RESUMEN
Integrin receptors and their extracellular matrix ligands provide cues to cell proliferation, survival, differentiation and migration. Here, we show that alpha2beta1 integrin, when ligated to the basement membrane component laminin-1, triggers a proliferation arrest in primary endothelial cells. Indeed, in the presence of strong growth signals supplied by growth factors and fibronectin, alpha2beta1 engagement alters assembly of mature focal adhesions by alpha5beta1 and leads to impairment of downstream signaling and cell-cycle arrest in the G1 phase. Although the capacity of alpha5beta1 to signal for GTP loading of Rac is preserved, the joint engagement of alpha2beta1 interferes with membrane anchorage of Rac. Adapting the 'split-ubiquitin' sensor to screen for membrane-proximal alpha2 integrin partners, we identified the CD9 tetraspanin and further establish its requirement for destabilization of focal adhesions, control of Rac subcellular localization and growth arrest induced by alpha2beta1 integrin. Altogether, our data establish that alpha2beta1 integrin controls endothelial cell commitment towards quiescence by triggering a CD9-dependent dominant signaling.
Asunto(s)
Antígenos CD/metabolismo , Células Endoteliales/metabolismo , Integrina alfa2beta1/metabolismo , Laminina/farmacología , Glicoproteínas de Membrana/metabolismo , Proteínas de Unión al GTP rac/metabolismo , Animales , Antígenos CD/genética , Proliferación Celular/efectos de los fármacos , Células Cultivadas , Células Endoteliales/efectos de los fármacos , Células Endoteliales/patología , Femenino , Factor 2 de Crecimiento de Fibroblastos/farmacología , Fibronectinas/farmacología , Adhesiones Focales/genética , Adhesiones Focales/metabolismo , Humanos , Integrina alfa2beta1/agonistas , Integrina alfa5beta1/agonistas , Integrina alfa5beta1/metabolismo , Glicoproteínas de Membrana/genética , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Neovascularización Fisiológica/efectos de los fármacos , Neovascularización Fisiológica/genética , Transporte de Proteínas/efectos de los fármacos , Transporte de Proteínas/genética , ARN Interferente Pequeño/genética , Transducción de Señal/efectos de los fármacos , Tetraspanina 29RESUMEN
In melanocytes and melanoma cells alpha-melanocyte stimulating hormone (alpha-MSH), via the cAMP pathway, elicits a large array of biological responses that control melanocyte differentiation and influence melanoma development or susceptibility. In this work, we show that cAMP transcriptionally activates Hif1a gene in a melanocyte cell-specific manner and increases the expression of a functional hypoxia-inducible factor 1alpha (HIF1alpha) protein resulting in a stimulation of Vegf expression. Interestingly, we report that the melanocyte-specific transcription factor, microphthalmia-associated transcription factor (MITF), binds to the Hif1a promoter and strongly stimulates its transcriptional activity. Further, MITF "silencing" abrogates the cAMP effect on Hif1a expression, and overexpression of MITF in human melanoma cells is sufficient to stimulate HIF1A mRNA. Our data demonstrate that Hif1a is a new MITF target gene and that MITF mediates the cAMP stimulation of Hif1a in melanocytes and melanoma cells. Importantly, we provide results demonstrating that HIF1 plays a pro-survival role in this cell system. We therefore conclude that the alpha-MSH/cAMP pathway, using MITF as a signal transducer and HIF1alpha as a target, might contribute to melanoma progression.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Melanocitos/metabolismo , Melanoma/metabolismo , Factores de Transcripción/metabolismo , Animales , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/fisiología , AMP Cíclico/metabolismo , AMP Cíclico/farmacología , Proteínas de Unión al ADN/genética , Progresión de la Enfermedad , Regulación Neoplásica de la Expresión Génica/genética , Genes Reguladores/genética , Humanos , Subunidad alfa del Factor 1 Inducible por Hipoxia , Melanocitos/citología , Melanocitos/efectos de los fármacos , Melanoma/genética , Ratones , Factor de Transcripción Asociado a Microftalmía , Células 3T3 NIH , Regiones Promotoras Genéticas/fisiología , Interferencia de ARN/efectos de los fármacos , Interferencia de ARN/fisiología , ARN Mensajero/genética , ARN Mensajero/metabolismo , Transducción de Señal/fisiología , Factores de Transcripción/genética , Activación Transcripcional/efectos de los fármacos , Activación Transcripcional/fisiología , Células Tumorales Cultivadas , Factor A de Crecimiento Endotelial Vascular/genética , alfa-MSH/metabolismoRESUMEN
Chronic sun exposure can lead to severe skin disorders such as carcinogenesis. The cell death process triggered by ultraviolet B (UVB) irradiation is crucial because it protects the surrounding tissue from the emergence and the accumulation of cells that bear the risk of becoming transformed. Here, we show that repression of NF-kappaB and Egr-1 expression drastically inhibits UVB-mediated cell death. Furthermore, we demonstrate that Egr-1 is induced upon UVB irradiation through NF-kappaB activation and the binding of p65/RelA within the Egr-1 promoter. We show that Egr-1 contributes to the regulation of the Gadd45a and Gadd45b genes, which are involved in the control of cell cycle, DNA repair and apoptosis, by direct binding to their promoter. Our study demonstrates for the first time a signaling cascade involving sequential activation of NF-kappaB, Egr-1 and Gadd45 to induce UVB-mediated cell death. Failure in the induction of each protagonist of this pathway alters the UVB-mediated cell death process. Therefore, impairment of the cascade could be at the onset of skin carcinogenesis mediated by genotoxic stress.