Ribozyme-Mediated Targeting of IκBγ Inhibits Melanoma Invasion and Metastasis

I kappa B gamma Is one member of a family of proteins that can inhibit the nuclear localization of nuclear factor-kappa B. However, the other specific functions of I kappa B gamma are still poorly understood, and its effects on tumor metastasis have not yet been characterized. We examined the consequences of targeting I kappa B gamma in melanoma cells using a hammerhead ribozyme. We developed stable transformant B16-F10 melanoma cell lines that express a ribozyme that targets mouse I kappa B gamma (I kappa B gamma-144-Rz). Tail-vein injection of B16-F10 cells that stably express I kappa B gamma-144-Rz into mice resulted in a significant reduction of the metastatic potential of these cells. I kappa B gamma-144-Rz-expressing B16 cells were shown to have increased transcriptional activity of nuclear factor-kappa B. We then showed that I kappa B gamma-144-Rz-expressing cells demonstrated both reduced invasion and increased apoptosis, suggesting the existence of pathways through which I kappa B gamma promotes melanoma metastasis. Using gene expression profiling, we identified a differentially expressed gene set that is regulated by the stable suppression of I kappa B gamma that may participate in mediating its anti-metastatic effects; we also confirmed the altered expression levels of several of these genes by quantitative real time polymerase chain reaction. Plasmid-mediated expression of I kappa B gamma-144-Rz produced a significant inhibition of the metastatic progression of B16-F10 cells to the lung and resulted in significant anti-invasive and proapoptotic effect's on murine Lewis lung carcinoma cells. Our results suggest a novel role for I kappa B gamma in promoting the metastatic progression of melanoma. (Am J Pathol 2009, 174:1009-1016; DOI: 10.2353/ajpath.2009,080207)