Effect of SOM230 (pasireotide) on corticotropic cells: action in dogs with Cushing's disease.

SOM230 (pasireotide) is a multiligand somatostatin (SRIF) analog able to bind to somatostatin receptor (SSTR) subtypes 1, 2, 3 and 5, and trigger antisecretory and antiproliferative signaling cascades. Canines have become in vivo models to test the pharmacological treatment of corticotropinomas because they frequently develop Cushing's disease in a spontaneous manner, due to adrenocorticotropic hormone (ACTH)-producing pituitary adenomas. Different levels of expression of SSTR2 and SSTR5 have been shown in both mouse AtT20 cells and canine tumoral corticotropinoma cells. The objective of this study was to evaluate whether SOM230 controls both tumor cell growth and hormone synthesis, therefore controlling the disease. SOM230 was tested in dogs suffering from Cushing's disease (10 animals were treated continuously during 6 months, and another 10 were treated with 3 cycles consisting of 2 months of treatment followed by a 2-month rest period). A significant decrease in ACTH, urinary cortisol creatinine ratio, adenoma size (magnetic nuclear resonance) and improvement of clinical signs were obtained, without side effects. AtT20 cells treated with SOM230 suppressed pro-opiomelanocortin (POMC) promoter activity through SSTR2, via the G(i) α-subunit, and reduced Nur77/Nurr1 transcriptional activity. We conclude that SOM230, in addition to its well-described antisecretory effects, inhibits, as shown in AtT20 cells, ACTH synthesis at the POMC transcriptional level, an effect mediated mainly through SSTR2, and limits tumor growth. The controlled Cushing's disease in the dogs that received the treatment indicates that SOM230 has a potential therapeutic use in humans suffering from Cushing's disease.

Molecular mechanisms of glucocorticoid receptor signaling.

This review highlights the most recent findings on the molecular mechanisms of the glucocorticoid receptor (GR). Most effects of glucocorticoids are mediated by the intracellular GR which is present in almost every tissue and controls transcriptional activation via direct and indirect mechanisms. Nevertheless the glu-cocorticoid responses are tissue -and gene- specific. GR associates selectively with corticosteroid ligands produced in the adrenal gland in response to changes of humoral homeostasis. Ligand interaction with GR promotes either GR binding to genomic glucocorticoid response elements, in turn modulating gene transcription, or interaction of GR monomers with other transcription factors activated by other signalling pathways leading to transrepression. The GR regulates a broad spectrum of physiological functions, including cell differentiation, metabolism and inflammatory responses. Thus, disruption or dysregulation of GR function will result in severe impairments in the maintenance of homeostasis and the control of adaptation to stress.

Molecular mechanisms of glucocorticoid receptor signaling / Mecanismos moleculares de señalización del receptor de glucocorticoides

This review highlights the most recent findings on the molecular mechanisms of the glucocorticoid receptor (GR). Most effects of glucocorticoids are mediated by the intracellular GR which is present in almost every tissue and controls transcriptional activation via direct and indirect mechanisms. Nevertheless the glucocorticoid responses are tissue -and gene- specific. GR associates selectively with corticosteroid ligands produced in the adrenal gland in response to changes of humoral homeostasis. Ligand interaction with GR promotes either GR binding to genomic glucocorticoid response elements, in turn modulating gene transcription, or interaction of GR monomers with other transcription factors activated by other signalling pathways leading to transrepression. The GR regulates a broad spectrum of physiological functions, including cell differentiation, metabolism and inflammatory responses. Thus, disruption or dysregulation of GR function will result in severe impairments in the maintenance of homeostasis and the control of adaptation to stress.

Esta revisión destaca los más recientes hallazgos sobre los mecanismos moleculares del receptor de glucocorticoides (GR). La mayoría de los efectos de los glucocorticoides son mediados por los GR intracelulares presentes en casi todos los tejidos y controlan la activación transcripcional por mecanismos directos e indirectos. Las respuestas a los glucocorticoides son específicas para cada gen y tejido. Los GR se asocian en forma selectiva con ligandos producidos en la glándula adrenal, corticosteroides, en respuesta a cambios neuroendocrinos. La interacción del ligando con el GR promueve: a) la unión del GR a elementos genómicos de respuesta a glucocorticoides, modulando la transcripción; b) la interacción de monómeros del GR con otros factores de transcripción activados por otras vías, llevando a la transrepresión. El GR regula un amplio espectro de funciones fisiológicas, incluyendo la diferenciación celular y las respuestas metabólicas e inflamatorias. Así, la desregulación de la función del GR resulta en graves defectos en el mantenimiento de la homeostasis y el control de la adaptación al estrés.

Regulation of pituitary function by cytokines.

Research performed on the pituitary has proven that cytokines play an important role in maintaining pituitary physiology, affecting not only cell proliferation but also hormone secretion. The effects of cytokines can be autocrine or paracrine. This review gives an overview on the effects of the most studied cytokines in the pituitary. Special interest is focused on interleukin-6 (IL-6) because it has the distinctive characteristic of stimulating pituitary tumor cell growth, but has the opposite effect on normal pituitary cells. On the other hand, IL-6 is a cytokine of interest in the pituitary because recent work has shown that it promotes and maintains senescence in certain types of tumors. Given that the majority of pituitary adenomas are microadenomas and the fact that clinically inapparent pituitary tumors are quite common, senescence, perhaps mediated by IL-6, is an attractive mechanism for explaining the benign nature of pituitary tumors.

Differential gene expression in models of pituitary prolactin-producing tumoral cells.

Although several genes and signalling pathways have been identified as important effectors in the development of pituitary tumours, our understanding of pituitary tumorigenesis remains incomplete and is the focus of much current research. Use of the mRNA differential display technique in prolactinomas from D2-receptor knockout mice and in stable GH3 cell line clones with enhanced tumorigenicity in vivo has led to the identification of two genes that are involved in the pathogenic process--BMP-4 and RSUME. Bone morphogenetic protein-4 (BMP-4) has been found to have a crucial role in prolactinoma development and also in signalling crosstalk with oestrogens. In contrast, BMP-4 has an inhibitory role in corticotrophinomas. RSUME (RWD-containing sumoylation enhancer) was identified from a transformed lactosomatotrophic cell line that had increased tumorigenic and angiogenic potential. Expression of RSUME was induced under hypoxic conditions and it has a potential role during vascularization. The differential expression and action of BMP-4 in prolactinomas and corticotrophinomas highlights the importance of studying a gene with contrasting actions in two cell lineages of the same organ in order to understand the pituitary transformation process. Both BMP-4 and RSUME may be interesting targets for inhibiting steps involved in pituitary tumorigenesis.

Pituitary action of cytokines: focus on BMP-4 and gp130 family.

The anterior pituitary can develop benign tumors of different sizes, classified as micro- and macroadenomas, frequently associated with high levels of hormone production, leading to different associated syndromes like Cushing's disease, acromegaly or prolactinomas. Much work has been done in order to understand the signaling pathways and the factors and hormones involved in the pituitary tumorigenic process. In recent years, much evidence has been collected and it is now well documented that cytokines of the gp130 family, such as interleukin-6, that use gp130 as a common signaling protein stimulate not only the proliferation but also the hormone secretion of pituitary cells. Experiments in vivo have shown that the overexpression of the gp130 receptor resulted in pituitary abnormal growth. Moreover, it has been recently described that bone morphogenetic protein-4 (BMP-4), a member of the TGF-beta family, has a stimulatory role on lactosomatotropic cells promoting the development of prolactinomas but it has an inhibitory action on the corticotropic lineage. This inhibitory action prevents Cushing's disease progression. Furthermore, BMP-4 mediates the antiproliferative action of retinoic acid in these cells. The present review highlights the most recent work about gp130 and TGF-beta cytokine families and their role in pituitary tumorigenesis.

Bone morphogenetic protein-4 control of pituitary pathophysiology.

Bone morphogenetic protein-4 (BMP-4), a member of the transforming growth factor-Beta(TGF-Beta) family, is overexpressed in different prolactinoma models and induces the development of these lineage adenomas. SMAD proteins activated by growth factors of the TGF-Beta and BMP family interact with estrogen receptors to stimulate the proliferation of prolactin and growth hormone-secreting cells. Furthermore, BMP-4 presents differential expression in normal and adenomatous corticotropes and inhibitory action on corticotropinoma cell proliferation. Moreover, BMP-4 mediates the antiproliferative action of retinoic acid in these cells. The present review highlights not only the crucial and opposite role of BMP-4 in the progression of pituitary adenomas but also that BMP-4 and retinoic acid interaction might serve as a potential new mechanism target for therapeutic approaches for Cushing disease.

Retinoic acid as a novel medical therapy for Cushing's disease in dogs.

Cushing's disease is almost always caused by an ACTH-secreting pituitary tumor, but effective medical therapy is currently limited. Because retinoic acid has been shown to be potentially useful in decreasing corticotroph secretion and proliferation in rodent models, we have studied its action in dogs with Cushing's disease. A randomized treatment with retinoic acid (n = 22) vs. ketoconazole (n = 20) in dogs with Cushing's disease was assigned for a period of 180 d. Clinical signs, plasma ACTH and alpha-MSH, the cortisol/creatinine urine ratio, and pituitary magnetic resonance imaging were assessed and compared at different time points. We recorded a significant reduction in plasma ACTH and alpha-MSH, and also in the cortisol/creatinine urine ratio, of the dogs treated with retinoic acid. Pituitary adenoma size was also significantly reduced at the end of retinoic acid treatment. Survival time and all the clinical signs evaluated showed an improvement in the retinoic-acid-treated dogs. No adverse events or signs of hepatotoxicity were observed, suggesting that the drug is not only effective but also safe. Retinoic acid treatment controls ACTH and cortisol hyperactivity and tumor size in dogs with ACTH-secreting tumors, leading to resolution of the clinical phenotype. This study highlights the possibility of using retinoic acid as a novel therapy in the treatment of ACTH-secreting tumors in humans with Cushing's disease.

Bone morphogenetic protein-4 inhibits corticotroph tumor cells: involvement in the retinoic acid inhibitory action.

The molecular mechanisms governing the pathogenesis of ACTH-secreting pituitary adenomas are still obscure. Furthermore, the pharmacological treatment of these tumors is limited. In this study, we report that bone morphogenetic protein-4 (BMP-4) is expressed in the corticotrophs of human normal adenohypophysis and its expression is reduced in corticotrophinomas obtained from Cushing's patients compared with the normal pituitary. BMP-4 treatment of AtT-20 mouse corticotrophinoma cells has an inhibitory effect on ACTH secretion and cell proliferation. AtT-20 cells stably transfected with a dominant-negative form of the BMP-4 signal cotransducer Smad-4 or the BMP-4 inhibitor noggin have increased tumorigenicity in nude mice, showing that BMP-4 has an inhibitory role on corticotroph tumorigenesis in vivo. Because the activation of the retinoic acid receptor has an inhibitory action on Cushing's disease progression, we analyzed the putative interaction of these two pathways. Indeed, retinoic acid induces both BMP-4 transcription and expression and its antiproliferative action is blocked in Smad-4dn- and noggin-transfected Att-20 cells that do not respond to BMP-4. Therefore, retinoic acid induces BMP-4, which participates in the antiproliferative effects of retinoic acid. This new mechanism is a potential target for therapeutic approaches for Cushing's disease.

Nur77 induction and activation are necessary for interleukin-1 stimulation of proopiomelanocortin in AtT-20 corticotrophs.

Nur77 and Nurr1 are critical for proopiomelanocortin (POMC) regulation by corticotrophin releasing hormone (CRH) in corticotrophs. We analyze the regulation and activity of Nur77 by interleukin (IL)-1 in AtT-20 corticotrophic cells and its consequences on POMC regulation. IL-1 induces Nur77 and not Nurr1 mRNA and shows an increased transcriptional activity on the NurRE site, an effect dependent of p38 protein kinase activity. A NurRE mutation abrogates POMC promoter transcription by IL-1 and a stable AtT-20 clone overexpressing a dominant negative form of Nur77 is unresponsive to IL-1-dependent POMC induction and adrenocorticotrophin (ACTH) secretion. These results demonstrate that Nur77 is essential for POMC stimulation by IL-1 in corticotrophs.

El sistema nervioso central y el sistema neuroendocrino en la regulacion de la respuesta inmune / The central nervous system and the neuroendocrine system in the regulation of the immune response

Existe actualmente una orientación definida hacia el estudio de los fenómeno psiconeuro inmunorregulatorios. Diversos modelos experimentales han demonstrado: a) la participación del stress y factores psicosociales y el sistema nervioso central en la regulación de la respuesta inmune; b) una inervación bien desarrollada por el sistema nervioso autónomo en los órganos linféticos; c) la presencia de receptores para mediadores neuroendócrinos en células mononucleares periféricas; d) la actividad de neuropéptidos, hormonas y neurotransmisores en la activación y acción linfocitaria; e) la producción de sustancias neuroendócrinas por linfocitos; f) la existencia de vías de retroalimentación por parte del sistema inmune. En nuestro laboratorio hemos contribuído a esta orientación con la descripción de a) la actividad regulatoria de diversas sustancias neuroendócrinas sobre la producción de interferón-gama; b) la caracterización de la inmunorregulación ejercida por el sistema colinérgico muscarínico; c) la descripción de la actividad in vitro de las indolaminas serotonina y melatonina sobre el sistema inmune y la producción de estas indolaminas por linfocitos y monocitos, constituyendo un modelo de regulación parácrina. Actualmente se están ampliando las investigaciones desarrollando además líneas de estudios integrativas de la función del sistema nervioso central en la regulación del sistema inmune an animales y humanos

El sistema nervioso central y el sistema neuroendocrino en la regulacion de la respuesta inmune / The central nervous system and the neuroendocrine system in the regulation of the immune response

Existe actualmente una orientación definida hacia el estudio de los fenómeno psiconeuro inmunorregulatorios. Diversos modelos experimentales han demonstrado: a) la participación del stress y factores psicosociales y el sistema nervioso central en la regulación de la respuesta inmune; b) una inervación bien desarrollada por el sistema nervioso autónomo en los órganos linféticos; c) la presencia de receptores para mediadores neuroendócrinos en células mononucleares periféricas; d) la actividad de neuropéptidos, hormonas y neurotransmisores en la activación y acción linfocitaria; e) la producción de sustancias neuroendócrinas por linfocitos; f) la existencia de vías de retroalimentación por parte del sistema inmune. En nuestro laboratorio hemos contribuído a esta orientación con la descripción de a) la actividad regulatoria de diversas sustancias neuroendócrinas sobre la producción de interferón-gama; b) la caracterización de la inmunorregulación ejercida por el sistema colinérgico muscarínico; c) la descripción de la actividad in vitro de las indolaminas serotonina y melatonina sobre el sistema inmune y la producción de estas indolaminas por linfocitos y monocitos, constituyendo un modelo de regulación parácrina. Actualmente se están ampliando las investigaciones desarrollando además líneas de estudios integrativas de la función del sistema nervioso central en la regulación del sistema inmune an animales y humanos (AU)