Audrey Roussel-Gervais1, Catherine Couture1, David Langlais1, Shinobu Takayasu1, Aurelio Balsalobre1, Bo R Rueda1, Lawrence R Zukerberg1, Dominique Figarella-Branger1, Thierry Brue1, Jacques Drouin1. 1. Laboratoire de Génétique Moléculaire (A.R.-G., C.C., D.L., S.T., A.B., J.D.), Institut de Recherches Cliniques de Montréal, Montréal, Quebec H2W 1R7, Canada; Massachusetts General Hospital (B.R.R., L.R.Z., J.D.), Boston, Massachusetts 02114; Aix-Marseille Université (D.F.-B., T.B.), Centre National de la Recherche Scientifique, Center for Research in Neurobiology and Neurophysiology of Marseille, Unité Mixte de Recherche 7286, 13344 Marseille, France; and Assistance Publique-Hôpitaux de Marseille (D.F.-B., T.B.), Hôpital Conception, Service d'Endocrinologie, Diabète et Maladies Métaboliques, Centre de Référence des Maladies Rares d'Origine Hypophysaire, 13285 Marseille, France.
Abstract
CONTEXT: Cushing disease (CD) is due to pituitary corticotrope adenomas that produce unrestrained ACTH secretion and have lost the negative feedback exerted by glucocorticoids (GCs). GCs also restrain corticotrope proliferation, and the mechanisms of this inhibition are poorly understood. OBJECTIVE: The aim of the study was to identify cell cycle regulatory genes that are regulated by GCs and the glucocorticoid receptor and to assess regulatory genes that have a rate-limiting action on corticotrope proliferation and may be disregulated in CD. DESIGN: The mouse corticotrope tumor cells AtT-20 were used to identify GC-regulated genes that contribute to control of cell cycle progression. Surgery sections from patients with CD were used to assess expression of CABLES1 in corticotrope adenomas. METHODS: Gene expression profiling, small interfering RNA knockdowns, cell cycle analyses, and genetic manipulations were performed in AtT-20 cells. Sequencing of chromatin immunoprecipitation for pituitary-restricted transcription factors and RNA polymerase II were used to identify regulatory elements and genes that bind GR and are direct transcriptional targets. A panel of previously well-characterized corticotrope adenomas was used to correlate expression of CABLES1 with that of other markers. RESULTS: GCs altered expression of 3 positive and 3 negative regulators of cell cycle progression. Two Myc genes (L-Myc and N-Myc) and E2F2 are repressed by GCs, whereas genes for the negative regulators of the cell cycle, Gadd45β, Gadd45γ, and Cables1 are activated by GCs. Cables1 small interfering RNA knockdown strongly stimulates AtT-20 cell proliferation and antagonizes the growth inhibition produced by GCs. The Gadd45 and Cables1 genes have the hallmarks of direct GC targets. CABLES1 is expressed in normal human pituitary cells, but expression is lost in ∼55% of corticotrope adenomas, and this is strongly correlated with the loss of p27(Kip1) expression. CONCLUSIONS: CABLES1 is a critical regulator of corticotrope proliferation that defines a pathway often inactivated in CD and links proliferation to GC resistance.
CONTEXT: Cushing disease (CD) is due to pituitary corticotrope adenomas that produce unrestrained ACTH secretion and have lost the negative feedback exerted by glucocorticoids (GCs). GCs also restrain corticotrope proliferation, and the mechanisms of this inhibition are poorly understood. OBJECTIVE: The aim of the study was to identify cell cycle regulatory genes that are regulated by GCs and the glucocorticoid receptor and to assess regulatory genes that have a rate-limiting action on corticotrope proliferation and may be disregulated in CD. DESIGN: The mouse corticotrope tumor cells AtT-20 were used to identify GC-regulated genes that contribute to control of cell cycle progression. Surgery sections from patients with CD were used to assess expression of CABLES1 in corticotrope adenomas. METHODS: Gene expression profiling, small interfering RNA knockdowns, cell cycle analyses, and genetic manipulations were performed in AtT-20 cells. Sequencing of chromatin immunoprecipitation for pituitary-restricted transcription factors and RNA polymerase II were used to identify regulatory elements and genes that bind GR and are direct transcriptional targets. A panel of previously well-characterized corticotrope adenomas was used to correlate expression of CABLES1 with that of other markers. RESULTS: GCs altered expression of 3 positive and 3 negative regulators of cell cycle progression. Two Myc genes (L-Myc and N-Myc) and E2F2 are repressed by GCs, whereas genes for the negative regulators of the cell cycle, Gadd45β, Gadd45γ, and Cables1 are activated by GCs. Cables1 small interfering RNA knockdown strongly stimulates AtT-20 cell proliferation and antagonizes the growth inhibition produced by GCs. The Gadd45 and Cables1 genes have the hallmarks of direct GC targets. CABLES1 is expressed in normal human pituitary cells, but expression is lost in ∼55% of corticotrope adenomas, and this is strongly correlated with the loss of p27(Kip1) expression. CONCLUSIONS:CABLES1 is a critical regulator of corticotrope proliferation that defines a pathway often inactivated in CD and links proliferation to GC resistance.
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