I-KAPPA-B-ALPHA DEGRADATION AND NUCLEAR FACTOR-KAPPA-B DNA-BINDING ARE INSUFFICIENT FOR INTERLEUKIN-1-BETA AND TUMOR NECROSIS FACTOR-ALPHA-INDUCED KAPPA-B-DEPENDENT TRANSCRIPTION - REQUIREMENT FOR AN ADDITIONAL ACTIVATION PATHWAY

Two closely related I kappa B alpha kinases as well as the upstream ki nase, 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 emerg ing pathway the role of previously identified components of cytokine-i nduced NF-kappa B activation, namely phosphatidylcholine-specific phos pholipase C and protein kinase C, remains unclear, We now show that, i n A549 human alveolar epithelial cells, the activation of a stably tra nsfected NF-kappa B dependent reporter gene by TNF-alpha and IL-1 beta is completely blocked by the phosphatidylcholine-specific phospholipa se C inhibitor D609 and the protein kinase C inhibitor RO31-8220. Howe ver, IL-1 beta-induced I kappa B alpha degradation as well as NF-kappa B nuclear translocation and DNA binding, as determined by Western blo t and electro-mobility shift assay, respectively, are not affected by these inhibitors, A similar effect, although less pronounced, is obser ved with the p38 mitogen-activated protein kinase inhibitor SE 203580. On the basis of these data we propose the existence of a second signa ling pathway induced by IL-1 beta and TNF-alpha that is activated in p arallel to the cascade leading to I kappa B alpha degradation and is s pecifically required for NF-kappa B-dependent transcriptional competen cy.