1445

The transcription factors, nuclear factor kappa B (NFκB) and β -catenin coordinate the expression of genes that control cell proliferation, survival, and transformation. Recently our laboratory has delineated a direct role of the phosphatidylinositol 3’ kinase (PI3K)/AKT and PTEN pathways in regulating the anti-apoptotic transcription factor NFκB. AKT and PTEN control the ability of IκBkinase (IKK) to phosphorylate and activate the p65 subunit of NFκB. In addition, our preliminary data from IKKα/β-null mouse embryo fibroblasts (MEFs) reveal that the IKKs in response the PI3K/AKT pathway also play a role in the regulation of β -catenin. β -catenin is a transcriptional regulator which, when bound to T cell factor (TCF) and lymphoid-enhancer factor (LEF), provides a potent transcriptional transactivation domain. Many colorectal cancer (CRC) cell lines and tissues demonstrate inappropriate constitutive activation of both NFκB and β -catenin transcriptional activities and maintenance of these activities seems to be necessary for CRC cell proliferation and resistance to apoptosis. Therefore, we investigated the effect of inhibiting the PI3K/AKT/IKK pathway in regulating the inappropriate constitutive transcriptional activation of both NFκB and β -catenin in CRC cell lines. The RKO CRC cells were engineered to inducibly express either wild type (WT) PTEN to inhibit PI3K/ AKT or kinase dead (KD) IKKα to inhibit IKK activation. Inducible expression of either WT PTEN or KD IKKα inhibited both the constitutive NFκB and β –catenin promoter activity in these cells. An affymetrix gene chip assay was also performed on these inducible cell lines, which revealed many potential CRC genes downregulated by both WT PTEN and KD IKKα. These included several EGF ligands, uPA, IL-8, VEGF and MMP’s. We decided to study the regulation of the PI3K/AKT/IKK pathway and its regulated genes in several CRC cell lines. Both RKO and SW480 CRC cell lines had the highest levels of activated AKT and several of the identified genes including EGF, TGFα, uPA. Activated AKT as well as levels of EGF Receptor and several of the identified genes are dramatically reduced following treatment with the PI3K inhibitor LY294002. Collectively this data indicates a novel role of the PI3K/ AKT/IKK pathway in regulating the inappropriate constitutive activation of both NFκB and β -catenin in colorectal cancer. We plan to further investigate the effect of inhibiting the PI3K/ AKT/IKK pathway on controlling the proliferation, survival, and metstatic potential of colorectal cancer cells using this model system.

[Proc Amer Assoc Cancer Res, Volume 45, 2004]