Hypoxia-induced regulation of MAPK phosphatase-1 as identified by subtractive suppression hybridization and cDNA microarray analysis

The hypoxia response pathway in the Antarctic fish Notothenia coriiceps is functional despite a poly Q/E insertion mutation in HIF-1α

Antarctic notothenioid fishes, inhabiting the oxygen-rich Southern Ocean, possess a polyglutamine and glutamic acid (poly Q/E) insertion mutation in the master transcriptional regulator of oxygen homeostasis, hypoxia- inducible factor-1α (HIF-1α). To determine if this mutation impairs the ability of HIF-1 to regulate gene expression in response to hypoxia, we exposed Notothenia coriiceps, with a poly Q/E insertion mutation in HIF-1α that is 9 amino acids long, to hypoxia (2.3 mg L-1 O2) or normoxia (10 mg L -1 O2) for 12 h. Heart ventricles, brain, liver, and gill tissue were harvested and changes in gene expression quantified using RNA sequencing. Levels of glycogen and lactate were also quantified to determine if anaerobic metabolism increases in response to hypoxia. Exposure to hypoxia resulted in 818 unique differentially expressed genes (DEGs) in liver tissue of N. coriiceps. Many hypoxic genes were induced, including ones involved in the MAP kinase and FoxO pathways, glycolytic metabolism, and vascular remodeling. In contrast, there were fewer than 104 unique DEGs in each of the other tissues sampled. Lactate levels significantly increased in liver in response to hypoxia, indicating that anaerobic metabolism increases in response to hypoxia in this tissue. Overall, our results indicate that the hypoxia response pathway is functional in N. coriiceps despite a poly Q/E mutation in HIF-1α, and confirm that Antarctic fishes are capable of altering gene expression in response to hypoxia.

Identification of m6A modification patterns and development of m6A-hypoxia prognostic signature to characterize tumor microenvironment in triple-negative breast cancer

Background

N6-methylation (m6A) modification of RNA has been found to have essential effects on aspects of the tumor microenvironment (TME) including hypoxia status and mobilization of immune cells. However, there are no studies to explore the combined effect of m6A modification and hypoxia on molecular heterogeneity and TME of triple-negative breast cancer (TNBC).

Methods

We collected The Cancer Genome Atlas (TCGA-TNBC, N=139), the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC-TNBC, N=297), the GSE103091, GSE21653, and GSE135565 series from the Gene Expression Omnibus (GEO-TNBC, N=247), and FUSCCTNBC (N=245) for our study. The non-negative matrix factorization algorithm was used to cluster TNBC samples. Immune cell infiltration was analyzed by the CIBERSORT algorithm. The enrichment scores were calculated by single-sample gene set enrichment analysis(ssGSEA) to characterize TME in TNBC samples. Immunohistochemistry (IHC) and qRT-PCR were performed to detect the gene expression.

Results

Based on the expression of m6A-related genes, we identified three distinct m6A clusters (denoted A, B, and C) in TNBC samples. Comparing the TME characteristics among the three clusters, we observed that cluster C was strongly related to hypoxia status and immune suppression, whereas clusters A and B displayed more immune cell infiltration. Therefore, we combine m6A and hypoxia related genes to classify two m6A-hypoxia clusters of TNBC and screened six prognostic genes by LASSO-Cox regression to construct a m6A-hypoxia signature(MHPS), which divided TNBC samples into high- and low-risk groups. We identified different TME features, immune cell infiltration between the two groups, and a better immunotherapy response was observed in the low-risk group. A nomogram was constructed with tumor size, lymph node, and risk score to improve clinical application of MHPS.

Conclusion

We identified distinct TME characteristics of TNBC based on three different m6A modification patterns. Then, we constructed a specific m6A-hypoxia signature for TNBC to evaluate risk and predict immunotherapy response of patients, to enable more accurate treatment in the future.

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.

Model for the prediction of mechanical asphyxia as the cause of death based on four biological indexes in human cardiac tissue

Determination of mechanical asphyxia as the cause of death has always been difficult for forensic pathologists, particularly when signs of asphyxia are not obvious on the body. Currently, depending on only physical examination of corpses, pathologists must be cautious when making cause-of-death appraisals. In a previous study, four biomarkers-dual-specificity phosphatase 1 (DUSP1), potassium voltage-gated channel subfamily J member 2 (KCNJ2), miR-122, and miR-3185-were screened in human cardiac tissue from cadavers that died from mechanical asphyxia compared with those that died from craniocerebral injury, hemorrhagic shock, or other causes. Expression of the markers correlated with death from mechanical asphyxia regardless of age, environmental temperature, and postmortem interval. However, a single biological index is not an accurate basis for the identification of the cause of death. In this study, receiver operating characteristic curves of the ΔCq values of the four indexes were generated. The diagnostic accuracy of the indexes was judged according to their area under the curve (DUSP1: 0.773, KCNJ2: 0.775, miR-122: 0.667, and miR-3185: 0.801). Finally, a nomogram was generated, and single blind experiment was conducted to verify the cause of death of mechanical asphyxia.

Hypoxia Downregulates MAPK/ERK but Not STAT3 Signaling in ROS-Dependent and HIF-1-Independent Manners in Mouse Embryonic Stem Cells

Hypoxia is involved in the regulation of stem cell fate, and hypoxia-inducible factor 1 (HIF-1) is the master regulator of hypoxic response. Here, we focus on the effect of hypoxia on intracellular signaling pathways responsible for mouse embryonic stem (ES) cell maintenance. We employed wild-type and HIF-1α-deficient ES cells to investigate hypoxic response in the ERK, Akt, and STAT3 pathways. Cultivation in 1% O₂ for 24 h resulted in the strong dephosphorylation of ERK and its upstream kinases and to a lesser extent of Akt in an HIF-1-independent manner, while STAT3 phosphorylation remained unaffected. Downregulation of ERK could not be mimicked either by pharmacologically induced hypoxia or by the overexpression. Dual-specificity phosphatases (DUSP) 1, 5, and 6 are hypoxia-sensitive MAPK-specific phosphatases involved in ERK downregulation, and protein phosphatase 2A (PP2A) regulates both ERK and Akt. However, combining multiple approaches, we revealed the limited significance of DUSPs and PP2A in the hypoxia-mediated attenuation of ERK signaling. Interestingly, we observed a decreased reactive oxygen species (ROS) level in hypoxia and a similar phosphorylation pattern for ERK when the cells were supplemented with glutathione. Therefore, we suggest a potential role for the ROS-dependent attenuation of ERK signaling in hypoxia, without the involvement of HIF-1.

DUSP1 and KCNJ2 mRNA upregulation can serve as a biomarker of mechanical asphyxia-induced death in cardiac tissue

The incidence of death by asphyxia is second to the incidence of death by mechanical injury; however, death by mechanical asphyxia may be difficult to prove in court, particularly in cases in which corpses do not exhibit obvious signs of asphyxia. To identify a credible biomarker of asphyxia, we first examined the expression levels of 47,000 mRNAs in human cardiac tissue specimens from individuals who died of mechanical asphyxia and compared the expression levels with the levels of the corresponding mRNAs in specimens from individuals who died of craniocerebral injury using microarray. We selected 119 differentially expressed mRNAs, examined the expression levels of these mRNAs in 44 human cardiac tissue specimens of individuals who died of mechanical asphyxia, craniocerebral injury, hemorrhagic shock, or other causes. That the expression of dual-specificity phosphatase 1 (DUSP1) and potassium voltage-gated channel subfamily J member 2 (KCNJ2) was upregulated in human cardiac tissues from the mechanical asphyxia group compared with control tissues, regardless of age, environmental temperature, and postmortem interval (PMI), indicating that DUSP1 and KCNJ2 may be associated with mechanical asphyxia-induced death and can thus serve as useful biomarkers of death by mechanical asphyxia.

The molecular fingerprint of lung inflammation after blunt chest trauma

Background

After severe blunt chest trauma, the development of an acute lung injury (ALI) is often associated with severe or even lethal complications. Especially in multiple injured patients after blunt chest trauma ALI/ARDS [acute respiratory distress syndrome (ARDS)] is frequent. However, in the initial posttraumatic phase, inflammatory clinical signs are often not apparent and underlying changes in gene-expression profile are unknown.

Methods

Therefore, inflammation in lung tissue following blunt chest trauma was characterized in a well-defined bilateral lung injury model. Using DNA microarrays representing 9240 genes, the temporal sequence of blunt chest trauma-induced gene-expression patterns in lung tissue was examined.

Results

The results suggest an activation of a highly complex transcriptional program in response to chest trauma. Chest trauma led to elevated expression levels of inflammatory and coagulatory proteins (such as TNFα receptor, IL-1α, IL-1β, C3, NF-κB and plasminogen activator). However, upregulation of proteins was found, usually incoherent of exerting effects in blunt thoracic trauma (pendrin, resistin, metallothionein and glucocorticoid-induced leucine zipper). Furthermore, significant downregulation was observed as early as 10 min after trauma for cytokines and complement factors (LCR-1, C4) as well as for intracellular signaling molecules (inhibitory protein phosphatase) and ion-channels (voltage-dependent Ca²⁺ channel).

Conclusions

Taken together, the provided global perspective of the inflammatory response following blunt chest trauma could provide a molecular framework for future research in trauma pathophysiology.

Obstructive sleep apnea and intermittent hypoxia increase expression of dual specificity phosphatase 1

OBJECTIVE

Dual specificity phosphatase 1 (DUSP1) inhibits mitogen activated protein kinase activity, and is activated by several stimuli such as sustained hypoxia, oxidative stress, and hormones. However, the effect of intermittent hypoxia is not known. The aim of this study was to evaluate the role of intermittent hypoxia on DUSP1 expression, and to validate its role in a human model of intermittent hypoxia, as seen in obstructive sleep apnea (OSA). OSA is characterized by recurrent episodes of hypoxemia/reoxygenation and is a known risk factor for cardiovascular morbidity.

METHODS

In-vitro studies using human coronary artery endothelial cells (HCAEC) and ex-vivo studies using white blood cells isolated from healthy and OSA subjects.

RESULTS

Intermittent hypoxia induced DUSP1 expression in human coronary artery endothelial cells (HCAEC), and in granulocytes isolated from healthy human subjects. Functionally, DUSP1 increased the expression and activity of manganese superoxide dismutase (MnSOD) in HCAEC. Further, significant increases in DUSP1 mRNA from total blood, and in DUSP1 protein in mononuclear cells and granulocytes isolated from OSA subjects, were observed in the early morning hours after one night of intermittent hypoxemia due to untreated OSA. This early-morning OSA-induced augmentation of DUSP1 gene expression was attenuated by continuous positive airway pressure (CPAP) treatment of OSA.

CONCLUSION

Intermittent hypoxia increases MnSOD activity via increased DUSP1 expression in HCAEC. Similarly, overnight intermittent hypoxemia in patients with OSA induces expression of DUSP1, which may mediate increases of MnSOD expression and activity. This may contribute significantly to neutralizing the effects of reactive oxygen species, a consequence of the intermittent hypoxemia/reperfusion elicited by OSA.

Kaposi's sarcoma-associated herpesvirus suppression of DUSP1 facilitates cellular pathogenesis following de novo infection

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma (KS), and KSHV activation of mitogen-activated protein kinases (MAPKs) initiates a number of key pathogenic determinants of KS. Direct inhibition of signal transduction as a therapeutic approach presents several challenges, and a better understanding of KSHV-induced mechanisms regulating MAPK activation may facilitate the development of new treatment or prevention strategies for KS. MAPK phosphatases, including dual-specificity phosphatase-1 (DUSP1), negatively regulate signal transduction and cytokine activation through MAPK dephosphorylation or interference with effector molecule binding to MAPKs, including the extracellular signal-regulated kinase (ERK). We found that ERK-dependent latent viral gene expression, the induction of promigratory factors, and cell invasiveness following de novo infection of primary human endothelial cells are in part dependent on KSHV suppression of DUSP1 expression during de novo infection. KSHV-encoded miR-K12-11 upregulates the expression of xCT (an amino acid transporter and KSHV fusion/entry receptor), and existing data indicate a role for xCT in the regulation of 14-3-3β, a transcriptional repressor of DUSP1. We found that miR-K12-11 induces endothelial cell secretion of promigratory factors and cell invasiveness through upregulation of xCT-dependent, 14-3-3β-mediated suppression of DUSP1. Finally, proof-of-principle experiments revealed that pharmacologic upregulation of DUSP1 inhibits the induction of promigratory factors and cell invasiveness during de novo KSHV infection. These data reveal an indirect role for miR-K12-11 in the regulation of DUSP1 and downstream pathogenesis.

Depression and treatment response: dynamic interplay of signaling pathways and altered neural processes

Since the 1960s, when the first tricyclic and monoamine oxidase inhibitor antidepressant drugs were introduced, most of the ensuing agents were designed to target similar brain pathways that elevate serotonin and/or norepinephrine signaling. Fifty years later, the main goal of the current depression research is to develop faster-acting, more effective therapeutic agents with fewer side effects, as currently available antidepressants are plagued by delayed therapeutic onset and low response rates. Clinical and basic science research studies have made significant progress towards deciphering the pathophysiological events within the brain involved in development, maintenance, and treatment of major depressive disorder. Imaging and postmortem brain studies in depressed human subjects, in combination with animal behavioral models of depression, have identified a number of different cellular events, intracellular signaling pathways, proteins, and target genes that are modulated by stress and are potentially vital mediators of antidepressant action. In this review, we focus on several neural mechanisms, primarily within the hippocampus and prefrontal cortex, which have recently been implicated in depression and treatment response.

Signaling pathways underlying the rapid antidepressant actions of ketamine

Currently available medications have significant limitations, most notably low response rate and time lag for treatment response. Recent clinical studies have demonstrated that ketamine, an NMDA receptor antagonist produces a rapid antidepressant response (within hours) and is effective in treatment resistant depressed patients. Molecular and cellular studies in rodent models demonstrate that ketamine rapidly increases synaptogenesis, including increased density and function of spine synapses, in the prefrontal cortex (PFC). Ketamine also produces rapid antidepressant actions in behavioral models of depression, and reverses the deficits in synapse number and behavior resulting from chronic stress exposure. These effects of ketamine are accompanied by stimulation of the mammalian target of rapamycin (mTOR), and increased levels of synaptic proteins. Together these studies indicate that ketamine rapidly reverses the atrophy of spines in the PFC and thereby causes a functional reconnection of neurons that underlies the rapid behavioral responses. These findings identify new targets for rapid acting antidepressants that are safer than ketamine. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Microarray expression profiling in 6-hydroxydopamine-induced dopaminergic neuronal cell death

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by a loss of dopaminergic neurons in the substantia nigra pars compacta. To discover potential key molecules in this process, we utilized cDNA microarray technology to obtain an expression profile of transcripts in MN9D dopaminergic neuronal cells treated with 6-hydroxydopamine. Using a self-organizing map algorithm, data mining and clustering were combined to identify distinct functional subgroups of genes. We identified alterations in the expression of 81 genes in eight clusters. Among these genes, we verified protein expression patterns of MAP kinase phosphatase 1 and sequestosome 1 using both cell culture and rat brain models of PD. Immunological analyses revealed increased expression levels as well as aggregated distribution patterns of these gene products in 6-hydroxydopamine-treated dopaminergic neurons. In addition to the identification of other proteins that are known to be associated with protein aggregation, our results raise the possibility that a more widespread set of proteins may be associated with the generation of protein aggregates in dying neurons. Further research to determine the functional roles of other altered gene products within the same cluster as well as the seven remaining clusters may provide new insights into the neurodegeneration that underlies PD pathogenesis.

The role of mitogen-activated protein kinases in crystalline silica-induced cyclooxygenase-2 expression in A549 human lung epithelial cells

We examined the role of mitogen-activated protein kinase (MAPK) signaling pathways in crystalline silica-induced expression of cyclooxygenase (COX)-2, an important mediator of airway inflammation, in A549 human lung epithelial cells. The levels of COX-2 mRNA increased after a 30-min exposure, and COX-2 protein increased after a 2-h exposure to crystalline silica. Both remained elevated at 8 h; however, no change was observed in the expression of the constitutive COX-1 isoform. The level of prostaglandin E(2), a major product of COX enzymes, increased in response to crystalline silica exposure. Phosphorylated forms of MAPKs including extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal kinase, and p38 were also increased after crystalline silica exposure. COX-2 expression was markedly suppressed by treatment with the p38 inhibitor, SB203580, and mildly suppressed by the MAPK/ERK kinase inhibitor, U0126. Treatment with the nuclear factor-κB (NF-κB) inhibitor, BAY11-7082, markedly suppressed silica-induced COX-2 expression. These results show that crystalline silica exposure induces COX-2 expression in A549 cells in a manner that is dependent on the MAPK and NF-κB pathways. Although a marked induction of MAPK phosphatase (MKP)-1 expression was observed in A549 cells exposed to crystalline silica, the silencing of MKP-1 expression using short interference RNA did not affect silica-induced COX-2 expression, suggesting that the down-regulation of COX-2 expression by MKP-1 is unlikely.

Mitogen-activated protein kinase phosphatase-1 is a key regulator of hypoxia-induced vascular endothelial growth factor expression and vessel density in lung

Although mitogen-activated protein kinase phosphatase-1 (MKP-1) is a key deactivator of MAP kinases, known effectors of lung vessel formation, whether it plays a role in the expression of proangiogenic vascular endothelial growth factor (VEGF) in hypoxic lung is unknown. We therefore hypothesized that MKP-1 is a crucial modulator of hypoxia-stimulated vessel development by regulating lung VEGF levels. Wild-type MKP-1(+/+), heterozygous MKP-1(+/-), and deficient MKP-1(-/-) mice were exposed to sea level (SL), Denver altitude (DA) (1609 m [5280 feet]), and severe high altitude (HYP) (∼5182 m [∼17,000 feet]) for 6 weeks. Hypoxia enhanced phosphorylation of p38 MAP kinase, a substrate of MKP-1, as well as α smooth muscle actin (αSMA) expression in vessels, respiratory epithelium, and interstitium of phosphatase-deficient lung. αSMA-positive vessel (<50 μm outside diameter) densities were markedly reduced, whereas vessel wall thickness was increased in hypoxic MKP-1(-/-) lung. Mouse embryonic fibroblasts (MEFs) of all three genotypes were isolated to pinpoint the mechanism involved in hypoxia-induced vascular abnormalities of MKP-1(-/-) lung. Sustained phosphorylation of p38 MAP kinase was observed in MKP-1-null MEFs in response to hypoxia exposure. Although hypoxia up-regulated VEGF levels in MKP-1(+/+) MEFs eightfold, only a 70% increase in VEGF expression was observed in MKP-1-deficient cells. Therefore, our data strongly suggest that MKP-1 might be the key regulator of vascular densities through the regulation of VEGF levels in hypoxic lung.

Post-transcriptional regulation of the DUSP6/MKP-3 phosphatase by MEK/ERK signaling and hypoxia

DUSP6/MKP-3 is a cytoplasmic dual-specificity phosphatase specific for the MAP kinases ERK1/2. Previous data have shown that the MEK/ERK axis exerts a retro-control on its own signaling through transcriptional and post-translational regulation of DUSP6. We first confirm the key role of MEK/ERK in maintaining the levels of dusp6 mRNA, while PI3K/mTOR, p38 MAPK, and JNK signaling pathways had no significant effects. We further show that regulation of dusp6 mRNA stability plays a critical role in ERK-dependent regulation of dusp6 expression. Luciferase reporter constructs indicated that MEK/ERK signaling increased the half-life of dusp6 mRNA in a 3'untranslated region (3'UTR)-dependent manner. In addition, hypoxia, a hallmark of tumor growth, was found to increase both endogenous levels of dusp6 mRNA and the stability of the luciferase reporter constructs containing its 3'UTR, in a HIF-1-dependent manner. Nevertheless, a basal ERK activity was required for the response to hypoxia. Finally, Tristetraprolin (TTP), a member of the TIS11 CCCH zinc finger protein family, and PUM2, an homolog of drosophila pumilio, two proteins regulating mRNA stability reduced the levels of endogenous dusp6 mRNA and the activity of the dusp6/3'UTR luciferase reporter constructs. This study shows that post-transcriptional regulation is a key process in the control of DUSP6 expression.

Mitogen-activated protein kinase phosphatase-1 (MKP-1) in retinal ischemic preconditioning

We previously described the phenomenon of retinal ischemic pre-conditioning (IPC) and we have shown the role of various signaling proteins in the protective pathways, including the mitogen-activated protein kinase p38. In this study we examined the role in IPC of mitogen-activated protein kinase phosphatase-1 (MKP-1), which inactivates p38. Ischemia was produced by elevation of intraocular pressure above systolic arterial blood pressure in adult Wistar rats. Preconditioning was produced by transient retinal ischemia for 5 min, 24 h prior to ischemia. Small interfering RNA (siRNA) to MKP-1 or a control non-silencing siRNA, was injected into the vitreous 6 h prior to IPC. Recovery was assessed by electroretinography (ERG) and histology. The a-and b-waves, and oscillatory potentials (OPs), measured before and 1 week after ischemia, were then normalized relative to pre-ischemic baseline, and corrected for diurnal variation in the normal non-ischemic eye. The P2, or post-photoreceptor component of the ERG (which reflects function of the rod bipolar cells in the inner retina), was derived using the Hood-Birch model. MKP-1 was localized in specific retinal cells using immunohistochemistry; levels of mitogen-activated protein kinases were measured using Western blotting. Injection of siRNA to MKP-1 significantly attenuated the protective effect of IPC as reflected by decreased recovery of the electroretinogram a and b-waves and the P2 after ischemia. The injection of siRNA to MKP-1 reduced the number of cells in the retinal ganglion cell and outer nuclear layers after IPC and ischemia. Blockade of MKP-1 by siRNA also increased the activation of p38 at 24 h following IPC. MKP-1 siRNA did not alter the levels of phosphorylated jun N-terminal kinase (JNK) or extracellular signal-regulated kinase (ERK) after IPC. The results suggest the involvement of dual-specificity phosphatase MKP-1 in IPC and that MKP-1 is involved in IPC by regulating levels of activated MAPK p38.

A negative regulator of MAP kinase causes depressive behavior

The lifetime prevalence (∼16%) and the economic burden ($100 billion annually) associated with major depressive disorder (MDD) make it one of the most common and debilitating neurobiological illnesses. To date, the exact cellular and molecular mechanisms underlying the pathophysiology of MDD have not been identified. Here we use whole-genome expression profiling of postmortem tissue and show significantly increased expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1, encoded by DUSP1, but hereafter called MKP-1) in the hippocampal subfields of subjects with MDD compared to matched controls. MKP-1, also known as dual-specificity phosphatase-1 (DUSP1), is a member of a family of proteins that dephosphorylate both threonine and tyrosine residues and thereby serves as a key negative regulator of the MAPK cascade, a major signaling pathway involved in neuronal plasticity, function and survival. We tested the role of altered MKP-1 expression in rat and mouse models of depression and found that increased hippocampal MKP-1 expression, as a result of stress or viral-mediated gene transfer, causes depressive behaviors. Conversely, chronic antidepressant treatment normalizes stress-induced MKP-1 expression and behavior, and mice lacking MKP-1 are resilient to stress. These postmortem and preclinical studies identify MKP-1 as a key factor in MDD pathophysiology and as a new target for therapeutic interventions.

The dual-specificity MAP kinase phosphatases: critical roles in development and cancer

Intracellular signaling by mitogen-activated protein (MAP) kinases (MAPK) is involved in many cellular responses and in the regulation of various physiological and pathological conditions. Tight control of the localization and duration of extracellular-regulated kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), or p38 MAPK activity is thus a fundamental aspect of cell biology. Several members of the dual-specificity phosphatase (DUSPs) family are able to dephosphorylate MAPK isoforms with different specificity, cellular, and tissue localization. Understanding how these phosphatases are themselves regulated during development or in physiological and pathological conditions is therefore fundamental. Over the years, gene deletion and knockdown studies have completed initial in vitro studies and shed a new light on the global and specific roles of DUSPs in vivo. Whereas DUSP1, DUSP2, and DUSP10 appear as crucial players in the regulation of immune responses, other members of the family, like the ERK-specific DUSP6, were shown to play a major role in development. Recent findings on the involvement of DUSPs in cancer progression and resistance will also be discussed.

Mice deficient in Mkp-1 develop more severe pulmonary hypertension and greater lung protein levels of arginase in response to chronic hypoxia

The mitogen-activated protein (MAP) kinases are involved in cellular responses to many stimuli, including hypoxia. MAP kinase signaling is regulated by a family of phosphatases that include MAP kinase phosphatase-1 (MKP-1). We hypothesized that mice lacking the Mkp-1 gene would have exaggerated chronic hypoxia-induced pulmonary hypertension. Wild-type (WT) and Mkp-1(-/-) mice were exposed to either 4 wk of normoxia or hypobaric hypoxia. Following chronic hypoxia, both genotypes demonstrated elevated right ventricular pressures, right ventricular hypertrophy as demonstrated by the ratio of the right ventricle to the left ventricle plus septum weights [RV(LV + S)], and greater vascular remodeling. However, the right ventricular systolic pressures, the RV/(LV + S), and the medial wall thickness of 100- to 300-microm vessels was significantly greater in the Mkp-1(-/-) mice than in the WT mice following 4 wk of hypobaric hypoxia. Chronic hypoxic exposure caused no detectable change in eNOS protein levels in the lungs in either genotype; however, Mkp-1(-/-) mice had lower levels of eNOS protein and lower lung NO production than did WT mice. No iNOS protein was detected in the lungs by Western blotting in any condition in either genotype. Both arginase I and arginase II protein levels were greater in the lungs of hypoxic Mkp-1(-/-) mice than those in hypoxic WT mice. Lung levels of proliferating cell nuclear antigen were greater in hypoxic Mkp-1(-/-) than in hypoxic WT mice. These data are consistent with the concept that MKP-1 acts to restrain hypoxia-induced arginase expression and thereby reduces vascular remodeling and the severity of pulmonary hypertension.

Cyclic AMP represses the hypoxic induction of hypoxia-inducible factors in PC12 cells

Hypoxia-inducible factor 1 (HIF-1) is a master regulator for hypoxic activation of genes for angiogenesis, hormone synthesis, glycolysis and cell survival. In addition to hypoxic stimulus, various effectors and reagents were reported to affect HIF-1 activity. Here, we show that cyclic AMP (cAMP) down-regulates the HIF-1 activity in pheochromocytoma PC12 cells but not in Hep3B and HeLa cells. Hypoxia response element-dependent reporter activity was decreased by the addition of dibutyryl cAMP. Expression of protein kinase A (PKA) catalytic alpha-subunits repressed the HIF-1 activity. HIF-1alpha and HLF (HIF-2alpha or EPAS1) protein levels were decreased by the treatment with dibutyryl cAMP. Although CREB was served as a negative factor for the HIF-1 activity, it may not be a major PKA target in the cAMP-dependent HIF-alpha repression pathway. Induction of hypoxia responsive genes was suppressed by dibutyryl cAMP. Our results provide additional insight into a regulatory mechanism of hypoxic response.

Mitogen-activated protein (MAP) kinase/MAP kinase phosphatase regulation: roles in cell growth, death, and cancer

Mitogen-activated protein kinase dual-specificity phosphatase-1 (also called MKP-1, DUSP1, ERP, CL100, HVH1, PTPN10, and 3CH134) is a member of the threonine-tyrosine dual-specificity phosphatases, one of more than 100 protein tyrosine phosphatases. It was first identified approximately 20 years ago, and since that time extensive investigations into both mkp-1 mRNA and protein regulation and function in different cells, tissues, and organs have been conducted. However, no general review on the topic of MKP-1 exists. As the subject matter pertaining to MKP-1 encompasses many branches of the biomedical field, we focus on the role of this protein in cancer development and progression, highlighting the potential role of the mitogen-activated protein kinase (MAPK) family. Section II of this article elucidates the MAPK family cross-talk. Section III reviews the structure of the mkp-1 encoding gene, and the known mechanisms regulating the expression and activity of the protein. Section IV is an overview of the MAPK-specific dual-specificity phosphatases and their role in cancer. In sections V and VI, mkp-1 mRNA and protein are examined in relation to cancer biology, therapeutics, and clinical studies, including a discussion of the potential role of the MAPK family. We conclude by proposing an integrated scheme for MKP-1 and MAPK in cancer.

Sanguinarine induces apoptosis in A549 human lung cancer cells primarily via cellular glutathione depletion

Sanguinarine is a plant-derived benzophenanthridine alkaloid and has been shown to possess anti-tumor activities against various cancer cells. In this study, we investigated whether sanguinarine induces apoptosis in A549 human lung cancer cells. Treatment of A549 cells with sanguinarine induced apoptosis in a dose- and time-dependent manner. Treatment with sanguinarine led to activation of caspases and MAPKs as well as increased MKP-1 expression. Importantly, pretreatment with z-VAD-fmk, a pan caspase inhibitor suppressed the sanguinarine-induced apoptosis in A549 cells. Moreover, pretreatment with NAC, a sulfhydryl group-containing reducing agent strongly suppressed the apoptotic response and caspase activation to sanguinarine. However, the sanguinarine-mediated cytotoxicity in A549 cells was not protected by pharmacological inhibition of MAPKs or MKP-1 siRNA-mediated knockdown of MKP-1. These results collectively suggest that sanguinarine induces apoptosis in A549 cells through cellular glutathione depletion and the subsequent caspase activation.

Cadmium specifically induces MKP-1 expression via the glutathione depletion-mediated p38 MAPK activation in C6 glioma cells

Cadmium is a toxic heavy metal and an environmental pollutant. Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) is a negative regulator of the family of MAPK. In this study, we investigated the effect of heavy metals on MKP-1 expression in C6 rat glioma cells. Cadmium treatment induced MKP-1 at both protein and mRNA levels while cobalt or manganese treatment did not, suggesting the specificity. Cadmium treatment also depleted intracellular GSH and activated p38 MAPK, JNKs, and AKT. Profoundly, pretreatment with thiol-containing compounds NAC or GSH, but not vitamin E, blocked GSH depletion, 38 MAPK activation and MKP-1 expression by cadmium. Moreover, pharmacological inhibition of p38 MAPK by SB203580 suppressed the cadmium-induced MKP-1. Collectively, these results demonstrate that cadmium specifically induces MKP-1 by transcriptional up-regulation in C6 cells in a mechanism associated with the glutathione depletion-dependent p38 MAPK activation.

Okadaic acid-sensitive protein phosphatases constrain phrenic long-term facilitation after sustained hypoxia

Phrenic long-term facilitation (pLTF) is a serotonin-dependent form of pattern-sensitive respiratory plasticity induced by intermittent hypoxia (IH), but not sustained hypoxia (SH). The mechanism(s) underlying pLTF pattern sensitivity are unknown. SH and IH may differentially regulate serine/threonine protein phosphatase activity, thereby inhibiting relevant protein phosphatases uniquely during IH and conferring pattern sensitivity to pLTF. We hypothesized that spinal protein phosphatase inhibition would relieve this braking action of protein phosphatases, thereby revealing pLTF after SH. Anesthetized rats received intrathecal (C4) okadaic acid (25 nm) before SH (25 min, 11% O(2)). Unlike (vehicle) control rats, SH induced a significant pLTF in okadaic acid-treated rats that was indistinguishable from rats exposed to IH (three 5 min episodes, 11% O(2)). IH and SH with okadaic acid may elicit pLTF by similar, serotonin-dependent mechanisms, because intravenous methysergide blocks pLTF in rats receiving IH or okadaic acid plus SH. Okadaic acid did not alter IH-induced pLTF. In summary, pattern sensitivity in pLTF may reflect differential regulation of okadaic acid-sensitive serine/threonine phosphatases; presumably, these phosphatases are less active during/after IH versus SH. The specific okadaic acid-sensitive phosphatase(s) constraining pLTF and their spatiotemporal dynamics during and/or after IH and SH remain to be determined.

Targeting dual-specificity phosphatases: manipulating MAP kinase signalling and immune responses

Dual-specificity phosphatases (DUSPs) are a subset of protein tyrosine phosphatases, many of which dephosphorylate threonine and tyrosine residues on mitogen-activated protein kinases (MAPKs), and hence are also referred to as MAPK phosphatases (MKPs). The regulated expression and activity of DUSP family members in different cells and tissues controls MAPK intensity and duration to determine the type of physiological response. For immune cells, DUSPs regulate responses in both positive and negative ways, and DUSP-deficient mice have been used to identify individual DUSPs as key regulators of immune responses. From a drug discovery perspective, DUSP family members are promising drug targets for manipulating MAPK-dependent immune responses in a cell-type and disease-context-dependent manner, to either boost or subdue immune responses in cancers, infectious diseases or inflammatory disorders.

Differential expression and oxidation of MKP-1 modulates TNF-alpha gene expression

Monocytic cells are integral in the pathogenesis of inflammatory disorders. We have shown previously that asbestos-induced p38 mitogen-activated protein (MAP) kinase activation and TNF-alpha expression are mediated by H(2)O(2) in blood monocytes. Due to the high expression and activity of catalase and glutathione peroxidase, normal alveolar macrophages do not respond in a manner similar to that of blood monocytes. Since kinase activity is tightly regulated by phosphatases, we hypothesized that the dual specificity phosphatase MAP kinase phosphatase (MKP)-1 regulates p38 activity and TNF-alpha production in alveolar macrophages due to insufficient H(2)O(2) generation in response to asbestos. We found that MKP-1 was highly expressed in alveolar macrophages, while blood monocytes had minimal expression. Inhibition of expression and activity of MKP-1 or overexpression of a catalytic mutant MKP-1 recovered p38 activity in alveolar macrophages. We questioned whether MKP-1 oxidation played a role dictating the contrasting responses of these cells to asbestos exposure, and found that overexpressed wild-type MKP-1 in monocytes was oxidized, while the mutant MKP-1 remained in the reduced form. Monocytes overexpressing either catalase or wild-type MKP-1 had decreased p38 activation and TNF-alpha production, respectively. In addition, TNF-alpha gene expression was regained in alveolar macrophages overexpressing the catalytic mutant MKP-1. These data suggest that MKP-1, through increased expression and lack of oxidation, modulates the inflammatory response in alveolar macrophages exposed to asbestos.

DUSP meet immunology: dual specificity MAPK phosphatases in control of the inflammatory response

The MAPK family members p38, JNK, and ERK are all activated downstream of innate immunity's TLR to induce the production of cytokines and inflammatory mediators. However, the relative intensity and duration of the activation of different MAPK appears to determine the type of immune response. The mammalian genome encodes a large number of dual specificity phosphatases (DUSP), many of which act as MAPK phosphatases. In this study, we review the emergence of several DUSP as genes that are differentially expressed and regulated in immune cells. Recently, a series of investigations in mice deficient in DUSP1, DUSP2, or DUSP10 revealed specificity in the regulation of the different MAPK proteins, and defined essential roles in models of local and systemic inflammation. The DUSP family is proposed as a set of molecular control devices specifying and modulating MAPK signaling, which may be targeted to unleash or attenuate innate and adaptive immune effector functions.

Reactive oxygen species in the control of hypoxia-inducible factor-mediated gene expression

Reactive oxygen species (ROS) have long been considered as cytotoxic. However, recent evidence indicates a prominent role of ROS as signaling molecules in the response to hormones, growth and coagulation factors, cytokines and other factors as well as to changes in oxygen tension. The hypoxia-inducible transcription factors (HIFs) are key players in the cellular response to changes in oxygen tension. Recently, HIFs have also been shown to respond to the above-mentioned non-hypoxic stimuli. In this article, the role of ROS in the regulation of HIF-1 under hypoxic and non-hypoxic conditions is summarized.

Protein kinase Czeta attenuates hypoxia-induced proliferation of fibroblasts by regulating MAP kinase phosphatase-1 expression

We have previously found that hypoxia stimulates proliferation of vascular fibroblasts through Galphai-mediated activation of ERK1/2. Here, we demonstrate that hypoxia also activates the atypical protein kinase Czeta (PKCzeta) isozyme and stimulates the expression of ERK1/2-specific phosphatase, MAP kinase phosphatase-1 (MKP-1), which attenuates ERK1/2-mediated proliferative signals. Replication repressor activity is unique to PKCzeta because the blockade of classical and novel PKC isozymes does not affect fibroblast proliferation. PKCzeta is phosphorylated upon prolonged (24 h) exposure to hypoxia, whereas ERK1/2, the downstream kinases, are maximally activated in fibroblasts exposed to acute (10 min) hypoxia. However, PKCzeta blockade results in persistent ERK1/2 phosphorylation and marked increase in hypoxia-induced replication. Similarly prolonged ERK1/2 phosphorylation and increase in hypoxia-stimulated proliferation are also observed upon blockade of MKP-1 activation. Because of the parallel suppressive actions of PKCzeta and MKP-1 on ERK1/2 phosphorylation and proliferation, the role of PKCzeta in the regulation of MKP-1 expression was evaluated. PKCzeta attenuation reduces MKP-1 expression, whereas PKCzeta overexpression increases MKP-1 levels. In conclusion, our results indicate for the first time that hypoxia activates PKCzeta, which acts as a terminator of ERK1/2 activation through the regulation of downstream target, MKP-1 expression and thus serves to limit hypoxia-induced proliferation of fibroblasts.

DUAL SPECIFICITY PROTEIN PHOSPHATASES: Therapeutic Targets for Cancer and Alzheimer's Disease

The complete sequencing of the human genome is generating many novel targets for drug discovery. Understanding the pathophysiological roles of these putative targets and assessing their suitability for therapeutic intervention has become the major hurdle for drug discovery efforts. The dual-specificity phosphatases (DSPases), which dephosphorylate serine, threonine, and tyrosine residues in the same protein substrate, have important roles in multiple signaling pathways and appear to be deregulated in cancer and Alzheimer's disease. We examine the potential of DSPases as new molecular therapeutic targets for the treatment of human disease.

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.

Fer kinase sustains the activation level of ERK1/2 and increases the production of VEGF in hypoxic cells

Fer is a nuclear and cytoplasmic tyrosine kinase that is ubiquitously expressed in mammalian cells. Herein we show that Fer sustains a key signaling step in hypoxic cells. Knock-down of the Fer protein using a specific siRNA decreased the production of VEGF by the hypoxic cells. Conversely, ectopic expression of this kinase led to an elevated production of VEGF under hypoxia. At the molecular level, Fer was found to associate with ERK1/2 and this interaction was intensified under hypoxia. Moreover, Fer increased the activation levels of ERK1/2, and reducing the level of Fer, impaired the activation of ERK1/2 in hypoxic cells. Blocking the MEK-ERK1/2 signaling pathway with the MEK inhibitors U0126, or PD98059 led to the abrogation of ERK1/2 activity in hypoxic cells, an effect that was counteracted by Fer. Hence, Fer sustains the activation of ERK1/2 and increases the production of VEGF in hypoxic cells, without affecting the MEK-ERK signaling pathway.

Glucocorticoid receptor-induced MAPK phosphatase-1 (MPK-1) expression inhibits paclitaxel-associated MAPK activation and contributes to breast cancer cell survival

Glucocorticoid receptor (GR) activation has recently been shown to inhibit apoptosis in breast epithelial cells. We have previously described a group of genes that is rapidly up-regulated in these cells following dexamethasone (Dex) treatment. In an effort to dissect the mechanisms of GR-mediated breast epithelial cell survival, we now examine the molecular events downstream of GR activation. Here we show that GR activation leads to both the rapid induction of MAPK phosphatase-1 (MKP-1) mRNA and its sustained expression. Induction of the MKP-1 protein in the MCF10A-Myc and MDA-MB-231 breast epithelial cell lines was also seen. Paclitaxel treatment resulted in MAPK activation and apoptosis of MDA-MB-231 breast cancer cells, and both processes were inhibited by Dex pretreatment. Furthermore, induction of MKP-1 correlated with the inhibition of extracellular signal-regulated kinase (ERK1/2) and c-Jun N-terminal kinase (JNK) activity, whereas p38 activity was minimally affected. Blocking Dex-induced MKP-1 induction using small interfering RNA increased ERK1/2 and JNK phosphorylation and decreased cell survival. ERK1/2 and JNK inactivation was associated with Ets-like transcription factor-1 (ELK-1) dephosphorylation. To explore the gene expression changes that occur downstream of ELK-1 dephosphorylation, we used a combination of temporal gene expression data and promoter element analyses. This approach revealed a previously unrecognized transcriptional target of ELK-1, the human tissue plasminogen activator (tPA). We verified the predicted ELK-1--> tPA transcriptional regulatory relationship using a luciferase reporter assay. We conclude that GR-mediated MAPK inactivation contributes to cell survival and that the potential transcriptional targets of this inhibition can be identified from large scale gene array analysis.

Adenosine and glutamate extracellular concentrations and mitogen-activated protein kinases in the striatum of Huntington transgenic mice. Selective antagonism of adenosine A2A receptors reduces transmitter outflow

The basal ganglia and deep layers of cerebral cortex neurodegeneration typically characterize the postmortem brain of Huntington disease (HD) patients. In this study, we employed 10- to 11-week-old transgenic HD mice (R6/2 line), in which the striatal adenosine extracellular levels, measured using the microdialysis technique, are significantly increased in comparison to wild-type mice. An increase in striatal adenosine is probably a precocious index of mitochondrial dysfunction that is described in both the postmortem brain of HD patients and transgenic mice striatal cells. The adenosine increase is matched by activation of the p38 mitogen-activated protein kinase (MAPK) in the striatal neurons of R6/2 mouse but not in the cortex. This result indicates that p38 MAPK is a correlate of striatal damage and suggests a role for p38 in the striatal neuron suffering and apoptosis described in this disease. The selective adenosine A(2A) receptor antagonist SCH 58261, administered through microdialysis fiber into the striatum, significantly decreases the outflow of glutamate in R6/2 mice. Antagonism of adenosine A(2A) receptors might be regarded as potentially useful in the treatment of this disease to control striatal excitotoxicity.

The role of calcium in hypoxia-induced signal transduction and gene expression

Mammalian cells require a constant supply of oxygen in order to maintain adequate energy production, which is essential for maintaining normal function and for ensuring cell survival. Sustained hypoxia can result in cell death. Sophisticated mechanisms have therefore evolved which allow cells to respond and adapt to hypoxia. Specialized oxygen-sensing cells have the ability to detect changes in oxygen tension and transduce this signal into organ system functions that enhance the delivery of oxygen to tissue in a wide variety of different organisms. An increase in intracellular calcium levels is a primary response of many cell types to hypoxia/ischemia. The response to hypoxia is complex and involves the regulation of multiple signaling pathways and coordinated expression of perhaps hundreds of genes. This review discusses the role of calcium in hypoxia-induced regulation of signal transduction pathways and gene expression. An understanding of the molecular events initiated by changes in intracellular calcium will lead to the development of therapeutic approaches toward the treatment of hypoxic/ischemic diseases and tumors.

Role of CL-100, a dual specificity phosphatase, in thrombin-induced endothelial cell activation

Using a cDNA microarray screening approach, we have identified seven novel thrombin-responsive genes in human umbilical vein endothelial cells that were verifiable by Northern blot analysis. Among them CL-100, a dual-specificity phosphatase also known as MAP kinase phosphatase-1 (MKP-1), showed greatest induction by thrombin. Steady-state levels of CL-100 mRNA induction by thrombin peaked at 1 h and declined rapidly (t1/2 approximately 45 min). Induction by thrombin was protease-activated receptor-1-mediated, protein synthesis-independent, and transcriptionally regulated. Metabolic labeling followed by immunoprecipitation verified that the thrombin-induced CL-100 mRNA was translated into protein. We found that both Src-kinase and p42/p44 ERK activity are critical for thrombin-induced CL-100 expression, whereas phosphatidylinositol 3-kinase and protein kinase C activity were not required. Antisense-mediated inhibition of CL-100 was shown to prolong thrombin-induced ERK activity in endothelial cells, concomitant with an inhibition in thrombin-induced PDGF-A (platelet-derived growth factor A) and PDGF-B gene expression and an up-regulation in thrombin-induced VCAM-1 and E-selectin gene expression. Inhibition of ERK activation by PD98059 in endothelial cells was shown to potentiate thrombin-induced expression of PDGF-B (approximately 3-fold) while inhibiting thrombin-induced VCAM-1 and E-selectin gene expression by 60 and 70%, respectively. These results suggested that induced expression of the CL-100 phosphatase and its subsequent regulation of ERK activity play a key regulatory role in the thrombin signaling pathway and in the transcriptional regulation of pathologically important "endothelial cell activation genes."

Modulation of tumor-host interactions, angiogenesis, and tumor growth by tissue inhibitor of metalloproteinase 2 via a novel mechanism

Solid tumors depend on angiogenesis for sustained growth. Tissue inhibitor of metalloproteinase 2 (TIMP-2) is an angiogenesis inhibitor initially characterized for its ability to block matrix metalloproteinases; however, recent data suggest that the antiangiogenic action of TIMP-2 may rely on matrix metalloproteinase-independent mechanisms. The aim of this study was to identify molecular pathways involved in the effects of TIMP-2 on processes dependent on tumor-host interactions such as angiogenesis. Using in vitro cell culture and a syngeneic murine tumor model, we compared the effects of TIMP-2 overexpression on gene expression profiles in vitro to those observed in vivo. Validating these findings by real-time quantitative PCR and layered protein scanning, we identified up-regulation of mitogen-activated protein kinase phosphatase 1 as an effector of the antiangiogenic function of TIMP-2. Up-regulation of mitogen-activated protein kinase phosphatase 1 in tumors overexpressing TIMP-2 leads to dephosphorylation of p38 mitogen-activated protein kinase and inhibition of tumor growth and angiogenesis. Phosphatase activity appears important in regulating tumor angiogenesis, offering a promising direction for the identification of novel molecular targets and antiangiogenic compounds for the treatment of cancer.

Mechanisms regulating the recruitment of macrophages into hypoxic areas of tumors and other ischemic tissues

The mechanisms responsible for recruiting monocytes from the bloodstream into solid tumors are now well characterized. However, recent evidence has shown that these cells then differentiate into macrophages and accumulate in large numbers in avascular and necrotic areas where they are exposed to hypoxia. This parallels their tendency to congregate in ischemic areas of other diseased tissues such as atherosclerotic plaques and arthritic joints. In tumors, macrophages appear to undergo marked phenotypic changes when exposed to hypoxia and to switch on their expression of a number of mitogenic and proangiogenic cytokines and enzymes. This then promotes tumor growth, angiogenesis, and metastasis. Here, we compare the various mechanisms responsible for monocyte recruitment into tumors with those regulating the accumulation of macrophages in hypoxic/necrotic areas. Because the latter are best characterized in human tumors, we focus mainly on these but also discuss their relevance to macrophage migration in ischemic areas of other diseased tissues. Finally, we discuss the relevance of these mechanisms to the development of novel cancer therapies, both in providing targets to reduce the proangiogenic contribution made by hypoxic macrophages in tumors and in developing the use of macrophages to deliver therapeutic gene constructs to hypoxic areas of diseased tissues.

Protein-trap version 2.1: screening for expressed proteins in mammalian cells based on their localizations

Background

"Protein-trap" is a method that allows epitope-tagging of endogenous proteins. This method allows for the identification of endogenously expressed proteins that exhibit specific localization of interest. This method has been recently reported for its application in the study of Drosophila development by using a relatively large epitope, green-fluorescent-protein (GFP).

Result

Herein, we report a new "protein-trap" vector for mammalian cells. This new method utilizes a much smaller epitope-tag and also allows for drug-selection prior to the epitope-tagging. Pre-selection by drug resulted in the highly efficient protein-trapping frequency.

Conclusion

The "protein-trap" method based on this new vector is expected to serve as a complimentary approach to the previously reported GFP-based method.

Functional genomics approach to hypoxia signaling

Mammalian cells require a constant supply of oxygen to maintain energy balance, and sustained hypoxia can result in cell death. It is therefore not surprising that sophisticated adaptive mechanisms have evolved that enhance cell survival during hypoxia. During the past few years, there have been a growing number of reports on hypoxia-induced transcription of specific genes. In this review, we describe a unique experimental approach that utilizes focused cDNA libraries coupled to microarray analyses to identify hypoxia-responsive signal transduction pathways and genes that confer the hypoxia-tolerant phenotype. We have used the subtractive suppression hybridization (SSH) method to create a cDNA library enriched in hypoxia-regulated genes in oxygen-sensing pheochromocytoma cells and have used this library to create microarrays that allow us to examine hundreds of genes at a time. This library contains over 300 genes and expressed sequence tags upregulated by hypoxia, including tyrosine hydroxylase, vascular endothelial growth factor, and junB. Hypoxic regulation of these and other genes in the library has been confirmed by microarray, Northern blot, and real-time PCR analyses. Coupling focused SSH libraries with microarray analyses allows one to specifically study genes relevant to a phenotype of interest while reducing much of the biological noise associated with these types of studies. When used in conjunction with high-throughput, dye-based assays for cell survival and apoptosis, this approach offers a rapid method for discovering validated therapeutic targets for the treatment of cardiovascular disease, stroke, and tumors.

Suppression of the dual-specificity phosphatase MKP-1 enhances HIF-1 trans-activation and increases expression of EPO

Hypoxia-inducible factor 1 (HIF-1) is a phosphorylated protein and its phosphorylation is involved in HIF-1alpha subunit stabilization as well as in the regulation of HIF-1 transcriptional activity. In a variety of cell lines, the phosphorylation of HIF-1alpha is dependent on ERK or p38, two members of the mitogen-activated protein kinase (MAPK) superfamily. In addition, active MAPK could be inactivated through dephosphorylation by mitogen-activated protein kinase phosphatase-1 (MKP-1). MKP-1 has been identified as a hypoxia responsive gene, but its role in the response of cells to hypoxia is poorly understood. Here we found that hypoxia induces MKP-1 expression in human hepatoma cells HepG2 in a time-dependent manner. Inhibition of MKP-1 expression using siRNA technique could enhance HIF-1alpha phosphorylation, accompanied by an increase in transcriptionally active HIF-1 as well as a rise in the levels of HIF-1-induced erythropoietin expression.

The role of HIF-1 alpha in transcriptional regulation of the proximal tubular epithelial cell response to hypoxia

Epithelial cells of the kidney represent a primary target for hypoxic injury in ischemic acute renal failure (ARF); however, the underlying transcriptional mechanism(s) remain undefined. In this study, human proximal tubular epithelial cells (HK-2) exposed to hypoxia in vitro demonstrated a non-lethal but dysfunctional phenotype, closely reflective of the epithelial pathobiology of ARF. HK-2 cells exposed to hypoxia demonstrated increased paracellular permeability, decreased proliferation, loss of tight junctional integrity, and significant actin disassembly in the absence of cell death. Microarray analysis of transcriptomic changes underlying this response identified a distinct cohort of 48 genes with a closely shared hypoxia-dependent expression profile. Within this hypoxia-sensitive cluster were genes identified previously as hypoxia-inducible factor-1 (HIF-1)-dependent (e.g. vascular endothelial growth factor and adrenomedullin) as well as genes not previously known to be hypoxia-responsive (e.g. stanniocalcin 2). In hypoxia, HIF-1 bound to evolutionarily conserved hypoxia-response elements (HRE) in the promoters of these genes as well as to the HRE consensus motif. A further subset of these genes, not associated with transcriptional regulation by HIF-1, was also present, suggesting alternative HIF-1-independent pathways. Overexpression of HIF-1 alpha in normoxia induced the expression of a significant number of the hypoxia-dependent genes; however, it did not induce the pathophysiologic epithelial response. In summary, hypoxia-elicited alterations in renal proximal tubular epithelial cells in vitro closely resemble the epithelial pathophysiology of ARF. Our data indicate that although this event may rely heavily on HIF-1-dependent gene transcription, it is likely that separate hypoxia-dependent transcriptional regulators also play a role.

The use of suppression subtractive hybridization for the study of SDF-1α induced gene-expression in human endothelial cells

Stromal cell-derived factor-1 (SDF-1), the only ligand of the CXCR4 receptor, is mainly known as a chemotactic factor for hematopoietic progenitor cells. However, studies of knock-out mice have shown malformation of different organ-systems suggesting that SDF-1 may have a role in angiogenesis and cardiac and cerebral development. However, the underlying mechanisms of its action are largely unknown. Therefore, we performed suppression subtractive hybridization (SSH) in order to identify genes that are differentially expressed after stimulation of human arterial endothelial cells (HUAEC) with SDF-1. Using SSH we found ten genes, with varied functions, whose mRNA expression is induced by SDF-1alpha in HUAEC. We show that SSH is a reliable method for identifying differentially expressed genes and that SDF-1alpha may have more functions than previously reported.

Identification of tissue-specific genes in nasopharyngeal epithelial tissue and differentially expressed genes in nasopharyngeal carcinoma by suppression subtractive hybridization and cDNA microarray

Suppression subtractive hybridization (SSH) was performed for isolation of tissue-specific genes in nasopharyngeal epithelial tissue, by use of cDNAs from human adult nasopharyngeal epithelial tissue as tester and mixed cDNAs from esophagus, lung, liver, heart, stomach, spleen, skeletal muscle, kidney, and skin as drivers. Fourteen differentially expressed genes in nasopharyngeal epithelial tissue were obtained. Among these genes, LPLUNC1 and SPLUNC1 were confirmed to be specifically expressed in nasopharyngeal epithelial tissue and the trachea. A novel transcript of SPLUNC1, which we designate NASG, was found. We also combined SSH and cDNA microarray hybridization to identify genes whose expressions were altered in nasopharyngeal carcinoma (NPC). We used NPC cell line HNE1 and primary human embryo nasopharyngeal epithelial cells in one SSH experiment, and NPC biopsies and normal adult nasopharyngeal epithelial tissue in another. Some 1,200 SSH inserts from four subtractive cDNA libraries were arrayed onto nylon membranes by use of robotic printing. Differential gene expression was verified by hybridizing of the membranes with radioactively labeled first-strand cDNA from NPC cell line HNE1, primary human embryo nasopharyngeal epithelial cells, NPC biopsies, and normal adult nasopharyngeal epithelial tissue. Seventeen differentially expressed genes in NPC were obtained. Among these genes, we identified SPLUNC1 and LPLUNC1 to be down-expressed in NPC biopsies (34/48, 33/48).

Profile of gene expression induced by the tumour promotor TPA in murine epithelial cells

Malignant transformation of mouse skin by chemical carcinogens and tumour promoters, such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), is a multistage process that leads to squamous cell carcinoma (SCC) formation. In an effort to identify tumour-associated genes, we studied the influence of short-term TPA-treatment on the gene expression profile of murine skin. A comprehensive microarray with some 5,000 murine gene specific cDNA fragments was established and hybridised with pooled RNA derived from control and TPA-treated dorsal skin samples. Of these genes, 54 were up- and 35 were down-regulated upon TPA application. Additionally, we performed suppression subtractive hybridisation (SSH) with respective RNA pools to generate and analyse a cDNA library enriched for TPA-inducible genes. Expression data of selected genes were confirmed by quantitative real-time PCR and Northern blot analysis. Comparison of microarray and SSH data revealed that 26% of up-regulated genes identified by expression profiling matched with those present in the SSH library. Besides numerous known genes, we identified a large set of unknown cDNAs that represent previously unrecognised TPA-regulated genes in murine skin with potential function in tumour promotion. Additionally, some TPA-induced genes, such as Sprr1A, Saa3, JunB, Il4ralpha, Gp38, RalGDS and Slpi exhibit high basal level in advanced stages of skin carcinogenesis, suggesting that at least a subgroup of the identified TPA-regulated genes may contribute to tumour progression and metastasis.

Comprehensive analysis of gene expression in rat and human hepatoma cells exposed to the peroxisome proliferator WY14,643

Peroxisome proliferators (PPs) are an important class of chemicals that act as hepatic tumor promoters in laboratory rodents. The key target for PPs is the nuclear receptor peroxisome proliferator-activated receptor-alpha (PPARalpha) and these chemicals cause cancer by altering the expression of a subset of genes involved in cell growth regulation. The purpose of the present study was to utilize high-density gene expression arrays to examine the genes regulated by the potent PP Wy14,643 (50 microM, 6 h) in both rat (FaO) and human (HepG2) hepatoma cells. Treatment of FaO cells, but not HepG2, revealed the expected fatty acid catabolism genes. However, a larger than expected number of protein kinases, phosphatases, and signaling molecules were also affected exclusively in the FaO cells, including MAPK-phosphatase 1 (MKP-1), Janus-activated kinases 1 and 2 (JAK1 and 2), and glycogen synthetase kinase alpha and beta (GSKalpha and beta). The mRNA accumulation of these genes as well as the protein level for GSK3alpha, JAK1, and JAK2 and MKP-1 activity was corroborated. Due to the importance of MKP-1 in cell signaling, this induction was examined further and was found to be controlled, at least in part, at the level of the gene's promoter. Interestingly, overexpression of MKP-1 in turn affected the constitutive activity of PPARalpha. Taken together, the gene expression arrays revealed an important subset of PP-regulated genes to be kinases and phosphatases. These enzymes not only would affect growth factor signaling and cell cycle control but also could represent feedback control mechanisms and modulate the activity of PPARalpha.

Effect of hypoxia on gene expression by human hepatocytes (HepG2)

The full extent to which hypoxia produces gene expression changes in human cells is unknown. We used late-generation oligonucleotide arrays to catalog hypoxia-induced changes in gene expression in HepG2 cells. Five paired sets of cultures were subjected to either control (room air-5% CO(2)) or hypoxic (1% O(2)-5% CO(2)) conditions for 24 h, and RNA was analyzed on an Affymetrix cDNA array containing approximately 12,600 sequences. A statistically significant change in expression was shown by 2,908 sequences (1,255 increased and 1,653 decreased). The observed changes were highly concordant with published literature on hypoxic stress but showed relatively little overlap (12-22%) with changes in gene expression that have been reported to occur after heat stress in other systems. Of note, of these 2,908 sequences, only 387 (213 increased and 174 decreased) both exhibited changes in expression of twofold or greater and were highly expressed in at least three of the five experiments. We conclude that the effect of hypoxia on gene expression by HepG2 cells is broad, has a significant component of downregulation, and includes a relatively small number of genes whose response is truly independent of cell and stress type.