To evaluate the role of the NF-κB signaling pathway in oncogenic transformation, we expressed IκBβ, a specific inhibitor of NF-κB, in two human lung adenocarcinoma cell lines, A549 and H441. Expression of IκBβ significantly reduced NF-κB activation induced by cotransfection with p65/RelA or TNF-α and abrogated the basal NF-κB activity in A549 cells. Transfection of IκBβ into A549, H441 and K-ras-transformed NIH3T3 cells suppressed anchorage-independent growth as measured by colony formation in soft agar. Anchorage-independent growth of vector-transfected A549 cells in reduced serum could be enhanced by both EGF and IGF-I. In contrast, only EGF but not IGF-I could induce anchorage-independent growth of IκBβ-expressing A549 cells, suggesting that the IGF-I signaling pathway regulating growth and survival may be blocked by IκBβ. Interestingly, expression of IκBβ suppressed growth of A549 cells in low serum in vitro without affecting in vivo growth subcutaneously in nude mice. However, metastatic growth of IκBβ-expressing A549 cells in the lungs of nude mice was significantly inhibited. These results provide evidence that NFκB plays an important role in anchorage-independent growth and metastatic growth of lung carcinoma cells.