Type II tumour necrosis factor-alpha receptor (TNFR2) activates c-Jun N-terminal kinase (JNK) but not mitogen-activated protein kinase (MAPK) or p38 MAPK pathways

JNK and p38 gene and protein expression during liver ischemia-reperfusion in a rat model treated with silibinin

OBJECTIVES

Signal transduction of mitogen-activated protein kinases (MAPKs) is activated during ischemia. In this study, c-Jun N-terminal Kinase (JNK) and p38 MAPK (p38) gene and protein expression were evaluated as two members of the MAPK family during liver ischemia-reperfusion in rats.

MATERIALS AND METHODS

Thirty-two male Wistar rats were divided into four groups of eight: Vehicle, ischemia-reperfusion (IR), ischemia-reperfusion+silibinin (IR+SILI), and SILI. The IR and IR+SILI groups differed from the other two groups in that they underwent one hour of ischemia followed by three hr of reperfusion. The Vehicle and IR groups received normal saline while the SILI and IR+SILI groups were treated with silibinin (50 mg/kg). At the end of the reperfusion time, blood and ischemic liver tissue were collected for further experiments.

RESULTS

The expression of JNK and p38 gene, the amount of serum hepatic injury indices, and malondialdehyde (MDA) in the IR group increased significantly compared with the vehicle group. The JNK and p38 gene expression decreased significantly in the IR + SILI group compared with the IR group. Glutathione peroxidase (GPx) and total antioxidant capacity (TAC) levels decreased in the IR group while increasing in the IR+SILI group. Histological examination showed that silibinin significantly reduced the severity of hepatocyte degradation. Western blot results were completely consistent with real-time PCR results.

CONCLUSION

The possible pathways of the protective effect of silibinin against hepatic ischemia damages is to reduce the expression of the p38 and JNK gene and protein.

Targeting TNFR2 in Cancer: All Roads Lead to Rome

TNF receptor 2 (TNFR2) has become one of the best potential immune checkpoints that might be targeted, mainly because of its vital role in tumor microenvironments (TMEs). Overexpression of TNFR2 in some tumor cells and essential function in immunosuppressive cells, especially regulatory T cells (Tregs), makes blocking TNFR2 an excellent strategy in cancer treatment; however, there is evidence showing that activating TNFR2 can also inhibit tumor progression in vivo. In this review, we will discuss drugs that block and activate TNFR2 under clinical trials or preclinical developments up till now. Meanwhile, we summarize and explore the possible mechanisms related to them.

Role of the Interaction of Tumor Necrosis Factor-α and Tumor Necrosis Factor Receptors 1 and 2 in Bone-Related Cells

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine expressed by macrophages, monocytes, and T cells, and its expression is triggered by the immune system in response to pathogens and their products, such as endotoxins. TNF-α plays an important role in host defense by inducing inflammatory reactions such as phagocytes and cytocidal systems activation. TNF-α also plays an important role in bone metabolism and is associated with inflammatory bone diseases. TNF-α binds to two cell surface receptors, the 55kDa TNF receptor-1 (TNFR1) and the 75kDa TNF receptor-2 (TNFR2). Bone is in a constant state of turnover; it is continuously degraded and built via the process of bone remodeling, which results from the regulated balance between bone-resorbing osteoclasts, bone-forming osteoblasts, and the mechanosensory cell type osteocytes. Precise interactions between these cells maintain skeletal homeostasis. Studies have shown that TNF-α affects bone-related cells via TNFRs. Signaling through either receptor results in different outcomes in different cell types as well as in the same cell type. This review summarizes and discusses current research on the TNF-α and TNFR interaction and its role in bone-related cells.

TNFα in MS and Its Animal Models: Implications for Chronic Pain in the Disease

Multiple Sclerosis (MS) is a debilitating autoimmune disease often accompanied by severe chronic pain. The most common type of pain in MS, called neuropathic pain, arises from disease processes affecting the peripheral and central nervous systems. It is incredibly difficult to study these processes in patients, so animal models such as experimental autoimmune encephalomyelitis (EAE) mice are used to dissect the complex mechanisms of neuropathic pain in MS. The pleiotropic cytokine tumor necrosis factor α (TNFα) is a critical factor mediating neuropathic pain identified by these animal studies. The TNF signaling pathway is complex, and can lead to cell death, inflammation, or survival. In complex diseases such as MS, signaling through the TNFR1 receptor tends to be pro-inflammation and death, whereas signaling through the TNFR2 receptor is pro-homeostatic. However, most TNFα-targeted therapies indiscriminately block both arms of the pathway, and thus are not therapeutic in MS. This review explores pain in MS, inflammatory TNF signaling, the link between the two, and how it could be exploited to develop more effective TNFα-targeting pain therapies.

A variable-gain stochastic pooling motif mediates information transfer from receptor assemblies into NF-κB

A myriad of inflammatory cytokines regulate signaling pathways to maintain cellular homeostasis. The IκB kinase (IKK) complex is an integration hub for cytokines that govern nuclear factor κB (NF-κB) signaling. In response to inflammation, IKK is activated through recruitment to receptor-associated protein assemblies. How and what information IKK complexes transmit about the milieu are open questions. Here, we track dynamics of IKK complexes and nuclear NF-κB to identify upstream signaling features that determine same-cell responses. Experiments and modeling of single complexes reveal their size, number, and timing relays cytokine-specific control over shared signaling mechanisms with feedback regulation that is independent of transcription. Our results provide evidence for variable-gain stochastic pooling, a noise-reducing motif that enables cytokine-specific regulation and parsimonious information transfer. We propose that emergent properties of stochastic pooling are general principles of receptor signaling that have evolved for constructive information transmission in noisy molecular environments.

Mechanistic insights into TNFR1/MADD death domains in Alzheimer's disease through conformational molecular dynamic analysis

Proteins are tiny players involved in the activation and deactivation of multiple signaling cascades through interactions in cells. The TNFR1 and MADD interact with each other and mediate downstream protein signaling pathways which cause neuronal cell death and Alzheimer’s disease. In the current study, a molecular docking approach was employed to explore the interactive behavior of TNFR1 and MADD proteins and their role in the activation of downstream signaling pathways. The computational sequential and structural conformational results revealed that Asp400, Arg58, Arg59 were common residues of TNFR1 and MADD which are involved in the activation of downstream signaling pathways. Aspartic acid in negatively charged residues is involved in the biosynthesis of protein. However, arginine is a positively charged residue with the potential to interact with oppositely charged amino acids. Furthermore, our molecular dynamic simulation results also ensured the stability of the backbone of TNFR1 and MADD death domains (DDs) in binding interactions. This DDs interaction mediates some conformational changes in TNFR1 which leads to the activation of mediators proteins in the cellular signaling pathways. Taken together, a better understanding of TNFR1 and MADD receptors and their activated signaling cascade may help treat Alzheimer’s disease. The death domains of TNFR1 and MADD could be used as a novel pharmacological target for the treatment of Alzheimer’s disease by inhibiting the MAPK pathway.

Lung macrophages drive mucus production and steroid-resistant inflammation in chronic bronchitis

Background

Patients with chronic obstructive pulmonary disease (COPD) frequently suffer from chronic bronchitis (CB) and display steroid-resistant inflammation with increased sputum neutrophils and macrophages. Recently, a causal link between mucus hyper-concentration and disease progression of CB has been suggested.

Methods

In this study, we have evaluated the steroid sensitivity of purified, patient-derived sputum and alveolar macrophages and used a novel mechanistic cross-talk assay to examine how macrophages and bronchial epithelial cells cross-talk to regulate MUC5B production.

Results

We demonstrate that sputum plug macrophages isolated from COPD patients with chronic bronchitis (COPD/CB) are chronically activated and only partially respond to ex vivo corticosteroid treatment compared to alveolar macrophages isolated from lung resections. Further, we show that pseudo-stratified bronchial epithelial cells grown in air–liquid-interface are inert to direct bacterial lipopolysaccharide stimulation and that macrophages are able to relay this signal and activate the CREB/AP-1 transcription factor complex and subsequent MUC5B expression in epithelial cells through a soluble mediator. Using recombinant protein and neutralizing antibodies, we identified a key role for TNFα in this cross-talk.

Conclusions

For the first time, we describe ex vivo pharmacology in purified human sputum macrophages isolated from chronic bronchitis COPD patients and identify a possible basis for the steroid resistance frequently seen in this population. Our data pinpoint a critical role for chronically activated sputum macrophages in perpetuating TNFα-dependent signals driving mucus hyper-production. Targeting the chronically activated mucus plug macrophage phenotype and interfering with aberrant macrophage-epithelial cross-talk may provide a novel strategy to resolve chronic inflammatory lung disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01762-4.

Selective Targeting of TNF Receptors as a Novel Therapeutic Approach

Tumor necrosis factor (TNF) is a central regulator of immunity. Due to its dominant pro-inflammatory effects, drugs that neutralize TNF were developed and are clinically used to treat inflammatory and autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease and psoriasis. However, despite their clinical success the use of anti-TNF drugs is limited, in part due to unwanted, severe side effects and in some diseases its use even is contraindicative. With gaining knowledge about the signaling mechanisms of TNF and the differential role of the two TNF receptors (TNFR), alternative therapeutic concepts based on receptor selective intervention have led to the development of novel protein therapeutics targeting TNFR1 with antagonists and TNFR2 with agonists. These antibodies and bio-engineered ligands are currently in preclinical and early clinical stages of development. Preclinical data obtained in different disease models show that selective targeting of TNFRs has therapeutic potential and may be superior to global TNF blockade in several disease indications.

Tumor Necrosis Factor α Blockade: An Opportunity to Tackle Breast Cancer

Breast cancer is the most frequently diagnosed cancer and the principal cause of mortality by malignancy in women and represents a main problem for public health worldwide. Tumor necrosis factor α (TNFα) is a pro-inflammatory cytokine whose expression is increased in a variety of cancers. In particular, in breast cancer it correlates with augmented tumor cell proliferation, higher malignancy grade, increased occurrence of metastasis and general poor prognosis for the patient. These characteristics highlight TNFα as an attractive therapeutic target, and consequently, the study of soluble and transmembrane TNFα effects and its receptors in breast cancer is an area of active research. In this review we summarize the recent findings on TNFα participation in luminal, HER2-positive and triple negative breast cancer progression and metastasis. Also, we describe TNFα role in immune response against tumors and in chemotherapy, hormone therapy, HER2-targeted therapy and anti-immune checkpoint therapy resistance in breast cancer. Furthermore, we discuss the use of TNFα blocking strategies as potential therapies and their clinical relevance for breast cancer. These TNFα blocking agents have long been used in the clinical setting to treat inflammatory and autoimmune diseases. TNFα blockade can be achieved by monoclonal antibodies (such as infliximab, adalimumab, etc.), fusion proteins (etanercept) and dominant negative proteins (INB03). Here we address the different effects of each compound and also analyze the use of potential biomarkers in the selection of patients who would benefit from a combination of TNFα blocking agents with HER2-targeted treatments to prevent or overcome therapy resistance in breast cancer.

Distinct modes of TNF signaling through its two receptors in health and disease

TNF is a key proinflammatory and immunoregulatory cytokine whose deregulation is associated with the development of autoimmune diseases and other pathologies. Recent studies suggest that distinct functions of TNF may be associated with differential engagement of its two receptors: TNFR1 or TNFR2. In this review, we discuss the relative contributions of these receptors to pathogenesis of several diseases, with the focus on autoimmunity and neuroinflammation. In particular, we discuss the role of TNFRs in the development of regulatory T cells during neuroinflammation and recent findings concerning targeting TNFR2 with agonistic and antagonistic reagents in various murine models of autoimmune and neuroinflammatory disorders and cancer.

Cordyceps militaris induces apoptosis in ovarian cancer cells through TNF-α/TNFR1-mediated inhibition of NF-κB phosphorylation

BACKGROUND

Cordyceps militaris (L.) Fr. (C. militaris) exhibits pharmacological activities, including antitumor properties, through the regulation of the nuclear factor kappa B (NF-κB) signaling. Tumor Necrosis Factor (TNF) and TNF-α modulates cell survival and apoptosis through NF- κB signaling. However, the mechanism underlying its mode of action on the NF-κB pathway is unclear.

METHODS

Here, we analyzed the effect of C. militaris extract (CME) on the proliferation of ovarian cancer cells by confirming viability, morphological changes, migration assay. Additionally, CME induced apoptosis was determined by apoptosis assay and apoptotic body formation under TEM. The mechanisms of CME were determined through microarray, immunoblotting and immunocytochemistry.

RESULTS

CME reduced the viability of cells in a dose-dependent manner and induced morphological changes. We confirmed the decrease in the migration activity of SKOV-3 cells after treatment with CME and the consequent induction of apoptosis. Immunoblotting results showed that the CME-mediated upregulation of tumor necrosis factor receptor 1 (TNFR1) expression induced apoptosis of SKOV-3 cells via the serial activation of caspases. Moreover, CME negatively modulated NF-κB activation via TNFR expression, suggestive of the activation of the extrinsic apoptotic pathway. The binding of TNF-α to TNFR results in the disassociation of IκB from NF-κB and the subsequent translocation of the active NF-κB to the nucleus. CME clearly suppressed NF-κB translocation induced by interleukin (IL-1β) from the cytosol into the nucleus. The decrease in the expression levels of B cell lymphoma (Bcl)-xL and Bcl-2 led to a marked increase in cell apoptosis.

CONCLUSION

These results suggest that C. militaris inhibited ovarian cancer cell proliferation, survival, and migration, possibly through the coordination between TNF-α/TNFR1 signaling and NF-κB activation. Taken together, our findings provide a new insight into a novel treatment strategy for ovarian cancer using C. militaris.

The dual role of tumor necrosis factor-alpha (TNF-α) in breast cancer: molecular insights and therapeutic approaches

BACKGROUND

Breast cancer is the most prevalent cancer among women worldwide and the fifth cause of death among all cancer patients. Breast cancer development is driven by genetic and epigenetic alterations, with the tumor microenvironment (TME) playing an essential role in disease progression and evolution through mechanisms like inflammation promotion. TNF-α is one of the essential pro-inflammatory cytokines found in the TME of breast cancer patients, being secreted both by stromal cells, mainly by tumor-associated macrophages, and by the cancer cells themselves. In this review, we explore the biological and clinical impact of TNF-α in all stages of breast cancer development. First of all, we explore the correlation between TNF-α expression levels at the tumor site or in plasma/serum of breast cancer patients and their respective clinical status and outcome. Secondly, we emphasize the role of TNF-α signaling in both estrogen-positive and -negative breast cancer cells. Thirdly, we underline TNF-α involvement in epithelial-to-mesenchymal transition (EMT) and metastasis of breast cancer cells, and we point out the contribution of TNF-α to the development of acquired drug resistance.

CONCLUSIONS

Collectively, these data reveal a pro-tumorigenic role of TNF-α during breast cancer progression and metastasis. We systemize the knowledge regarding TNF-α-related therapies in breast cancer, and we explain how TNF-α may act as both a target and a drug in different breast cancer therapeutic approaches. By corroborating the known molecular effects of TNF-α signaling in breast cancer cells with the results from several preclinical and clinical trials, including TNF-α-related clinical observations, we conclude that the potential of TNF-α in breast cancer therapy promises to be of great interest.

Small tumor necrosis factor receptor biologics inhibit the tumor necrosis factor-p38 signalling axis and inflammation

Despite anti-TNF therapy advancements for inflammatory diseases such as rheumatoid arthritis, the burden of diseases remains high. An 11-mer TNF peptide, TNF_70-80, is known to stimulate selective functional responses compared to the parent TNF molecule. Here, we show that TNF_70-80 binds to the TNF receptor, activating p38 MAP kinase through TNF receptor-associated factor 2. Using truncated TNFR mutants, we identify the sequence in TNFRI which enables p38 activation by TNF_70-80. Peptides with this TNFRI sequence, such as TNFRI_206-211 bind to TNF and inhibit TNF-induced p38 activation, respiratory burst, cytokine production and adhesion receptor expression but not F-Met-Leu-Phe-induced respiratory burst in neutrophils. TNFRI_206-211 does not prevent TNF binding to TNFRI or TNF-induced stimulation of ERK, JNK and NF-κB. TNFRI_206-211 inhibits bacterial lipopolysaccharide-induced peritonitis, carrageenan-induced and antigen-induced paw inflammation, and respiratory syncytial virus-induced lung inflammation in mice. Our findings suggest a way of targeting TNF-p38 pathway to treat chronic inflammatory disorders.

Tumor Necrosis Factor Alpha Inhibits L-Type Ca(2+) Channels in Sensitized Guinea Pig Airway Smooth Muscle through ERK 1/2 Pathway

Tumor necrosis factor alpha (TNF-α) is a potent proinflammatory cytokine that plays a significant role in the pathogenesis of asthma by inducing hyperresponsiveness and airway remodeling. TNF-α diminishes the L-type voltage dependent Ca²⁺ channel (L-VDCC) current in cardiac myocytes, an observation that seems paradoxical. In guinea pig sensitized tracheas KCl responses were lower than in control tissues. Serum from sensitized animals (Ser-S) induced the same phenomenon. In tracheal myocytes from nonsensitized (NS) and sensitized (S) guinea pigs, an L-VDCC current (ICa) was observed and diminished by Ser-S. The same decrease was detected in NS myocytes incubated with TNF-α, pointing out that this cytokine might be present in Ser-S. We observed that a small-molecule inhibitor of TNF-α (SMI-TNF) and a TNF-α receptor 1 (TNFR1) antagonist (WP9QY) reversed ICa decrease induced by Ser-S in NS myocytes, confirming the former hypothesis. U0126 (a blocker of ERK 1/2 kinase) also reverted the decrease in ICa. Neither cycloheximide (a protein synthesis inhibitor) nor actinomycin D (a transcription inhibitor) showed any effect on the TNF-α-induced ICa reduction. We found that Ca_V1.2 and Ca_V1.3 mRNA and proteins were expressed in tracheal myocytes and that sensitization did not modify them. In cardiac myocytes, ERK 1/2 phosphorylates two sites of the L-VDCC, augmenting or decreasing ICa; we postulate that, in guinea pig tracheal smooth muscle, TNF-α diminishes ICa probably by phosphorylating the L-VDCC site that reduces its activity through the ERK1/2 MAP kinase pathway.

Poncirus trifoliata Rafin. induces the apoptosis of triple-negative breast cancer cells via activation of the c-Jun NH(2)-terminal kinase and extracellular signal-regulated kinase pathways

Background:

Poncirus trifoliata Rafin. is a traditional medicine with known anti-inflammatory and anti-cancer properties. Traditionally, it is used to control chronic inflammation, allergy and gastrointestinal diseases such as digestive ulcers gastritis in China, Japan, and Korea.

Objectives:

To evaluate the apoptosis-inducing activity of a P. trifoliata methanol extract (MEPT) and elucidate the molecular mechanisms.

Materials and Methods:

The anti-cancer effect of MEPT and its underlying mechanisms were investigated in breast cancer cells using 3,4,5-dimethyl N-methylthiazol-2-yl-2, 5-d-phenyl tetrazolium bromide assay, cell cycle analysis, and western blotting.

Results:

MEPT suppressed the proliferation of MDA-MB-231 cells with inhibition dose 50% value of 119.44 μg/mL at 24 h, which have features typical of triple-negative breast cancer cells. MEPT also altered the characteristic features of the MDA-MB-231 cells and increased the proportion of cells undergoing sub-G1 arrest. In addition, MEPT increased levels of caspase 8 and 3 in MDA-MB-231 cells, whereas caspase 9 was not detected. In addition, MEPT-induced tumor necrosis factor receptor (TNFR) and TNFR type 1-associated death domain (TRADD) protein and the activations of c-Jun NH(2)-terminal kinase (JNK) and extracellular signal-regulated kinases (ERK).

Conclusion:

Our results indicate that MEPT has chemotherapeutic potential in triple-negative breast cancer and that at the molecular level its effects are derived from the activations of TNFR and of the mitogen-activated protein kinase pathway.

The Drosophila TIPE family member Sigmar interacts with the Ste20-like kinase Misshapen and modulates JNK signaling, cytoskeletal remodeling and autophagy

TNFAIP8 and other mammalian TIPE family proteins have attracted increased interest due to their associations with disease-related processes including oncogenic transformation, metastasis, and inflammation. The molecular and cellular functions of TIPE family proteins are still not well understood. Here we report the molecular and genetic characterization of the Drosophila TNFAIP8 homolog, CG4091/sigmar. Previous gene expression studies revealed dynamic expression of sigmar in larval salivary glands prior to histolysis. Here we demonstrate that in sigmar loss-of-function mutants, the salivary glands are morphologically abnormal with defects in the tubulin network and decreased autophagic flux. Sigmar localizes subcellularly to microtubule-containing projections in Drosophila S2 cells, and co-immunoprecipitates with the Ste20-like kinase Misshapen, a regulator of the JNK pathway. Further, the Drosophila TNF ligand Eiger can induce sigmar expression, and sigmar loss-of-function leads to altered localization of pDJNK in salivary glands. Together, these findings link Sigmar to the JNK pathway, cytoskeletal remodeling and autophagy activity during salivary gland development, and provide new insights into TIPE family member function.

Aminopeptidase P3, a new member of the TNF-TNFR2 signaling complex, induces phosphorylation of JNK1 and JNK2

Tumor necrosis factor (TNF) is an important mediator that triggers onset of autoimmune diseases and exerts its biological effects by interacting through two receptors, TNFR1 (also known as TNFRSF1A) and TNFR2 (also known as TNFRSF1B). TNFR2 signaling has significant potential to exert pro-survival and protective roles in several diseases. Unlike TNFR1 signaling, however, the mechanism of TNFR2 signal transduction is poorly understood, and few of its adaptor molecules are known. The present study utilized a proteomics approach to search for adaptor molecules in the TNFR2 signaling complex and identified aminopeptidase P3 (APP3, also known as XPNPEP3) to be a key molecule. One of its two isoforms, mitochondrial APP3 (APP3m) but not cytosolic APP3 (APP3c), was recruited to TNFR2 and shown to regulate TNF-TNFR2-dependent phosphorylation of JNK1 (also known as MAPK8) and JNK2 (also known as MAPK9). Furthermore, APP3m was released from mitochondria upon TNF stimulation in the absence of mitochondrial outer membrane permeabilization (MOMP). The observation of increased cell death upon downregulation of APP3m also suggested that APP3m exerts an anti-apoptotic function. These findings reveal that APP3m is a new member of the TNF-TNFR2 signaling complex and characterize an APP3-mediated TNFR2 signal transduction mechanism that induces activation of JNK1 and JNK2.

Tumor necrosis factor receptor 2: its contribution to acute cellular rejection and clear cell renal carcinoma

Tumor necrosis factor receptor 2 (TNFR2) is a type I transmembrane glycoprotein and one of the two receptors that orchestrate the complex biological functions of tumor necrosis factor (TNF, also designed TNF-α). Accumulating experimental evidence suggests that TNFR2 plays an important role in renal disorders associated with acute cellular rejection and clear cell renal carcinoma but its exact role in these settings is still not completely understood. This papers reviews the factors that may mediate TNFR2 induction in acute cellular rejection and clear cell renal carcinoma and its contribution to these conditions and discusses its therapeutic implications. A greater understanding of the function of TNFR2 may lead to the development of new anti-TNF drugs.

The acute phase reactant orosomucoid-1 is a bimodal regulator of angiogenesis with time- and context-dependent inhibitory and stimulatory properties

Background

Tissues respond to injury by releasing acute phase reaction (APR) proteins which regulate inflammation and angiogenesis. Among the genes upregulated in wounded tissues are tumor necrosis factor-alpha (TNFα) and the acute phase reactant orosomucoid-1 (ORM1). ORM1 has been shown to modulate the response of immune cells to TNFα, but its role on injury- and TNFα-induced angiogenesis has not been investigated. This study was designed to characterize the role of ORM1 in the angiogenic response to injury and TNFα.

Methods and Results

Angiogenesis was studied with in vitro, ex vivo, and in vivo angiogenesis assays. Injured rat aortic rings cultured in collagen gels produced an angiogenic response driven by macrophage-derived TNFα. Microarray analysis and qRT-PCR showed that TNFα and ORM1 were upregulated prior to angiogenic sprouting. Exogenous ORM1 delayed the angiogenic response to injury and inhibited the proangiogenic effect of TNFα in cultures of aortic rings or isolated endothelial cells, but stimulated aortic angiogenesis over time while promoting VEGF production and activity. ORM1 inhibited injury- and TNFα-induced phosphorylation of MEK1/2 and p38 MAPK in aortic rings, but not of NFκB. This effect was injury/TNFα-specific since ORM1 did not inhibit VEGF-induced signaling, and cell-specific since ORM1 inhibited TNFα-induced phosphorylation of MEK1/2 and p38 MAPK in macrophages and endothelial cells, but not mural cells. Experiments with specific inhibitors demonstrated that the MEK/ERK pathway was required for angiogenesis. ORM1 inhibited angiogenesis in a subcutaneous in vivo assay of aortic ring-induced angiogenesis, but stimulated developmental angiogenesis in the chorioallantoic membrane (CAM) assay.

Conclusion

ORM1 regulates injury-induced angiogenesis in a time- and context-dependent manner by sequentially dampening the initial TNFα-induced angiogenic response and promoting the downstream stimulation of the angiogenic process by VEGF. The context-dependent nature of ORM1 angioregulatory function is further demonstrated in the CAM assay where ORM1 stimulates developmental angiogenesis without exerting any inhibitory activity.

Characterization of TNF receptor subtype expression and signaling on pulmonary endothelial cells in mice

TNF plays a crucial role in the pathogenesis of acute lung injury. However, the expression profile of its two receptors, p55 and p75, on pulmonary endothelium and their influence on TNF signaling during lung microvascular inflammation remain uncertain. Using flow cytometry, we characterized the expression profile of TNF receptors on the surface of freshly harvested pulmonary endothelial cells (PECs) from mice and found expression of both receptors with dominance of p55. To investigate the impact of stimulating individual TNF receptors, we treated wild-type and TNF receptor knockout mice with intravenous TNF and determined surface expression of adhesion molecules (E-selectin, VCAM-1, ICAM-1) on PECs by flow cytometry. TNF-induced upregulation of all adhesion molecules was substantially attenuated by absence of p55, whereas lack of p75 had a similar but smaller effect that varied between adhesion molecules. Selective blockade of individual TNF receptors by specific antibodies in wild-type primary PEC culture confirmed that the in vivo findings were due to direct effects of TNF receptor inhibition on endothelium and not other cells (e.g., circulating leukocytes). Finally, we found that PEC surface expression of p55 dramatically decreased in the early stages of endotoxemia following intravenous LPS, while no change in p75 expression was detected. These data demonstrate a crucial in vivo role of p55 and an auxiliary role of p75 in TNF-mediated adhesion molecule upregulation on PECs. It is possible that the importance of the individual receptors varies at different stages of pulmonary microvascular inflammation following changes in their relative expression.

Report of the ECCO workshop on anti-TNF therapy failures in inflammatory bowel diseases: biological roles and effects of TNF and TNF antagonists

This second section of the first ECCO pathogenesis workshop on anti-TNF therapy failures in inflammatory bowel diseases addresses the biological roles of TNFα and the effects and mechanisms of action of TNFα antagonists. Mechanisms underlying their failure, including induction of TNF-independent inflammatory pathways and phenomena of paradoxical inflammation are discussed.

Anti-inflammatory effects of tumour necrosis factor (TNF)-alpha are mediated via TNF-R2 (p75) in tolerogenic transforming growth factor-beta-treated antigen-presenting cells

Exposure of macrophages to transforming growth factor (TGF)-beta is known to alter their functional phenotype such that antigen presentation by these cells leads to tolerance rather than an inflammatory immune response. Typically, eye-derived antigen-presenting cells (APCs) exposed to TGF-beta in the local environment are known to induce a form of peripheral tolerance and protect the eye from inflammatory immune effector-mediated damage. In response to TGF-beta, APCs increase their expression of tumour necrosis factor (TNF)-alpha and TNF receptor 2 (TNF-R2). Although TNF-alpha has been implicated in tolerance and the associated regulation of the inflammatory immune response, its source and the receptors involved remain unclear. In this report we determined the contribution of TNF-alpha and TNF-R2 expressed by TGF-beta-treated APCs to their anti-inflammatory tolerogenic effect. Our results indicate that APC-derived TNF-alpha is essential for the ability of APCs to regulate the immune response and their IL-12 secretion. Moreover, in the absence of TNF-R2, APCs exposed to TGF-beta failed to induce tolerance or regulatory cells known to participate in this tolerance. Also, blocking of TNF-R1 signalling enhanced the ability of the APCs to secrete increased TGF-beta in response to TGF-beta exposure. Together our results support an anti-inflammatory role of TNF-alpha in regulation of an immune response by TGF-beta-treated APCs and suggest that TNF-R2 contributes significantly to this role.

TNF-alpha-induced apoptosis is prevented by erythropoietin treatment on SH-SY5Y cells

The growth factor erythropoietin (Epo) has shown neuronal protective action in addition to its well known proerythroid activity. Furthermore, Epo has dealt with cellular inflammation by inhibiting the expression of several proinflammatory cytokines, such as IL-1 and TNF-alpha. The action of TNF can have both apoptotic and antiapoptotic consequences due to altered balance between different cell signalling pathways. This work has focused on the apoptotic effects of this cytokine and the potential protective action of Epo. The model we used was neuroblastoma SH-SY5Y cells cultured in the presence of 25 ng/ml TNF-alpha or pretreated with 25 U/ml Epo for 12 h before the addition of TNF-alpha. Apoptosis was evaluated by differential cell count after Hoechst staining, analysis of DNA ladder pattern, and measurement of caspase activity. Despite its ability to induce NF-kappaB nuclear translocation, TNF-alpha induced cell death, which was found to be associated to upregulation of TNF Receptor 1 expression. On the other hand, cells activated by Epo became resistant to cell death. Prevention of death receptor upregulation and caspase activation may explain this antiapoptotic effect of Epo, which may be also favoured by the induction of a higher expression of protective factors, such as Bcl-2 and NF-kappaB, through mechanisms involving Jak/STAT and PI3K signalling pathways.

TNF alpha acting on TNFR1 promotes breast cancer growth via p42/P44 MAPK, JNK, Akt and NF-kappa B-dependent pathways

Tumor necrosis factor alpha (TNF alpha) enhances proliferation of chemically-induced mammary tumors and of T47D human cell line through not fully understood pathways. Here, we explored the intracellular signaling pathways triggered by TNF alpha, the participation of TNF alpha receptor (TNFR) 1 and TNFR2 and the molecular mechanism leading to breast cancer growth. We demonstrate that TNFalpha induced proliferation of C4HD murine mammary tumor cells and of T47D cells through the activation of p42/p44 MAPK, JNK, PI3-K/Akt pathways and nuclear factor-kappa B (NF-kappa B) transcriptional activation. A TNF alpha-specific mutein selectively binding to TNFR1 induced p42/p44 MAPK, JNK, Akt activation, NF-kappa B transcriptional activation and cell proliferation, just like wild-type TNF alpha, while a mutein selective for TNFR2 induced only p42/p44 MAPK activation. Interestingly, blockage of TNFR1 or TNFR2 with specific antibodies was enough to impair TNF alpha signaling and biological effect. Moreover, in vivo TNF alpha administration supported C4HD tumor growth. We also demonstrated, for the first time, that injection of a selective inhibitor of NF-kappa B activity, Bay 11-7082, resulted in regression of TNF alpha-promoted tumor. Bay 11-7082 blocked TNF alpha capacity to induce cell proliferation and up-regulation of cyclin D1 and of Bcl-xLin vivo and in vitro. Our results reveal evidence for TNF alpha as a breast tumor promoter, and provide novel data for a future therapeutic approach using TNF alpha antagonists and NF-kappa B pharmacological inhibitors in established breast cancer treatment.

Elevated NF-kappaB responses and FLIP levels in leukemic but not normal lymphocytes: reduction by salicylate allows TNF-induced apoptosis

As its name suggests, tumor necrosis factor (TNF) is known to induce cytotoxicity in a wide variety of tumor cells and cell lines. However, its use as a chemotherapeutic drug has been limited by its deleterious side effects of systemic shock and widespread inflammatory responses. Some nonsteroidal antiinflammatory drugs, such as sodium salicylate, have been shown to have a chemopreventive role in certain forms of cancer. Here, we reveal that sodium salicylate selectively enhances the apoptotic effects of TNF in human erythroleukemia cells but does not affect primary human lymphocytes or monocytes. Sodium salicylate did not affect the intracellular distribution of TNF receptors (TNFRs) but stimulated cell surface TNFR2 shedding. Erythroleukemia cells were shown to possess markedly greater basal NF-kappaB responses and elevated Fas-associated protein with death domain-like IL-1 converting enzyme (FLIP) levels. Sodium salicylate achieved its effects by reducing the elevated NF-kappaB responsiveness and FLIP levels and restoring the apoptotic response of TNF rather than the proliferative/proinflammatory effects of the cytokine in these cancer cells. Inhibition of NF-kappaB or FLIP levels in human erythroleukemia cells by pharmacological or molecular-biological means also resulted in switching the character of these cells from a TNF-responsive proliferative phenotype into an apoptotic one. These findings expose that the enhanced proliferative nature of human leukemia cells is caused by elevated NF-kappaB and FLIP responses and basal levels, reversible by sodium salicylate to allow greater apoptotic responsiveness of cytotoxic stimuli such as TNF. Such findings provide insight into the molecular mechanisms by which human leukemia cells can switch from a proliferative into an apoptotic phenotype.

Critical role of c-jun (NH2) terminal kinase in paracetamol- induced acute liver failure

BACKGROUND

Acute hepatic failure secondary to paracetamol poisoning is associated with high mortality. C-jun (NH2) terminal kinase (JNK) is a member of the mitogen-activated protein kinase family and is a key intracellular signalling molecule involved in controlling the fate of cells.

AIM

To examine the role of JNK in paracetamol-induced acute liver failure (ALF).

METHODS

A previously developed mouse model of paracetamol poisoning was used to examine the role of JNK in paracetamol-induced ALF.

RESULTS

Paracetamol-induced hepatic JNK activation both in human and murine paracetamol hepatotoxicity and in our murine model preceded the onset of hepatocyte death. JNK inhibition in vivo (using two JNK inhibitors with different mechanisms of action) markedly reduced mortality in murine paracetamol hepatotoxicity, with a significant reduction in hepatic necrosis and apoptosis. In addition, delayed administration of the JNK inhibitor was more effective than N-acetylcysteine after paracetamol poisoning in mice. JNK inhibition was not protective in acute carbon tetrachloride-mediated or anti-Fas antibody-mediated hepatic injury, suggesting specificity for the role of JNK in paracetamol hepatotoxicity. Furthermore, disruption of the JNK1 or JNK2 genes did not protect against paracetamol-induced hepatic damage. Pharmacological JNK inhibition had no effect on paracetamol metabolism, but markedly inhibited hepatic tumour necrosis foctor alpha (TNF alpha) production after paracetamol poisoning.

CONCLUSIONS

These data demonstrated a central role for JNK in the pathogenesis of paracetamol-induced liver failure, thereby identifying JNK as an important therapeutic target in the treatment of paracetamol hepatotoxicity.

TNFR1-induced NF-kappaB, but not ERK, p38MAPK or JNK activation, mediates TNF-induced ICAM-1 and VCAM-1 expression on endothelial cells

Tumour necrosis factor (TNF) is a pro-inflammatory cytokine, whose primary targets include vascular endothelial cells. TNF-mediated adhesion molecule expression has been shown to play a central role in endothelial cells inflammatory responses and disorders such as atherosclerosis. However it is not fully understand how the TNF receptor subtypes, namely TNFR1 and TNFR2, regulate inflammatory responses in endothelial cells. The aim of this study was to elucidate the kinase signalling pathways that TNF receptors activate, and determine the pathways responsible for downstream expression of adhesion molecules, intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in human endothelial cells. Using human umbilical vein endothelial cells (HUVEC), we demonstrated that TNF activates a range of mitogen-activated protein kinases (MAPKs), including the extracellular-regulated kinase (ERK) pathway and the p38MAPK and c-Jun N-terminal kinase (JNK) stress kinase pathways. Human endothelial cells express both TNF receptor subtypes at low levels, however using TNFR-specific agonistic agents, we uncovered that TNF acts through its TNFR1 receptor subtype to activate NF-kappaB transcriptional pathways. Further investigation revealed that ICAM-1 and VCAM-1 mRNA and protein are induced by TNFR1 (but not TNFR2) in a wholly NF-kappaB-dependent manner. These findings reveal for the first time that TNF stimulation of adhesion molecules ICAM-1 and VCAM-1 in human endothelial cells occurs through the TNFR1 subtype and is mediated by the NF-kappaB pathway, but not the ERK, p38MAPK or JNK kinase pathways.

TNF-alpha regulates myogenesis and muscle regeneration by activating p38 MAPK

Although p38 MAPK activation is essential for myogenesis, the upstream signaling mechanism that activates p38 during myogenesis remains undefined. We recently reported that p38 activation, myogenesis, and regeneration in cardiotoxin-injured soleus muscle are impaired in TNF-alpha receptor double-knockout (p55(-/-)p75(-/-)) mice. To fully evaluate the role of TNF-alpha in myogenic activation of p38, we tried to determine whether p38 activation in differentiating myoblasts requires autocrine TNF-alpha, and whether forced activation of p38 rescues impaired myogenesis and regeneration in the p55(-/-)p75(-/-) soleus. We observed an increase of TNF-alpha release from C2C12 or mouse primary myoblasts placed in low-serum differentiation medium. A TNF-alpha-neutralizing antibody added to differentiation medium blocked p38 activation and suppressed differentiation markers myocyte enhancer factor (MEF)-2C, myogenin, p21, and myosin heavy chain in C2C12 myoblasts. Conversely, recombinant TNF-alpha added to differentiation medium stimulated myogenesis at 0.05 ng/ml while inhibited it at 0.5 and 5 ng/ml. In addition, differentiation medium-induced p38 activation and myogenesis were compromised in primary myoblasts prepared from p55(-/-)p75(-/-) mice. Increased TNF-alpha release was also seen in cardiotoxin-injured soleus over the course of regeneration. Forced activation of p38 via the constitutive activator of p38, MKK6bE, rescued impaired myogenesis and regeneration in the cardiotoxin-injured p55(-/-)p75(-/-) soleus. These results indicate that TNF-alpha regulates myogenesis and muscle regeneration as a key activator of p38.

Spatial compartmentalization of tumor necrosis factor (TNF) receptor 1-dependent signaling pathways in human airway smooth muscle cells. Lipid rafts are essential for TNF-alpha-mediated activation of RhoA but dispensable for the activation of the NF-kappaB and MAPK pathways

Tumor necrosis factor (TNF)-alpha-induced activation of RhoA, mediated by TNF receptor 1 (TNFR1), is a prerequisite step in a pathway that leads to increased 20-kDa light chain of myosin (MLC20) phosphorylation and airway smooth muscle contraction. In this study, we have investigated the proximal events in TNF-alpha-induced RhoA activation. TNFR1 is localized to both lipid raft and nonraft regions of the plasma membrane in primary human airway smooth muscle cells. TNF-alpha engagement of TNFR1 recruited the adaptor proteins TRADD, TRAF-2, and RIP into lipid rafts and activated RhoA, NF-kappaB, and MAPK pathways. Depletion of cholesterol from rafts with methyl-beta-cyclodextrin caused a redistribution of TNFR1 to nonraft plasma membrane and prevented ligand-induced RhoA activation. By contrast, TNF-alpha-induced activation of NF-kappaB and MAPKs was unaffected by methyl-beta-cyclodextrin indicating that, in airway smooth muscle cells, activation of these pathways occurred independently of lipid rafts. Targeted knockdown of caveolin-1 completely abrogated TNF-alpha-induced RhoA activation, identifying this raft-resident protein as a positive regulator of the activation process. The signaling adaptors TRADD and RIP were also found to be necessary for ligand-induced RhoA activation. Taken together, our results suggest that in airway smooth muscle cells, spatial compartmentalization of TNFR1 provides a mechanism for generating distinct signaling outcomes in response to ligand engagement and define a mechanistic role for lipid rafts and caveolin-1 in TNF-alpha-induced activation of RhoA.

Time-dependent apoptosis of alveolar macrophages from rats exposed to bleomycin: involvement of tnf receptor 2

Tumor necrosis factor-alpha (TNF-a) is produced by alveolar macrophages (AM) in response to bleomycin (BLM) exposure. This cytokine has been linked to BLM-induced pulmonary inflammation, an early drug effect, and to lung fibrosis, the ultimate toxic effect of BLM. The present study was carried out to study the time dependence of apoptotic signaling pathways and the potential roles of TNF receptors in BLM-induced AM apoptosis. Male Sprague-Dawley rats were exposed to saline or BLM (1 mg/kg) by intratracheal instillation. At 1, 3, or 7 d postexposure, AM were isolated by bronchoalveolar (BAL) lavage and evaluated for apoptosis by ELISA. The release of cytochrome c from mitochrondria, the activation of caspase-3, -8, and -9, the cleavage of nuclear poly(ADP-ribose) polymerase (PARP), and the expression of TNF receptors (TNF-R1/p55 and TNF-R2/p75), TNF-R-associated factor 2 (TRAF2), and cellular inhibitor of apoptosis 1 (c-IAP1) were determined by immunoblotting. The results showed that BLM exposure induced AM apoptosis, with the highest apoptotic effect occurring at 1 d after exposure and gradually decreasing at 3 and 7 d postexposure, but still remaining significantly above the control level. The maximal translocation of cytochromec from mitochondria into the cytosol was observed at 1 d postexposure, whereas the activation of caspase-9 and caspase-3 and caspase-3-dependent cleavage of PARP was found to reach a peak level at 3 d postexposure. BLM exposure had no marked effect on AM expression of TNF-R1 or caspase-8 activation, but significantly increased the expression of TNF-R2 that was accompanied by a rise in c-IAP1 and a decrease in TRAF2. This induction of TNF-R2 by BLM was significant on d 1 and increased with greater exposure time. In vitro studies showed that pretreatment of naive AM with a TNF-R2 antibody significantly inhibited BLM-induced caspase-3 activity and apoptosis. These results suggest that BLM-induced apoptosis involves multiple pathways in a time-dependent manner. Since maximal BLM-induced AM apoptosis (1 d postexposure) preceded maximal changes in caspase-9 and -3 (3 d postexposure), it is possible that a caspase-independent mechanism is involved in this initial response. These results indicate that the sustained expression of TNF-R2 in AM by BLM exposure may sensitize these cells to TNF-a-mediated toxicity.

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.

Vitamin C is a kinase inhibitor: dehydroascorbic acid inhibits IkappaBalpha kinase beta

Reactive oxygen species (ROS) are key intermediates in cellular signal transduction pathways whose function may be counterbalanced by antioxidants. Acting as an antioxidant, ascorbic acid (AA) donates two electrons and becomes oxidized to dehydroascorbic acid (DHA). We discovered that DHA directly inhibits IkappaBalpha kinase beta (IKKbeta) and IKKalpha enzymatic activity in vitro, whereas AA did not have this effect. When cells were loaded with AA and induced to generate DHA by oxidative stress in cells expressing a constitutive active IKKbeta, NF-kappaB activation was inhibited. Our results identify a dual molecular action of vitamin C in signal transduction and provide a direct linkage between the redox state of vitamin C and NF-kappaB signaling events. AA quenches ROS intermediates involved in the activation of NF-kappaB and is oxidized to DHA, which directly inhibits IKKbeta and IKKalpha enzymatic activity. These findings define a function for vitamin C in signal transduction other than as an antioxidant and mechanistically illuminate how vitamin C down-modulates NF-kappaB signaling.

Distinct regulation of cytosolic phospholipase A2 phosphorylation, translocation, proteolysis and activation by tumour necrosis factor-receptor subtypes

The hormonally regulated Ca(2+)-dependent enzyme, cytosolic phospholipase A(2) (cPLA(2)) is activated by a range of inflammatory stimuli. Tumour necrosis factor-alpha (TNF) is one of the first known stimuli for cPLA(2) but it is not known whether both TNF receptor subtypes are involved in activating the lipase. In the present study, we show for the first time that both type I 55 kDa TNFR (TNFR1) and type II 75 kDa TNFR (TNFR2) stimulate cPLA(2) enzyme, but with distinct signalling mechanisms. TNFR1 activates mitogen-activated protein kinase (MAPK) and p38MAPK. TNFR1 then phosphorylates and activates cPLA(2) in a MAPK-dependent fashion. Furthermore, TNFR1 causes the translocation and caspase-dependent proteolysis of cPLA(2) as part of its activation profile. TNFR2, on the other hand, does not cause the phosphorylation of cPLA(2) as it does not activate MAPK or p38MAPK, but instead activates cPLA(2) by causing its translocation to plasma membrane and perinuclear subcellular regions. TNFR2 activation causes a delayed, slight increase in [Ca(2+)](i) of <50 nM that may contribute towards the translocation and activation of cPLA(2). Therefore both TNF receptor subtypes play a role in cPLA(2) activation, but by means of separate signal-transduction pathways.

Tpl2 transduces CD40 and TNF signals that activate ERK and regulates IgE induction by CD40

Macrophages from Tpl2 knockout (Tpl2(-/-)) mice exhibit a defect in ERK activation by lipopolysaccharide (LPS). This impairs the nucleocytoplasmic transport of the tumor necrosis factor alpha (TNF-alpha) mRNA and prevents the induction of TNF-alpha by LPS. As a result, Tpl2(-/-) mice are resistant to LPS/D-galactosamine-induced shock. We demonstrate that Tpl2 is essential for ERK signals transduced by members of the TNF receptor superfamily, such as CD40 and the TNF receptor 1. Thus, ERK activation was impaired in Tpl2(-/-) B cells and macrophages stimulated with agonistic CD40 antibody or TNF-alpha, whereas the induction of other mitogen-activated protein kinases, such as JNK and p38, and the activation of NF-kappaB were unaffected. Tpl2 was recruited to a CD40/TRAF6 complex in response to CD40 stimulation. Moreover, TRAF6, which when overexpressed activates ERK, failed to do so in Tpl2(-/-) cells. The selective signaling defect resulting from the inactivation of Tpl2 allowed us to demonstrate that CD40-mediated ERK activation contributes to immunoglobulin production but is not essential for B-cell proliferation.

Tumour necrosis factor-induced activation of c-Jun N-terminal kinase is sensitive to caspase-dependent modulation while activation of mitogen-activated protein kinase (MAPK) or p38 MAPK is not

The activation of the extracellular signal-regulated kinases (ERKs) by tumour necrosis factor-alpha (TNF) receptors (TNFRs) is an integral part of the cytokine's pleiotropic cellular responses. Here we report differences in the caspase sensitivity and TNFR subtype activation of members of the ERK family. Inhibition in HeLa cells of caspase function by pharmacological inhibitors or the expression of CrmA (cytokine response modifier A), a viral modifier protein, blocks TNF-induced apoptosis or caspase-dependent protein kinase Cdelta and poly(ADP-ribose) polymerase protein degradation. TNFR1- or TNFR2-stimulated c-Jun N-terminal kinase (JNK) activity was attenuated in cells in which caspase activity was inhibited either by pharmacological blockers or CrmA expression. Both TNFR1- and TNFR2-stimulated JNK activity was caspase-sensitive; however, only TNFR1 was capable of stimulating p42/44 mitogen-activated protein kinase (MAPK) and p38 MAPK activities. TNFR1-stimulated p42/44 MAPK and p38 MAPK activities were insensitive to pharmacological caspase inhibition or CrmA. These findings were supported when measuring TNF-induced cytosolic phospholipase A(2) activation, which is a downstream target for MAPK and p38 MAPK. Profiling caspase enzymes activated by TNF in HeLa cells showed sequential caspase-8, -3, -7, -6 and -9 activation, with their inhibition characteristics suggesting a role for caspase-3 and/or caspase-6 in modulating JNK activity. Taken together these results show delineated ERK-activation pathways employed by TNFR subtypes.