The NF-KappaB inducing IKK signalsome complex is the final receiver and integrator of a host of extracellular stress-like and inflammatory response stimuli. The IKK complex consists of two serinelthreonine kinases (IKKalpha and IKKbeta) and a con-catalytic regulatory/docking protein (NEMO/IKKy). IKK(3 and NEMO/IKKgamma are essential for inducing NF-KB nuclear translocation and DNA binding activity in response to mediators of inflammatory responses like TNFalpha and IL-1, while IKKalpha is largely believed to be dispensible for activating NF-KappaB by these stimuli. Surprisingly, we have recently found that IKKalpha is essential for inducing the transcriptional competence of nuclear NF-KappaB subunits in response to inflammatory cytokines, implying that it plays a critical role in activating NF-KB independent of its DNA binding activity. Consequently, one aim of this proposal will be to elaborate the molecular requirements and mechanisms of action of IKKalpha as a co-global mediator (along with IKKbeta and NEMO/IKKgamma) of stress-like responses culminating in NF-kappaB activation. We have also discovered that the IKK signalsome simultaneously co-ordinates the global induction and repression of cellular gene expression. In a second aim we will elaborate the mechanisms of action of the IKK signalsome as a mediator of NF-KappaB dependent gene repression. We have hypothesized that IKK mediated NF-KappaB activation operates like a co-ordinately controlled on/off switch that alters physiological responses in vivo. Interestingly a subset of the genes, which are repressed in response to extracellular stimulus dependent and IKK mediated NF-KB activation, are also induced targets of the E2F-I. E2F-1 is capable of inducing cell cycle arrest, apoptosis and cell cycle progression depending on its degree of activation and the physiological state of the cell. Experimental conditions in primary and established cells will be established, which lead to interference between NF-KB and E2F on specific genomic targets. The physiological effects of IKK/NF-KappaB mediated repression of cell cycle regulated, E2F target genes will also be evaluated.
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