Novel Strategy to Isolate Invasion-Inducing Proteins From Human Breast Tumors

摘要

Retroviral-based expression libraries have been developed from breast tumor cells, and then screened for cDNAs whose expression confers an invasive phenotype on non-invasive breast tumor cells. Four independent cDNAs have been recovered and restested in these- screens (DAP-l, LIPE, HSPA5, ABLIM). The Dap-l cDNA was orientated in the antisense and is by far the most invasive of the four. When tested in other cell types, only the Dap-l cDNA exhibited transforming properties. Since Dap-l has been attributed tumor suppressor properties in other biological systems, it was selected for a more detailed analysis. Anti-sense expression of DAP-l was associated with activation of the small GTPase RhoA in NIH 3T3 cells, but-downregulation of RhoA in MCF-7 cells. No effects were noted for Raci or Cdc42, or when DAP-l was expressed in the sense orientation. Analysis of the actin cytoskeleton of MCF-7 cells in which DAP-l is suppressed revealed a phenotype that is consistent with loss of RhoA function, and the motile phenotype could be suppressed by expression of activated RhoA. To summarize, we have identified DAP-l as a tumor suppressor in breast cancer cells that can regulate motility and invasion through regulation of the small GTPase RhoA.