Regulation of vascular endothelial growth factor by hypoxia and its modulation by the von Hippel-Lindau tumor suppressor gene

Roles of pigment epithelium-derived factor in cardiomyocytes: implications for use as a cardioprotective therapeutic

OBJECTIVES

Cardiovascular diseases are the leading cause of death worldwide, with patients having limited options for treatment. Pigment epithelium-derived factor (PEDF) is an endogenous multifunctional protein with several mechanisms of action. Recently, PEDF has emerged as a potential cardioprotective agent in response to myocardial infarction. However, PEDF is also associated with pro-apoptotic effects, complicating its role in cardioprotection. This review summarises and compares knowledge of PEDF's activity in cardiomyocytes with other cell types and draws links between them. Following this, the review offers a novel perspective of PEDF's therapeutic potential and recommends future directions to understand the clinical potential of PEDF better.

KEY FINDINGS

PEDF's mechanisms as a pro-apoptotic and pro-survival protein are not well understood, despite PEDF's implication in several physiological and pathological activities. However, recent evidence suggests that PEDF may have significant cardioprotective properties mediated by key regulators dependent on cell type and context.

CONCLUSIONS

While PEDF's cardioprotective activity shares some key regulators with its apoptotic activity, cellular context and molecular features likely allow manipulation of PEDF's cellular activity, highlighting the importance of further investigation into its activities and its potential to be applied as a therapeutic to mitigate damage from a range of cardiac pathologies.

Exploiting E3 ubiquitin ligases to reeducate the tumor microenvironment for cancer therapy

Tumor development relies on a complex and aberrant tissue environment in which cancer cells receive the necessary nutrients for growth, survive through immune escape, and acquire mesenchymal properties that mediate invasion and metastasis. Stromal cells and soluble mediators in the tumor microenvironment (TME) exhibit characteristic anti-inflammatory and protumorigenic activities. Ubiquitination, which is an essential and reversible posttranscriptional modification, plays a vital role in modulating the stability, activity and localization of modified proteins through an enzymatic cascade. This review was motivated by accumulating evidence that a series of E3 ligases and deubiquitinases (DUBs) finely target multiple signaling pathways, transcription factors and key enzymes to govern the functions of almost all components of the TME. In this review, we systematically summarize the key substrate proteins involved in the formation of the TME and the E3 ligases and DUBs that recognize these proteins. In addition, several promising techniques for targeted protein degradation by hijacking the intracellular E3 ubiquitin-ligase machinery are introduced.

Now a Nobel gas: oxygen

The recent bestowal of the Nobel Prize 2019 in Physiology or Medicine to Gregg L. Semenza, Sir Peter J. Ratcliffe, and William G. Kaelin Jr. celebrates a series of remarkable discoveries that span from the physiological research question on how oxygen deficiency (hypoxia) induces the red blood cell forming hormone erythropoietin (Epo) to the first clinical application of a novel family of Epo-inducing drugs to treat patients suffering from renal anemia. This review looks back at the most important findings made by the three Nobel laureates, highlights current research trends, and sheds an eye on future perspectives of hypoxia research, including emerging and potential clinical applications.

Plasmatic carbonic anhydrase IX as a diagnostic marker for clear cell renal cell carcinoma

Carbonic anhydrase (CA, EC 4.2.1.1) IX is regarded as a tumour hypoxia marker and CA inhibitors have been proposed as a new class of antitumor agents, with one such agent in Phase II clinical trials. The expression of some CAs, in particular the isoforms CA IX and CA XII, has been correlated with tumour aggressiveness and progression in several cancers. The aim of this study was to evaluate the possibility that CA IX could represent a marker related to clear cell Renal Cell Carcinoma (ccRCC). Bcl-2 and Bax, and the activity of caspase-3, evaluated in tissue biopsies from patients, were congruent with resistance to apoptosis in ccRCCs with respect to healthy controls, respectively. In the same samples, the CA IX and pro-angiogenic factor VEGF expressions revealed that both these hypoxia responsive proteins were strongly increased in ccRCC with respect to controls. CA IX plasma concentration and CA activity were assessed in healthy volunteers and patients with benign kidney tumours and ccRCCs. CA IX expression levels were found strongly increased only in plasma from ccRCC subjects, whereas, CA activity was found similarly increased both in plasma from ccRCC and benign tumour patients, compared to healthy volunteers. These results show that the plasmatic level of CA IX, but not the CA total activity, can be considered a diagnostic marker of ccRCCs. Furthermore, as many reports exist relating CA IX inhibition to a better outcome to anticancer therapy in ccRCC, plasma levels of CA IX could be also predictive for response to therapy.

Hypoxic stabilization of mRNA is HIF-independent but requires mtROS

Background

Tissue ischemia can arise in response to numerous physiologic and pathologic conditions. The cellular response to decreased perfusion, most notably a decrease in glucose and oxygen, is important for cellular survival. In response to oxygen deprivation or hypoxia, one of the key response elements is hypoxia inducible factor (HIF) and a key protein induced by hypoxia is vascular endothelial growth factor (VEGF). Under hypoxia, we and others have reported an increase in the half-life of VEGF and other hypoxia related mRNAs including MYC and CYR61; however, the mediator of this response has yet to be identified. For this study, we sought to determine if HIF-mediated transcriptional activity is involved in the mRNA stabilization induced by hypoxia.

Methods

HEK293T or C6 cells were cultured in either normoxic or hypoxic (1% oxygen) conditions in the presence of 1 g/L glucose for all experiments. Pharmacological treatments were used to mimic hypoxia (desferroxamine, dimethyloxaloglutamate, CoCl₂), inhibit mitochondrial respiration (rotenone, myxothiazol), scavenge reactive oxygen species (ROS; ebselen), or generate mitochondrial ROS (antimycin A). siRNAs were used to knock down components of the HIF transcriptional apparatus. mRNA half-life was determined via actinomycin D decay and real time PCR and western blotting was used to determine mRNA and protein levels respectively.

Results

Treatment of HEK293T or C6 cells with hypoxic mimetics, desferroxamine, dimethyloxaloglutamate, or CoCl₂ showed similar induction of HIF compared to hypoxia treatment, however, in contrast to hypoxia, the mimetics caused no significant increase in VEGF, MYC or CYR61 mRNA half-life. Knockdown of HIF-alpha or ARNT via siRNA also had no effect on hypoxic mRNA stabilization. Interestingly, treatment of HEK293T cells with the mitochondrial inhibitors rotenone and myxothiazol, or the glutathione peroxidase mimetic ebselen did prevent the hypoxic stabilization of VEGF, MYC, and CYR61, suggesting a role for mtROS in the process. Additionally, treatment with antimycin A, which has been shown to generate mtROS, was able to drive the normoxic stabilization of these mRNAs.

Conclusion

Overall these data suggest that hypoxic mRNA stabilization is independent of HIF transcriptional activity but requires mtROS.

Effects of hypoxia and hyperoxia on the differential expression of VEGF-A isoforms and receptors in Idiopathic Pulmonary Fibrosis (IPF)

Dysregulation of VEGF-A bioavailability has been implicated in the development of lung injury/fibrosis, exemplified by Idiopathic Pulmonary Fibrosis (IPF). VEGF-A is a target of the hypoxic response via its translational regulation by HIF-1α. The role of hypoxia and hyperoxia in the development and progression of IPF has not been explored. In normal lung (NF) and IPF-derived fibroblasts (FF) VEGF-A_xxxa protein expression was upregulated by hypoxia, mediated through activation of VEGF-A_xxxa gene transcription. VEGF-A receptors and co-receptors were differentially expressed by hypoxia and hyperoxia. Our data supports a potential role for hypoxia, hyperoxia and VEGF-A_xxxa isoforms as drivers of fibrogenesis.

HIF1 activity in granulosa cells is required for FSH-regulated Vegfa expression and follicle survival in mice

Recent evidence has suggested that vascular endothelial growth factor A (VEGFA) is an important regulator of ovarian follicle development and survival. Both LH and FSH regulate Vegfa expression in granulosa cells and signal via the transcription factor hypoxia inducible factor 1 (HIF1). To further study the mechanism of action of HIF1 in the regulation of Vegfa, we studied Vegfa(delta/delta) mice, which lack a hypoxia response element in the Vegfa promoter. Granulosa cells from Vegfa(delta/delta) mice failed to respond to FSH or LH with an increase in Vegfa mRNA expression in vitro, and granulosa cells isolated from eCG-treated immature Vegfa(delta/delta) mice had significantly lower Vegfa mRNA levels compared to controls. However, normal Vegfa mRNA levels were detected in the granulosa cells from immature Vegfa(delta/delta) mice following hCG treatment. Vegfa(delta/delta) females produced infrequent litters, and their pups died shortly after birth. Ovaries from Vegfa(delta/delta) mice were much smaller than controls and contained few antral follicles and corpora lutea. Antral follicles numbers were decreased by nearly 50% in ovaries from Vegfa(delta/delta) mice relative to controls, and 74% of antral follicles in Vegfa(delta/delta) ovaries were atretic. Serum progesterone levels in adult Vegfa(delta/delta) females were significantly lower, apparently reflecting reduced numbers of corpora lutea. This study demonstrates for the first time the requirement of HIF1 for FSH-regulated Vegfa expression in vivo and that HIF1 acts via a single hypoxia response element in the Vegfa promoter to exert its regulatory functions. Our findings also further define the physiological role of VEGFA in follicle development.

Otitis media in the Tgif knockout mouse implicates TGFβ signalling in chronic middle ear inflammatory disease

Otitis media with effusion (OME) is the most common cause of hearing loss in children and tympanostomy to alleviate the condition remains the commonest surgical intervention in children in the developed world. Chronic and recurrent forms of OM are known to have a very significant genetic component, however, until recently little was known of the underlying genes involved. The identification of mouse models of chronic OM has indicated a role of transforming growth factor beta (TGFβ) signalling and its impact on responses to hypoxia in the inflamed middle ear. We have, therefore, investigated the role of TGFβ signalling and identified and characterized a new model of chronic OM carrying a mutation in the gene for transforming growth interacting factor 1 (Tgif1). Tgif1 homozygous mutant mice have significantly raised auditory thresholds due to a conductive deafness arising from a chronic effusion starting at around 3 weeks of age. The OM is accompanied by a significant thickening of the middle ear mucosa lining, expansion of mucin-secreting goblet cell populations and raised levels of vascular endothelial growth factor, TNF-α and IL-1β in ear fluids. We also identified downstream effects on TGFβ signalling in middle ear epithelia at the time of development of chronic OM. Both phosphorylated SMAD2 and p21 levels were lowered in the homozygous mutant, demonstrating a suppression of the TGFβ pathway. The identification and characterization of the Tgif mutant supports the role of TGFβ signalling in the development of chronic OM and provides an important candidate gene for genetic studies in the human population.

The erythropoietin/erythropoietin receptor signaling pathway promotes growth and invasion abilities in human renal carcinoma cells

Co-expression of erythropoietin (Epo) and erythropoietin receptor (EpoR) has been found in various non-hematopoietic cancers including hereditary and sporadic renal cell carcinomas (RCC), but the Epo/EpoR autocrine and paracrine mechanisms in tumor progression have not yet been identified. In this study, we used RNA interference method to down-regulate EpoR to investigate the function of Epo/EpoR pathway in human RCC cells. Epo and EpoR co-expressed in primary renal cancer cells and 6 human RCC cell lines. EpoR signaling was constitutionally phosphorylated in primary renal cancer cells, 786-0 and Caki-1 cells, and recombinant human Epo (rhEpo) stimulation had no significant effects on further phosphorylation of EpoR pathway, proliferation, and invasiveness of the cells. Down-regulation of EpoR expression in 786-0 cells by lentivirus-introduced siRNA resulted in inhibition of growth and invasiveness in vitro and in vivo, and promotion of cell apoptosis. In addition, rhEpo stimulation slightly antagonized the anti-tumor effect of Sunitinib on 786-0 cells. Sunitinib could induce more apoptotic cells in 786-0 cells with knockdown EpoR expression. Our results suggested that Epo/EpoR pathway was involved in cell growth, invasion, survival, and sensitivity to the multi-kinases inhibitor Sunitinib in RCC cells.

Family history of von Hippel-Lindau disease was uncommon in Chinese patients: suggesting the higher frequency of de novo mutations in VHL gene in these patients

Von Hippel-Lindau (VHL) disease is an autosomal dominant familial cancer syndrome caused by germline mutations in VHL tumor suppressor gene. It is characterized by hemangioblastoma in central nervous system and retina, renal cell carcinoma or cyst, pheochromocytoma, pancreatic cyst and tumor, endolymphatic-sac tumor, and papillary cystadenoma in epididymis and broad ligament. Here, we used PCR-direct sequencing and universal primer quantitative fluorescent multiplex PCR (UPQFM-PCR) to detect VHL mutations in 16 patients clinically diagnosed with VHL disease. PCR-direct sequencing detected 12 germline mutations (75%, 12/16), in which a novel mutation of c.451A>T/p.Ile151Phe found in one proband had not been reported previously. UPQFM-PCR found two large deletions (12.5%, 2/16). The two remaining patients carried non-typical disease-causing mutations, including one silent mutation (c.481C>A/p.Arg161Arg) and one mutation in 3'-UTR (c.642+70C>A). Remarkably, 56.3% (9/16) probands did not have family history of VHL disease, suggesting the higher frequency of de novo mutations in Chinese patients. We also summarized Chinese VHL disease patients with VHL mutation findings published in the literature to provide information about the spectrum of VHL mutations in Chinese VHL disease patients.

Control of cytokine mRNA expression by RNA-binding proteins and microRNAs

Cytokines are critical mediators of inflammation and host defenses. Regulation of cytokines can occur at various stages of gene expression, including transcription, mRNA export, and post- transcriptional and translational levels. Among these modes of regulation, post-transcriptional regulation has been shown to play a vital role in controlling the expression of cytokines by modulating mRNA stability. The stability of cytokine mRNAs, including TNFα, IL-6, and IL-8, has been reported to be altered by the presence of AU-rich elements (AREs) located in the 3'-untranslated regions (3'UTRs) of the mRNAs. Numerous RNA-binding proteins and microRNAs bind to these 3'UTRs to regulate the stability and/or translation of the mRNAs. Thus, this paper describes the cooperative function between RNA-binding proteins and miRNAs and how they regulate AU-rich elements containing cytokine mRNA stability/degradation and translation. These mRNA control mechanisms can potentially influence inflammation as it relates to oral biology, including periodontal diseases and oral pharyngeal cancer progression.

Tristetraprolin regulates expression of VEGF and tumorigenesis in human colon cancer

Tristetraprolin (TTP) is an AU-rich element-binding protein that regulates mRNA stability. Here, we report that TTP suppress the growth of human colon cancer cells both in vivo and in vitro by regulating of the expression of vascular endothelial growth factor (VEGF). TTP protein expression in human colonic tissues was markedly decreased in colonic adenocarcinoma compared with in normal mucosa and adenoma. VEGF expression was higher in colonic adenocarcinoma than in normal mucosa and adenoma. Specific inhibition of TTP expression by RNA-interference increased the expression of VEGF in cultured human colon cancer cells, and TTP overexpression markedly decreased it. In addition, elevated expression of TTP decreased the expression level of luciferase linked to a 3' terminal AU-rich element (ARE) of VEGF mRNA. Colo320/TTP cells overexpressing TTP grew slowly in vitro and became tumors small in size when xenografted s.c into nude mice. These findings demonstrate that TTP acts as a negative regulator of VEGF gene expression in colon cancer cells, suggesting that it can be used as novel therapeutic agent to treat colon cancer.

Von Hippel Lindau syndrome

Von Hippel-Lindau syndrome (VHLS) is an autosomal dominant familial cancer syndrome arising from germ-line inactivation of the VHL gene on the short arm of chromosome 3. VHLS manifests in a myriad of hyper-vascular tumors of both benign and malignant nature. Incidence of VHLS is roughly 1 in 36,000 live births and has over 90% penetrance by the age of 65. Improved understanding of the natural history and biology of VHLS has led to the introduction of screening protocols, early interventions and improved treatments, all of which resulted in a substantially improved prognosis for this disease. Further details regardingvariegated molecular pathways and mechanisms ofVHLS are emerging with the subsequent advent of novel treatment protocols that are currently in clinical trials.

Phase II study of erlotinib in patients with locally advanced or metastatic papillary histology renal cell cancer: SWOG S0317

PURPOSE

Patients with advanced papillary renal cell cancer (pRCC) have poor survival after systemic therapy; the reported median survival time is 7 to 17 months. In this trial, we evaluated the efficacy of erlotinib, an oral epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor in patients with advanced pRCC, a tumor type associated with wild-type von Hippel Lindau gene.

PATIENTS AND METHODS

Patients with histologically confirmed, advanced, or metastatic pRCC were treated with erlotinib 150 mg orally once daily. A RECIST (Response Evaluation Criteria in Solid Tumors) response rate (RR) of > or = 20% was considered a promising outcome. Secondary end points included overall survival and 6-month probability of treatment failure.

RESULTS

Of 52 patients registered, 45 were evaluable. The overall RR was 11% (five of 45 patients; 95% CI, 3% to 24%), and the disease control rate was 64% (ie five partial response and 24 stable disease). The median overall survival time was 27 months (95% CI, 13 to 36 months). Probability of freedom from treatment failure at 6 months was 29% (95% CI, 17% to 42%). There was one grade 5 adverse event (AE) of pneumonitis, one grade 4 thrombosis, and nine other grade 3 AEs.

CONCLUSION

Although the RECIST RR of 11% did not exceed prespecified estimates for additional study, single-agent erlotinib yielded disease control and survival outcomes of interest with an expected toxicity profile. The design of future trials of the EGFR axis in pRCC should be based on preclinical or molecular data that define appropriate patient subgroups, new drug combinations, or potentially more active alternative schedules.

Von Hippel-Lindau gene product modulates TIS11B expression in renal cell carcinoma: impact on vascular endothelial growth factor expression in hypoxia

TIS11B belongs to a group of RNA-binding proteins (including TIS11/tristetraprolin and TIS11D) that share characteristic tandem CCCH-type zinc-finger domains and can be rapidly induced by multiple stimuli. TIS11B has been shown to regulate vascular endothelial growth factor (VEGF) mRNA stability in adrenocorticotropic hormone-stimulated primary adrenocortical cells. TIS11B has also been documented as a negative regulator of VEGF during development, but nothing has yet been reported in the context of human cancers. The Von Hippel-Lindau (VHL) tumor suppressor protein regulates VEGF gene expression at both the transcriptional and post-transcriptional levels in normoxia. However, whether it can do so in hypoxia is still unclear. Here, we report a unique regulatory function of VHL in VEGF expression in hypoxia that is mediated through modulation of TIS11B protein levels in renal cancer cells. In normoxia, we detected increased expression of the microRNA hsa-miR-29b in the VHL-overexpressing renal cancer cell line 786-O. We also show that this increased expression of hsa-miR-29b decreased TIS11B protein expression by post-transcriptional regulation in normoxia. In contrast, in hypoxia, increased TIS11B expression paralleled an increased TIS11B mRNA stability in VHL-overexpressing 786-O cells. This VHL-mediated TIS11B up-regulation in hypoxia may be important for TIS11B-regulated gene expression: we observed a down-regulation of VEGF mRNA in hypoxia in VHL-overexpressing cells compared with parental 786-O cells, and this effect was reversible by silencing TIS11B expression.

The von Hippel-Lindau gene: turning discovery into therapy

Mutations or aberrations of the von Hippel-Lindau gene are responsible for the hereditary neoplastic syndrome that bears the same name, as well as for the majority of sporadic clear cell renal cell carcinomas. The discovery of this gene and subsequent clarification of its mechanism of action have led to a series of targeted treatments for advanced kidney cancer and have dramatically changed how we manage this disease. The discovery of the VHL gene is a prime example of how discoveries at the bench can inform and revolutionize therapeutics at the bedside. In this review, the authors trace this illuminating tale, from the cloning of the VHL gene, to elucidating its biologic function, to the development of novel therapeutics that have dramatically changed the paradigm of managing advanced renal cell carcinoma.

VEGF-A and the induction of pathological angiogenesis

Tumors, wounds, and chronic inflammatory disorders generate a new vascular supply by a process known as pathological angiogenesis. Whereas formation of the normal blood vasculature requires the interaction of many different agonists and inhibitors, including vascular endothelial growth factor-A (VEGF-A) and other members of the vascular permeability factor/VEGF family, pathological angiogenesis is a cruder, simpler process that can be replicated by a single VEGF-A isoform, VEGF-A(164/5). VEGF-A(164/5) induces the formation of several distinctly different types of new blood vessels that differ from normal blood vessels with respect to organization, structure, and function. Elucidating the properties of these new vessels has led to a better understanding of angiogenesis and will hopefully lead to new approaches to antiangiogenic therapy.

Divergent effects of hypoxia on dendritic cell functions

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that patrol tissues to sense danger signals and activate specific immune responses. In addition, they also play a role in inflammation and tissue repair. Here, we show that oxygen availability is necessary to promote full monocyte-derived DC differentiation and maturation. Low oxygen tension (hypoxia) inhibits expression of several differentiation and maturation markers (CD1a, CD40, CD80, CD83, CD86, and MHC class II molecules) in response to lipopolysaccharide (LPS), as well as their stimulatory capacity for T-cell functions. These events are paralleled by impaired up-regulation of the chemokine receptor CCR7, an otherwise necessary event for the homing of mature DCs to lymph nodes. In contrast, hypoxia strongly up-regulates production of proinflammatory cytokines, particularly TNFalpha and IL-1beta, as well as the inflammatory chemokine receptor CCR5. Subcutaneous injection of hypoxic DCs into the footpads of mice results in defective DC homing to draining lymph nodes, but enhanced leukocyte recruitment at the site of injection. Thus, hypoxia uncouples the promotion of inflammatory and tissue repair from sentinel functions in DCs, which we suggest is a safeguard mechanism against immune reactivity to damaged tissues.

Von Hippel-Lindau (VHL) disease: an update on the clinico-pathologic and genetic aspects

von Hippel-Lindau (VHL) disease is an inherited multisystem familial cancer syndrome caused by mutations of the VHL gene on chromosome 3p25. A wide variety of neoplastic processes are known to be associated with VHL disease. The consequences of the VHL mutations and the pathway for tumor development continue to be elucidated. This paper will detail the variety of tumors associated with VHL disease and discuss the genetic mechanisms that lead to the predisposition for neoplasia.

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.

c-Jun kinase mediates expression of VEGF induced at transcriptional level by Rac1 and Cdc42Hs but not by RhoA

Tumour angiogenesis is mediated by increased levels of vascular endothelial growth factor (VEGF). We have studied the mechanism by which endogenous activation of Rho oncoproteins regulates VEGF expression in COS-7 and NIH3T3 cells. We carried out transient and stable transfection with constitutively activated rhoA, rac1, and cdc42 mutants in COS-7 and NIH3T3 cells, respectively in the absence of external stimuli. Western blot and inmunohistochemistry assays of those cells revealed increased VEGF protein expression. Cotransfection with constitutively activated rhoA, rac1, and cdc42 mutants and a VEGF promoter-reporter construct showed an increase in VEGF promoter transcriptional activity induced by Rho oncoproteins in COS-7 and NIH3T3. c-Jun kinase had been described as a MAPK involved in Rho oncoproteins pathways. Interestingly, we found that c-Jun kinase chemical inhibition as well as transient transactivation assays using dominant negative c-Jun kinase mutant abolished the VEGF promoter transcriptional induction by Rac1 and Cdc42 but not by RhoA. These findings indicate that Rho oncoprotein endogenously activated regulates VEGF expression through a transcriptional mechanism, and that the c-Jun kinase activity is a mediator in the expression of VEGF induced by Rac1 and Cdc42 oncoproteins, but not of that induced by RhoA.

Effects of peritoneal fluid from endometriosis patients on the release of vascular endothelial growth factor by neutrophils and monocytes

BACKGROUND

An increase in the level of the vascular endothelial growth factor (VEGF) production has been reported in the peritoneal fluid (PF) of endometriosis patients. This suggests that changes in the vascular permeability and angiogenesis play an important role in the pathophysiology of this disease. This study examined the effects of the PF obtained from endometriosis patients on the release of VEGF by neutrophils and monocytes.

METHODS

Neutrophils and monocytes were obtained from young healthy volunteers and cultured with the PF obtained from either endometriosis patients (EPF) (n=18) or a control group (CPF) (n=4). A human monocyte/macrophage cell line, THP-1, was cultured with either 10% EPF or 10% CPF. The PF and culture supernatants were assayed for VEGF using ELISA. Real-time PCR and Western blotting were used to measure the VEGF mRNA and protein expression level, respectively.

RESULTS

The VEGF levels were higher in the EPF than in the CPF (591+/-75 versus 185+/-31 pg/ml, P<0.05). However, the level of VEGF released by THP-1 cells in CPF and EPF was similar. The EPF induced the release of VEGF by neutrophils, but no VEGF was released by monocytes. The VEGF mRNA expression levels in the neutrophils were higher in the EPF, which was abrogated by cycloheximide, suggesting that the EPF induces the production of VEGF in neutrophils. Neutralizing antibodies against IL-8 and TNF-alpha did not completely prevent the EPF-induced release of VEGF by the neutrophils, even though these growth factors stimulated the release of VEGF by neutrophils. There was a positive correlation between the VEGF and IL-10 concentrations in the EPF (correlation coefficient=0.549, P=0.012, n=18), but the neutralizing antibody of IL-10 did not affect the release of VEGF by the EPF-treated neutrophils.

CONCLUSION

The EPF induced the production and release of VEGF by neutrophils, suggesting that neutrophils may be a source of peritoneal VEGF. In addition, neutrophil-derived VEGF might be a marker for diagnosing endometriosis.

Antagonistic functions of tetradecanoyl phorbol acetate-inducible-sequence 11b and HuR in the hormonal regulation of vascular endothelial growth factor messenger ribonucleic acid stability by adrenocorticotropin

Expression of vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen and a potent angiogenic factor, is up-regulated by a variety of factors including hypoxia, growth factors, and hormones. In the adrenal cortex, regulation of VEGF expression by the pituitary hormone ACTH ensures the maintenance of the organ vasculature. We have previously shown that ACTH evokes a rapid and transient increase in VEGF mRNA levels in primary adrenocortical cells through transcription-independent mechanisms. We further demonstrated that the zinc finger RNA-binding protein Tis11b (tetradecanoyl phorbol acetate-inducible-sequence 11b) destabilizes VEGF mRNA through its 3'-untranslated region (3'-UTR) and that Tis11b is involved in the decay phase of ACTH-induced VEGF mRNA expression. In the present study, we attempted to determine the mechanisms underlying ACTH-elicited increase in VEGF mRNA levels in adrenocortical cells. We show that ACTH triggers an increase in the levels of the mRNA-stabilizing protein HuR in the cytoplasm and a concomitant decrease in the levels of HuR in the nucleus. This process is accompanied by an increased association of HuR with the nucleocytoplasmic shuttling protein pp32, indicating that ACTH induces HuR translocation from the nuclear to the cytoplasmic compartment. Leptomycin B, a specific inhibitor of CRM1-dependent nuclear export of pp32, significantly reduced ACTH-induced VEGF mRNA levels. Furthermore, RNA interference-mediated depletion of HuR in adrenocortical cells abrogated ACTH-induced VEGF mRNA expression. Finally, we show that Tis11b and HuR exert antagonistic effects on VEGF 3'-UTR in vitro. Although both proteins could bind simultaneously on VEGF 3'-UTR, Tis11b markedly decreases HuR-binding to this RNA sequence. Altogether, these results suggest that the RNA-stabilizing protein HuR is instrumental to ACTH-induced expression of VEGF mRNA and that the nuclear export of HuR is a rate-limiting step in this process. HuR appears to transiently stabilize VEGF transcripts after ACTH stimulation of adrenocortical cells, and Tis11b appears to subsequently trigger their degradation.

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.

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.

Metastatic renal cell carcinoma

Patients with renal cell cancer (RCC) develop metastatic spread in approximately 33% of cases. The clinical management of patients with metastatic RCC is complicated by the lack of significant efficacy from available therapies. Common sites of metastases include the lung, liver, bone, brain, and adrenal gland, with case reports detailing the capacity of RCC to appear almost anywhere in the body. More than one organ system is often involved in the metastatic process. Metastases may be found at diagnosis or at some interval after nephrectomy. Approximately 20% to 50% of patients will eventually develop metastatic disease after nephrectomy. A shorter interval between nephrectomy and the development of metastases is associated with a poorer prognosis. Patients with metastatic RCC face a dismal prognosis, with a median survival time of only 6 to 12 months and a 2-year survival rate of 10% to 20%. Recent advances in biologic response modifier therapy have brought new hope to a small percentage of patients who respond to this therapy and rekindled interest in cytoreductive nephrectomy as an integral part of the management of these patients.

Angiogenesis in brain tumors

Angiogenesis is a complex process regulated by multiple stimulatory and inhibitory factors that are able to modulate the migration and/or proliferation of microvascular cells with the objective of formation of neovasculature from preexisting vessels. It involves well-coordinated steps including production and release of angiogenic factors, proteolytic degradation of extracellular matrix components to allow formation of capillary sprout, proliferation and directional migration of microvascular cells, and the final composition of new vessels [Senger (1996) Am. J. Pathol. 149:1-7]. Angiogenesis is present in a number of hypoxic and/or ischemic conditions in the central nervous system, in particular in infarctions and infectious processes. Angiogenesis also plays an important role in malignant primary tumors. Glioblastomas, the most malignant gliomas in adults, are among the most angiogenic of all human tumors. This review will examine recent data of the role of angiogenic growth factors in the neoplastic and reactive conditions in the brain.

Natural antisense transcripts of hypoxia-inducible factor 1alpha are detected in different normal and tumour human tissues

Hypoxia-inducible factor 1 is a heterodimeric transcription factor, made up of two subunits called HIF-1alpha and aryl receptor nuclear translocator, that regulates the expression of genes associated with adaptation to reduced oxygen pressure. The HIF-1alpha messenger RNA (mRNA) and protein are both up-regulated in common human cancers where this transcription factor is known to be involved in tumour progression. In renal carcinoma, a natural antisense of HIF-1alpha transcript (aHIF) that is complementary to the 3'untranslated region of HIF-1alpha mRNA has been described. Here, we provide a grown work for further characterisation of this natural antisense and we show that: (1) aHIF is widely expressed in normal foetal and adult human tissues as in tumour tissues. Foetal aHIF expression level is higher than adult one and high enough to affect the HIF-1alpha mRNA/aHIF transcripts ratio; (2) aHIF could expose AU rich elements present in the 3' untranslated region of HIF-1alpha mRNA and thus possibly increase the degradation speed of HIF-1alpha mRNA; and (3) aHIF promoter possesses several putative hypoxia response elements which could explain the overexpression of aHIF under hypoxic conditions, creating a negative loop of regulation of HIF-1alpha expression.

Hu protein R-mediated posttranscriptional regulation of VEGF expression in rat gastrocnemius muscle

Hypoxic exercise increases VEGF expression and the formation of new capillaries. In addition to hypoxia-inducible factor regulation at the transcriptional level, VEGF message stabilization is also a key regulatory step for VEGF expression. In vitro experiments have identified Hu protein R (HuR) as a potential posttranscriptional regulator of VEGF gene expression. Here, we report that in rat skeletal muscle (gastrocnemius muscle), 1) HuR binds to a known regulatory sequence located in the VEGF mRNA 3'-untranslated region (1,631-1,678 bp); 2) HuR specifically binds to the A/U-rich element AUUUUA (1,665-1,670 bp) and an additional A/U-rich region containing the consensus sequence UUUUUUA (1,658-1,664 bp); 3) binding of HuR to VEGF mRNA is seen already 5 min after acute ischemia, remaining elevated throughout a 60-min ischemic period; 4) a second inducible HuR-VEGF mRNA binding factor is evident 30 and 60 min postischemia; and 5) VEGF mRNA and protein levels are increased 20 and 30 min, respectively, after acute ischemia. These findings suggest that acute ischemia induces a rapid binding of HuR to the VEGF mRNA 3'-untranslated region. In skeletal muscle, this specific protein-RNA interaction may be an important posttranscriptional regulatory mechanism for increasing VEGF expression in response to hypoxia or acute ischemia.

Responding to hypoxia: lessons from a model cell line

Mammalian cells require a constant supply of oxygen to maintain adequate energy production, which is essential for maintaining normal function and for ensuring cell survival. Sustained hypoxia can result in cell death. It is, therefore, not surprising that sophisticated mechanisms have evolved that allow cells to adapt to hypoxia. "Oxygen-sensing" is a special phenotype that functions to detect changes in oxygen tension and to transduce this signal into organ system functions that enhance the delivery of oxygen to tissue in various organisms. Oxygen-sensing cells can be segregated into two distinct cell types: those that functionally depolarize (excitable) and those that do not functionally depolarize (nonexcitable) in response to reduced oxygen. Theoretically, excitable cells have all the same signaling capabilities as the nonexcitable cells, but the nonexcitable cells cannot have all the signaling capabilities as excitable cells. A number of signaling pathways have been identified that regulate gene expression during hypoxia. These include the Ca2+-calmodulin pathway, the 3'-5' adenosine monophosphate (cAMP)-protein kinase A (PKA) pathway, the p42 and p44 mitogen-activated protein kinase [(MAPK); also known as the extracellular signal-related kinase (ERK) for ERK1 and ERK2] pathway, the stress-activated protein kinase (SAPK; also known as p38 kinase) pathway, and the phosphatidylinositol 3-kinase (PI3K)-Akt pathway. In this review, we describe hypoxia-induced signaling in the model O2-sensing rat pheochromocytoma (PC12) cell line, the current level of understanding of the major signaling events that are activated by reduced O2, and how these signaling events lead to altered gene expression in both excitable and nonexcitable oxygen-sensing cells.

Effects of cytokines on VEGF expression and secretion by human first trimester trophoblast cell line

PROBLEM

The mechanism through which vascular endothelial growth factor (VEGF) regulation occurs at the feto-maternal interface is poorly understood. The aim of this study was to investigate the effects of various cytokines on VEGF expression and secretion by trophoblast cells.

METHOD OF STUDY

We investigated the effects of cytokines on VEGF expression in human first trimester trophoblast cell line by analyzing VEGF messenger RNA (mRNA) by reverse transcription-polymerase chain reaction and VEGF protein secretion by enzyme linked immunosorbent assay.

RESULTS

The trophoblast cells expressed VEGF mRNA constitutively and the main subtypes were identified as VEGF121 and VEGF165. When cultured in the presence of interferon (IFN)-gamma, interleukin (IL)- 1beta, tumor necrosis factor (TNF)-alpha, IL-2, or IL-10, VEGF mRNA expression was found to be significantly increased by IL-1beta, IFN-gamma and TNF-alpha but to be unaffected by IL-2 and IL-10. Moreover, VEGF secretion was most significantly increased by IFN-gamma treatment.

CONCLUSION

These results suggest that IL-1beta, IFN-gamma, and TNF-alpha may regulate the production of VEGF in early gestational trophoblasts.

Ras regulation of vascular endothelial growth factor and angiogenesis

Given the multifaceted role of Ras in tumor angiogenesis, pharmacologic targeting of such proteins may bring about at least three important consequences: (1) partial obliteration of the angiogenic competence of tumor cells, (2) an increase in vascular dependence and sensitization to apoptosis, and (3) a direct inhibition of endothelial cell responses to proangiogenic stimuli. Exploration of some of these possibilities, using various pharmacological compounds and antibodies, has already begun. An intriguing possibility is that Ras antagonists and signal transduction inhibitors may synergize with a number of other antiangiogenic modalities such as direct acting antiangiogenic agents (e.g., endostatin) or antivascular regimens involving low-dose continuous chemotherapy as a vasculature-targeting strategy.

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

Hypoxia is an important pathophysiological stress that occurs during blood vessel injuries and tumor growth. It is now well documented that hypoxia leads to the activation of several transcription factors which participate in the adaptive response of the cells to hypoxia. Among these transcription factors, AP-1 is rapidly activated by hypoxia and triggers bFGF, VEGF, and tyrosine hydroxylase gene expression. However, the mechanisms of AP-1 activation by hypoxia are not well understood. In this report, we studied the events leading to AP-1 activation in hypoxia. We found that c-jun protein accumulates in hypoxic HepG2 cells. This overexpression is concomitant with c-jun phosphorylation and JNK activation. Moreover, we showed that AP-1 is transcriptionally active. We also observed that AP-1 transcriptional activity is inhibited by a MEKK1 dominant negative mutant. Moreover, the MEKK1 dominant negative mutant as well as deletion of the AP-1 binding sites within the c-jun promoter inhibited the c-jun promoter activation by hypoxia. All together, these results indicate that, in hypoxic HepG2 cells, AP-1 is activated through a JNK-dependent pathway and that it is involved in the regulation of the c-jun promoter, inducing a positive feedback loop on AP-1 activation via c-jun overexpression.

Oncogenes and angiogenesis: signaling three-dimensional tumor growth

Three-dimensional tumor growth is dependent on the perpetual recruitment of host blood vessels to the tumor site. This recruitment process (mainly via angiogenesis) is thought to be triggered, at least in part, by the very same set of genetic alterations (activated oncogenes, inactivated/lost tumor suppressor genes) as those responsible for other aspects of malignant transformation (e.g., aberrant mitogenesis, resistance to apoptosis). Potent oncogenes are able to deregulate expression of both angiogenesis stimulators and inhibitors in cancer cells. For example, mutant ras expression is associated with increased production of vascular endothelial growth factor (VEGF) and downregulation of thrombospondin-1 (TSP-1). Upregulation of VEGF and angiogenesis can also be induced by constitutive activation of other oncogenic proteins (e.g., EGFR, Raf, MEK, PI3K) acting at various levels on the Ras signaling pathway. The mode and the magnitude of such proangiogenic influences can be significantly modified by cell type (fibroblastic or epithelial origin), epigenetic factors (hypoxia, changes in cell density), and/or presence of additional genetic lesions (e.g., preceding loss of p16 or p53 tumor suppressor genes). Activated oncogenes (e.g., ras, src, HER-2) induce co-expression of angiogenic properties concomitantly with several highly selectable traits (increased mitogenesis, resistance to apoptosis), a circumstance that may accelerate selection of the angiogenic phenotype at the cell population level. On the other hand oncogene-induced reduction in growth requirements may also endow tumor cells with a diminished (albeit not abrogated) dependence on (close) proximity to blood vessels, i.e., with reduced vascular dependence. Thus, oncogenes can impact several interconnected aspects of cellular growth, survival, and angiogenesis. Experimental evidence suggests that, in principle, many of these properties (including angiogenesis) can be simultaneously suppressed (and tumor stasis or regression induced) by effective use of the specific oncogene antagonists and signal transduction inhibitors.

Expression and regulation of vascular endothelial growth factor in a first trimester trophoblast cell line

Embryo implantation and development are critically dependent upon the spatial and temporal regulation of angiogenesis and localized vascular permeability. A key mediator of these effects is the endothelial cell mitogen vascular endothelial growth factor (VEGF). VEGF has been shown to promote endometrial vascular permeability, fetal vasculogenesis and placental, fetal and maternal angiogenesis. However, the mechanism through which this regulation occurs in the placenta is poorly understood. This study was conducted to determine if the pro-angiogenic cytokines, TNF-alpha and TGF-beta1, affect VEGF expression in human first trimester trophoblasts. Culture of a first trimester trophoblast cell line (HTR-8/SVneo), in the presence of either TNF-alpha or TGF-beta1, resulted in the expression of significant levels of VEGF in culture. The trophoblast cell line also showed a time-dependent and a dose-dependent increase in VEGF mRNA levels when cultured in the presence of either TNF-alpha or TGF-beta1. These results suggest that both TNF-alpha and TGF-beta1 may regulate the production of VEGF in early gestational trophoblasts and may therefore serve to modulate placental vascular permeability and angiogenesis that are necessary for embryo implantation and placentation.

Renal lesions in von Hippel-Lindau disease: immunohistochemical expression of nephron differentiation molecules, adhesion molecules and apoptosis proteins

AIMS

Renal lesions in von Hippel-Lindau disease comprise clear cell simple cysts, atypical cysts and carcinomas. Although histological and molecular studies suggest that cystic lesions may represent precursors of carcinomas, there is no detailed phenotypic evidence of their relationship.

METHODS AND RESULTS

To investigate such a possible relationship between cystic lesions and solid carcinomas, we studied the pathological and immunohistochemical features of 328 lesions of 33 kidneys originating from 23 patients with von Hippel-Lindau disease, using a panel of antibodies directed against cytoskeleton proteins, cell surface proteins, integrin subunits, adhesion molecules, lectins, and apoptosis and proliferation markers. Solid carcinomas (n = 175) were all of clear cell type and mostly nuclear grade 1. Cystic lesions (n = 138) consisted of cystic clear cell carcinomas (n = 15), atypical cysts (n = 20) and simple cysts (n = 103). Clear cells of the simple cysts, atypical cysts and solid carcinomas coexpressed cytokeratins (CK8, CK19) and vimentin, and expressed a similar pattern of tubular markers (CD24, tetraglonolobus), integrin subunits (alpha3, alpha5, alpha6, alphav, beta1) and cell adhesion molecules (ICAM 1, VCAM 1). In all lesions studied, proliferation rate (MIB1 index) was low, and apoptosis marker expression (fragmented DNA, p53, bcl-2) inconspicuous.

CONCLUSIONS

Phenotypic alterations found in solid renal cell carcinomas are already present in simple and atypical renal cysts of von Hippel-Lindau disease.

Vascular endothelial growth factor expression is independent of hypoxia in human malignant glioma spheroids and tumours

We recently showed that severe hypoxia was not universally present adjacent to necrosis in human glioma xenografts and spheroids established from the M059K, M006, M006X, M006XLo and M010b cell lines. Using these glioma models, we wished to test whether oxygen serves as a regulator of cellular VEGF expression in situ. In situ hybridization (ISH) and immunohistochemistry (IHC) were used to detect vascular endothelial growth factor (VEGF) mRNA and protein expression in sections of glioma xenografts and spheroids in which hypoxic regions and regions with well-oxygenated necrosis were identified on contiguous sections by use of the hypoxia-specific marker, 3H-misonidazole. Independent validation of the presence of radiobiologically hypoxic cells in M006 xenografts was undertaken using the comet assay. Northern blotting analyses of monolayer cells demonstrated significant up-regulation of VEGF mRNA in the M006X line at oxygen concentrations of 6% and below. ISH analysis of VEGF mRNA showed unexpectedly strong staining for VEGF mRNA across the entire viable rim of M006X and M006XLo glioma spheroids. Similarly, in virtually all xenograft tumours of the M059K, M006 and M010b lines, VEGF ISH showed similar staining across all regions of healthy cells up to the border of necrosis. Only in one M006X tumour was there a suggestion of increased VEGF expression in cells adjacent to necrosis. IHC for VEGF showed good concordance with the ISH results. IHC analysis of the VEGF receptor flt-1 showed strong tumour cell staining in M006XLo glioma cells. In human glioma spheroids and xenograft tumours, regions of severe hypoxia do not correspond to areas of up-regulated VEGF expression; in fact, VEGF expression is quite uniform. Furthermore, this and our previous study demonstrate that levels of VEGF expression vary among sublines (M006, M006X and M006XLo) derived from a single human glioma specimen.

Hypothermia abolishes hypoxia-induced hyperpermeability in brain microvessel endothelial cells

The effect of mild (32 degrees C) and deep (22 degrees C) hypothermia on hypoxia-induced hyperpermeability was examined using an in vitro model of brain derived microvascular endothelial cells (BMEC). It was shown that hypoxia-induced hyperpermeability to inulin across the BMEC monolayer was completely abolished at 32 degrees C and 22 degrees C for up to 24 h of hypoxia. During normoxia, no influence of hypothermia on BMEC monolayer permeability was observed. The hypoxia-induced decrease of the cyclic AMP level after 6 h was abolished at 32 degrees C as well as at 22 degrees C of hypoxia. But after 24 h of hypoxia, hypothermia did no longer prevent the hypoxia-induced decrease of the cAMP level, which suggests that the effect of hypothermia on hypoxia-induced hyperpermeability is not caused by maintenance of the cAMP level. Because vascular endothelial growth factor (VEGF) has been shown to be the mediator of hypoxia-induced permeability changes of BMEC via the release of nitric oxide (NO), the effect of hypothermia on the VEGF expression was evaluated. During normoxia, hypothermia did not change the VEGF expression significantly but the hypoxia-induced increase in VEGF mRNA and protein expression was completely abolished at 32 degrees C and 22 degrees C respectively. Accordingly, the hypoxia-induced increase of the cGMP level was depressed by hypothermia, which demonstrates that also the amount of NO released during hypoxia is decreased at lower temperatures. Results suggest that deep as well as mild hypothermia decreased hypoxia-induced hyperpermeability by lowering the expression of the permeability-increasing protein VEGF and with it the release of NO.

Urological malignancies and the proteomic-genomic interface

The urological malignancies, renal, bladder and prostate cancer, account for approximately 16% of all cancer cases. Unfortunately 5-year survival rates are relatively poor, largely a result of many cases not being diagnosed before the tumour has metastasised. There is a clear need for the identification of markers which will allow earlier detection of disease, and predict prognosis and response to therapy. In addition, they may be of use as therapeutic targets. Current advances in molecular biology are allowing the identification of a number of tumour-associated changes which could be of clinical use in the future. However, with the rapid technological advances being made in the field of proteomics, this approach could be integrated with genomics providing a complementary alternative, overcoming disparities between mRNA levels and protein production, and additionally allowing the identification of tumour-associated post-translational modifications. These approaches have already been used to identify novel genes and other cancer-related changes involved in the pathogenesis of urological malignancies. This review describes current progress in the genomic and proteomic study of urological malignancies, and highlights the potential of using proteomic technologies in the study of this group of diseases.

Altered gene expression during hypoxia and reoxygenation of the heart

The heart is exposed to alterations in oxygen tension under different pathophysiological conditions. In order to maintain function, changes in the pattern of cardiac gene expression arise. Through the activity of multiple transcription factors, which include activating protein-1, hypoxia-inducible factor-1, and nuclear factor kappaB, there is up-regulation of mRNA encoding factors that enable the cardiomyocyte to adapt to the new environment. In the case of hypoxia or anoxia, there is an increased expression of growth factors, glucose transporters, enzymes associated with anaerobic glycolysis, and stress proteins. When the cardiomyocyte is reoxygenated after hypoxia, there is a rapid increase in antioxidants, pro-inflammatory cytokines, and stress proteins.

Targeting cancer therapy

Cellular responses to hypoxia include modulation of respiration rate and up-regulation of genes which encode for angiogenesis factors. We tested whether human malignant glioma cells vary in their response to hypoxic stress over the range of oxygen concentrations which exist in tumours. In five cell lines tested, decreased oxygen availability resulted in decreased rates of oxygen utilization, however substantial differences in the magnitude of the response were observed. Northern blot analysis was used to study induction of vascular endothelial growth factor mRNA in response to hypoxia. In two cell lines, modest hypoxia increased vascular endothelial growth factor mRNA levels compared with those of aerobic controls. In two additional cell lines, vascular endothelial growth factor mRNA was constituitively expressed under aerobic conditions and was not further increased by hypoxia. These findings demonstrate that differences in the response to hypoxia exist among human malignant glioma cell lines and suggest that therapies designed to exploit tumour hypoxia may have varying effects in tumours with different hypoxic stress responses. © 1999 Cancer Research Campaign

Protective function of von Hippel-Lindau protein against impaired protein processing in renal carcinoma cells

The absence of functional von Hippel-Lindau (VHL) tumor suppressor gene leads to the development of neoplasias characteristic of VHL disease, including renal cell carcinoma (RCC). Here, we compared the sensitivity of RCC cells lacking VHL gene function with that of RCC cells expressing the wild-type VHL gene (wtVHL) after exposure to various stresses. While the response to most treatments was not affected by the VHL gene status, glucose deprivation was found to be much more cytotoxic for RCC cells lacking VHL gene function than for wtVHL-expressing cells. The heightened sensitivity of VHL-deficient cells was not attributed to dissimilar energy requirements or to differences in glucose uptake, but more likely reflects a lesser ability of VHL-deficient cells to handle abnormally processed proteins arising from impaired glycosylation. In support of this hypothesis, other treatments which act through different mechanisms to interfere with protein processing (i.e., tunicamycin, brefeldin A, and azetidine) were also found to be much more toxic for VHL-deficient cells. Furthermore, ubiquitination of cellular proteins was elevated in VHL-deficient cells, particularly after glucose deprivation, supporting a role for the VHL gene in ubiquitin-mediated proteolysis. Accordingly, the rate of elimination of abnormal proteins was lower in cells lacking a functional VHL gene than in wtVHL-expressing cells. Thus, pVHL appears to participate in the elimination of misprocessed proteins, such as those arising in the cell due to the unavailability of glucose or to other stresses.