Modulation by caspases of tumor necrosis factor-stimulated c-Jun N-terminal kinase activation but not nuclear factor-kappaB signaling

De-ubiquitinating protease USP2a targets RIP1 and TRAF2 to mediate cell death by TNF

Components of the TNFR1 complex are subject to dynamic ubiquitination that impacts on their effects as signalling factors. We have found that the ubiquitin-specific protease USP2a has a pivotal role in the decision for cell death or survival by the TNFR1 complex. This enzyme is a novel component of the TNFR1 complex that is recruited upon ligand binding and controls the signalling activity of the TNFR1-interacting protein RIP1 by removing its K63-linked ubiquitin chains. USP2a similarly de-ubiquitinates TRAF2, a ubiquitin-ligase recruited to the TNFR1 complex. During the TNF response the activity of USP2a on RIP1 and TRAF2 is required for the efficient reappearance of IκBα, which is essential to inactivate the anti-apoptotic transcription factor NF-κB. The effects of USP2a culminate in the conversion of the anti-apoptotic TNFR1 complex I into the pro-apoptotic TNFR1 complex II. Consequently, downregulation of USP2a promotes NF-κB activation and protects cells against TNF-induced cell death.

Recommendations for the design, optimization, and qualification of cell-based assays used for the detection of neutralizing antibody responses elicited to biological therapeutics

The administration of biological therapeutics can evoke some level of immune response to the drug product in the receiving subjects. An immune response comprised of neutralizing antibodies can lead to loss of efficacy or potentially more serious clinical sequelae. Therefore, it is important to monitor the immunogenicity of biological therapeutics throughout the drug product development cycle. Immunoassays are typically used to screen for the presence and development of anti-drug product antibodies. However, in-vitro cell-based assays prove extremely useful for the characterization of immunoassay-positive samples to determine if the detected antibodies have neutralizing properties. This document provides scientific recommendations based on the experience of the authors for the development of cell-based assays for the detection of neutralizing antibodies in non-clinical and clinical studies.

Neuroprotection by ovarian hormones in animal models of neurological disease

Ovarian hormones can protect against brain injury, neurodegeneration, and cognitive decline. Most attention has focused on estrogens and accumulating data demonstrate that estrogen seems to specifically protect cortical and hippocampal neurons from ischemic injury and from damage due to severe seizures. Although multiple studies demonstrate protection by estrogen, in only a few instances is the issue of how the steroid confers protection known. Here, we first review data evaluating the neuroprotective effects of estrogens, a selective estrogen receptor modulator (SERM), and estrogen receptor alpha- and beta-selective ligands in animal models of focal and global ischemia. Using focal ischemia in ovariectomized ERalphaKO, ERbetaKO, and wild-type mice, we clearly established that the ERalpha subtype is the critical ER mediating neuroprotection in mouse focal ischemia. In rats and mice, the middle cerebral artery occlusion (MCAO) model was used to represent cerebrovascular stroke, while in gerbils the two-vessel occlusion model, representing global ischemia, was used. The gerbil global ischemia model was used to evaluate the neuroprotective effects of estrogen, SERMs, and ERalpha- and ERbeta-selective compounds in the hippocampus. Analysis of neurogranin mRNA, a marker of viability of hippocampal neurons, with in situ hybridization, revealed that estrogen treatment protected the dorsal CA1 regions not only when administered before, but also when given 1 h after occlusion. Estrogen rarely is secreted alone and studies of neuroprotection have been less extensive for a second key ovarian hormone progesterone. In the second half of this review, we present data on neuroprotection by estrogen and progesterone in animal model of epilepsy followed by exploration into ovarian steroid effects on neuronal damage in models of multiple sclerosis and traumatic brain injury.

Alpha-lipoic acid inhibits TNF-alpha-induced apoptosis in human bone marrow stromal cells

TNF-alpha is an important mediator of bone loss. In the HS-5 hBMSC, TNF-alpha and H2O2 increased intracellular ROS levels and induced cell apoptosis through activation of caspases, JNK and NF-kappaB. alpha-Lipoic acid prevented these changes induced by TNF-alpha and H2O2, suggesting its potential therapeutic applications in attenuating bone loss.

INTRODUCTION

Oxidative stress is an important mediator of bone loss. TNF-alpha, which plays a critical role in the bone loss after menopause, has been shown to increase intracellular oxidative stress. Because oxidative stress is associated with cell death, we analyzed the apoptotic effects of TNF-alpha and H2O2 on human bone marrow stromal cells (hBMSCs). We also examined the protective effects of an important biological thiol antioxidant, alpha-lipoic acid (alpha-LA), against TNF-alpha- and H2O2-induced apoptosis.

MATERIALS AND METHODS

Using the HS-5 hBMSC cell line, we tested whether TNF-alpha-induced apoptosis was mediated by the generation of excessive reactive oxygen species (ROS). Apoptosis was determined by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay, trypan blue exclusion assay, quantitation of histone-associated DNA fragments in cytosol, and the activation of caspases. The mechanisms mediating these apoptotic effects were determined by Western blotting and enzyme immunoassay.

RESULTS

Both TNF-alpha and H2O2 increased intracellular ROS levels, reduced total cellular glutathione levels, activated caspases-3, -9, and -8, and enhanced hBMSC apoptosis. The activation of c-jun N-terminal kinase (JNK) and NF-kappaB mediated these apoptotic effects. Pretreatment of cells with alpha-LA prevented these changes induced by TNF-alpha and H2O2.

CONCLUSIONS

Our data show that TNF-alpha increases intracellular ROS in hBMSC and that TNF-alpha and H2O2 induce apoptosis in hBMSC through the activation of JNK and NF-kappaB. Our findings also suggest that alpha-LA may have therapeutic applications in halting or attenuating bone loss associated with increased oxidative stress.

Switching leukemia cell phenotype between life and death

Divergent life or death responses of a cell can be controlled by a single cytokine (tumor necrosis factor alpha, TNF) via the signaling pathways that respond to activation of its two receptors (TNFR1 and TNFR2). Here, we show that the choice of life or death can be controlled by manipulation of TNFR signals. In human erythroleukemia patient myeloid progenitor stem cells (TF-1) as well as chronic myelogenous leukemia cells (K562), granulocyte-macrophage colony-stimulating factor primes cells for apoptosis. These death-responsive cells show prolonged TNF stimulation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase, but no NF-kappaB transcriptional activity as a consequence of receptor-interacting protein degradation by caspases. Conversely, cells of a proliferative phenotype display antiapoptotic NF-kappaB responses that antagonize c-Jun N-terminal kinase and p38 mitogen-activated protein kinase stress kinase effects. These proliferative effects of TNF are apparently due to enhanced basal expression of the caspase-8/FLICE-inhibitory protein FLIP. Manipulation of the NF-kappaB, c-Jun N-terminal kinase, or p38 mitogen-activated protein kinase signals switches leukemia cells from a proliferative to an apoptotic phenotype; consequently, these highly proliferative cells die rapidly. In addition, sodium salicylate mimics the death phenotype signals and causes selective destruction of leukemia cells. These findings reveal the signaling mechanisms underlying the phenomenon of human leukemia cell life/death switching. Additionally, through knowledge of the signals that control TNF life/death switching, we have identified several therapeutic targets for selectively killing these cells.

Expression of both TNF-alpha receptor subtypes is essential for optimal skin tumour development

Keratinocyte-derived TNF-alpha acts as an endogenous tumour promoter and can also regulate AP-1 activity in mouse epidermis. To gain further insight into TNF-alpha signalling during skin tumour formation, mice deficient in TNFR1 (TNFR1-/- mice) or TNFR2 (TNFR2-/- mice) were subjected to chemical carcinogenesis. Tumour multiplicity was significantly reduced in TNFR1-/- and TNFR2-/- mice compared to wild-type (wt) mice, suggesting that both receptors have protumour activity. However, TNFR1-/- mice were markedly more resistant to tumour development than TNFR2-/- mice indicating that TNFR1 is the major mediator of TNF-alpha-induced tumour formation. TNFR1 and TNFR2 were both expressed in wt epidermis during tumour promotion and by primary keratinocytes in vitro. TPA-induced c-Jun expression was transient in TNFR1-/- and TNFR2-/- compared to wt epidermis and this was reflected by reduced induction of the AP-1-responsive genes granulocyte/macrophage-colony stimulating factor, matrix metalloproteinase-9 and matrix metalloproteinase-3. These genes were differentially regulated in TNFR1-/- compared to TNFR2-/- epidermis, suggesting that the TNF-alpha receptors act independently via different AP-1 complexes to transduce TNF-alpha signals during tumour promotion. In addition, TNFR2 cooperated with TNFR1 to optimise TNFR1-mediated TNF-alpha bioactivity on keratinocytes in vitro. Our data provide further insight into TNF-alpha signalling in malignancy and provide some rationale for the use of TNF-alpha antagonists in the treatment of cancer.

Prevention of TNF-alpha-induced apoptosis in polyamine-depleted IEC-6 cells is mediated through the activation of ERK1/2

It has been documented that polyamines play a critical role in the regulation of apoptosis in intestinal epithelial cells. We have recently reported that protection from TNF-alpha/cycloheximide (CHX)-induced apoptosis in epithelial cells depleted of polyamines is mediated through the inactivation of a proapoptotic mediator, JNK. In this study, we addressed the involvement of the MAPK pathway in the regulation of apoptosis after polyamine depletion of IEC-6 cells. Polyamine depletion by alpha-difluromethylornithine (DFMO) resulted in the sustained activation of ERK in response to TNF-alpha/CHX treatment. Pretreatment of polyamine-depleted IEC-6 cells with a cell membrane-permeable MEK1/2 inhibitor, U-0126, significantly inhibited TNF-alpha/CHX-induced ERK phosphorylation and significantly increased DNA fragmentation, JNK activity, and caspase-3 activity in response to TNF-alpha/CHX. Moreover, the dose dependency of U-0126-mediated inhibition of TNF-alpha/ CHX-induced ERK phosphorylation correlated with the reversal of the antiapoptotic effect of DFMO. IEC-6 cells expressing constitutively active MEK1 had decreased TNF-alpha/CHX-induced JNK phosphorylation and were significantly protected from apoptosis. Conversely, a dominant-negative MEK1 resulted in high basal activation of JNK, cytochrome c release, and spontaneous apoptosis. Polyamine depletion of the dominant-negative MEK1 cells did not prevent JNK activation or cytochrome c release and failed to confer protection from both TNF-alpha/CHX and camptothecin-induced apoptosis. Finally, expression of a dominant-negative mutant of JNK significantly protected IEC-6 cells from TNF-alpha/CHX-induced apoptosis. These data indicate that polyamine depletion results in the activation of ERK, which inhibits JNK activation and protects cells from apoptosis.

Regulation of cytokine-induced neuron death by ovarian hormones: involvement of antiapoptotic protein expression and c-JUN N-terminal kinase-mediated proapoptotic signaling

Mechanisms underlying the divergent effects of ovarian hormones on neuron death induced by TNFalpha were investigated in differentiated PC12 cells (dPC12). dPC12 cells were exposed to 17beta-estradiol (E, 1.0 nm), progesterone (P, 100 nm), or a combination of both hormones for 0-72 h before treatment with TNFalpha (0-150 ng) to induce cell death. Cells undergoing apoptosis were identified by a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling assay and fluorescence-activated cell sorting after 18 h. Cell death induced by TNFalpha was decreased 89% after E treatment and increased 2-fold after P treatment compared with cells treated with TNFalpha alone. Treatment with E for 24 h before TNFalpha exposure was required for maximum neuroprotection, whereas P-enhanced death was maximal after a 30-min P treatment. TNFalpha induced a 3-fold increased activity of c-JUN-N-terminal kinase (JNK) 1 in d PC12 cells within 20 min that could be increased 5- to 8-fold by P together with TNFalpha. A peptide inhibitor of JNK1 abrogated P enhancement of TNFalpha-mediated dPC12 death but had only a minimal effect on cell death by TNFalpha alone. Inhibition of caspase-8 activation reduced death induced by TNFalpha alone but was much less effective for P+TNF. P alone did not activate caspase-8. E increased estrogen receptor alpha (ERalpha) and Bcl-xL expression and all but abolished TNFalpha receptor 1 (TNFR1) expression. P decreased ERalpha and Bcl-xL expression and doubled TNFR1 expression. These data suggest that P regulates apoptosis or survival through augmentation of JNK signaling and altered TNFR1 expression, whereas E mainly affects the expression of BCL-xL, TNFR1, and ERalpha.