Constitutive NF-κB Activation in Colorectal Carcinoma Plays a Key Role in Angiogenesis, Promoting Tumor Growth

Purpose: Nuclear factor kappa B (NF-kappa B) is an important transcription factor in various biological processes. Constitutive NF-kappa B activation has been noted in many tumors, including colorectal cancers. However, the precise role of this activation in colorectal cancer is unclear. Experimental Design: Constitutive NF-kappa B activation was evaluated in colorectal cancer tissues and cell lines. To inhibit NF-kappa B activation, we established cancer cells with stable knockdown of I kappa B kinase gamma (NF-kappa B essential modulator), which is the regulatory subunit of the I kappa B kinase complex, by RNA interference. Cell growth and apoptosis were evaluated in wild-type cells (WT) and knocked-down cells (KD). Microarray and protein array analysis were also done. To determine involvement of angiogenesis, human umbilical vein endothelial cells were used. By s.c. transplantation of the cells into nude mice, tumor sizes, vascularity, and chemodrug sensitivity were analyzed. Results: Constitutive NF-kappa B activation was observed in 40% of colorectal cancer tissues and 67% of cell lines. Cell proliferation was not different between WT and KID in vitro, whereas apoptosis mediated by tumor necrosis factor-alpha and 5-fluorouracil were increased in KD. Several angiogenic chemokines were decreased in KD. Human umbilical vein endothelial cells incubated in WT supernatant showed more branch points than in KD, suggesting that constitutive NF-kappa B activation was involved in angiogenesis. Subcutaneous tumor expansion was suppressed to 23% in KD, and vessels were also decreased. By 5-fluoruracil treatment, tumor expansion was suppressed to a greater extent in KID (to 6%) than in WT (to 50%). Conclusion: NF-kappa B inhibition may represent a potent treatment modality in colorectal cancer, especially in cases with constitutive NF-kappa B activation.