ZAP-70 tyrosine kinase, CD45, and T cell receptor involvement in UV- and H2O2-induced T cell signal transduction

Role of antioxidants in modulating anti-tumor T cell immune resposne

It has been well established that in addition to oxygen's vital in cellular respiration, a disruption of oxygen balance can lead to increased stress and oxidative injury. Similarly, reduced oxygen during tumor proliferation and invasion generates a hypoxic tumor microenvironment, resulting in dysfunction of immune cells and providing a conducive milieu for tumors to adapt and grow. Strategies to improve the persistence tumor reactive T cells in the highly oxidative tumor environment are being pursued for enhancing immunotherapy outcomes. To this end, we have focused on various strategies that can help increase or maintain the antioxidant capacity of T cells, thus reducing their susceptibility to oxidative stress/damage. Herein we lay out an overview on the role of oxygen in T cell signaling and how pathways regulating oxidative stress or antioxidant signaling can be targeted to enhance immunotherapeutic approaches for cancer treatment.

Reactive Oxygen Species: Do They Play a Role in Adaptive Immunity?

The immune system protects the host from a plethora of microorganisms and toxins through its unique ability to distinguish self from non-self. To perform this delicate but essential task, the immune system relies on two lines of defense. The innate immune system, which is by nature fast acting, represents the first line of defense. It involves anatomical barriers, physiological factors as well as a subset of haematopoietically-derived cells generically call leukocytes. Activation of the innate immune response leads to a state of inflammation that serves to both warn about and combat the ongoing infection and delivers the antigenic information of the invading pathogens to initiate the slower but highly potent and specific second line of defense, the adaptive immune system. The adaptive immune response calls on T lymphocytes as well as the B lymphocytes essential for the elimination of pathogens and the establishment of the immunological memory. Reactive oxygen species (ROS) have been implicated in many aspects of the immune responses to pathogens, mostly in innate immune functions, such as the respiratory burst and inflammasome activation. Here in this mini review, we focus on the role of ROS in adaptive immunity. We examine how ROS contribute to T-cell biology and discuss whether this activity can be extrapolated to B cells.

The early proximal αβ TCR signalosome specifies thymic selection outcome through a quantitative protein interaction network

During αβ T cell development, T cell antigen receptor (TCR) engagement transduces biochemical signals through a protein-protein interaction (PPI) network that dictates dichotomous cell fate decisions. It remains unclear how signal specificity is communicated, instructing either positive selection to advance cell differentiation or death by negative selection. Early signal discrimination might occur by PPI signatures differing qualitatively (customized, unique PPI combinations for each signal), quantitatively (graded amounts of a single PPI series), or kinetically (speed of PPI pathway progression). Using a novel PPI network analysis, we found that early TCR-proximal signals distinguishing positive from negative selection appeared to be primarily quantitative in nature. Furthermore, the signal intensity of this PPI network was used to find an antigen dose that caused a classic negative selection ligand to induce positive selection of conventional αβ T cells, suggesting that the quantity of TCR triggering was sufficient to program selection outcome. Because previous work had suggested that positive selection might involve a qualitatively unique signal through CD3δ, we reexamined the block in positive selection observed in CD3δ⁰ mice. We found that CD3δ⁰ thymocytes were inhibited but capable of signaling positive selection, generating low numbers of MHC-dependent αβ T cells that expressed diverse TCR repertoires and participated in immune responses against infection. We conclude that the major role for CD3δ in positive selection is to quantitatively boost the signal for maximal generation of αβ T cells. Together, these data indicate that a quantitative network signaling mechanism through the early proximal TCR signalosome determines thymic selection outcome.

C reactive protein impairs adaptive immunity in immune cells of patients with melanoma

BACKGROUND

High C reactive protein (CRP) levels have been reported to be associated with a poor clinical outcome in a number of malignancies and with programmed cell death protein 1 immune checkpoint blockade in patients with advanced cancer. Little is known about the direct effects of CRP on adaptive immunity in cancer. Therefore, we investigated how CRP impacted the function of T cells and dendritic cells (DCs) from patients with melanoma.

METHODS

The effects of CRP on proliferation, function, gene expression and phenotype of patient T cells and DCs, and expansion of MART-1 antigen-specific T cells were analyzed by multicolor flow cytometry and RNA-seq. Additionally, serum CRP levels at baseline from patients with metastatic melanoma treated on the Checkmate-064 clinical trial were assessed by a Luminex assay.

RESULTS

In vitro, CRP inhibited proliferation, activation-associated phenotypes and the effector function of activated CD4+ and CD8+ T cells from patients with melanoma. CRP-treated T cells expressed high levels of interleukin-1β, which is known to enhance CRP production from the liver. CRP also suppressed formation of the immune synapse and inhibited early events in T-cell receptor engagement. In addition, CRP downregulated the expression of costimulatory molecules on mature DCs and suppressed expansion of MART-1-specific CD8+ T cells in a dose-dependent manner by impacting on both T cells and antigen-presenting cells. High-serum CRP levels at baseline were significantly associated with a shorter survival in both nivolumab-treated and ipilimumab-treated patients.

CONCLUSIONS

These findings suggest that high levels of CRP induce an immunosuppressive milieu in melanoma and support the blockade of CRP as a therapeutic strategy to enhance immune checkpoint therapies in cancer.

TRIAL REGISTRATION NUMBER

NCT01783938 and NCT02983006.

Reactive Oxygen Species and Their Implications on CD4+ T Cells in Type 1 Diabetes

Previous work has indicated that type 1 diabetes (T1D) pathology is highly driven by reactive oxygen species (ROS). One way in which ROS shape the autoimmune response demonstrated in T1D is by promoting CD4⁺ T cell activation and differentiation. As CD4⁺ T cells are a significant contributor to pancreatic β cell destruction in T1D, understanding how ROS impact their development, activation, and differentiation is critical. Recent Advances: CD4⁺ T cells themselves generate ROS via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase expression and electron transport chain activity. Moreover, T cells can also be exposed to exogenous ROS generated by other immune cells (e.g., macrophages and dendritic cells) and β cells. Genetically modified animals and ROS inhibitors have demonstrated that ROS blockade during activation results in CD4⁺ T cell hyporesponsiveness and reduced diabetes incidence. Critical Issues and Future Directions: Although the majority of studies with regard to T1D and CD4⁺ T cells have been done to examine the influence of redox on CD4⁺ T cell activation, this is not the only circumstance in which a T cell can be impacted by redox. ROS and redox have also been shown to play roles in CD4⁺ T cell-related tolerogenic mechanisms, including thymic selection and regulatory T cell-mediated suppression. However, the effect of these mechanisms with respect to T1D pathogenesis remains elusive. Therefore, pursuing these avenues may provide valuable insight into the global role of ROS and redox in autoreactive CD4⁺ T cell formation and function.

Oxidative stress, consequences and ROS mediated cellular signaling in rheumatoid arthritis

There are numerous extra- and intra-cellular processes involved in the production of reactive oxygen species (ROS). Augmented ROS generation can cause the damage of biomolecules such as proteins, nucleic acid and lipids. ROS act as an intracellular signaling component and is associated with various inflammatory responses, chronic arthropathies, including rheumatoid arthritis (RA). It is well documented that ROS can activate different signaling pathways having a vital importance in the patho-physiology of RA. Hence, understanding of the molecular pathways and their interaction might be advantageous in the development of novel therapeutic approaches for RA.

Gastrointestinal Microbiome Dysbiosis in Infant Mice Alters Peripheral CD8+ T Cell Receptor Signaling

We recently reported that maternal antibiotic treatment (MAT) of mice in the last days of pregnancy and during lactation dramatically alters the density and composition of the gastrointestinal microbiota of their infants. MAT infants also exhibited enhanced susceptibility to a systemic viral infection and altered adaptive immune cell activation phenotype and function. CD8⁺ effector T cells from MAT infants consistently demonstrate an inability to sustain interferon gamma (IFN-γ) production in vivo following vaccinia virus infection and in vitro upon T cell receptor (TCR) stimulation. We hypothesize that T cells developing in infant mice with gastrointestinal microbiota dysbiosis and insufficient toll-like receptor (TLR) exposure alters immune responsiveness associated with intrinsic T cell defects in the TCR signaling pathway and compromised T cell effector function. To evaluate this, splenic T cells from day of life 15 MAT infant mice were stimulated in vitro with anti-CD3 and anti-CD28 antibodies prior to examining the expression of ZAP-70, phosphorylated ZAP-70, phospho-Erk-1/2, c-Rel, total protein tyrosine phosphorylation, and IFN-γ production. We determine that MAT infant CD8⁺ T cells fail to sustain total protein tyrosine phosphorylation and Erk1/2 activation. Lipopolysaccharide treatment in vitro and in vivo, partially restored IFN-γ production in MAT effector CD8⁺ T cells and reduced mortality typically observed in MAT mice following systemic viral infection. Our results demonstrate a surprising dependence on the gastrointestinal microbiome and TLR ligand stimulation toward shaping optimal CD8⁺ T cell function during infancy.

Mechanistic basis for protection of differentiated SH-SY5Y cells by oryzanol-rich fraction against hydrogen peroxide-induced neurotoxicity

BACKGROUND

Apoptosis is often the end result of oxidative damage to neurons. Due to shared pathways between oxidative stress, apoptosis and antioxidant defence systems, an oxidative insult could end up causing cellular apoptosis or survival depending on the severity of the insult and cellular responses. Plant bioresources have received close attention in recent years for their potential role in regulating the pathways involved in apoptosis and oxidative stress in favour of cell survival. Rice bran is a bioactive-rich by-product of rice milling process. It possesses antioxidant properties, making it a promising source of antioxidants that could potentially prevent oxidative stress-induced neurodegenerative diseases.

METHODS

Thus, the present study investigated the neuroprotective properties of oryzanol-rich fraction (ORF) against hydrogen peroxide (H2O2)-induced neurotoxicity in differentiated human neuroblastoma SH-SY5Y cells. ORF was extracted from rice bran using a green technology platform, supercritical fluid extraction system. Furthermore, its effects on cell viability, morphological changes, cell cycle, and apoptosis were evaluated. The underlying transcriptomic changes involved in regulation of oxidative stress, apoptosis and antioxidant defence systems were equally studied.

RESULTS

ORF protected differentiated SH-SY5Y cells against H2O2-induced neurotoxicity through preserving the mitochondrial metabolic enzyme activities, thus reducing apoptosis. The mechanistic basis for the neuroprotective effects of ORF included upregulation of antioxidant genes (catalase, SOD 1 and SOD 2), downregulation of pro-apoptotic genes (JNK, TNF, ING3, BAK1, BAX, p21 and caspase-9), and upregulation of anti-apoptotic genes (ERK1/2, AKT1 and NF-Kβ).

CONCLUSION

These findings suggest ORF may be an effective antioxidant that could prevent oxidative stress-induced neurodegenerative disorders.

NKG2D triggers cytotoxicity in murine epidermal γδ T cells via PI3K-dependent, Syk/ZAP70-independent signaling pathway

Murine epidermal γδ T cells, known as dendritic epidermal T cells (DETCs), survey tissue stress through the invariant T-cell receptor (TCR) and non-clonotypic receptors such as NKG2D. NKG2D signaling via the DAP10-phosphatidylinositol 3-kinase (PI3K) pathway directly stimulates cytotoxicity in natural killer (NK) cells and costimulates CD8(+) T cells to augment TCR signals. In activated murine NK cells, NKG2D signals also via the DAP12-Syk/ZAP70 pathway that triggers both cytotoxicity and cytokine production. It remains controversial whether NKG2D on DETCs is a primary activating receptor or functions only as a costimulatory receptor, and signaling pathways initiated by NKG2D ligation in DETCs have not been analyzed. We show that stimulation of short-term DETC lines with recombinant NKG2D ligands triggers degranulation (exocytosis of cytotoxic granules) via the PI3K-dependent signaling pathway, but does not induce cytokine production or Syk/ZAP70 activation. Coengagement of TCR or Syk/ZAP70 signaling was not crucial for DETC-mediated killing of NKG2D ligand-expressing target cells. Thus, NKG2D can function as a coactivating stress receptor that directly triggers cytotoxicity in DETCs, at least after priming, via the PI3K-dependent, Syk/ZAP70-independent signaling pathway.

The membrane adaptor LAT is proteolytically cleaved following Fas engagement in a tyrosine phosphorylation-dependent fashion

Engagement of the TCR (T-cell receptor) induces tyrosine phosphorylation of the LAT (linker for the activation of T-cells) adaptor, and thereby it recruits several cytosolic mediators for downstream signalling pathways. The Fas protein is essential for T-lymphocyte apoptosis, and following Fas engagement, many proteins are proteolytically cleaved, including several molecules that are important for the transduction of TCR intracellular signals. In the present study, we demonstrate that the adaptor LAT is also subject to a proteolytic cleavage in mature T-lymphocytes and thymocytes in response to Fas engagement, and also on TCR stimulation, and we identify three aspartic acid residues at which LAT is cleaved. Interestingly, these aspartic acid residues are located in proximity to several functionally important tyrosine residues of LAT, raising the possibility that their phosphorylation could modulate LAT cleavage. Consistent with that hypothesis, we show that induction of phosphorylation by pervanadate or H2O2 in Jurkat cells and thymocytes inhibits Fas-mediated cleavage of LAT. Moreover, we show that LAT proteolysis is also enhanced during anergy induction of primary human T-cells, suggesting that LAT cleavage may act as a regulator of TCR-mediated activation of T-cells and not only as a transducer of cell death promoting stimuli.

Activation of spleen tyrosine kinase is required for TNF-α-induced endothelin-1 upregulation in human aortic endothelial cells

Endothelin-1 (ET-1) promotes atherosclerosis. We tested whether spleen tyrosine kinase (Syk) mediates tumor necrosis factor-α (TNF-α)-induced ET-1 upregulation in human aortic endothelial cells (HAECs) and sought to identify the signal pathways involved. TNF-α-induced reactive oxygen species (ROS) activated Syk and phosphatidylinositol 3-kinase (PI3K), which was required for the activation of AP-1 and subsequent ET-1 gene transcription. ROS mediated c-Jun NH(2)-terminal kinase (JNK) is also required for AP-1 activation, but Syk and PI3K regulated AP-1 activation independently of JNK. Through regulation of ET-1 production, Syk could be implicated in atherosclerosis.

Chronic inflammatory disorders and their redox control: from molecular mechanisms to therapeutic opportunities

A chronic inflammatory disease is a condition characterized by persistent inflammation. A number of human pathologies fall into this category, and a great deal of research has been conducted to learn more about their characteristics and underlying mechanisms. In many cases, a genetic component has been identified, but also external factors like food, smoke, or environmental pollutants can significantly contribute to worsen their symptoms. Accumulated evidence clearly shows that chronic inflammatory diseases are subjected to a redox control. Here, we shall review the identity, source, regulation, and biological activity of redox molecules, to put in a better perspective their key-role in cancer, diabetes, cardiovascular diseases, atherosclerosis, chronic obstructive pulmonary diseases, and inflammatory bowel diseases. In addition, the impact of redox species on autoimmune disorders (rheumatoid arthritis, systemic lupus erythematosus, psoriasis, and celiac disease) and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis) will be discussed, along with their potential therapeutic implications as novel drugs to combat chronic inflammatory disorders.

Activation of ERK1/2 by protein kinase C-alpha in response to hydrogen peroxide-induced cell death in human gingival fibroblasts

Hydrogen peroxide (H(2)O(2)) increases protein tyrosine phosphorylation of numerous proteins in human gingival fibroblasts (HGFs). Two main proteins, with an apparent molecular weight of 44 and 42kDa, were phosphorylated after hydrogen peroxide stimulation of the human gingival fibroblasts. Further analysis identified these two proteins as ERK1/2. Maximum phosphorylation was detected at 10min post-H(2)O(2) treatment. Pretreatment with an MEK inhibitor, PD98059, inhibited H(2)O(2)-stimulated ERK1/2 phosphorylation in a dose-dependent manner. Treatment with H(2)O(2) also induced phosphorylation of protein kinase C-alpha (PKCalpha). Staurosporine, a PKC inhibitor, blocked ERK1/2 phosphorylation induced by H(2)O(2). In addition, H(2)O(2)-induced cell death was prevented by PD98059, SB203580, and calphostin C, which are MEK, p38 and PKC inhibitors, respectively. These results suggest that H(2)O(2) leads to the phosphorylation and activation of ERK1/2 in a PKC-dependent manner. These findings demonstrate that the MAPK signaling pathway plays an active role in mediating the H(2)O(2)-induced decrease in HGF cell viability and ATP depletion.

Molecular mechanisms of MHC class I-antigen processing: redox considerations

Major histocompatibility complex (MHC) class I molecules present antigenic peptides to the cell surface for screening by CD8(+) T cells. A number of ER-resident chaperones assist the assembly of peptides onto MHC class I molecules, a process that can be divided into several steps. Early folding of the MHC class I heavy chain is followed by its association with beta(2)-microglobulin (beta(2)m). The MHC class I heavy chain-beta(2)m heterodimer is incorporated into the peptide-loading complex, leading to peptide loading, release of the peptide-filled MHC class I molecules from the peptide-loading complex, and exit of the complete MHC class I complex from the ER. Because proper antigen presentation is vital for normal immune responses, the assembly of MHC class I molecules requires tight regulation. Emerging evidence indicates that thiol-based redox regulation plays critical roles in MHC class I-restricted antigen processing and presentation, establishing an unexpected link between redox biology and antigen processing. We review the influences of redox regulation on antigen processing and presentation. Because redox signaling pathways are a rich source of validated drug targets, newly discovered redox biology-mediated mechanisms of antigen processing may facilitate the development of more selective and therapeutic drugs or vaccines against immune diseases.

Intracellular Phospho-Flow cytometry reveals novel insights into TCR proximal signaling events. A comparison with Western blot

Phospho-site specific antibodies become increasingly available, enabling the study of signaling events by Western blotting (WB) or intracellular flow cytometry (Phospho-Flow). Here we compared data generated by WB or Phospho-Flow regarding the kinetics and degree of phosphorylation of membrane proximal TCR signaling molecules. Phosphorylation events in Jurkat T cells were triggered by anti-CD3 stimulation (OKT3) or by oxidative stress (H(2)O(2)) and were analyzed by Phospho-Flow or WB. Both techniques showed that OKT3- or H(2)O(2)-induced, transient phosphorylation of ZAP70 or LAT was dependent on functional Lck. Phospho-Flow data revealed differences in the kinetics and the degree of H(2)O(2)- or OKT3-mediated protein phosphorylation compared with WB data. In addition, using Phospho-Flow we discovered that H(2)O(2)-induced phosphorylation of TCR signaling proteins was inhibited by small molecular weight kinase inhibitors far more potently than OKT3-triggered protein phosphorylation, despite a superior induction of phosphorylation by H(2)O(2). This finding was confirmed by WB. Interestingly, we identified by Phospho-Flow that, in P116 Jurkat cells lacking ZAP70 protein expression, H(2)O(2) potently triggered the phosphorylation of ZAP70 residues Y493 and Y292 but not Y319. The phosphorylation of these ZAP70 tyrosine residues cells was blocked by an Lck inhibitor, suggesting the existence of an Lck-coupled truncated ZAP70 protein or a novel isoform of ZAP70 in P116 cells. Phospho-Flow is a largely quantitative technology with excellent throughput, highly suited in studying the function or inhibition of TCR signaling pathways and allowing the detection of novel pathway insights. It can serve as a good complement to Western blot analysis.

Protein tyrosine phosphorylation and protein tyrosine nitration in redox signaling

Reversible phosphorylation of protein tyrosine residues by polypeptide growth factor-receptor protein tyrosine kinases is implicated in the control of fundamental cellular processes including the cell cycle, cell adhesion, and cell survival, as well as cell proliferation and differentiation. During the last decade, it has become apparent that receptor protein tyrosine kinases and the signaling pathways they activate belong to a large signaling network. Such a network can be regulated by various extracellular cues, which include cell adhesion, agonists of G protein-coupled receptors, and oxidants. It is well documented that signaling initiated by receptor protein tyrosine kinases is directly dependent on the intracellular production of oxidants, including reactive oxygen and nitrogen species. Accumulated evidence indicates that the intracellular redox environment plays a major role in the mechanisms underlying the actions of growth factors. Oxidation of cysteine thiols and nitration of tyrosine residues on signaling proteins are described as posttranslational modifications that regulate, positively or negatively, protein tyrosine phosphorylation (PTP). Early observations described the inhibition of PTP activities by oxidants, resulting in increased levels of proteins phosphorylated on tyrosine. Therefore, a redox circuitry involving the increasing production of intracellular oxidants associated with growth-factor stimulation/cell adhesion, oxidative reversible inhibition of protein tyrosine phosphatases, and the activation of protein tyrosine kinases can be delineated.

A role for PLCγ2 in platelet activation by homocysteine

The aim of this study was to examine the homocysteine effect on phospholipase Cgamma2 (PLCgamma2) activation and to investigate the signaling pathway involved. We found that homocysteine stimulated the tyrosine phosphorylation and activation of platelet PLCgamma2. The tyrosine kinases p60src and p72syk appeared to be involved upstream. Reactive oxygen species were increased in homocysteine treated platelets. Likely oxidative stress could prime the non receptor-mediated tyrosine kinase p60src, inducing phosphorylation and activation of p72syk. The antioxidant N-acetyl-L-cysteine prevented the activation of these kinases. The phosphorylation and activation of PLCgamma2 were greatly reduced by the inhibition of p72syk through piceatannol. Moreover indomethacin diminished the homocysteine effect on p60src, p72syk and PLCgamma2, suggesting that thromboxane A(2) could be involved. In addition the treatment of platelets with homocysteine caused intracellular calcium rise and protein kinase C activation. Finally homocysteine induced platelet aggregation, that was partially reduced by indomethacin and by N-acetyl-L-cysteine of 35% or 50% respectively, while the PLCgamma2 specific inhibitor U73122 diminished platelet response to homocysteine of 70%. Altogether the data indicate that PLCgamma2 plays an important role in platelet activation by homocysteine and that the stimulation of this pathway requires signals through oxygen free radicals and thromboxane A(2).

Mutual cross-talk between reactive oxygen species and nuclear factor-kappa B: molecular basis and biological significance

Reactive oxygen species (ROS) are emerging as key effectors in signal transduction. This role of ROS is especially evident in the pathways leading to programmed cell death (PCD) elicited in response to certain stress stimuli and cytokines. In these pathways, cytotoxic ROS signaling appears to be mediated in part by activation of the c-Jun-N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) cascade. Another pathway that is under ROS-mediated control in some systems is that leading to activation of transcription factor nuclear factor-kappa B (NF-kappaB), which is a central regulator of immunity, inflammation and cell survival. Remarkably, new evidence has unveiled the existence of a reciprocal, negative control that NF-kappaB exerts on ROS and JNK activities. This NF-kappaB-imposed restraint on ROS and JNK signaling is crucial for antagonism of PCD elicited by the proinflammatory cytokine tumor necrosis factor (TNF)alpha and likely other triggers. Effectors of this antagonistic cross-talk between NF-kappaB and ROS/JNK pathways have recently been identified. Because of the key roles that the prosurvival function of NF-kappaB plays in organismal physiology and disease, gaining a further mechanistic understanding of this cross-talk and NF-kappaB-dependent survival may be key to developing new therapies for the treatment of widespread human illnesses, such as cancer and chronic inflammatory conditions.

REDOX REGULATION BY INTRINSIC SPECIES AND EXTRINSIC NUTRIENTS IN NORMAL AND CANCER CELLS

Cells in multicellular organisms are exposed to both endogenous oxidative stresses generated metabolically and to oxidative stresses that originate from neighboring cells and from other tissues. To protect themselves from oxidative stress, cells are equipped with reducing buffer systems (glutathione/GSH and thioredoxin/thioredoxin reductase) and have developed several enzymatic mechanisms against oxidants that include catalase, superoxide dismutase, and glutathione peroxidase. Other major extrinsic defenses (from the diet) include ascorbic acid, beta-carotene and other carotenoids, and selenium. Recent evidence indicates that in addition to their antioxidant function, several of these redox species and systems are involved in regulation of biological processes, including cellular signaling, transcription factor activity, and apoptosis in normal and cancer cells. The survival and overall well-being of the cell is dependent upon the balance between the activity and the intracellular levels of these antioxidants as well as their interaction with various regulatory factors, including Ref-1, nuclear factor-kappaB, and activating protein-1.

Effect of EGF on H2O2-induced inhibition of ?-MG uptake in renal proximal tubule cells: Involvement of MAPK and AA release

Both oxidative stress and epidermal growth factor (EGF) contribute to the initiation and progression of renal proximal tubular dysfunction under pathophysiologic conditions. Thus, this study was performed (1) to examine both the individual, and the combined effects of H2O2 and EGF on alpha-methyl-D-glucopyranoside uptake (alpha-MG uptake) in the primary cultured renal proximal tubule cells (PTCs), and (2) to elucidate the involvement of p44/42 mitogen activated protein kinase (MAPK) and phospholipase A2 in mediating these actions. Both H2O2 and EGF inhibited alpha-MG uptake individually, while the combination of H2O2 and EGF further potentiated the inhibitory effect on alpha-MG uptake, which was elicited by each agent. H2O2 not only caused a rapid increase in the phosphorylation of p44/42 MAPK, but also promoted the translocation of cytosolic phospholipase A2 (cPLA2) from the cytosolic to particulate fraction, and stimulated cellular [3H]-arachidonic acid (AA) release. EGF similarly activates phosphorylation of p44/42 MAPK and stimulates [3H]-AA release. When PTCs were exposed to 100 microM H2O2 and 50 ng/ml EGF simultaneously, a further increase in the phosphorylation of p44/42 MAPK, of [3H]-AA release, and of prostaglandin E2 (PGE2) production was elicited as compared with the effects of each individual agonist alone. Moreover, the additive phosphorylation of p44/42 MAPK, [3H]-AA release, and PGE2 production by H2O2 and EGF was almost completely inhibited by the p44/42 MAPK inhibitor, PD 98059. In conclusion, these results are consistent with the hypothesis that under conditions of oxidative stress, the H2O2-induced inhibition of alpha-MG uptake in the renal proximal tubule is mediated through a modulation of the EGF signaling pathway, promoting further phosphorylation of p44/42 MAPK, activation of PLA2.

Hydrogen Peroxide-Induced Extracellular Signal-Regulated Kinase Activation in Cultured Feline Ileal Smooth Muscle Cells

H(2)O(2) has been shown to act as a signaling molecule involved in many cellular functions such as apoptosis and proliferation. In the present study, we characterized the effects of H(2)O(2) on the activation of mitogen-activated protein (MAP) kinases and examined the factors involved in the process of extracellular signal-regulated kinase (ERK) activation by H(2)O(2) in ileal smooth muscle cells (ISMC). ISMC were cultured and exposed to H(2)O(2). Western blot analysis was performed with phosphospecific MAP kinase antibodies. Potent activation of ERK and moderate activation of stress-activated protein kinase/c-Jun NH(2)-terminal kinase occurred within 30 min of 1 mM H(2)O(2) treatment. However, p38 MAP kinase was not activated by H(2)O(2). The activation of ERK by H(2)O(2) was reduced by the mitogen-activated/ERK-activating kinase inhibitor PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one], Ras inhibitor S-farnesylthiosalicylic acid, removal of extracellular Ca(2+), depletion of the intracellular Ca(2+) pool by thapsigargin, or pretreatment of ISMC with the calmodulin antagonist W-7. Also, H(2)O(2)-induced ERK activation was attenuated by a receptor tyrosine kinase inhibitor, tyrphostin 51, but not by down-regulation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate or by a PKC inhibitor, GF109203X [3-[1-(dimethylaminopropyl)indol-3-yl]-4-(indol-3-yl)maleimide hydrochloride]. Growth factor receptor antagonist suramin pretreatment inhibited H(2)O(2)-induced ERK activation, highlighting a role for growth factor receptors in this activation. Furthermore, the ERK activation by H(2)O(2) was blocked by pretreatment with either N-acetyl-cysteine, o-phenanthroline, or mannitol indicating that metal-catalyzed free radical formation may mediate the initiation of signal transduction by H(2)O(2). These data suggest that short-term stimulation with H(2)O(2) activates the signaling pathways of cell mitogenic effects which are thought to be a protective response against intestinal oxidative stress.

Antipsoriatic drug anthralin induces EGF receptor phosphorylation in keratinocytes: requirement for H(2)O(2) generation

Even though anthralin is a well-established topical therapeutic agent for psoriasis, little is known about its effects and biochemical mechanisms of signal transduction. In contrast to a previous report, we found that anthralin induced time- and concentration-dependent phosphorylation of epidermal growth factor receptor in primary human keratinocytes. Four lines of evidence show that this process is mediated by reactive oxygen species. First, we found that anthralin induces time-dependent generation of H(2)O(2). Second, there is a correlation between a time-dependent increase in anthralin-induced epidermal growth factor receptor phosphorylation and H(2)O(2) generation. Third, the structurally different antioxidants n-propyl gallate and N-acetylcysteine inhibited epidermal growth factor receptor phosphorylation induced by anthralin. Fourth, overexpression of catalase inhibited this process. The epidermal growth factor receptor-specific tyrosine kinase inhibitor PD153035 abrogated anthralin-induced epidermal growth factor receptor phosphorylation and activation of extracellular-regulated kinase 1/2. These findings establish the following sequence of events: (1) H(2)O(2) generation, (2) epidermal growth factor receptor phosphorylation, and (3) extracellular-regulated kinase activation. Our data identify anthralin-induced reactive oxygen species and, more specifically, H(2)O(2) as an important upstream mediator required for ligand-independent epidermal growth factor receptor phosphorylation and downstream signaling.

p38 mitogen-activated protein kinase activation by ultraviolet A radiation in human dermal fibroblasts

UVA radiation penetrates deeply into the skin reaching both the epidermis and the dermis. We thus investigated the effects of naturally occurring doses of UVA radiation on mitogen-activated protein kinase (MAPK) activities in human dermal fibroblasts. We demonstrated that UVA selectively activates p38 MAPK with no effect on extracellular-regulated kinases (ERK1-ERK2) or JNK-SAPK (cJun NH2-terminal kinase-stress-activated protein kinase) activities. We then investigated the signaling pathway used by UVA to activate p38 MAPK. L-Histidine and sodium azide had an inhibitory effect on UVA activation of p38 MAPK, pointing to a role of singlet oxygen in transduction of the UVA effect. Afterward, using prolonged cell treatments with growth factors to desensitize their signaling pathways or suramin to block growth factor receptors, we demonstrated that UVA signaling pathways shared elements with growth factor signaling pathways. In addition, using emetine (a translation inhibitor altering ribosome functioning) we detected the involvement of ribotoxic stress in p38 MAPK activation by UVA. Our observations suggest that p38 activation by UVA in dermal fibroblasts involves singlet oxygen-dependent activation of ligand-receptor signaling pathways or ribotoxic stress mechanism (or both). Despite the activation of these two distinct signaling mechanisms, the selective activation of p38 MAPK suggests a critical role of this kinase in the effects of UVA radiation.

Expression of the pro-apoptotic gene gadd153/chop is elevated in liver with aging and sensitizes cells to oxidant injury

Aging is generally accompanied by reduced tolerance to oxidative stress and altered responsiveness to proliferative signals. We have shown that hepatocytes derived from aged rats (24-26 months) exhibit greater sensitivity to H(2)O(2) treatment and reduced proliferation following epidermal growth factor (EGF) treatment than cells of young adult rats (5-6 months). Here we examined the effects of aging and calorie restriction (CR) on expression of the oxidative stress-inducible and pro-apoptotic gene gadd153 (chop) in these hepatocytes, and we investigated its influence on sensitivity to oxidants. We show that aging was associated with elevated expression of gadd153, both basally and in response to H(2)O(2) treatment. CR, which attenuates age-associated declines in stress tolerance, prevented the age-related increase in gadd153 expression. EGF treatment also resulted in gadd153 induction in old cells. This effect was absent in young cells and in old cells of CR rats. gadd153 induction by EGF was reactive oxygen species-dependent and correlated with heightened sensitivity to subsequent H(2)O(2) treatment, suggesting that elevated Gadd153 contributes to the greater sensitivity of EGF-pretreated old cells to oxidative stress. Additional support for this hypothesis was provided by experiments with Rat1 fibroblasts in which conditional expression of Gadd153 conferred increased sensitivity to H(2)O(2). We propose a model whereby the diminished ability of old hepatocytes to overcome an EGF-triggered reactive oxygen species load leads to induction of the proapoptotic gene gadd153, which, in turn, sensitizes the cells to oxidant injury. Our findings point to gadd153 expression levels as an important factor in liver aging.

Involvement of CD4 D3-D4 membrane proximal extracellular domain for the inhibitory effect of oxidative stress on activation-induced CD4 down-regulation and its possible role for T cell activation

During antigen presentation, CD4 functions to stabilize T cell receptor (TCR)-class II MHC interactions and coordinate Ag-induced T cell activation signals. These activation signals cause CD4 down-regulation, presumably acting to optimize T cell activation. We previously reported that oxidative stress interferes with activation-induced CD4 down-regulation in T cells. In this study, we have further investigated inhibition of CD4 down-regulation by oxidative stress and its role for T cell activation. A construct comprised of the mouse FcgammaRIIB extracellular domain and the transmembrane/cytoplasmic domains of human CD4 (FcgammaR/CD4) was expressed in a human T cell line. Oxidant actually potentiated down-regulation of the FcgammaR/CD4 chimera and induced Lck dissociation from both CD4 and FcgammaR/CD4, which is a crucial intracellular process for activation-induced CD4 down-regulation, suggesting a critical role of CD4 ectodomain in the inhibition of CD4 down-regulation by oxidative stress. Furthermore, insertion of CD4 D3-D4 membrane proximal extracellular region between FcgammaR extracellular domain and CD4 transmembrane/cytoplasmic domains in FcgammaR/CD4 chimera made this molecule behave like native CD4 molecule under oxidative stress condition. These data imply that the inhibitory effect of oxidative stress on CD4 down-regulation is executed via D3-D4 domain of CD4 ectodomain. As to its role for T cell activation, CD4 coaggregation with CD3 under the oxidative conditions enhanced activation signal induced by CD3 aggregation. Our results demonstrate that Ag-induced T cell activation which is normally concomitant with CD4 down-regulation may be disturbed through the aberrant regulation of CD4 expression by oxidative stress.

Age-related decline in cellular response to oxidative stress: links to growth factor signaling pathways with common defects

Accumulation of oxidative damage is believed to be a major contributor to the decline in physiologic function that characterizes mammalian aging, and recent studies suggest that how well you respond to acute oxidative stress is an important factor in determining longevity. Oxidant injury elicits a wide spectrum of responses ranging from proliferation to cell death. The particular outcome observed largely reflects the severity of the stress encountered and the relative degree of activation of various signal transduction pathways aimed at enhancing survival or inducing cell death. Herein we examine the relationship between pathways important in supporting cell survival in response to oxidant injury and those involved in regulating proliferation. We review evidence indicating that [Curr. Opin. Cell Biol. 10 (1998) 248] common pathways are indeed involved in regulating these responses, and [Physiol. Rev. 82 (2002) 47] alterations in shared signaling events likely account for the age-related decline in the ability of cells to respond to both proliferative signals and oxidant stimuli.

Cellular response to oxidative stress: signaling for suicide and survival

Reactive oxygen species (ROS), whether produced endogenously as a consequence of normal cell functions or derived from external sources, pose a constant threat to cells living in an aerobic environment as they can result in severe damage to DNA, protein, and lipids. The importance of oxidative damage to the pathogenesis of many diseases as well as to degenerative processes of aging has becoming increasingly apparent over the past few years. Cells contain a number of antioxidant defenses to minimize fluctuations in ROS, but ROS generation often exceeds the cell's antioxidant capacity, resulting in a condition termed oxidative stress. Host survival depends upon the ability of cells and tissues to adapt to or resist the stress, and repair or remove damaged molecules or cells. Numerous stress response mechanisms have evolved for these purposes, and they are rapidly activated in response to oxidative insults. Some of the pathways are preferentially linked to enhanced survival, while others are more frequently associated with cell death. Still others have been implicated in both extremes depending on the particular circumstances. In this review, we discuss the various signaling pathways known to be activated in response to oxidative stress in mammalian cells, the mechanisms leading to their activation, and their roles in influencing cell survival. These pathways constitute important avenues for therapeutic interventions aimed at limiting oxidative damage or attenuating its sequelae.

Redox-linked signal transduction pathways for protein tyrosine kinase activation

The signaling for activation of protein tyrosine kinases (PTKs) is usually started by binding of ligands to cell-surface receptors. However, recent evidence suggests the presence of ligand binding-independent signaling pathways that are mediated by oxidative stress. Oxidation and reduction of protein cysteine sulfhydryl (SH) groups may work as a molecular switch to start or to stop the signaling. It is known that oxidation of cysteine SH groups on protein tyrosine phosphatases switches off the action of protein tyrosine phosphatases. This event may not, however, signal for initial autophosphorylation of previously unphosphorylated PTKs, whereas it certainly prevents dephosphorylation of once-phosphorylated PTKs. We have suggested new mechanisms for oxidative stress-mediated PTK activation. First, cell-surface glycosylphosphatidylinositol-anchoring proteins and a phosphoglycolipid/cholesterol-enriched membrane microdomain termed a "raft" can be the direct targets of oxidative stress for inducing their clustering through an S-S-bonded or S-X-S-bonded crosslinking of cell-surface proteins and subsequent activation of raft-associating Src family PTKs. Second, intracellular specific cysteine SH groups on PTK proteins can be another target of oxidative stress for inducing a conformational change necessary for initial activation of PTKs. A possible relationship between cell-surface and intracellular events is that the former frequently induces superoxide production as the second messenger for the latter.

Role of protein-tyrosine kinase syk in oxidative stress signaling in B cells

Oxidative stress induces the activation of multiple signaling pathways related to various cellular responses. In B cells, Syk has a crucial role in intracellular signal transduction induced by oxidative stress as well as antigen receptor engagement. Treatment of B cells with hydrogen peroxide (H(2)O(2)) induces enzymatic activation of Syk. Syk is essential for Ca(2+) release from intracellular pools through phospholipase C-gamma2 and the activation of c-Jun N-terminal kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol 3-kinase-Akt survival pathway following H(2)O(2) stimulation. Oxidative stress-induced cellular responses in B cells follow different patterns, such as necrosis, apoptosis, and mitotic arrest, according to the intensity of H(2)O(2) stimulation. Syk is involved in the protection of cells from apoptosis and induction of G2/M arrest. Syk leads to the activation of the phosphatidylinositol 3-kinase-Akt survival pathway, thereby enhancing cellular resistance to oxidative stress-induced apoptosis. On the other hand, Syk-dependent phospholipase C-gamma2 activation is required for acceleration toward apoptosis following oxidative stress. These findings suggest that oxidative stress-induced Syk activation triggers the activation of several pathways, such as proapoptotic and survival pathways, and the balance among these various pathways is a key factor in determining the fate of a cell exposed to oxidative stress.

Hypochlorous acid activates tyrosine phosphorylation signal pathways leading to calcium signaling and TNFalpha production

Hypochlorous acid is an important oxidizing agent produced by neutrophils to aid in defense against pathogens. Although hypochlorous acid is known to cause tissue damage due to its cytotoxicity, the effect of this oxidizing agent on signal transduction by cells of the immune system and its effects on their responses are not well understood. In this study, hypochlorous acid was found to induce cellular tyrosine phosphorylation in both T and B lymphocytes, activate the ZAP-70 tyrosine kinase, and induce cellular calcium signaling in a tyrosine kinase-dependent manner. These signaling events also occurred in T cell lines that did not express the T-cell receptor, indicating the ability of hypochlorous acid to bypass normal receptor control. Hypochlorous acid induced tumor necrosis factor-alpha production in peripheral blood mononuclear cells in a tyrosine kinase-dependent manner. These results suggest that hypochlorous acid may contribute to inflammatory responses by activating signal pathways in cells of the immune system.

Tyrosine phosphatase CD45 regulates hydrogen peroxide-induced calcium mobilization in B cells

By taking advantage of established CD45-deficient DT40 cells, the roles of CD45 in oxidative stress signaling were investigated. Using p-nitrophenyl phosphate as substrate, it was found that CD45 constituted nearly 40% of the total protein-tyrosine phosphatase activity. Almost 90% of the phosphatase activity was rapidly inactivated upon hydrogen peroxide treatment. Hydrogen peroxide-induced tyrosine phosphorylation of cellular proteins and c-Jun N-terminal kinase activation were markedly enhanced in CD45-deficient cells relative to that in its parental cells. In comparison, hydrogen peroxide-induced inositol 1,4,5-trisphosphate production and Ca(2+) mobilization were impaired in CD45-deficient DT40 cells. However, hydrogen peroxide-induced tyrosine phosphorylation of phospholipase Cgamma2 (PLCgamma2), phosphatidylinositol 3-kinase activity precipitated by anti-phosphotyrosine antibody, and activation of Bruton's tyrosine kinase appeared intact in CD45-deficient DT40 cells. This suggests that CD45 mediates the ability of hydrogen peroxide-activated PLCgamma2 to hydrolyze its substrate via a mechanism independent of both tyrosine phosphorylation of PLCgamma2 and phosphatidylinositol 3-kinase, as well as activation of Bruton's tyrosine kinase. Taken together, our observations demonstrated that, in addition to its negative regulatory or phosphatase activity, CD45 has a positive role in oxidative stress signaling.

Oxidants and tyrosine phosphorylation: role of acute and chronic oxidative stress in T-and B-lymphocyte signaling

The cellular response to an extracellular signal starts with the induction of a signaling cascade that transmits the signal through the cytoplasm to the nucleus, resulting in the activation of transcription factors that activate specific target genes. The signaling cascade involves a series of biochemical modifications that include phosphorylation events on tyrosine residues due to the activation of specific protein kinases. Recently, evidence accumulated that reactive oxygen species, including hydrogen peroxide, superoxide, and the hydroxyl radical, are important chemical mediators that regulate the transduction of signals from the membrane to the nucleus by modulating the protein activity by oxidation and reduction. In this report, the redox regulation of signaling involving protein tyrosine kinase activity, in particular in T- and B-lymphocyte signaling, is reviewed.

Reactive oxygen species differentially affect T cell receptor-signaling pathways

Oxidative stress plays an important role in the induction of T lymphocyte hyporesponsiveness observed in several human pathologies including cancer, rheumatoid arthritis, leprosy, and AIDS. To investigate the molecular basis of oxidative stress-induced T cell hyporesponsiveness, we have developed an in vitro system in which T lymphocytes are rendered hyporesponsive by co-culture with oxygen radical-producing activated neutrophils. We have observed a direct correlation between the level of T cell hyporesponsiveness induced and the concentration of reactive oxygen species produced. Moreover, induction of T cell hyporesponsiveness is blocked by addition of N-acetyl cysteine, Mn(III)tetrakis(4-benzoic acid)porphyrin chloride, and catalase, confirming the critical role of oxidative stress in this system. The pattern of tyrosine-phosphorylated proteins was profoundly altered in hyporesponsive as compared with normal T cells. In hyporesponsive T cells, T cell receptor (TCR) ligation no longer induced phospholipase C-gamma1 activation and caused reduced Ca(2+) flux. In contrast, despite increased levels of ERK1/2 phosphorylation, TCR-dependent activation of mitogen-activated protein kinase ERK1/2 was unaltered in hyporesponsive T lymphocytes. A late TCR-signaling event such as caspase 3 activation was as well unaffected in hyporesponsive T lymphocytes. Our data indicate that TCR-signaling pathways are differentially affected by physiological levels of oxidative stress and would suggest that although "hyporesponsive" T cells have lost certain effector functions, they may have maintained or gained others.

Effect of age and oxidative stress on tyrosine phosphorylation of ZAP-70

Oxidative stress is believed to be one of the leading contributors to the aging process and loss of cellular function with aging. Although, several age-associated phenomena have been correlated with reactive oxygen species, the role of oxidative stress in the age-related decline of T-cell activity is not yet clear. The present study was carried out to determine the effect of reactive oxygen species on tyrosine phosphorylation of ZAP-70, a key enzyme in the T-cell signal transduction pathway. Our previous as well as present studies have demonstrated an age-related down-regulation of tyrosine phosphorylation of ZAP-70 following activation of freshly isolated T cells with various stimulating agents. Currently, we observe that under mild and chronic oxidative stress, tyrosine phosphorylation of ZAP-70 is impaired following stimulation of the T cells with anti-CD3 antibody. Interestingly, in contrast to our observation using freshly isolated T cells, there is no age-associated impairment of tyrosine phosphorylation of ZAP-70 when T cells, cultured for 2 days in a serum-free medium in the presence or in the absence of oxidative stress, are stimulated with anti-CD3 antibody. The current observation suggests that the age-associated down-regulation of tyrosine phosphorylation of ZAP-70 is not an intrinsic defect inherent of the T cells due to aging and is reversible. We also observed that under oxidative stress in vitro, there was no significant difference in inhibition of tyrosine phosphorylation of ZAP-70 in T cells isolated from elderly and young donors. Finally, it was also noted that the down-regulation of tyrosine phosphorylation of ZAP-70 under oxidative stress in young and elderly donors was not due to impairment in the net expression of ZAP-70 under oxidative stress thereby suggesting that dysregulation in the balance of kinase-phosphatase activities under oxidative stress might have been implicated in the observed phenomenon.

Free radicals in the physiological control of cell function

At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis." Higher organisms, however, have evolved the use of NO and ROS also as signaling molecules for other physiological functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin production, and signal transduction from membrane receptors in various physiological processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amounts of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metabolism. An excessive and/or sustained increase in ROS production has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addition, free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 years ago by Harman (J Gerontol 11: 298-300, 1956). There is growing evidence that aging involves, in addition, progressive changes in free radical-mediated regulatory processes that result in altered gene expression.

UV-induced tyrosine phosphorylation of PKC delta and promotion of apoptosis in the HaCaT cell line

Protein kinase C delta (PKC delta) is activated through tyrosine phosphorylation and is involved in apoptosis induction in the H(2)O(2)-treated fibroblasts. In the human keratinocyte HaCaT cell line, ultraviolet radiation, which induces apoptosis, promoted tyrosine phosphorylation and activation of PKC delta, but neither enhanced threonine phosphorylation in the activation loop nor generated the catalytic fragment of the PKC isoform. Tyrosine phosphorylation of PKC delta was prevented by a radical scavenger, N-acetyl-l-cysteine, and by a tyrosine kinase inhibitor, genistein, in the ultraviolet-irradiated keratinocyte cell line. Ultraviolet radiation-induced apoptosis was attenuated by N-acetyl-l-cysteine and genistein as well as by a PKC inhibitor, bisindolylmaleimide I. These results indicate that reactive oxygen species generated by ultraviolet radiation enhance tyrosine phosphorylation of PKC delta, and the PKC isoform thus activated by the modification reaction contributes to induction of apoptotic cell death in keratinocytes.

Oxidant-dependent phosphorylation of p40phox in B lymphocytes

As with the neutrophil NADPH oxidase, the B lymphocyte NADPH oxidase consists of a membrane-bound flavocytochrome b and regulatory factors including Rac and the cytosolic phox protein triad p67phox, p47phox, and p40phox. Here we demonstrate by phosphoamino acid analysis and the use of the potent PKC inhibitor GFX that, in response to stimulation of B lymphocytes with sodium orthovanadate and H(2)O(2), the p40phox component of the cytosolic phox triad is selectively phosphorylated on serine and threonine residues by a PKC-type protein kinase. The pattern of p40phox phosphorylation was closely related to the kinetics of tyrosine phosphorylation of PKC-delta, the main PKC isotype of B lymphocytes. Blocking H(2)O(2)-dependent tyrosine phosphorylation of PKC by genistein resulted in inhibition of p40phox phosphorylation. The correlation between the tyrosine phosphorylation of PKC-delta and the serine/threonine phosphorylation of p40phox, together with the inhibition of p40phox phosphorylation by rottlerin, a selective inhibitor of PKC-delta, makes the activated PKC-delta a likely candidate in the process of the oxidant-dependent phosphorylation of p40phox in B cells.

Vitamin E-enhanced IL-2 production in old mice: naive but not memory T cells show increased cell division cycling and IL-2-producing capacity

Aging is associated with reduced T cell function, as demonstrated by decreased T cell proliferation and IL-2 production. These changes respond to supplemental vitamin E both in animals and humans, in part by the reduction of T cell suppressive PGE(2), the production of which by macrophages is increased with age. To evaluate whether vitamin E has a direct PGE(2)-independent effect on T cell responses, T cells purified from the spleens of young and old mice were preincubated with vitamin E or vehicle control. Activation-induced cell division of T cells from old mice was lower than that by young, and the production of IL-2 following 48-h activation was less by T cells from old mice. There was an age-related decline in both the number of IL-2+ T cells and the amount of IL-2 produced per cell. Despite decreased IL-2 protein at 48 h, the expression of IL-2 mRNA at 6 h and IL-2 protein production at 6 and 16 h was greater by T cells from old mice compared with that of young. Age-related decline in cell division and IL-2 production at 48 h was only observed within the naive T cell subpopulation. Vitamin E increased both cell-dividing and IL-2-producing capacity of naive T cells from old mice, with no effect on memory T cells. These data indicate that naive T cells exhibit the greatest age-related defect and show for the first time that supplemental vitamin E has direct immunoenhancing effect on naive T cells from old mice.

Bruton's tyrosine kinase is essential for hydrogen peroxide-induced calcium signaling

Using Btk-deficient DT40 cells and the transfectants expressing wild-type Btk or Btk mutants in either kinase (Arg(525) to Gln), Src homology 2 (SH2, Arg(307) to Ala), or pleckstrin homology (PH, Arg(28) to Cys) domains, we investigated the roles and structure-function relationships of Btk in hydrogen peroxide-induced calcium mobilization. Our genetic evidence showed that Btk deficiency resulted in a significant reduction in hydrogen peroxide-induced calcium response. This impaired calcium signaling is correlated with the complete elimination of IP3 production and the significantly reduced tyrosine phosphorylation of PLCgamma2 in Btk-deficient DT40 cells. All of these defects were fully restored by the expression of wild-type Btk in Btk-deficient DT40 cells. The data from the point mutation study revealed that a defect at any one of the three functional domains would prevent a full recovery of Btk-mediated hydrogen peroxide-induced intracellular calcium mobilization. However, mutation at either the SH2 or PH domain did not affect the hydrogen peroxide-induced activation of Btk. Mutation at the SH2 domain abrogates both IP3 generation and calcium release, while the mutant with the nonfunctional PH domain can partially activate PLCgamma2 and catalyze IP3 production but fails to produce significant calcium mobilization. Thus, these observations suggest that Btk-dependent tyrosine phosphorylation of PLCgamma2 is required but not sufficient for hydrogen peroxide-induced calcium mobilization. Furthermore, hydrogen peroxide stimulates a Syk-, but not Btk-, dependent tyrosine phosphorylation of B cell linker protein BLNK. The overall results, together with those reported earlier [Qin et al. (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 7118], are consistent with the notion that functional SH2 and PH domains are required for Btk to form a complex with PLCgamma2 through BLNK in order to position the Btk, PLCgamma2, and phosphatidylinositol 4,5-bisphosphate in close proximity for efficient activation of PLCgamma2 and to maximize its catalytic efficiency for IP3 production.

H(2)O(2) mediates oxidative stress-induced epidermal growth factor receptor phosphorylation

We used a well-established thiol-alkylating agent, N-ethylmaleimide (NEM), to oxidatively stress human keratinocytes. Time course studies revealed that NEM rapidly depleted keratinocytes of reduced glutathione (GSH), which was followed by rapidly increasing levels of intracellular reactive oxygen species (ROS) and subsequently by phosphorylation of epidermal growth factor receptor (EGFR). Pretreatment with antioxidants or enhanced catalase activity in keratinocytes inhibited ROS/H(2)O(2) accumulation and EGFR phosphorylation, demonstrating that H(2)O(2) production is a mediator required for EGFR phosphorylation. Collectively, these results suggest a sequence of events leading to EGFR phosphorylation which is likely shared by oxidative stress-inducing agents, namely: (1) GSH depletion; (2) H(2)O(2) accumulation; and (3) EGFR phosphorylation. We propose that depletion of GSH and accumulation of H(2)O(2) are upstream events and critical mediators required for ligand-independent phosphorylation of growth factor receptors in response to oxidative stress.

Inhibition of phosphatidylserine synthesis in Jurkat T cells by hydrogen peroxide

Incubation of Jurkat cells in the presence of H2O2 either directly added to the culture medium or generated with glucose oxidase, menadione or the couple xanthine/xanthine oxidase induced a marked decrease of phosphatidylserine synthesis in the absence of changes in the synthesis of phosphatidylcholine and phosphatidylethanolamine. Concentration dependent response curves indicated that H2O2 induced inhibition of phosphatidylserine synthesis with an IC(50)=5 microM while both induction of tyrosine phosphorylation of proteins and Ca(2+) signals were obtained with an EC(50)=300 microM. The tyrosine kinase and Ca(2+) independent mechanism was confirmed by comparing the H2O2-induced and the CD3-induced inhibition of phosphatidylserine synthesis using several Jurkat clones differing in the expression of cell surface receptors such as CD3/TCR and CD45 and protein tyrosine kinase such as p72syk, ZAP-70 and p56lck. While CD3-induced inhibition of phosphatidylserine synthesis necessitates protein tyrosine phosphorylation and Ca(2+) signals, H2O2 provoked its effect in all the clones studied independently of the presence or absence of the proteins previously shown to be key elements in T cell signal transduction. Conversely, the antioxidant molecule, butylated hydroxanisole, generates an increased PtdSer synthesis, suggesting that the synthesis of this phospholipid is regulated by the redox status of the cells.

Tyrosine phosphorylation-dependent activation of NF-kappa B. Requirement for p56 LCK and ZAP-70 protein tyrosine kinases

Phosphorylation of the N-terminal domain of I kappa B inhibitory subunits induces activation of the transcription factor NF-kappa B. Although serine phosphorylation has been shown to induce ubiquitination and subsequent proteasome-mediated degradation of I kappa B-alpha, little is known about the mechanisms that lead to release of active NF-kappa B in T cells as a consequence of tyrosine phosphorylation of I kappa B-alpha [Imbert, V., Rupec, R.A., Livolsi, A., Pahl, H.L., Traenckner, B.M., Mueller-Dieckmann, C., Farahifar, D., Rossi, B., Auberger, P., Baeuerle, P. & Peyron, J.F. (1996) Cell 86, 787--798]. The involvement of the tyrosine kinases p56(lck) and ZAP-70 in this reaction is demonstrated here using specific pharmacological inhibitors and Jurkat mutants unable to express these kinases. Although the inhibitors prevented both pervanadate-induced phosphorylation of I kappa B-alpha on Tyr42 and NF-kappa B activation, we observed that, in p56(lck)-deficient Jurkat mutants, NF-kappa B could still associate with I kappa B-alpha despite phosphorylation on Tyr42. Furthermore, the SH2 domain of p56(lck) appeared to be required for pervanadate-induced NF-kappa B activation but not for Tyr42 phosphorylation. These results show that p56(lck) and ZAP-70 are key components of the signaling pathway that leads to phosphotyrosine-dependent NF-kappa B activation in T cells and confirm that tyrosine kinases must control at least two different steps to induce activation of NF-kappa B. Finally, we show that H(2)O(2), which stimulates p56(lck) and ZAP-70 in T cells, is an activator of NF-kappa B through tyrosine phosphorylation of I kappa B-alpha.

CHOP/GADD153 gene expression response to cellular stresses inhibited by prior exposure to ultraviolet light wavelength band C (UVC). Inhibitory sequence mediating the UVC response localized to exon 1

CHOP/GADD153 is both an activating and repressing transcription factor that is markedly induced in response to a variety of cellular stresses. The CHOP/GADD153 gene was originally cloned because of its inducibility by ultraviolet light wavelength band C (UVC) and has since been found to be activated in response to many different cellular stresses. Some of the recent studies have questioned the UVC responsiveness of the CHOP gene. Contradiction in our own data led us to reexamine the UVC effects on CHOP expression. UVC is capable of strongly activating the mouse CHOP promoter in stably transfected NIH 3T3 cells but has only a modest and transient effect on the level of the CHOP messenger RNA. In addition to its positive effect on CHOP promoter activity, we show that UVC negatively affects CHOP mRNA and protein expression. Pretreatment of NIH 3T3 cells with UVC markedly attenuates the subsequent induction of CHOP mRNA by the cellular stress activators methylmethane sulfate, tunicamycin, glucose deprivation, and methionine deprivation for as long as at least 16 h. This inhibitory effect of UVC on CHOP expression in response to stress is independent of the presence or absence of p53 and does not involve mRNA degradation as opposed to the UVC effect that inhibits p21 expression seen only in the absence of p53. The target of the inhibitory effect of UVC on CHOP expression is located in the first exon of the gene, a 5'-untranslated region that is unusually conserved between different species. These findings suggest that an unknown function encoded by the 5'-untranslated region somehow modifies the response of CHOP gene transcription to UVC.

Enhancement of T cell receptor signaling by a mild oxidative shift in the intracellular thiol pool

Exposure of T cells to the macrophage products hydrogen peroxide (HP) or L-lactate (LAC) was previously shown to enhance IL-2 production and to modulate glutathione (GSH) status. We now found that 50 microM HP and 30 mM LAC enhanced strongly the transcription from the IL-2 promoter in Jurkat T cells after stimulation with anti-CD28 together with or without anti-CD3 but not with anti-CD3 Abs alone. Therefore, we used anti-CD3 plus anti-CD28-stimulated cells to investigate the effect of the GSH reductase inhibitor 1, 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) on the signal cascade. BCNU enhanced the transcription to a similar extent as HP or LAC. Lowering the intracellular GSH/GSH disulfide ratio by BCNU, HP, or NO resulted in all cases in the fulminant enhancement of Jun-N-terminal kinase and p38 mitogen-activated protein kinase but not extracellular signal-regulated kinase 1/2. Jun-N-terminal kinase and NF-kappaB activation was enhanced through pathways involving Rac, Vav1, PKCTheta, p56(lck), p59(fyn), and IkappaB kinases. In a cell-free system, the autophosphorylation of rFyn was stimulated by GSH disulfide but not by HP. These findings suggest that the oxidation of the cellular thiol pool may play a role as an amplifying mechanism for TCR/CD3 signals in immune responses.