c-JUN gene induction and AP-1 activity is regulated by a JNK-dependent pathway in hypoxic HepG2 cells

Hypoxia-induced conversion of sensory Schwann cells into repair cells is regulated by HDAC8

After a peripheral nerve injury, Schwann cells (SCs), the myelinating glia of the peripheral nervous system, convert into repair cells that foster axonal regrowth, and then remyelinate or re-ensheath regenerated axons, thereby ensuring functional recovery. The efficiency of this mechanism depends however on the time needed for axons to regrow. Here, we show that ablation of histone deacetylase 8 (HDAC8) in SCs accelerates the regrowth of sensory axons and sensory function recovery. We found that HDAC8 is specifically expressed in sensory SCs and regulates the E3 ubiquitin ligase TRAF7, which destabilizes hypoxia-inducible factor 1-alpha (HIF1α) and counteracts the phosphorylation and upregulation of c-Jun, a major inducer of the repair SC phenotype. Our study indicates that this phenotype switch is regulated by different mechanisms in sensory and motor SCs and is accelerated by HDAC8 downregulation, which promotes sensory axon regeneration and sensory function recovery.

Probenecid Inhibits Extracellular Signal-Regulated Kinase and c-Jun N-Terminal Kinase Mitogen-Activated Protein Kinase Pathways in Regulating Respiratory Syncytial Virus Response

We examined the effect of probenecid in regulating the ERK and JNK downstream MAPK pathways affecting respiratory syncytial virus replication.

BACKGROUND

We have previously shown that probenecid inhibits RSV, influenza virus, and SARS-CoV-2 replication in vitro in preclinical animal models and in humans. In a Phase two randomized, placebo-controlled, single-blind, dose range-finding study using probenecid to treat non-hospitalized patients with symptomatic, mild-to-moderate COVID-19, we previously showed that a 1000 mg twice daily treatment for 5 days reduced the median time to viral clearance from 11 to 7 days, and a 500 mg twice daily treatment for 5 days reduced the time to viral clearance from 11 to 9 days more than the placebo.

METHODS

In this study, we sought to determine the mechanism of action of the probenecid inhibition of RSV replication in human respiratory epithelial (A549) cells.

RESULTS

We show that probenecid inhibits the RSV-induced phosphorylation of JNKs and ERKs and the downstream phosphorylation of c-jun, a component of the AP-1 transcription complex needed for virus replication. The inhibition of JNKs by probenecid reversed the repression of transcription factor HNF-4.

CONCLUSION

The probenecid inhibition of JNK and ERK phosphorylation involves the MAPK pathway that precludes virus replication.

Protein kinases: The key contributors in pathogenesis and treatment of nonalcoholic fatty liver disease-derived hepatocellular carcinoma

Protein kinases (PKs), one of the largest protein families, can be further divided into different groups based on their substrate or structure and function. PKs are important signaling messengers in numerous life activities, including cell metabolism, proliferation, division, differentiation, senescence, death, and disease. Among PK-related diseases, nonalcoholic fatty liver disease (NAFLD) has been recognized as a major contributor to hepatocellular carcinoma (HCC) and liver transplantation. Unfortunately, NAFLD-derived HCC (NAFLD-HCC) has poor prognosis because it is typically accompanied by older age, multiple metabolic syndromes, obstacles in early-stage diagnosis, and limited licensed drugs for treatment. Accumulating evidence suggests that PKs are implicated in the pathogenic process of NAFLD-HCC, via aberrant metabolism, hypoxia, autophagy, hypoxia, gut microbiota dysbiosis, and/or immune cell rearrangement. The present review aims to summarize the latest research advances and emphasize the feasibility and effectiveness of therapeutic strategies that regulate the expression and activities of PKs. This might yield clinically significant effects and lead to the design of novel PK-targeting therapies. Furthermore, we discuss emerging PK-based strategies for the treatment of other malignant diseases similar to NAFLD-HCC.

Acute normobaric hypoxia blunts contraction-mediated mTORC1- and JNK-signaling in human skeletal muscle

Aim

Hypoxia has been shown to reduce resistance exercise‐induced stimulation of protein synthesis and long‐term gains in muscle mass. However, the mechanism whereby hypoxia exerts its effect is not clear. Here, we examine the effect of acute hypoxia on the activity of several signalling pathways involved in the regulation of muscle growth following a bout of resistance exercise.

Methods

Eight men performed two sessions of leg resistance exercise in normoxia or hypoxia (12% O₂) in a randomized crossover fashion. Muscle biopsies were obtained at rest and 0, 90,180 minutes after exercise. Muscle analyses included levels of signalling proteins and metabolites associated with energy turnover.

Results

Exercise during normoxia induced a 5‐10‐fold increase of S6K1^Thr389 phosphorylation throughout the recovery period, but hypoxia blunted the increases by ~50%. Phosphorylation of JNK^{Thr183/Tyr185} and the JNK target SMAD2^{Ser245/250/255} was increased by 30‐ to 40‐fold immediately after the exercise in normoxia, but hypoxia blocked almost 70% of the activation. Throughout recovery, phosphorylation of JNK and SMAD2 remained elevated following the exercise in normoxia, but the effect of hypoxia was lost at 90‐180 minutes post‐exercise. Hypoxia had no effect on exercise‐induced Hippo or autophagy signalling and ubiquitin‐proteasome related protein levels. Nor did hypoxia alter the changes induced by exercise in high‐energy phosphates, glucose 6‐P, lactate or phosphorylation of AMPK or ACC.

Conclusion

We conclude that acute severe hypoxia inhibits resistance exercise‐induced mTORC1‐ and JNK signalling in human skeletal muscle, effects that do not appear to be mediated by changes in the degree of metabolic stress in the muscle.

Chronic and Cycling Hypoxia: Drivers of Cancer Chronic Inflammation through HIF-1 and NF-κB Activation: A Review of the Molecular Mechanisms

Chronic (continuous, non-interrupted) hypoxia and cycling (intermittent, transient) hypoxia are two types of hypoxia occurring in malignant tumors. They are both associated with the activation of hypoxia-inducible factor-1 (HIF-1) and nuclear factor κB (NF-κB), which induce changes in gene expression. This paper discusses in detail the mechanisms of activation of these two transcription factors in chronic and cycling hypoxia and the crosstalk between both signaling pathways. In particular, it focuses on the importance of reactive oxygen species (ROS), reactive nitrogen species (RNS) together with nitric oxide synthase, acetylation of HIF-1, and the action of MAPK cascades. The paper also discusses the importance of hypoxia in the formation of chronic low-grade inflammation in cancerous tumors. Finally, we discuss the effects of cycling hypoxia on the tumor microenvironment, in particular on the expression of VEGF-A, CCL2/MCP-1, CXCL1/GRO-α, CXCL8/IL-8, and COX-2 together with PGE₂. These factors induce angiogenesis and recruit various cells into the tumor niche, including neutrophils and monocytes which, in the tumor, are transformed into tumor-associated neutrophils (TAN) and tumor-associated macrophages (TAM) that participate in tumorigenesis.

Febuxostat, a Xanthine Oxidase Inhibitor, Decreased Macrophage Matrix Metalloproteinase Expression in Hypoxia

Macrophages in the atheroma region produce matrix metalloproteinases (MMPs) and decrease plaque stability. Tissue oxygen tension decreases in the arterial wall of the atherosclerotic region. Hypoxia inducible factor (HIF)-1α plays a critical role in the transcriptional activation of hypoxia inducible genes. However, the precise roles of HIF-1α independent pathways in hypoxic responses are largely unknown. Xanthine oxidase (XO) is an enzyme that utilizes molecular oxygen and produces reactive oxygen species (ROS). Here, we show that ROS derived from XO increases MMP-3, -10, and -13 expression in murine macrophages. We found that the transcript levels of macrophage MMP-3, -10, and -13 were increased in hypoxic conditions. Hypoxia induced MMP expression in HIF-1α deficient macrophages. N-acetylcysteine (NAC) or febuxostat, an XO inhibitor, suppressed MMP expression in murine macrophages. Febuxostat decreased the incidence of plaque rupture in apolipoprotein-E-deficient mice. Our results indicate that febuxostat stabilized atherosclerotic plaque via suppressing the activities of macrophage MMP-9 and -13. Febuxostat administration is a potential therapeutic option in the management of atherosclerotic patients.

The transcriptional coactivator WBP2 primes triple-negative breast cancer cells for responses to Wnt signaling via the JNK/Jun kinase pathway

The transcriptional coactivator WW domain-binding protein 2 (WBP2) is an emerging oncogene and serves as a node between the signaling protein Wnt and other signaling molecules and pathways, including epidermal growth factor receptor, estrogen receptor/progesterone receptor, and the Hippo pathway. The upstream regulation of WBP2 is well-studied, but its downstream activity remains unclear. Here, we elucidated WBP2's role in triple-negative breast cancer (TNBC), in which Wnt signaling is predominantly activated. Using RNAi coupled with RNA-Seq and MS analyses to identify Wnt/WBP2- and WBP2-dependent targets in MDA-MB-231 TNBC cells, we found that WBP2 is required for the expression of a core set of genes in Wnt signaling. These included AXIN2, which was essential for Wnt/WBP2-mediated breast cancer growth and migration. WBP2 also regulated a much larger set of genes and proteins independently of Wnt, revealing that WBP2 primes cells to Wnt activity by up-regulating G protein pathway suppressor 1 (GPS1) and TRAF2- and NCK-interacting kinase (TNIK). GPS1 activated the c-Jun N-terminal kinase (JNK)/Jun pathway, resulting in a positive feedback loop with TNIK that mediated Wnt-induced AXIN2 expression. WBP2 promoted TNBC growth by integrating JNK with Wnt signaling, and its expression profoundly influenced the sensitivity of TNBC to JNK/TNIK inhibitors. In conclusion, WBP2 links JNK to Wnt signaling in TNBC. GPS1 and TNIK are constituents of a WBP2-initiated cascade that primes responses to Wnt ligands and are also important for TNBC biology. We propose that WBP2 is a potential drug target for JNK/TNIK-based precision medicine for managing TNBC.

Functional cooperation between HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR

OBJECTIVE

Hypoxia-inducible factor 1 (HIF-1) and activator protein 1 (AP-1) are important transcription factors regulating expression of genes involved in cell survival. HIF-1α and c-Jun are key components of HIF-1 and AP-1, respectively, and are regulated by epidermal growth factor receptor (EGFR)-mediated cell signaling and tumor microenvironmental cues. The roles of HIF-1α and c-Jun in development of resistance to EGFR tyrosine kinase inhibitor (TKI) in non-small cell lung cancer (NSCLC) with activating mutation of EGFR have not been explored. In this study, we investigated the roles of HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR.

MATERIALS AND METHODS

Changes in HIF-1α protein and in total and phosphorylated c-Jun levels in relation to changes in total and phosphorylated EGFR levels before and after gefitinib treatment were measured using Western blot analysis in NSCLC cells sensitive or resistant to gefitinib. The impact of overexpression of a constitutively expressed HIF-1α (HIF-1α/ΔODD) or a constitutively active c-Jun upstream regulator (SEK1 S220E/T224D mutant) on cell response to gefitinib was also examined. The effect of pharmacological inhibition of SEK1-JNK-c-Jun pathway on cell response to gefitinib was evaluated.

RESULTS

Downregulation of HIF-1α and total and phosphorylated c-Jun levels correlated with cell inhibitory response to gefitinib better than decrease in phosphorylated EGFR did in NSCLC cells with intrinsic or acquired resistance to gefitinib. Overexpression of HIF-1α/ΔODD or SEK1 S220E/T224D mutant conferred resistance to gefitinib. There exists a positive feed-forward regulation loop between HIF-1 and c-Jun. The JNK inhibitor SP600125 sensitized gefitinib-resistant NSCLC cells to gefitinib.

CONCLUSIONS

HIF-1α and c-Jun functionally cooperate in development of resistance to gefitinib in NSCLC cells. The translational value of inhibiting HIF-1α/c-Jun cooperation in overcoming resistance to EGFR TKI treatment of NSCLC cells with activating mutation of EGFR deserves further investigation.

Systematic Analysis of Quantitative Logic Model Ensembles Predicts Drug Combination Effects on Cell Signaling Networks

A major challenge in developing anticancer therapies is determining the efficacies of drugs and their combinations in physiologically relevant microenvironments. We describe here our application of "constrained fuzzy logic" (CFL) ensemble modeling of the intracellular signaling network for predicting inhibitor treatments that reduce the phospho-levels of key transcription factors downstream of growth factors and inflammatory cytokines representative of hepatocellular carcinoma (HCC) microenvironments. We observed that the CFL models successfully predicted the effects of several kinase inhibitor combinations. Furthermore, the ensemble predictions revealed ambiguous predictions that could be traced to a specific structural feature of these models, which we resolved with dedicated experiments, finding that IL-1α activates downstream signals through TAK1 and not MEKK1 in HepG2 cells. We conclude that CFL-Q2LM (Querying Quantitative Logic Models) is a promising approach for predicting effective anticancer drug combinations in cancer-relevant microenvironments.

Common responses of tumors and wounds to hypoxia

Hypoxia is a characteristic of tumors and wounds. Hypoxic cells develop 2 common strategies to face hypoxia: the glycolytic switch and the angiogenic switch. At the onset of hypoxia, alleviation of the Pasteur effect ensures short-term cell survival. Long-term hypoxic cell survival requires a further acceleration of the glycolytic flux under the control of hypoxia-inducible factor 1 that stimulates the expression of most glycolytic transporters and enzymes, uncouples glycolysis from the TCA cycle, and rewires glycolysis to lactic fermentation. Hypoxic cells also trigger angiogenesis, a process that aims to restore normal microenvironmental conditions. Transcription factors (hypoxia-inducible factor 1, nuclear factor κB, activator protein 1) and lactate cooperate to stimulate the expression of proangiogenic agents. Cancer cells differ from normal hypoxic cells by their proliferative agenda and by a high metabolic heterogeneity. These effects in tumor account for further molecular and metabolic changes and for a persistent stimulation of angiogenesis.

Hypoxia leads to abnormal epidermal differentiation via HIF-independent pathways

Atmospheric oxygen is important for the epidermis, as the skin epidermis is not greatly affected by blood circulation. Therefore, it is necessary to understand the effect of hypoxic signals on the epidermis as some environmental stimuli can induce skin hypoxia. Here, we investigated how hypoxia (1% O2) affected skin equivalents (SEs) and normal human epidermal keratinocytes. We found that hypoxia specifically decreased the protein levels of keratin 1 (K1)/keratin 10 (K10), a representative marker of the epidermal spinous layer in the epidermis. However, hypoxia-inducible factors, the major regulators of hypoxia, did not affect hypoxia-induced down-regulation of K1/K10. We also found that N-acetyl-l-cysteine (NAC), a reactive oxygen species scavenger, antagonized the hypoxia-induced reduction of K1/K10 in keratinocytes and SEs. In contrast to the findings for NAC, inhibitors that blocked reactive oxygen species generation did not cause recovery of K1/K10 protein levels under hypoxic conditions. Taken together, these results indicate that hypoxia leads to abnormal keratinocyte differentiation by down-regulating K1/K10 and that this phenomenon can be ameliorated by NAC.

Low dose nicotine attenuates Aβ neurotoxicity through activation early growth response gene 1 pathway

Epidemiological studies indicate that smoking is negatively correlated with the incidence and development of Alzheimer's disease (AD). Nicotine was reported to be the active factor. However, the detailed mechanisms still remain to be fully elucidated. Early growth response gene 1 (EGR-1) plays important roles in several important biological processes such as promoting cell growth, differentiation, anti oxidative stress, and apoptosis, but few in the pathogenesis of AD. In the present study, we show that nicotine can activate the MAPK/ERK/EGR-1 signaling pathway partially through α7 nAChR. In addition, the up-regulation of EGR-1 by nicotine can also increase the phosphorylation of CyclinD1 which contributes to the attenuation of amyloid-β (Aβ(25-35)) -induced neurotoxicity. Although nicotine and Aβ(25-35) can activate EGR-1, the expression of EGR-1 is down-regulated following treatment with nicotine and Aβ(25-35). This study demonstrates that low dose nicotine attenuates Aβ(25-35)-induced neurotoxicity in vitro and in vivo through activating EGR-1 pathway.

MDR1 will play a key role in pharmacokinetic changes under hypoxia at high altitude and its potential regulatory networks

Some newest studies indicated that drug transports may play the key role in pharmacokinetics changes under hypoxia at high altitude; MDR1 is now known to affect the disposition of many administered drugs and make a major contribution to absorption, distribution, metabolism, excretion. Different expression of MDR1 is frequently found in different normal tissues and tumor cells; it is important to better understand how MDR1 is regulated under hypoxia, which seems to be a complex and highly controlled process. Several signaling pathways and transcription factors have been described as being involved in the regulation of MDR1 expression, such as MAPK/ERK, nuclear factor-kappaB, hypoxia-inducible factor-1a, pregnane × receptor, constitutive androstane receptor and microRNA. Recently, researches have been increasingly appreciating long non-coding RNAs (lncRNAs) as an integral component of gene regulatory networks. lncRNAs play crucial roles in various biological processes ranging from epigenetic gene regulation, transcriptional control, post-transcriptional regulation, pre-mRNA processing and nuclear organization. A last recent research showed that H19 gene non-coding RNA is believed to induce P-glycoprotein expression under hypoxia.

Cytochrome P450 2J2: distribution, function, regulation, genetic polymorphisms and clinical significance

Cytochrome P450 2J2 (CYP2J2) is an enzyme mainly found in human extrahepatic tissues, with predominant expression in the cardiovascular systems and lower levels in the intestine, kidney, lung, pancreas, brain, liver, etc. During the past 15 years, CYP2J2 has attracted much attention for its epoxygenase activity in arachidonic acid (AA) metabolism. It converts AA to four epoxyeicosatrienoic acids (EETs) that have various biological effects, especially in the cardiovascular systems. In recent publications, CYP2J2 is shown highly expressed in various human tumor cells, and its EET metabolites are demonstrated to implicate in the pathologic development of human cancers. CYP2J2 is also a human CYP that involved in phase I xenobiotics metabolism. Antihistamine drugs and many other compounds were identified as the substrates of CYP2J2, and studies have demonstrated that these substrates have a broad structural diversity. CYP2J2 is found not readily induced by known P450 inducers; however, its expression could be regulated in some pathological conditions, might through the activator protein-1(AP-1), the AP-1-like element and microRNA let-7b. Several genetic mutations in the CYP2J2 gene have been identified in humans, and some of them have been shown to have potential associations with some diseases. With the increasing awareness of its roles in cancer disease and drug metabolism, studies about CYP2J2 are still going on, and various inhibitors of CYP2J2 have been determined. Further studies are needed to delineate the roles of CYP2J2 in disease pathology, drug development and clinical practice.

Deregulation of the miRNAs expression in cervical cancer: human papillomavirus implications

MicroRNAs (miRNAs) are a class of small non coding RNAs of 18-25 nucleotides in length. The temporal or short-lived expression of the miRNAs modulates gene expression post transcriptionally. Studies have revealed that miRNAs deregulation correlates and is involved with the initiation and progression of human tumors. Cervical cancer (CC) displays notably increased or decreased expression of a large number of cellular oncogenic or tumor suppressive miRNAs, respectively. However, understanding the potential role of miRNAs in CC is still limited. In CC, the high-risk human papillomaviruses (HR-HPVs) infection can affect the miRNAs expression through oncoprotein E6 and E7 that contribute to viral pathogenesis, although other viral proteins might also be involved. This deregulation in the miRNAs expression has an important role in the hallmarks of CC. Interestingly, the miRNA expression profile in CC can discriminate between normal and tumor tissue and the extraordinary stability of miRNAs makes it suitable to serve as diagnostic and prognostic biomarkers of cancer. In this review, we will summarize the role of the HR-HPVs in miRNA expression, the role of miRNAs in the hallmarks of CC, and the use of miRNAs as potential prognostic biomarkers in CC.

Hypoxia and lymphangiogenesis in tumor microenvironment and metastasis

Hypoxia and lymphangiogenesis are closely related processes that play a pivotal role in tumor invasion and metastasis. Intratumoral hypoxia is exacerbated as a result of oxygen consumption by rapidly proliferating tumor cells, insufficient blood supply and poor lymph drainage. Hypoxia induces functional responses in lymphatic endothelial cells (LECs), including cell proliferation and migration. Multiple factors (e.g., ET-1, AP-1, C/EBP-δ, EGR-1, NF-κB, and MIF) are involved in the events of hypoxia-induced lymphangiogenesis. Among them, HIF-1α is known to be the master regulator of cellular oxygen homeostasis, mediating transcriptional activation of lymphangiogenesis via regulation of signaling cascades like VEGF-A/-C/-D, TGF-β and Prox-1 in experimental and human tumors. Although the underlying molecular mechanisms remain incompletely elucidated, the investigation of lymphangiogenesis in hypoxic conditions may provide insight into potential therapeutic targets for lymphatic metastasis.

12-Deoxyphorbol 13-palmitate inhibit VEGF-induced angiogenesis via suppression of VEGFR-2-signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

12-Deoxyphorbol 13-palmitate (G) is one toxic compound isolated from Euphorbia fischeriana, an Asian spice used for cancer treatment as a folk remedy. However, whether 12-deoxyphorbol 13-palmitate affects angiogenesis remains unclear.

AIM OF THE STUDY

To explore the in vitro and in vivo antiangiogenic effects of 12-deoxyphorbol 13-palmitate and its underlying mechanisms.

MATERIALS AND METHODS

We explored antigenic functions in human umbilical vein endothelial cells (HUVEC) by 12-deoxyphorbol 13-palmitate, including proliferation, migration and metastasis through matrigel plug assay, chorioallantoic membrane assay, in vitro migration assay, tube formation assay, motility assay. Antibody chip was applied to screen differentially expressed proteins modulated by 12-deoxyphorbol 13-palmitate, and was further confirmed by RT-PCR and western blot analysis. Tumor xenograft mice were applied to investigate whether 12-deoxyphorbol 13-palmitate could inhibit microvessel density in vivo.

RESULTS

12-Deoxyphorbol 13-palmitate inhibited vascular endothelial growth factor (VEGF)-induced angiogenic processes in vitro, such as proliferation, in vitro migration, and tube formation of HUVEC. In chorioallantoic membrane assay, 12-deoxyphorbol 13-palmitate significantly inhibited neovessel formation. Antibody chip technology demonstrated decreased expression of TIMP-1, TIMP-2, VEGF, basic fibroblast growth factor (bFGF), matrix metalloproteinases (MMP)-2, VEGFR-2 and VEGFR-3 proteins in HUVEC after 24h. In addition, 12-deoyphorbol 13-palmitate inhibited the in vivo growth of MCF-7 cells in grafted mouse model. Immunohistochemistry staining showed decreased microvessel density (CD31) and attenuated VEGFR-2 signaling pathways by 12-deoxyphorbol 13-palmitate.

CONCLUSION

12-Deoxyphorbol 13-palmitate may be utilized to target active angiogenesis through VEGF/VEGFR2 signal pathway for cancer.

Role of VEGF/VEGFR in the pathogenesis of leukemias and as treatment targets (Review)

Angiogenesis plays an important role in solid tumor growth, progression and metastasis. Evidence suggests that the progression of hematolymphoid malignancies also depends on the induction of new blood vessel formation under the influence of acute leukemia, myelodysplastic syndromes, myeloproliferative neoplasms, multiple myeloma and lymphomas. The vascular endothelial growth factor (VEGF) is the most important proangiogenic agent that activates receptors on vascular endothelial cells and promotes blood vessel regeneration. It has been demonstrated that VEGF/VEGF receptor (VEGFR) expression is upregulated in several types of hematolymphoid tumor cells accompanied with angiogenesis. The levels of VEGF/VEGFR are correlated with the treatment, relapse and prognosis of hematolymphoid tumors. In order for VEGF family and their receptors as antiangiogenic targets to treat solid tumors, several antiangiogenic agents targeting VEGF-related pathways have been used for the treatment of hematolymphoid malignancies in clinical trials. The results demonstrate a promising therapeutic intervention in multiple types of hematolymphoid tumors. This review aims to summarize recent advances in understanding the role of VEGF and angiogenesis in leukemias, mainly focusing on their upstream transcriptors, downstream targets and the correlation of VEGF/VEGFR with the treatment, relapse or prognosis of leukemia. The progress of VEGF and its receptors as attractive targets for therapies are also discussed in clinical application.

Genome-wide functional screening of miR-23b as a pleiotropic modulator suppressing cancer metastasis

miRNA globally deregulates human carcinoma. A critical open question is how many miRNAs functionally participate in cancer development, particularly in metastasis. We systematically evaluate the capability of all known human miRNAs to regulate certain metastasis-relevant cell behaviours. To perform the high-throughput screen of miRNAs, which regulate cell migration, we developed a novel self-assembled cell microarray. Here we show that over 20% of miRNAs have migratory regulation activity in diverse cell types, indicating a general involvement of miRNAs in migratory regulation. MiR-23b, which is downregulated in human colon cancer samples, potently mediates the multiple steps of metastasis, including tumour growth, invasion and angiogenesis in vivo. It regulates a cohort of prometastatic targets, including FZD7 or MAP3k1. These findings provide new insight into the physiological and potential therapeutic importance of miRNAs as a new class of functional modulators.

Cell-specific and hypoxia-dependent regulation of human HIF-3α: inhibition of the expression of HIF target genes in vascular cells

Hypoxia-inducible factors (HIF) are transcription factors responding to reduced oxygen levels and are of utmost importance for regulation of a widespread of cellular processes, e.g., angiogenesis. In contrast to HIF-1α/HIF-2α, the relevance of HIF-3α for the regulation of the HIF pathway in human vascular cells is largely unknown. HIF-3α mRNA increases under hypoxia in endothelial and vascular smooth muscle cells. Analysis of HIF-3α isoforms revealed a cell type-specific pattern, but only one isoform, HIF-3α2, is hypoxia-inducible. Reporter gene assays of the appropriate promoter localized a 31-bp fragment, mediating this hypoxic regulation. The contribution of HIF-1/2 and NFκB to the HIF-3α induction was verified. Functional studies focused on overexpression of HIF-3α isoforms, which decrease the hypoxia-mediated expression of VEGFA and Enolase2. These data support the notion of a hypoxia-induced inhibitory function of HIF-3α and demonstrate for the first time the existence of this negative regulation of HIF-signaling in vascular cells.

Plant polyphenols attenuate hepatic injury after hemorrhage/resuscitation by inhibition of apoptosis, oxidative stress, and inflammation via NF-kappaB in rats

PURPOSE

Oxidative stress and inflammation contribute to hepatic injury after hemorrhage/resuscitation (H/R). Natural plant polyphenols, i.e., green tea extract (GTE) possess high anti-oxidant and anti-inflammatory activities in various models of acute inflammation. However, possible protective effects and feasible mechanisms by which plant polyphenols modulate pro-inflammatory, apoptotic, and oxidant signaling after H/R in the liver remain unknown. Therefore, we investigated the effects of GTE and its impact on the activation of NF-kappaB in the pathogenesis of hepatic injury induced by H/R.

METHODS

Twenty-four female LEWIS rats (180-250 g) were fed a standard chow (ctrl) or a diet containing 0.1% polyphenolic extracts (GTE) from Camellia sinensis starting 5 days before H/R. Rats were hemorrhaged to a mean arterial pressure of 30 ± 2 mmHg for 60 min and resuscitated (H/R and GTE H/R groups). Control groups (sham, ctrl, and GTE) underwent surgical procedures without H/R. Two hours after resuscitation, tissues were harvested.

RESULTS

Plasma alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) increased 3.5-fold and fourfold, respectively, in vehicle-treated rats as compared to GTE-fed rats. Histopathological analysis revealed significantly decreased hepatic necrosis and apoptosis in GTE-fed rats after H/R. Real-time PCR showed that GTE diminished gene expression of pro-apoptotic caspase-8 and Bax, while anti-apoptotic Bcl-2 was increased after H/R. Hepatic oxidative (4-hydroxynonenal) and nitrosative (3-nitrotyrosine) stress as well as systemic IL-6 level and hepatic IL-6 mRNA were markedly reduced in GTE-fed rats compared with controls after H/R. Plant polyphenols also decreased the activation of both JNK and NFκB.

CONCLUSIONS

Taken together, GTE application blunts hepatic damage, apoptotic, oxidative, and pro-inflammatory changes after H/R. These results underline the important roles of JNK and NF-kappaB in inflammatory processes after H/R and the beneficial impact of plant polyphenols in preventing their activation.

Regulation of Cyr61/CCN1 expression by hypoxia through cooperation of c-Jun/AP-1 and HIF-1α in retinal vascular endothelial cells

Hypoxia is the most important factor in the pathogenesis of diabetic retinopathy. Cysteine-rich 61 (Cyr61) is one of the angiogenic factors involved in the development of proliferative diabetic retinopathy (PDR). The aim of this study was to investigate the mechanism of hypoxia-induced Cyr61 expression in retinal vascular endothelial cells. The hypoxia-induced expression of mRNA and protein of Cyr61 was studied in monkey choroidal retinal vascular endothelial (RF/6A) cells. Luciferase reporter assays and electrophoretic mobility shift assays were used to identify the hypoxia responsible region and transcription factors in the Cyr61 promoter. Chromatin immunoprecipitation and immunoprecipitation were performed to study the role of hypoxia-inducible factor (HIF)-1α and c-Jun/activator protein-1 (AP-1) in Cyr61 transcriptional regulation. The results showed that hypoxia significantly induced Cyr61 mRNA and protein expression in RF/6A cells. The effect was mediated through phosphorylation of c-Jun. Luciferase assays, electrophoretic mobility shift assays, chromatin immunoprecipitation and immunoprecipitation showed that HIF-1α interacted with c-Jun/AP-1 and their binding on the AP-1 binding motif within the Cyr61 promoter induced the expression of Cyr61. In conclusion, hypoxia controlled the transcriptional regulation of the Cyr61 gene in RF/6A cells by cooperation of HIF-1α and c-Jun/AP-1. Cyr61 might play an important role in ischemic retinal diseases, such as PDR.

MLK3 is critical for breast cancer cell migration and promotes a malignant phenotype in mammary epithelial cells

The malignant phenotype in breast cancer is driven by aberrant signal transduction pathways. Mixed-lineage kinase-3 (MLK3) is a mammalian mitogen-activated protein kinase kinase kinase (MAP3K) that activates multiple MAPK pathways. Depending on the cellular context, MLK3 has been implicated in apoptosis, proliferation, migration and differentiation. Here we investigated the effect of MLK3 and its signaling to MAPKs in the acquisition of malignancy in breast cancer. We show that MLK3 is highly expressed in breast cancer cells. We provide evidence that MLK3's catalytic activity and signaling to c-jun N-terminal kinase (JNK) is required for migration of highly invasive breast cancer cells and for MLK3-induced migration of mammary epithelial cells. Expression of active MLK3 is sufficient to induce the invasion of mammary epithelial cells, which requires AP-1 activity and is accompanied by the expression of several proteins corresponding to AP-1-regulated invasion genes. To assess MLK3's contribution to the breast cancer malignant phenotype in a more physiological setting, we implemented a strategy to inducibly express active MLK3 in the preformed acini of MCF10A cells grown in 3D Matrigel. Induction of MLK3 expression dramatically increases acinar size and modestly perturbs apicobasal polarity. Remarkably, MLK3 expression induces luminal repopulation and suppresses the expression of the pro-apoptotic protein BimEL, as has been observed in Her2/Neu-expressing acini. Taken together, our data show that MLK3-JNK-AP-1 signaling is critical for breast cancer cell migration and invasion. Our current study uncovers both a proliferative and novel antiapoptotic role for MLK3 in the acquisition of a malignant phenotype in mammary epithelial cells. Thus, MLK3 may be an important therapeutic target for the treatment of invasive breast cancer.

Inhibition of c-Jun N-terminal kinase after hemorrhage but before resuscitation mitigates hepatic damage and inflammatory response in male rats

Inhibition of c-Jun N-terminal kinase (JNK) by a cell-penetrating, protease-resistant JNK peptide (D-JNKI-1) before hemorrhage and resuscitation (H/R) ameliorated the H/R-induced hepatic injury and blunted the proinflammatory changes. Here we tested the hypothesis if JNK inhibition at a later time point-after hemorrhagic shock but before the onset of resuscitation-in a rat model of H/R also confers protection. Twenty-four male Sprague-Dawley rats (250 - 350 g) were randomly divided into 4 groups: 2 groups of shock animals were hemorrhaged to a MAP of 32 to 37 mmHg for 60 min and randomly received either D-JNKI-1 (11 mg/kg i.p.) or sterile saline as vehicle immediately before the onset of resuscitation. Two groups of sham-operated animals underwent surgical procedures without H/R and were either D-JNKI-1 or vehicle treated. Rats were killed 2 h later. Serum activity of alanine aminotransferase and serum lactate dehydrogenase after H/R increased 3.5-fold in vehicle-treated rats as compared with D-JNKI-1-treated rats. Histopathological analysis revealed that hepatic necrosis and apoptosis (hematoxylin-eosin, TUNEL, and M30, respectively) were significantly inhibited in D-JNKI-1-treated rats after H/R. Hepatic oxidative (4-hydroxynonenal) and nitrosative (3-nitrotyrosine) stress as well as markers of inflammation (hepatic and serum IL-6 levels and hepatic infiltration with polymorphonuclear leukocytes) were also reduced in D-JNKI-1-treated rats. LPS-stimulated TNF-alpha release from whole blood from hemorrhaged and resuscitated animals was higher in vehicle-treated rats as compared with D-JNKI-1-treated rats. c-Jun N-terminal kinase inhibition after hemorrhage before resuscitation resulted in a reduced activation of c-Jun. Taken together, these results indicate that D-JNKI-1 application after hemorrhagic shock before resuscitation blunts hepatic damage and proinflammatory changes during resuscitation. Hence, JNK inhibition is even protective when initiated after blood loss before resuscitation. These experimental results indicate that the JNK pathway may be a possible treatment option for the harmful consequences of H/R.

Hypoxia-induced transcription of dopamine D3 and D4 receptors in human neuroblastoma and astrocytoma cells

Background

Dopaminergic pathways that influence mood and behaviour are severely affected in cerebral hypoxia. In contrast, hypoxia promotes the differentiation of dopaminergic neurons. In order to clarify the hypoxic sensitivity of key dopaminergic genes, we aimed to study their transcriptional regulation in the context of neuroblastoma and astrocytoma cell lines exposed to 1% hypoxia.

Results

Quantitative RT-PCR assays revealed that the transcription of both type D3 and D4 postsynaptic dopamine receptors (DRD3 and DRD4) was induced several fold upon 2-day hypoxia in a cell-specific manner, while the vascular endothelial growth factor gene was activated after 3-hr incubation in hypoxia. On the other hand, mRNA levels of type 2 dopamine receptor, dopamine transporter, monoamino oxidase and catechol-O-methyltransferase were unaltered, while those of the dopamine receptor regulating factor (DRRF) were decreased by hypoxia. Notably, 2-day hypoxia did not result in elevation of protein levels of DRD3 and DRD4.

Conclusion

In light of the relatively delayed transcriptional activation of the DRD3 and DRD4 genes, we propose that slow-reacting hypoxia sensitive transcription factors might be involved in the transactivation of DRD3 and DRD4 promoters in hypoxia.

Genetic and pharmacological inhibition of JNK ameliorates hypoxia-induced retinopathy through interference with VEGF expression

Many ocular pathologies, including retinopathy of prematurity (ROP), diabetic retinopathy, and age-related macular degeneration, result in vision loss because of aberrant neoangiogenesis. A common feature of these conditions is the presence of hypoxic areas and overexpression of the proangiogenic vascular endothelial growth factor (VEGF). The prevailing current treatment, laser ablation of the retina, is destructive and only partially effective. Preventive and less destructive therapies are much more desirable. Here, we show that mice lacking c-Jun N-terminal kinase 1 (JNK1) exhibit reduced pathological angiogenesis and lower levels of retinal VEGF production in a murine model of ROP. We found that hypoxia induces JNK activation and regulates VEGF expression by enhancing the binding of phospho-c-Jun to the VEGF promoter. Intravitreal injection of a specific JNK inhibitor decreases retinal VEGF expression and reduces pathological retinal neovascularization without obvious side effects. These results strongly suggest that JNK1 plays a key role in retinal neoangiogenesis and that it represents a new pharmacological target for treatment of diseases where excessive neoangiogenesis is the underlying pathology.

Should I stay or should I go: beta-catenin decides under stress

Reactive oxygen species (ROS) are essential for efficient and proper execution of a large number of cellular processes including signalling induced by exogenous factors. However, ROS are highly reactive in nature and excessive or prolonged ROS formation can result in considerable damage to cellular constituents and is implicated in the onset of a large variety of diseases as well as in the process of ageing [reviewed in [1] T.M. Paravicini, R.M. Touyz, Redox signaling in hypertension, Cardiovasc. Res. 71 (2006) 247-258, [2] P. Chiarugi, From anchorage dependent proliferation to survival: lessons from redox signalling, IUBMB life 60 (2008) 301-307, [3] M. Valko, D. Leibfritz, J. Moncol, M.T. Cronin, M. Mazur, J. Telser, Free radicals and antioxidants in normal physiological functions and human disease, Int. J. Biochem. Cell Biol. 39 (2007) 44-84]. Management of ROS to prevent potential damage, yet enabling its signalling function is achieved through numerous enzyme systems e.g. peroxidases, superoxide dismutases etc. and small molecules e.g. glutathione that collectively form the cellular anti-oxidant system. The O-class of Forkhead box (FOXO) transcription factors regulates amongst others cellular resistance against oxidative stress [[4] Y. Honda, S. Honda, The daf-2 gene network for longevity regulates oxidative stress resistance and Mn-superoxide dismutase gene expression in Caenorhabditis elegans, Faseb J. 13 (1999) 1385-1393]. In turn FOXOs themselves are regulated by ROS and cellular oxidative stress results in the activation of FOXOs [[5] M.A. Essers, S. Weijzen, A.M. de Vries-Smits, I. Saarloos, N.D. de Ruiter, J.L. Bos, B.M. Burgering, FOXO transcription factor activation by oxidative stress mediated by the small GTPase Ral and JNK, EMBO J. 23 (2004) 4802-4812]. A prominent feature of ROS-induced FOXO activation is ROS-induced binding of beta-catenin to FOXO [[6] M.A. Essers, L.M. de Vries-Smits, N. Barker, P.E. Polderman, B.M. Burgering, H.C. Korswagen, Functional interaction between beta-catenin and FOXO in oxidative stress signaling, Science (New York, NY) 308 (2005) 1181-1184, [7] M. Almeida, L. Han, M. Martin-Millan, C.A. O'Brien, S.C. Manolagas, Oxidative stress antagonizes Wnt signaling in osteoblast precursors by diverting beta-catenin from T cell factor- to forkhead box O-mediated transcription, J. Biol. Chem. 282 (2007) 27298-27305, [8] D. Hoogeboom, M.A. Essers, P.E. Polderman, E. Voets, L.M. Smits, B.M. Burgering, Interaction of FOXO with beta-catenin inhibits beta-catenin/T cell factor activity, J. Biol. Chem. 283 (2008) 9224-9230]. However, ROS affect many transcriptional programs besides that of FOXOs. Here, we discuss the recent progress in our understanding as to how ROS may regulate the interplay between some of the ROS-sensitive transcription factors through diverting beta-catenin binding to these transcription factors. We propose that beta-catenin acts as a key switch between the various ROS-sensitive transcription programs.

Decursin and decursinol angelate inhibit VEGF-induced angiogenesis via suppression of the VEGFR-2-signaling pathway

Inhibition of angiogenesis is an attractive approach for the treatment of angiogenic diseases, such as cancer. Vascular endothelial growth factor (VEGF) is one of the most important activators of angiogenesis and interacts with the high-affinity tyrosine kinase receptors, VEGFR-1 and VEGFR-2. The pyranocoumarin compounds decursin and decursinol angelate isolated from the herb, Angelica gigas, are known to possess potent anti-inflammatory activities. However, little is known about their antiangiogenic activity or their underlying mechanisms. Here, we show the antiangiogenic effects of decursin and decursinol angelate using in vitro assays and in vivo animal experiments. Decursin and decursinol angelate inhibited VEGF-induced angiogenic processes in vitro, including proliferation, migration and tube formation of human umbilical vein endothelial cells. Decursin and decursinol angelate significantly suppressed neovessel formation in chick chorioallantoic membrane and tumor growth in a mouse model. The microvessel density in tumors treated with decursin for 14 days was significantly decreased compared with a vehicle control group. Decursin and decursinol angelate inhibited VEGF-induced phosphorylation of VEGFR-2, extracellular signal-regulated kinases and c-Jun N-terminal kinase mitogen-activated protein kinases. Taken together, these results demonstrate that decursin and decursinol angelate are novel candidates for inhibition of VEGF-induced angiogenesis.

Current insights on the biology and clinical aspects of VEGF regulation

Vascular endothelial growth factor (VEGF) is a key molecule that orchestrates the formation and function of vascular networks. Impaired regulation of angiogenesis is implicated in a number of pathologic states. For instance, neoplasias exhibit uncontrolled angiogenesis, whereas ischemia and states of vascular insufficiency involve reduced VEGF activity. As the role of VEGF has been elucidated in these disease processes, its therapeutic role has been developed. The Food and Drug Administration has approved several anti-VEGF agents for treating colorectal, lung, and kidney cancer. VEGF-inducing agents have also been used experimentally to induce angiogenesis in patients with critical limb ischemia. As more knowledge is gathered about the biology of VEGF and its receptors, there is greater promise for therapeutic modulation of VEGF expression. The purpose of this review is to describe the various therapeutic and biologic factors that regulate the expression of VEGF.

Regulation of gene expression by hypoxia

Hypoxia induces profound changes in the cellular gene expression profile. The discovery of a major transcription factor family activated by hypoxia, HIF (hypoxia-inducible factor), and the factors that contribute to HIF regulation have greatly enhanced our knowledge of the molecular aspects of the hypoxic response. However, in addition to HIF, other transcription factors and cellular pathways are activated by exposure to reduced oxygen. In the present review, we summarize the current knowledge of how additional hypoxia-responsive transcription factors integrate with HIF and how other cellular pathways such as chromatin remodelling, translation regulation and microRNA induction, contribute to the co-ordinated cellular response observed following hypoxic stress.

YC-1 induces apoptosis of human renal carcinoma A498 cells in vitro and in vivo through activation of the JNK pathway

BACKGROUND AND PURPOSE

The aim of this study was to elucidate the mechanism of YC-1{3-(5'-hydroxy methyl-2'-furyl)-1-benzylindazole}-induced human renal carcinoma cells apoptosis and to evaluate the potency of YC-1 in models of tumour growth in mice.

EXPERIMENTAL APPROACH

YC-1-mediated apoptosis was assessed by analysis of MTT, SRB, DAPI staining and flow cytometry analysis. Knockdown of JNK protein was achieved by transient transfection using siRNA. The mechanisms of action of YC-1 on different signalling pathways involved were studied using western blot. Fas clustering was analysed by confocal microscopy and in vivo efficacy was examined in a A498 xenograft model.

KEY RESULTS

YC-1 displayed cytotoxicity in renal carcinoma cells at 10(-7)-10(-8) M. Increased condensation of chromatin was observed and an increase in the cell population in subG1 phase. Moreover, YC-1 triggered mitochondria-mediated and caspase-dependent pathways. YC-1 significantly induced Fas ligand expression, but did not modify either the protein levels of death receptors or ligands. In addition, Fas clustering in cells responsive to YC-1 was observed, suggesting involvement of a Fas-mediated pathway. Furthermore, YC-1 markedly induced phosphorylation of JNK and a JNK inhibitor, SP600125, and siRNA JNK1/2 significantly reversed YC-1-induced cytotoxicity and protein expression. We suggest that YC-1 induced JNK phosphorylation, the upregulation of FasL and Fas receptor clustering to promote the activation of caspases 8 and 3, resulting in apoptosis. Finally, we demonstrated the antitumour effect of YC-1 in vivo.

CONCLUSIONS AND IMPLICATIONS

These data suggest that YC-1 is a good candidate for development as an anticancer drug.

Disruption of signaling through SEK1 and MKK7 yields differential responses in hypoxic colon cancer cells treated with oxaliplatin

Transcriptional changes in response to hypoxia are regulated in part through mitogen-activated protein (MAP) kinase signaling to activator protein 1 (AP-1), and thus contribute to resistance of cancer cells to therapy, including platinum compounds. A key role for JNK in pro-apoptotic signaling in hypoxic cells has previously been established. Here we analyze hypoxic signaling through MAPK kinases to AP-1/c-Jun in the HT29 colon adenocarcinoma cell line, and observe activation of stress-activated pathways mediated predominantly by SEK1 and MKK7. In transient transfection assays, introduction of dominant-negative constructs for both MKK7 and SEK1 abolished hypoxia-induced AP-1 activation. Functional studies of the pathway using HT29-derived cell lines stably expressing mutant SEK1 or MKK7 showed impaired activation of Jun NH2-terminal kinase (JNK) and AP-1 in response to hypoxia, more marked in MKK7-deficient than SEK1-deficient cells. Inhibition of SEK1 rendered hypoxic cells more sensitive to oxaliplatin in vitro, whereas the opposite effect was observed in MKK7-deficient cells. The mutant cell lines grown as mouse xenografts were treated with oxaliplatin, bevacizumab, or both. The SEK1-deficient tumors exhibited greater sensitivity to all treatments, whereas MKK7-deficient cells were resistant in vivo, consistent with in vitro observations. These data support a positive contribution of MKK7/JNK to oxaliplatin cytotoxicity and identify SEK1 as a potential target for reversal of hypoxic resistance to oxaliplatin.

Hypoxia induces protection against etoposide-induced apoptosis: molecular profiling of changes in gene expression and transcription factor activity

Background

it is now well established that hypoxia renders tumor cells resistant to radio- but also chemotherapy. However, few elements are currently available as for the mechanisms underlying this protection.

Results

in this study, physiological hypoxia was shown to inhibit apoptosis induced in HepG2 cells by etoposide. Indeed, hypoxia reduced DNA fragmentation, caspase activation and PARP cleavage. The DNA binding activity of 10 transcription factors was followed while the actual transcriptional activity was measured using specific reporter plasmids. Of note is the inhibition of the etoposide-induced activation of p53 under hypoxia. In parallel, data from low density DNA microarrays indicate that the expression of several pro- and anti-apoptotic genes was modified, among which are Bax and Bak whose expression profile paralleled p53 activity. Cluster analysis of data unravels several possible pathways involved in the hypoxia-induced protection against etoposide-induced apoptosis: one of them could be the inhibition of p53 activity under hypoxia since caspase 3 activity parallels Bax and Bak expression profile. Moreover, specific downregulation of HIF-1α by RNA interference significantly enhanced apoptosis under hypoxia possibly by preventing the hypoxia mediated decrease in Bak expression without altering Bax expression.

Conclusion

these results are a clear demonstration that hypoxia has a direct protective effect on apoptotic cell death. Moreover, molecular profiling points to putative pathways responsible for tumor growth in challenging environmental conditions and cancer cell resistance to chemotherapeutic agents.

Upregulation of DR5 by proteasome inhibitors potently sensitizes glioma cells to TRAIL-induced apoptosis

This study was undertaken to explore the potential of new therapeutic approaches designed to reactivate cell death pathways in apoptosis-refractory gliomas and to characterize the underlying molecular mechanisms of this reactivation. Here we investigated the sensitivity of a panel of glioma cell lines (U87, U251, U343, U373, MZ-54, and MZ-18) to apoptosis induced by the death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), TRAIL in combination with gamma irradiation, and TRAIL in combination with proteasome inhibitors (MG132 and epoxomicin). Analysis of these six glioma cell lines revealed drastic differences in their sensitivity to these treatments, with two of the six cell lines revealing no significant induction of cell death in response to TRAIL alone. Interestingly, the proteasome inhibitors MG132 and epoxomicin were capable of potentiating TRAIL-induced apoptosis in TRAIL-sensitive U87 and U251 cells and of reactivating apoptosis in TRAIL-resistant U343 and U373 cells. In contrast, gamma irradiation had no synergistic effects with TRAIL in the two TRAIL-resistant cell lines. RNA interference against death receptor 5 (DR5) revealed that reactivation of TRAIL-induced apoptosis by proteasome inhibitors depended on enhanced transcription and surface expression of DR5. Transient knockdown of the transcription factor GADD153/C/EBP homologous protein and application of the synthetic c-Jun N-terminal kinase inhibitor SP600125 indicated that enhanced DR5 expression occurred independently of GADD153/C/EBP homologous protein, but required activation of the c-Jun N-terminal kinase/c-Jun signaling pathway. Novel therapeutic approaches using TRAIL or agonistic TRAIL receptor antibodies in combination with proteasome inhibitors may represent a promising approach to reactivate apoptosis in therapy-resistant high-grade gliomas.

Prolyl 4-hydroxylase activity-responsive transcription factors: from hydroxylation to gene expression and neuroprotection

Most homeostatic processes including gene transcription occur as a result of deviations in physiological tone that threatens the survival of the organism. A prototypical homeostatic stress response includes changes in gene expression following alterations in oxygen, iron or 2-oxoglutarate levels. Each of these cofactors plays an important role in cellular metabolism. Accordingly, a family of enzymes known as the Prolyl 4-hydroxylase (PHD) enzymes are a group of dioxygenases that have evolved to sense changes in 2-oxoglutarate, oxygen and iron via changes in enzyme activity. Indeed, PHDs are a part of an established oxygen sensor system that regulates transcriptional regulation of hypoxia/stress-regulated genes and thus are an important component of events leading to cellular rescue from oxygen, iron or 2-oxoglutarate deprivations. The ability of PHD activity to regulate homeostatic responses to oxygen, iron or 2-oxoglutarate metabolism has led to the development of small molecule inhibitors of the PHDs as a strategy for activating or augmenting cellular stress responses. These small molecules are proving effective in preclinical models of stroke and Parkinson's disease. However the precise protective pathways engaged by PHD inhibition are only beginning to be defined. In the current review, we summarize the role of iron, 2-oxoglutarate and oxygen in the PHD catalyzed hydroxylation reaction and provide a brief discussion of some of the transcription factors that play an effective role in neuroprotection against oxidative stress as a result of changes in PHD activity.

ERK- and JNK-signalling regulate gene networks that stimulate metamorphosis and apoptosis in tail tissues of ascidian tadpoles

In ascidian tadpoles, metamorphosis is triggered by a polarized wave of apoptosis, via mechanisms that are largely unknown. We demonstrate that the MAP kinases ERK and JNK are both required for the wave of apoptosis and metamorphosis. By employing a gene-profiling-based approach, we identified the network of genes controlled by either ERK or JNK activity that stimulate the onset of apoptosis. This approach identified a gene network involved in hormonal signalling, in innate immunity, in cell-cell communication and in the extracellular matrix. Through gene silencing, we show that Ci-sushi, a cell-cell communication protein controlled by JNK activity, is required for the wave of apoptosis that precedes tail regression. These observations lead us to propose a model of metamorphosis whereby JNK activity in the CNS induces apoptosis in several adjacent tissues that compose the tail by inducing the expression of genes such as Ci-sushi.

Critical role for NF-kappaB-induced JunB in VEGF regulation and tumor angiogenesis

Regulation of vascular endothelial growth factor (VEGF) expression is a complex process involving a plethora of transcriptional regulators. The AP-1 transcription factor is considered as facilitator of hypoxia-induced VEGF expression through interaction with hypoxia-inducible factor (HIF) which plays a major role in mediating the cellular hypoxia response. As yet, both the decisive AP-1 subunit leading to VEGF induction and the molecular mechanism by which this subunit is activated have not been deciphered. Here, we demonstrate that the AP-1 subunit junB is a target gene of hypoxia-induced signaling via NF-kappaB. Loss of JunB in various cell types results in severely impaired hypoxia-induced VEGF expression, although HIF is present and becomes stabilized. Thus, we identify JunB as a critical independent regulator of VEGF transcription and provide a mechanistic explanation for the inherent vascular phenotypes seen in JunB-deficient embryos, ex vivo allantois explants and in vitro differentiated embryoid bodies. In support of these findings, tumor angiogenesis was impaired in junB(-/-) teratocarcinomas because of severely impaired paracrine-acting VEGF and the subsequent inability to efficiently recruit host-derived vessels.

Jak3- and JNK-dependent vascular endothelial growth factor expression in cutaneous T-cell lymphoma

Biopsies from patients with cutaneous T-cell lymphoma (CTCL) exhibit stage-dependent increase in angiogenesis. However, the molecular mechanisms responsible for the increased angiogenesis are unknown. Here we show that malignant CTCL T cells spontaneously produce the potent angiogenic protein, vascular endothelial growth factor (VEGF). Dermal infiltrates of CTCL lesions show frequent and intense staining with anti-VEGF antibody, indicating a steady, high production of VEGF in vivo. Moreover, the VEGF production is associated with constitutive activity of Janus kinase 3 (Jak3) and the c-Jun N-terminal kinases (JNKs). Sp600125, an inhibitor of JNK activity and activator protein-1 (AP-1) binding to the VEGF promoter, downregulates the VEGF production without affecting Jak3 activity. Similarly, inhibitors of Jak3 inhibit the VEGF production without affecting JNK activity. Downregulation of Stat3 with small interfering RNA has no effect, whereas curcumin, an inhibitor of both Jak3 and the JNKs, almost completely blocks the VEGF production. In conclusion, we provide evidence of VEGF production in CTCL, which is promoted by aberrant activation of Jak3 and the JNKs. Inhibition of VEGF-inducing pathways or neutralization of VEGF itself could represent novel therapeutic modalities in CTCL.

Activation of the mTOR signalling pathway is required for pancreatic growth in protease-inhibitor-fed mice

Cholecystokinin (CCK)-induced pancreatic growth in mice involves parallel increases in DNA and protein. The mammalian target of rapamycin (mTOR) signalling pathway regulates mRNA translation and its activation is implicated in growth of various tissues. The aim of this study was to elucidate whether mTOR activation is required for pancreatic growth in a mouse model of increased endogenous CCK release. In mice fed chow containing the synthetic protease inhibitor camostat, protein synthetic rates and phosphorylation of two downstream targets of mTOR, eukaryotic initiation factor 4E binding protein 1 (4E-BP1) and the ribosomal protein S6 (S6), increased in comparison with fasted controls. The camostat-induced increases in protein synthesis and 4E-BP1 and S6 phosphorylation were almost totally abolished by administration of the mTOR inhibitor rapamycin 1 h prior to camostat feeding. In contrast, the phosphorylation of ERK1/2 and JNK and the expression of the early response genes c-jun, c-fos, ATF3 and egr-1 induced by camostat feeding were not affected by rapamycin. In mice fed camostat for 7 days, the ratio of pancreatic to body weight increased by 143%, but when rapamycin was administered daily this was reduced to a 22% increase. Changes in pancreatic mass were paralleled by protein and DNA content following camostat feeding and rapamycin administration. Moreover, while BrdU incorporation, an indicator of DNA synthesis, was increased to 448% of control values after 2 days of camostat feeding, rapamycin administration completely inhibited this increase. We conclude that the mTOR signalling pathway is required for CCK-induced cell division and pancreatic growth.

Hypoxia protects HepG2 cells against etoposide-induced apoptosis via a HIF-1-independent pathway

Tumor hypoxia has been described to increase the resistance of cancer cells to radiation therapy and chemotherapy. It also supports the invasiveness and metastatic potential of the tumor. However, few data are available on the transduction pathway set up under hypoxia and leading to this resistance against anti-cancer therapies. HIF-1, the main transcription factor activated by hypoxia, has been recently shown to participate to this process although its role as an anti- or a pro-apoptotic protein is still controversy. In this study, we showed that hypoxia protected HepG2 cells against etoposide-induced apoptosis. The effect of hypoxia on cell death was assayed by measuring different parameters of the apoptotic pathway, like DNA fragmentation, caspase activity and PARP-1 cleavage. The possible implication of HIF-1 in the anti-apoptotic role of hypoxia was investigated using HIF-1alpha siRNA. Our results indicated that HIF-1 is not involved in the hypoxia-induced anti-apoptotic pathway. Another transcription factor, AP-1, was studied for its potential role in the hypoxia-induced protection against apoptosis. Specific inhibition of AP-1 decreased the protection effect of hypoxia against etoposide-induced apoptosis. Together, all these data underline that hypoxia could mediate its anti-apoptotic role via different transcription factors depending on the cellular context and pro-apoptotic stimuli.

Hypoxic regulation of vascular endothelial growth factor through the induction of phosphatidylinositol 3-kinase/Rho/ROCK and c-Myc

The induction of vascular endothelial growth factor (VEGF) is an essential feature of tumor angiogenesis. Hypoxia is a potent stimulator of VEGF expression, and hypoxia-inducible factor-1 (HIF-1) is considered to be critical for this induction. However, we have previously demonstrated that induction of VEGF by hypoxia was preserved when HIF-1alpha was silenced. We sought to better define the molecular basis of this HIF-1-independent regulation. In colon cancer cells, hypoxia stimulated multiple K-ras effector pathways including phosphatidylinositol 3-kinase. VEGF promoter deletion studies identified a novel promoter region between -418 and -223 bp that was responsive to hypoxia in a PI3K/Rho/ROCK-dependent manner. Electrophoretic mobility shift assays identified a fragment between -300 and -251 bp that demonstrated a unique shift only in hypoxic conditions. Inhibition of PI3K or ROCK blocked the formation of this complex. A binding site for c-Myc, a target of ROCK, was identified at -271 bp. A role for c-Myc in the hypoxic induction of VEGF was demonstrated by site-directed mutagenesis of the VEGF promoter and silencing of c-Myc by small interfering RNA. Collectively, these findings suggest an alternative mechanism for the hypoxic induction of VEGF in colon cancer that does not depend upon HIF-1alpha but instead requires the activation of PI3K/Rho/ROCK and c-Myc.

Role for casein kinase 2 in the regulation of HIF-1 activity

Hypoxia-inducible factor-1 (HIF-1) is a heterodimeric transcription factor that plays a major role in cellular adaptation to hypoxia. The mechanisms regulating HIF-1 activity occurs at multiple levels in vivo. The HIF-1alpha subunit is highly sensible to oxygen and is rapidly degraded by the proteasome 26S in normoxia. Activation in hypoxia occurs through a multistep process including inhibition of HIF-1alpha degradation, but also increase in the transactivation activity of HIF-1. Several data indicate that phosphorylation could play a role in this regulation. In this report, we investigated the role of casein kinase 2 (CK2), an ubiquitous serine/threonine kinase, in the regulation of HIF-1 activity. Hypoxia was capable of increasing the expression of the beta subunit of CK2, of inducing a relocalization of this subunit at the plasma membrane, of inducing nuclear translocation of the alpha subunit and of increasing CK2 activity. Three inhibitors of this kinase, DRB (5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole), TBB (4,5,6,7-tetrabromotriazole) and apigenin, as well as overexpression of a partial dominant negative mutant of CK2alpha, were shown to inhibit HIF-1 activity as measured by a reporter assay and through hypoxia-induced VEGF and aldolase expression. This does not occur at the stabilization process since they did not affect HIF-1alpha protein level. DNA-binding activity was also not inhibited. We conclude that CK2 is an important regulator of HIF-1 transcriptional activity but the mechanism of this regulation remains to be determined. Since HIF-1 plays a major role in tumor angiogenesis and since CK2 has been described to be overexpressed in tumor cells, this new pathway of regulation can be one more way for tumor cells to survive.

Reversing chemoresistance in cisplatin-resistant human ovarian cancer cells: A role of c-Jun NH2-terminal kinase 1

To investigate the role of activation of c-Jun NH2-terminal kinase 1 (JNK1) in mediating cisplatin-induced apoptosis and the possibility of induction of JNK activity in triggering relation to DNA damage and drug resistance. We investigated the difference of cisplatin-induced activation of JNK pathway and H2O2 alteration between cisplatin-sensitive human ovarian carcinoma cell line A2780 and its resistant variant A2780/DDP. JNK, p-JNK protein, and extracellular H2O2 levels were determined in both A2780 and A2780/DDP cells which were transfected with dominant negative allele of JNK and recombinant JNK1 separately. Both A2780 and A2780/DDP were treated with CDDP, the JNK pathway was activated and a prolonged JNK activation was maintained for at least 12 h in A2780, and only a transient activation (3 h) was detected in A2780/DDP in response to cisplatin treatment. Inhibition of JNK activity by transfection with a dominant negative allele of JNK blocked CDDP-induced apoptosis significantly in A2780 cells. Selective stimulation of the JNK pathway by lipofectamine-mediated delivery of recombinant JNK1 led to activation of c-Jun and decrease of extracellular H2O2, as well as apoptosis sensitization to CDDP in A2780/DDP cells. We concluded that JNK pathway might play an important role in mediating cisplatin-induced apoptosis in A2780 cells, and the duration of JNK activation might be critical in determining whether cells survive or undergo apoptosis. The resistance to CDDP can be reversed through activating c-Jun and decreasing extracellular generation of H2O2 by pcDNA3(FLAG)-JNK1-wt transfection in A2780/DDP cells.

Protein kinase p-JNK is correlated with the activation of AP-1 and its associated Jun family proteins in hepatocellular carcinoma

To study the role of c-Jun N-terminal kinase (JNK) and its relation to transcription factor AP-1 and Jun family proteins in hepatocellular carcinoma (HCC) with or without hepatitis B virus (HBV) infection. Immunohistochemical and in situ hybridization techniques were performed for studying phosphorylated JNK (p-JNK), c-Jun, JunB, JunD and AP-1 in 40 cases of human HCC and corresponding nontumoral tissues. Positive staining of nucleus for p-JNK, c-Jun, JunD and AP-1 was presented in 28 (70%), 29 (72.5%), 32 (80%) and 25 (62.5%) in cancer cells respectively, while 0%, 28%, 17.5% and 10% in adjacent non-tumor tissues. The expression levels of p-JNK, c-Jun, JunD and AP-1 were significantly and positively correlated with each other and with HBsAg positive rate (P<0.05). JunB was negative staining in both cancer cells and non-tumor tissues of all cases. JNK phosphorylation may correlate with AP-1 activation and the expression of c-Jun and JunD in HCC. JNK/c-Jun/JunD/AP-1 signaling pathway may play an important role in the pathogenesis of HBV-associated HCC. JunB may not be involved in the process.

Regulation of gene expression by the amyloid precursor protein: inhibition of the JNK/c-Jun pathway

The amyloid precursor protein (APP) has been suggested to regulate gene expression. GeneChip analysis and in vitro kinase assays revealed potent APP-dependent repression of c-Jun, its target gene SPARC and reduced basal c-Jun N-terminal kinase (JNK) activity in PC12 cells overexpressing APP. UV-induced activation of the JNK signalling pathway and subsequent apoptosis were likewise reduced by APP and this effect could be mimicked by the indirect JNK inhibitor CEP-11004. Treatment with a gamma-secretase inhibitor did not affect APP-mediated downmodulation of the JNK signalling pathway, suggesting that the effects might be mediated via alpha-secretase processing of APP. In support of these data, overexpression of the Swedish mutant of APP did not inhibit SPARC expression, UV-induced JNK activation and cell death. Our data suggest an important physiological role of APP and alpha-secretase activity in the control of JNK/c-Jun signalling, target gene expression and cell death activation in response to cytotoxic stress.

Hypoxia-responsive transcription factors

Hypoxia is a common pathophysiological occurrence with a profound impact on the cellular transcriptome. The consequences of hypoxia-induced or hypoxia-repressed gene expression have important implications in disease processes as diverse as tumour development and chronic inflammation. While the hypoxia-inducible factor (HIF-1) plays a major role in controlling the ubiquitous transcriptional response to hypoxia, it is clear that a number of other transcription factors are also activated either directly or indirectly. In this review, we comprehensively discuss the transcription factors that have been reported to be hypoxia-responsive and the signalling mechanisms leading to their activation. Understanding such events will enhance our understanding of cellular oxygen sensing.

The interaction between HIF-1 and AP-1 transcription factors in response to low oxygen

Hypoxia-inducible factor-1 (HIF-1) is a critical regulator of the transcriptional response to low oxygen conditions (hypoxia/anoxia) experienced by mammalian cells in both physiological and pathophysiological circumstances. As our understanding of the biology and biochemistry of HIF-1 has grown, it has become apparent that cells adapt to signals generated by low oxygen through a network of stress responsive transcription factors or complexes, which are influenced by HIF-1 activity. This review summarizes our current understanding of the interaction of HIF-1 with AP-1, a classic example of a family of pleiotropic transcription factors that impact on diverse cellular processes and phenotypes, including the adaptation to low oxygen stress. The review focuses on experimental studies involving cultured cells exposed to hypoxia/anoxia, and describes both established and possible interactions between HIF-1 and AP-1 at different levels of cellular organization.