Hypoxic regulation of vascular endothelial growth factor mRNA stability requires the cooperation of multiple RNA elements

Cathepsin L expression is up-regulated by hypoxia in human melanoma cells: role of its 5'-untranslated region

Overexpression of cathepsin L, a cysteine protease, and consequently procathepsin L secretion switch the phenotype of human melanoma cells to highly tumorigenic and strongly metastatic. This led us to identify the DNA regulatory sequences involved in the regulation of cathepsin L expression in highly metastatic human melanoma cells. The results of the present study demonstrated the presence of regulatory sequences in the 3' region downstream of the cathepsin L gene and in the 3'- and 5'-flanking regions of GC/CCAAT sites of its promoter. In addition, we established that the 5'-UTR (untranslated region) was the most important region for cathepsin L expression. This 5'-UTR integrated an alternative promoter and sequences involved in post-transcriptional regulation. Transfection experiments of bicistronic reporter vectors and RNAs demonstrated that the cathepsin L 5'-UTR contained a functional IRES (internal ribosome entry site). This complete IRES was present only in one of the three splice variants, which differed in their 5'-UTR. Then, we analysed cathepsin L expression in this human melanoma cell line grown under hypoxia. We demonstrated that under moderate hypoxic conditions (1% O2) intracellular expression of cathepsin L was up-regulated. Hypoxia significantly increased only the expression of the transcript which contains the complete IRES, but inhibited promoter activity. These results suggest that the presence of an IRES allowed cathepsin L mRNA translation to be efficient under hypoxic conditions. Altogether, our results indicated that in vivo a tumour hypoxic environment up-regulates cathepsin L expression which promotes tumour progression.

An upstream open reading frame within an IRES controls expression of a specific VEGF-A isoform

Vascular endothelial growth factor A (VEGF-A) is a potent secreted mitogen critical for physiological and pathological angiogenesis. Regulation of VEGF-A occurs at multiple levels, including transcription, mRNA stabilization, splicing, translation and differential cellular localization of various isoforms. Recent advances in our understanding of the posttranscriptional regulation of VEGF-A are comprised of the identification of stabilizing mRNA-binding proteins and the discovery of two internal ribosomal entry sites (IRES) as well as two alternative initiation codons in the 5′UTR of the VEGF-A mRNA. We have previously reported that VEGF-A translation initiation at both the AUG and CUG codons is dependent on the exon content of the coding region. In this report, we show that the expression of different VEGF-A isoforms is regulated by a small upstream open reading frame (uORF) located within an internal ribosome entry site, which is translated through a cap-independent mechanism. This uORF acts as a cis-regulatory element that regulates negatively the expression of the VEGF 121 isoform. Our data provide a framework for understanding how VEGF-A mRNAs are translated, and how the production of the VEGF 121 isoform is secured under non-hypoxic environmental conditions.

Inhibitory effect of electrolyzed reduced water on tumor angiogenesis

Vascular endothelial growth factor (VEGF) is a key mediator of tumor angiogenesis. Tumor cells are exposed to higher oxidative stress compared to normal cells. Numerous reports have demonstrated that the intracellular redox (oxidation/reduction) state is closely associated with the pattern of VEGF expression. Electrolyzed reduced water (ERW) produced near the cathode during the electrolysis of water scavenged intracellular H(2)O(2) and decreased the release of H(2)O(2) from a human lung adenocarcinoma cell line, A549, and down-regulated both VEGF transcription and protein secretion in a time-dependent manner. To investigate the signal transduction pathway involved in regulating VEGF expression, mitogen-activated kinase (MAPK) specific inhibitors, SB203580 (p38 MAPK inhibitor), PD98059 (ERK1/2 inhibitor) and JNKi (c-Jun N-terminal protein kinase inhibitor) were applied. The results showed that only PD98059 blocks VEGF expression, suggesting an important role for ERK1/2 in regulating VEGF expression in A549 cells. As well, ERW inhibited the activation of extracellular signal-regulated kinase (ERK) in a time-dependent manner. Co-culture experiments to analyze in vitro tubule formation assay revealed that A549 cell-derived conditioned medium significantly stimulated the formation of vascular tubules in all analyzed parameters; tubule total area, tubule junction, number of tubules, and total tubule length. ERW counteracted the effect of A549 cell-conditioned medium and decreased total tube length (p<0.01). The present study demonstrated that ERW down-regulated VEGF gene transcription and protein secretion through inactivation of ERK.

Mechanisms of radiation-induced brain toxicity and implications for future clinical trials

Radiation therapy is widely used in the treatment of primary malignant brain tumors and metastatic tumors of the brain with either curative or palliative intent. The limitation of cancer radiation therapy does not derive from the inability to ablate tumor, but rather to do so without excessively damaging the patient. Among the varieties of radiation-induced brain toxicities, it is the late delayed effects that lead to severe and irreversible neurological consequences. Following radiation exposure, late delayed effects within the CNS have been attributable to both parenchymal and vascular damage involving oligodendrocytes, neural progenitors, and endothelial cells. These reflect a dynamic process involving radiation-induced death of target cells and subsequent secondary reactive neuroinflammatory processes that are believed to lead to selective cell loss, tissue damage, and functional deficits. The progressive, late delayed damage to the brain after high-dose radiation is thought to be caused by radiation-induced long-lived free radicals, reactive oxygen species, and pro-inflammatory cytokines. Experimental studies suggest that radiation-induced brain injury can be successfully mitigated and treated with several well established drugs in wide clinical use which exert their effects by blocking pro-inflammatory cytokines and reactive oxygen species. This review highlights preclinical and early clinical data that are translatable for future clinical trials.

The 3' untranslated region of human Cyclin-Dependent Kinase 5 Regulatory subunit 1 contains regulatory elements affecting transcript stability

BACKGROUND

CDK5R1 plays a central role in neuronal migration and differentiation during central nervous system development. CDK5R1 has been implicated in neurodegenerative disorders and proposed as a candidate gene for mental retardation. The remarkable size of CDK5R1 3'-untranslated region (3'-UTR) suggests a role in post-transcriptional regulation of CDK5R1 expression.

RESULTS

The bioinformatic study shows a high conservation degree in mammals and predicts several AU-Rich Elements (AREs). The insertion of CDK5R1 3'-UTR into luciferase 3'-UTR causes a decreased luciferase activity in four transfected cell lines. We identified 3'-UTR subregions which tend to reduce the reporter gene expression, sometimes in a cell line-dependent manner. In most cases the quantitative analysis of luciferase mRNA suggests that CDK5R1 3'-UTR affects mRNA stability. A region, leading to a very strong mRNA destabilization, showed a significantly low half-life, indicating an accelerated mRNA degradation. The 3' end of the transcript, containing a class I ARE, specifically displays a stabilizing effect in neuroblastoma cell lines. We also observed the interaction of the stabilizing neuronal RNA-binding proteins ELAV with the CDK5R1 transcript in SH-SY5Y cells and identified three 3'-UTR sub-regions showing affinity for ELAV proteins.

CONCLUSION

Our findings evince the presence of both destabilizing and stabilizing regulatory elements in CDK5R1 3'-UTR and support the hypothesis that CDK5R1 gene expression is post-transcriptionally controlled in neurons by ELAV-mediated mechanisms. This is the first evidence of the involvement of 3'-UTR in the modulation of CDK5R1 expression. The fine tuning of CDK5R1 expression by 3'-UTR may have a role in central nervous system development and functioning, with potential implications in neurodegenerative and cognitive disorders.

Double-stranded RNA-binding protein regulates vascular endothelial growth factor mRNA stability, translation, and breast cancer angiogenesis

Vascular endothelial growth factor (VEGF) is a key angiogenic factor expressed under restricted nutrient and oxygen conditions in most solid tumors. The expression of VEGF under hypoxic conditions requires transcription through activated hypoxia-inducible factor 1 (HIF-1), increased mRNA stability, and facilitated translation. This study identified double-stranded RNA-binding protein 76/NF90 (DRBP76/NF90), a specific isoform of the DRBP family, as a VEGF mRNA-binding protein which plays a key role in VEGF mRNA stability and protein synthesis under hypoxia. The DRBP76/NF90 protein binds to a human VEGF 3' untranslated mRNA stability element. RNA interference targeting the DRBP76/NF90 isoform limited hypoxia-inducible VEGF mRNA and protein expression with no change in HIF-1-dependent transcriptional activity. Stable repression of DRBP76/NF90 in MDA-MB-435 breast cancer cells demonstrated reduced polysome-associated VEGF mRNA levels under hypoxic conditions and reduced mRNA stability. Transient overexpression of the DRBP76/NF90 protein increased both VEGF mRNA and protein levels synthesized under normoxic and hypoxic conditions. Cells with stable repression of the DRBP76/NF90 isoform showed reduced tumorigenic and angiogenic potential in an orthotopic breast tumor model. These data demonstrate that the DRBP76/NF90 isoform facilitates VEGF expression by promoting VEGF mRNA loading onto polysomes and translation under hypoxic conditions, thus promoting breast cancer growth and angiogenesis in vivo.

VEGF: an essential mediator of both angiogenesis and endochondral ossification

During bone growth, development, and remodeling, angiogenesis as well as osteogenesis are closely associated processes, sharing some essential mediators. Vascular endothelial growth factor (VEGF) was initially recognized as the best-characterized endothelial-specific growth factor, which increased vascular permeability and angiogenesis, and it is now apparent that this cytokine regulates multiple biological functions in the endochondral ossification of mandibular condylar growth, as well as long bone formation. The complexity of VEGF biology is paralleled by the emerging complexity of interactions between VEGF ligands and their receptors. This narrative review summarizes the family of VEGF-related molecules, including 7 mammalian members, namely, VEGF, placenta growth factor (PLGF), and VEGF-B, -C, -D, -E, and -F. The biological functions of VEGF are mediated by at least 3 corresponding receptors: VEGFR-1/Flt-1, VEGFR-2/Flk-1, VEGFR-3/Flt-4 and 2 co-receptors of neuropilin (NRP) and heparan sulfate proteoglycans (HSPGs). Current findings on endochondral ossification are also discussed, with emphasis on VEGF-A action in osteoblasts, chondroblasts, and chondroclasts/osteoclasts and regulatory mechanisms involving oxygen tension, and some growth factors and hormones. Furthermore, the therapeutic implications of recombinant VEGF-A protein therapy and VEGF-A gene therapy are evaluated. Abbreviations used: VEGF, Vascular endothelial growth factor; PLGF, placenta growth factor; NRP, neuropilin; HSPGs, heparan sulfate proteoglycans; FGF, fibroblast growth factor; TGF, transforming growth factor; HGF, hepatocyte growth factor; TNF, tumor necrosis factor; ECM, extracellular matrix; RTKs, receptor tyrosine kinases; ERK, extracellular signal kinases; HIF, hypoxia-inducible factor.

Bevacizumab in non small cell lung cancer

Angiogenesis, the growth of new vessels from preexisting vessels, is a fundamental step in tumor growth and progression. Vascular endothelial growth factor (VEGF) is a key angiogenic factor implicated in tumor blood vessel formation and permeability. Overexpression of VEGF has been observed in a variety of cancers and has been associated with a worse relapse-free and overall survival. The antiangiogenic agent bevacizumab, a monoclonal antibody directed against VEGF, has shown clinical benefit in multiple cancers, including non-small cell lung cancer (NSCLC). Based on the favorable results of a prior randomized, phase II trial, the Eastern Cooperative Oncology Group conducted a trial (E4599) to evaluate the efficacy of bevacizumab in combination with paclitaxel and carboplatin in patients with recurrent or advanced stage IIIB or IV nonsquamous cell NSCLC. Exclusion criteria included squamous cell histology, brain metastases, significant hemoptysis, or inadequate organ function or performance status >1. The primary study end point was overall survival. The median duration of survival in the chemotherapy plus bevacizumab group was 12.3 months compared with 10.3 months in the chemotherapy alone group (P = 0.003). Significant bleeding was more frequent in the chemotherapy plus bevacizumab group, 4.4% compared with 0.9% (P = 0.001). There were 15 treatment-related deaths in the chemotherapy plus bevacizumab group, including 5 due to pulmonary hemorrhage. Future and current directions include evaluation of bevacizumab in earlier stages of NSCLC, in SCLC, and in combination with other targeted agents, such as erlotinib.

Cardiac metabolic adaptations in response to chronic hypoxia

Since a constant supply of oxygen is essential to sustain life, organisms have evolved multiple defence mechanisms to ensure maintenance of the delicate balance between oxygen supply and demand. However, this homeostatic balance is perturbed in response to a severe impairment of oxygen supply, thereby activating maladaptive signalling cascades that result in cardiac damage. Past research efforts have largely focused on determining the pathophysiological effects of severe lack of oxygen. By contrast, and as reviewed here, exposure to moderate chronic hypoxia may induce cardioprotective properties. The hypothesis put forward is that chronic hypoxia triggers regulatory pathways that mediate long-term cardiac metabolic remodelling, particularly at the transcriptional level. The novel proposal is that exposure to chronic hypoxia triggers (a) oxygen-sensitive transcriptional modulators that induce a switch to increased carbohydrate metabolism (fetal gene programme) and (b) enhanced mitochondrial respiratory capacity to sustain and increase efficiency of mitochondrial energy production. These compensatory protective mechanisms preserve contractile function despite hypoxia.

Chemotherapy and Antiangiogenic Agents in Non-Small-Cell Lung Cancer

Angiogenesis, the growth of new vessels from preexisting vessels, is a fundamental step in tumor growth and progression. Tumor-related angiogenesis has become an attractive target for anticancer therapy. Vascular endothelial growth factor (VEGF) is a key angiogenic factor implicated in tumor blood vessel formation and permeability. Overexpression of VEGF has been observed in a variety of cancers and has been associated with a worse relapse-free and overall survival. A large randomized trial recently demonstrated an improvement in overall survival when bevacizumab, a humanized monoclonal antibody against VEGF, was combined with chemotherapy in patients with advanced non-small-cell lung cancer. Small molecule inhibitors targeting the VEGF receptor and the tyrosine kinase receptor have also shown promise when combined with standard chemotherapeutic agents in patients with advanced non-small-cell lung cancer. There is emerging evidence that inhibition of a single target leads to upregulation of other angiogenic signaling cascades. Future directions will include the use of these agents in combination with one another as well as in combination with chemotherapy and radiation therapy in patients with early-stage (IA-IIIB) disease.

Facultative or obligate anaerobic bacteria have the potential for multimodality therapy of solid tumours

Recent understanding of the unique pathology of solid tumours has shed light on the difficult and disappointing nature of their clinical treatment. All solid tumours undergo angiogenesis that results in biological changes and adaptive metabolisms, i.e. formation of defective vessels, appearance of hypoxic areas, and emergence of an heterogeneous tumour cell population. This micro-milieu provides a haven for anaerobic bacteria. The strictly anaerobic clostridia have several advantages over other facultative anaerobes such as salmonella or lactic acid-producing, Gram-positive, obligate, anaerobic bifidobacteria. Both pathogenic and non-pathogenic clostridia have been demonstrated to specifically colonise and destroy solid tumours. Early trials of non-pathogenic strains in humans had shown plausible safety. Genetic modifications and adaptation of pathogenic and non-pathogenic strains have further created improved features. However, these manipulations rarely generate strains that resulted in complete tumour control alone. Combined modalities of therapies with chemo and radiation therapies, on the other hand, often perform better, including 'cure' of solid tumours in a high percentage of animals. Considering that clostridia have unlimited capacities for genetic improvement, we predict that designer clostridia forecast a promising future for the development of potent strains for tumour destruction, incorporating mechanisms such as immunotherapy to overcome immune suppression and to elicit strong anti-tumour responses.

Interaction between stromal fibroblasts and colorectal cancer cells in the expression of vascular endothelial growth factor

BACKGROUND

Vascular endothelial growth factor (VEGF), a potent angiogenic factor, has been implicated in metastasis of colorectal cancer (CRC). The present study aimed to clarify whether cancer-stromal interaction induces the production of VEGF.

MATERIALS AND METHODS

Human colonic fibroblasts (CCD-18Co) and CRC (SW480, SW620) cells were analyzed in this study. The cell cycle of colonic fibroblasts during co-culture was analyzed by flow cytometry. VEGF and TGF-beta1 released into the conditioned media in co-culture models were measured. Northern blot with human specific VEGF probe was performed to identify the expression of VEGF in this model.

RESULTS

Co-culture of colonic fibroblasts with CRC cells increased the viability of fibroblasts during co-culture. Cell cycle analysis revealed that most of the fibroblasts co-cultured with CRC cells were arrested at G1 phase and few cells were in sub-G1 phase that indicates apoptosis. Although VEGF protein was detected in the culture media of all of the monocultures, co-cultivation of CRC with fibroblasts resulted in synergistic increase of VEGF production compared with monocultures. However TGF-beta1 protein was not detected in any conditioned medium. VEGF mRNA was detected in both CRC and fibroblasts. Under co-culture condition, an abundance of VEGF mRNA expression was noted in fibroblasts relative to CRC cells.

CONCLUSIONS

The present study suggests that CRC manipulates the host stroma to suppress apoptosis and up-regulate VEGF production.

The exon 6ABC region of amelogenin mRNA contribute to increased levels of amelogenin mRNA through amelogenin protein-enhanced mRNA stabilization

We recently demonstrated that the reuptake of full-length amelogenin protein results in increased levels of amelogenin mRNA through enhanced mRNA stabilization (Xu, L., Harada, H., Tamaki, T. Y., Matsumoto, S., Tanaka, J., and Taniguchi, A. (2006) J. Biol. Chem. 281, 2257-2262). Here, we examined the molecular mechanism of enhanced amelogenin mRNA stabilization. To identify the cis-regulatory region within amelogenin mRNA, we tested various reporter systems using a deletion series of reporter plasmids. A deletion at exon 6ABC of amelogenin mRNA resulted in a 2.5-fold increase in the amelogenin mRNA expression level when compared with that of full-length mRNA, indicating that a cis-element exists in exon 6ABC of amelogenin mRNA. Furthermore, Northwestern analysis demonstrated that amelogenin protein binds directly to its mRNA in vitro, suggesting that amelogenin protein acts as a trans-acting protein that specifically binds to this cis-element. Moreover, recombinant mouse amelogenin protein extended the half-life of full-length amelogenin mRNA but did not significantly alter the half-life of exon 6ABC-deletion mutant mRNA. The splice products produced by deletion of exon 6ABC are known as leucine-rich amelogenin peptides and have signaling effects on cells. Our findings also suggest that the regulation of full-length amelogenin protein expression differs from the regulation of leucine-rich amelogenin peptide expression.

Loss of hepatic NF-kappa B activity enhances chemical hepatocarcinogenesis through sustained c-Jun N-terminal kinase 1 activation

A major link between inflammation and cancer is provided by NF-kappaB transcription factors. Ikkbeta(Deltahep) mice, which specifically lack IkappaB kinase beta (IKKbeta), an activator of NF-kappaB, in hepatocytes, are unable to activate NF-kappaB in response to proinflammatory stimuli, such as TNF-alpha. Surprisingly, Ikkbeta(Deltahep) mice are hypersusceptible to diethylnitrosamine (DEN)-induced hepatocarcinogenesis. Because defective NF-kappaB activation promotes sustained c-Jun N-terminal kinase (JNK) activation in cells exposed to TNF-alpha, whose expression is induced by DEN, and JNK activity is required for normal hepatocyte proliferation, we examined whether increased susceptibility to DEN-induced hepatocarcinogenesis in Ikkbeta(Deltahep) mice requires JNK activation. Hepatocytes express both JNK1 and JNK2, but previous studies indicate that JNK1 is more important for hepatocyte proliferation. We therefore investigated this hypothesis using mice homozygous for a JNK1 deficiency either in wild-type or Ikkbeta(Deltahep) backgrounds. In both cases, mice lacking JNK1 were much less susceptible to DEN-induced hepatocarcinogenesis. This impaired tumorigenesis correlated with decreased expression of cyclin D and vascular endothelial growth factor, diminished cell proliferation, and reduced tumor neovascularization. Whereas hepatocyte-specific deletion of IKKbeta augmented DEN-induced hepatocyte death and cytokine-driven compensatory proliferation, disruption of JNK1 abrogated this response. In addition to underscoring the importance of JNK1-mediated hepatocyte death and compensatory proliferation, these results strongly suggest that the control of tissue renewal through the IKK and JNK pathways plays a key role in liver carcinogenesis.

OSI-930: A Novel Selective Inhibitor of Kit and Kinase Insert Domain Receptor Tyrosine Kinases with Antitumor Activity in Mouse Xenograft Models

OSI-930 is a novel inhibitor of the receptor tyrosine kinases Kit and kinase insert domain receptor (KDR), which is currently being evaluated in clinical studies. OSI-930 selectively inhibits Kit and KDR with similar potency in intact cells and also inhibits these targets in vivo following oral dosing. We have investigated the relationships between the potency observed in cell-based assays in vitro, the plasma exposure levels achieved following oral dosing, the time course of target inhibition in vivo, and antitumor activity of OSI-930 in tumor xenograft models. In the mutant Kit-expressing HMC-1 xenograft model, prolonged inhibition of Kit was achieved at oral doses between 10 and 50 mg/kg and this dose range was associated with antitumor activity. Similarly, prolonged inhibition of wild-type Kit in the NCI-H526 xenograft model was observed at oral doses of 100 to 200 mg/kg, which was the dose level associated with significant antitumor activity in this model as well as in the majority of other xenograft models tested. The data suggest that antitumor activity of OSI-930 in mouse xenograft models is observed at dose levels that maintain a significant level of inhibition of the molecular targets of OSI-930 for a prolonged period. Furthermore, pharmacokinetic evaluation of the plasma exposure levels of OSI-930 at these effective dose levels provides an estimate of the target plasma concentrations that may be required to achieve prolonged inhibition of Kit and KDR in humans and which would therefore be expected to yield a therapeutic benefit in future clinical evaluations of OSI-930.

Posttranscriptional mechanisms regulating the inflammatory response

The inflammatory response is a complex physiologic process that requires the coordinate induction of cytokines, chemokines, angiogenic factors, effector-enzymes, and proteases. Although transcriptional activation is required to turn on the inflammatory response, recent studies have revealed that posttranscriptional mechanisms play an important role by determining the rate at which mRNAs encoding inflammatory effector proteins are translated and degraded. Most posttranscriptional control mechanisms function to dampen the expression of pro-inflammatory proteins to ensure that potentially injurious proteins are not overexpressed during an inflammatory response. Here we discuss the factors that regulate the stability and translation of mRNAs encoding pro-inflammatory proteins.

Corticotropin-releasing hormone induces vascular endothelial growth factor release from human mast cells via the cAMP/protein kinase A/p38 mitogen-activated protein kinase pathway

Mast cells are involved in allergic reactions but also in innate immunity and inflammation. Corticotropin-releasing hormone (CRH), the key regulator of the hypothalamic-pituitary-adrenal axis, also has proinflammatory effects, apparently through mast cells. We showed recently that CRH selectively stimulates human leukemic mast cells and human umbilical cord blood-derived mast cells to release newly synthesized vascular endothelial growth factor (VEGF) without release of either preformed mediators or cytokines. This effect was mediated through the activation of CRH receptor-1 and adenylate cyclase with increased intracellular cAMP. However, the precise mechanism by which CRH induces VEGF secretion has not yet been defined. Here, we show that CRH-induced VEGF release was dose-dependently inhibited by the specific protein kinase A inhibitor N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89) or the p38 mitogen-activated protein kinase (MAPK) inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580) but not by the specific inhibitor 2'-amino-3'-methoxyflavone (PD98059) of mitogen-activated protein kinase kinase, the upstream kinase of the extracellular signal-regulated protein kinase (ERK) or the c-Jun N-terminal kinase (JNK) inhibitor 1,9-pyrazoloanthrone anthra-(1,9-cd)pyrazol-6(2H)-one (SP600125). Furthermore, CRH significantly increased protein kinase A activity, which could be mimicked by the cell-permeable cAMP analog 8-bromo-cAMP, and was blocked by H89 or the adenylate cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ22536). CRH also induced rapid phosphorylation of p38 MAPK, which was mimicked by 8-bromo-cAMP and was inhibited by H89 or SB203580. CRH did not stimulate ERK or JNK phosphorylation and did not increase intracellular calcium levels. These results indicate that CRH induces VEGF release in human mast cells via selective activation of the cAMP/protein kinase A/p38 MAPK signaling pathway, thereby providing further insight into the molecular mechanism of how CRH affects the release of a key proinflammatory mediator.

Cellular response to tissue hypoxia and its involvement in disease progression

Multicellular organisms show adaptive reactions for their survival when they are exposed to an atmosphere with reduced oxygen concentration. These reactions include increase in respiratory volume, switch from aerobic to anaerobic metabolism, erythropoiesis and angiogenesis. For these reactions, cells must change the expression of several hypoxia-responsive molecules such as erythropoietin and vascular endothelial growth factor. Hypoxia-responsible element (HRE) was delineated in the genes of hypoxia-responsive molecules as the sequence indispensable for their hypoxia-induced transcriptional activation, and hypoxia-inducible factor 1 (HIF-1) was identified as a transcriptional factor that binds to HRE and regulates the expression of various hypoxia-responsive molecules. Increasing evidence has revealed that HIF-1 is a key molecule regulating the cellular response to tissue hypoxia. HIF-1 is composed of two subunits, HIF-1alpha and HIF-1beta, and HIF-1 activity depends mainly on the intracellular level of HIF-1alpha protein, which is regulated to be in inverse relation to the oxygen concentration by an oxygen-dependent enzyme, prolyl hydroxylase 2 (PHD2). Thus, cells respond to tissue hypoxia by sensing the oxygen concentration as the enzyme activity of PHD2, regulating the HIF-1 activity and consequently changing the expression of various hypoxia-responsive molecules. Cellular response controlled by hypoxia-HIF-1 cascade is also involved in pathological situations such as solid tumor growth, diabetic retinopathy and rheumatoid arthritis. Under these pathological situations, the activation of hypoxia-HIF-1 cascade often leads to the acceleration of disease progression. Understanding an aspect of disease progression triggered by tissue hypoxia might provide a clue to new therapeutic strategies for intractable diseases.

Gene codon composition determines differentiation-dependent expression of a viral capsid gene in keratinocytes in vitro and in vivo

By establishing mouse primary keratinocytes (KCs) in culture, we were able, for the first time, to express papillomavirus major capsid (L1) proteins by transient transfection of authentic or codon-modified L1 gene expression plasmids. We demonstrate in vitro and in vivo that gene codon composition is in part responsible for differentiation-dependent expression of L1 protein in KCs. L1 mRNA was present in similar amounts in differentiated and undifferentiated KCs transfected with authentic or codon-modified L1 genes and had a similar half-life, demonstrating that L1 protein production is posttranscriptionally regulated. We demonstrate further that KCs substantially change their tRNA profiles upon differentiation. Aminoacyl-tRNAs from differentiated KCs but not undifferentiated KCs enhanced the translation of authentic L1 mRNA, suggesting that differentiation-associated change to tRNA profiles enhances L1 expression in differentiated KCs. Thus, our data reveal a novel mechanism for regulation of gene expression utilized by a virus to direct viral capsid protein expression to the site of virion assembly in mature KCs. Analysis of two structural proteins of KCs, involucrin and keratin 14, suggests that translation of their mRNAs is also regulated, in association with KC differentiation in vitro, by a similar mechanism.

A reassessment of vascular endothelial growth factor in central nervous system pathology

✓ Overexpression of vascular endothelial growth factor (VEGF) is associated with several central nervous system (CNS) diseases and abnormalities, and is often postulated as a causative factor and promising therapeutic target in these settings. The authors' goal was to reassess the contribution of VEGF to the biology and pathology of the CNS.

The authors review the literature relating to the following aspects of VEGF: 1) the biology of VEGF in normal brain; 2) the involvement of VEGF in CNS disorders other than tumors (traumatic and ischemic injuries, arteriovenous malformations, inflammation); and 3) the role of VEGF in brain tumor biology (gliomas and the associated vasogenic edema, and hemangioblastomas).

The authors conclude the following: first, that VEGF overexpression contributes to the phenotype associated with many CNS disorders, but VEGF is a reactive rather than a causative factor in many cases; and second, that use of VEGF as a therapeutic agent or target is complicated by the effects of VEGF not only on the cerebral vasculature, but also on astrocytes, neurons, and inflammatory cells. In many cases, therapeutic interventions targeting the VEGF/VEGF receptor axis are likely to be ineffective or even detrimental. Clinical manipulation of VEGF levels in the CNS must be approached with caution.

Role of elongin-binding domain of von hippel lindau gene product on HuR-mediated VPF/VEGF mRNA stability in renal cell carcinoma

Vascular endothelial growth factor (VEGF), also known as vascular permeability factor (VPF), is a key mediator of angiogenesis for both physiological and pathological conditions. It is well established that the hypoxic induction of VPF/VEGF is in large part an increase in the stability of its mRNA. A Hu family ubiquitously expressed RNA-binding protein HuR has recently been shown to be important for VPF/VEGF mRNA stabilization. In renal cancer cells, the inactivation of the tumor suppressor protein von Hippel Lindau (VHL) leads to an increase in VPF/VEGF expression. VHL not only inhibits the transcription of VPF/VEGF but also plays a significant role in decreasing its mRNA stability. Here we delineate a possible mechanism by which VHL can control the function of HuR in order to regulate the stability of VPF/VEGF mRNA. The experiments presented here suggest that the association of the elongin-binding domain of VHL with a specific RNA-binding domain of HuR (RRM1) is important for the destabilizing function of VHL on VPF/VEGF mRNA.

The effects of ZD6474, an inhibitor of VEGF signaling, on cutaneous wound healing in mice

BACKGROUND

ZD6474 is an inhibitor of the VEGFR-2 receptor tyrosine kinase with additional activity against EGFR-1 receptor tyrosine kinases that has been shown to inhibit tumor growth and wound-induced neovascularization in pre-clinical studies and phase I clinical trials. The purpose of this study was to determine the effects of ZD6474 on breaking strength in a murine model of cutaneous wound healing.

MATERIALS AND METHODS

Balb/C mice were given ZD6474 (50 or 100 mg/kg p.o.) or vehicle starting 7 days before wounding. Two full-thickness incisions were made in each mouse and closed using suture. On post-wounding day 7 or 28, laser Doppler blood flow measurements were made, and the breaking strength of the wounded skin was determined. Microvessel density measurements were performed using computer image analysis of CD31-stained sections.

RESULTS

Compared with controls, mice treated with ZD6474 showed a significantly reduced dose-dependent decline in breaking strength, both at POD 7 (P < 0.001) and at POD 28 (P < 0.005). Histologically, the ZD6474-treated mice showed a qualitative reduction in the degree of fibrosis and epithelial proliferation at the wound site, but no significant difference was noted between the 50 mg/kg and 100 mg/kg ZD6474-treated groups. Also, microvessel density measurements demonstrated no significant difference between groups.

CONCLUSION

In a murine model of wound healing, ZD6474 treatment did not prevent wound healing, but was associated with a reduced skin breaking strength compared with vehicle-treated controls at both 7 and 28 days post-wounding. These observations may have clinical relevance for the perioperative management of patients treated with inhibitors of angiogenesis.

Hypoxia-induced tumor angiogenic pathway in head and neck cancer: an in vivo study

Numerous studies indicate the importance of hypoxia-induced pathway in tumor angiogenesis, but in vivo studies examining the importance of this mechanism in prognosis of patients with head and neck squamous cell carcinoma present conflicting results. We performed a retrospective analysis of 81 patients with head and neck squamous cell carcinoma in order to investigate whether hypoxia-inducible factor 1a (HIF-1a) immunohistochemical expression correlates with vascular endothelial growth factor (VEGF) expression and clinicopathologic parameters or prognosis. Our results showed a statistically significant association between HIF-1a and VEGF expression in tumors located in the lower lip and in larynx, but not in those located in the oral cavity. HIF-1a expression had no impact on prognosis, while VEGF expression correlated significantly with adverse prognosis. These findings support the hypothesis that tumor angiogenesis is close related, but not strictly dependent, on the hypoxic conditions of tumor's microenvironment.

Vascular endothelial growth factor in salivary pleomorphic adenomas: one of the reasons for their poorly vascularized stroma

To better understand the poorly vascularized background of the stroma of pleomorphic adenomas, we attempted to determine the expression of molecules related to blood vessels and hypoxic conditions in pleomorphic adenoma. Surgical specimens and tumor cells in primary culture of salivary pleomorphic adenomas were used for immunohistochemistry for CD31, vascular endothelial growth factor (VEGF) and its receptors Flk-1 and Flt-1, as well as for hypoxia markers, such as hypoxia-inducible factor-1alpha (HIF-1alpha) and lactate dehydrogenase-1 (LDH). At the same time, alternative splicing modes of the VEGF gene and expression levels of the HIF-1alpha gene were analyzed in surgical specimens by means of reverse-transcription polymerase chain reaction (RT-PCR) and direct sequencing of the PCR products. In addition to co-immunolocalization with CD31+ vascular endothelial cells, VEGF and its receptors were demonstrated in normal duct epithelial and myoepithelial cells as well as in tumor cells in ductal structures and in myxochondroid stromata. Immunolocalizations for HIF-1alpha and LDH were confirmed in the VEGF-positive area. Immunofluorescence signals for VEGF and others were confirmed in pleomorphic adenoma cells in culture. RT-PCR results showed that there were at least four splicing modes of the VEGF gene, among which VEGF(121) was most enhanced, and higher HIF-1alpha levels in pleomorphic adenomas. The results suggest that pleomorphic adenoma cells produce VEGF in several functional forms for their own proliferation or differentiation, and that the VEGF expression is controlled by hypoxic circumstances of poorly vascularized pleomorphic adenomas.

Vascular endothelial growth factor gene expression in middle cerebral artery occlusion in the rat

BACKGROUND

Focal cerebral ischemia induces up-regulation of angiogenic growth factors such as vascular endothelial growth factor (VEGF), which may have both beneficial and harmful effects to the ischemic brain. Vascular endothelial growth factor is up-regulated in models of brain ischemia, but the underlying mechanisms in vivo remain unclear. In the present report we have investigated the concomitant changes in VEGF and glyceraldehyde dehydrogenase (GAPDH) mRNA expression in a model of permanent and transient cerebral ischemia.

METHODS

Male Sprague-Dawley rats were exposed to permanent or transient (2 h) middle cerebral artery occlusion (PMCAO, TMCAO). Brain samples were collected at survival times ranging from 6 h to 1 week, and the levels of VEGF164 and GAPDH mRNA were determined using reverse-transcriptase real-time polymerase chain reaction (RT-PCR).

RESULTS

The VEGF mRNA levels decreased gradually over the observation period in a similar manner in both PMCAO and TMCAO. Maximum levels, seen at early observation time points, did not significantly deviate from sham controls. No statistically significant changes in GAPDH mRNA levels were observed, but there was a tendency towards a postischemic decrease with subsequent return to control levels over time. The VEGF/GAPDH ratio followed a pattern of decrease similar to VEGF mRNA alone.

CONCLUSION

The VEGF mRNA levels at 6 h after MCAO remain near baseline and thereafter decline, regardless of whether the occlusion is permanent or transient (2 h). The findings raise the question of other than transcriptional regulation of VEGF in cerebral ischemia.

Constitutive and inducible expression and regulation of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF), which was originally discovered as vascular permeability factor, is critical to human cancer angiogenesis through its potent functions as a stimulator of endothelial cell survival, mitogenesis, migration, differentiation and self-assembly, as well as vascular permeability, immunosuppression and mobilization of endothelial progenitor cells from the bone marrow into the peripheral circulation. Genetic alterations and a chaotic tumor microenvironment, such as hypoxia, acidosis, free radicals, and cytokines, are clearly attributed to numerous abnormalities in the expression and signaling of VEGF and its receptors. These perturbations confer a tremendous survival and growth advantage to vascular endothelial cells as manifested by exuberant tumor angiogenesis and a consequent malignant phenotype. Understanding the regulatory mechanisms of both inducible and constitutive VEGF expression will be crucial in designing effective therapeutic strategies targeting VEGF to control tumor growth and metastasis. In this review, molecular regulation of VEGF expression in tumor cells is discussed.

Cellular reaction to hypoxia: sensing and responding to an adverse environment

Multicellular organisms have developed sophisticated physiologic mechanisms by which they maintain their tissues at the optimal oxygen concentration. This level is important so that the benefits of free oxygen can be realized, while limiting the potential harms. Despite these efforts, there exist physiologic and pathophysiologic conditions where oxygen delivery drops below what is necessary for the tissue. Under these circumstances, the cell then goes through a series of coordinated responses in a time and oxygen concentration-dependent manner. The gene expression changes are designed to maintain cellular and tissue viability, and are comprised of transcriptional as well as post-transcriptional events. As we understand more about the hypoxic response, we realize how it can impact normal development, wound healing, and the malignant progression of a solid tumor.

Pathophysiology of capillary haemangioma growth after birth

Capillary haemangiomas (CHs) are the most common soft tissue tumours of infancy. It is generally believed that the primary defect in CHs is intrinsic to endothelial cells, but their pathogenesis is yet poorly understood. The relatively low oxygen environment, in which the human foeto-placental unit develops, during the first trimester, is necessary to induce vasculo-angiogenesis via embryonic endothelial cells proliferation, since these cells are sensitive to hypoxia and acidosis. In newborn infants with haemangioma, persistent embryonic primitive endothelial cells trapped in the intimae underneath the developing vessels, and representing "leader" endothelial cells, can stabilise the labile vascular endothelial growth factor mRNA (VEGF mRNA), produce other angiogenic factors, degrade the underlying basement membrane and invade into the stroma of the neighbouring tissue. With bearing down, the transition from intra- to extra-uterine life is accompanied by more or less pronounced hypoxia. Consequently, in babies with haemangioma, hypoxia can act as a switch to activate these "leader" endothelial cells and thereby initiate a cascade of reactions leading to CH proliferation. As they are regulated by embryonic cells, the haemangioma growth mechanisms pursue the pathway of embryonic angiogenesis and it will stop at the end of the embryonic endothelial cell cycle. Addressing this mechanism in vivo has partly been done (the angiogenic peptide bFGF varies with haemangioma growth). Thus, early treatment seems necessary in infants with haemangioma, before the endothelial cells achieve their proliferative stage. The use of an antibody to interfere with VEGF receptors provides a particular attractive strategy.

Interleukin-1 homologues IL-1F7b and IL-18 contain functional mRNA instability elements within the coding region responsive to lipopolysaccharide

IL-1F7b, a novel homologue of the IL-1 (interleukin 1) family, was discovered by computational cloning. We demonstrated that IL-1F7b shares critical amino acid residues with IL-18 and binds to the IL-18-binding protein enhancing its ability to inhibit IL-18-induced interferon-gamma. We also showed that low levels of IL-1F7b are constitutively present intracellularly in human blood monocytes. In this study, we demonstrate that similar to IL-18, both mRNA and intracellular protein expression of IL-1F7b are up-regulated by LPS (lipopolysaccharide) in human monocytes. In stable transfectants of murine RAW264.7 macrophage cells, there was no IL-1F7b protein expression despite a highly active CMV promoter. We found that IL-1F7b-specific mRNA was rapidly degraded in transfected cells, via a 3'-UTR (untranslated region)-independent control of IL-1F7b transcript stability. After LPS stimulation, there was a rapid transient increase in IL-1F7b-specific mRNA and concomitant protein levels. Using sequence alignment, we found a conserved ten-nucleotide homology box within the open reading frame of IL-F7b, which is flanking the coding region instability elements of some selective genes. In-frame deletion of downstream exon 5 from the full-length IL-1F7b cDNA markedly increased the levels of IL-1F7b mRNA. A similar coding region element is located in IL-18. When transfected into RAW264.7 macrophages, IL-18 mRNA was also unstable unless treated with LPS. These results indicate that both IL-1F7b and IL-18 mRNA contain functional instability determinants within their coding region, which influence mRNA decay as a novel mechanism to regulate the expression of IL-1 family members.

Quantitative evaluation of catecholamine enzymes gene expression in adrenal medulla and sympathetic Ganglia of stressed rats

Stress-induced changes in mRNA levels of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) have been expressed as relative arbitrary units compared with a control group. The aim of this study was to quantify basal and stress-induced levels of TH, DBH, and PNMT mRNAs in rat adrenal medulla (AM) and stellate ganglia (SG) by the RT-competitive PCR method using corresponding competitors of known concentration. In rats stressed by immobilization (IMO) once for 2 h, the concentration of mRNAs was determined in various intervals after the end of stress stimulus. In SG, the basal concentration of TH mRNA was 0.017 amol/ng of total RNA, which is approximately 30 times lower than in the AM (0.460 amol/ng RNA). The basal concentration of DBH mRNA in SG was 2.60 amol/ng of total RNA, which is about 150 times more than TH mRNA in SG but only two times less than DBH mRNA in the AM in which PNMT mRNA is present in the highest concentration. After a single 2-h IMO, the peak elevation of TH and DBH mRNA concentration in SG occurred 24 h after the termination of stress stimulus, when their AM mRNA concentrations were already at control values. Presence of PNMT mRNA levels in the SG, of control and stressed rats has been demonstrated for the first time. Repeated IMO (7 days, 2 h daily) did not produce further increase in the mRNA concentrations compared with the elevated values found in adapted control groups. Levels of TH protein were significantly increased only after repeated IMO in SG and AM. Thus, our data show for the first time the exact concentrations of TH, DBH, and PNMT mRNA in SG and AM of rats under control and stress conditions. The lowest concentration of TH mRNA in the AM and SG supports the hypothesis that tyrosine hydroxylation is the rate-limiting step in catecholamine biosynthesis.

Vascular endothelial growth factor and the nervous system

Vascular endothelial growth factor (VEGF) is an angiogenic factor essential for the formation of new blood vessels during embryogenesis and in many pathological conditions. A new role for VEGF as a neurotrophic factor has recently emerged. In the developing nervous system, VEGF plays a pivotal role not only in vascularization, but also in neuronal proliferation, and the growth of coordinated vascular and neuronal networks. After injury to the nervous system, activation of VEGF and its receptors may restore blood supply and promote neuronal survival and repair. There is a growing body of evidence that VEGF is essential for motor neurone survival, and that aberrant regulation of VEGF may play a role in the degeneration of neurones in diseases such as amyotrophic lateral sclerosis.

Molecular targeting of angiogenesis for imaging and therapy

Angiogenesis, i.e. the proliferation of new blood vessels from pre-existing ones, is an underlying process in many human diseases, including cancer, blinding ocular disorders and rheumatoid arthritis. The ability to selectively target and interfere with neovascularisation would potentially be useful in the diagnosis and treatment of angiogenesis-related diseases. This review presents the authors' views on some of the most relevant markers of angiogenesis described to date, as well as on specific ligands which have been characterised in pre-clinical animal models and/or clinical studies. Furthermore, we present an overview on technologies which are likely to have an impact on the way molecular targeting of angiogenesis is performed in the future.

Discovery of a novel control element within the 5'-untranslated region of the vascular endothelial growth factor. Regulation of expression using sense oligonucleotides

The regulation of vascular endothelial growth factor (VEGF), a potent stimulator of angiogenesis, is controlled primarily through the interactions of control elements located within the 5'- and 3'-untranslated regions, many of which are yet to be described. In this study we examined the 5'-untranslated region of human VEGF for control elements with the aim of regulating expression both in vitro and in vivo using oligonucleotide gene therapy. A potential control element was located, two sense oligonucleotides (S(1) and S(2)) were designed based on its sequence, and a third oligonucleotide (S(3)) was designed as a control and mapped to the 16 base pairs immediately upstream. Retinal cells cultured in the presence of S(1) and S(2) resulted in a 2-fold increase of VEGF protein and a 1.5-fold increase in mRNA 24 h post-transfection whereas S(3) had no significant effect (p > 0.05) compared with controls. Subsequent reporter gene studies confirmed the necessity of this element for up-regulation by S(1). Further in vivo studies showed that S(1) and S(2) mediated an increase in VEGF protein in a rodent ocular model that resulted in angiogenesis. In addition to providing insight into the regulation of the vascular endothelial growth factor, the use of these oligonucleotides to stimulate vascular growth may prove useful for the treatment of ischemic tissues such as those found in the heart following infarct.

Oxygen-regulated gene expression in bovine blastocysts

Oxygen concentrations used during in vitro embryo culture can influence embryo development, cell numbers, and gene expression. Here we propose that the preimplantation bovine embryo possesses a molecular mechanism for the detection of, and response to, oxygen, mediated by a family of basic helix-loop-helix transcription factors, the hypoxia-inducible factors (HIFs). Day 5 compacting bovine embryos were cultured under different oxygen tensions (2%, 7%, 20%) and the effect on the expression of oxygen-regulated genes, development, and cell number allocation and HIFalpha protein localization were examined. Bovine in vitro-produced embryos responded to variations in oxygen concentration by altering gene expression. GLUT1 expression was higher following 2% oxygen culture compared with 7% and 20% cultured blastocysts. HIF mRNA expression (HIF1alpha, HIF2alpha) was unaltered by oxygen concentration. HIF2alpha protein was predominantly localized to the nucleus of blastocysts. In contrast, HIF1alpha protein was undetectable at any oxygen concentration or in the presence of the HIF protein stabilizer desferrioxamine (DFO), despite being detectable in cumulus cells following normal maturation conditions, acute anoxic culture, or in the presence of DFO. Oxygen concentration also significantly altered inner cell mass cell proportions at the blastocyst stage. These results suggest that oxygen can influence gene expression in the bovine embryo during postcompaction development and that these effects may be mediated by HIF2alpha.

A multi-protein complex containing cold shock domain (Y-box) and polypyrimidine tract binding proteins forms on the vascular endothelial growth factor mRNA. Potential role in mRNA stabilization

Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis and post-transcriptional regulation plays a major role in VEGF expression. Both the 5'- and 3'-UTR are required for VEGF post-transcriptional regulation but factors binding to functional sequences within the 5'-UTR have not been fully characterized. We report here the identification of complexes, binding to the VEGFmRNA 5'- and 3'-UTR, that contain cold shock domain (CSD) and polypyrimidine tract binding (PTB) RNA binding proteins. Analysis of the CSD/PTB binding sites revealed a potential role in VEGF mRNA stability, in both noninduced and induced conditions, demonstrating a general stabilizing function. Such a stabilizing mechanism had not been reported previously for the VEGF gene. We further found that the CSD/PTB-containing complexes are large multiprotein complexes that are most likely preformed in solution and we demonstrate that PTB is associated with the VEGF mRNA in vivo. Complex formation between CSD proteins and PTB has not been reported previously. Analysis of the CSD/PTB RNA binding sites revealed a novel CSD protein RNA recognition site and also demonstrated that CSD proteins may direct the binding of CSD/PTB complexes. We found the same complexes binding to an RNA-stabilizing element of another growth factor gene, suggesting a broader functional role for the CSD/PTB complexes. Finally, as the VEGF gene is also regulated at the transcriptional level by CSD proteins, we propose a combined transcriptional/post-transcriptional role for these proteins in VEGF and other growth factor gene regulation.

Role of the 3'-untranslated region of human endothelin-1 in vascular endothelial cells. Contribution to transcript lability and the cellular heat shock response

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide expressed in the vascular endothelium. Stringent control over ET-1 expression is achieved through a highly regulated promoter and rapid mRNA turnover. Since little is known about mechanisms governing ET-1 post-transcriptional regulation, and changes in ET-1 mRNA stability are implicated in disease processes, we characterized these pathways using a variety of functional approaches. We expressed human ET-1 and luciferase transcripts with or without a wild type ET-1 3'-untranslated region (3'-UTR) and found that the 3'-UTR had potent mRNA destabilizing activity. Deletion analysis localized this activity to two domains of the 3'-UTR we have termed destabilizing elements 1 and 2 (DE1 and DE2). Mutational studies revealed that DE1 functions as an AU-rich element (ARE) dependent on a 100-nucleotide region. This activity was further localized to a 10-nucleotide region at position 978-987 of the 3'-UTR. Depletion of AUF1 by RNA interference up-regulated ET-1 in endothelial cells suggesting AUF1-dependent regulation. Since AUF1 functions through the ubiquitin-proteasome pathway, we disrupted this pathway with heat shock and proteasome inhibitor in endothelial cells and observed stabilization of endogenous ET-1 mRNA. Chimeric transcripts bearing wild type ET-1 3'-UTRs were also stabilized in response to proteasome inhibition whereas DE1 mutants failed to respond. Taken together, these findings suggest a complex model of ARE-mediated mRNA turnover dependent on two 3'-UTR domains, DE1 and DE2. Furthermore, DE1 functions as an ARE directing mRNA half-life through the proteasome. Finally, this data provides evidence for a novel pathway of ET-1 mRNA stabilization by heat shock.

Homocysteine increases the expression of vascular endothelial growth factor by a mechanism involving endoplasmic reticulum stress and transcription factor ATF4

Vascular endothelial growth factor (VEGF) plays a key role in the development and progression of diabetic retinopathy. We previously demonstrated that amino acid deprivation and other inducers of endoplasmic reticulum-stress (ER stress) up-regulate the expression of VEGF in the retinal-pigmented epithelial cell line ARPE-19. Because homocysteine causes ER stress, we hypothesized that VEGF expression is increased by ambient homocysteine. dl-Homocysteine-induced VEGF expression was investigated in confluent ARPE-19 cultures. Northern analysis showed that homocysteine increased steady state VEGF mRNA levels 4.4-fold. Other thiol-containing compounds, including l-homocysteine thiolactone and DTT, induced VEGF expression 7.9- and 8.8-fold. Transcriptional run-on assays and mRNA decay studies demonstrated that the increase in VEGF mRNA levels was caused by increased transcription rather than mRNA stabilization. VEGF mRNA induction paralleled that of the ER-stress gene GRP78. Homocysteine treatment caused transient phosphorylation of eIF2alpha and an increase in ATF4 protein level. Overexpression of a dominant-negative ATF4 abolished the VEGF response to homocysteine treatment and to amino acid deprivation. VEGF mRNA expression by ATF4-/- MEF did not respond to homocysteine treatment and the response was restored with expression of wild-type ATF4. These studies indicate that expression of the pro-angiogenic factor VEGF is increased by homocysteine and other thiol-containing reductive compounds via ATF4-dependent activation of VEGF transcription.

Use of dynamic contrast-enhanced MRI to evaluate acute treatment with ZD6474, a VEGF signalling inhibitor, in PC-3 prostate tumours

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), using gadopentetate dimeglumine, was used to monitor acute effects on tumour vascular permeability following inhibition of vascular endothelial growth factor-A (VEGF-A) signal transduction. Mice bearing PC-3 human prostate adenocarcinoma xenografts were treated with ZD6474, a VEGF receptor-2 (KDR) tyrosine kinase inhibitor. The pharmacokinetic parameter K^trans was obtained, which reflects vascular permeability and perfusion. Mice were imaged immediately before, and following, acute treatment with ZD6474 (12.5–100 mg kg⁻¹ orally). Whole tumours were analysed to obtain mean K^trans values, and a histogram approach was used to examine intratumour heterogeneity. Reproducibility of K^trans measurements gave inter- and intra-animal coefficients of variation of 40 and 18%, respectively. Dose-related reductions in K^trans were evident following acute ZD6474 treatment. A K^trans reduction of approximately 30% (P<0.001) was evident with 50 and 100 mg kg⁻¹ ZD6474, a reduction of 12.5% (P<0.05) at 25 mg kg⁻¹, and a reduction that did not reach statistical significance at 12.5 mg kg⁻¹. A correlation between this dose response and the growth inhibitory effect of ZD6474 following chronic treatment was also observed. The histogram analysis of the data indicated that ZD6474-induced a K^trans reduction in both the most enhancing rim and the core of PC-3 tumours. Dynamic contrast-enhanced magnetic resonance imaging may have a role in assessing the acute effects of VEGF signalling inhibition, in clinical dose-ranging studies.

Hypoxia-inducible VEGF gene delivery to ischemic myocardium using water-soluble lipopolymer

Therapeutic angiogenesis with gene encoding vascular endothelial growth factor (VEGF) is a new potential treatment in cardiovascular disease. However, unregulated VEGF-mediated angiogenesis has the potential to promote tumor growth, accelerate diabetic proliferative retinopathy, and promote rupture of atherosclerotic plaque. To be safe and effective, gene therapy with VEGF must be regulated. To limit the risk of pathological angiogenesis, we developed a hypoxia-inducible VEGF gene therapy system using the erythropoietin (Epo) enhancer and water-soluble lipopolymer (WSLP). pEpo-SV-VEGF or pSV-VEGF-Epo was constructed by insertion of the Epo enhancer upstream of the Simian Virus 40 (SV40) promoter or downstream of the poly(A) signal of pSV-VEGF. In vitro transfection showed that pEpo-SV-VEGF, not pSV-VEGF-Epo, induced the VEGF expression in hypoxic cells. In addition, the VEGF protein, which was produced from the Epo-SV-VEGF-transfected and hypoxia-incubated cells, was able to enhance the proliferation of the endothelial cells. Injection of the pEpo-SV-VEGF/WSLP complex showed that the expression of VEGF was induced in ischemic myocardium, compared to normal myo-cardium. Therefore, with the localized induction of VEGF and the low cytotoxicity of WSLP, the pEpo-SV-VEGF/WSLP system may be helpful to eventually treat ischemic heart disease.

Increasedin vitroandin vivotransgene expression levels mediated throughcis-acting elements

BACKGROUND

Gene therapy for neurodegenerative diseases depends critically on the vector system to direct sustained and stable expression of the transgene. It is, however, a commonly observed phenomenon that transgene expression from currently available vectors is down-regulated following ex vivo gene transfer to the central nervous system (CNS). In an attempt to circumvent this problem, we have systematically evaluated the potential of different cis-acting elements to increase and stabilize transgene expression in vitro and after grafting of engineered cell lines to the CNS.

METHODS

Plasmid vector constructs incorporating Woodchuck hepatitis post-transcriptional regulatory element (WPRE), cHS4 insulator elements and/or the translational enhancer element SP163 were produced. Stable, polyclonal cultures of HiB5 cells were generated by transfection with reporter constructs, and in vitro transgene mRNA and protein levels were determined. Finally, HiB5 clones engineered to express the enhanced green fluorescent protein (EGFP) were grafted to the rat striatum and expression levels were evaluated.

RESULTS

Inserting the WPRE element downstream of the open reading frame (ORF) of a reporter gene and flanking the transcriptional unit with cHS4 insulator elements significantly increased protein and mRNA expression levels. Surprisingly, the SP163 element, previously reported to be a translational enhancer, apparently did not promote any translational enhancing activity. Furthermore, the SP163 element exerted a negative effect on transcription. The ability of cHS4 and WPRE elements to stabilize in vivo transgene expression was demonstrated by transplantation of HiB5 clones containing expression constructs into the rat striatum.

CONCLUSION

The data suggest that incorporating cis-acting elements in gene therapy vectors may result in improvements to currently available therapeutic vectors.

Regulation of vascular endothelial growth factor gene expression in murine macrophages by nitric oxide and hypoxia

Vascular endothelial growth factor (VEGF) expression in murine peritoneal macrophages is strongly upregulated by hypoxia via transcriptional and posttranscriptional mechanisms. Interferon-gamma (IFN-gamma) with Escherichia coli lipopolysaccharide (LPS) also upregulates expression of VEGF, as well as of the inducible nitric oxide synthase (iNOS). Hypoxia (1% O(2)) upregulates VEGF expression in macrophages from both wild-type and iNOS knockout mice, indicating that hypoxic upregulation of VEGF is independent of iNOS. However, the iNOS inhibitor aminoguanidine (AG) decreases the VEGF expression induced by LPS/IFN-gamma, indicating an important role for NO. NO-dependent induction of VEGF is strongly dependent on cell density. LPS/IFN-gamma treatment induces minimal VEGF protein expression in macrophages cultured at low cell densities (<0.25 x 10(6) cells/cm(2)); at higher cell densities (>0.25 x 10(6) cells/cm(2)) that lead to conditions of pericellular hypoxia, however, induction of VEGF expression was strong. Transient transfection of RAW 264.7 cells with luciferase reporter constructs of the murine VEGF promoter indicates that both hypoxia and LPS/IFN-gamma independently induce VEGF promoter activity, irrespective of cell density. Although LPS/IFN-gamma treatment induces transcriptional activation of the VEGF promoter, significant levels of VEGF protein are only expressed by cells at high density under conditions of pericellular hypoxia. This suggests an important regulatory role for hypoxia at the posttranscriptional level. Deletion analysis of the VEGF promoter shows that the hypoxia response element region and its immediate flanking sequences are essential for both hypoxia and LPS/IFN-gamma-induced VEGF promoter activation.

Role of ERK and calcium in the hypoxia-induced activation of HIF-1

Oxygen-dependent regulation of HIF-1 activity occurs at multiple levels in vivo. The mechanisms regulating HIF-1alpha protein expression have been most extensively analyzed but the ones modulating HIF-1 transcriptional activity remain unclear. Changes in the phosphorylation and/or redox status of HIF-1alpha certainly play a role. Here, we show that ionomycin could activate HIF-1 transcriptional activity in a way that was additive to the effect of hypoxia without affecting HIF-1alpha protein level. In addition, a calmodulin dominant negative mutant and W7, a calmodulin antagonist, as well as BAPTA, an intracellular calcium chelator, inhibited the hypoxia-induced HIF-1 activation. These results indicate that elevated calcium in hypoxia could participate in HIF-1 activation. Furthermore, ERK but not JNK phosphorylation was evidenced in both conditions, ionomycin and hypoxia. PD98059, an inhibitor of the ERK pathway as well as a ERK1 dominant negative mutant also blocked HIF-1 activation by hypoxia and by ionomycin. A MEKK1 (a kinase upstream of JNK) dominant negative mutant had no effect. In addition, BAPTA, calmidazolium, a calmodulin antagonist and PD98059 inhibited VEGF secretion by hypoxic HepG2. All together, these results suggest that calcium and calmodulin would act upstream of ERK in the hypoxia signal transduction pathway.

Glucocorticoids inhibit vascular endothelial growth factor expression in growth plate chondrocytes

Vascular endothelial growth factor (VEGF) plays an essential role in angiogenesis in the growth plate and ultimately in regulating endochondral ossification. Since longitudinal bone growth is often disturbed in children who are treated with glucocorticoids, we investigated the effects of dexamethasone on VEGF expression by epiphyseal chondrocytes. Cells were cultured from tibial growth plates of neonatal piglets. Using Northern blotting and RT-PCR techniques, the chondrocyte-specific markers aggrecan, collagen II and CD-RAP were detected. Also the glucocorticoid receptor (GR) was expressed. VEGF protein secreted from these cells was examined by ELISA and Western immunoblotting. The VEGF(121) and VEGF(165) isoforms were detected in the supernatant. As determined by RT-PCR, all three major mRNA splice variants were produced, including the species encoding VEGF(189). Dexamethasone (100 nM) inhibited both protein and mRNA expression by approximately 45%. Hydrocortisone (cortisol) and prednisolone also inhibited VEGF secretion, but they were less active than dexamethasone. The inhibitory actions of dexamethasone were almost completely blocked by the GR antagonist Org34116, indicating that the GR mediates these actions. Degradation of the VEGF mRNA was not accelerated by dexamethasone. Therefore, a transcriptional mechanism seems likely. Downregulation of this important growth factor could lead to disruption of the normal invasion of blood vessels in the growth plate, which could contribute to disturbed endochondral ossification and growth.

A novel mechanism of repression of the vascular endothelial growth factor promoter, by single strand DNA binding cold shock domain (Y-box) proteins in normoxic fibroblasts

Overexpression of vascular endothelial growth factor (VEGF) is implicated in a number of diseases. It is therefore critical that mechanisms exist to strictly regulate VEGF expression. A hypoxia-responsive (HR) region of the VEGF promoter which binds the HIF-1 transcription factor is a target for many signals that up-regulate VEGF transcription. Repressors targeting the HIF-1 transcription factor have been identified but no repressors directly binding the HR promoter region had been reported. We now report a novel mechanism of repression of the VEGF HR region involving DNA binding. We find that single strand DNA-specific cold shock domain (CSD or Y-box) proteins repress the HR region via a binding site downstream of the HIF-1 site. The repressor site is functional in unstimulated, normoxic fibroblasts and represents a novel means to prevent expression of VEGF in the absence of appropriate stimuli. We characterized complexes forming on the VEGF repressor site and identified a previously unreported nuclear CSD protein complex containing dbpA. Nuclear dbpA appears to bind as a dimer and we determined a means by which nuclear CSD proteins may enter double strand DNA to bind to their single strand sites to bring about repression of the VEGF HR region.

Single nucleotide polymorphisms in the 3' untranslated region of vascular endothelial growth factor gene in Japanese population with or without renal cell carcinoma

We investigated native Japanese subjects whether C702T, C936T and G1612A polymorphisms in the 3' untranslated region (3'-UTR) of vascular endothelial growth factor (VEGF) gene are associated with the risk of renal cell carcinoma (RCC). Genomic DNAs from 145 RCC patients and 145 healthy controls were examined by polymerase chain reaction-based restriction fragment length polymorphism. Variant allele frequencies of C702T, C936T and G1612A were 0.00, 0.20 and 0.13 in the controls, respectively. The C702T and G1612A allele frequencies were significantly different between the Japanese population and the Caucasian population reported elsewhere. For each of C936T and G1612A polymorphisms, there was no statistically significant difference in the distribution of genotype frequencies between the cases and controls. Odds ratios and 95% confidence intervals computed by logistic regression analyses were not statistically significant. Stratification for the RCC cases according to pathological cell subtype, grade or stage failed to reveal any significant heterogeneity with respect to the genotype of each VEGF polymorphism. We revealed that there are significant ethnic differences in the C702T and G1612A allele frequencies, but suggested that C702T, C936T and G1612A polymorphisms in the 3'-UTR of VEGF gene are not associated with the risk of RCC, at least in Japanese population.

Regulation of gene expression for neurotransmitters during adaptation to hypoxia in oxygen-sensitive neuroendocrine cells

Reduced oxygen tension (hypoxia) in the environment stimulates oxygen-sensitive cells in the carotid body (CB). Upon exposure to hypoxia, the CB immediately triggers a reflexive physiological response, thereby increasing respiration. Adaptation to hypoxia involves changes in the expression of various CB genes, whose products are involved in the transduction and modulation of the hypoxic signal to the central nervous system (CNS). Genes encoding neurotransmitter-synthesizing enzymes and receptors are particularly important in this regard. The cellular response to hypoxia correlates closely with the release and biosynthesis of catecholamines. The gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme for catecholamine biosynthesis, is regulated by hypoxia in the CB and in the oxygen-sensitive cultured PC12 cell line. Recently, genomic microarray studies have identified additional genes regulated by hypoxia. Patterns of gene expression vary, depending on the type of applied hypoxia, e.g., intermittent vs. chronic. Construction of a hypoxia-regulated, CB-specific, subtractive cDNA library will enable us to further characterize regulation of gene expression in the CB.

Post-transcriptional regulation of VEGF expression by oxidised LDL in human macrophages

BACKGROUND

Accumulation of oxidised low density lipoproteins (oxLDL) in macrophages and their subsequent transformation into lipid-filled foam cells is generally considered an early event in atherosclerosis. Vascular Endothelial Growth Factor (VEGF) may contribute to atherogenesis through increased vascular permeability, chemoattraction towards monocytes and intraplaque vessel formation. In this study we investigate the effect and regulation of VEGF expression in human macrophages stimulated with oxLDL.

MATERIALS AND METHODS

Vascular Endothelial Growth Factor mRNA and protein expression was assayed using RT-PCR and ELISA, respectively. The activity of mitogen-activated protein kinases (MAPKs) was investigated using Western blots.

RESULTS

In human monocyte-derived macrophages, oxLDL significantly increased VEGF mRNA expression and subsequent protein secretion in a concentration-dependent manner after 6 h and 18 h, respectively. Using an in vitro mRNA decay assay, we show that this oxLDL-induced VEGF expression partly is regulated through increased stability of the VEGF mRNA. Involvement of MAPKs has previously been implicated in the stabilisation of VEGF mRNA. Activity of the p38 MAPK, but not the c-jun-N-terminal kinase (JNK), increased in macrophages stimulated with oxLDL (50 micro g mL-1) for 5-15 min. Preincubation with SB202190 (20 micro M), a specific inhibitor of p38 MAPK, significantly decreased the oxLDL-induced VEGF mRNA expression by 40%. The prolonged half-life of VEGF mRNA, induced by oxLDL, was not inhibited by SB202190.

CONCLUSIONS

OxLDL increases VEGF expression and p38 MAPK activity in human macrophages. The increased VEGF mRNA expression by oxLDL is mediated through at least two intracellular pathways, one involving p38 MAPK and another that independently of p38 MAPK activity increases VEGF mRNA stability.

mRNA degradation machines in eukaryotic cells

The steady-state levels of mRNAs depend upon their combined rates of synthesis and processing, transport from the nucleus to cytoplasm, and decay in the cytoplasm. In eukaryotic cells, the degradation of mRNA is an essential determinant in the regulation of gene expression, and it can be modulated in response to developmental, environmental, and metabolic signals. This level of regulation is particularly important for proteins that are active for a brief period, such as growth factors, transcription factors, and proteins that control cell cycle progression. The mechanisms by which mRNAs are degraded and the sequence elements within the mRNAs that affect their stability are the subject of this review. We will summarize the current state of knowledge regarding cis-acting elements in mRNA and trans-acting factors that contribute to mRNA regulation decay. We will then consider the mechanisms by which specific signaling proteins seem to contribute to a dynamic organization of the mRNA degradation machinery in response to physiological stimuli.

Assembly of the ribonucleoprotein complex containing the mRNA of the beta-subunit of the mitochondrial H+-ATP synthase requires the participation of two distal cis-acting elements and a complex set of cellular trans-acting proteins

The mRNA encoding the beta-subunit of the mitochondrial H(+)-ATP synthase (beta-F1-ATPase) is localized in an approx. 150 nm structure of the hepatocyte of mammals. In the present study, we have investigated the cis- and trans-acting factors involved in the generation of the ribonucleoprotein complex containing beta-F1-ATPase mRNA. Two cis-acting elements (beta1.2 and 3'beta) have been identified. The beta1.2 element is placed in the open reading frame, downstream of the region encoding the mitochondrial pre-sequence of the protein. The 3'beta element is the 3' non-translated region of the mRNA. Complex sets of proteins from the soluble and non-soluble fractions of the liver interact with the beta1.2 and 3'beta elements. A soluble p88, present also in reticulocyte lysate, displays binding specificity for both the cis-acting elements. Sedimentation and high-resolution in situ hybridization experiments showed that the structure containing the rat liver beta-F1-ATPase mRNA is found in fractions of high sucrose concentration, where large polysomes sediment. Treatment of liver extracts with EDTA promoted the mobilization of beta-F1-ATPase mRNA to fractions of lower sucrose concentration, suggesting that the structure containing beta-F1-ATPase mRNA is a large polysome. Finally, in vitro reconstitution experiments with reticulocyte lysate, using either the full-length, mutant or chimaeric versions of beta-F1-ATPase mRNA, reveal that the assembly of the beta-F1-ATPase mRNA polysome requires the co-operation of both the cis-acting mRNA determinants. The present study illustrates the existence of an intramolecular RNA cross-talking required for the association of the mRNA with the translational machinery.