RESUMEN
CONTEXT: Somatotroph adenomas harboring aryl hydrocarbon receptor interacting protein (AIP) mutations respond less well to somatostatin analogs, suggesting that the effects of somatostatin analogs may be mediated by AIP. OBJECTIVE: The objective of the investigation was to study the involvement of AIP in the mechanism of effect of somatostatin analogs. DESIGN: In the human study, a 16-wk somatostatin analog pretreatment compared with no pretreatment. In the in vitro cell line study, the effect of somatostatin analog treatment or small interfering RNA (siRNA)/plasmid transfection were studied. SETTING: The study was conducted at a university hospital. PATIENTS: Thirty-nine sporadic and 10 familial acromegaly patients participated in the study. INTERVENTION: Interventions included preoperative lanreotide treatment and pituitary surgery. OUTCOME: For the human study, GH and IGF-I levels, AIP, and somatostatin receptor staining were measured. For the cell line, AIP and ZAC1 (zinc finger regulator of apoptosis and cell cycle arrest) expression, metabolic activity, and clone formation were measured. RESULTS: Lanreotide pretreatment reduced GH and IGF-I levels and tumor volume (all P < 0.0001). AIP immunostaining was stronger in the lanreotide-pretreated group vs. the surgery-only group (P < 0.001). After lanreotide pretreatment, the AIP score correlated to IGF-I changes in females (R = 0.68, P < 0.05). Somatostatin receptor staining was not reduced in samples with AIP mutations. In GH3 cells, 1 nm octreotide increased AIP mRNA and protein (both P < 0.01) and ZAC1 mRNA expression (P < 0.05). Overexpression of wild-type (but not mutant) AIP increased ZAC1 mRNA expression, whereas AIP siRNA knockdown reduced ZAC1 mRNA (both P < 0.05). The siRNA-mediated knockdown of AIP led to an increased metabolic activity and clonogenic ability of GH3 cells compared with cells transfected with a nontargeting control (both P < 0.001). CONCLUSION: These results suggest that AIP may play a role in the mechanism of action of somatostatin analogs via ZAC1 in sporadic somatotroph tumors and may explain their lack of effectiveness in patients with AIP mutations.
Asunto(s)
Adenoma/tratamiento farmacológico , Proteínas de Ciclo Celular/fisiología , Adenoma Hipofisario Secretor de Hormona del Crecimiento/tratamiento farmacológico , Péptidos y Proteínas de Señalización Intracelular/fisiología , Somatostatina/análogos & derivados , Factores de Transcripción/fisiología , Proteínas Supresoras de Tumor/fisiología , Animales , Proteínas de Ciclo Celular/análisis , Línea Celular Tumoral , Humanos , Péptidos y Proteínas de Señalización Intracelular/análisis , Ratas , Receptores de Somatostatina/análisis , Transducción de Señal , Factores de Transcripción/análisis , Proteínas Supresoras de Tumor/análisisRESUMEN
CONTEXT: Mutations have been identified in the aryl hydrocarbon receptor-interacting protein (AIP) gene in familial isolated pituitary adenomas (FIPA). It is not clear, however, how this molecular chaperone is involved in tumorigenesis. OBJECTIVE: AIP sequence changes and expression were studied in FIPA and sporadic adenomas. The function of normal and mutated AIP molecules was studied on cell proliferation and protein-protein interaction. Cellular and ultrastructural AIP localization was determined in pituitary cells. PATIENTS: Twenty-six FIPA kindreds and 85 sporadic pituitary adenoma patients were included in the study. RESULTS: Nine families harbored AIP mutations. Overexpression of wild-type AIP in TIG3 and HEK293 human fibroblast and GH3 pituitary cell lines dramatically reduced cell proliferation, whereas mutant AIP lost this ability. All the mutations led to a disruption of the protein-protein interaction between AIP and phosphodiesterase-4A5. In normal pituitary, AIP colocalizes exclusively with GH and prolactin, and it is found in association with the secretory vesicle, as shown by double-immunofluorescence and electron microscopy staining. In sporadic pituitary adenomas, however, AIP is expressed in all tumor types. In addition, whereas AIP is expressed in the secretory vesicle in GH-secreting tumors, similar to normal GH-secreting cells, in lactotroph, corticotroph, and nonfunctioning adenomas, it is localized to the cytoplasm and not in the secretory vesicles. CONCLUSIONS: Our functional evaluation of AIP mutations is consistent with a tumor-suppressor role for AIP and its involvement in familial acromegaly. The abnormal expression and subcellular localization of AIP in sporadic pituitary adenomas indicate deranged regulation of this protein during tumorigenesis.
Asunto(s)
Adenoma/genética , Neoplasias Hipofisarias/genética , Proteínas/fisiología , Acromegalia/genética , Acromegalia/metabolismo , Adenoma/metabolismo , Adolescente , Adulto , Anciano , Proliferación Celular , Niño , Fosfodiesterasas de Nucleótidos Cíclicos Tipo 4/metabolismo , Femenino , Regulación Neoplásica de la Expresión Génica , Pruebas Genéticas , Hormona de Crecimiento Humana/metabolismo , Humanos , Péptidos y Proteínas de Señalización Intracelular , Masculino , Persona de Mediana Edad , Neoplasias Hipofisarias/metabolismo , Unión Proteica , Proteínas/genética , Proteínas/metabolismo , Transfección , Células Tumorales CultivadasRESUMEN
Chronic exposure to glucocorticoid hormones, resulting from either drug treatment or Cushing's syndrome, results in insulin resistance, central obesity, and symptoms similar to the metabolic syndrome. We hypothesized that the major metabolic effects of corticosteroids are mediated by changes in the key metabolic enzyme adenosine monophosphate-activated protein kinase (AMPK) activity. Activation of AMPK is known to stimulate appetite in the hypothalamus and stimulate catabolic processes in the periphery. We assessed AMPK activity and the expression of several metabolic enzymes in the hypothalamus, liver, adipose tissue, and heart of a rat glucocorticoid-excess model as well as in in vitro studies using primary human adipose and primary rat hypothalamic cell cultures, and a human hepatoma cell line treated with dexamethasone and metformin. Glucocorticoid treatment inhibited AMPK activity in rat adipose tissue and heart, while stimulating it in the liver and hypothalamus. Similar data were observed in vitro in the primary adipose and hypothalamic cells and in the liver cell line. Metformin, a known AMPK regulator, prevented the corticosteroid-induced effects on AMPK in human adipocytes and rat hypothalamic neurons. Our data suggest that glucocorticoid-induced changes in AMPK constitute a novel mechanism that could explain the increase in appetite, the deposition of lipids in visceral adipose and hepatic tissue, as well as the cardiac changes that are all characteristic of glucocorticoid excess. Our data suggest that metformin treatment could be effective in preventing the metabolic complications of chronic glucocorticoid excess.