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The transcription factor NF-kappaB controls the expression of hundreds of genes involved in the regulation of the immune/inflammatory response, development, and apoptosis. In resting cells, NF-kappaB proteins are sequestered in the cytoplasm through their tight association with IkappaB proteins. NF-kappaB activation relies on the signal-induced IkappaB phosphorylation and degradation, thereby allowing the nuclear translocation of NF-kappaB proteins. In the nucleus, several post-translational modifications of NF-kappaB and chromatin remodeling of target genes are mandatory for NF-kappaB DNA binding and full transcription. Since 1991, reactive oxygen species (ROS) have been implicated in NF-kappaB activation. ROS enhance the cytoplasmic signaling pathways leading to NF-kappaB nuclear translocation, but reduction/oxidation (redox) also controls several key steps in the nuclear phase of the NF-kappaB program, including chromatin remodeling, recruitment of co-activators, and DNA binding. Here we describe the redox regulation of NF-kappaB activity in the nucleus.

Photosynthetic activities were analyzed in Chlamydomonas reinhardtii mitochondrial mutants affected in different complexes (I, III, IV, I ϩ III, and I ϩ IV) of the respiratory chain. Oxygen evolution curves showed a positive relationship between the apparent yield of photosynthetic linear electron transport and the number of active proton-pumping sites in mitochondria. Although no significant alterations of the quantitative relationships between major photosynthetic complexes were found in the mutants, 77 K fluorescence spectra showed a preferential excitation of photosystem I (PSI) compared with wild type, which was indicative of a shift toward state 2. This effect was correlated with high levels of phosphorylation of lightharvesting complex II polypeptides, indicating the preferential association of light-harvesting complex II with PSI. The transition to state 1 occurred in untreated wild-type cells exposed to PSI light or in 3-(3,4-dichlorophenyl)-1,1-dimethylureatreated cells exposed to white light. In mutants of the cytochrome pathway and in double mutants, this transition was only observed in white light in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. This suggests higher rates of nonphotochemical plastoquinone reduction through the chlororespiratory pathway, which was confirmed by measurements of the complementary area above the fluorescence induction curve in dark-adapted cells. Photo-acoustic measurements of energy storage by PSI showed a stimulation of PSI-driven cyclic electron flow in the most affected mutants. The present results demonstrate that in C. reinhardtii mutants, permanent defects in the mitochondrial electron transport chain stabilize state 2, which favors cyclic over linear electron transport in the chloroplast.Metabolic processes of photosynthetic organisms depend on the regeneration of ATP through photosynthesis and respiration. Although these two processes are now well understood at the molecular and physiological levels, less is known about their mutual regulation. In eukaryotic cells, complex interactions between photosynthesis and respiration occur because both processes are linked by common key metabolites such as ADP/ATP, NAD(P)H, triose-P, and hexose-P (for review, see Hoefnagel et al., 1998).When the dependence of respiration on photosynthesis seems to rely essentially on the availability of substrates, the influence of respiration on photosynthesis is suggested to involve complex organizational changes in the PSs, known as state transitions. The transition from states 1 to 2 corresponds to the reversible transfer of a mobile pool of PSII lightharvesting complexes II (LHCII) from PSII to PSI along the thylakoid membrane (state 2 transition) and is triggered by persistent reduction of the plastoquinone (PQ) pool. This reduction causes the activation of an LHCII-kinase interacting with the quinine oxidizing site of cytochrome (Cyt) b6/f (for review, see Allen, 1992;Wollman, 2001). Due to its high affinity for the PSI-h subunit, phospho-LHCII then is bound preferential...

Previous studies have implicated acetylases and deacetylases in regulating the transcriptional activity of NF-B. Here, we show that inhibitors of deacetylases such as trichostatin A (TSA) and sodium butyrate (NaBut) potentiated TNF-induced expression of several natural NF-B-driven promoters. This transcriptional synergism observed between TNF and TSA (or NaBut) required intact B sites in all promoters tested and was biologically relevant as demonstrated by RNase protection on two instances of endogenous NF-B-regulated gene transcription. Importantly, TSA prolonged both TNF-induced DNA-binding activity and the presence of NF-B in the nucleus. We showed that the p65 subunit of NF-B was acetylated in vivo. However, this acetylation was weak, suggesting that other mechanisms could be implicated in the potentiated binding and transactivation activities of NF-B after TNF plus TSA versus TNF treatment. Western blot and immunofluorescence confocal microscopy experiments revealed a delay in the cytoplasmic reappearance of the IB␣ inhibitor that correlated temporally with the prolonged intranuclear binding and presence of NF-B. This delay was due neither to a defect in IB␣ mRNA production nor to a nuclear retention of IB␣ but was rather due to a persistent proteasome-mediated degradation of IB␣. A prolongation of IB kinase activity could explain, at least partially, the delayed IB␣ cytoplasmic reappearance observed in presence of TNF plus TSA.NF-B is a ubiquitously expressed family of transcription factors controlling the expression of numerous genes involved in inflammatory and immune responses and cellular proliferation (reviewed in references 4, 5, 19, and 26). There are five known members of the mammalian NF-B/Rel family: p50 (NF-B1), p52 (NF-B2), p65 (RelA), c-Rel, and RelB. The most abundant form of NF-B is a heterodimer of p50 and p65. In unstimulated cells, NF-B is sequestered in the cytoplasm in an inactive form through interaction with the IB inhibitory proteins (including IB␣, IB␤, and IBε, of which the best studied is IB␣). Upon stimulation of cells by specific inducers, such as the proinflammatory cytokine tumor necrosis factor SF2 (referred to as TNF hereinafter), IB␣ is phosphorylated on two specific serine residues by a large cytoplasmic IB kinase (IKK) complex that consists of the kinase catalytic subunits IKK␣ and IKK␤ and the regulatory subunit NEMO/ IKK␥ (reviewed in references 23 and 26). This phosphorylation marks IB␣ for polyubiquitination by the E3-SCF ␤-TrCP ubiquitin ligase complex, a specific ubiquitin ligase belonging to the SCF (i.e., Skp-1/Cul/Fbox) family, and for degradation by the 26S proteasome (reviewed in reference 5). Degradation of IB␣ allows a rapid and transient translocation of NF-B to the nucleus, where it activates transcription from a wide variety of promoters-including that of its own inhibitor, IB␣. The newly synthesized IB␣ enters the nucleus and removes NF-B from its DNA binding sites and transports it back to the cytoplasm, thereby terminating NF-B-dependent transcription (...

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