticotropic hormone (ACTH), which leads to excessive production of glucocorticoids by the adrenal cortex and the resulting hypercortisolemia causes Cushing’s syndrome. Medical treatments for corticotrophinomas are limited, and we have previously reported that (+)-JQ1 (JQ1), an epigenetic inhibitor of the bromo and extra-terminal (BET) protein family, which bind acetylated histones to regulate gene transcription, significantly reduced cell proliferation, and increased apoptosis of the murine ACTH-secreting corticotrophinoma cell line AtT20. Here, we report the results of RNA Sequencing analysis, which reveals that JQ1 treatment could also down regulate expression of the pro-opiomelanocortin (Pomc) gene that encodes the precursor protein of ACTH. Using quantitative reverse transcription PCR, we confirmed the down regulation of Pomc (16.7-fold, P<0.005), in JQ1 treated, compared to control compound (JQ1-) treated cells. Western blot analysis also confirmed that POMC protein expression was decreased after JQ1 treatment, with significant reductions observed after 24 h (4.4-fold, P<0.0005), 48h (6.3-fold, P<0.0005) and 72 h (5.1-fold, P<0.005), compared to control JQ1- treated cells. To determine if the reduction in POMC expression also resulted in a reduction of ACTH secretion we performed an enzyme linked immunosorbant assay (ELISA) on AtT20 cell media collected up to 72 h after JQ1 treatment. We found that the levels of ACTH in cell media were significantly decreased at 48 h (1.4-fold, P<0.0005) and 72 h (1.2-fold, P<0.05) after JQ1 treatment, when compared to JQ1- treatment. Thus, our data indicate that JQ1 can significantly decrease ACTH secretion, through reduction of POMC expression, and therefore JQ1 may provide a novel approach for the control of hormone secretion in corticotrophinomas.