IκBα degradation and nuclear factor-κB DNA binding are insufficient for interleukin-1β and tumor necrosis factor-α-induced κB-dependent transcription -: Requirement for an additional activation pathway

Two closely related I kappa B alpha kinases as well as the upstream kinase, NIK, which integrates interleukin-1 beta (IL-1 beta)- and tumor necrosis factor (TNF)-alpha-dependent activation of the transcription factor NF-kappa B have recently been described. However, in this emerging pathway the role of previously identified components of cytokine-induced NF-kappa B activation, namely phosphatidylcholine-specific phospholipase C and protein kinase C, remains unclear, We now show that, in A549 human alveolar epithelial cells, the activation of a stably transfected NF-kappa B dependent reporter gene by TNF-alpha and IL-1 beta is completely blocked by the phosphatidylcholine-specific phospholipase C inhibitor D609 and the protein kinase C inhibitor RO31-8220. However, IL-1 beta-induced I kappa B alpha degradation as well as NF-kappa B nuclear translocation and DNA binding, as determined by Western blot and electro-mobility shift assay, respectively, are not affected by these inhibitors, A similar effect, although less pronounced, is observed with the p38 mitogen-activated protein kinase inhibitor SE 203580. On the basis of these data we propose the existence of a second signaling pathway induced by IL-1 beta and TNF-alpha that is activated in parallel to the cascade leading to I kappa B alpha degradation and is specifically required for NF-kappa B-dependent transcriptional competency.