Mechanism of PP2A-mediated IKKβ dephosphorylation: a systems biological approach

BACKGROUND: Biological effects of nuclear factor-kappaB (NF kappaB) can differ tremendously depending on the cellular context. For example, NF kappaB induced by interleukin-1 (IL-1) is converted from an inhibitor of death receptor induced apoptosis into a promoter of ultraviolet-B radiation (UVB)-induced apoptosis. This conversion requires prolonged NF kappaB activation and is facilitated by IL-1 + UVB-induced abrogation of the negative feedback loop for NF kappaB, involving a lack of inhibitor of kappaB (I kappaB alpha) protein reappearance. Permanent activation of the upstream kinase IKK beta results from UVB-induced inhibition of the catalytic subunit of Ser-Thr phosphatase PP2A (PP2Ac), leading to immediate phosphorylation and degradation of newly synthesized I kappaB alpha. RESULTS: To investigate the mechanism underlying the general PP2A-mediated tuning of IKK beta phosphorylation upon IL-1 stimulation, we have developed a strictly reduced mathematical model based on ordinary differential equations which includes the essential processes concerning the IL-1 receptor, IKK beta and PP2A. Combining experimental and modelling approaches we demonstrate that constitutively active, but not post-stimulation activated PP2A, tunes out IKK beta phosphorylation thus allowing for I kappaB alpha resynthesis in response to IL-1. Identifiability analysis and determination of confidence intervals reveal that the model allows reliable predictions regarding the dynamics of PP2A deactivation and IKK beta phosphorylation. Additionally, scenario analysis is used to scrutinize several hypotheses regarding the mode of UVB-induced PP2Ac inhibition. The model suggests that down regulation of PP2Ac activity, which results in prevention of I kappaB alpha reappearance, is not a direct UVB action but requires instrumentality. CONCLUSION: The model developed here can be used as a reliable building block of larger NF kappa B models and offers comprehensive simplification potential for future modeling of NF kappa B signaling. It gives more insight into the newly discovered mechanisms for IKK deactivation and allows for substantiated predictions and investigation of different hypotheses. The evidence of constitutive activity of PP2Ac at the IKK complex provides new insights into the feedback regulation of NF kappa B, which is crucial for the development of new anti-cancer strategies

WIP1 phosphatase is a negative regulator of NF-κB signalling

10.1038/ncb1873Nature Cell Biology115659-666NCBI

Role of IL-23 in the pathogenesis of psoriasis: A novel potential therapeutic target?

Introduction: Psoriasis is a chronic inflammatory skin disorder determined by the activation of several immune cells and resident tissue cells. Various cytokines mediate inflammatory signals, including IL-23, which is an important factor involved in the differentiation of T helper (Th17) cells. Areas covered: Increasing evidence suggests that IL-23 is a central cytokine to the pathogenesis of psoriasis. An overview on both experimental and human data will be reported in order to support the hypothesis of a key pathogenic role of IL-23/Th17 axis. Expert opinion: Targeting IL-23 might be a more selective, valid and effective therapeutic approach, which, potentially, may show important advantages in terms of long-term efficacy and safety in the treatment of psoriasis. © 2014 Informa UK, Ltd

Aquaporin-3-mediated hydrogen peroxide transport is required for NF-κB signalling in keratinocytes and development of psoriasis

Aquaporin 3 (AQP3), a water/glycerol channel protein, has been found to transport hydrogen peroxide (H2O2). Here, we show that H2O2, imported via AQP3, is involved in nuclear factor-κB (NF-κB) signalling in keratinocytes and in the pathogenesis of psoriasis. IL-23-mediated induction of psoriasis is reduced in AQP3 knockout mice (AQP3(-/-)), and is accompanied by impaired NF-κB activation and intracellular H2O2 accumulation. In primary keratinocyte cultures, cellular import of H2O2 produced by membrane NADPH oxidase 2 (Nox2) in response to TNF-α is facilitated by AQP3 and required for NF-κB activation by regulation of protein phosphatase 2A. As AQP3 associates with Nox2, we propose that this interplay constitutes H2O2-mediated signalling in response to TNF-α stimulation. Collectively, these data indicate that AQP3-facilitated H2O2 transport is required for NF-κB activation in keratinocytes in the development of psoriasis