RESUMEN
We have previously cloned a type I serine/threonine kinase receptor from Xenopus, namely XTrR-I. We show here that XTrR-I is able to bind and mediate the activity of TGFbeta1, but is unable to mediate response to activin or BMP-4. We have made a truncated receptor construct that can act as a dominant negative mutant receptor, and this can block the activity of TGFbeta2 but not that of activin. Overexpression of either the full-length or truncated receptor has a drastic effect on mesoderm differentiation. The truncated receptor inhibits expression of notochord and muscle in mesodermalised animal caps, while the full-length receptor greatly increases the amount of notochord. In addition, the truncated receptor blocks the axis duplicating activity of both siamois and Xwnt8. We conclude that XTrR-I is involved in mediating a dorsalising activity important for mesoderm differentiation.
Asunto(s)
Tipificación del Cuerpo/fisiología , Receptores de Factores de Crecimiento Transformadores beta/metabolismo , Activinas , Animales , Proteína Morfogenética Ósea 4 , Proteínas Morfogenéticas Óseas/metabolismo , Embrión no Mamífero/química , Embrión no Mamífero/efectos de los fármacos , Embrión no Mamífero/fisiología , Eliminación de Gen , Expresión Génica , Regulación del Desarrollo de la Expresión Génica , Inhibinas/metabolismo , Mesodermo/química , Mesodermo/efectos de los fármacos , Músculos/efectos de los fármacos , Músculos/embriología , Mutación , Notocorda/efectos de los fármacos , Notocorda/embriología , ARN Mensajero/genética , ARN Mensajero/farmacología , Receptores de Factores de Crecimiento Transformadores beta/genética , Factor de Crecimiento Transformador beta/farmacología , Xenopus , Proteínas de XenopusRESUMEN
Transforming growth factor beta (TGF-beta) and activin bind to receptor complexes that contain two distantly related transmembrane serine/threonine kinases known as receptor types I and II. The type II receptors determine ligand binding specificity, and each interacts with a distinct repertoire of type I receptors. Here we identify a new type I receptor for activin, ActR-IB, whose kinase domain is nearly identical to that of the recently cloned TGF-beta type I receptor, T beta R-I. ActR-IB has the structural and binding properties of a type I receptor: it binds activin only in the presence of an activin type II receptor and forms a heteromeric noncovalent complex with activin type II receptors. In Mv1Lu lung epithelial cells, ActR-IB and T beta R-I signal a common set of growth-inhibitory and transcriptional responses in association with their corresponding ligands and type II receptors. The transcriptional responses include elevated expression of fibronectin and plasminogen activator inhibitor 1. Although T beta R-I and ActR-IB are nearly identical in their kinase domains (90% amino acid sequence identity), their corresponding type II receptor kinase domains are very different from each other (42% amino acid sequence identity). Therefore, signaling of a specific set of responses by TGF-beta and activin correlates with the presence of similar type I kinases in their complex. Indeed, other TGF-beta and activin type I receptors (TSR-I and ActR-I) whose kinase domains significantly diverge from those of T beta R-I and ActR-IB do not substitute as mediators of these growth-inhibitory and extracellular matrix transcriptional responses. Hence, we conclude that the type I receptor subunits are primary specifiers of signals sent by TGF-beta and activin receptor complexes.
Asunto(s)
División Celular/fisiología , Expresión Génica/efectos de los fármacos , Inhibinas/farmacología , Receptores de Factores de Crecimiento/fisiología , Receptores de Factores de Crecimiento Transformadores beta/metabolismo , Factor de Crecimiento Transformador beta/farmacología , Receptores de Activinas , Receptores de Activinas Tipo I , Activinas , Secuencia de Aminoácidos , Animales , Secuencia de Bases , División Celular/efectos de los fármacos , Línea Celular , Chlorocebus aethiops , Cartilla de ADN , ADN Complementario/aislamiento & purificación , ADN Complementario/metabolismo , Humanos , Inhibinas/metabolismo , Riñón , Luciferasas/biosíntesis , Luciferasas/metabolismo , Pulmón , Visón , Datos de Secuencia Molecular , Mutagénesis , Reacción en Cadena de la Polimerasa , Receptores de Factores de Crecimiento/biosíntesis , Receptores de Factores de Crecimiento/metabolismo , Receptores de Factores de Crecimiento Transformadores beta/biosíntesis , Homología de Secuencia de Aminoácido , Porcinos , Transcripción Genética/efectos de los fármacos , Transcripción Genética/fisiología , Transfección , Factor de Crecimiento Transformador beta/metabolismoRESUMEN
Transforming growth factor beta (TGF beta) and activin each bind to pairs of membrane proteins, known as receptor types I and II, that associate to form a signaling complex. We report that TSR-I and ActR-I, two human transmembrane serine/threonine kinases distantly related to TGF beta and activin type II receptors, act as type I receptors for these factors. TSR-I is a type I receptor shared by TGF beta and activin, whereas ActR-I is an activin type I receptor. ActR-I, but not TSR-I, signals a particular transcriptional response in concert with activin type II receptors. The results indicate that type I receptors are transmembrane protein kinases that associate with type II receptors to generate diverse heteromeric serine/threonine kinase complexes of different signaling capacities.
Asunto(s)
Inhibinas/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Receptores de Superficie Celular/metabolismo , Receptores de Factores de Crecimiento/metabolismo , Receptores de Factores de Crecimiento Transformadores beta/metabolismo , Factor de Crecimiento Transformador beta/metabolismo , Receptores de Activinas , Activinas , Clonación Molecular , Cartilla de ADN/química , ADN Complementario/genética , Regulación de la Expresión Génica , Humanos , Ligandos , Sustancias Macromoleculares , Datos de Secuencia Molecular , ARN Mensajero/genética , Receptores de Factores de Crecimiento/química , Receptores de Factores de Crecimiento Transformadores beta/química , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Transducción de Señal , Especificidad de la EspecieRESUMEN
This chapter has described some of the most salient features of the biology of the TGF-beta s. The TGF-beta s are of great interest as growth inhibitors, regulators of cell phenotype and regulators of cell adhesion. The various TGF-beta isoforms are highly conserved and display a complex pattern of interactions with multiple membrane receptor components. Activation of these receptors leads to inhibition of epithelial cell proliferation by a mechanism that may involve proteins related to the growth suppressor, RB. TGF-beta receptors are also coupled to mechanisms that control expression of differentiation commitment genes and differentiated cell functions. TGF-beta can affect cell proliferation and differentiation through indirect mechanisms involving regulation of expression of cytokines, extracellular matrix molecules and their respective receptors. These responses strongly influence the growth and phenotype of an array of cell types. Excess or reduced TGF-beta activity may contribute to the pathogenesis of certain fibrotic disorders and certain hyperproliferative disorders including cancer, respectively.
Asunto(s)
Diferenciación Celular/fisiología , División Celular/fisiología , Proteínas Quinasas/fisiología , Proteína de Retinoblastoma/fisiología , Factor de Crecimiento Transformador beta/fisiología , Inhibidores de Crecimiento/fisiología , Humanos , Neoplasias/genética , Unión Proteica , Transducción de Señal/genética , Factor de Crecimiento Transformador beta/químicaRESUMEN
The growth-suppressive function of the retinoblastoma susceptibility gene product, RB, has been implicated in the mediation of growth inhibition and negative regulation of certain proliferation related genes by transforming growth factor-beta 1 (TGF-beta 1). Early gene responses to TGF-beta 1 were examined in order to determine their dependence on the cell cycle and on the growth-suppressive function of RB. TGF-beta 1, which rapidly elevates the steady-state level of junB and PAI-1 mRNAs and decreases that of c-myc mRNA, induces these responses in S-phase populations of Mv1Lu lung epithelial cells containing RB in a phosphorylated state. Since in this state RB is presumed to lack growth-suppressive activity, the response to TGF-beta 1 was also examined in DU145 human prostate carcinoma cells whose mutant RB product lacks growth-suppressive function. In these cells, TGF-beta 1 also decreases c-myc expression at the transcription initiation level. These results suggests that the c-myc, junB, and PAI-1 responses to TGF-beta 1 are not restricted to the G1 phase of the cell cycle and that down-regulation of c-myc expression by TGF-beta 1 can occur through a mechanism independent from the growth-suppressive function of RB.
Asunto(s)
Ciclo Celular/efectos de los fármacos , Regulación hacia Abajo/efectos de los fármacos , Genes de Retinoblastoma , Proteína de Retinoblastoma/fisiología , Transcripción Genética/efectos de los fármacos , Factor de Crecimiento Transformador beta/farmacología , Animales , Northern Blotting , Línea Celular , Humanos , Cinética , Visón , Mutación/genética , Proteína Oncogénica p65(gag-jun)/genética , Inactivadores Plasminogénicos , Proteínas Proto-Oncogénicas c-myc/genética , Células Tumorales CultivadasRESUMEN
Selection of mutant Mv1Lu mink lung epithelial cells resistant to growth inhibition by transforming growth factor-beta (TGF-beta) has led to the isolation of cell clones with distinct alterations in type I and II TGF-beta receptors. Certain mutant clones present a decreased number or complete loss of detectable type I receptor. Other clones show a loss and/or altered electrophoretic mobility of the type II receptor, with concomitant loss of the type I receptor. Using somatic cell hybridization analysis we demonstrate the recessive nature of these mutants with respect to the wild-type phenotype and define various mutant complementation groups. Among these, hybrids between cells that express only type II receptor (R mutants) and cells that express neither receptor type (DRa mutants) rescue wild-type expression of type I receptors. Moreover, these hybrids regain full responsiveness to TGF-beta 1, as measured by inhibition of DNA synthesis as well as stimulation of fibronectin and plasminogen activator inhibitor-1 production. These results provide evidence for an interaction between TGF-beta receptor components I and II and show that, in Mv1Lu cells, expression of both receptor types is required for mediation of biological responses to TGF-beta 1.
Asunto(s)
Receptores de Superficie Celular/fisiología , Factor de Crecimiento Transformador beta/fisiología , Animales , División Celular/efectos de los fármacos , Línea Celular , Fibronectinas/metabolismo , Genes Recesivos , Prueba de Complementación Genética , Células Híbridas , Técnicas In Vitro , Visón , Inactivadores Plasminogénicos/metabolismo , Receptores de Factores de Crecimiento Transformadores beta , Transducción de Señal , Factor de Crecimiento Transformador beta/farmacologíaRESUMEN
The addition of gangliosides to tissue culture cells causes a decrease in the tyrosine protein kinase activity of the epidermal growth factor (EGF) receptor and an inhibition of EGF-stimulated growth. Based on these data, the hypothesis that the EGF receptor is physiologically regulated by gangliosides has been proposed by E.G. Bremer, J. Schlessinger, and S. Hakomori (J. Biol. Chem. (1986) 261, 2434-2440). To test this hypothesis, a mutant Chinese hamster ovary cell line (clone Idl D) that has a reversible defect in the biosynthesis of gangliosides (Kingsley, D.M., Kozarsky, K. F., Hobbie, L., and Krieger, M. (1986) Cell 44, 749-759) was investigated. The human EGF receptor cDNA was expressed in the mutant cells, and the properties of the EGF receptor were examined using cells grown under permissive and nonpermissive conditions. Changes in ganglioside expression were not observed to cause any significant alterations in the affinity or number of EGF receptors detected at the cell surface. However, decreased levels of ganglioside expression were associated with 1) increased EGF receptor autophosphorylation on tyrosine residues, and 2) increased EGF-stimulated cellular proliferation. The inverse correlation observed between the level of ganglioside expression and signal transduction by the EGF receptor is consistent with the hypothesis that the function of the EGF receptor is physiologically regulated by gangliosides.