Certain chymotrypsin-like protease inhibitors such as TPCK exhibit a well described anti-tumorigenic activity by an as yet undescribed mechanism. One potential cellular target for TPCK in transformed cells is the ms-inducible NF-kappa B family of transcription factors. We therefore used TPCK to examine the physiologic role of NF-kappa B during Ha-ras induced transformation, independent of another major downstream effector of Ha-ras, AP-1. Using a conditionally transformed NIH3T3 cell line, we found that TPCK (but not the control inhibitor TLME) inhibited the anchorage-independent growth of Ha-ras transformed cells, but not their anchorage-dependent growth on plastic tissue culture dishes. Likewise, TPCK reduced the ability of Ha-ras to stimulate DNA synthesis in growth factor depleted cells, but not the ability of serum to stimulate DNA synthesis in the same growth factor depleted cells. Gel shift analysis and reporter gene expression indicated that TPCK blocked Ha-ras-induced NF-kappa B activity, while only having minimal effects on Ha-ras-induced AP-1 activity. TPCK is therefore able to Inhibit the Ha-ras transformed phenotype of cells by inhibiting the transcriptional activity of NF-kappa B, while having little effect upon transcriptional activity of AP-1.

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