. Redox signaling: thiol chemistry defines which reactive oxygen and nitrogen species can act as second messengers. Am J Physiol Cell Physiol 287: C246 -C256, 2004; 10.1152/ ajpcell.00516.2003.-Except for the role of NO in the activation of guanylate cyclase, which is well established, the involvement of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in signal transduction remains controversial, despite a large body of evidence suggestive of their participation in a variety of signaling pathways. Several problems have limited their acceptance as signaling molecules, with the major one being the difficulty in identifying the specific targets for each pathway and the chemical reactions supporting reversible oxidation of these signaling components, consistent with a second messenger role for ROS and RNS. Nevertheless, it has become clear that cysteine residues in the thiolate (i.e., ionized) form that are found in some proteins can be specific targets for reaction with H 2O2 and RNS. This review focuses on the chemistry of the reversible oxidation of those thiolates, with a particular emphasis on the critical thiolate found in protein tyrosine phosphatases as an example. hydrogen peroxide; thiolate; nitrosothiol; nitric oxide; signal transduction ALTHOUGH THE INVOLVEMENT OF FREE RADICALS in biology was assumed for many years to be restricted to damaging reactions, the discovery of the endogenous generation of NO in mammalian systems and the finding that this small, freely diffusing, chemically unique species participates in specific signal transduction pathways represented an important new paradigm and expanded views of the possible nature of cell communication and/or signaling processes. This novel role in signal transduction for ⅐NO and other reactive nitrogen species (RNS) now extends to reactive oxygen species (ROS) such as H 2 O 2 and is gaining greater acceptance. The skepticism that still exists about these molecules acting as second messengers in various signaling pathways may vanish with better understanding of their chemistry, particularly regarding the differences in reactivity at high concentrations (mainly associated with pathology and toxicology) from those at low concentrations generated under physiological conditions in response to stimuli. Several excellent reviews have been published regarding evidence supporting a role for ROS and RNS in signaling (26,32,75,82,87,117,119), and we (35, 36) previously described the general properties that define a second messenger and showed how ROS and RNS fit into this role. In this review, the main focus is on the chemistry that may provide specificity, a necessary property of second messengers that has remained the most elusive in the study of ROS and RNS. REACTIVE SPECIES AS SECOND MESSENGERSSecond messengers are generated at the time of receptor activation, are short-lived, and act specifically on effectors to transiently alter their activity. Indeed, ROS and RNS can be generated at the time of receptor activation and are short-lived, as a...

The mitogen-activated protein (MAP) kinases are a large family of proline-directed, serine/threonine kinases that require tyrosine and threonine phosphorylation of a TxY motif in the activation loop for activation through a phosphorylation cascade involving a MAPKKK, MAPKK and MAPK, often referred to as the MAP kinase module. Three separate such modules have been identified, based on the TxY motif of the MAP kinase and the dual-specificity kinases that strictly phosphorylate their specific TxY sequence. They are the extracellular signal regulated kinases (ERKs), c-jun N-terminal kinases (JNKs) and p38 MAPKs. The ERKs are mainly associated with proliferation and differentiation while the JNKs and p38MAP kinases regulate responses to cellular stresses. Redox homeostasis is critical for proper cellular function. While reactive oxygen species (ROS) and oxidative stress have been implicated in injury, a rapidly growing literature suggests that a transient increase in ROS levels is an important mediator of proliferation and results in activation of various signaling molecules and pathways, among which the MAP kinases. This review will summarize the role of ROS in MAP kinase activation in various systems, including in macrophages, cells of myeloid origin that play an essential role in inflammation and express a multi-component NADPH oxidase that catalyzes the receptor-regulated production of ROS.

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Transcranial Doppler (TCD) is used to detect children with sickle cell anemia (SCA) who are at risk for stroke, and transfusion programs significantly reduce stroke risk in patients with abnormal TCD. We describe the predictive factors and outcomes of cerebral vasculopathy in the Cré teil newborn SCA cohort (n ‫؍‬ 217 SS/ S␤ 0 ), who were early and yearly screened with TCD since 1992. Magnetic resonance imaging/magnetic resonance angiography was performed every 2 years after age 5 (or earlier in case of abnormal TCD). A transfusion program was recommended to patients with abnormal TCD and/or stenoses, hydroxyurea to symptomatic patients in absence of macrovasculopathy, and stem cell transplantation to those with human leukocyte antigengenoidentical donor. Mean follow-up was 7.7 years (1609 patient-years). The cumulative risks by age 18 years were 1.9% (95% confidence interval [95% CI] 0.6%-5.9%) for overt stroke, 29.6% (95% CI 22.8%-38%) for abnormal TCD, which reached a plateau at age 9, whereas they were 22.6% (95% CI 15.0%-33.2%) for stenosis and 37.1% (95% CI 26.3%-50.7%) for silent stroke by age 14. Cumulating all events (stroke, abnormal TCD, stenoses, silent strokes), the cerebral risk by age 14 was 49.9% (95% CI 40.5%-59.3%); the independent predictive factors for cerebral risk were baseline reticulocytes count (hazard ratio 1.003/L ؋ 10 9 /L increase, 95% CI 1.000-1.006; P ‫؍‬ .04) and lactate dehydrogenase level (hazard ratio 2.78/1 IU/mL increase, 95% CI1.33-5.81; P ‫؍‬ .007). Thus, early TCD screening and intensification therapy allowed the reduction of stroke-risk by age 18 from the previously reported 11% to 1.9%. In contrast, the 50% cumulative cerebral risk suggests the need for more preventive intervention. (Blood. 2011;117(4):1130-1140)

Phagocytes such as neutrophils and macrophages produce reactive oxygen species (ROS) during phagocytosis or stimulation with a wide variety of agents through activation of nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase that is assembled at the plasma membrane from resident plasma membrane and cytosolic protein components. One of the subunits of the phagocyte NADPH oxidase is now recognized as a member of a family of NADPH oxidases, or NOX, present in cells other than phagocytes. Physiologic generation of ROS has been implicated in a variety of physiologic responses from transcriptional activation to cell proliferation and apoptosis. The increase in superoxide and hydrogen peroxide (H2O2) that results from stimulation of the NADPH oxidase is transient, in part due to the presence of the antioxidant enzymes, which return their concentrations to the prestimulation steady state level. Thus, the antioxidant enzymes may function in the "turn-off" phase of signal transduction by ROS. During its transient elevation, H2O2 may act as a modifier of key signaling enzymes through reversible oxidation of critical thiols. The rapid reaction of thiols with H2O2 when in their unprotonated state would provide a potential mechanism for the specificity that is necessary for physiologic cell signaling.

Changes in the ratio of intracellular reduced and disulfide forms of glutathione (GSH/GSSG) can affect signaling pathways that participate in various physiological responses from cell proliferation to gene expression and apoptosis. It is also now known that many proteins have a highly conserved cysteine (sulfhydryl) sequence in their active/regulatory sites, which are primary targets of oxidative modifications and thus important components of redox signaling. However, the mechanism by which oxidants and GSH/protein-cysteine-thiols actually participate in redox signaling still remains to be elucidated. Initial studies involving the role of cysteine in various proteins have revealed that cysteine-SH may mediate redox signaling via reversible or irreversible oxidative modification to Cys-sulfenate or Cys-sulfinate and Cys-sulfonate species, respectively. Oxidative stress possibly via the modification of cysteine residues activates multiple stress kinase pathways and transcription factors nuclear factor-kappaB and activator protein-1, which differentially regulate the genes for proinflammatory cytokines as well as the protective antioxidant genes. Understanding the redox signaling mechanisms for differential gene regulation may allow for the development of novel pharmacological approaches that preferentially up-regulate key antioxidants genes, which, in turn, reduce or resolve inflammation and injury. This forum article features the current knowledge on the role of GSH in redox signaling, particularly the regulation of transcription factors and downstream signaling in lung inflammation.

Stroke is predicted by abnormally high cerebral velocities by transcranial doppler (TCD).

It has been known for quite some time that proper cellular function requires tight control of the cellular redox state. In recent years, a growing body of literature has provided evidence of a role for reactive oxygen species (ROS) as important mediators of proliferation, acting as second messengers to modulate the activation of various signaling molecules and pathways. In contrast to high levels of ROS that may induce modifications that inhibit the activity of cellular components or result in damage, repair and cell death, the hypothesis that low levels of ROS, produced enzymatically and in a regulated fashion, are required participants of signaling pathways controlling essential cellular function is gaining grounds. The concept that ROS specifically target components of these pathways is only beginning to be examined. The mitogen-activated protein kinases (MAPK) are a large family of proline-directed, serine/threonine kinases that require tyrosine and threonine phosphorylation of a ThrXTyr motif in the activation loop for activation. Receptor-ligand interaction leads to activation of a phosphorylation cascade where the minimal module is formed by MAPK, MAPK kinase and MAPK kinase kinase. Four separate MAPK and activating cascades have been identified, based on the TXY motif and the dual-specificity kinases that strictly phosphorylate their particular TXY sequence. They are the extracellular signal regulated kinases (ERK), c-jun N-terminal kinases (JNK), p38MAPK and ERK5. This review will summarize recent findings regarding the activation of the MAPK and the role played by ROS in their activation.