No abstract

Macrophage activation in response to proinflammatory cytokines and bacterial cell wall products constitutes a key component of the immune response (23,31,50). Resolution of the process occurs after removal of the proinflammatory stimuli and through the action of negative regulators of the activationsignaling pathways, among them interleukin-10 (IL-10), IL-13, alpha/beta interferons (IFN-␣/␤), and more recently several cyclopentenone prostaglandins (PGs) (8,21,35,36,49). In particular, 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15dPGJ 2 ) has been shown to exert important anti-inflammatory effects on several cell types such as monocytes/macrophages and microglia (4,16,35,36). Controversy exists about the identification of intracellular targets involved in the mechanism of action of cyclopentenone PGs: some of these effects have been explained through the transcriptional inhibition exerted by 15dPGJ 2 -activated peroxisome proliferator receptor gamma (PPAR␥) (12,14,36,39); however, other data suggest a main contribution of PPAR␥-independent mechanisms on the antiinflammatory action of this PG, in view of the lack of effect of synthetic PPAR␥ ligands such as thiazolidinediones (17,35).It has been shown that 15dPGJ 2 inhibits the expression of genes requiring the activation of the transcription factors NF-B, AP-1, and Stat1 (17, 35, 36), which are involved in the induction of several enzymes participating in the development of the inflammatory process, such as type 2 nitric oxide synthase (NOS-2) and cyclooxygenase 2 (COX-2) (7,42,51). In macrophages, activated NF-B complexes are composed mainly of p50 and p65 subunits that translocate to the nucleus in response to cell stimulation with lipopolysaccharide (LPS) and proinflammatory cytokines (13,45,48). This activation of NF-B requires phosphorylation by IB kinase (IKK) of IB proteins in specific serine residues that target these proteins for ubiquitin conjugation and degradation by the 26S proteasome (26, 45). The IKK complex contains two catalytic subunits, IKK1 and IKK2, and a regulatory subunit termed NF-B essential modulator (10,54,56). In turn, activation of IKK is mediated by phosphorylation through NF-B-inducing kinase, which acts preferentially over IKK1, and MEK kinase 1 (MEKK1), which phosphorylates IKK2 (6, 30). Biochemical and genetic data indicate that IKK1 and IKK2, despite the sequence similarity, have different functions (15,55). IKK1 participates in differentiation of various cell types (20), whereas IKK2 is involved in LPS signaling in monocytes/macrophages and in general the response to proinflammatory stimuli (34, 55). IKK2 is rapidly activated after cell challenge with LPS, IL-1␤, or tumor necrosis factor alpha (TNF-␣) and progressively undergoes phosphorylation at multiple serine residues that decreases the kinase activity and therefore contributes to the transient activation of this enzyme (6). In this regard, we have investigated the possibility of early effects of 15dPGJ 2 on LPS and IFN-␥ (collectively termed LPS/IFN-␥) cooperative signaling in R...

Incubation of ex vivo cultured mature B cells in the presence of nitric oxide or nitric oxide-donor substances delays programmed cell death as determined by the appearance of DNA laddering in agarose gel electrophoresis or by flowcytometry analysis of DNA. Nitric oxide also rescues B cells from antigen-induced apoptosis but fails to provide a costimulatory signal that converts the signal elicited by the antigen into a proliferative response. The protective effects of nitric oxide against programmed cell death can be reproduced by treatment of the cells with permeant analogues of cyclic GMP. Regarding the mechanisms by which nitric oxide prevents apoptosis in B cells, we have observed that nitric oxide release prevents the drop in the expression of the protooncogene bcl-2, both at the mRNA and protein levels, suggesting the existence of an unknown pathway that links nitric oxide signaling with Bcl-2 expression. (J. Clin.

Nitric oxide (NO) induces apoptosis in thymocytes, peripheral T cells, myeloid cells and neurons.Here we show that NO is highly efficient in inducing mitochondrial permeability transition, thereby causing the liberation of apoptogenic factors from mitochondria which can induce nuclear apoptosis (DNA condensation and DNA fragmentation) in isolated nuclei in vitro. In intact thymocytes, NO triggers disruption of the mitochondrial transmembrane potential, followed by hypergeneration of reactive oxygen species, exposure of phosphatidyl serine on the outer plasma membrane leaflet, and nuclear apoptosis. Inhibitors of mitochondrial permeability transition such as bongkrekic acid and a cyclophilin D-binding cyclosporin A derivative, /V-methylVal-4-cyclosporin A, prevent the mitochondrial as well as all post-mitochondrial signs of apoptosis induced by NO including nuclear DNA fragmentation and exposure of phosphatidylserine residues on the cell surface. These findings indicate that NO can cause apoptosis via triggering of permeability transition.