RESUMEN
The RAS-RAF-MEK-extracellular-regulated kinase (RAS/ERK) pathway is a major intracellular route used by metazoan cells to channel to downstream targets a diverse array of signals, including those controlling cell proliferation and survival. Recent findings suggest that the pathway is assembled by specific scaffolding proteins that in turn regulate the efficiency, the location and/or the duration of signal transmission. Here, through the angle of studies conducted in Drosophila and C. elegans, we present two such proteins, the kinase suppressor of RAS (KSR) and connector enhancer of KSR (CNK) scaffolds, and highlight their implication in a novel mechanism regulating RAS-mediated RAF activation. Based on recent findings, we discuss the possibility that KSR, a RAF-like protein, does not solely act as a scaffold, but directly induces RAF catalytic function by a kinase-independent mechanism apparently shared by RAF-like proteins.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/fisiología , Proteínas de Caenorhabditis elegans/fisiología , Proteínas de Drosophila/fisiología , Péptidos y Proteínas de Señalización Intracelular/fisiología , Proteínas Quinasas/fisiología , Quinasas raf/metabolismo , Proteínas ras/fisiología , Secuencia de Aminoácidos , Animales , Catálisis , Activación Enzimática/fisiología , Humanos , Datos de Secuencia Molecular , Proteínas Quinasas/genéticaAsunto(s)
Principio del Doble Efecto , Análisis Ético , Homicidio/ética , Lactante , Procedimientos Quirúrgicos Operativos/ética , Gemelos Siameses/cirugía , Femenino , Humanos , Intención , Calidad de Vida , Negativa del Paciente al Tratamiento/ética , Negativa del Paciente al Tratamiento/legislación & jurisprudenciaRESUMEN
kinase suppressor of Ras (ksr) encodes a putative protein kinase that by genetic criteria appears to function downstream of RAS in multiple receptor tyrosine kinase (RTK) pathways. While biochemical evidence suggests that the role of KSR is closely linked to the signal transduction mechanism of the MAPK cascade, the precise molecular function of KSR remains unresolved. To further elucidate the role of KSR and to identify proteins that may be required for KSR function, we conducted a dominant modifier screen in Drosophila based on a KSR-dependent phenotype. Overexpression of the KSR kinase domain in a subset of cells during Drosophila eye development blocks photoreceptor cell differentiation and results in the external roughening of the adult eye. Therefore, mutations in genes functioning with KSR might modify the KSR-dependent phenotype. We screened approximately 185,000 mutagenized progeny for dominant modifiers of the KSR-dependent rough eye phenotype. A total of 15 complementation groups of Enhancers and four complementation groups of Suppressors were derived. Ten of these complementation groups correspond to mutations in known components of the Ras1 pathway, demonstrating the ability of the screen to specifically identify loci critical for Ras1 signaling and further confirming a role for KSR in Ras1 signaling. In addition, we have identified 4 additional complementation groups. One of them corresponds to the kismet locus, which encodes a putative chromatin remodeling factor. The relevance of these loci with respect to the function of KSR and the Ras1 pathway in general is discussed.
Asunto(s)
Drosophila melanogaster/genética , Proteínas Quinasas/genética , Transducción de Señal/fisiología , Secuencia de Aminoácidos , Animales , Mapeo Cromosómico , Cruzamientos Genéticos , Drosophila melanogaster/anatomía & histología , Drosophila melanogaster/enzimología , Metanosulfonato de Etilo , Ojo/anatomía & histología , Ojo/ultraestructura , Femenino , Genes Dominantes , Genes de Insecto , Prueba de Complementación Genética , Masculino , Microscopía Electrónica de Rastreo , Datos de Secuencia Molecular , Mutagénesis , Fenotipo , Proteínas Tirosina Quinasas Receptoras/genética , Recombinación Genética , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
Glutaminol adenylate 5 is a competitive inhibitor of glutaminyl-tRNA synthetase with respect to glutamine (Ki = 280 nM) and to ATP (Ki = 860 nM). The corresponding methyl phosphate ester 4 is a weaker inhibitor (Ki approximately 10 microM) with respect to glutamine.
Asunto(s)
Adenina/análogos & derivados , Adenina/síntesis química , Aminoacil-ARNt Sintetasas/antagonistas & inhibidores , Inhibidores Enzimáticos/síntesis química , Adenina/química , Adenina/farmacología , Aminoacil-ARNt Sintetasas/metabolismo , Inhibidores Enzimáticos/química , Inhibidores Enzimáticos/farmacología , Escherichia coli/efectos de los fármacos , Escherichia coli/enzimología , Cinética , Estructura MolecularRESUMEN
Connector enhancer of KSR (CNK) is a multidomain protein required for RAS signaling. Its C-terminal portion (CNK(C-term)) directly binds to RAF. Herein, we show that the N-terminal portion of CNK (CNK(N-term)) strongly cooperates with RAS, whereas CNK(C-term) efficiently blocks RAS- and RAF-dependent signaling when overexpressed in the Drosophila eye. Two effector loop mutants of RAS(V12), S35 and C40, which selectively activate the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase pathways, respectively, do not cooperate with CNK. However, a strong cooperation is observed between CNK and RAS(V12G37), an effector loop mutant known in mammals to activate specifically the RAL pathway. We have identified two domains in CNK(N-term) that are critical for cooperation with RAS. Our results suggest that CNK functions in more than one pathway downstream of RAS. CNK(c-term) seems to regulate RAF, a component of the MAPK pathway, whereas CNK(N-term) seems to be involved in a MAPK-independent pathway.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales , Proteínas Portadoras/fisiología , Proteínas de Drosophila , Sistema de Señalización de MAP Quinasas/fisiología , Proteínas ras/metabolismo , Animales , Proteínas Portadoras/genética , Línea Celular , Drosophila , Ojo/enzimología , Ojo/metabolismo , Ojo/ultraestructura , Microscopía Electrónica de Rastreo , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Mutación , TransfecciónRESUMEN
Genetic and biochemical studies have identified kinase suppressor of Ras (KSR) to be a conserved component of Ras-dependent signaling pathways. To better understand the role of KSR in signal transduction, we have initiated studies investigating the effect of phosphorylation and protein interactions on KSR function. Here, we report the identification of five in vivo phosphorylation sites of KSR. In serum-starved cells, KSR contains two constitutive sites of phosphorylation (Ser297 and Ser392), which mediate the binding of KSR to the 14-3-3 family of proteins. In the presence of activated Ras, KSR contains three additional sites of phosphorylation (Thr260, Thr274, and Ser443), all of which match the consensus motif (Px[S/T]P) for phosphorylation by mitogen-activated protein kinase (MAPK). Further, we find that treatment of cells with the MEK inhibitor PD98059 blocks phosphorylation of the Ras-inducible sites and that activated MAPK associates with KSR in a Ras-dependent manner. Together, these findings indicate that KSR is an in vivo substrate of MAPK. Mutation of the identified phosphorylation sites did not alter the ability of KSR to facilitate Ras signaling in Xenopus oocytes, suggesting that phosphorylation at these sites may serve other functional roles, such as regulating catalytic activity. Interestingly, during the course of this study, we found that the biological effect of KSR varied dramatically with the level of KSR protein expressed. In Xenopus oocytes, KSR functioned as a positive regulator of Ras signaling when expressed at low levels, whereas at high levels of expression, KSR blocked Ras-dependent signal transduction. Likewise, overexpression of Drosophila KSR blocked R7 photoreceptor formation in the Drosophila eye. Therefore, the biological function of KSR as a positive effector of Ras-dependent signaling appears to be dependent on maintaining KSR protein expression at low or near-physiological levels.
Asunto(s)
Proteínas Quinasas Dependientes de Calcio-Calmodulina/metabolismo , Proteínas Quinasas/metabolismo , Proteínas/metabolismo , Tirosina 3-Monooxigenasa , Proteínas ras/metabolismo , Proteínas 14-3-3 , Células 3T3 , Animales , Sitios de Unión , Línea Celular , Línea Celular Transformada , Drosophila melanogaster , Ratones , Mutación , Fosforilación , Unión Proteica , Proteínas Quinasas/genética , Conejos , SerinaRESUMEN
Kinase suppressor of ras (ksr) is required for efficient signal transmission within the RAS/MAPK cascade. A screen for mutations that modify a ksr-dependent phenotype identified a novel gene, connector enhancer of ksr (cnk), that functions upstream or in parallel to RAF in the RAS pathway. cnk encodes a protein containing several protein-protein interaction domains, suggesting that it brings different signaling molecules together. CNK is required in multiple receptor tyrosine kinase pathways where it appears to be a tyrosine phosphorylation target. Finally, CNK physically interacts with RAF and appears to localize to cell-cell contact regions. Together, these findings suggest that CNK is a novel component of a RAS-dependent signaling pathway that regulates RAF function and/or targets RAF to a specific subcellular compartment upon RAS activation.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Proteínas de Drosophila , Drosophila melanogaster/genética , Proteínas de Insectos/genética , Proteínas de Insectos/metabolismo , Proteínas Quinasas/genética , Proteínas Proto-Oncogénicas c-raf/metabolismo , Transducción de Señal , Proteínas ras/metabolismo , Secuencia de Aminoácidos , Animales , Proteínas Portadoras/química , Diferenciación Celular , Línea Celular , Supervivencia Celular , Drosophila melanogaster/crecimiento & desarrollo , Drosophila melanogaster/metabolismo , Evolución Molecular , Ojo/química , Ojo/crecimiento & desarrollo , Genes Dominantes , Genes Supresores , Humanos , Proteínas de Insectos/química , Uniones Intercelulares/metabolismo , Datos de Secuencia Molecular , Mutagénesis , Fenotipo , Fosforilación , Proteínas Tirosina Quinasas Receptoras/metabolismo , Alas de Animales/crecimiento & desarrollo , Proteínas ras/antagonistas & inhibidoresRESUMEN
OBJECTIVES: We sought to 1) determine the proportion of appropriate elderly patients admitted to the hospital with unstable angina who are treated with aspirin and heparin; 2) identify patient factors associated with the Agency for Health Care Policy and Research (AHCPR) guideline-based use of aspirin and heparin; and 3) compare practice patterns and patient outcomes before and after publication of the AHCPR guidelines. BACKGROUND: Improving the care of patients with unstable angina may provide immediate opportunities to mitigate the adverse consequences of unstable angina. However, despite the importance of this diagnosis, there is a paucity of information on the patterns of treatment and outcomes across diverse sites and recent trends in practice that have occurred, especially since the publication of the AHCPR practice guidelines. METHOD: We performed a retrospective cohort study using data created from medical charts and administrative files. The sample included 300 consecutive patients admitted to one of three Connecticut hospitals in the period 1993 to 1994 and 150 consecutive patients admitted in 1995 with a principal discharge diagnosis of unstable angina or chest pain. RESULTS: Of the 384 patients > or =65 years old who had no contraindications to aspirin on hospital admission, 276 (72%) received it. Of the 369 patients > or =65 years old who had no contraindications to heparin on admission, 88 (24%) received it. Among the 321 patients > or =65 years old who had no contraindications to aspirin at hospital discharge, 208 (65%) were prescribed it. When 1995 was compared with 1993 to 1994, the use of aspirin (odds ratio [OR] 2.3, 95% confidence interval [CI] 1.3 to 4.0) and heparin (OR 2.8, 95% CI 1.6 to 4.9) on hospital admission significantly increased, and the use of aspirin at discharge (OR 1.4, 95% CI 0.8 to 2.4) increased. Concomitantly, there was a significant reduction in 30-day readmission (OR 0.52, 95% CI 0.27 to 0.99). CONCLUSIONS: Our results indicate an improvement in the care and outcomes of elderly patients with unstable angina, but there remain opportunities for further improvement.
Asunto(s)
Angina Inestable/tratamiento farmacológico , Anticoagulantes/uso terapéutico , Aspirina/uso terapéutico , Adhesión a Directriz , Heparina/uso terapéutico , Hospitales/normas , Medicare/normas , Inhibidores de Agregación Plaquetaria/uso terapéutico , Calidad de la Atención de Salud/tendencias , Anciano , Anciano de 80 o más Años , Angina Inestable/mortalidad , Connecticut , Femenino , Humanos , Masculino , Guías de Práctica Clínica como Asunto , Indicadores de Calidad de la Atención de Salud , Estudios Retrospectivos , Análisis de Supervivencia , Estados UnidosRESUMEN
Kinase suppressor of Ras (KSR) is an evolutionarily conserved component of Ras-dependent signaling pathways. Here, we find that murine KSR (mKSR1) translocates from the cytoplasm to the plasma membrane in the presence of activated Ras. At the membrane, mKSR1 modulates Ras signaling by enhancing Raf-1 activity in a kinase-independent manner. The activation of Raf-1 is mediated by the mKSR1 cysteine-rich CA3 domain and involves a detergent labile cofactor that is not ceramide. These findings reveal another point of regulation for Ras-mediated signal transduction and further define a noncatalytic role for mKSR1 in the multistep process of Raf-1 activation.
Asunto(s)
Proteínas Quinasas/metabolismo , Proteínas Proto-Oncogénicas c-raf/metabolismo , Animales , Células COS , Membrana Celular/metabolismo , Ceramidas/farmacología , Activación EnzimáticaRESUMEN
BACKGROUND: State-based peer review organizations (PROs) and individual hospitals are challenged to achieve their quality improvement (QI) goals with shrinking resources. In 1993-1994 the Connecticut PRO and 15 local hospitals generated a comparative QI database on acute myocardial infarction (AMI) care for 1,202 Medicare and non-Medicare patients discharged in 1992 and 1993. METHODS: A steering committee composed of hospital and PRO representatives was assembled to provide oversight. PRO staff developed a chart abstraction tool and trained hospital abstracters who collected and submitted data to the PRO for comparative analyses. Written feedback was provided to all hospitals and supplemented with onsite presentations when requested. Each hospital prepared a written QI plan based on its unique data profile. RESULTS: Opportunities for improvement were identified at all hospitals. The most commonly targeted areas for improvement included the use of thrombolytics at presentation, aspirin at presentation and at discharge, and beta blockers at discharge. Improvement interventions included staff education sessions, development of AMI critical paths and standing orders, and storage of appropriate medications in emergency departments. Self-report data from the hospitals indicate improvements in care. DISCUSSION: PROs and hospitals can augment their individual QI activities by working together to share data, resources, and lessons learned. Twenty-three hospitals are now collaborating with the Connecticut PRO on a similarly designed QI project aimed at improving the care of patients hospitalized with atrial fibrillation. This project includes a more formal means of communicating QI interventions.
Asunto(s)
Hospitales/normas , Relaciones Interinstitucionales , Infarto del Miocardio/terapia , Organizaciones de Normalización Profesional , Garantía de la Calidad de Atención de Salud , Anciano , Connecticut , Femenino , Humanos , Masculino , Persona de Mediana EdadRESUMEN
During the course of our screening for squalene synthase inhibitors and Ras farnesylation inhibitors, a novel fungal culture was discovered to produce two structurally unique compounds, CP-225,917 and CP-263,114, as well as zaragozic acid A (squalestatin I). The two compounds are characterized by a bicyclo[4.3.1]dec-1,6-diene core plus two extended alkyl chains. CP-225,917 and CP-263,114 inhibit Ras farnesyl transferase from rat brain with IC50 values of 6 microM and 20 microM, respectively. CP-225,917 inhibits squalene synthase with an IC50 value of 43 microM and CP-263,114 with an IC50 of 160 microM. The producing organism, though not fully classified, exhibits the characteristics of a sterile Phoma species.
Asunto(s)
Transferasas Alquil y Aril , Inhibidores Enzimáticos/aislamiento & purificación , Fermentación , Hongos/clasificación , Anhídridos Maleicos/aislamiento & purificación , Transferasas/antagonistas & inhibidores , Animales , Inhibidores Enzimáticos/farmacología , Farnesil Difosfato Farnesil Transferasa/antagonistas & inhibidores , Hongos/metabolismo , Anhídridos Maleicos/farmacología , RatasRESUMEN
Kinase suppressor of Ras (KSR) is a recently identified component of Ras-dependent signaling pathways. In this report, we show that murine KSR1 (mKSR1) cooperates with activated Ras to promote Xenopus oocyte maturation and cellular transformation and provide evidence that this cooperation occurs by accelerating mitogen and extracellular regulated kinase (MEK) and mitogen-activated protein kinase (MAPK) activation. We also find that mKSR1 associates with Raf-1 at the plasma membrane in a Ras-dependent manner, indicating the presence of a membrane-bound kinase signaling complex. Although mKSR1 is related structurally to Raf-1, our findings reveal striking functional differences between these proteins. In marked contrast to the isolated amino- and carboxy-terminal domains of Raf-1, the KSR amino terminus also cooperates with Ras, whereas the carboxy-terminal kinase domain blocks Ras signaling as well as MEK and MAPK activation. The isolated KSR kinase domain suppressed Xenopus oocyte maturation, cellular transformation, and Drosophila eye development, suggesting that separation of the amino- and carboxy-terminal domains has uncoupled the normal regulation of KSR as a positive effector of Ras signaling. Together, our findings indicate that mKSR1 is an integral component of the MAPK module functioning via a novel mechanism to modulate signal propagation between Raf-1, MEK1, and MAPK.
Asunto(s)
Proteínas Quinasas/metabolismo , Transducción de Señal , Células 3T3 , Animales , Línea Celular Transformada , Drosophila/genética , Ojo/metabolismo , Ojo/ultraestructura , Genes ras , Ratones , Ratones Endogámicos BALB C , Microscopía Electrónica de Rastreo , Oocitos/fisiología , Células Fotorreceptoras/citología , Células Fotorreceptoras/metabolismo , Inhibidores de Proteínas Quinasas , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-raf , XenopusRESUMEN
BACKGROUND: State-based peer review organizations (PROs) and individual hospitals are challenged to achieve their quality improvement (QI) goals with shrinking resources. In 1993-1994 the Connecticut PRO and 15 local hospitals generated a comparative QI database on acute myocardial infarction (AMI) care for 1,202 Medicare and non-Medicare patients discharged in 1992 and 1993. METHODS: A steering committee composed of hospital and PRO representatives was assembled to provide oversight. PRO staff developed a chart abstraction tool and trained hospital abstractors who collected and submitted data to the PRO for comparative analyses. Written feedback was provided to all hospitals and supplemented with onsite presentations when requested. Each hospital prepared a written QI plan based on its unique data profile. RESULTS: Opportunities for improvement were identified at all hospitals. The most commonly targeted areas for improvement included the use of thrombolytics at presentation, aspirin at presentation and at discharge, and beta blockers at discharge. Improvement interventions included staff education sessions, development of AMI critical paths and standing orders, and storage of appropriate medications in emergency departments. Self-report data from the hospitals indicate improvements in care. DISCUSSION: PROs and hospitals can augment their individual QI activities by working together to share data, resources, and lessons learned. Twenty-three hospitals are now collaborating with the Connecticut PRO on a similarly designed QI project aimed at improving the care of patients hospitalized with atrial fibrillation. This project includes a more formal means of communicating QI interventions.
Asunto(s)
Servicio de Cardiología en Hospital/normas , Infarto del Miocardio/terapia , Organizaciones de Normalización Profesional , Terapia Trombolítica/normas , Gestión de la Calidad Total/organización & administración , Anciano , Connecticut , Conducta Cooperativa , Bases de Datos Factuales , Femenino , Humanos , Masculino , Persona de Mediana Edad , Evaluación de Procesos y Resultados en Atención de Salud , Terapia Trombolítica/estadística & datos numéricos , Factores de TiempoRESUMEN
The pituitary gland contains six distinct hormone-producing cell types that arise sequentially during organogenesis. The first cells to differentiate are those that express the pro-opiomelanocortin (POMC) gene in the anterior pituitary lobe. The other lineages, which appear later, include cells that are dependent on the POU factor Pit-1 and another POMC-expressing lineage in the intermediate pituitary lobe. Using AtT-20 cells as a model for early expression of POMC in the anterior pituitary, we have defined a regulatory element conferring cell specificity of transcription and cloned a cognate transcription factor. This factor, Ptx1 (pituitary homeo box 1), contains a homeo box related to those of the anterior-specific genes bicoid and orthodenticle in Drosophila, and Otx-1 and Otx-2 in mammals. Ptx1 activates transcription upon binding a sequence related to the Drosophila bicoid target sites. Ptx1 is the only nuclear factor of this DNA-binding specificity that is detected in AtT-20 cells, and it is expressed at high levels in a subset of adult anterior pituitary cells that express POMC. However, Ptx1 is expressed in most cells of Rathke's pouch at an early time during pituitary development and before final differentiation of hormone-producing cells. Thus, Ptx1 may have a role in differentiation of pituitary cells, and its early expression pattern suggests that it may have a role in pituitary formation. In the adult pituitary gland, Ptx1 appears to be recruited for cell-specific transcription of the POMC gene.
Asunto(s)
Proteínas de Homeodominio/metabolismo , Proopiomelanocortina/genética , Transactivadores , Factores de Transcripción/metabolismo , Secuencia de Aminoácidos , Animales , Línea Celular , Proteínas de Drosophila , Regulación de la Expresión Génica , Hormonas de Insectos/química , Hormonas de Insectos/metabolismo , Células L , Ratones , Datos de Secuencia Molecular , Factores de Transcripción Paired Box , Adenohipófisis/metabolismo , Ratas , Secuencias Reguladoras de Ácidos Nucleicos , Homología de Secuencia de Aminoácido , Transcripción GenéticaRESUMEN
Cell-fate specification of the R7 photoreceptor cell is controlled by the sevenless receptor tyrosine kinase (SevRTK) and Ras1, the Drosophila homologue of mammalian H-ras, K-ras and N-ras oncogenes. An activated form of Ras1 expressed under control of the sevenless enhancer/promoter (sev-Ras1V12) induces production of supernumerary R7 photoreceptor cells, which causes the eye to become rough in appearance. To isolate mutations in genes functioning downstream of Ras1, we carried out a screen for dominant suppressors and enhancers of this rough eye phenotype. Approximately 850,000 mutagenized flies were screened, and 282 dominant suppressors and 577 dominant enhancers were isolated. Mutations in the Drosophila homologues of Raf, MEK, MAPK, type I Geranylgeranyl Transferase and Protein Phosphatase 2A were isolated, as were mutations in several novel signaling genes. Some of these mutant genes appear to be general signaling factors that function in other Ras1 pathways, while one seems to be more specific for photoreceptor development. At least two suppressors appear to function either between Ras1 and Raf or in parallel to Raf.
Asunto(s)
Drosophila/genética , Regulación del Desarrollo de la Expresión Génica , Genes de Insecto , Genes ras/genética , Animales , Mapeo Cromosómico , Cruzamientos Genéticos , Drosophila/crecimiento & desarrollo , Elementos de Facilitación Genéticos , Ojo/crecimiento & desarrollo , Femenino , Genes Dominantes , Genes Letales , Genes Supresores , Prueba de Complementación Genética , Ligamiento Genético , Masculino , Mamíferos , Mutagénesis , Fenotipo , Cromosoma X , Proteínas ras/genéticaRESUMEN
Protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine phosphatase present in most tissues and cell types, has been implicated in the regulation of cell cycle progression, DNA replication, transcription, and translation. Here we present genetic evidence suggesting that PP2A functions downstream of Ras1 in the Sevenless receptor tyrosine kinase (RTK) signal transduction pathway that specifies R7 photoreceptor cell fate in the developing Drosophila eye. Ras1 and downstream cytoplasmic kinases, Raf, MEK, and MAPK, comprise an evolutionarily conserved cascade that mediates the transmission of signals from RTKs at the plasma membrane to specific factors in the nucleus. Using transgenic flies expressing constitutively activated Ras1 or Raf proteins that function independently of upstream signaling events, we show that a reduction in the dose of the gene encoding the catalytic subunit of PP2A stimulates signaling from Ras1 but impairs signaling from Raf. This suggests that PP2A both negatively and positively regulates the Ras1 cascade by dephosphorylating factors that function at different steps in the cascade.
Asunto(s)
Proteínas de Drosophila , Drosophila/crecimiento & desarrollo , Fosfoproteínas Fosfatasas/fisiología , Células Fotorreceptoras de Invertebrados/crecimiento & desarrollo , Transducción de Señal/fisiología , Proteínas ras/fisiología , Animales , Animales Modificados Genéticamente , Ojo/citología , Proteínas del Ojo/fisiología , Femenino , Genes de Insecto , Masculino , Glicoproteínas de Membrana/fisiología , Mutación , Fosfoproteínas Fosfatasas/genética , Células Fotorreceptoras de Invertebrados/enzimología , Proteína Fosfatasa 2 , Proteínas Serina-Treonina Quinasas/fisiología , Proteínas Proto-Oncogénicas/fisiología , Proteínas Proto-Oncogénicas c-raf , Proteínas Tirosina Quinasas Receptoras/fisiologíaRESUMEN
We have identified and characterized two genes in Drosophila whose products are required for activated RAS to signal with normal efficiency, but do not appear to effect signaling by activated RAF. One encodes the beta subunit of type I geranylgeranyl transferase, a prenylation enzyme essential for targeting RAS to the plasma membrane. The other encodes a protein kinase that we have named kinase suppressor of ras (ksr). By genetic criteria, we show that KSR functions in multiple receptor tyrosine kinase pathways. We have isolated mammalian homologs of KSR that, together with the Drosophila gene, define a novel class of kinases. Our results suggest that KSR is a general and evolutionarily conserved component of the RAS signaling pathway that acts between RAS and RAF.
Asunto(s)
Proteínas de Drosophila , Genes Supresores/genética , Proteínas Quinasas/genética , Transducción de Señal/fisiología , Transferasas/genética , Proteínas ras/fisiología , Secuencia de Aminoácidos , Animales , Mapeo Cromosómico , Clonación Molecular , Drosophila melanogaster/embriología , Drosophila melanogaster/enzimología , Drosophila melanogaster/genética , Femenino , Genes de Insecto/genética , Humanos , Datos de Secuencia Molecular , Células Fotorreceptoras de Invertebrados/crecimiento & desarrollo , Polimorfismo de Longitud del Fragmento de Restricción , Proteínas Quinasas/fisiología , Proteínas Serina-Treonina Quinasas/fisiología , Proteínas Tirosina Quinasas/fisiología , Proteínas Proto-Oncogénicas/fisiología , Proteínas Proto-Oncogénicas c-raf , Proteínas Tirosina Quinasas Receptoras/fisiología , Homología de Secuencia de AminoácidoRESUMEN
During Drosophila eye development, a Ras cascade mediates the decision between neuronal and non-neuronal differentiation of the R7 photoreceptor precursor. Recent genetic and molecular studies have identified a set of protein kinases as components of the Ras cascade and nuclear targets of the cascade, including Yan, Pointed, Jun, and Phyllopod. The Ras cascade functions in other Drosophila signal transduction pathways, eliciting a distinct response in each case, presumably through phosphorylation of specific transcription factors.
Asunto(s)
Proteínas de Drosophila , Drosophila/metabolismo , Proteínas Tirosina Quinasas Receptoras , Transducción de Señal , Proteínas ras/metabolismo , Animales , Drosophila/crecimiento & desarrollo , Ojo/crecimiento & desarrollo , Proteínas del Ojo/metabolismo , Genes ras , Glicoproteínas de Membrana/metabolismo , Células Fotorreceptoras de Invertebrados/metabolismo , Proteínas Quinasas/metabolismoRESUMEN
phyllopod (phyl) encodes a novel protein required for fate determination of photoreceptors R1, R6, and R7, the last three photoreceptors to be recruited into the ommatidia of the developing Drosophila eye. Genetic data suggests that phyl acts downstream of Ras1, raf, and yan to promote neuronal differentiation in this subset of photoreceptors. Ectopic expression of phyl in the cone cell precursors mimics the effect of ectopic activation of Ras1, suggesting that phyl expression is regulated by Ras1. phyl is also required for embryonic nervous system and sensory bristle development.