ABSTRACT
To discover novel metastasis suppressor genes that are clinically relevant in common human cancers, we used isogenic human bladder cancer cell lines and used DNA microarray technology to identify genes whose expression diminishes as a function of invasive and metastatic competence. We then evaluated the expression profile of such genes in 105 pathologically characterized tumors from seven common organ sites, and we identified one gene, RhoGDI2, whose expression was diminished as a function of primary tumor stage and grade. When RhoGDI2 was transferred back into cells with metastatic ability that lacked its expression, it suppressed experimental lung metastasis but did not affect in vitro growth, colony formation, or in vivo tumorigenicity. In addition, RhoGDI2 reconstitution in these cells blocked invasion in an organotypic assay and led to a reduction of in vitro motility. These results indicate that RhoGDI2 is a metastasis suppressor gene, a marker of aggressive human cancer, and a promising target for therapy.
Subject(s)
Adenocarcinoma/genetics , Genes, Tumor Suppressor , Guanine Nucleotide Dissociation Inhibitors/genetics , Tumor Suppressor Proteins/genetics , Urinary Bladder Neoplasms/genetics , Adenocarcinoma/metabolism , Adenocarcinoma/pathology , Gene Expression Profiling , Guanine Nucleotide Dissociation Inhibitors/biosynthesis , Humans , Neoplasm Invasiveness , Neoplasm Metastasis , RNA, Neoplasm/genetics , Transfection , Tumor Cells, Cultured , Tumor Suppressor Proteins/biosynthesis , Urinary Bladder Neoplasms/metabolism , Urinary Bladder Neoplasms/pathology , rho Guanine Nucleotide Dissociation Inhibitor beta , rho-Specific Guanine Nucleotide Dissociation InhibitorsABSTRACT
Tumor cell motility is one of the rate-limiting steps of invasion, which defines progression toward a more malignant phenotype. Elevated expression of epidermal growth factor (EGF) receptor in many cancers is associated with progression of superficial to invasive forms of the disease and is sometimes found in tumors that also have activating Ras mutations, suggesting that both events contribute to tumor invasion. Here we show that EGF stimulates motility in human tumor cell lines, which harbor activating Ha-RasV12 via a novel signal transduction pathway mediated by the small GTP-binding proteins RalA and RhoA but independent of Rac1 and Cdc42. On EGF stimulation, RalA localizes to the cell membrane. In addition, activation of RalA and expression of Rho were increased by EGF stimulation in both the nonmetastatic and metastatic variants of the same cell line. However, elevated levels of constitutively activated RalA were only found in the metastatic variant. This is the first demonstration of an essential role for Ral in EGF-mediated cell motility and its potential contribution to tumor metastasis in human cancer.
