The NF-κB transcription factors control various biological processes including the immune response, acute phase reastion and cell cycle regulation. NF-κB complexes are retained in the cytoplasm in the basal state and various stimuli cause a translocation of the NF-κB complexes into the nucleus where they bind to the κB elements and regulate the transcription of the target genes. Recent reports also suggest that NF-κB proteins are involved in oncogenesis, tumor growth and metastasis. High expression of NF-κB expression was reported in many cancer cell lines and tissues. The constitutive activation of NF-κB was also reported in several cancer cell lines supporting its role in cancer development and survival. The anti-apoptotic action of NF-κB is important for cancer survival. NF-κB also controls the expression of several proteins that are important for cellular adhesion (ICAM-1, VCAM-1) suggesting a role in cancer metastasis. In lung cancer, high expression levels of the NF-κB subunit p50 and c-Rel were reported. In fact, high expression does not mean a high activity, and the activation pattern of NF-κB in lung cancer has not been reported.

In this study, the NF-κB nuclear binding activity in the basal and TNF-α stimulated states were examined in various lung cancer cell lines and compared with the normal bronchial epithelial cell line. Twleve lung cancer cell lines including the non-small cell and small cell lung cancer cell lines (A549, NCL-H358, NCI-H441, NCL-H522, NCL-H2009, NCI-H460, NCI-H1229, NCI-H1703, NCL-H157, NCL-H187, NCI-H417, NCI-H526) and BEAS-2B bronchial epithelial cell line were used. To evaluate the NF-κB expression amd DNA binding activity, western blot analysis and an electrophoretic mobility shift assay with the nuclear protein extracts.

The basal expressions of the p50 subunits were observed in the BEAS-2B cell line and all lung cancer cell lines except for NCI-H358 and NCI-H460. The expression levels of p65 and p50 were increased 30 minutes after stimulation with TNF-α in BEAS-2B and in 10 lung cancer cell lines. In the NCI-H358 and NCI-H460 cell lines, p65 expression was not observed in the basal and stimulated states and the two p50 related protein levels were higher after stimulation with TNF-α. These new proteins were smaller than p50 and are thought to be variants of p50. In the basal state, NF-κB was nearly activated in the BEAS-2B and all lung cancer cell lines. The DNA binding activity of the NF-κB complexes was markedly higher after stimulation with TNF-α. In the BEAS-2B and all lung cancer cell lines except for NCI-H358 and NCI-H460, the activated NF-κB complex was a p65/p60 heterodimer. In the NCI-H358 and NCI-H460 lung cancer cell lines, the NF-κB complex was variant of a p50/p50 homodimer.

The NF-κB activation pattern in the lung cancer cell lines and the normal bronchial epithelial cell lines was similar except for the activatio of a variant of the p50/p50 homodimer in some lung cancer cell lines.