UV irradiation and heat shock mediate JNK activation via alternate pathways

Hepatocyte-specific damage in acute toxicity of sodium ferrous citrate: Presentation of a human autopsy case and experimental results in mice

Acute iron overload is known to exert deleterious effects in the liver, but detailed pathology has yet to be documented. Here, we report pathological findings in an autopsy case of acute iron toxicity and validation of the findings in mouse experiments. In a 39-year-old woman who intentionally ingested a large amount of sodium ferrous citrate (equivalent to 7.5 g of iron), severe disturbance of consciousness and fulminant hepatic failure rapidly developed. Liver failure was refractory to treatment and the patient died on Day 13. Autopsy revealed almost complete loss of hepatocytes, while bile ducts were spared. To examine the detailed pathologic processes induced by excessive iron, mice were orally administered equivalent doses of ferrous citrate. Plasma aminotransferase levels markedly increased after 6 h, which was preceded by increased plasma iron levels. Hepatocytes were selectively damaged, with more prominent damage in the periportal area. Phosphorylated c-Jun was detected in hepatocyte nuclei after 3 h, which was followed by the appearance of γ-H2AX expression. Hepatocyte injury in mice was associated with the expression of Myc and p53 after 12 and 24 h, respectively. Even at lethal doses, the bile ducts were morphologically intact and fully viable. Our findings indicate that acute iron overload induces hepatocyte-specific liver injury, most likely through hydroxyl radical-mediated DNA damage and subsequent stress responses.

The good Samaritan glutathione-S-transferase P1: An evolving relationship in nitric oxide metabolism mediated by the direct interactions between multiple effector molecules

Glutathione-S-transferases (GSTs) are phase II detoxification isozymes that conjugate glutathione (GSH) to xenobiotics and also suppress redox stress. It was suggested that GSTs have evolved not to enhance their GSH affinity, but to better interact with and metabolize cytotoxic nitric oxide (NO). The interactions between NO and GSTs involve their ability to bind and store NO as dinitrosyl-dithiol iron complexes (DNICs) within cells. Additionally, the association of GSTP1 with inducible nitric oxide synthase (iNOS) results in its inhibition. The function of NO in vasodilation together with studies associating GSTM1 or GSTT1 null genotypes with preeclampsia, additionally suggests an intriguing connection between NO and GSTs. Furthermore, suppression of c-Jun N-terminal kinase (JNK) activity occurs upon increased levels of GSTP1 or NO that decreases transcription of JNK target genes such as c-Jun and c-Fos, which inhibit apoptosis. This latter effect is mediated by the direct association of GSTs with MAPK proteins. GSTP1 can also inhibit nuclear factor kappa B (NF-κB) signaling through its interactions with IKKβ and Iκα, resulting in decreased iNOS expression and the stimulation of apoptosis. It can be suggested that the inhibitory activity of GSTP1 within the JNK and NF-κB pathways may be involved in crosstalk between survival and apoptosis pathways and modulating NO-mediated ROS generation. These studies highlight an innovative role of GSTs in NO metabolism through their interaction with multiple effector proteins, with GSTP1 functioning as a "good Samaritan" within each pathway to promote favorable cellular conditions and NO levels.

Protective effects of volatile components of aged garlic extract against ultraviolet B-induced apoptosis in human skin fibroblasts

Aged garlic extract (AGE) has been shown to protect the skin against UV-induced damage, but effects of its volatile components remain unknown. We investigated the effects of the volatile fraction of AGE on the responses of cultured skin fibroblasts subjected to UV-B irradiation. UV-B irradiation (20 mJ/cm² ) reduced the cell viability to 55% of control. The nonvolatile and volatile fractions of AGE inhibited the UV-B-induced reduction of cell viability; the cell viabilities were 100% and 73%, respectively. The volatile fraction inhibited the UV-B-induced increase in apoptotic cell death by 28%. The volatile fraction also inhibited the phosphorylation of mitogen-activated protein kinases (MAPKs) induced by UV-B irradiation. GC-MS analysis revealed that a large number of volatile compounds were generated during aging of garlic. These results suggest that the volatile fraction of AGE has protective effects against the UV-B-induced death of skin fibroblasts, and that this effect may partly be due to an inhibition of apoptosis via the downregulation of MAPK signaling. The volatile compounds of AGE may have beneficial applications for skin health. PRACTICAL APPLICATIONS: In this study, we investigated the effects of AGE against cell damage of UV-B-irradiated human skin fibroblasts. The aging process of garlic produced characteristic volatile compounds that have significant protective effects against UV-induced cell damage. Our results demonstrated that the aging process is a suitable method to develop added value in garlic extracts to improve skin health.

Alternative Functions of Cell Cycle-Related and DNA Repair Proteins in Post-mitotic Neurons

Proper regulation of neuronal morphological changes is essential for neuronal migration, maturation, synapse formation, and high-order function. Many cytoplasmic proteins involved in the regulation of neuronal microtubules and the actin cytoskeleton have been identified. In addition, some nuclear proteins have alternative functions in neurons. While cell cycle-related proteins basically control the progression of the cell cycle in the nucleus, some of them have an extra-cell cycle-regulatory function (EXCERF), such as regulating cytoskeletal organization, after exit from the cell cycle. Our expression analyses showed that not only cell cycle regulators, including cyclin A1, cyclin D2, Cdk4/6, p21cip1, p27kip1, Ink4 family, and RAD21, but also DNA repair proteins, including BRCA2, p53, ATM, ATR, RAD17, MRE11, RAD9, and Hus1, were expressed after neurogenesis, suggesting that these proteins have alternative functions in post-mitotic neurons. In this perspective paper, we discuss the alternative functions of the nuclear proteins in neuronal development, focusing on possible cytoplasmic roles.

Fish c-Jun N-Terminal Kinase (JNK) Pathway Is Involved in Bacterial MDP-Induced Intestinal Inflammation

The c-Jun NH₂-terminal kinases (JNKs) are an evolutionarily conserved family of serine/threonine protein kinases that play critical roles in the pathological process in species ranging from insects to mammals. However, the function of JNKs in bacteria-induced intestinal inflammation is still poorly understood. In this study, a fish JNK (CiJNK) pathway was identified, and its potential roles in bacterial muramyl dipeptide (MDP)-induced intestinal inflammation were investigated in Ctenopharyngodon idella. The present CiJNK was found to possess a conserved dual phosphorylation motif (TPY) in a serine/threonine protein kinase (S_TKc) domain and to contain several potential immune-related transcription factor binding sites, including nuclear factor kappa B (NF-κB), activating protein 1 (AP-1), and signal transducer and activator of downstream transcription 3 (STAT3), in its 5′ flanking regions. Quantitative real-time PCR results revealed that the mRNA levels of the JNK pathway genes in the intestine were significantly upregulated after challenge with a bacterial pathogen (Aeromonas hydrophila) and MDP in a time-dependent manner. Additionally, the JNK pathway was found to be involved in regulating the MDP-induced expression levels of inflammatory cytokines (IL-6, IL-8, and TNF-α) in the intestine of grass carp. Moreover, the nutritional dipeptide carnosine and Ala–Gln could effectively alleviate MDP-induced intestinal inflammation by regulating the intestinal expression of JNK pathway genes and inflammatory cytokines in grass carp. Finally, fluorescence microscopy and dual-reporter assays indicated that CiJNK could associate with CiMKK4 and CiMKK7 involved in the regulation of the AP-1 signaling pathway. Overall, these results provide the first experimental demonstration that the JNK signaling pathway is involved in the intestinal immune response to MDP challenge in C. idella, which may provide new insight into the pathogenesis of inflammatory bowel disease.

Pro-apoptotic and pro-proliferation functions of the JNK pathway of Drosophila: roles in cell competition, tumorigenesis and regeneration

The Jun N-terminal kinase (JNK) is a member of the mitogen-activated protein kinase family. It appears to be conserved in all animal species where it regulates important physiological functions involved in apoptosis, cell migration, cell proliferation and regeneration. In this review, we focus on the functions of JNK in Drosophila imaginal discs, where it has been reported that it can induce both cell death and cell proliferation. We discuss this apparent paradox in the light of recent findings and propose that the pro-apoptotic and the pro-proliferative functions are intrinsic properties of JNK activity. Whether one function or another is predominant depends on the cellular context.

Phosphorylation of xeroderma pigmentosum group C regulates ultraviolet-induced DNA damage repair

Nucleotide excision repair (NER) is the most versatile DNA repair system that removes bulky DNA damage induced by various endogenous and exogenous factors, including UV radiation. Defects in NER can lead to the xeroderma pigmentosum (XP) syndrome, mainly characterized by increased carcinogenesis in the skin. The function of NER factors, including xeroderma pigmentosum group C (XPC), can be regulated by post-translational modifications such as ubiquitination. However, the role of phosphorylation in XPC function remains unknown. Here, we show that phosphorylation of XPC acts as a novel post-translational regulatory mechanism of the NER pathway. We show that XPC is phosphorylated at serine 94. Moreover, after UVB irradiation, XPC phosphorylation regulates recruitment of ubiquitinated XPC and its downstream NER factors to the chromatin. In addition, upon evaluating the predicted kinases for XPC phosphorylation, we found that casein kinase II (CK2) promotes NER. Furthermore, CK2 kinase mediates XPC phosphorylation at serine 94, and also promotes recruitment of ubiquitinated XPC to the chromatin after UVB irradiation. Our findings have identified XPC phosphorylation as a new mechanism for regulating NER following UV-induced DNA damage.

Hsp70 interactions with membrane lipids regulate cellular functions in health and disease

Beyond guarding the cellular proteome the major stress inducible heat shock protein Hsp70 has been shown to interact with lipids. Non-cytosolic Hsp70 stabilizes membranes during stress challenges and, in pathophysiological states, facilitates endocytosis, counteracts apoptotic mechanisms, sustains survival pathways or represents a signal that can be recognized by the immune system. Disease-coupled lipid-associated functions of Hsp70 may be targeted via distinct subcellular localizations of Hsp70 itself or its specific interacting lipids. With a special focus on interacting lipids, here we discuss localization-dependent roles of the membrane-bound Hsp70 in the context of its therapeutic potential, particularly in cancer and neurodegenerative diseases.

Heat induces myogenic transcription factors of myoblast cells via transient receptor potential vanilloid 1 (Trpv1)

Exercise generates heat, blood flow, and metabolic changes, thereby inducing hypertrophy of skeletal muscle cells. However, the mechanism by which heat incudes hypertrophy in response to heat is not well known. Here, we hypothesized that heat would induce differentiation of myoblast cells. We investigated the underlying mechanism by which myoblast cells respond to heat. When mouse myoblast cells were exposed to 42 °C for over 30 min, the phosphorylation level of protein kinase C (PKC) and heat shock factor 1 (Hsf1) increased, and the mRNA and protein expression level of heat shock protein 70 (Hsp70) increased. Inhibitors of transient receptor potential vanilloid 1 (Trpv1), calmodulin, PKC, and Hsf1, and the small interfering RNA‐mediated knockdown of Trpv1 diminished those heat responses. Heat exposure increased the phosphorylation levels of thymoma viral proto‐oncogene 1 (Akt), mammalian target of rapamycin (mTOR), eukaryotic translation initiation factor 4E binding protein 1 (Eif4ebp1), and ribosomal protein S6 kinase, polypeptide 1 (S6K1). The knockdown of Trpv1 decreased these heat‐induced responses. Antagonists of Hsp70 inhibited the phosphorylation level of Akt. Finally, heat increased the protein expression level of skeletal muscle markers such as myocyte enhancer factor 2D, myogenic factor 5, myogenic factor 6, and myogenic differentiation 1. Heat also increased myotube formation. Knockdown of Trpv1 diminished heat‐induced increases of those proteins and myotube formation. These results indicate that heat induces myogenic transcription factors of myoblast cells through the Trpv1, calmodulin, PKC, Hsf1, Hsp70, Akt, mTOR, Eif4ebp1, and S6K1 pathway. Moreover, heat increases myotube formation through Trpv1.

p63α protein up-regulates heat shock protein 70 expression via E2F1 transcription factor 1, promoting Wasf3/Wave3/MMP9 signaling and bladder cancer invasion

Bladder cancer (BC) is the sixth most common cancer in the United States and is the number one cause of death among patients with urinary system malignancies. This makes the identification of invasive regulator(s)/effector(s) as the potential therapeutic targets for managing BC a high priority. p63 is a member of the p53 family of tumor suppressor genes/proteins, plays a role in the differentiation of epithelial tissues, and is believed to function as a tumor suppressor. However, it remains unclear whether and how p63 functions in BC cell invasion after tumorigenesis. Here, we show that p63α protein levels were much higher in mouse high-invasive BC tissues than in normal tissues. Our results also revealed that p63α is crucial for heat shock protein 70 (Hsp70) expression and subsequently increases the ability of BC invasion. Mechanistic experiments demonstrated that p63α can transcriptionally up-regulate Hsp70 expression, thereby promoting BC cell invasion via the Hsp70/Wasf3/Wave3/MMP-9 axis. We further show that E2F transcription factor 1 (E2F1) mediates p63α overexpression-induced Hsp70 transcription. We also found that p63α overexpression activates E2F1 transcription, which appears to be stimulated by p63α together with E2F1. Collectively, our results demonstrate that p63α is a positive regulator of BC cell invasion after tumorigenesis, providing significant insights into the biological function of p63α in BC and supporting the notion that p63α might be a potential target for invasive BC therapy.

Heat induces interleukin-6 in skeletal muscle cells via TRPV1/PKC/CREB pathways

Interleukin-6 (IL-6) is released from skeletal muscle cells and induced by exercise, heat, catecholamine, glucose, lipopolysaccharide, reactive oxygen species, and inflammation. However, the mechanism that induces release of IL-6 from skeletal muscle cells remains unknown. Thermosensitive transient receptor potential (TRP) proteins such as TRPV1-4 play vital roles in cellular functions. In this study we hypothesized that TRPV1 senses heat, transmits a signal into the nucleus, and produces IL-6. The purpose of the present study is to investigate the underlying mechanisms whereby skeletal muscle cells sense and respond to heat. When mouse myoblast cells were exposed to 37-42°C for 2 h, mRNA expression of IL-6 increased in a temperature-dependent manner. Heat also increased IL-6 secretion in myoblast cells. A fura 2 fluorescence dual-wavelength excitation method showed that heat increased intracellular calcium flux in a temperature-dependent manner. Intracellular calcium flux and IL-6 mRNA expression were increased by the TRPV1 agonists capsaicin and N-arachidonoyldopamine and decreased by the TRPV1 antagonists AMG9810 and SB366791 and siRNA-mediated knockdown of TRPV1. TRPV2, 3, and 4 agonists did not change intracellular calcium flux. Western blotting with inhibitors demonstrated that heat increased phosphorylation levels of TRPV1, followed by PKC and cAMP response element-binding protein (CREB). PKC inhibitors, Gö6983 and staurosporine, CREB inhibitors, curcumin and naphthol AS-E, and knockdown of CREB suppressed the heat-induced increases in IL-6. These results indicate that heat increases IL-6 in skeletal muscle cells through the TRPV1, PKC, and CREB signal transduction pathway.NEW & NOTEWORTHY Heat increases the release of interleukin-6 (IL-6) from skeletal muscle cells. IL-6 has been shown to serve immune responses and metabolic functions in muscle. It can be anti-inflammatory as well as proinflammatory. However, the mechanism that induces release of IL-6 from skeletal muscle cells remains unknown. Here we show that heat increases IL-6 in skeletal muscle cells through the transient receptor potential vannilloid 1, PKC, and cAMP response element-binding protein signal transduction pathway.

Development of a Nonradioactive, Time-Resolved Fluorescence Assay for the Measurement of Jun N-Terminal Kinase Activity

Activated transcription factor AP-1 is composed of c-Jun homodimers or c-Jun/c-Fos heterodimers and mediates expression of several gene products that have been implicated in disease pathogenesis. Activation of AP-1 is dependent on phosphorylation of c-Jun by Jun N-terminal kinase (JNK). Therefore, identification of inhibitors of JNK-mediated phosphorylation of c-Jun may lead to a novel class of therapeutics. A nonradioactive, high-through-put, time-resolved fluorescence assay was developed to measure and identify inhibitors of JNK activity. This assay utilized a lanthanide (europium)-labeled antibody that was specific for N-terminally phosphorylated c-Jun. The optimized europium-based assay was approximately 15-fold more sensitive compared to a similar 32P-based JNK assay. Compounds that were identified as inhibitors of JNK using the europium-based assay also inhibited JNK activity in the 32P-based assay with similar IC50 values. The europium-based JNK assay eliminates the contamination problems associated with the use of radioactivity. The sensitivity and safety of the europium-based assay make it amenable to robotics that will significantly increase screening throughput.

Activation of the JNK-c-Jun pathway in response to irradiation facilitates Fas ligand secretion in hepatoma cells and increases hepatocyte injury

Background

It is well established that some irradiated liver non-parenchymal cells secrete pro-inflammatory cytokines to facilitate the development of radiation-induced liver disease. However, little is known on whether the irradiated hepatoma cells-mediated non-irradiated hepatocyte injury occurs in HCC patients. Here, we elucidated the roles of the irradiated hepatoma cells in driving non-irradiated hepatocyte injury and its underlying mechanism.

Methods

SMMC7721 cells were cultured and divided into irradiated (4-Gy X-ray, R) and non-irradiated (NR) groups. At 24th hour after irradiation, conditioned medium (CM) from these cultures was mixed with normal culture medium in specific proportions, and termed as 7721-R-CM and 7721-NR-CM. Following incubation with these CM compound, the biological characteristics of L02 cells related to liver cell injury including viability, apoptosis and liver dysfunction indices were comparatively analyzed. Simultaneously, the levels of proliferation- and apoptosis-related cytokines in irradiated and non-irradiated SMMC7721 cells were also measured. FasL as a cytokine with significantly differential expression, was selected to clarify its effects on L02 apoptosis. Subsequently, FasL expression following irradiation was examined in SMMC7721 and other HCC cells with varying malignant potentials, as well as in HCC tissues, the related mechanism of higher expression of FasL in irradiated HCC cells was further investigated.

Results

Apoptosis and liver dysfunction indices were all significantly enhanced in L02 cells treated with 7721-R-CM, whereas viability was suppressed, compared to those with 7721-NR-CM stimulation. FasL was identified as a leading differential cytokine in the irradiated SMMC7721 cells. Higher proportion of apoptosis was also found in L02 cells following FasL incubation. A recombinant Fas-Fc protein, which blocks Fas-FasL interaction, ameliorated 7721-R-CM-induced apoptosis in L02 cells. FasL was highly expressed in a dose-dependent manner, and peaked at the 24th hour post-irradiation in different HCC cells and their culture supernatant. Meanwhile, phosphorylation levels of JNK, ERK, Akt, and p38 were all upregulated significantly in irradiated HCC cells. But, only JNK inhibition was validated to block radiation-induced FasL expression in HCC cells. c-Jun, the target transcription factor of JNK, was also activated.

Conclusion

In HCC cells, the JNK-c-Jun pathway plays an important role in mediating irradiation- induced FasL expression, which may be critical in determining non-irradiated hepatocyte injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0394-z) contains supplementary material, which is available to authorized users.

Cytoprotective effects of cerium and selenium nanoparticles on heat-shocked human dermal fibroblasts: an in vitro evaluation

It is a widely accepted fact that environmental factors affect cells by modulating the components of subcellular compartments and altering metabolic enzymes. Factors (such as oxidative stress and heat-shock-induced proteins and heat shock factors, which upregulate stress-response related genes to protect affected cells) are commonly altered during changes in environmental conditions. Studies by our group and others have shown that nanoparticles (NPs) are able to efficiently attenuate oxidative stress by penetrating into specific tissues or organs. Such findings warrant further investigation on the effects of NPs on heat-shock-induced stress, specifically in cells in the presence or absence (pretreated) of NPs. Here, we examined the cytoprotective effects of two different NPs (cerium and selenium) on heat-induced cell death for a model cell using dermal fibroblasts. We report for the first time that both ceria and selenium NPs (at 500 µg/mL) possess stress-relieving behavior on fibroblasts undergoing heat shock. Such results indicate the need to further develop these NPs as a novel treatment for heat shock.

The adaptor protein Cindr regulates JNK activity to maintain epithelial sheet integrity

Epithelia are essential barrier tissues that must be appropriately maintained for their correct function. To achieve this a plethora of protein interactions regulate epithelial cell number, structure and adhesion, and differentiation. Here we show that Cindr (the Drosophila Cin85 and Cd2ap ortholog) is required to maintain epithelial integrity. Reducing Cindr triggered cell delamination and movement. Most delaminating cells died. These behaviors were consistent with JNK activation previously associated with loss of epithelial integrity in response to ectopic oncogene activity. We confirmed a novel interaction between Cindr and Drosophila JNK (dJNK), which when perturbed caused inappropriate JNK signaling. Genetically reducing JNK signaling activity suppressed the effects of reducing Cindr. Furthermore, ectopic JNK signaling phenocopied loss of Cindr and was partially rescued by concomitant cindr over-expression. Thus, correct Cindr-dJNK stoichiometry is essential to maintain epithelial integrity and disturbing this balance may contribute to the pathogenesis of disease states, including cancer.

Visible light-induced ion-selective optodes based on a metastable photoacid for cation detection

A new platform of ion-selective optodes is presented here to detect cations under thermodynamic equilibriumviaratiometric analysis.

RITA can induce cell death in p53-defective cells independently of p53 function via activation of JNK/SAPK and p38

Significant advances have been made in the development of small molecules blocking the p53/MDM2 interaction. The Mdm2 inhibitor Nutlin-3 is restricted to tumors carrying wtp53. In contrast, RITA, a compound that binds p53, has recently been shown also to restore transcriptional functions of mtp53. As more than 50% of solid tumors carry p53 mutations, RITA promises to be a more effective therapeutic strategy than Nutlin-3. We investigated effects of RITA on apoptosis, cell cycle and induction of 45 p53 target genes in a panel of 14 cell lines from different tumor entities with different p53 status as well as primary lymphocytes and fibroblasts. Nine cell strains expressed wtp53, four harbored mtp53, and three were characterized by the loss of p53 protein. A significant induction of cell death upon RITA was observed in 7 of 16 cell lines. The nonmalignant cells in our panel were substantially less sensitive. We found that in contrast to Nultin-3, RITA is capable to induce cell death not only in tumor cells harboring wtp53 and mtp53 but also in p53-null cells. Importantly, whereas p53 has a central role for RITA-mediated effects in wtp53 cells, neither p53 nor p63 or p73 were essential for the RITA response in mtp53 or p53-null cells in our panel demonstrating that besides the known p53-dependent action of RITA in wtp53 cells, RITA can induce cell death also independently of p53 in cells harboring defective p53. We identified an important role of both p38 and JNK/SAPK for sensitivity to RITA in these cells leading to a typical caspase- and BAX/BAK-dependent mitochondrial apoptosis. In conclusion, our data demonstrate that RITA can induce apoptosis through p38 and JNK/SAPK not only in tumor cells harboring wtp53 and mtp53 but also in p53-null cells, making RITA an interesting tumor-selective drug.

The complex function of hsp70 in metastatic cancer

Elevated expression of the inducible heat shock protein 70 (Hsp70) is known to correlate with poor prognosis in many cancers. Hsp70 confers survival advantage as well as resistance to chemotherapeutic agents, and promotes tumor cell invasion. At the same time, tumor-derived extracellular Hsp70 has been recognized as a "chaperokine", activating antitumor immunity. In this review we discuss localization dependent functions of Hsp70 in the context of invasive cancer. Understanding the molecular principles of metastasis formation steps, as well as interactions of the tumor cells with the microenvironment and the immune system is essential for fighting metastatic cancer. Although Hsp70 has been implicated in different steps of the metastatic process, the exact mechanisms of its action remain to be explored. Known and potential functions of Hsp70 in controlling or modulating of invasion and metastasis are discussed.

Heat shock instructs hESCs to exit from the self-renewal program through negative regulation of OCT4 by SAPK/JNK and HSF1 pathway

Environmental factors affect self-renewal of stem cells by modulating the components of self-renewal networks. Heat shock, an environmental factor, induces heat shock factors (HSFs), which up-regulate stress response-related genes. However, the link of heat shock to self-renewal of stem cells has not been elucidated yet. Here, we present the direct link of heat shock to a core stem cell regulator, OCT4, in the self-renewal network through SAPK/JNK and HSF1 pathway. We first showed that heat shock initiated differentiation of human embryonic stem cells (hESCs). Gene expression analysis revealed that heat shock increased the expression of many genes involved in cellular processes related to differentiation of stem cells. We then examined the effects of HSFs induced by heat shock on core self-renewal factors. Among HSFs, heat shock induced mainly HSF1 in hESCs. The HSF1 repressed the expression of OCT4, leading to the differentiation of hESCs and the above differentiation-related gene expression change. We further examined the effects of the upstream MAP (mitogen-activated protein) kinases of HSF1 on the repression of OCT4 expression by HSF1. Among the MAP kinases, SAPK/JNK controlled predominantly the repression of the OCT4 expression by HSF1. The direct link of heat shock to the core self-renewal regulator through SAPK/JNK and HSF1 provides a fundamental basis for understanding the effect of heat and other stresses involving activation of HSF1 on the self-renewal program and further controlling differentiation of hESCs in a broad spectrum of stem cell applications using these stresses.

Cellular stress response and innate immune signaling: integrating pathways in host defense and inflammation

Extensive research in the past decade has identified innate immune recognition receptors and intracellular signaling pathways that culminate in inflammatory responses. Besides its role in cytoprotection, the importance of cell stress in inflammation and host defense against pathogens is emerging. Recent studies have shown that proteins in cellular stress responses, including the heat shock response, ER stress response, and DNA damage response, interact with and regulate signaling intermediates involved in the activation of innate and adaptive immune responses. The effect of such regulation by cell stress proteins may dictate the inflammatory profile of the immune response during infection and disease. In this review, we describe the regulation of innate immune cell activation by cell stress pathways, present detailed descriptions of the types of stress response proteins and their crosstalk with immune signaling intermediates that are essential in host defense, and illustrate the relevance of these interactions in diseases characteristic of aberrant immune responses, such as chronic inflammatory diseases, autoimmune disorders, and cancer. Understanding the crosstalk between cellular stress proteins and immune signaling may have translational implications for designing more effective regimens to treat immune disorders.

Skeletal muscle interleukin-6 regulation in hyperthermia

We previously reported that IL-6 production is acutely elevated in skeletal muscles exposed to ≥41°C, but the regulatory pathways are poorly understood. The present study characterizes the heat-induced transcriptional control of IL-6 in C2C12 muscle fibers. Hyperthermia exposure (42°C for 1 h) induced transcription from an IL-6 promoter-luciferase reporter plasmid. Heat shock factor-1 (HSF-1), a principal mediator of the heat shock response, was then tested for its role in IL-6 regulation. Overexpression of a constitutively active HSF-1 construct increased basal (37°C) promoter activity, whereas overexpression of a dominant negative HSF-1 reduced IL-6 promoter activity during basal and hyperthermia conditions. Since hyperthermia also induces stress-activated protein kinase (SAPK) signaling, we tested whether mutation of a transcription site downstream of SAPK, (i.e., activator protein-1, AP-1) influences IL-6 transcription in hyperthermia. The mutation had no effect on baseline reporter activity but completely inhibited heat-induced activity. We then tested whether pharmacologically induced states of protein stress, characteristic of cellular responses to hyperthermia and known to induce SAPKs and HSF-1, would induce IL-6 production in the absence of heat. The proteasome was inhibited with MG-132 in one set of experiments, and the unfolded protein response was stimulated with dithiothreitol, thapsigargin, tunicamycin, or castanospermine in other experiments. All treatments stimulated IL-6 protein secretion in the absence of hyperthermia. These studies demonstrate that IL-6 regulation in hyperthermia is directly controlled by HSF-1 and AP-1 signaling and that the IL-6 response in C2C12 myotubes is sensitive to categories of protein stress that reflect accumulation of damaged or unfolded proteins.

HSP47 regulates ECM accumulation in renal proximal tubular cells induced by TGF-β1 through ERK1/2 and JNK MAPK pathways

Heat shock protein (HSP)47 is a collagen-specific molecular chaperone that is essential for the biosynthesis of collagen molecules. It is likely that increased levels of HSP47 contribute to the assembly of procollagen and thereby cause an excessive accumulation of collagens in disease processes associated with fibrosis. Although HSP47 promotes renal fibrosis, the underlying mechanism and associated signaling events have not been clearly delineated. We examined the role of HSP47 in renal fibrosis using a rat unilateral ureteral obstruction model and transforming growth factor (TGF)-β(1)-treated human proximal tubular epithelial (HK-2) cells. An upregulation of HSP47 in both in vivo and in vitro models was observed, which correlated with the increased synthesis of extracellular matrix (ECM) proteins and expression of tissue-type plasminogen activator inhibitor (PAI)-1. Blockade of HSP47 by short interfering RNA suppressed the expression of ECM proteins and PAI-1. In addition, TGF-β(1)-induced HSP47 expression in HK-2 cells was attenuated by ERK1/2 and JNK MAPK inhibitors. These data suggest that ERK1/2 and JNK signaling events are involved in modulating the expression of HSP47, the chaperoning effect of which on TGF-β(1) would ultimately contribute to renal fibrosis by enhancing the synthesis and deposition of ECM proteins.

c-Jun and Ets2 proteins regulate expression of spleen tyrosine kinase in T cells

Effector T cells and T cells from patients with systemic lupus erythematosus (SLE) express increased levels of the spleen tyrosine kinase (Syk). Syk binds to the T cell receptor (TCR)-CD3 complex and transduces the TCR-mediated signal in the cell more efficiently than the canonical CD3ζ chain. The reasons for the increased expression of Syk are unclear. In the present study, we found that Syk is regulated by the transcription factor c-Jun in cooperation with Ets2. c-Jun and Ets2 bound to the SYK promoter in close proximity and increased the promoter activity in a specific manner. Disruption of c-Jun and Ets2 expression by siRNA resulted in decreased expression of Syk. Overexpression of c-Jun but not Ets2 resulted in increase in Syk protein. c-Jun and Ets2 co-immunoprecipitated and had an additive effect on Syk expression. c-Jun-driven SYK promoter activation showed a similar pattern in B cells; however, as expected, basal promoter activity was much higher in B cells as compared with T cells. Overexpression of c-Jun led to increase in intracytoplasmic calcium flux following TCR stimulation. Moreover, we found that SLE T cells had increased levels of c-Jun at baseline and phosphorylated c-Jun upon activation. Finally, disruption of c-Jun and Ets2 in SLE T cells resulted in a decrease in calcium flux upon TCR stimulation. In conclusion, c-Jun in cooperation with Ets2 increases the expression of Syk and contributes to Syk-mediated heightened calcium responses in SLE T cells.

Off-target lapatinib activity sensitizes colon cancer cells through TRAIL death receptor up-regulation

Lapatinib, a dual HER2/EGFR (human epidermal growth factor receptor 2/epidermal growth factor receptor) inhibitor, is a recently approved targeted therapy for metastatic breast cancer. Because lapatinib enhances the efficacy of the chemotherapeutic agent capecitabine in breast cancer patients, we tested whether lapatinib also enhances the activity of anticancer agents in colorectal cancer. We found that lapatinib improved the proapoptotic effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and two TRAIL receptor agonists, the antibodies mapatumumab and lexatumumab. Tumors from mice treated with a combination of lapatinib and TRAIL exhibited more immunostaining for cleaved caspase-8, a marker of the extrinsic cell death pathway, than did tumors from mice treated with lapatinib or TRAIL alone. Furthermore, combination therapy suppressed tumor growth more effectively than either agent alone. Lapatinib up-regulated the proapoptotic TRAIL death receptors DR4 and DR5, leading to more efficient induction of apoptosis in the presence of TRAIL receptor agonists. This activity of lapatinib was independent of EGFR and HER2. The off-target induction of DR5 by lapatinib resulted from activation of the c-Jun amino-terminal kinase (JNK)/c-Jun signaling axis. This activity of lapatinib on TRAIL death receptor expression and signaling may confer therapeutic benefit when increased doses of lapatinib are used in combination with TRAIL receptor-activating agents.

Regulation of autophagy by kinases

Autophagy is a process of self-degradation that maintains cellular viability during periods of metabolic stress. Although autophagy is considered a survival mechanism when faced with cellular stress, extensive autophagy can also lead to cell death. Aberrations in autophagy are associated with several diseases, including cancer. Therapeutic exploitation of this process requires a clear understanding of its regulation. Although the core molecular components involved in the execution of autophagy are well studied there is limited information on how cellular signaling pathways, particularly kinases, regulate this complex process. Protein kinases are integral to the autophagy process. Atg1, the first autophagy-related protein identified, is a serine/threonine kinase and it is regulated by another serine/threonine kinase mTOR. Emerging studies suggest the participation of many different kinases in regulating various components/steps of this catabolic process. This review focuses on the regulation of autophagy by several kinases with particular emphasis on serine/threonine protein kinases such as mTOR, AMP-activated protein kinase, Akt, mitogen-activated protein kinase (ERK, p38 and JNK) and protein kinase C that are often deregulated in cancer and are important therapeutic targets.

Signal Transduction Pathways Leading to Heat Shock Transcription

Heat shock proteins (HSP) are essential for intracellular protein folding during stress and protect cells from denaturation and aggregation cascades that can lead to cell death. HSP genes are regulated at the transcriptional level by heat shock transcription factor 1 (HSF1) that is activated by stress and binds to heat shock elements in HSP genes. The activation of HSF1 during heat shock involves conversion from an inert monomer to a DNA binding trimer through a series of intramolecular folding rearrangements. However, the trigger for HSF1 at the molecular level is unclear and hypotheses for this process include reversal of feedback inhibition of HSF1 by molecular chaperones and heat-induced binding to large non-coding RNAs. Heat shock also causes a profound modulation in cell signaling pathways that lead to protein kinase activation and phosphorylation of HSF1 at a number of regulatory serine residues. HSP genes themselves exist in an accessible chromatin conformation already bound to RNA polymerase II. The RNA polymerase II is paused on HSP promoters after transcribing a short RNA sequence proximal to the promoter. Activation by heat shock involves HSF1 binding to the promoter and release of the paused RNA polymerase II followed by further rounds of transcriptional initiation and elongation. HSF1 is thus involved in both initiation and elongation of HSP RNA transcripts. Recent studies indicate important roles for histone modifications on HSP genes during heat shock. Histone modification occurs rapidly after stress and may be involved in promoting nucleosome remodeling on HSP promoters and in the open reading frames of HSP genes. Understanding these processes may be key to evaluating mechanisms of deregulated HSP expression that plays a key role in neurodegeneration and cancer.

Increased interaction between heat shock protein 27 and mitogen-activated protein kinase (p38 and extracellular signal-regulated kinase) in pre-eclamptic placentas

AIMS

Heat shock protein 27 (Hsp27) is a well-known stress response protein that is characterized by its phosphorylative capacity. Hsp27 becomes phosphorylated in response to various stimuli through interaction with several different kinases. The purpose of this study was to evaluate the interaction between Hsp27 and mitogen-activated protein kinase (MAPK) (p38, extracellular signal-regulated kinase [ERK], and c-Jun N-terminal kinase) in the human placenta derived from patients with pre-eclampsia.

METHODS

Western blot analysis was used to examine the levels of expression of Hsp27 and MAPK (p38, ERK, and c-Jun N-terminal kinase). Immunoprecipitation analysis was used to determine the interaction between Hsp27 and MAPK (p38 and ERK).

RESULTS

Western blotting analysis and immunohistochemistry showed that the expression of Hsp27 and p-Hsp27 in the placental tissues of the pre-eclampsia group were significantly higher than that in the normal pregnancy group. Immunoprecipitation analysis showed that the interaction between Hsp27 and MAPK (p38 and ERK) was significantly increased in the pre-eclamptic placenta tissues.

CONCLUSION

The interaction between Hsp27 and MAPK was increased, suggesting that phosphorylation of Hsp27 might be induced by p38 and ERK in placentas from patients with pre-eclampsia.

Hyperthermia-induced Hsp70 and MT20 transcriptional upregulation are mediated by p38-MAPK and JNKs in Mytilus galloprovincialis (Lamarck); a pro-survival response

In the present study we investigated the signal transduction cascades triggered by acute thermal stress in Mytilus galloprovincialis gills. This particular species has been reported to exhibit a significant tolerance to high temperatures; thus, it was intriguing to examine the molecular mechanisms responsible for this extraordinary trait. In particular, exposure to 30 degrees C was found to cause a significant and sustained stimulation of p38-MAPK phosphorylation while the activation profile of JNKs was transient and relatively moderate. We also observed that hyperthermia induced apoptosis as a delayed response, with both MAPK subfamilies rapidly translocating to the nucleus. The phosphorylation of cJun, ATF2 and NFkappaB was detected next. Using selective inhibitors, phosphorylation of these transcription factors was established to be dependent on p38-MAPK or JNKs. Subsequently, potential changes in gene expression were assessed. In this context, hyperthermia resulted in the transcriptional upregulation of Hsp70 and MT20 genes with a widely known salutary effect, preserving mussel fitness and performance under adverse environmental conditions. Interestingly, p38-MAPK and JNKs were found to mediate the hyperthermia-induced Hsp70 and MT20 upregulation as well as the delayed induction of apoptosis under the interventions studied. Overall this is, to our knowledge, the first time that an insight into the compensatory survival ;programme' initiated in Mytilus galloprovincialis gills, contributing to this organism's exceptional tolerance to thermal stress, has been gained. In particular, we provide evidence demonstrating the principal role of p38-MAPK and JNKs in transducing the stress signal via mobilization of specific transcription factors and the transcriptional upregulation of cytoprotective genes.

Inhibition of hepatic mitochondrial aldehyde dehydrogenase by carbon tetrachloride through JNK-mediated phosphorylation

The aim of this study was to investigate the mechanism of inhibition of mitochondrial aldehyde dehydrogenase (ALDH2) by carbon tetrachloride (CCl(4)). CCl(4) administration caused marked hepatocyte ballooning and necrosis in the pericentral region. CCl(4) also inhibited hepatic ALDH2 activity in a time-dependent manner without altering the protein level, suggesting ALDH2 inhibition through covalent modifications such as phosphorylation by JNK. To demonstrate phosphorylation, the isoelectric point (pI) of ALDH2 in CCl(4)-exposed rats was compared to that of untreated controls. Immunoblot analysis revealed that immunoreactive ALDH2 bands in CCl(4)-exposed rats were shifted to acidic pI ranges on two-dimensional electrophoresis (2-DE) gels. Incubation with alkaline phosphatase significantly restored the suppressed ALDH2 activity with a concurrent alkaline pI shift of the ALDH2 spots. Both JNK and activated JNK were translocated to mitochondria after CCl(4) exposure. In addition, incubation with catalytically active JNK led to significant inhibition of ALDH2 activity, with an acidic pI shift on 2-DE gels. Furthermore, immunoprecipitation followed by immunoblot analysis with anti-phospho-Ser-Pro antibody revealed phosphorylation of a Ser residue(s) of ALDH2. These results collectively indicate a novel underlying mechanism by which CCl(4) exposure activates JNK, which translocates to mitochondria and phosphorylates ALDH2, contributing to inhibition of ALDH2 activity accompanied by decreased cellular defense capacity and increased lipid peroxidation.

Endoplasmic reticulum stress and the unfolded protein response

The endoplasmic reticulum (ER) is the key cellular organelle involved in protein homoeostasis. The unfolded protein response (UPR) is a fundamental cellular process triggered by ER stress because of lack of ATP or primary ER dysfunction. The UPR is activated and dysregulated in non-alcoholic fatty liver disease (NAFLD). The UPR has been shown to be involved in both normal physiologic functions and the cellular response to a host of pathologic states. This article reviews the pathways by which the UPR unfolds and its potential role in the development and progression of NAFLD.

Posttranslational regulation of the NKG2D ligand Mult1 in response to cell stress

NKG2D is a major stimulatory receptor expressed by natural killer (NK) cells and some T cells. The receptor recognizes major histocompatability complex class I–like cell surface ligands that are poorly expressed by normal tissues but are often induced in transformed and infected cells. The existence of several NKG2D ligands in each individual, some with strikingly divergent protein sequences, raises the possibility that different ligands are regulated by distinct disease-associated stresses. The transcripts for some ligands, including murine UL16-binding proteinlike transcript 1 (Mult1), are abundant in certain normal tissues where cell surface expression is absent, suggesting the existence of translational or posttranslational regulation. We report here that under normal conditions, Mult1 protein undergoes ubiquitination dependent on lysines in its cytoplasmic tail and lysosomal degradation. Mult1 degradation and ubiquitination is reduced in response to stress imparted by heat shock or ultraviolet irradiation, but not by other forms of genotoxicity, providing a novel mechanism for stress-mediated cellular control of NKG2D ligand expression.

Akt depletion is an important determinant of L929 cell death following heat stress

Exposure of mammalian cells to heat stress causes impairment of numerous physiological functions and activates a number of signaling pathways. Some of these pathways, such as induction of heat-shock proteins and activation of Akt, enhance the ability of cells to survive heat stress. On the other hand, heat stress can trigger cell-death signaling via activation of the stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/Jnk). Recently, it has been shown that kinases activated by heat stress can regulate synthesis and functioning of the molecular chaperones, and these chaperones modulate the activity of the cell death and survival pathways. We have found that Akt plays a central role in determining the fate of L929 fibroblast cells exposed to heat stress. In our experiments heat stress causes Akt depletion and L929 cells to undergo cell death. Heat-shock protein 70 (Hsp70) is known to prevent stress-induced cell death by interfering with the SAPK/Jnk signaling pathway. In our study, there is a very high level of induction of Hsp70, yet this is not sufficient to rescue Akt depletion and L929 from cell death. The Akt depletion is specific, since actin protein level does not change during the heat stress. Moreover, our studies show that L929 cells can recover from a short-term heat shock, whereby, Akt level is returned to normal following recovery from heat shock. Therefore, it appears that the fate of the prolonged heat-stressed fibroblast cells is determined by Akt level, and that return of Akt protein level to normal prevents cell death.

Differential roles of p38-MAPK and JNKs in mediating early protection or apoptosis in the hyperthermic perfused amphibian heart

In the present study the activation of p38 mitogen-activated protein kinase(p38-MAPK) and c-Jun N-terminal kinases (JNKs) by hyperthermia was investigated in the isolated perfused Rana ridibunda heart. Hyperthermia (42°C) was found to profoundly stimulate p38-MAPK phosphorylation within 0.5 h, with maximal values being attained at 1 h[4.503(±0.577)-fold relative to control, P<0.01]. JNKs were also activated under these conditions in a sustained manner for at least 4 h[2.641(±0.217)-fold relative to control, P<0.01]. Regarding their substrates, heat shock protein 27 (Hsp27) was maximally phosphorylated at 1 h [2.261(±0.327)-fold relative to control, P<0.01] and c-Jun at a later phase [3 h: 5.367(±0.081)-fold relative to control, P<0.001]. Hyperthermia-induced p38-MAPK activation was found to be dependent on the Na+/H+ exchanger 1 (NHE1) and was also suppressed by catalase (Cat) and superoxide dismutase (SOD), implicating the generation of reactive oxygen species (ROS). ROS were also implicated in the activation of JNKs by hyperthermia, with the Na+/K+-ATPase acting as a mediator of this effect at an early stage and the NHE1 getting involved at a later time point. Finally, JNKs were found to be the principal mediators of the apoptosis induced under hyperthermic conditions, as their inhibition abolished poly(ADP-ribose)polymerase (PARP) cleavage after 4 h at 42°C. Overall, to our knowledge,this study highlights for the first time the variable mediators implicated in the transduction of the hyperthermic signal in the isolated perfused heart of an ectotherm and deciphers a potential salutary effect of p38-MAPK as well as the fundamental role of JNKs in the induced apoptosis.

Protection against heat and staurosporine mediated apoptosis by the HSV-1 US11 protein

US11 protein, one of herpes simplex virus type 1 (HSV-1) true late gene products, plays a role in the virally induced post-transcriptional control of gene expression. In addition, US11 expression also interferes with the cellular response to HSV-1 infection that can lead to apoptosis. We have previously shown that US11 expression enhanced the recovery of cellular protein synthesis and increased cell survival in response to thermal stress. Since heat shock can activate apoptosis, we tested for a possible anti-apoptotic behavior of US11. Here, we show that, in HeLa cells, US11 expression strongly reduced heat induced apoptosis, a phenomenon independent of Hsp expression and characterized by a delayed cytochrome c efflux from mitochondria and reduced caspase 3 activation. Moreover, US11 expression also protected against staurosporine induced apoptosis. Hence, our results favor an anti-apoptotic activity of US11 polypeptide that appears to be located at the level of mitochondria or upstream signaling pathways.

15-Deoxy-delta 12,14-prostaglandin J2 induces apoptosis via JNK-mediated mitochondrial pathway in osteoblastic cells

The cyclopentenone prostaglandin 15-deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) induces apoptosis in various cell types. However, the underlying mechanism of 15d-PGJ2-induced apoptosis is not fully understood. The present study was undertaken to determine the molecular mechanism by which 15d-PGJ2 induces apoptosis in MC3T3-E1 mouse osteoblastic cells. 15d-PGJ2 caused a concentration- and time-dependent apoptotic cell death. 15d-PGJ2 induced a transient activation of ERK1/2 and sustained activation of JNK. 15d-PGJ2-induced cell death was prevented by the JNK inhibitor SP6001, but not by inhibitors of ERK1/2 and p38. JNK activation by 15d-PGJ2 was blocked by antioxidants N-acetylcysteine (NAC) and GSH. 15d-PGJ2 caused ROS generation and 15d-PGJ2-induced cell death was prevented by antioxidants, suggesting involvement of ROS generation in 15d-PGJ2-induced cell death. 15d-PGJ2 triggered the mitochondrial apoptotic pathway indicated by enhanced Bax expression, loss of mitochondrial membrane potential, cytochrome c release, and caspase-3 activation. The JNK inhibitor blocked these events induced by 15d-PGJ2. Taken together, these results suggest that the 15d-PGJ2 induces cell death through the mitochondrial apoptotic pathway dependent of ROS and JNK activation in osteoblastic cells.

Understanding signaling cascades in melanoma

Understanding regulatory pathways involved in melanoma development and progression has advanced significantly in recent years. It is now appreciated that melanoma is the result of complex changes in multiple signaling pathways that affect growth control, metabolism, motility and the ability to escape cell death programs. Here we review the major signaling pathways currently known to be deregulated in melanoma with an implication to its development and progression. Among these pathways are Ras, B-Raf, MEK, PTEN, phosphatidylinositol-3 kinase (PI3Ks) and Akt which are constitutively activated in a significant number of melanoma tumors, in most cases due to genomic change. Other pathways discussed in this review include the [Janus kinase/signal transducer and activator of transcription (JAK/STAT), transforming growth factor-beta pathways which are also activated in melanoma, although the underlying mechanism is not yet clear. As a paradigm for remodeled signaling pathways, melanoma also offers a unique opportunity for targeted drug development.

A Polypodium leucotomos extract inhibits solar-simulated radiation-induced TNF-alpha and iNOS expression, transcriptional activation and apoptosis

In this report, we have examined the molecular basis of the photoprotective effect of a hydrophilic extract of the fern Polypodium leucotomos (PL) in vitro, using a solar simulator as the source of UV radiation (SSR). We found that pretreatment of human keratinocytes with PL inhibited SSR-mediated increase of tumor necrosis factor (TNF)-alpha and also abrogated nitric oxide (NO) production. Consistent with this, PL blocked the induction of inducible nitric oxide synthase (iNOS) elicited by SSR. In addition, PL inhibited the SSR-mediated transcriptional activation of NF-kappaB and AP1. Finally, we demonstrated that pretreatment with PL exerted a cytoprotective effect against SSR-induced damage, resulting in increased cell survival. Together, these data postulate a multifactor mechanism of protection not exclusively reliant on the antioxidant capability of PL, and strengthen the basic knowledge on the photoprotective effect of this botanical agent.

Mechanisms of Activation and Regulation of the Heat Shock-Sensitive Signaling Pathways

Heat shock (HS), like many other stresses, induces specific and highly regulated signaling cascades that promote cellular homeostasis. The three major mitogen-activated protein kinases (MAPK) and protein kinase B (PKB/Akt) are the most notable of these HS-stimulated pathways. Their activation occurs rapidly and sooner than the transcriptional upregulation of heat shock proteins (Hsp), which generate a transient state of extreme resistance against subsequent thermal stress. The direct connection of these signaling pathways to cellular death or survival mechanisms suggests that they contribute importantly to the HS response. Some of them may counteract early noxious effects of heat, while others may bolster key apoptosis events. The triggering events responsible for activating these pathways are unclear. Protein denaturation, specific and nonspecific receptor activation, membrane alteration and chromatin structure perturbation are potential initiating factors.

The oxidative stress response regulates DKK1 expression through the JNK signaling cascade in multiple myeloma plasma cells

Multiple myeloma (MM) plasma cells, but not those from healthy donors and patients with monoclonal gammopathy of undetermined significance or other plasma cell dyscrasias involving the bone marrow, express the Wnt-signaling antagonist DKK1. We previously reported that secretion of DKK1 by MM cells likely contributes to osteolytic lesions in this disease by inhibiting Wnt signaling, which is essential for osteoblast differentiation and survival. The mechanisms responsible for activation and regulation of DKK1 expression in MM are not known. Herein, we could trace DKK1 expression changes in MM cells to perturbations in the JNK signaling cascade, which is differentially modulated through oxidative stress and interactions between MM cells with osteoclasts in vitro. Despite its role as a tumor suppressor and mediator of apoptosis in other cell types including osteoblasts, our data suggest that DKK1, a stress-responsive gene in MM, does not mediate apoptotic signaling, is not activated by TP53, and its forced overexpression could not inhibit cell growth or sensitize MM cells to apoptosis following treatment with thalidomide or lenalidomide. We conclude that specific strategies to modulate persistent activation of the JNK pathway may be beneficial in preventing disease progression and treating myeloma-associated bone disease by inhibiting DKK1 expression.

Poly(ADP-ribosyl)ation regulates heat shock factor-1 activity and the heat shock response in murine fibroblasts

Poly(ADP-ribose) polymerase-1 (PARP-1)-dependent poly(ADP-ribose) formation is emerging as a key regulator of transcriptional regulation, even though the targets and underlying molecular mechanisms have not yet been clearly identified. In this study, we gathered information on the role of PARP-1 activity in the heat shock response of mouse fibroblasts. We show that DNA binding of heat shock factor (HSF)-1 was impaired by PARP-1 activity in cellular extracts, and was higher in PARP-1(-/-) than in PARP-1+/+ cells. No evidence for HSF-1 poly(ADP-ribosyl)ation or PARP-1 interaction was found, but a poly(ADP-ribose) binding motif was identified in the transcription factor amino acid sequence. Consistent with data on HSF-1, the expression of heat-shock protein (HSP)-70 and HSP-27 was facilitated in cells lacking PARP-1. Thermosensitivity, however, was higher in PARP-1(-/-) than in PARP-1+/+ cells. Accordingly, we report that heat-shocked PARP-1 null fibroblasts showed an increased activation of proapoptotic JNK and decreased transcriptional efficiency of prosurvival NF-kappaB compared with wild-type counterparts. The data indicate that poly(ADP-ribosyl)ation finely regulates HSF-1 activity, and emphasize the complex role of PARP-1 in the heat-shock response of mammalian cells.

The isoform-specific functions of the c-Jun N-terminal Kinases (JNKs): differences revealed by gene targeting

The c-Jun N-terminal kinases (JNKs) are members of the mitogen-activated protein kinase (MAPK) family. In mammalian genomes, three genes encode the JNK family. To evaluate JNK function, mice have been created with deletions in one or more of three Jnk genes. Initial studies on jnk1(-/-) or jnk2(-/-) mice have shown roles for these JNKs in the immune system whereas studies on jnk3(-/-) mice have highlighted roles for JNK3 in the nervous system. Further studies have highlighted the contributions of JNK1 and/or JNK2 to a range of biological and pathological processes. These include bone remodelling and joint disease, inflammatory and autoimmune diseases, obesity, diabetes, cardiovascular disease, liver disease and tumorigenesis in addition to effects in neurons. These results emphasise the differences in the roles played by JNK isoforms in vivo and suggest that the design of JNK inhibitors for subsequent therapeutic uses may benefit from selective inhibition of individual JNK isoforms.

c-Jun NH2-terminal kinase decreases ubiquitination and promotes stabilization of p21(WAF1/CIP1) in K562 cell

Proteasome-dependent degradation of regulatory proteins is a known mechanism of cell cycle control. p21(WAF1/CIP1) (p21), a negative regulator of the cell division cycle, exhibits proteasome-sensitive turnover and ubiquitination. In the present study, we analyzed the regulatory effects of JNK1 on p21 protein accumulation in p53 null K562 cells. We found that JNK1 (wild type, WT) mediated H(2)O(2)-induced p21 protein up-regulation. Over-expression of JNK1 (WT) could elevate endogenous p21 protein level but did not affect p21 mRNA level and also prolong the p21 half-life as well as inhibited the p21 ubiquitination. These findings indicated that JNK1 could regulate cellular p21 level via inhibiting ubiquitination of p21, which provided a new insight for analyzing the regulatory effect of JNK after stress.

Identification of a hydrogen peroxide-induced PP1-JNK1-Sp1 signaling pathway for gene regulation

Oxidative stress often results in changes in gene expression through the regulation of transcription factors. In this study, we examine how Sp1 phosphorylation is regulated by H2O2 in a human alveolar epithelial cell line (HAE). Treatment of HAE cells with H2O2 increases phosphorylation of Sp1 and activates JNK. To establish a relationship between JNK and Sp1, we show that JNK activator anisomycin increases Sp1 phosphorylation, and JNK inhibitors as well as dominant-negative JNK1 attenuate H2O2-induced Sp1 phosphorylation. Additionally, JNK1 directly phosphorylates Sp1 in vitro, reducing Sp1 binding to DNA. These results demonstrate the role of JNK in H2O2-induced Sp1 phosphorylation. Because H2O2 inhibits Ser/Thr protein phosphatase-1 (PP1), we examined the role of PP1 in the regulation of JNK. Similar to H2O2, inhibition of PP1 induces phosphorylation of Sp1 and activation of JNK in HAE cells. Inhibition of JNK activity using either inhibitors or dominant-negative mutant JNK1 suppresses PP1 inhibition-induced Sp1 phosphorylation. Furthermore, PP1 directly inactivates JNK1 in vitro. These data suggest that 1) H2O2 increases the phosphorylation level of Sp1, 2) Sp1 is a target of the JNK pathway, 3) PP1 regulates JNK activation, and 4) the “PP1-JNK” pathway plays a role in H2O2-induced Sp1 phosphorylation in lung epithelial cells.