MEKK1-induced apoptosis requires TRAIL death receptor activation and is inhibited by AKT/PKB through inhibition of MEKK1 cleavage

Label-free quantification proteomics analysis reveals acute hyper-osmotic responsive proteins in the gills of Chinese mitten crab (Eriocheir sinensis)

Chinese mitten crab (Eriocheir sinensis) is a typical euryhaline crustacean to study osmotic regulation of crustaceans. Osmotic-regulation of Chinese mitten crab is a complex process. In order to study the osmotic-regulation related proteins of Chinese mitten crab, we domesticated Chinese mitten crab for 144 h with 25 salinity sea water (SW) and 0 salinity fresh water (FW) respectively, and then analyzed the proteome of its posterior gills. A total of 1453 proteins were identified by label free proteomics. Under the threshold of 2 fold change (FC), 242 differentially expressed proteins (DEPs) were screened, including 122 up-regulated DEPs and 120 down-regulated DEPs. GO database and KEGG database were used to annotate and enrich DEPs. It was found that DEPs were significantly enriched in energy metabolism, signal transduction, ion transport, actin cytoskeleton, immunity, lipid metabolism, amino acid metabolism and other biological functions. After 144 h of high salinity stress, the energy metabolism of Chinese mitten crab decreased and the expression of actin and cytoskeleton protein increased. In order to cope with oxidative damage caused by high salinity, Chinese mitten crab improved its immunity and antioxidant capacity.

Cell death-independent activities of the death receptors CD95, TRAILR1, and TRAILR2

Since their identification more than 20 years ago, the death receptors CD95, TRAILR1, and TRAILR2 have been intensively studied with respect to their cell death-inducing activities. These receptors, however, can also trigger a variety of cell death-independent cellular responses reaching from the activation of proinflammatory gene transcription programs over the stimulation of proliferation and differentiation to induction of cell migration. The cell death-inducing signaling mechanisms of CD95 and the TRAIL death receptors are well understood. In contrast, despite the increasing recognition of the biological and pathophysiological relevance of the cell death-independent activities of CD95, TRAILR1, and TRAILR2, the corresponding signaling mechanisms are less understood and give no fully coherent picture. This review is focused on the cell death-independent activities of CD95 and the TRAIL death receptors and addresses mainly three questions: (a) how are these receptors linked to noncell death pathways at the molecular level, (b) which factors determine the balance of cell death and cell death-independent activities of CD95 and the TRAIL death receptors at the cellular level, and (c) what are the consequences of the cell death-independent functions of these receptors for their role in cancer and inflammatory diseases.

Hepatitis C virus sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1-dependent pathway

Background

Hepatitis C virus (HCV) is the leading cause of liver fibrosis, cirrhosis and hepatocellular carcinoma. It is believed that continuous liver cell apoptosis contributes to HCV pathogenesis. Recent studies have shown that HCV infection can sensitize host cells to TNF-related apoptosis-inducing ligand (TRAIL) induced apoptosis, but the mechanism by which HCV regulates the TRAIL pathway remains unclear.

Methods and Results

Using a sub-genomic replicon and full length virus, JFH-1, we demonstrate that HCV can sensitize host cells to TRAIL-induced apoptosis by up-regulating two TRAIL receptors, death receptor 4 (DR4) and death receptor 5 (DR5). Furthermore, the HCV replicon enhanced transcription of DR5 via Sp1, and the HCV-mediated up-regulation of DR4 and DR5 required MEK1 activity. HCV infection also stimulated the activity of MEK1, and the inhibition of MEK1 activity or the knockdown of MEK1 increased the replication of HCV.

Conclusions

Our studies demonstrate that HCV replication sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1 dependent pathway. These findings may help to further understand the pathogenesis of HCV infection and provide a therapeutic target.

Apoptosis signaling kinases: from stress response to health outcomes

Apoptosis is a highly regulated process essential for the development and homeostasis of multicellular organisms. Whereas caspases, a large family of intracellular cysteine proteases, play central roles in the execution of apoptosis, other proapoptotic and antiapoptotic regulators such as the members of the Bcl-2 family are also critically involved in the regulation of apoptosis. A large body of evidence has revealed that a number of protein kinases are among such regulators and regulate cellular sensitivity to various proapoptotic signals at multiple steps in apoptosis. However, recent progress in the analysis of these apoptosis signaling kinases demonstrates that they generally act as crucial regulators of diverse cellular responses to a wide variety of stressors, beyond their roles in apoptosis regulation. In this review, we have cataloged apoptosis signaling kinases involved in cellular stress responses on the basis of their ability to induce apoptosis and discuss their roles in stress responses with particular emphasis on health outcomes upon their dysregulation.

Large-scale production and characterization of novel CD4+ cytotoxic T cells with broad tumor specificity for immunotherapy

Immune-cell-based approaches using cytotoxic and dendritic cells are under constant scrutiny to design novel therapies for the treatment of tumors. These strategies are hampered by the lack of efficient and economical large-scale production methods for effector cells. Here we describe the propagation of large amounts of a unique population of CD4(+) cytotoxic T cells, which we termed tumor killer T cells (TKTC), because of their potent and broad antitumor cell activity. With this cultivation strategy, TKTCs from peripheral blood mononuclear cells are generated within a short period of time using a pulse with a stimulating cell line followed by continuous growth in serum-free medium supplemented with a mixture of interleukin-2 and cyclosporin A. Expression and functional profiling did not allow a classification of TKTCs to any thus far defined subtype of T cells. Cytotoxic assays showed that TKTCs kill a panel of tumor targets of diverse tissue origin while leaving normal cells unaffected. Blocking experiments revealed that TKTC killing was, to a significant extent, mediated by tumor necrosis factor-related apoptosis-inducing ligand and was independent of MHC restriction. These results suggest that TKTCs have a high potential as a novel tool in the adoptive immunotherapy of cancer.

Death receptor-4 (DR4) expression is regulated by transcription factor NF-kappaB in response to etoposide treatment

Tumour necrosis factor related apoptosis inducing ligand (TRAIL) binds to death receptor 4 (DR4) activating the apoptotic signalling pathway. DNA damaging agents (genotoxins) such as etoposide increase DR4 expression and when combined with TRAIL induce a synergistic apoptotic response. The mechanism for up-regulation of DR4 expression following genotoxin treatment is not well understood. Herein, we determined that transcription factor NF-kappaB plays a role in genotoxin induced DR4 expression. Increased expression of DR4 following etoposide treatment is blocked by inhibition of the NF-kappaB pathway. Moreover, expression of the p65 subunit of NF-kappaB is sufficient to increase DR4 protein levels. Indeed, knockdown of p65 by RNA interference blocked etoposide up-regulation of DR4. We further identified a functional NF-kappaB binding site located in the DR4 promoter. Mutation of this site abrogates the induction of luciferase activity after p65 over-expression. Furthermore, electromobility shift assays and chromatin immunoprecipitaton suggest that NF-kappaB binds to this site upon etoposide treatment. MEK kinase 1 (MEKK1) is a serine threonine kinase that is activated following etoposide treatment and activates NF-kappaB. Expression of the kinase inactive MEKK1 (MEKK1-KM) abrogates the up-regulation of DR4 after etoposide treatment. Taken together, NF-kappaB plays a role in up-regulation of DR4 following etoposide treatment.

Two distinct steps of Bak regulation during apoptotic stress signaling: different roles of MEKK1 and JNK1

Stress-activated protein (SAP) kinases and the mitochondrial pro-apoptotic Bcl-2 protein Bak are important regulators of apoptosis. Reduced expression of Bak increases cellular resistance to the anticancer agent cisplatin, and we report here that mouse embryo fibroblasts deficient in the SAP kinase jnk1 are highly resistant to apoptosis induced by cisplatin. When human melanoma cells were treated with cisplatin, Bak function was found to be regulated in two distinct steps by two SAP kinases, MEKK1 and JNK1. The first of these steps involves MEKK1-controlled conformational activation of Bak. The second step leads to formation of 80-170 kDa Bak complexes correlating with apoptosis, and is controlled by JNK1. Inhibition of MEKK1 blocked the initial Bak conformational activation but did not block JNK1 activation, and deficiency in, or inhibition of, JNK1 did not prevent conformational activation of Bak. Furthermore, inducible expression of a constitutively active form of MEKK1 led to Bak conformational activation, but not to 80-170 kDa complexes. Consequently, apoptosis was delayed unless JNK was exogenously stimulated, indicating that Bak conformational activation is not necessarily an apoptotic marker. The two-step regulation of Bak revealed here may be important for tight control of mitochondrial factor release and apoptosis.

MEKK1-induced apoptosis is mediated by Smac/Diablo release from the mitochondria

During apoptotic stimulation, the serine threonine kinase, MEKK1, is cleaved into an activated 91 kDa kinase fragment. This cleavage is mediated by caspase 3 and leads to further caspase 3 activation and apoptosis. Forced expression of the 91 kDa kinase fragment induces apoptosis through changes in membrane potential of the mitochondria mediated by permeability transition pore opening. MEKK1 activation, however, fails to release cytochrome c from the mitochondria. Herein, we determined that overexpression of MEKK1 causes mitochondrial Smac/Diablo release correlating with MEKK1-induced apoptosis. Furthermore, using siRNA that lowers Smac/Diablo expression, MEKK1-induced apoptosis was significantly reduced. Mouse embryonic fibroblast cells lacking MEKK1 expression are also resistant to etoposide-induced mitochondrial Smac/Diablo release. In contrast, etoposide-induced mitochondrial cytochrome c release was not inhibited. MEKK1 also activates the MAP kinase JNK, but MEKK1-induced mitochondrial Smac/Diablo release and apoptosis are independent of MEKK1 mediated JNK activation. Taken together, release of Smac/Diablo from the mitochondria plays a role in MEKK1-induced apoptosis.

Evaluation of the anti-inflammatory and atopic dermatitis-mitigating effects of BSASM, a multicompound preparation

For effective management of atopic dermatitis (AD), it is important to introduce a therapeutic agent, which although having the fewest side effects, has the greatest anti-inflammatory effect. In the course of screening anti-inflammatory agents, we obtained BSASM, a mixture of several plant extracts. This study was designed to investigate the AD-mitigating effect of BSASM in patients, as well as its anti-inflammatory and immunomodulatory effects in an in vitro experiment. The anti-inflammatory effects of BSASM were evaluated by the level of production of proinflammatory cytokines. Clinical evaluation was also done using eczema area severity index (EASI) score in AD patients. BSASM inhibited LPS-induced activation of NF-kappaB promoter. In addition, LPS-induced an increase of IL-8, and the TNF-alpha production in THP-1 cells was also inhibited. These results suggest that BSASM has an anti-inflammatory activity. A clinical study in patients with AD showed that BSASM induced a reduction of EASI score, degree of pruritus, and TEWL on both the antecubital fossa and abdomen. Besides, BSASM had no irritative or allergic effects. Based on these results, we conclude that BSASM has anti-inflammatory and AD-mitigating effects.

Regulation of TRAIL-Induced Apoptosis by Ectopic Expression of Antiapoptotic Factors

The discovery of an agent that selectively kills tumor cells and not normal cells is the dream of every cancer researcher. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), first discovered in 1995, was heralded as a selective killer of tumor cells, and its potential is still thought to be high. Almost immediately, broad efforts were made to understand its activity at the molecular level. TRAIL has been shown to interact with the cell surface through five distinct receptors, named death receptor (DR) 4, DR5, decoy receptor (Dc)R1, DcR2, and osteoprotegrin. It activates nuclear factor (NF)-kappaB, c-Jun N-terminal kinases, and apoptosis. The apoptotic signals are mediated through Fas-associated death domain protein (FADD)-mediated recruitment of caspase-8 and caspase-3. Additionally, caspase-8 can cleave Bcl-2 homology domain 3 (BH3)-interfering domain death agonist (Bid), and the cleaved Bid then causes the release of mitochondrial cytochrome c, leading to the activation of pro-caspase-9, which can then activate pro-caspase-3. TRAIL-induced apoptosis is negatively regulated by numerous cellular factors including decoy receptors, cellular FADD-like interleukin 1 beta-converting enzyme (FLICE) interacting protein (cFLIP), cellular inhibitor of apoptosis protein (cIAP), X-linked IAP (XIAP), survivin, and NF-kappaB. Second mitochondria-derived activator of caspases (Smac)?direct IAP binding protein with low pI (DIABLO) mediates proapoptotic signals through inaction of IAP. How the TRAIL-induced apoptosis is downregulated by these factors is discussed in detail in this review. Whether TRAIL selectively kills tumor cells without harming normal cells is also discussed.

Synthetic retinoids as inducers of apoptosis in ovarian carcinoma cell lines

Apoptosis is also known as programmed cell death. Apoptosis plays an essential role in maintaining normal tissue and cell physiology in multicellular organisms. Clearance of aberrant or pre-cancerous cells occurs through the induction of apoptosis. It has been reported that many tumors and tumor cell lines have dysfunctional apoptosis signaling, causing these tumors to escape immune monitoring and internal cellular control mechanisms. One potential cause of this dysfunctional apoptosis is the tumor suppressor p53, an important regulator of growth arrest and apoptosis that is mutated in over 50% of all cancers. Retinoids have great potential in the areas of cancer therapy and chemoprevention. While some tumor cells are sensitive to the growth inhibitory effects of natural retinoids such as all-trans-retinoic acid (ATRA), many ovarian tumor cells are not. 6-[3-(1-Admantyl)]-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) and fenretinide N-[4-hydroxyphenyl] retinamide (4-HPR) are conformationally restricted synthetic retinoids that induce growth arrest and apoptosis in both ATRA-sensitive and ATRA-resistant ovarian tumor cell lines. Recently, we have identified the molecular pathways of apoptosis induced by treatment of ovarian carcinoma cells with mutated p53 by CD437 and 4-HPR.

Early events in the induction of apoptosis in ovarian carcinoma cells by CD437: activation of the p38 MAP kinase signal pathway

Retinoids have great potential in the areas of cancer therapy and chemoprevention. 6-[3-(1-admantyl)]-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437) is a conformationally restricted synthetic retinoid that has been reported to induce growth arrest and apoptosis in ovarian tumor cell lines but the entire mechanism for apoptotic induction has not been fully defined. We set out to identify the early events of CD437-induced apoptosis of the CA-OV-3 cell line and determine if these occur in a CA-OV-3 cell line resistant to CD437 (CA-CD437R). Using inhibitors for the MAP kinase cascade, we determined that MEK and p38 inhibitors could block CD437-induced apoptosis of the CA-OV-3 cell line. Moreover, treatment of CA-OV-3 and CA-CD437R cells with CD437 resulted in increased phosphorylation and activity of p38 independent of caspase-3 activation. Furthermore, p38 induced the phosphorylation of MEF2 in both CA-OV-3 and CA-CD437R cells after CD437 treatment. Finally, GFP-TR3 protein translocated to the cytosol and associated with mitochondria in both cell lines in response to CD437 treatment. This leads to depolarization of mitochondria and subsequent induction of apoptosis only in CA-OV-3 cells. These results identify a number of initial molecular events in the induction of apoptosis by CD437 in CA-OV-3 cells and demonstrate that the alteration in CA-CD437R cells, which results in resistance to CD437 maps downstream of these early events after TR3 translocation but prior to mitochondrial depolarization.