Akt1 was revealed to interact with Ki-Ras in the cytoplasm of Ki-Ras-transformed human prostate epithelial cells, 267B1/K-ras. Moreover, p65/RelA in the nucleus was found to interact with both Ki-Ras and Akt1, suggesting the nuclear translocation of Akt1:Ki-Ras complex for NF- kappa B activation. In support of this, compared with wild type Akt1, the dominant negative Akt1 mutant was decreased in its nuclear expression, reducing the Ki-Ras-induced NF-kappa B transcriptional activation. Moreover, inhibitors of Ras (sulindac sulfide and farnesyltransferase inhibitor I) or PI3K/Akt (wortmannin), reduced the amounts of Akt1 and Ki-Ras in the nucleus as well as partial NF-kappa B activity. The complete inhibition of Ki-Ras-induced NF-kappa B activation, however, could only be obtained by combined treatment with wortmannin and proteasome inhibitor-1. Accordingly, clonogenic assay showed Akt1 contribution to I kappa B alpha-mediated NF-kappa B activation for oncogenic cell growth by Ki-Ras. Our data suggest a crucial role of Ki-Ras:Akt1 complex in NF-kappa B transcriptional activation and enhancement of cell survival. (C) 2007 Elsevier Inc. All rights reserved.