Role of the ubiquitin/proteasome system on ACTH turnover in rat corticotropes
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ORIGINAL ARTICLE
Role of the ubiquitin/proteasome system on ACTH turnover in rat corticotropes Antonella Sesta1 Maria Francesca Cassarino1 Francesco Cavagnini1 Francesca Pecori Giraldi ●
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Received: 16 November 2017 / Accepted: 26 February 2018 © The Author(s) 2018. This article is an open access publication
Abstract Purpose A large number of studies has investigated proopiomelanocortin processing in anterior pituitary corticotropes but little is known on proopiomelanocortin/ACTH degradation within these cells. The ubiquitin-proteasome system is an intracellular protein degradation pathway which has garnered considerable interest in recent times, given its role in maintenance of protein homeostasis. Aim of the present study was to evaluate the role of the ubiquitin-proteasome system in proopiomelanocortin/ACTH turnover in pituitary corticotropes. Methods Rat anterior pituitary primary cultures were treated with 0.01–100 nM MG132, a proteasome inhibitor, or 0.1–100 nM K48R, an inhibitor of polyubiquitylation, for 4 and 24 h and ACTH concentrations in medium and cell lysates estimated by immunometric assay. Co-immunoprecipitation for ubiquitin and ACTH was carried out to establish ubiquitintagged protein products. Results Inhibition of proteasome-mediated degradation with MG132 lead to an increase in ACTH concentrations, both as regards secretion and cell content. Likewise, inhibition of polyubiquitylation was associated with increased ACTH secretion and cell content. Ubiquitin/ACTH co-immunoprecipitation revealed that proopiomelanocortin was a target of ubiquitylation. Conclusions We provide the first evidence that the ubiquitin-proteasome system is involved in proopiomelanocortin/ACTH degradation in corticotropes. Indeed, proopiomelanocortin is a target of ubiquitylation and modulation of ubiquitinproteasome system affects ACTH turnover. This study shows that regulation of ACTH proteolytic degradation may represent a means to control ACTH secretion. Keywords Proopiomelanocortin ACTH Ubiquitin-proteasome Ubiquitylation ●
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Introduction ACTH is a major component of the hypothalamo-pituitary adrenal axis and, thus, pivotal to survival. ACTH is synthesized in anterior pituitary corticotropes upon processing of its precursor, proopiomelanocortin (POMC) and indeed POMC null mice [1] or patients carrying a mutation in the
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12020-018-1573-9) contains supplementary material, which is available to authorized users. * Francesca Pecori Giraldi [email protected] 1
Neuroendocrinology Research Laboratory, Istituto Auxologico Italiano IRCCS, Cusano Milanino (Milan), Milan, Italy
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Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy
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POMC gene [2] have severe hypocortisolism. POMC, a 241-aminoacid prohormone, is synthesized in the rough endoplasmic reticulum, sorted in the Golgi complex and processed to 39-aminoacid ACTH in secretory granules by prohormone convertase
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