MULTIPLE REDOX REGULATION IN NF-KAPPA-B TRANSCRIPTION FACTOR ACTIVATION

The well-known Rel/NF-kappa B family of vertebrate transcription facto rs comprises a number of structurally related, interacting proteins th at bind DNA as dimers and whose activity is regulated by subcellular l ocation. This family includes many members (p50, p52, RelA, RelB, c-Re l, ...), most of which can form DNA-binding home-or hetero-dimers. All Rel proteins contain a highly conserved domain of approximately 300 a mino-acids, called the Rel homology domain (RH), which contains sequen ces necessary for the formation of dimers, nuclear localization, DNA b inding and I kappa B binding. Nuclear expression and consequent biolog ical action of the eukaryotic NF-KB transcription factor complex are t ightly regulated through its cytoplasmic retention by ankyrin-rich inh ibitory proteins known as I kappa B. The I kappa B proteins include a group of related proteins that interact with Rel dimers and regulate t heir activities. The interaction of a given I kappa B protein with a R el complex can affect the Rel complex in distinct ways. In the best ch aracterized example, I kappa B-alpha interacts with a p50/RelA (NF-kap pa B) heterodimer to retain the complex in the cytoplasm and inhibit i ts DNA-binding activity. The NF-kappa B/I kappa B-alpha complex is loc ated in the cytoplasm of most resting cells, but can be rapidly induce d to enter the cell nucleus. Upon receiving a variety of signals, many of which are probably mediated by the generation of reactive oxygen s pecies (ROS), I kappa B-alpha undergoes phosphorylation at serine resi dues by a ubiquitin-dependent protein kinase, is then ubiquitinated at nearby lysine residues and finally degraded by the proteasome, probab ly while still complexed with NF-kappa B. Removal of I kappa B-alpha u ncovers the nuclear localization signals on subunits of NF-kappa B, al lowing the complex to enter the nucleus, bind to DNA and affect gene e xpression. Like proinflammatory cytokines (e.g. IL-1, TNF), various RO S (peroxides, singlet oxygen, ...) as well as UV (C to A) light are ca pable of mediating NF-kappa B nuclear translocation, while the sensor molecules which are sensitive to these agents and trigger I kappa B-al pha proteolysis are still unidentified. We also show that a ROS-indepe ndent mechanism is activated by IL-1 beta in epithelial cells and seem s to involve the acidic sphingomyelinase/ceramide transduction pathway .