Cell Death and Differentiation (2006) 13, 730–737 & 2006 Nature Publishing Group All rights reserved 1350-9047/06 $30.00 www.nature.com/cdd Review Reactive oxygen species mediate crosstalk between NF-jB and JNK H Nakano*,1, A Nakajima1, S Sakon-Komazawa1, J-H Piao1, Introduction X Xue1 and K Okumura1 NF-kB is a collective term used to describe members of the 1,2 1 Department of Immunology, Juntendo University School of Medicine, Tokyo, Rel family of dimeric transcription factors. The Rel family Japan regulates transcription of a large number of genes that control * Corresponding author. H Nakano, Department of Immunology, Juntendo cell survival and differentiation including various proinflam- University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, matory cytokines, chemokines, and adhesion molecules. Japan. Tel: þ 81-3-5802-1045; Fax: þ 81-3-3813-0421; Many of these same proinflammatory molecules, including E-mail: [email protected] cytokines such as tumor necrosis factor (TNF)a and inter- Received 23.9.05; revised 28.10.05; accepted 03.11.05; published online 09.12.05 leukin-1 (IL-1), are able to activate NF-kB, initiating a signaling Edited by G Kroemer cascade of activation. NF-kB can also be activated by Toll-like receptors that recognize pathogen-associated molecules or by cellular stress induced following UV or g-irradiation. The Abstract recent identification of molecules, which regulate the activa- k The activation of NF-jB inhibits apoptosis via a mechanism tion of the NF- B heterodimer, RelA(p65) and p50 has enhanced our understanding of the molecular mechanisms involving upregulation of various antiapoptotic genes, such controlling inflammation (Figure 1). Signaling systems in- as cellular FLICE-inhibitory protein (c-FLIP), Bcl-xL, A1/Bfl-1, duced by a variety of stimuli activate two serine kinases, and X chromosome-liked inhibitor of apoptosis (XIAP). In termed IkB kinase (IKK)a and IKKb (or IKK1; IKK2), which contrast, the activation of c-Jun N-terminal kinase (JNK) target the inhibitors of kB(IkB). The subsequent phosphory- promotes apoptosis in a manner that is dependent on the cell lation by these kinases leads to eventual ubiquitination and type and the context of the stimulus. Recent studies have proteasome-dependent degradation of IkB, releasing the indicated that one of the antiapoptotic functions of NF-jBis latent dimeric transcription factor to the nucleus. A key 3–5 to downregulate JNK activation. Further studies have also mechanism by which NF-kB controls cell survival is to revealed that NF-jB inhibits JNK activation by suppressing enhance transcription of various antiapoptotic genes, includ- accumulation of reactive oxygen species (ROS). In this ing cellular FLICE-inhibitory protein (c-FLIP), Bcl-xL, A1 (also review, we will focus on the signaling crosstalk between the known as Bfl-1), and XIAP (X chromosome-liked inhibitor of apoptosis).6,7 NF-jB and JNK cascades via ROS. Regulation of cell death and survival is also controlled Cell Death and Differentiation (2006) 13, 730–737. in part by another signaling cascade activated by the mitogen- doi:10.1038/sj.cdd.4401830; published online 9 December 2005 activated protein kinase (MAPK), which is induced following cellular stress or cytokine signaling.8,9 In mammals, the Keywords: NF-kB; c-Jun N-terminal kinase (JNK); reactive MAPK cascades are composed of three distinct signaling oxygen species (ROS); apoptosis; antiapoptotic genes; necrosis modules, the c-Jun N-terminal kinase (JNK) cascade, the p38MAPK cascade, and the extracellular signal-regulated Abbreviations: JNK, c-Jun N-terminal kinase; c-FLIP, cellular kinase (ERK) cascade. Each MAPK is activated by sequential FLICE-inhibitory protein; XIAP, X chromosome-linked inhibitor of protein phosphorylation through a MAPK module; for example apoptosis; ROS, reactive oxygen species; TNF, tumor necrosis MAPK kinase kinase (MAPKKK) phosphorylates MAPK factor; IL-1, interleukin-1; IkB, inhibitor of kB; IKK, IkB kinase; kinase (MAPKK), which in turn phosphorylates MAPK MAPK, mitogen-activated protein kinase; ERK, extracellular (Figure 2). In the case of the JNK cascade, the MAPKKKs signal-regulated kinase; ASK1, apoptosis-signal regulating include apoptosis-signal regulating kinase (ASK)1, MAP/ERK kinase 1; MEKK, MAP/ERK kinase kinase; TAK1, TGFb- kinase kinase (MEKK)s, MTK1 (also known as MEKK4), and activated kinase 1; MEFs, murine embryonic fibroblasts; TRAF, TGFb-activated kinase (TAK)1. These MAPKKKs activate TNF rceptor-associated factor; c-IAP, cellular inhibitor of apop- MKK4 and/or MKK7, which then in turn activate JNK, the tosis; ES, embrynonic stem; GADD, growth arrest and DNA targets of which include the AP1-related transcription factors, damage-inducing protein; SOD, superoxide dismutase; GPx, such as c-Jun.8,9 Cytokines and growth factors including glutathione peroxidase; PRx, peroxiredoxin; NOX, NADPH TNFa and IL-1 induce rapid (within 10 min) yet transient oxidase; BHA, butylated hydroxylanisole; NAC, N-acetyl cystein; activation of MAPK, whereas cellular stresses, such as UV or MKP, MAP kinase phosphatase; MnSOD, manganese-depen- g-irradiation, induce prolonged MAPK activation. Several lines dent SOD; FHC, ferritin heavy chain; mPT, membrane perme- of evidence suggest that transient MAPK activation is ability transition; AIF, apoptosis-inducing factor; HSP, heat shock associated with gene expression, proliferation, and differen- protein; CHX, cycloheximide tiation, whereas prolonged MAPK activation promotes cell Crosstalk between NF-jB and JNK H Nakano et al 731 TNFR1 LT-βR TRADD RIP TRAF2 TRAF3 TRAF2 TRAF5 TRAF5 ? MAPKKKs NIK α IKKα IKK IKK complex IKKγ IKKβ IKKα complete IkBα p100 partial degradation degradation p50 RelA RelB p50 RelA p52 RelB nucleus inflammatory cytokines organogenic chemokines adhesion molecules lymph node development Figure 1 The classical and nonclassical NF-kB activation pathways. The classical NF-kB pathway is activated by inflammatory cytokines including TNFa and IL-1. Activation of the classical pathway depends on TRAFs, MAPKKKs including TAK1 and MEKK3, and the IKK complex containing IKKb and IKKg subunits. Activation of the IKK complex results in degradation of the inhibitor protein, IkBa and subsequent nuclear translocation of RelA/p50 dimers. The classical pathway mediates coordinate expression of inflammatory cytokines and adhesion molecules. The nonclassical pathway induces nuclear translocation of RelB/p52 dimers, is strictly dependent on IKKa homodimers and is activated by members of the TNF receptor family, such as lymphotoxin-b receptor (LT-bR) and CD40 via NF-kB-inducing kinase (NIK). NIK is also involved in activation of the classical pathway by CD27 and CD40, but not TNFR. The nonclassical pathway plays a central role in the expression of genes involved in development and maintenance of secondary lymphoid organs. The roles of TRAFs in activation of the nonclassical pathway remain unclear death, by a mechanism that does not solely involve gene exposure to anisomycin, methylmethanesulfonate, and UV,15 activation, and is cell type- and stimuli-dependent10,11 although a recent study has challenged this conclusion.16 Consistent with these results, primary neurons from both neuron-specific JNK3 isoform knockout mice, and knockin mice expressing the nonphosphorylated form of c-Jun Pro- and Antiapoptotic Roles of JNK (c-JunAA), are resistant to excitotoxic glutamate-receptor Although the activation mechanisms of JNK have been agonist, kainate-induced apoptosis.17,18 Moreover, MEFs extensively investigated, the biological consequence of JNK from ASK1 knockout mice exhibit decreased sensitivity to 7,8,12,13 19 activation in cell death is still controversial. The most TNFa- and H2O2-induced apoptosis. convincing evidence that JNK signaling promotes apoptosis Several lines of evidence demonstrate that the proapoptotic comes from the experiments using mice deficient in the JNK JNK cascade ultimately induces apoptosis via the mitochon- activation cascade. In JNK1 and JNK2 double knockout mice, dria-dependent pathway. JNK phosphorylates members of neuronal apoptosis is suppressed in the hindbrain, but the Bcl-2 family of proteins, such as Bcl-2 and Bcl-xL, and increased in the forebrain, indicating that both JNK1 and inactivates their antiapoptotic function.20–24 Moreover, the JNK2 regulate region-specific apoptosis during early brain ectopic expression of constitutively active JNK (using the development.14 Moreover, murine embryonic fibroblasts MKK7-JNK1 fusion protein) efficiently induces apoptosis in (MEFs) from JNK1 and JNK2 double knockout mice are wild-type cells, but not cells lacking the proapoptotic Bcl-2 resistant to apoptosis induced by genotoxic stress including family members, Bax and Bak, which are essential for the Cell Death and Differentiation Crosstalk between NF-jB and JNK H Nakano et al 732 Growth Factors Cytokines TNF receptor-associated factor (TRAF)2 and the cellular Phorbol ester Stress inhibitors of apoptosis (c-IAPs) complex, resulting in caspase 8 activation and ultimately the induction of apoptosis. Finally, Tsuruta et al.28 have recently reported that JNK phosphory- Raf-1, A-Raf MEKK1-3 ASK1, MTK1 MAPKKK lates the 14-3-3 protein, a cytoplasmic anchor of Bax, and B-Raf, Mos Tpl-2 TAK1, MLK3 that phosphorylated 14-3-3 fails to sequestrate Bax into the cytoplasm, therefore inhibiting its translocation to the mitochondria. MEK1/2 MKK4/7 MKK3/6 MAPKK In contrast to the proapoptotic function of JNK as described above, numerous studies demonstrate an antiapoptotic role for JNK. Nishina et al.29,30 have illustrated that MKK4 knockout mice die due to massive hepatocyte apoptosis, and ERK1/2 JNK1/2/3 p38α/β/γ/δ MAPK that MKK4-deficient T cells exhibit increased sensitivity to anti-Fas and anti-CD3-induced apoptosis, indicating that the JNK pathway mediates survival signals. Furthermore, differ- Elk-1 ATF-2 ATF-2 entiated embryonic stem (ES) cells lacking MEKK1 showed Elk-1 Elk-1 reduced oxidative stress-induced JNK activation and were c-Jun MEF-2C more susceptible to apoptosis.31 Moreover, Lamb et al.32 Figure 2 Three MAP kinase modules in mammals.