Kinetic control of negative feedback regulators of NF-κB/RelA determines their pathogen- and cytokine-receptor signaling specificity

Abstract

Mammalian signaling networks contain an abundance of negative feedback regulators that may have overlapping (''fail-safe'') or specific functions. Within the NF-B signaling module, I B␣ is known as a negative feedback regulator, but the newly characterized inhibitor I B␦ is also inducibly expressed in response to inflammatory stimuli. To examine I B␦'s roles in inflammatory signaling, we mathematically modeled the 4-I B-containing NF-B signaling module and developed a computational phenotyping methodology of general applicability. We found that I B␦, like I B␣, can provide negative feedback, but each functions stimulusspecifically. Whereas I B␦ attenuates persistent, pathogen-triggered signals mediated by TLRs, the more prominent I B␣ does not. Instead, I B␣, which functions more rapidly, is primarily involved in determining the temporal profile of NF-B signaling in response to cytokines that serve intercellular communication. Indeed, when removing the inducing cytokine stimulus by compound deficiency of the tnf gene, we found that the lethality of i b␣ ؊/؊ mouse was rescued. Finally, we found that I B␦ provides signaling memory owing to its long half-life; it integrates the inflammatory history of the cell to dampen NF-B responsiveness during sequential stimulation events.inflammation ͉ mathematical modeling ͉ NF-kappaB ͉ pathogen

B-cell CLL/Lymphoma 10 (BCL10) Is Required for NF-κB Production by Both Canonical and Noncanonical Pathways and for NF-κB-inducing Kinase (NIK) Phosphorylation

“…The complexity of the negative feedback on NF-B, involving mediators such as IB␦, as well as IB-␣, -␤, and -⑀, may include stimulus specific responses and different, but specified kinetic rate constants (25)(26)(27)(28). Also, the protein content of RelB was reported to be significantly reduced when p105 and p100 were absent, suggesting that the noncanonical pathway may be FIGURE 5.…”

A single NFκB system for both canonical and non-canonical signaling

“…Because p100 expression is inducible by RelA:p50, this forms a negative feedback loop that has slow kinetics, yet is not degraded when canonical IKK activity persists. Computational simulations-directed experimental studies revealed that IκBδ forms a negative feedback loop to regulate RelA:p50 activity in a stimulus-specific manner, such that it is effective to LPS but not to TNF [3]. Indeed, the work revealed that IκBα provides effective negative feedback only to cytokine stimuli that produce transient canonical IKK activity.…”

“…Moreover, size exclusion chromatography analyses suggest that IκBδ activity is mediated by a ~650 kDa high molecular weight npg complex, termed the IκBsome, which also contains IκBγ activity from p105 protein [2]. The pathways that govern IκBsome assembly and degradation are critical for regulating NFκB activity [3].…”

“…Further, IκBε appears to dampen IκBα-mediated NFκB oscillations, because its mRNA induction is delayed to occur in anti-phase with that of IκBα [49]. In addition, newly synthesized IκBδ forms a negative feedback loop to regulate RelA:p50 activity in a stimulus-specific manner, as described above [3]. Singlecell studies with fluorescent fusion proteins of RelA and IκBα have drawn attention to the potential for oscillatory control of NFκB, suggesting that frequency of successive NFκB peaks is a critical feature of the temporal code [50,51].…”

p100/IκBδ sequesters and inhibits NF-κB through kappaBsome formation

“…Because expression of all IκBs, barring IκBβ, is under feedback regulation by NF-κB, postinduction synthesis of these inhibitors dampens the nuclear activity of NF-κB by preventing it from undergoing persistent gene activation (3). This negative feedback loop is critical to involvement of IκBδ in long-lasting signals to pathogenic stimuli such as lipopolysaccharides; in contrast, other IκBs mediate signals for rapid NF-κB activation (19,20).…”