Nerve growth factor-induced neuronal differentiation requires generation of Rac1-regulated reactive oxygen species

Neuregulin induces sustained reactive oxygen species generation to mediate neuronal differentiation

Neuregulins (NRGs), which are highly expressed in the nervous system, bind and activate two receptor tyrosine kinases, ErbB-3 and ErbB-4. Recently, we have shown that ErbB-4 receptors expressed in PC12 cells mediate NRG-induced differentiation through the MAPK signaling pathway. Here we demonstrate that NRG induces an increase in the intracellular concentration of reactive oxygen species (ROS). N-acetylcysteine, a ROS scavenger, inhibited NRG-induced activation of Ras and Erk and PC12-ErbB-4 cell differentiation. These results suggest that ROS production is involved in NRG-mediated neuronal differentiation and that ROS can regulate activation of Ras and Erk. Constitutively active Ras enhanced ROS production and dominant negative Ras inhibited NRG-induced ROS production, suggesting, a positive regulatory loop between Ras and ROS. The mitogen, EGF, induced short-term ROS production whereas NRG and NGF, which induce cell differentiation, induced prolonged ROS production. These results strongly suggest that the kinetics of ROS production may determine whether the cells will differentiate or proliferate.

Oxidative stress in scleroderma: maintenance of scleroderma fibroblast phenotype by the constitutive up-regulation of reactive oxygen species generation through the NADPH oxidase complex pathway

OBJECTIVE

To explore the role of reactive oxygen species (ROS) in the in vitro activation of skin fibroblasts from patients with systemic sclerosis (SSc).

METHODS

Fibroblasts were obtained from involved skin of patients with limited or diffuse SSc. Oxidative activity imaging in living cells was carried out using confocal microscopy. Levels of O2- and H2O2 released from fibroblasts were estimated by the superoxide dismutase (SOD)-inhibitable cytochrome c reduction and homovanilic acid assays, respectively. To verify NADPH oxidase activation, the light membrane of fibroblasts was immunoblotted with an anti-p47phox-specific antibody. Fibroblasts were stimulated with various cytokines and growth factors to determine whether any of these factors modulate ROS generation. Cell proliferation was estimated by 3H-thymidine incorporation. Northern blot analysis was used to study alpha1 and alpha2 type I collagen gene expression.

RESULTS

Unstimulated skin fibroblasts from SSc patients released more O2- and H2O2 in vitro through the NADPH oxidase complex pathway than did normal fibroblasts, since incubation of SSc fibroblasts with diphenylene iodonium, a flavoprotein inhibitor, suppressed the generation of ROS. This suppression was not seen with rotenone, a mitochondrial oxidase inhibitor, or allopurinol, a xanthine oxidase inhibitor. Furthermore, the cytosolic component of NADPH oxidase, p47phox, was translocated to the plasma membrane of resting SSc fibroblasts. A transient increase in ROS production was induced in normal but not in SSc fibroblasts by interleukin-1beta (IL-1beta), platelet-derived growth factor type BB (PDGF-BB), transforming growth factor beta1 (TGFbeta1), and H2O2. Treatment of normal and SSc fibroblasts with tumor necrosis factor a (TNFalpha), IL-2, IL-4, IL-6, IL-10, interferon-alpha (IFNalpha), IFNgamma, granulocyte-macrophage colony-stimulating factor (GM-CSP), G-CSF, or connective tissue growth factor (CTGF) had no effect on ROS generation. Constitutive ROS production by SSc fibroblasts was not inhibited when these cells were treated with catalase, SOD, IL-1 receptor antagonist, or antibodies blocking the effect of TGFbeta1, PDGF-BB, and other agonists (IL-4, IL-6, TNFalpha, CTGF). In contrast, treatment of SSc fibroblasts with the membrane-permeant antioxidant N-acetyl-L-cysteine inhibited ROS production, and this was accompanied by decreased proliferation of these cells and down-regulation of alpha1(I) and alpha2(I) collagen messenger RNA.

CONCLUSION

The constitutive intracellular production of ROS by SSc fibroblasts derives from the activation of an NADPH oxidase-like system and is essential to fibroblast proliferation and expression of type I collagen genes in SSc cells. Our results also exclude O2-, H2O2, IL-1beta, TGFbeta1, PDGF-BB, IL-4, IL-6, TNFalpha, or CTGF as mediators of a positive, autocrine feedback mechanism of ROS generation.

Induction of neurite outgrowth in PC12 cells by alpha -phenyl-N-tert-butylnitron through activation of protein kinase C and the Ras-extracellular signal-regulated kinase pathway

The spin trap alpha-phenyl-N-tert-butylnitron (PBN) is widely used for studies of the biological effects of free radicals. We previously reported the protective effects of PBN against ischemia-reperfusion injury in gerbil hippocampus by its activation of extracellular signal-regulated kinase (ERK) and suppression of both stress-activated protein kinase and p38 mitogen-activated protein kinase. In the present study, we found that PBN induced neurite outgrowth accompanied by ERK activation in PC12 cells in a dose-dependent manner. The induction of neurite outgrowth was inhibited significantly not only by transient transfection of PC12 cells with dominant negative Ras, but also by treatment with mitogen-activated protein kinase/ERK kinase inhibitor PD98059. The activation of receptor tyrosine kinase TrkA was not involved in PBN-induced neurite outgrowth. A protein kinase C (PKC) inhibitor, GF109203X, was found to inhibit neurite outgrowth. The activation of PKCepsilon was observed after PBN stimulation. PBN-induced neurite outgrowth and ERK activation were counteracted by the thiol-based antioxidant N-acetylcysteine. From these results, it was concluded that PBN induced neurite outgrowth in PC12 cells through activation of the Ras-ERK pathway and PKC.

The involvement of hydroxyl free radicals in differentiation of the PC-12 rat pheochromocytoma cell line

These experiments tested the differentiation properties of the PC-12 cell line under conditions of in vitro generation of OH&z.rad; free radicals by Fenton reaction. This involves the simultaneous addition of the following reactants: ADP-Fe(2+)-complex (0.1 mM for iron) and H(2)O(2) (0.025 mM), final concentrations. Superoxide dismutase activity, the increase of which is considered as a marker of differentiation, catalase and glutathione peroxidase enzyme activities were investigated, which all displayed significant increases after single and repeated interventions with hydroxyl free radicals, while the cell number remained nearly at the starting-value. It is known that the differentiation takes place when the cell number has reached a plateau. These data, therefore, suggest that hydroxyl free radicals can induce in vitro cell differentiation, and that they play a more complex role in cell physiology than simply causing oxidative damages. It is interesting that the cells can maintain high levels of these enzyme activities for a relatively long time (2 or 4 days) after a very short flux of hydroxyl free radicals.

Role of reactive oxygen species generated by NADPH oxidase in the mechanism of activation of K(+)-Cl(-)-cotransport by N-ethylmaleimide in HepG2 human hepatoma cells

K(+)-Cl(-)-cotransport (KCC) is ubiquitously present in all cells, and plays an essential role in ion and volume regulation. In this study we investigated the role of reactive oxygen species (ROS) in regulation of KCC in HepG2 human hepatoblastoma cells. N-ethylmaleimide (NEM), a KCC activator, induced Cl(-)-dependent K+ efflux, which was markedly prevented by KCC inhibitors (calyculin-A, genistein and BaCl2), indicating that KCC is activated by NEM in the HepG2 cells. Treatment with NEM also induced a sustained increase in the level of intracellular ROS assessed by 2',7'-dichlorofluorescein fluorescence. Antioxidants, N-acetyl cysteine or N,N'-diphenyl-p-phenylenediamine significantly inhibited both ROS generation and KCC activation induced by NEM. The NEM-induced ROS production was significantly suppressed by inhibitors of NADPH oxidase (diphenylene iodonium, apocynin and neopterine). These inhibitors also significantly inhibited the NEM-induced KCC activation. Taken together, these results suggest that ROS generated by NADPH oxidase may mediate the NEM-induced activation of KCC in human hepatoma cells.

Reactive oxygen species regulate signaling pathways induced by M1 muscarinic receptors in PC12M1 cells

Activation of the m1 muscarinic receptor subtype in rat pheochromocytoma (PC12) cells stably expressing cloned m1 muscarinic acetylcholine receptors was previously shown to induce morphological changes and growth arrest. However, the signaling pathways which lead to these effects were not identified. In an attempt to characterize the intracellular signaling that might be involved in the muscarinic-induced effects, we investigated the role of reactive oxygen species in the regulation of these processes. Stimulation of the muscarinic receptor in these cells increased the intracellular concentrations of reactive oxygen species. Muscarinic activation induced intracellular signaling pathways that involve activation of Ras, extracellular signal-regulated kinase (ERK), and p38. These pathways were partially blocked when reactive oxygen species (ROS) production was prevented by the antioxidant N-acetylcysteine. Other muscarinic-induced signals, such as activation of c-Jun NH(2)-terminal kinase (JNK) or an increase in the binding activity of the transcription factors nuclear factor-kappa B and activator protein-1, were inhibited by the antioxidant dicoumarol. N-Acetylcysteine also blocked the growth arrest and changes in cell shape induced by stimulation of the muscarinic receptor in PC12M1 cells. These findings suggest that ROS act as second messengers in muscarinic-induced cellular signaling. Moreover, generation of ROS appears to be an early and critical intermediary event, which occurs immediately after stimulation of the muscarinic receptor and affects in a variety of mechanisms the muscarinic-mediated cellular signaling.

Regulation of protein function by S-glutathiolation in response to oxidative and nitrosative stress

Protein S-glutathiolation, the reversible covalent addition of glutathione to cysteine residues on target proteins, is emerging as a candidate mechanism by which both changes in the intracellular redox state and the generation of reactive oxygen and nitrogen species may be transduced into a functional response. This review will provide an introduction to the concepts of oxidative and nitrosative stress and outline the molecular mechanisms of protein regulation by oxidative and nitrosative thiol-group modifications. Special attention will be paid to recently published work supporting a role for S-glutathiolation in stress signalling pathways and in the adaptive cellular response to oxidative and nitrosative stress. Finally, novel insights into the molecular mechanisms of S-glutathiolation as well as methodological problems related to the interpretation of the biological relevance of this post-translational protein modification will be discussed.