NFkB

In the vasculature, ANG H not only increases contraction of smooth muscle cells, but is also able to induce vascular injury. This can be prevented by blocking NFkB activation [3] suggesting a link between ANG II and inflammation processes involved in the pathogenesis of arteriosclerosis (see below). Thus, ACE inhibitors not only decrease vascular tone but probably also exert vasoprotective effects. 

In addition to those described above, some of the newest compounds emerging in SERM development are ER 3-selective ligands and pathway-selective modulators that target the interaction of the ERs with the transcription factor NFkB. While such compounds are in the early stages of clinical evaluation, thus far they demonstrate great potential for use in the treatment of inflammatory disorders such as arthritis, inflammatory bowel disease, and like other SERMs, cancer [4]. 

Once the TLRs have bound their respective ligand they initiate a signalling cascade to alert the host to the presence of a threat. This signal begins with specific adapter proteins and leads to the activation of transcription factors such as NFkB, ERF-3 and IRF-7 as shown in Fig. 1. These activated transcription factors cause changes in gene expression typically leading to the production of cytokines. 

Hyperphosphorylation of ERAK-1 by itself and ERAK-4 causes ERAK-1 to dissociate from the membrane-bound complex. Tumour necrosis factor (TNF) receptor-associated factor-6 ( TRAF-6), a cytoplasmic protein, is activated by ERAK-1 and with TAB-2, another cytoplasmic protein, activates transforming growth factor-P (TFG-P)-activating kinase (TAK-1). During this process both TRAF-6 and TAK-1 become ubiquitinated. TAK-1 then promotes activation of the IkB kinases, or the IKK family, EKKa and EKK 3 (found in a complex with NFicB-essential modulator [NEMO]), which phosphorylate the IkB family, notably IkB-u. IkB-u is an inhibitor of NFkB as it sequesters NFkB in an... 

This second pathway begins with the direct binding of TRIF to TLR-3 and the activation by it of two kinases inducible IKK (EECK-i also known as EECK-s) and TRAF family member-associated NFkB activator (TANK)-binding kinase-1 (TBK-1). The activation of these two kinases leads to the phosphorylation of IRF-3 and IRF-7 allowing them to enter the nucleus and induce the expression of IFN-a (IRF-7) and EFN- 3 (IRF-3 7). It has been shown that TBK-1 binds to the N-terminus of TREF in the same area as TRAF-6 suggesting that in a TLR-3 response either TBK-1 or TRAF-6 bind TLR-3, but never both. 

The third signalling pathway of TRIF utilises its C-terminus. This region contains a RJQP homology interaction motif (RHIM) that binds RJQP-1 and REP-3. RIP-1 phosphorylates IKK-(3 and the NFkB pathway can be activated. REP-3 is a negative regulator of TREF competing for REP-1 [2]. 

The key end result of TLR signalling is the induction of cytokines. Cytokines are proteins produced during an immune response that allow the maturation, activation and differentiation of effector cells in the immune system. The activation of NFkB and AP-1 by the MyD88 and the TREF dependent pathways leads to the production of proinflammatory cytokines such as IL-6, TNF-a and various chemokines. This pathway can also activate IRF-7 via TLR-7and TLR-9 allowing Type-I interferons to be produced. 

BAEUERLE P A and HENKEL T (1994) Fimction and activation of NFkB in the immune system Annual Review in Immunology 12, 141-79. 

Low levels of hypochlorous acid can function as a mediator in cell activation, induce NFKB heterodimer p50 /p65 in a T-lymphocytic cell line through proteolysis of IKB and pl05 inhibitors. Hypochlorous acid will also contribute to the release of TNFo in cellular supernatants of T-lymphocytes which are capable of commencing activation in non-induced cells (Schoonbroodt et ah, 1997). Hypochlorous acid can react with amines to produce chloroamines and N-chlorinated derivatives that have a long lifetime in plasma. Taurine, a sulfonated amino acid, will finally combine with these two products to reduce their toxicity. 

Activation of cells results in the release of IKB, followed by the rapid proteolysis of IKB. Although phosphorylation of serine 32 and 36 in the amino-terminal part of IKBa occurs when the proinflammatory cytokines or mitogens are administered to a T lymphocytic cell line, a different site of action has been found after H2O2 incubation (Schoonbroodt et al., 2000). The tyrosine residue 42 and the C-terminal PEST (Pro-Glu-Ser-Thr) domain plays a major role in the phosphorlylation of IKB after treatment with H2O2. Furthermore the CVinducible phosphorylation was not dependent upon IKB kinase activation but involved casein kinase II. The importance of iron for the activation of NFKB was underlined by the fact that... 

Figure 10.3 (a) Proposed mechanism for induction of NFKB proteins (from Suzuki et al., 1994) (b) interaction with iron metabolism. Reproduced with permission from Cairo and Pietrangelo, 2000, the Biochemical Society. 

Signals from neighbouring cells or tissues will instruct a particular cell to proliferate, differentiate into another cell type or to commit suicide by programmed cell death. Figure 10.4 shows that NFKB can play a major role in countering programmed cell death and hence survival of the cell after stimulation of the TNFa pathway. Such a pathway depends upon the activation of NFKB which will activate a variety of anti-apoptopic genes. 

One of the major sites of action of NFKB is the activation of iNOS. In 1993, it was shown that the murine gene coding iNOS contained two putative NFKB... 

Figure 10.4 Life and death decisions in cells. Cellular stimulation with tumour necrosis factor-a (TNFa) simultaneously activates survival and death signalling pathways. Reprinted with permission from Nature (from Pomerantz and Baltimore, 2000). Copyright (2000) Macmillan Magazines Limited. p50 and p65 are subunits of NFKB...

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