RESUMEN
Understanding the mechanisms through which multicellular organisms regulate cell, organ and body growth is of relevance to developmental biology and to research on growth-related diseases such as cancer. Here we describe a new effector in growth control, the small GTPase Rheb (Ras homologue enriched in brain). Mutations in the Drosophila melanogaster Rheb gene were isolated as growth-inhibitors, whereas overexpression of Rheb promoted cell growth. Our genetic and biochemical analyses suggest that Rheb functions downstream of the tumour suppressors Tsc1 (tuberous sclerosis 1)-Tsc2 in the TOR (target of rapamycin) signalling pathway to control growth, and that a major effector of Rheb function is ribosomal S6 kinase (S6K).
Asunto(s)
División Celular/genética , Proteínas de Drosophila/metabolismo , Sustancias de Crecimiento/metabolismo , Proteínas de Unión al GTP Monoméricas/fisiología , Neuropéptidos/fisiología , Proteínas Quinasas S6 Ribosómicas/metabolismo , Animales , División Celular/fisiología , Tamaño de la Célula/genética , Tamaño de la Célula/fisiología , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Ojo/ultraestructura , Femenino , Eliminación de Gen , Genes de Insecto , Genes Supresores de Tumor , Sustancias de Crecimiento/genética , Proteínas de Unión al GTP Monoméricas/genética , Neuropéptidos/genética , Proteína Homóloga de Ras Enriquecida en el Cerebro , Proteínas Recombinantes de Fusión/metabolismo , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Proteínas Quinasas S6 Ribosómicas/genética , Transducción de Señal , Activación Transcripcional , TransgenesRESUMEN
The Phosphatidylinositol-3 kinase/Protein Kinase B (PI3K/PKB) signaling pathway controls growth, metabolism, and lifespan in animals, and deregulation of its activity is associated with diabetes and cancer in humans. Here, we describe Susi, a coiled-coil domain protein that acts as a negative regulator of insulin signaling in Drosophila. Whereas loss of Susi function increases body size, overexpression of Susi reduces growth. We provide genetic evidence that Susi negatively regulates dPI3K activity. Susi directly binds to dP60, the regulatory subunit of dPI3K. Since Susi has no overt similarity to known inhibitors of PI3K/PKB signaling, it defines a novel mechanism by which this signaling cascade is kept in check. The fact that Susi is expressed in a circadian rhythm, with highest levels during the night, suggests that Susi attenuates insulin signaling during the fasting period.
Asunto(s)
Proteínas de Drosophila/fisiología , Regulación de la Expresión Génica/fisiología , Insulina/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Transducción de Señal/fisiología , Animales , Animales Modificados Genéticamente , Tamaño Corporal/genética , Proteínas Portadoras/genética , Proteínas Portadoras/fisiología , Recuento de Células/métodos , Membrana Celular/metabolismo , Células Cultivadas , Drosophila , Proteínas de Drosophila/genética , Activación Enzimática , Expresión Génica/fisiología , Genómica/métodos , Humanos , Inmunohistoquímica/métodos , Inmunoprecipitación/métodos , Indoles , Biología Molecular/métodos , Receptor de Insulina/metabolismo , Transfección/métodosRESUMEN
BACKGROUND: Insulin and insulin-like growth factors (IGFs) signal through a highly conserved pathway and control growth and metabolism in both vertebrates and invertebrates. In mammals, insulin-like growth factor binding proteins (IGFBPs) bind IGFs with high affinity and modulate their mitogenic, anti-apoptotic and metabolic actions, but no functional homologs have been identified in invertebrates so far. RESULTS: Here, we show that the secreted Imaginal morphogenesis protein-Late 2 (Imp-L2) binds Drosophila insulin-like peptide 2 (Dilp2) and inhibits growth non-autonomously. Whereas over-expressing Imp-L2 strongly reduces size, loss of Imp-L2 function results in an increased body size. Imp-L2 is both necessary and sufficient to compensate Dilp2-induced hyperinsulinemia in vivo. Under starvation conditions, Imp-L2 is essential for proper dampening of insulin signaling and larval survival. CONCLUSION: Imp-L2, the first functionally characterized insulin-binding protein in invertebrates, serves as a nutritionally controlled suppressor of insulin-mediated growth in Drosophila. Given that Imp-L2 and the human tumor suppressor IGFBP-7 show sequence homology in their carboxy-terminal immunoglobulin-like domains, we suggest that their common precursor was an ancestral insulin-binding protein.
Asunto(s)
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Proteínas de Unión a Factor de Crecimiento Similar a la Insulina/metabolismo , Insulina/metabolismo , Inanición/metabolismo , Secuencia de Aminoácidos , Animales , Células Cultivadas , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Drosophila melanogaster/crecimiento & desarrollo , Femenino , Regulación del Desarrollo de la Expresión Génica , Proteínas Inmediatas-Precoces/genética , Proteínas Inmediatas-Precoces/metabolismo , Proteínas de Unión a Factor de Crecimiento Similar a la Insulina/genética , Masculino , Datos de Secuencia Molecular , Transducción de SeñalRESUMEN
Understanding the control of size is of fundamental biological and clinical importance. Insulin/IGF signaling during development controls growth and size, possibly by coordinating the activities of the Ras and PI 3-kinase signaling pathways. We show that in Drosophila mutating the consensus binding site for the Ras pathway adaptor Drk/Grb2 in Chico/IRS does not interfere with growth whereas mutating the binding sites of the PI 3-kinase adaptor p60 completely abrogates Chico function. Furthermore, we present biochemical and genetic evidence that loss of the homolog of the tumor suppressor gene, Pten, results in increased PtdInsP(3) levels and that these increased levels are sufficient to compensate for the complete loss of the Insulin/insulin-like growth factor receptor function. This reduction of Pten activity is also sufficient to vastly increase organism size. These results suggest that PtdInsP(3) is a second messenger for growth and that levels of PtdInsP(3) during development regulate organismal size.