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A protein turnover signaling motif controls the stimulus-sensitivity of stress response pathways.

Loriaux PM, Hoffmann A - PLoS Comput. Biol. (2013)

Bottom Line: In contrast, high flux of Mdm2 is not required for oscillations but preserves p53 sensitivity to sub-saturating doses of IR.In the NFκB system, degradation of NFκB-bound IκB by the IκB kinase (IKK) is required for activation in response to TNF, while high IKK-independent degradation prevents spurious activation in response to metabolic stress or low doses of TNF.Our work identifies flux pairs with opposing functional effects as a signaling motif that controls the stimulus-sensitivity of the p53 and NFκB stress-response pathways, and may constitute a general design principle in signaling pathways.

View Article: PubMed Central - PubMed

Affiliation: Signaling Systems Laboratory, Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America.

ABSTRACT
Stimulus-induced perturbations from the steady state are a hallmark of signal transduction. In some signaling modules, the steady state is characterized by rapid synthesis and degradation of signaling proteins. Conspicuous among these are the p53 tumor suppressor, its negative regulator Mdm2, and the negative feedback regulator of NFκB, IκBα. We investigated the physiological importance of this turnover, or flux, using a computational method that allows flux to be systematically altered independently of the steady state protein abundances. Applying our method to a prototypical signaling module, we show that flux can precisely control the dynamic response to perturbation. Next, we applied our method to experimentally validated models of p53 and NFκB signaling. We find that high p53 flux is required for oscillations in response to a saturating dose of ionizing radiation (IR). In contrast, high flux of Mdm2 is not required for oscillations but preserves p53 sensitivity to sub-saturating doses of IR. In the NFκB system, degradation of NFκB-bound IκB by the IκB kinase (IKK) is required for activation in response to TNF, while high IKK-independent degradation prevents spurious activation in response to metabolic stress or low doses of TNF. Our work identifies flux pairs with opposing functional effects as a signaling motif that controls the stimulus-sensitivity of the p53 and NFκB stress-response pathways, and may constitute a general design principle in signaling pathways.

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IκB flux controls the sensitivity of NFκB to stimulation by TNF and UV.(A) The futile flux of IκB was varied between  and  times its wildtype value prior to stimulation with variable doses of TNF (see Methods). For low, medium, high, and wildtype values of the futile flux, the area under the NFκB activation curve is plotted as a function of TNF dose. The region of the plot corresponding to low doses of TNF, where the activation of IKK does not exceed 10%, is shaded in pink. (B) As above, but variable doses of UV are used instead of TNF. Because the response to UV is sustained and not transient, we have plotted the value of  as a function of UV dose instead of the area under the NFκB activation curve.
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pcbi-1002932-g007: IκB flux controls the sensitivity of NFκB to stimulation by TNF and UV.(A) The futile flux of IκB was varied between and times its wildtype value prior to stimulation with variable doses of TNF (see Methods). For low, medium, high, and wildtype values of the futile flux, the area under the NFκB activation curve is plotted as a function of TNF dose. The region of the plot corresponding to low doses of TNF, where the activation of IKK does not exceed 10%, is shaded in pink. (B) As above, but variable doses of UV are used instead of TNF. Because the response to UV is sustained and not transient, we have plotted the value of as a function of UV dose instead of the area under the NFκB activation curve.

Mentions: In contrast to p53, the negative regulatory flux of IκB dominates the positive flux. We hypothesized that this imbalance must affect the sensitivity of NFκB to weak stimuli. To test this hypothesis we generated dose-response curves for TNF and UV using the following multipliers for the futile flux: , , , and (see Methods). The results confirm that reducing the futile flux of IκB results in hypersensitivity at low doses of TNF (Figure 7, Row 1). At one one-hundredth the wildtype flux, a ten-fold weaker TNF stimulus yields an equivalent NFκB response to the full TNF stimulus at the wildtype flux. Similarly, a high futile flux prevents strong activation of NFκB in response to UV (Figure 7, Row 2). At and times the futile flux, UV stimulation results in a 20-fold increase in NFκB activity, compared to just a 2-fold increase at the wildtype flux. We therefore conclude that turnover of unbound IκB controls the EC50 of the NFκB signaling module, and that rapid turnover renders NFκB resistant to metabolic and spurious inflammatory stimuli.


A protein turnover signaling motif controls the stimulus-sensitivity of stress response pathways.

Loriaux PM, Hoffmann A - PLoS Comput. Biol. (2013)

IκB flux controls the sensitivity of NFκB to stimulation by TNF and UV.(A) The futile flux of IκB was varied between  and  times its wildtype value prior to stimulation with variable doses of TNF (see Methods). For low, medium, high, and wildtype values of the futile flux, the area under the NFκB activation curve is plotted as a function of TNF dose. The region of the plot corresponding to low doses of TNF, where the activation of IKK does not exceed 10%, is shaded in pink. (B) As above, but variable doses of UV are used instead of TNF. Because the response to UV is sustained and not transient, we have plotted the value of  as a function of UV dose instead of the area under the NFκB activation curve.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3585401&req=5

pcbi-1002932-g007: IκB flux controls the sensitivity of NFκB to stimulation by TNF and UV.(A) The futile flux of IκB was varied between and times its wildtype value prior to stimulation with variable doses of TNF (see Methods). For low, medium, high, and wildtype values of the futile flux, the area under the NFκB activation curve is plotted as a function of TNF dose. The region of the plot corresponding to low doses of TNF, where the activation of IKK does not exceed 10%, is shaded in pink. (B) As above, but variable doses of UV are used instead of TNF. Because the response to UV is sustained and not transient, we have plotted the value of as a function of UV dose instead of the area under the NFκB activation curve.
Mentions: In contrast to p53, the negative regulatory flux of IκB dominates the positive flux. We hypothesized that this imbalance must affect the sensitivity of NFκB to weak stimuli. To test this hypothesis we generated dose-response curves for TNF and UV using the following multipliers for the futile flux: , , , and (see Methods). The results confirm that reducing the futile flux of IκB results in hypersensitivity at low doses of TNF (Figure 7, Row 1). At one one-hundredth the wildtype flux, a ten-fold weaker TNF stimulus yields an equivalent NFκB response to the full TNF stimulus at the wildtype flux. Similarly, a high futile flux prevents strong activation of NFκB in response to UV (Figure 7, Row 2). At and times the futile flux, UV stimulation results in a 20-fold increase in NFκB activity, compared to just a 2-fold increase at the wildtype flux. We therefore conclude that turnover of unbound IκB controls the EC50 of the NFκB signaling module, and that rapid turnover renders NFκB resistant to metabolic and spurious inflammatory stimuli.

Bottom Line: In contrast, high flux of Mdm2 is not required for oscillations but preserves p53 sensitivity to sub-saturating doses of IR.In the NFκB system, degradation of NFκB-bound IκB by the IκB kinase (IKK) is required for activation in response to TNF, while high IKK-independent degradation prevents spurious activation in response to metabolic stress or low doses of TNF.Our work identifies flux pairs with opposing functional effects as a signaling motif that controls the stimulus-sensitivity of the p53 and NFκB stress-response pathways, and may constitute a general design principle in signaling pathways.

View Article: PubMed Central - PubMed

Affiliation: Signaling Systems Laboratory, Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, United States of America.

ABSTRACT
Stimulus-induced perturbations from the steady state are a hallmark of signal transduction. In some signaling modules, the steady state is characterized by rapid synthesis and degradation of signaling proteins. Conspicuous among these are the p53 tumor suppressor, its negative regulator Mdm2, and the negative feedback regulator of NFκB, IκBα. We investigated the physiological importance of this turnover, or flux, using a computational method that allows flux to be systematically altered independently of the steady state protein abundances. Applying our method to a prototypical signaling module, we show that flux can precisely control the dynamic response to perturbation. Next, we applied our method to experimentally validated models of p53 and NFκB signaling. We find that high p53 flux is required for oscillations in response to a saturating dose of ionizing radiation (IR). In contrast, high flux of Mdm2 is not required for oscillations but preserves p53 sensitivity to sub-saturating doses of IR. In the NFκB system, degradation of NFκB-bound IκB by the IκB kinase (IKK) is required for activation in response to TNF, while high IKK-independent degradation prevents spurious activation in response to metabolic stress or low doses of TNF. Our work identifies flux pairs with opposing functional effects as a signaling motif that controls the stimulus-sensitivity of the p53 and NFκB stress-response pathways, and may constitute a general design principle in signaling pathways.

Show MeSH
Related in: MedlinePlus