Involvement of Raf-1/MEK/ERK1/2 signaling pathway in zinc-induced injury in rat renal cortical slices

Intracellular zinc release-activated ERK-dependent GSK-3β-p53 and Noxa-Mcl-1 signaling are both involved in cardiac ischemic-reperfusion injury

Oxidative stress and nitrosative stress are both suggested to be involved in cardiac ischemia-reperfusion (I/R) injury. Using time-lapse confocal microscopy of cardiomyocytes and high-affinity O(2)(-•) and Zn(2+) probes, this study is the first to show that I/R, reactive oxygen species (ROS), and reactive nitrogen species (RNS) all cause a marked increase in the [O(2)(-•)](i), resulting in cytosolic and mitochondrial Zn(2+) release. Exposure to a cell-penetrating, high-affinity Zn(2+)(i) chelator, TPEN, largely abolished the Zn(2+)(i) release and markedly protected myocytes from I/R-, ROS-, RNS-, or Zn(2+)/K(+) (Zn(2+)(i) supplementation)-induced myocyte apoptosis for at least 24 h after TPEN removal. Flavonoids and U0126 (a MEK1/2 inhibitor) largely inhibited the myocyte apoptosis and the TPEN-sensitive I/R- or Zn(2+)(i) supplement-induced persistent extracellular signal-regulated kinase 1 and 2 (ERK1/2) phosphorylation, dephosphorylation of p-Ser9 on glycogen synthase kinase 3β (GSK-3β), and the translocation into and accumulation of p-Tyr216 GSK-3β and p53 in, the nucleus. Silencing of GSK-3β or p53 expression was cardioprotective, indicating that activation of the ERK-GSK-3β-p53 signaling pathway is involved in Zn(2+)-sensitive myocyte death. Moreover, the ERK-dependent Noxa-myeloid cell leukemia-1 (Mcl-1) pathway is also involved, as silencing of Noxa expression was cardioprotective and U0126 abolished both the increase in Noxa expression and in Mcl-1 degradation. Thus, acute upstream Zn(2+)(i) chelation at the start of reperfusion and the use of natural products, that is, flavonoids, may be beneficial in the treatment of cardiac I/R injury.

ERK and cell death: mechanisms of ERK-induced cell death--apoptosis, autophagy and senescence

The Ras/Raf/extracellular signal-regulated kinase (ERK) signaling pathway plays a crucial role in almost all cell functions and therefore requires exquisite control of its spatiotemporal activity. Depending on the cell type and stimulus, ERK activity will mediate different antiproliferative events, such as apoptosis, autophagy and senescence in vitro and in vivo. ERK activity can promote either intrinsic or extrinsic apoptotic pathways by induction of mitochondrial cytochrome c release or caspase-8 activation, permanent cell cycle arrest or autophagic vacuolization. These unusual effects require sustained ERK activity in specific subcellular compartments and could depend on the presence of reactive oxygen species. We will summarize the mechanisms involved in Ras/Raf/ERK antiproliferative functions.

Expression of extracellular signal-regulated kinase in hepatic fibrosis and its correlation with collagen type I and III

AIM: To investigate the expression of ERK during the development of hepatic fibrosis and the correlation of ERK and I, III collagens.

METHODS: Hepatic fibrosis was induced by subcutaneous injection of DMN. Rats were killed for study at the end of first, second, third weeks and the clinical operative liver samples were collected. The development expression and location of the ERK in the hepatic tissue and the correlation of ERK with collagen I, III were assessed by means of immunohistochemistry.

RESULTS: The expression of ERK was increased and was closely correlated with that of collagen I and III during the development of rat fibrosis at every time point (1 wk: r = 0.75, 0.68, P < 0.05; 2 wk: r = 0.82, 0.78, P < 0.05; 3 wk: r = 0.74, 0.83, P < 0.05). Similarly, the expression of ERK was enhanced in human fibrotic tissues (1.068 ± 0.258 vs 0.035 ± 0.011, P < 0.05), which was correlated with that of collagen I and III (r = 0.87, 0.88, all P < 0.05).

CONCLUSION: The ERK signal pathway may play an important role in the pathogenesis of hepatic fibrosis.

Intracellular zinc release, 12-lipoxygenase activation and MAPK dependent neuronal and oligodendroglial death

Zinc translocation from presynaptic nerve terminals to postsynaptic neurons has generally been considered the critical step leading to the accumulation of intracellular free zinc and subsequent neuronal injury. Recent evidence, however, strongly suggests that the liberation of zinc from intracellular stores upon oxidative and nitrative stimulation contributes significantly to the toxicity of this metal not only to neurons, but also to oligodendrocytes. The exact cell death signaling pathways triggered by zinc are beginning to be deciphered. In this review, we describe how the activation of 12-lipoxygenase and mitogen-activated protein kinase (MAPK) contribute to the toxicity of liberated zinc to neurons and oligodendrocytes.

Intracellular zinc release, 12-lipoxygenase activation and MAPK dependent neuronal and oligodendroglial death

Zinc translocation from presynaptic nerve terminals to postsynaptic neurons has generally been considered the critical step leading to the accumulation of intracellular free zinc and subsequent neuronal injury. Recent evidence, however, strongly suggests that the liberation of zinc from intracellular stores upon oxidative and nitrative stimulation contributes significantly to the toxicity of this metal not only to neurons, but also to oligodendrocytes. The exact cell death signaling pathways triggered by zinc are beginning to be deciphered. In this review, we describe how the activation of 12-lipoxygenase and mitogen-activated protein kinase (MAPK) contribute to the toxicity of liberated zinc to neurons and oligodendrocytes.

Release of intracellular Zn2+ in cultured neurons after brief exposure to low concentrations of exogenous nitric oxide

Several studies have shown intracellular Zn(2+) release and concomitant cell death after prolonged exposure to exogenous NO. In the present study, we investigated whether cortical neurons briefly exposured to exogenous NO would demonstrate similar levels of intracellular Zn(2+) release and subsequent cell death. Cortical neurons were loaded with the Zn(2+) selective fluorophore FluoZin-3 and treated with various concentrations of the NO generator, spermine NONOate. Fluorescence microscopy was used to detect and quantify intracellular Zn(2+) levels. Concomitant EDTA perfusion was used to eliminate potential effects of extracellular Zn(2+). Neurons were perfused with the heavy metal chelator TPEN to selectively eliminate Zn(2+) induced fluorescence changes. A significant increase of intracellular fluorescence was detected during a 5 min perfusion with spermine NONOate. The increase in intracellular Zn(2+) release appeared to peak at 1 microM spermine NONOate (123.8 +/- 28.5%, increase above control n = 20, P < 0.001). Further increases in spermine NONOate levels as high as 1 mM failed to further increase detectable intracellular Zn(2+) levels. The NO scavenger hemoglobin blocked the effects of spermine NONOate and the inactive analog of the spermine NONOate, spermine, was without effect. No evidence of cell death induced by any of the brief treatments with exogenous NO was observed; only prolonged incubation with much larger amounts of exogenous NO resulted in significant cell death. These data suggest that in vivo release of NO may cause elevations of intracellular Zn(2+) in cortical neurons. The possibility that release of intracellular Zn(2+) in response to NO could play a role in intracellular signaling is discussed.