RESUMO
Ligand-receptor complexes formed at the plasma membrane are internalised via various endocytic pathways that influence the ultimate signalling output by regulating the selection of interaction partners by the complex along the trafficking route. We report that, in differentiated cells, activin A-receptor complexes are internalised via clathrin-mediated endocytosis (CME) and macropinocytosis (MP), whereas in human embryonic stem cells (hESCs) internalisation occurs via CME. We further show that hESCs are devoid of MP, which becomes functional upon differentiation towards endothelial cells through mesoderm mediators. Our results reveal, for the first time, that MP is an internalisation route for activin A in differentiated cells, and that MP is not active in hESCs and is induced as cells differentiate.
Assuntos
Ativinas , Células Endoteliais , Diferenciação Celular , Células-Tronco Embrionárias , Endocitose , HumanosRESUMO
This study examines the degree of convergence in health care expenditures among the US states from 1980 to 2004. Our results suggest that the US states form two clubs with specific geographical characteristics that converge to different equilibria. We also extend our analysis to investigate the cross-state disparities in nine major components of health expenditures. Our findings provide evidence for full convergence for only two components, namely 'physician and other professional services' and 'home health care'. However, for the remaining components, we can still identify various convergence clubs.
Assuntos
Economia Médica/estatística & dados numéricos , Gastos em Saúde/estatística & dados numéricos , Serviços de Saúde/estatística & dados numéricos , Serviços de Saúde/economia , Humanos , Estados UnidosRESUMO
SARA, an early endosomal protein, plays a key role in TGFß signalling, as it presents SMAD2 and SMAD3 for phosphorylation by the activated TGFß receptors. Here, we show that ERBIN is a new SARA-interacting protein that can be recruited by SARA to early endosomes. ERBIN was recently shown to bind and segregate phosphorylated SMAD2 and SMAD3 (SMAD2/3) in the cytoplasm, thereby inhibiting SMAD2/3-dependent transcription. SARA binds to ERBIN using a new domain, which we have called the ERBID (ERBIN-binding domain), whereas ERBIN binds to SARA using a domain (amino acids 1208-1265) that also interacts with SMAD2 and SMAD3, which we have called the SSID (SARA- and SMAD-interacting domain). We additionally show that SARA competes with SMAD2/3 for binding to ERBIN. In agreement, overexpression of SARA or the ERBID peptide reverses the inhibitory effect of ERBIN on SMAD2/3-dependent transcription. Taken together, these data suggest that the response of cells to TGFß and activin A can be influenced by the relative concentrations of SARA, ERBIN and SMAD2/3.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Serina Endopeptidases/metabolismo , Proteína Smad2/metabolismo , Proteína Smad3/metabolismo , Ativinas/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/genética , Animais , Linhagem Celular , Núcleo Celular/metabolismo , Genes Reporter , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/química , Peptídeos e Proteínas de Sinalização Intracelular/genética , Luciferases de Renilla/biossíntese , Luciferases de Renilla/genética , Camundongos , Fragmentos de Peptídeos/metabolismo , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Transporte Proteico , Interferência de RNA , Elementos de Resposta , Serina Endopeptidases/química , Serina Endopeptidases/genética , Ativação Transcricional , Fator de Crescimento Transformador beta/metabolismoRESUMO
Vascular endothelial growth factor (VEGF) is a key angiogenic factor that regulates proliferation and migration of endothelial cells via phosphorylation of extracellular signal-regulated kinase-1/2 (ERK1/2) and p38, respectively. Here, we demonstrate that VEGF strongly induces the transcription of two dual-specificity phosphatase (DUSP) genes DUSP1 and DUSP5 in endothelial cells. Using fluorescence microscopy, fluorescence lifetime imaging (FLIM), and fluorescence cross-correlation spectroscopy (FCCS), we found that DUSP1/mitogen-activated protein kinases phosphatase-1 (MKP-1) was localized in both the nucleus and cytoplasm of endothelial cells, where it existed in complex with p38 (effective dissociation constant, K(D)(eff), values of 294 and 197 nM, respectively), whereas DUSP5 was localized in the nucleus of endothelial cells in complex with ERK1/2 (K(D)(eff) 345 nM). VEGF administration affected differentially the K(D)(eff) values of the DUSP1/p38 and DUSP5/ERK1/2 complexes. Gain-of-function and lack-of-function approaches revealed that DUSP1/MKP-1 dephosphorylates primarily VEGF-phosphorylated p38, thereby inhibiting endothelial cell migration, whereas DUSP5 dephosphorylates VEGF-phosphorylated ERK1/2 inhibiting proliferation of endothelial cells. Moreover, DUSP5 exhibited considerable nuclear anchoring activity on ERK1/2 in the nucleus, thereby diminishing ERK1/2 export to the cytoplasm decreasing its further availability for activation.
Assuntos
Células Endoteliais/citologia , Células Endoteliais/enzimologia , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Homeostase , Fosfatases da Proteína Quinase Ativada por Mitógeno/metabolismo , Fator A de Crescimento do Endotélio Vascular/metabolismo , Movimento Celular/fisiologia , Núcleo Celular/efeitos dos fármacos , Núcleo Celular/metabolismo , Proliferação de Células , Células Cultivadas , Interações Medicamentosas , Fosfatase 1 de Especificidade Dupla/genética , Fosfatase 1 de Especificidade Dupla/metabolismo , Fosfatases de Especificidade Dupla/genética , Fosfatases de Especificidade Dupla/metabolismo , Humanos , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Fosforilação , Distribuição Tecidual , Transcrição Gênica/fisiologia , Veias Umbilicais/citologia , Regulação para Cima/fisiologia , Fator A de Crescimento do Endotélio Vascular/farmacologia , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismoRESUMO
The tumor suppressor function of activin A, together with our findings that activin A is an inhibitor of angiogenesis, which is down-regulated by the N-MYC oncogene, prompted us to investigate in more detail its role in the malignant transformation process of neuroblastomas. Indeed, neuroblastoma cells with restored activin A expression exhibited a diminished proliferation rate and formed smaller xenograft tumors with reduced vascularity, whereas lung metastasis rate remained unchanged. In agreement with the decreased vascularity of the xenograft tumors, activin A inhibited several crucial angiogenic responses of cultured endothelial cells, such as proteolytic activity, migration, and proliferation. Endothelial cell proliferation, activin A, or its constitutively active activin receptor-like kinase 4 receptor (ALK4T206D), increased the expression of CDKN1A (p21), CDKN2B (p15), and CDKN1B (p27) CDK inhibitors and down-regulated the expression of vascular endothelial growth factor receptor-2, the receptor of a key angiogenic factor in cancer. The constitutively active forms of SMAD2 and SMAD3 were both capable of inhibiting endothelial cell proliferation, whereas the dominant-negative forms of SMAD3 and SMAD4 released the inhibitory effect of activin A on endothelial cell proliferation by only 20%. Thus, the effects of activin A on endothelial cell proliferation seem to be conveyed via the ALK4/SMAD2-SMAD3 pathways, however, non-SMAD cascades may also contribute. These results provide novel information regarding the role of activin A in the malignant transformation process of neuroblastomas and the molecular mechanisms involved in regulating angiogenesis thereof.
Assuntos
Ativinas/uso terapêutico , Inibidores da Angiogênese/uso terapêutico , Antineoplásicos/uso terapêutico , Células Endoteliais/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica , Subunidades beta de Inibinas/uso terapêutico , Neuroblastoma/prevenção & controle , Transdução de Sinais , Receptores de Ativinas/metabolismo , Animais , Proteínas de Ciclo Celular/metabolismo , Movimento Celular/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Inibidor de Quinase Dependente de Ciclina p15 , Inibidor de Quinase Dependente de Ciclina p21 , Inibidor de Quinase Dependente de Ciclina p27 , Proteínas de Ligação a DNA/metabolismo , Células Endoteliais/metabolismo , Feminino , Humanos , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Nus , Neovascularização Patológica , Neuroblastoma/metabolismo , Neuroblastoma/patologia , Proteína Smad2 , Proteína Smad3 , Transativadores/metabolismo , Células Tumorais Cultivadas , Proteínas Supressoras de Tumor/metabolismo , Receptor 2 de Fatores de Crescimento do Endotélio Vascular/metabolismo , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Transforming growth factor beta (TGFbeta) receptors require SARA for phosphorylation of the downstream transducing Smad proteins. SARA, a FYVE finger protein, binds to membrane lipids suggesting that activated receptors may interact with downstream signaling molecules at discrete endocytic locations. In the present study, we reveal a critical role for the early endocytic compartment in regulating Smad-dependent signaling. Not only is SARA localized on early endosomes, but also its minimal FYVE finger sequence is sufficient for early endosomal targeting. Expression of a SARA mutant protein lacking the FYVE finger inhibits downstream activin A signaling in endothelial cells. Moreover, a dominant-negative mutant of Rab5, a crucial protein for early endosome dynamics, causes phosphorylation and nuclear translocation of Smads leading to constitutive (i.e. ligand independent) transcriptional activation of a Smad-dependent promoter in endothelial cells. As inhibition of endocytosis using the K44A negative mutant of dynamin and RN-tre did not lead to activation of Smad-dependent transcription, the effects of the dominant-negative Rab5 are likely to be a consequence of altered membrane trafficking of constitutively formed TGFbeta/activin type I/II receptor complexes at the level of early endosomes. The results suggest an important interconnection between early endosomal dynamics and TGFbeta/activin signal transduction pathways.