Mutations Drive Unrestrained Secretion

The USP8 mutations identified in adenomas of the pituitary gland lead to overproduction of ACTH. Panel A: ACTH-producing cells in a normal gland. The other panels show cells non-mutant (B) or mutant (C) for USP8. Credit: S. Sbiera, UniversitĂ€t WĂŒrzburg

The USP8 mutations identified in adenomas of the pituitary gland lead to overproduction of ACTH. Panel A: ACTH-producing cells in a normal gland. The other panels show cells non-mutant (B) or mutant (C) for USP8. Credit: S. Sbiera, UniversitĂ€t WĂŒrzburg

Benign tumors in the pituitary gland lead to uncontrolled secretion of the stress hormone cortisol by the cells of the adrenal cortex. An international research effort has now characterized a new mechanism that triggers the syndrome.

Many individuals who suffer from Cushing syndrome are easy to recognize: They tend to be overweight particularly around the waist, and have round faces and bull necks. In addition to these obvious features, most of them have high blood pressure, develop muscle weakness, become diabetic and are extremely susceptible to infection. Cushing syndrome can often be treated effectively by surgical intervention, but patients succumb to infections or cardiovascular disease if the condition is left untreated.

In their efforts to understand how benign tumors in the pituitary provoke the development of Cushing’s disease, researchers based in Munich, WĂŒrzburg and Tokyo led by Professor Martin Reincke (Director of LMU’s Medical Clinic IV at Munich University Medical Center) have now pinpointed a novel molecular mechanism responsible for the condition. The results of the study have just appeared in Nature Genetics.

The perils of incessant secretion

All of the symptoms that typify Cushing syndrome are attributable to the unregulated secretion of the hormone cortisol – generally referred to as cortisone. Cortisol is normally released into the bloodstream only in stress situations, and helps the organism to cope with the challenge. However, when secreted in an uncontrolled fashion, the result is physiological havoc. Cortisol is synthesized in, and secreted by specialized cells in the adrenal cortex in response to the binding of a different hormone, the adrenocorticotropic hormone (ACTH). ACTH in turn is produced in the pituitary gland. Excessive cell proliferation in the pituitary can result in the formation of benign tumors (adenomas), which may lead to overproduction of ACTH and a corresponding increase in the level of circulating cortisol. However, the connecting links between the two processes are incompletely understood.

“We have now shown that tumor cells in more than one-third of patients with Cushing’s disease carry a mutation in one specific gene, which codes for an enzyme called ubiquitin-specific protease 8,” says Martin Fassnacht (WĂŒrzburg University Hospital), one of the authors of the publication. The mutation was discovered in the course of a detailed genetic characterization of benign tumors of the pituitary gland that overproduced ACTH.

Protease defect sets off a chain reaction

Ubiquitin-specific protease 8 (USP8) is one of a family of enzymes which play a key role in the destruction of proteins that are required only transiently by cells. One such protein is the receptor for epidermal growth factor (EGF), which is degraded and disposed of only when the USP8 gene is inactive, and no USP8 protein is present. The collaboration found that the effect of the mutations identified in pituitary tumor tissues is to keep the USP8 permanently active. As a consequence, the EGF receptor escapes demolition, and is instead recycled to its site of action on the cell membrane. The upshot of this is a life-threatening chain reaction, in which unrestrained synthesis of ACTH leads to uninhibited secretion of cortisol. “The identification of mutations in USP8 is a significant finding, because it opens up entirely new diagnostic and therapeutic approaches to the management of Cushing’s disease,” Martin Reincke adds.

Long-term focus on Cushing’s disease

Indeed, this is not the first time that the collaboration between the teams in Munich and WĂŒrzburg has shed light on the pathogenesis of Cushing’s disease. The two groups have previously identified mutations in a gene that is expressed in the adrenal cortex as a frequent cause of the pathological secretion of cortisol in a different patient population. The results of that study appeared in February 2014 in the “New England Journal of Medicine“. And only last week, a paper providing a detailed characterization of the molecular effects of the latter set of mutations was published in “Nature Communications“.

More information: “Mutations in the deubiquitinase gene USP8 cause Cushing’s disease.” Nature Genetics (2014) DOI: 10.1038/ng.3166

ARMC5 Mutations in Macronodular Adrenal Hyperplasia with Cushing’s Syndrome

adrenal-hyperplasia

 

Guillaume Assié, M.D., Ph.D., Rossella Libé, M.D., Stéphanie Espiard, M.D., Marthe Rizk-Rabin, Ph.D., Anne Guimier, M.D., Windy Luscap, M.Sc., Olivia Barreau, M.D., Lucile LefÚvre, M.Sc., Mathilde Sibony, M.D., Laurence Guignat, M.D., Stéphanie Rodriguez, M.Sc., Karine Perlemoine, B.S., Fernande René-Corail, B.S., Franck Letourneur, Ph.D., Bilal Trabulsi, M.D., Alix Poussier, M.D., Nathalie Chabbert-Buffet, M.D., Ph.D., Françoise Borson-Chazot, M.D., Ph.D., Lionel Groussin, M.D., Ph.D., Xavier Bertagna, M.D., Constantine A. Stratakis, M.D., Ph.D., Bruno Ragazzon, Ph.D., and JérÎme Bertherat, M.D., Ph.D.

N Engl J Med 2013; 369:2105-2114 November 28, 2013 DOI: 10.1056/NEJMoa1304603

BACKGROUND

Corticotropin-independent macronodular adrenal hyperplasia may be an incidental finding or it may be identified during evaluation for Cushing’s syndrome. Reports of familial cases and the involvement of both adrenal glands suggest a genetic origin of this condition.

METHODS

We genotyped blood and tumor DNA obtained from 33 patients with corticotropin-independent macronodular adrenal hyperplasia (12 men and 21 women who were 30 to 73 years of age), using single-nucleotide polymorphism arrays, microsatellite markers, and whole-genome and Sanger sequencing. The effects of armadillo repeat containing 5 (ARMC5) inactivation and overexpression were tested in cell-culture models.

RESULTS

The most frequent somatic chromosome alteration was loss of heterozygosity at 16p (in 8 of 33 patients for whom data were available [24%]). The most frequent mutation identified by means of whole-genome sequencing was in ARMC5, located at 16p11.2. ARMC5 mutations were detected in tumors obtained from 18 of 33 patients (55%). In all cases, both alleles of ARMC5 carried mutations: one germline and the other somatic. In 4 patients with a germline ARMC5 mutation, different nodules from the affected adrenals harbored different secondary ARMC5 alterations. Transcriptome-based classification of corticotropin-independent macronodular adrenal hyperplasia indicated that ARMC5 mutations influenced gene expression, since all cases with mutations clustered together. ARMC5 inactivation decreased steroidogenesis in vitro, and its overexpression altered cell survival.

CONCLUSIONS

Some cases of corticotropin-independent macronodular adrenal hyperplasia appear to be genetic, most often with inactivating mutations of ARMC5, a putative tumor-suppressor gene. Genetic testing for this condition, which often has a long and insidious prediagnostic course, might result in earlier identification and better management. (Funded by Agence Nationale de la Recherche and others.)

Supported in part by grants from Agence Nationale de la Recherche (ANR-10-Blan-1136), CorticomedullosurrĂ©nale Tumeur Endocrine Network (Programme Hospitalier de Recherche Clinique grant AOM95201), Assistance Publique–HĂŽpitaux de Paris (Clinical Research Center Grant Genhyper P061006), Institut National du Cancer (Recherche Translationelle 2009-RT-02), the Seventh Framework Program of the European Commission (F2-2010-259735), INSERM (Contrat d’Interface, to Dr. AssiĂ©), the Conny-Maeva Charitable Foundation, and the intramural program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.

Drs. Assié, Libé, Espiard, Rizk-Rabin, Ragazzon, and Bertherat contributed equally to this article.

We thank Drs. J. Chelly and M. Delpech of the cell bank of Cochin Hospital and Dr. B. Terris of the tumor bank of Cochin Hospital for their help in sample collection; Dr. E. Clauser of the oncogenetic unit of Cochin Hospital for help in microsatellite analysis; Drs. J. Guibourdenche and E. Clauser of the hormone biology unit of Cochin Hospital for cortisol assays; Drs. F. Tissier and Pierre Colin for pathological analysis; Anne Audebourg for technical assistance; J. Metral and A. de Reynies of the Cartes d’IdentitĂ© des Tumeurs program of Ligue Nationale contre le Cancer for help in genomics studies and fruitful discussions; Dr. P. Nietschke of the bioinformatics platforms of Paris Descartes University for helpful discussions; all the members of the Genomics and Signaling of Endocrine Tumors team and of the genomic platform of Cochin Institute for their help in these studies; and the patients and their families, as well as the physicians and staff involved in patient care, for their active participation.

SOURCE INFORMATION

From INSERM UnitĂ© 1016, Centre National de la Recherche Scientifique UnitĂ© Mixte de Recherche 8104, Institut Cochin (G.A., R.L., S.E., M.R.-R., A.G., W.L., O.B., L.L., S.R., K.P., F.R.-C., F.L., L. Groussin, X.B., B.R., J.B.), FacultĂ© de MĂ©decine Paris Descartes, UniversitĂ© Paris Descartes, Sorbonne Paris CitĂ© (G.A., S.E., A.G., O.B., L.L., M.S., K.P., F.R.-C., L. Groussin, X.B., J.B.), Department of Endocrinology, Referral Center for Rare Adrenal Diseases (G.A., R.L., O.B., L. Guignat, L. Groussin, X.B., J.B.), and Department of Pathology (M.S.), Assistance Publique–HĂŽpitaux de Paris, HĂŽpital Cochin, and Unit of Endocrinology, Department of Obstetrics and Gynecology, HĂŽpital Tenon (N.C.-B.) — all in Paris; Unit of Endocrinology, Centre Hospitalier du Centre Bretagne, Site de KĂ©rio, Noyal-Pontivy (B.T.), Unit of Endocrinology, HĂŽtel Dieu du Creusot, Le Creusot (A.P.), and Department of Endocrinology Lyon-Est, Groupement Hospitalier Est, Bron (F.B.-C.) — all in France; and the Section on Endocrinology and Genetics, Program on Developmental Endocrinology and Genetics and the Pediatric Endocrinology Inter-Institute Training Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD (C.A.S.).

Address reprint requests to Dr. Bertherat at Service des Maladies Endocriniennes et Métaboliques, Centre de Référence des Maladies Rares de la Surrénale, HÎpital Cochin, 27 rue du Faubourg St. Jacques, 75014 Paris, France, or at jerome.bertherat@cch.aphp.fr.

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