RESUMO
The Hepatocyte Growth Factor receptor transduces proliferating and scattering signals in epithelial and endothelial cells. We have explored potential interactions of the HGF/SF receptor beta-subunit (p145(beta MET)) with F-actin binding partners aiming to identify novel downstream effectors implicated in HGF/SF pluripotent signalling. Cortactin, a p80/85 F-actin binding protein, was found phosphorylated on tyrosine in response to HGF-SF in A431 human epidermoid carcinoma cells, expressing the HGF/SF receptor (c-MET). The HGF/SF receptor was enriched in the detergent-insoluble fraction and was found to co-precipitate with cortactin and to associate in vitro with cortactin. The Grb2 small adapter protein known to associate via its Src homology 2 domain (SH2) with the MET C-terminus, was also associated with cortactin. Transient transfection of A431 cells with dominant-negative Grb2 constructs has revealed that the Grb2-C-SH3 domain possesses a central role in cortactin phosphorylation in response to HGF/SF. Finally, tyrosine phosphorylation of cortactin was found uncoupled of endogenous c-Src kinase activity, thus further supporting the hypothesis that cortactin is a direct target of the MET kinase. We propose that cortactin may constitute a docking site for MET-derived signals within the cytoskeleton.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal , Fator de Crescimento de Hepatócito/metabolismo , Proteínas dos Microfilamentos/metabolismo , Proteínas Tirosina Quinases/metabolismo , Proteína Tirosina Quinase CSK , Fracionamento Celular , Cortactina , Citoesqueleto/metabolismo , Detergentes , Proteína Adaptadora GRB2 , Hepatócitos , Humanos , Octoxinol , Fosforilação , Proteínas/genética , Proteínas/metabolismo , Proteínas Proto-Oncogênicas c-met/metabolismo , Células Tumorais Cultivadas , Tirosina/metabolismo , Domínios de Homologia de src , Quinases da Família srcRESUMO
Hepatocyte growth factor (HGF) identical to scatter factor (SF) is a glycoprotein involved in the development of a number of cellular phenotypes, including proliferation, mitogenesis, formation of branching tubules and, in the case of tumour cells, invasion and metastasis. This fascinating cytokine transduces its activities via its receptor encoded by the c-met oncogene, coupled to a number of transducers integrating the HGF/SF signal to the cytosol and the nucleus. The downstream transducers coupled to HGF/MET, most of which participate in overlapping pathways, determine the development of the cell's phenotype, which in most cell types is dual.
