RESUMO
The cytokine hepatocyte growth factor (HGF)/scatter factor-1 and its cognate receptor, Met, are involved in the etiology and progression of many types of cancer. Despite recent advances in understanding the signal transduction pathways activated by HGF, the mechanism by which HGF exerts its tumorigenic effect is not well understood. To identify proteins that may be involved in mediating HGF-induced cell motility, invasiveness, and tumorigenesis, we used two separate differential display screening methods to identify changes in gene expression that are initiated by HGF in an epithelial cell culture system. Among several known and unknown genes whose expression was modified, osteopontin (OPN), a protein previously associated with tumorigenesis, was found to be upregulated within 6 h following HGF stimulation. OPN expression was dependent on activation of the PI-3 kinase pathway. Autocrine secretion of HGF resulted in sustained expression of OPN. Downregulation of opn expression by stable antisense transfection attenuated OPN expression and repressed HGF-induced invasiveness in vitro and decreased HGF-mediated tumor growth and metastasis formation in vivo. Constitutive expression of OPN in itself exerted partial invasiveness in vitro, but its expression itself was not sufficient to initiate tumor growth or metastasis formation in vivo. Thus, together with other molecules, OPN activity contributes to HGF-induced tumor growth and invasiveness.
Assuntos
Fator de Crescimento de Hepatócito/metabolismo , Metástase Neoplásica , Neoplasias/metabolismo , Neoplasias/patologia , Sialoglicoproteínas/metabolismo , Transdução de Sinais , Animais , Linhagem Celular , Ativação Enzimática , Inibidores Enzimáticos/metabolismo , Células Epiteliais/citologia , Células Epiteliais/metabolismo , Perfilação da Expressão Gênica , Regulação da Expressão Gênica , Hepatócitos/citologia , Hepatócitos/metabolismo , Humanos , Camundongos , Osteopontina , Fosfatidilinositol 3-Quinases/metabolismo , Proteínas Proto-Oncogênicas c-met/metabolismo , Sialoglicoproteínas/genéticaRESUMO
Sendai virus P/C mRNA, human erythrocyte membrane protein 4.1 mRNA and PDGF-B chain mRNA were used to test whether translation initiation from non-AUG codons in COS1 cells was mRNA species dependent. Site-directed mutants of the authentic translation start sites of these mRNAs to alternate start codons showed that while P/C mRNA is capable of initiating translation from non-AUG start sites the other two mRNAs are not. Our study shows that translation initiation from non-AUG codons is mRNA species dependent and suggests that higher order structure of an mRNA determines the non-AUG translation start site.
