MODULATION OF POMC EXPRESSION IN HUMAN PITUITARY ACTH-SECRETING ADENOMAS IN VITRO

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 163-194-Pituitary Disorders & Case Reports
Basic/Clinical
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-187
Maria Francesca Cassarino1, Antonella Sesta1, Marco Losa2, Giovanni Lasio3, Francesco Cavagnini1 and Francesca Pecori Giraldi*4
1Istituto Auxologico Italiano IRCCS, Neuroendocrinology Research Lab, Cusano Milanino, Italy, 2Instituto Scientifico San Raffaele, Milano, Italy, 3Istituto Clinico Humanitas, Rozzano, Italy, 4Istituto Auxologico Italiano IRCCS, Neuroendocrinology Research Lab, University of Milan, Dept of Clinical Sciences and Community Health, Milan, Italy
Human pituitary ACTH-secreting adenomas are a difficult study matter given their small size and rarity. We recently published the results of over 70 primary cultures collected from patients with Cushing’s disease over the years  and reported on the considerable variability in the secretory response to CRH and dexamethasone in these adenomas (J Neuroendocrinol 2011). So far, few studies have evaluated POMC expression in human pituitary ACTH adenomas in vitro given their low RNA yield. Aim of the present study was to evaluate POMC synthesis, both spontaneous and modulated by CRH or dexamethasone, in ACTH-secreting adenoma primary cultures. Methods: Twenty-two pituitary adenomas were established in colture and incubated with 10 nM CRH or 10 nM dexamethasone for 4h, 24h or 48h then treated with Trizol for RNA extraction. RNA was reverse-transcribed and amplified by real-time PCR with primers specific to POMC and RPLP0. Medium ACTH concentrations were quantified by IRMA and specimens in whom ACTH or POMC deviated by at least 20% from values observed in unchallenged wells were considered responsive to CRH or dexamethasone. Results: An increase in ACTH secretion and POMC expression after 24h incubation with CRH was observed in 80% of specimens. Changes in the two parametres appeared concurrent as POMC expression was significantly greater in specimens in whom ACTH increased compared to ACTH non-responsive specimens (1.97 ± 0.33 vs 1.67 ± 0.09, p<0.05). Conversely, POMC expression was decreased after 24h-48h incubation with dexamethasone only in 25% of specimens, without a discernible parallelism between changes in ACTH and POMC. In fact, POMC was comparable in specimens in whom ACTH decreased or was unchanged by incubation with dexamethasone (0.84 ± 0.13 vs 1.10 ± 0.23, N.S.). Conclusions. This is the first large scale study to report changes in POMC in human pituitary ACTH-secreting adenomas in culture during incubation with CRH or dexamethasone. POMC appeared sensitive to CRH stimulation in the majority of tumoral specimens whereas the inhibitory effect of dexamethasone on POMC expression was evident only in a small proportion of pituitary adenomas. These results confirm the considerable variability in the adenomatous corticotrope response to the two main modulators of ACTH secretion and indicate the need for further studies on the divergent response of POMC and ACTH to dexamethasone.

Nothing to Disclose: MFC, AS, ML, GL, FC, FP

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