Role of the oncogenic Raf-1 in orchestration of discrete nuclear factor-kappaB-activating pathways.
Raf-1, a key kinase in the Ras signaling pathway, plays critical roles in cell differentiation, proliferation, and tumorigenesis. However, knowledge of the Raf-1 in inflammation is limited. Using an inducible oncogenic Raf-1, we show that the Raf-1 orchestrates the discrete NF-kappaB activating pathways. While the Raf-1 activation induces a modest IkappaB degradation by enhancing the basal IkappaB kinase activity, it contradictorily suppresses the proinflammatory cytokine inducible IkappaB kinase complex, leading to an inhibition of TNF-alpha- and IL-1beta-induced NF-kappaB activation. Despite considerable degrees of overlap, LPS signaling is not affected by Raf-1. By either conditionally reducing Raf-1 activity or completely disrupting the Raf-1 signaling by PD98059, a specific inhibitor of MEK1, the otherwise inhibited cytokine responses can be restored. Moreover, when the activity of Raf-1 is up-regulated during the cell cycle progression from the G(0) phase to the late G(1) phase, the enhanced Raf-1 activity suffices to shift the TNF-alpha response from the sensitive to the insensitive state. Together, these studies elucidate a mechanism by which signaling outputs are shaped by the intracellular Raf-1, thus explaining the "cellular context"-dependent cytokine response.
Liu
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Laboratory of Virology, Lindsley F. Kimball Research Institute of the New York Blood Center, New York, NY 10021, USA.
Fan
J
J
McMahon
M
M
Prince
A M
AM
Zhang
P
P
D000818:Animals; D015153:Blotting, Western; D002453:Cell Cycle; D002460:Cell Line; D016207:Cytokines / Q000096:biosynthesis / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D007375:Interleukin-1 / Q000378:metabolism; D008024:Ligands; D020935:MAP Kinase Signaling System; D008954:Models, Biological; D016328:NF-kappa B / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D012190:Retroviridae / Q000235:genetics; D015398:Signal Transduction; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation
D016207:Cytokines; D004791:Enzyme Inhibitors; D005419:Flavonoids; D020672:I-kappa B Proteins; D007375:Interleukin-1; D008024:Ligands; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D019908:Proto-Oncogene Proteins c-raf; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one