Conditional Overexpression of the Wild-Type Gsα as the gsp Oncogene Initiates Chronic Extracellularly Regulated Kinase 1/2 Activation and Hormone Hypersecretion in Pituitary Cell Lines

• Published in: Endocrinology (Philadelphia) 2007-06, Vol.148 (6), p.2973-2983
• Main Authors: Romano, D, Magalon, K, Pertuit, M, Rasolonjanahary, R, Barlier, A, Enjalbert, A, Gerard, C
• Format: Article
• Language: English
• Subjects: Adenoma; Adenylate cyclase; Adenylyl Cyclases - metabolism; Animals; Biological and medical sciences; Cell activation; Cell differentiation; Cell Line; Cell lines; Cell proliferation; Chromogranins; Cyclic AMP; Cyclic AMP - metabolism; Doxycycline; Doxycycline - pharmacology; Enzyme Activation; Extracellular signal-regulated kinase; Fundamental and applied biological sciences. Psychology; G protein-coupled receptors; Gene Expression Regulation, Enzymologic - drug effects; Growth Hormone - genetics; Growth Hormone - secretion; Growth hormones; GTP-Binding Protein alpha Subunits, Gs - genetics; Guanine nucleotide-binding protein; Kinases; MAP kinase; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Oncogene Proteins - genetics; Oncogenes; Phenotypes; Pituitary; Prolactin; Prolactin - genetics; Prolactin - secretion; Protein biosynthesis; Protein folding; Proteins; Rats; Somatotrophs - enzymology; Somatotrophs - metabolism; Somatotrophs - secretion; Time Factors; Transfection; Transgenes - drug effects; Tumors; Vertebrates: endocrinology
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/en.2006-1273

In pituitary cells, activation of the cAMP pathway by specific G protein-coupled receptors controls differentiative functions and proliferation. Constitutively active forms of the α subunit of the heterotrimeric Gs protein resulting from mutations at codon 201 or 227 (gsp oncogene) were first identified in 30–40% of human GH-secreting pituitary adenomas. This rate of occurrence suggests that the gsp oncogene is not responsible for initiating the majority of these tumors. Moreover, there is a large overlap between the clinical phenotypes observed in patients with tumors bearing the gsp oncogene and those devoid of this oncogene. To explore the role of Gsα in GH-secreting adenomas, we obtained somatolactotroph GH4C1 cell lines by performing doxycycline-dependent conditional overexpression of the wild-type Gsα protein and expression of the gsp oncogene. Although the resulting adenylyl cyclase and cAMP levels were 10-fold lower in the wild-type Gsα-overexpressing cell line, a sustained MAPK ERK1/2 activation was observed in both cell lines. Overexpression of the wild-type Gsα protein as the gsp oncogene initiated chronic activation of endogenous prolactin synthesis and release, as well as chronic activation of ERK1/2-sensitive human prolactin and GH promoters.