Von Hippel-Lindau tumor suppressor protein and hypoxia-inducible factor in kidney cancer

Deficits in mitochondrial TCA cycle and OXPHOS precede rod photoreceptor degeneration during chronic HIF activation

BACKGROUND

Major retinal degenerative diseases, including age-related macular degeneration, diabetic retinopathy and retinal detachment, are associated with a local decrease in oxygen availability causing the formation of hypoxic areas affecting the photoreceptor (PR) cells. Here, we addressed the underlying pathological mechanisms of PR degeneration by focusing on energy metabolism during chronic activation of hypoxia-inducible factors (HIFs) in rod PR.

METHODS

We used two-photon laser scanning microscopy (TPLSM) of genetically encoded biosensors delivered by adeno-associated viruses (AAV) to determine lactate and glucose dynamics in PR and inner retinal cells. Retinal layer-specific proteomics, in situ enzymatic assays and immunofluorescence studies were used to analyse mitochondrial metabolism in rod PRs during chronic HIF activation.

RESULTS

PRs exhibited remarkably higher glycolytic flux through the hexokinases than neurons of the inner retina. Chronic HIF activation in rods did not cause overt change in glucose dynamics but an increase in lactate production nonetheless. Furthermore, dysregulation of the oxidative phosphorylation pathway (OXPHOS) and tricarboxylic acid (TCA) cycle in rods with an activated hypoxic response decelerated cellular anabolism causing shortening of rod photoreceptor outer segments (OS) before onset of cell degeneration. Interestingly, rods with deficient OXPHOS but an intact TCA cycle did not exhibit these early signs of anabolic dysregulation and showed a slower course of degeneration.

CONCLUSION

Together, these data indicate an exceeding high glycolytic flux in rods and highlight the importance of mitochondrial metabolism and especially of the TCA cycle for PR survival in conditions of increased HIF activity.

MiRNAs in renal cell carcinoma

MicroRNAs (miRNAs) are small RNA sequences that act as post-transcriptional regulatory genes to control many cellular processes through pairing bases with a complementary messenger RNA (mRNA). A single miRNA molecule can regulate more than 200 different transcripts and the same mRNA can be regulated by multiple miRNAs. In this review, we highlight the importance of miRNAs and collect the existing evidence on their relationship with kidney cancer.

Abnormal expression and the significant prognostic value of aquaporins in clear cell renal cell carcinoma

Aquaporins (AQPs) are a kind of transmembrane proteins that exist in various organs of the human body. AQPs play an important role in regulating water transport, lipid metabolism and glycolysis of cells. Clear cell renal cell carcinoma (ccRCC) is a common malignant tumor of the kidney, and the prognosis is worse than other types of renal cell cancer (RCC). The impact of AQPs on the prognosis of ccRCC and the potential relationship between AQPs and the occurrence and development of ccRCC are demanded to be investigated. In this study, we first explored the expression pattern of AQPs by using Oncomine, UALCAN, and HPA databases. Secondly, we constructed protein-protein interaction (PPI) network and performed function enrichment analysis through STRING, GeneMANIA, and Metascape. Then a comprehensive analysis of the genetic mutant frequency of AQPs in ccRCC was carried out using the cBioPortal database. In addition, we also analyzed the main enriched biological functions of AQPs and the correlation with seven main immune cells. Finally, we confirmed the prognostic value of AQPs throughGEPIA and Cox regression analysis. We found that the mRNA expression levels of AQP0/8/9/10 were up-regulated in patients with ccRCC, while those of AQP1/2/3/4/5/6/7/11 showed the opposite. Among them, the expression differences of AQP1/2/3/4/5/6/7/8/9/11 were statistically significant. The differences in protein expression levels of AQP1/2/3/4/5/6 in ccRCC and normal renal tissues were consistent with the change trends of mRNA. The biological functions of AQPs were mainly concentrated in water transport, homeostasis maintenance, glycerol transport, and intracellular movement of sugar transporters. The high mRNA expression levels of AQP0/8/9 were significantly correlated with worse overall survival (OS), while those of AQP1/4/7 were correlated with better OS. AQP0/1/4/9 were prognostic-related factors, and AQP1/9 were independent prognostic factors. In general, this research has investigated the values of AQPs in ccRCC, which could become new survival markers for ccRCC targeted therapy.

Protein networks linking Warburg and reverse Warburg effects to cancer cell metabolism

It was 80 years after the Otto Warburg discovery of aerobic glycolysis, a major hallmark in the understanding of cancer. The Warburg effect is the preference of cancer cell for glycolysis that produces lactate even when sufficient oxygen is provided. "reverse Warburg effect" refers to the interstitial tissue communications with adjacent epithelium, that in the process of carcinogenesis, is needed to be explored. Among these cell-cell communications, the contact between epithelial cells; between epithelial cells and matrix; and between fibroblasts and inflammatory cells in the underlying matrix. Cancer involves dysregulation of Warburg and reverse Warburg cellular metabolic pathways. How these gene and protein-based regulatory mechanisms have functioned has been the basis for this review. The importance of the Warburg in oxidative phosphorylation suppression, with increased glycolysis in cancer growth and proliferation is emphasized. Studies that are directed at pathways that would be expected to shift cell metabolism to an increased oxidation and to a decrease in glycolysis are emphasized. Key enzymes required for oxidative phosphorylation, and affect the inhibition of fatty acid metabolism and glutamine dependence are conferred. The findings are of special interest to cancer pharmacotherapy. Studies described in this review are concerned with the effects of therapeutic modalities that are intimately related to the Warburg effect. These interactions described may be helpful as adjuvant therapy in controlling the process of proliferation and metastasis.

Effect of PACAP on Hypoxia-Induced Angiogenesis and Epithelial-Mesenchymal Transition in Glioblastoma

Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts different effects in various human cancer. In glioblastoma (GBM), PACAP has been shown to interfere with the hypoxic micro-environment through the modulation of hypoxia-inducible factors via PI3K/AKT and MAPK/ERK pathways inhibition. Considering that hypoxic tumor micro-environment is strictly linked to angiogenesis and Epithelial–Mesenchymal transition (EMT), in the present study, we have investigated the ability of PACAP to regulate these events. Results have demonstrated that PACAP and its related receptor, PAC1R, are expressed in hypoxic area of human GBM colocalizing either in epithelial or mesenchymal cells. By using an in vitro model of GBM cells, we have observed that PACAP interferes with hypoxic/angiogenic pathway by reducing vascular-endothelial growth factor (VEGF) release and inhibiting formation of vessel-like structures in H5V endothelial cells cultured with GBM-conditioned medium. Moreover, PACAP treatment decreased the expression of mesenchymal markers such as vimentin, matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9) as well as CD44 in GBM cells by affecting their invasiveness. In conclusion, our study provides new insights regarding the multimodal role of PACAP in GBM malignancy.

Tumor Hypoxia as a Barrier in Cancer Therapy: Why Levels Matter

Simple Summary

Hypoxia is a common feature of solid tumors and associated with poor outcome in most cancer types and treatment modalities, including radiotherapy, chemotherapy, surgery and, most likely, immunotherapy. Emerging strategies, such as proton therapy and combination therapies with radiation and hypoxia targeted drugs, provide new opportunities to overcome the hypoxia barrier and improve therapeutic outcome. Hypoxia is heterogeneously distributed both between and within tumors and shows large variations across patients not only in prevalence, but importantly, also in level. To best exploit the emerging strategies, a better understanding of how individual hypoxia levels from mild to severe affect tumor biology is vital. Here, we discuss our current knowledge on this topic and how we should proceed to gain more insight into the field.

Abstract

Hypoxia arises in tumor regions with insufficient oxygen supply and is a major barrier in cancer treatment. The distribution of hypoxia levels is highly heterogeneous, ranging from mild, almost non-hypoxic, to severe and anoxic levels. The individual hypoxia levels induce a variety of biological responses that impair the treatment effect. A stronger focus on hypoxia levels rather than the absence or presence of hypoxia in our investigations will help development of improved strategies to treat patients with hypoxic tumors. Current knowledge on how hypoxia levels are sensed by cancer cells and mediate cellular responses that promote treatment resistance is comprehensive. Recently, it has become evident that hypoxia also has an important, more unexplored role in the interaction between cancer cells, stroma and immune cells, influencing the composition and structure of the tumor microenvironment. Establishment of how such processes depend on the hypoxia level requires more advanced tumor models and methodology. In this review, we describe promising model systems and tools for investigations of hypoxia levels in tumors. We further present current knowledge and emerging research on cellular responses to individual levels, and discuss their impact in novel therapeutic approaches to overcome the hypoxia barrier.

MCPIP1 inhibits Wnt/β-catenin signaling pathway activity and modulates epithelial-mesenchymal transition during clear cell renal cell carcinoma progression by targeting miRNAs

Epithelial-mesenchymal transition (EMT) refers to the acquisition of mesenchymal properties in cells participating in tumor progression. One hallmark of EMT is the increased level of active β-catenin, which can trigger the transcription of Wnt-specific genes responsible for the control of cell fate. We investigated how Monocyte Chemotactic Protein-1-Induced Protein-1 (MCPIP1), a negative regulator of inflammatory processes, affects EMT in a clear cell renal cell carcinoma (ccRCC) cell line, patient tumor tissues and a xenotransplant model. We showed that MCPIP1 degrades miRNAs via its RNase activity and thus protects the mRNA transcripts of negative regulators of the Wnt/β-catenin pathway from degradation, which in turn prevents EMT. Mechanistically, the loss of MCPIP1 RNase activity led to the upregulation of miRNA-519a-3p, miRNA-519b-3p, and miRNA-520c-3p, which inhibited the expression of Wnt pathway inhibitors (SFRP4, KREMEN1, CXXC4, CSNK1A1 and ZNFR3). Thus, the level of active nuclear β-catenin was increased, leading to increased levels of EMT inducers (SNAI1, SNAI2, ZEB1 and TWIST) and, consequently, decreased expression of E-cadherin, increased expression of mesenchymal markers, and acquisition of the mesenchymal phenotype. This study revealed that MCPIP1 may act as a tumor suppressor that prevents EMT by stabilizing Wnt inhibitors and decreasing the levels of active β-catenin and EMT inducers.

Exploring New Therapeutic Pathways in Pulmonary Hypertension. Metabolism, Proliferation, and Personalized Medicine

In this review, we explore the main themes from the 62nd Annual Aspen Lung Conference (hypoxia, cellular metabolism, inflammatory pathways, aberrant proliferation, and personalized medicine) and highlight challenges and opportunities in the coming decade of pulmonary vascular disease.

Hypoxia-induced alternative splicing: the 11th Hallmark of Cancer

Hypoxia-induced alternative splicing is a potent driving force in tumour pathogenesis and progression. In this review, we update currents concepts of hypoxia-induced alternative splicing and how it influences tumour biology. Following brief descriptions of tumour-associated hypoxia and the pre-mRNA splicing process, we review the many ways hypoxia regulates alternative splicing and how hypoxia-induced alternative splicing impacts each individual hallmark of cancer. Hypoxia-induced alternative splicing integrates chemical and cellular tumour microenvironments, underpins continuous adaptation of the tumour cellular microenvironment responsible for metastatic progression and plays clear roles in oncogene activation and autonomous tumour growth, tumor suppressor inactivation, tumour cell immortalization, angiogenesis, tumour cell evasion of programmed cell death and the anti-tumour immune response, a tumour-promoting inflammatory response, adaptive metabolic re-programming, epithelial to mesenchymal transition, invasion and genetic instability, all of which combine to promote metastatic disease. The impressive number of hypoxia-induced alternative spliced protein isoforms that characterize tumour progression, classifies hypoxia-induced alternative splicing as the 11th hallmark of cancer, and offers a fertile source of potential diagnostic/prognostic markers and therapeutic targets.

Analysis of Multiplicity of Hypoxia-Inducible Factors in the Evolution of Triplophysa Fish (Osteichthyes: Nemacheilinae) Reveals Hypoxic Environments Adaptation to Tibetan Plateau

HIF (Hypoxia-inducible factor) gene family members function as master regulators of cellular and systemic oxygen homeostasis during changes in oxygen availability. Qinghai-Tibet Plateau is a natural laboratory for for long-term hypoxia and cold adaptation. In this context, T. scleroptera that is restricted to >3500 m high-altitude freshwater rivers was selected as the model to compare with a representative species from the plain, P. dabryanus. We cloned different HIF-α and carried out a phylogenetic analysis from invertebrates to vertebrates for identifying HIF-α genes and analyzing their evolutionary history. Intriguingly, the HIF-α has undergone gene duplications might be due to whole-genome duplication (WGD) events during evolution. PAML analysis indicated that HIF-1αA was subjected to positive selection acted on specific sites in Triplophysa lineages. To investigate the relationship between hypoxia adaptation and the regulation of HIF-α stability by pVHL in plateau and plain fish, a series of experiments were carried out. Comparison the luciferase transcriptional activity and protein levels of HIF-αs and the differing interactions of HIF-αs with pVHL, show clear differences between plateau and plain fish. T. scleroptera pVHL could enhance HIF-α transcriptional activity under hypoxia, and functional validation through pVHL protein mutagenesis showed that these mutations increased the stability of HIF-α and its hetero dimerization affinity to ARNT. Our research shows that missense mutations of pVHL induced evolutionary molecular adaptation in Triplophysa fishes living in high altitude hypoxic environments.

Various forms of HIF-1α protein characterize the clear cell renal cell carcinoma cell lines

Renal cell carcinoma (RCC) represents around 2-3% of all malignancies diagnosed in adult patients. Most frequent (around 70-80% cases) and the most aggressive subtype is clear cell RCC (ccRCC). Mutations in VHL (von Hippel Lindau) gene, characteristic for this cancer type, lead to altered activity of the trimeric VBC (pVHL-elongin B-C) complex and consequently to HIF-1α stabilization. In this study, we present results of exhaustive investigation of HIF-1α alternative transcript variants abundance in A498, CAKI-1, and 786-O ccRCC cell lines. We proved the existence of truncated HIF-1α protein form (HIF1A∆-6) in A498 and HIF1A gene rearrangements in 786-O cell lines. Subsequently, we found that HIF1A∆2-6 was more stable than the full-length HIF-1α. Moreover, the shorter HIF-1α was insensitive for hypoxia and was overaccumulated after proteasome inhibitor treatment indicative of potential diversified roles of full-length and truncated HIF-1α forms in the cell. We also showed that A498, CAKI-1, and 786-O exhibit differential expression of various regulatory genes involved in the control of metabolic processes, that is, glucose and lipid metabolism, and encoding subunits of such machineries like SWI/SNF chromatin remodeling complex. Furthermore, these cell lines exhibited differential responses to axitinib, everolimus, and sunitinib-anticancer drugs-in normoxia and hypoxia as well as various alterations in metabolism-related regulatory processes. Finally, we have shown that overexpression of truncated HIF1A∆2-6 form may affect the protein level of endogenous full-length HIF-1α protein. Thus, our study proves an important role of HIF-1α in the ccRCC development.

Sunitinib for Metastatic Renal Cell Carcinoma: A Systematic Review and Meta-Analysis of Real-World and Clinical Trials Data

Background

Randomized controlled trials (RCTs) have stringent inclusion criteria and may not fully represent patients seen in everyday clinical practice. Real-world data (RWD) can provide supportive evidence for the effectiveness of medical interventions in more heterogeneous populations than RCTs. Sunitinib is a widely used first-line treatment for patients with metastatic renal cell carcinoma (mRCC).

Objective

This is the first comprehensive meta-analysis to evaluate the efficacy of sunitinib using the novel approach of combining RCTs and RWD.

Methods

RCTs and RWD studies published between 2000 and 2017 were identified from PubMed, Ovid, MEDLINE, and EMBASE. Eligible studies contained a cohort of ≥ 50 adult patients with mRCC receiving first-line sunitinib treatment. The meta-analysis combined RWD and RCT treatment groups, adjusting for data type (RCT or RWD). Recorded outcomes were median progression-free survival (mPFS), median overall survival (mOS), and objective response rate (ORR). Publication bias was assessed via review of funnel plots for each outcome measure. A random effects model to account for study heterogeneity was applied to each endpoint. Sensitivity analyses evaluated the robustness of the overall estimates.

Results

Of the 3611 studies identified through medical database searches, 22 (15 RWD studies, 7 RCTs) met eligibility criteria and were analyzed. mPFS (18 studies), mOS (19 studies), and ORR (15 studies) were reported for aggregate measures based on 4815, 5321, and 4183 patients, respectively. Reported mPFS (RWD, 7.5–11.0 months; RCTs, 5.6–15.1 months) and ORR data (RWD, 14.0–34.6%; RCTs, 18.8–46.9%) were consistent with the overall confidence estimates (95% confidence interval [CI]) of 9.3 (8.6–10.2) months and 27.9% (24.2–32.0), respectively. Reported mOS showed greater variation in RWD (6.8–33.2 months) compared with RCTs (21.8–31.5 months), with an overall confidence estimate (95% CI) of 23.0 (19.2–27.6) months. Inspection of funnel plots and sensitivity analyses indicated that there was no publication bias for any efficacy endpoint. Sensitivity analyses showed no evidence of lack of robustness for mPFS, mOS, or ORR. Interpretation of these results is limited by differences in trial design, cohort characteristics, and missing data.

Conclusions

This novel, comprehensive meta-analysis validates sunitinib as an effective first-line treatment for patients with mRCC in both RCTs and everyday clinical practice. The methodology provides a framework for future analyses combining data from RCTs and RWD.

Electronic supplementary material

The online version of this article (10.1007/s11523-019-00653-5) contains supplementary material, which is available to authorized users.

Hypoxia and aging

Eukaryotic cells require sufficient oxygen (O₂) for biological activity and survival. When the oxygen demand exceeds its supply, the oxygen levels in local tissues or the whole body decrease (termed hypoxia), leading to a metabolic crisis, threatening physiological functions and viability. Therefore, eukaryotes have developed an efficient and rapid oxygen sensing system: hypoxia-inducible factors (HIFs). The hypoxic responses are controlled by HIFs, which induce the expression of several adaptive genes to increase the oxygen supply and support anaerobic ATP generation in eukaryotic cells. Hypoxia also contributes to a functional decline during the aging process. In this review, we focus on the molecular mechanisms regulating HIF-1α and aging-associated signaling proteins, such as sirtuins, AMP-activated protein kinase, mechanistic target of rapamycin complex 1, UNC-51-like kinase 1, and nuclear factor κB, and their roles in aging and aging-related diseases. In addition, the effects of prenatal hypoxia and obstructive sleep apnea (OSA)-induced intermittent hypoxia have been reviewed due to their involvement in the progression and severity of many diseases, including cancer and other aging-related diseases. The pathophysiological consequences and clinical manifestations of prenatal hypoxia and OSA-induced chronic intermittent hypoxia are discussed in detail.

The Plasticity of CD4+CD25+FOXP3+CD127low T Cells in Patients with Metastatic Renal Cell Carcinoma in the Course of Interferon-Alpha Immunotherapy

Aims

To examine changes in subpopulation of CD4⁺CD25⁺Foxp3⁺CD127^low T lymphocytes (Treg) and their association with the efficiency of the IFN-α therapy.

Materials and Methods

Pts with mRCC who had undergone nephrectomy were treated with IFN-α at a dose of 6 × 10⁶ U/day three times a week (n = 18). An immunophenotypic analysis of lymphocytes in peripheral blood expressing CD4, CD25, CD127, and Foxp3 antigens could be performed in 18 pts before, 2 weeks, and 2 mo after IFN-α therapy and 22 normal volunteers. Blood samples were collected at baseline and 2 mo after treatment start. Serum levels of TGF-β1, IL-17A, and Epo were measured by ELISA.

Results

PR was achieved in 3 (16.6%) pts who received first-line therapy. Long-lasting SD (≥6 months) was noted in 6 (33.3%) pts. The median progression free survival (PFS) was 4 mo (95% CI: 2-NE). The study of the population of Treg indicated that there were no significant differences in the groups depending on the effect (p = 0.71). In one patient, the reduction of Treg cells was associated with increased TGF-β and IL-17 levels, whereas in other two pts the increase in Treg cells was associated with decreased TGF-β and IL-17 levels. The endogenous levels of Epo did not show significant correlation with response to IFN-α immunotherapy. In the patient subgroup with an initial value of MCH > 31 pg, the median PFS was not achieved, but in the subgroup with an initial value of MCH < 31 pg, the median PFS was 2 months (p = 0.032).

Conclusions

In our study, we have described functional plasticity of Treg cells, which prevents them from being used as a prognostic marker. The conversion of Treg cells into Th17 can serve as a basis for the development of a new specific immunotherapeutic method in oncology after confirmation in the experiment in vitro. Given the small dataset, the results will need further validation.

Chromatin-Bound Cullin-Ring Ligases: Regulatory Roles in DNA Replication and Potential Targeting for Cancer Therapy

Cullin-RING (Really Interesting New Gene) E3 ubiquitin ligases (CRLs), the largest family of E3 ubiquitin ligases, are functional multi-subunit complexes including substrate receptors, adaptors, cullin scaffolds, and RING-box proteins. CRLs are responsible for ubiquitination of ~20% of cellular proteins and are involved in diverse biological processes including cell cycle progression, genome stability, and oncogenesis. Not surprisingly, cullins are deregulated in many diseases and instances of cancer. Recent studies have highlighted the importance of CRL-mediated ubiquitination in the regulation of DNA replication/repair, including specific roles in chromatin assembly and disassembly of the replication machinery. The development of novel therapeutics targeting the CRLs that regulate the replication machinery and chromatin in cancer is now an attractive therapeutic strategy. In this review, we summarize the structure and assembly of CRLs and outline their cellular functions and their diverse roles in cancer, emphasizing the regulatory functions of nuclear CRLs in modulating the DNA replication machinery. Finally, we discuss the current strategies for targeting CRLs against cancer in the clinic.

Regulation of erythropoiesis after normoxic return from chronic sustained and intermittent hypoxia

Hypoxia increases erythropoiesis mediated by hypoxia-inducible transcription factors (HIF), which regulate erythropoietin transcription. Neocytolysis is a physiological mechanism that corrects polycythemia from chronic sustained hypoxemia by transient, preferential destruction of young RBCs after normoxia is restored. We showed that neocytolysis is caused by excessive mitochondrial-derived reactive oxygen species in reticulocytes mediated by downregulation of HIF-controlled BNIP3L regulated mitophagy and a decrease in RBC antioxidant catalase (CAT) in hypoxia-produced erythrocytes. Decreased CAT results from hypoxia-induced miR-21 that downregulates CAT. This correlates with a transient acute decrease of HIF-1 at normoxic return that is associated with normalization of red cell mass.

Nap Interferes with Hypoxia-Inducible Factors and VEGF Expression in Retina of Diabetic Rats

The retinal microvascular damage is a complication of diabetic retinopathy (DR). Hyperglycemia and hypoxia are responsible of aberrant vessel's proliferation. The cellular response to hypoxia is mediated through activation of hypoxia-inducible factors (HIFs). Among these, HIF-1α modulates expression of its target gene, VEGF, whose upregulation controls the angiogenic event during DR development. In a previous study, we have demonstrated that a small peptide, NAP, is able to protect retina from hyperglycemic insult. Here, we have demonstrated that its intraocular administration in a rat model of diabetic retinopathy has reduced expression of HIF-1α, HIF-2α, and VEGF by increasing HIF-3α levels. These data have been also confirmed by immunolocalization study by confocal microscopy. Although these evidences need to be further deepened to understand the molecular mechanism involved in the protective NAP action, the present data suggest that this small peptide may be effective to prevent the development of this ocular pathology.

CXC motif chemokine receptor 4 gene polymorphism and cancer risk

BACKGROUND

Previous epidemiological studies have reported the relationship between CXC motif chemokine receptor 4 (CXCR4) synonymous polymorphism (rs2228014), and risk of cancer, but the results remained conflicting and controversial. Therefore, this study was devised to evaluate the genetic effects of the rs2228014 polymorphism on cancer risk in a large meta-analysis.

METHODS

The computer-based databases (EMBASE, Web of Science, and PubMed) were searched for all relevant studies evaluating rs2228014 and susceptibility to cancer. In the analysis, pooled odds ratios (ORs) with its corresponding 95% confidence intervals (CIs) were calculated in 5 genetic models to assess the genetic risk. Egger regression and Begg funnel plots test were conducted to appraise the publication bias.

RESULTS

Data on rs2228014 polymorphism and overall cancer risk were available for 3684 cancer patients and 5114 healthy controls participating in 11 studies. Overall, a significantly increased risk of cancer was associated with rs2228014 polymorphism in homozygote model (OR = 2.01, 95% CI: 1.22-3.33) and in recessive model (OR = 1.97, 95% CI: 1.23-3.16). When stratified by ethnicity, the results were positive only in Asian populations (heterozygote model: OR = 1.36, 95% CI: 1.13-1.65; homozygote model: OR = 2.43, 95% CI: 1.21-4.91; dominant model: OR = 1.47, 95% CI: 1.13-1.90; recessive model: OR = 2.25, 95% CI: 1.13-4.48; and allele model: OR = 1.48, 95% CI: 1.10-1.99). Besides, in the subgroup analysis by source of control, the result was significant only in population-based control (homozygote model: OR = 2.39, 95% CI: 1.06-5.40; recessive model: pooled OR = 2.24, 95% CI: 1.02-4.96).

CONCLUSION

In general, our results first indicated that the rs2228014 polymorphism in CXCR4 gene is correlated with an increased risk of cancer, especially among Asian ethnicity. Large, well-designed epidemiological studies are required to verify the current findings.

PACAP and VIP Inhibit the Invasiveness of Glioblastoma Cells Exposed to Hypoxia through the Regulation of HIFs and EGFR Expression

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) through the binding of vasoactive intestinal peptide receptors (VIPRs), perform a wide variety of effects in human cancers, including glioblastoma multiforme (GBM). This tumor is characterized by extensive areas of hypoxia, which triggers the expression of hypoxia-inducible factors (HIFs). HIFs not only mediate angiogenesis but also tumor cell migration and invasion. Furthermore, HIFs activation is linked to epidermal growth factor receptor (EGFR) overexpression. Previous studies have shown that VIP interferes with the invasive nature of gliomas by regulating cell migration. However, the role of VIP family members in GBM infiltration under low oxygen tension has not been clarified yet. Therefore, in the present study we have investigated, for the first time, the molecular mechanisms involved in the anti-invasive effect of PACAP or VIP in U87MG glioblastoma cells exposed to hypoxia induced by treatment with desferrioxamine (DFX). The results suggest that either PACAP or VIP exert an anti-infiltrative effect under low oxygen tension by modulating HIFs and EGFR expression, key elements involved in cell migration and angiogenesis. These peptides act through the inhibition of PI3K/Akt and MAPK/ERK signaling pathways, which are known to have a crucial role in HIFs regulation.

Parkin modulates expression of HIF-1α and HIF-3α during hypoxia in gliobastoma-derived cell lines in vitro

Mutation of the Parkin gene causes an autosomal recessive juvenile-onset form of Parkinson's disease. However, recently, it has been also linked to a wide variety of malignancies, including glioblastoma multiforme (GBM). In this pathology, Parkin exhibits a tumor suppressor role by mitigating the proliferation rate in both in vitro and in vivo models. However, Parkin involvement in the hypoxic process has not as yet been investigated. GBM is the most common and aggressive primary brain tumor in adults and is characterized by hypoxic areas. The low oxygen supply causes the expression of hypoxia-inducible factors (HIFs) leading to an accumulation of pro-angiogenic factors and tumoral invasiveness. We assess the relationship between Parkin and two HIFs expressed during hypoxic conditions, namely HIF-1α and HIF-3α. Our data show that Parkin is downregulated under hypoxia and that it interferes with HIF expression based on cellular oxygen tension. These results suggest a role for the involvement of Parkin in GBM, although further studies will be needed to understand the mechanism by which it modulates HIF-1α and HIF-3α expression.

Acquired Mitochondrial Abnormalities, Including Epigenetic Inhibition of Superoxide Dismutase 2, in Pulmonary Hypertension and Cancer: Therapeutic Implications

There is no cure for non-small-cell lung cancer (NSCLC) or pulmonary arterial hypertension (PAH). Therapies lack efficacy and/or are toxic, reflecting a failure to target disease abnormalities that are distinct from processes vital to normal cells. NSCLC and PAH share reversible mitochondrial-metabolic abnormalities which may offer selective therapeutic targets. The following mutually reinforcing, mitochondrial abnormalities favor proliferation, impair apoptosis, and are relatively restricted to PAH and cancer cells: (1) Epigenetic silencing of superoxide dismutase-2 (SOD2) by methylation of CpG islands creates a pseudohypoxic redox environment that causes normoxic activation of hypoxia inducible factor (HIF-1α). (2) HIF-1α increases expression of pyruvate dehydrogenase kinase (PDK), which impairs oxidative metabolism and promotes a glycolytic metabolic state. (3) Mitochondrial fragmentation, partially due to mitofusin-2 downregulation, promotes proliferation. This review focuses on the recent discovery that decreased expression of SOD2, a putative tumor-suppressor gene and the major source of H2O2, results from hypermethylation of CpG islands. In cancer and PAH hypermethylation of a site in the enhancer region of intron 2 inhibits SOD2 transcription. In normal PASMC, SOD2 siRNA decreases H2O2 and activates HIF-1α. In PAH, reduced SOD2 expression decreases H2O2, reduces the cytosol and thereby activates HIF-1α. This causes a glycolytic shift in metabolism and increases the proliferation/apoptosis ratio by downregulating Kv1.5 channels, increasing cytosolic calcium, and inhibiting caspases. The DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine, which restores SOD2 expression, corrects the proliferation/apoptosis imbalance in PAH and cancer cells. The specificity of PAH for lung vessels may relate to the selective upregulation of DNA methyltransferases that mediate CpG methylation in PASMC (DNA MT-1A and -3B). SOD2 augmentation inactivates HIF-1α in PAH PASMC and therapy with the SOD mimetic, MnTBAP, regresses experimental PAH. In conclusion, cancer and PAH share acquired mitochondrial abnormalities that increase proliferation and inhibit apoptosis, suggesting new therapeutic targets.

PACAP Modulates Expression of Hypoxia-Inducible Factors in Streptozotocin-Induced Diabetic Rat Retina

Retinal hypoxia has been related to the pathogenesis of diabetic retinopathy. This event is mediated by the hypoxia-inducible factors (HIFs), including HIF-1α, HIF-2α, and HIF-3α. Previously, we have demonstrated the protective role of pituitary adenylate cyclase-activating peptide (PACAP) in the early phase of diabetic retinopathy. In the present work, we investigated whether PACAP effect in hyperglycemic retina is mediated through modulation of HIFs' expression. Diabetes was induced with a single injection of streptozotocin (STZ) in rats. After 1 week, a group of diabetic animals was treated with a single intravitreal injection of 100 μM PACAP or saline solution. Then, changes in HIFs' expression levels were evaluated in the retina after 3 weeks of hyperglycemia. The expression of HIF-1α and HIF-2α was significantly (p < 0.001 vs control) increased in diabetic rats as compared to controls. Instead, their expression levels were significantly (p < 0.001 vs STZ) decreased after PACAP intraocular administration, as detected by Western blot analysis. Conversely, the expression of HIF-3α was significantly (p < 0.001 vs control) downregulated in retinas of STZ-injected rats and significantly (p < 0.001 vs control) increased after PACAP treatment. These data were supported by the immunohistochemical analysis. HIFs were localized either in inner and outer retinal layers. Diabetes interferes with their distribution, which is changed following intravitreal injection of PACAP. The present results suggest that the protective effect of the peptide in diabetic retina might be also mediated through modulation of HIFs' expression.

Sunitinib resistance in renal cell carcinoma

Of the many targeted therapies introduced since 2006, sunitinib has carved its way to become the most commonly used first-line therapy for the treatment of metastatic renal cell carcinoma (RCC). Despite significant improvements in progression-free survival, 30% of the patients are intrinsically resistant to sunitinib and the remaining 70% who respond initially will eventually become resistant in 6-15 months. While the molecular mechanisms of acquired resistance to sunitinib have been unravelling at a rapid rate, the mechanisms of intrinsic resistance remain elusive. Combination therapy, sunitinib rechallenge and sequential therapy have been investigated as means to overcome resistance to sunitinib. Of these, sequential therapy appears to be the most promising strategy. This mini review summarises our emerging understanding of the molecular mechanisms, and the strategies employed to overcome sunitinib resistance.

Insight into the intermolecular recognition mechanism between Keap1 and IKKβ combining homology modelling, protein-protein docking, molecular dynamics simulations and virtual alanine mutation

Degradation of certain proteins through the ubiquitin-proteasome pathway is a common strategy taken by the key modulators responsible for stress responses. Kelch-like ECH-associated protein-1(Keap1), a substrate adaptor component of the Cullin3 (Cul3)-based ubiquitin E3 ligase complex, mediates the ubiquitination of two key modulators, NF-E2-related factor 2 (Nrf2) and IκB kinase β (IKKβ), which are involved in the redox control of gene transcription. However, compared to the Keap1-Nrf2 protein-protein interaction (PPI), the intermolecular recognition mechanism of Keap1 and IKKβ has been poorly investigated. In order to explore the binding pattern between Keap1 and IKKβ, the PPI model of Keap1 and IKKβ was investigated. The structure of human IKKβ was constructed by means of the homology modeling method and using reported crystal structure of Xenopus laevis IKKβ as the template. A protein-protein docking method was applied to develop the Keap1-IKKβ complex model. After the refinement and visual analysis of docked proteins, the chosen pose was further optimized through molecular dynamics simulations. The resulting structure was utilized to conduct the virtual alanine mutation for the exploration of hot-spots significant for the intermolecular interaction. Overall, our results provided structural insights into the PPI model of Keap1-IKKβ and suggest that the substrate specificity of Keap1 depend on the interaction with the key tyrosines, namely Tyr525, Tyr574 and Tyr334. The study presented in the current project may be useful to design molecules that selectively modulate Keap1. The selective recognition mechanism of Keap1 with IKKβ or Nrf2 will be helpful to further know the crosstalk between NF-κB and Nrf2 signaling.

Gene expression in archived newborn blood spots distinguishes infants who will later develop cerebral palsy from matched controls

BACKGROUND

Gene expression in archived newborn blood spots remaining from newborn screening may reflect pathophysiological disturbances useful in understanding the etiology of cerebral palsy (CP).

METHODS

We quantified the expression of gene sets representing four physiological pathways hypothesized to contribute to CP in archived unfrozen residual newborn blood spot specimens from 53 children with CP and 53 age-, gender-, and gestational age-matched controls. We selected four empirical and three canonical gene sets representing the inflammatory, hypoxic, coagulative, and thyroidal pathways and examined mRNA expression using an 8 × 60,000 oligonucleotide microarray. The log2 fold change of gene expression between matched cases and controls was analyzed using the generally applicable gene set enrichment method.

RESULTS

The empirical inflammatory and empirical hypoxic gene sets were significantly downregulated in term-born CP cases (n = 33) as compared with matched controls (P = 0.0007 and 0.0009, respectively), whereas both gene sets were significantly upregulated (P =0.0055 and 0.0223, respectively) in preterm-born CP cases (n = 20). The empirical thyroidal gene set was significantly upregulated in preterm-born CP cases (P = 0.0023).

CONCLUSION

The newborn blood spot transcriptome can serve as a platform for investigating distinctive gene expression patterns in children who later develop CP.

Functional significance of erythropoietin in renal cell carcinoma

One of the molecules regulated by the transcription factor, hypoxia inducible factor (HIF), is the hypoxia-responsive hematopoietic factor, erythropoietin (EPO). This may have relevance to the development of renal cell carcinoma (RCC), where mutations of the von Hippel-Lindau (VHL) gene are major risk factors for the development of familial and sporadic RCC. VHL mutations up-regulate and stabilize HIF, which in turn activates many downstream molecules, including EPO, that are known to promote angiogenesis, drug resistance, proliferation and progression of solid tumours. HIFs typically respond to hypoxic cellular environment. While the hypoxic microenvironment plays a critical role in the development and progression of tumours in general, it is of special significance in the case of RCC because of the link between VHL, HIF and EPO. EPO and its receptor, EPOR, are expressed in many cancers, including RCC. This limits the use of recombinant human EPO (rhEPO) to treat anaemia in cancer patients, because the rhEPO may be stimulatory to the cancer. EPO may also stimulate epithelial-mesenchymal transition (EMT) in RCC, and pathological EMT has a key role in cancer progression. In this mini review, we summarize the current knowledge of the role of EPO in RCC. The available data, either for or against the use of EPO in RCC patients, are equivocal and insufficient to draw a definitive conclusion.

Progress and contrasts of the development of tivozanib for therapy of kidney cancer

INTRODUCTION

Targets for drug development for the treatment of kidney cancer (renal cell carcinoma; RCC) include vascular endothelial growth factor (VEGF) and its receptors and mammalian target of rapamycin. Currently available oral multitargeted VEGF tyrosine kinase inhibitors (TKIs) that have been approved by the US Food and Drug Administration for advanced RCC, include sunitinib, sorafenib and pazopanib. Off-target TKI inhibition can potentially preclude full-dose combination with other targeted and chemotherapeutic agents. There is a need to develop more potent and selective targeted agents for RCC therapy, which are more effective and have minimal off-target effects.

AREAS COVERED

This drug evaluation review addresses the ongoing development for the treatment of RCC with tivozanib: a potent, selective and long-half-life VEGF TKI. The testing for clinical efficacy alone or in combination with other therapies for RCC and for other tumor types, and the clinical and market relevance of introducing another RCC therapy are discussed.

EXPERT OPINION

Tivozanib is distinguished by its high potency, selectivity, long-half-life and its potential to be effectively combined with other agents in RCC. This may offer more effective, yet well-tolerated treatment options. The relative clinical and market relevance remain to be seen, both for RCC therapy and other tumor types.

Mechanism-based Screening for Cancer Therapeutics with Examples from the Discovery of Marine Natural Product-based HIF-1 Inhibitors

Recent advances in cancer genetics combined with an increasing number of new methods in molecular and cell biology provide exciting new antitumor drug targets and a wide array of means to design bioassay systems for the discovery of novel cancer chemotherapeutics. Marine natural products continue to play a vital role in molecular-targeted antitumor drug discovery. Although most recognize the critical and expanding role mechanism-based antitumor bioassays play in modern anticancer drug discovery, few natural products chemists have specific training in bioassay technology. Critical bioassay development factors are outlined and introduced at a level intended to provide a basic understanding to a general audience. These include molecular target identification, antitumor target validation, selection of assayable biochemical processes, data acquisition methods, experimental controls, bioassay validation and statistical methods, experimental artifacts, active compound identification, and the dereplication of nuisance compounds. Marine natural products have been identified that inhibit the activation of the anticancer drug target hypoxia-inducible factor-1 (HIF-1). Bioassay systems and recent results from marine HIF-1 inhibitor discovery programs are used to illustrate important factors that must be considered when using molecular-targeted antitumor bioassay methods.

Role of VHL gene mutation in human renal cell carcinoma

The Von Hippel-Lindau (VHL) is an inherited neoplasia syndrome caused by the inactivation of VHL tumor suppressor gene, and somatic mutation of this gene has been related to the development of sporadic clear cell renal carcinoma. The affected individuals are at higher risk for the development of tumor in other organs, which include pheochromocytomas, retinal angioma, pancreatic cysts, and CNS hemangioblastomas. The VHL mRNA encodes a protein (pVHL) that contains 213 amino acid residues which migrate with an apparent molecular weight of 24 to 30 kDa. The VHL gene protein has multiple functions that are linked to tumor suppression, but the best recognized and evidently linked to the development of renal cell carcinoma (RCC) is inhibition of hypoxia-inducible factor (HIF), as well as plays a role in targeting HIF for ubiquitin-mediated degradation. Aberrations in VHL's function, either through mutation or promoter hypermethylation, lead to the accumulation of HIF, which will transcriptionally upregulate a sequence of hypoxia responsive genes, including epidermal growth factor, vascular endothelial growth factor, platelet-derived growth factor, and other proangiogenic factors, resulting in upregulated blood vessel growth, one of the prerequisites of a tumor. HIF plays a critical role in pVHL-defective tumor formation, raising the possibility that drugs directed against HIF or its downstream targets (such as vascular endothelial growth factor) may one day play a role in the treatment of RCC. Moreover, a number of drugs have been developed that target HIF-responsive gene products, many of these targeted therapies have demonstrated significant activity in kidney cancer clinical trials and signify substantive advances in the treatment of this disease.

Conditional VHL gene deletion activates a local NO-VEGF axis in a balanced manner reinforcing resistance to endothelium-targeted glomerulonephropathy

BACKGROUND/AIMS

We have reported that tubular epithelial cell injury caused by renal ischemia-reperfusion is attenuated in conditional VHL knockout (VHL-KO) mice and also that induction of hypoxia-inducible factor (HIF) suppresses angiotensin II-accelerated Habu snake venom (HV) glomerulonephropathy in rats. However, it remains unknown whether VHL knockdown protects glomerular endothelial cells from endothelium-targeted glomerulonephritis.

METHODS AND RESULTS

VHL-KO mice with HV glomerulonephropathy (HV GN) had fewer injured glomeruli, a lower mesangiolysis score and reduced blood urea nitrogen levels. Immunoreactivity of vascular endothelial growth factor (VEGF) in the glomerular capillaries was enhanced by VHL knockdown and was conserved even in VHL-KO mice with HV GN, despite HV-attenuating endothelial VEGF expression in vitro. VHL-KO mice showed enhanced nitric oxide (NO) production in glomerular endothelial cells and tubular cells, associated with activated VEGF expression in the kidney (i.e. an activated NO-VEGF axis). The levels of NO in glomeruli and tubules were conserved even in mice with HV GN. In contrast, suppressing NO production in glomerular endothelial cells by an NO synthase inhibitor, N(ϖ)-nitro-L-arginase, completely blunted the protection of VHL-KO from HV GN. The activated NO-VEGF axis in the kidney of VHL-KO mice was also associated with an elevation in Flk-1 phosphorylation and increased levels of IL-10 and IP-10.

CONCLUSION

Conditional VHL knockdown may enhance the NO-VEGF axis and protect glomerular endothelial cells from HV GN, thereby providing resistance to injury of tubular epithelial cells and glomerular endothelial cells.

Molecular mechanisms of the Keap1–Nrf2 pathway in stress response and cancer evolution

The Keap1–Nrf2 regulatory pathway plays a central role in the protection of cells against oxidative and xenobiotic damage. Under unstressed conditions, Nrf2 is constantly ubiquitinated by the Cul3–Keap1 ubiquitin E3 ligase complex and rapidly degraded in proteasomes. Upon exposure to electrophilic and oxidative stresses, reactive cysteine residues of Keap1 become modified, leading to a decline in the E3 ligase activity, stabilization of Nrf2 and robust induction of a battery of cytoprotective genes. Biochemical and structural analyses have revealed that the intact Keap1 homodimer forms a cherry-bob structure in which one molecule of Nrf2 associates with two molecules of Keap1 by using two binding sites within the Neh2 domain of Nrf2. This two-site binding appears critical for Nrf2 ubiquitination. In many human cancers, missense mutations in KEAP1 and NRF2 genes have been identified. These mutations disrupt the Keap1–Nrf2 complex activity involved in ubiquitination and degradation of Nrf2 and result in constitutive activation of Nrf2. Elevated expression of Nrf2 target genes confers advantages in terms of stress resistance and cell proliferation in normal and cancer cells. Discovery and development of selective Nrf2 inhibitors should make a critical contribution to improved cancer therapy.

HIF-2alpha enhances beta-catenin/TCF-driven transcription by interacting with beta-catenin

The tumor-promoting factors β-catenin and hypoxia-inducible factor (HIF) are often found to be coactivated in rapidly growing tumors. Recently, it was shown that HIF-1α negatively regulates Wnt/β-catenin signaling by sequestering β-catenin from β-catenin/T-cell factor (TCF). However, no investigation has been undertaken on the involvement of HIF-2α in β-catenin regulation. In this study, it was found that, like HIF-1α, HIF-2α interacts with β-catenin, but at a different site. Furthermore, HIF-2α was found to assemble with β-catenin/TCF and facilitate gene transcription. Mutational analyses revealed that transactivation domains of HIF-2α promote p300 coactivator recruitment by β-catenin. Furthermore, HIF-2α and β-catenin were found to associate in the nuclei of 786-0 renal cell carcinoma cells, and HIF-2α was found to be required for β-catenin activation in these cells and for their proliferation. These results suggest that this interaction contributes to the unrestrained growth of tumor cells containing coactivated HIF-2α and β-catenin. Interestingly, these actions of HIF-2α oppose those of HIF-1α on β-catenin and cell growth, and this suggests that HIF-1α/HIF-2α balance may importantly determine cell growth when hypoxia and Wnt stimulation coexist.

Gensenoside Rg3 inhibits hypoxia-induced VEGF expression in human cancer cells

AIMS

The ginsenoside Rg3 (Rg3) inhibits xenograft growth and angiogenesis in tumors mainly via down-regulates VEGF expression. This study was designed to investigate the mechanisms by which Rg3 down-regulates VEGF expression.

METHODS

MTT assay was performed to investigate the effect of Rg3 on the growth of human esophageal carcinoma cell line Eca-109 and 786-0 cells under normoxic and hypoxic conditions. ELISA was used to detect VEGF protein secreted by the cells under normoxic and hypoxic conditions. Real-time quantitative reverse transcriptase polymerase chain reaction and Western blotting were used to detect gene expression and protein synthesis.

RESULTS

Rg3 inhibited Eca-109 and 786-0 cell proliferation and induced a significant reduction in VEGF mRNA under hypoxia conditions. Rg3 treatment inhibited hypoxia-induced expression HIF-1α, COX-2 and NF-κB under normoxic and hypoxic conditions. Treatment with Rg3 reduced the hypoxia-induced phosphorylation of STAT3 in a dose-dependent manner in the both cell lines. Rg3 treatment also inhibited the phosphorylation of ERK1/2 and JNK induced by hypoxia.

CONCLUSIONS

Rg3 targets hypoxia-induced multiple signaling pathways to down-regulate VEGF expression in cancer cells. These actions may contribute to the overall efficacy of Rg3 against tumor angiogenesis and growth.

Targeting mTOR in cancer: renal cell is just a beginning

The mammalian target of rapamycin (mTOR) is a key regulator of cell growth and proliferation. The mTOR pathway integrates signals from nutrients, energy status and extracellular growth factors to regulate many processes, including cell cycle progression, angiogenesis, ribosome biogenesis, and metabolism. Growth factors such as insulin-like growth factor, epidermal growth factor and vascular endothelial growth factor bind to and activate their corresponding tyrosine kinase receptors (TKR) located on the cell surface, to induce signal transduction to the nucleus. TKR induces intracellular signaling cascades via the phosphorylation of the phosphatidylinositol 3-kinase, which in turn phosphorylates Akt. Of particular interest among the Akt targets is the downstream effect on mTOR, which is responsible for protein synthesis of molecules necessary for nutrient uptake, angiogenesis, ribosome biogenesis, cell growth, and proliferation. Growing evidence suggests that mTOR deregulation is associated with many types of human cancer. The importance of mTOR signaling in tumor biology is now widely accepted. Consequently, a number of agents that selectively target mTOR are being developed for cancer treatment and currently temsirolimus and everolimus are approved for the treatment of advanced renal cell cancer. However, the therapeutic benefit of mTOR inhibitors in the clinic may vary depending on the activation state of the different components of the mTOR pathway in a given case. Therefore it seems clear that predicting sensitivity to rapamycins in different cancers will likely require assessing multiple molecular markers related to mTOR signaling pathway, such as phosphatase and tensin homolog (PTEN), phospho-Akt, cytoplasmic p27, and phospho-S6 kinase.

VHL deletion impairs mammary alveologenesis but is not sufficient for mammary tumorigenesis

Overexpression of hypoxia inducible factor-1 (HIF-1)alpha, which is common in most solid tumors, correlates with poor prognosis and high metastatic risk in breast cancer patients. Because HIF-1alpha protein stability is tightly controlled by the tumor suppressor von Hippel-Lindau (VHL), deletion of VHL results in constitutive HIF-1alpha expression. To determine whether VHL plays a role in normal mammary gland development, and if HIF-1alpha overexpression is sufficient to initiate breast cancer, Vhl was conditionally deleted in the mammary epithelium using the Cre/loxP system. During first pregnancy, loss of Vhl resulted in decreased mammary epithelial cell proliferation and impaired alveolar differentiation; despite these phenotypes, lactation was sufficient to support pup growth. In contrast, in multiparous dams, Vhl(-/-) mammary glands exhibited a progressive loss of alveolar epithelium, culminating in lactation failure. Deletion of Vhl in the epithelium also impacted the mammary stroma, as there was increased microvessel density accompanied by hemorrhage and increased immune cell infiltration. However, deletion of Vhl was not sufficient to induce mammary tumorigenesis in dams bred continuously for up to 24 months of age. Moreover, co-deletion of Hif1a could not rescue the Vhl(-/-)-dependent phenotype as dams were unable to successfully lactate during the first lactation. These results suggest that additional VHL-regulated genes besides HIF1A function to maintain the proliferative and regenerative potential of the breast epithelium.

Experimental and computational studies indicate specific binding of pVHL protein to Aurora-A kinase

Overexpression of Aurora-A kinase is commonly detected in many cancers, whereas the von Hippel-Lindau protein (pVHL) is frequently mutated or absent in renal cell carcinoma and is involved in the Ub proteasome complex, an important degradation pathway. In order to establish a link between Aurora-A overexpression and lack of pVHL protein, we hypothesized that pVHL regulates Aurora-A expression through a physical interaction. We present the first evidence, from both biological assays and computational biology techniques, that human pVHL binds strongly to Aurora-A kinase. Extensive molecular modeling, docking, and dynamic simulations demonstrate that the structure of the pVHL protein would allow it to bind to the TPX2 binding region of Aurora-A. In view of Aurora-A's importance as a therapeutic target for the treatment of cancer, this observation provides novel insights into the Aurora-A/pVHL pathway. In addition, the detailed Aurora-A/pVHL binding structure obtained will be valuable for the design of future Aurora-A inhibitors as therapeutic agents.

Oxygen-independent degradation of HIF-alpha via bioengineered VHL tumour suppressor complex

Tumour hypoxia promotes the accumulation of the otherwise oxygen-labile hypoxia-inducible factor (HIF)-alpha subunit whose expression is associated with cancer progression, poor prognosis and resistance to conventional radiation and chemotherapy. The oxygen-dependent degradation of HIF-alpha is carried out by the von Hippel-Lindau (VHL) protein-containing E3 that directly binds and ubiquitylates HIF-alpha for subsequent proteasomal destruction. Thus, the cellular proteins involved in the VHL-HIF pathway have been recognized as attractive molecular targets for cancer therapy. However, the various compounds designed to inhibit HIF-alpha or HIF-downstream targets, although promising, have shown limited success in the clinic. In the present study, we describe the bioengineering of VHL protein that removes the oxygen constraint in the recognition of HIF-alpha while preserving its E3 enzymatic activity. Using speckle variance-optical coherence tomography (sv-OCT), we demonstrate the dramatic inhibition of angiogenesis and growth regression of human renal cell carcinoma xenografts upon adenovirus-mediated delivery of the bioengineered VHL protein in a dorsal skin-fold window chamber model. These findings introduce the concept and feasibility of 'bio-tailored' enzymes in the treatment of HIF-overexpressing tumours.

Chemically induced pheochromocytomas in rats: mechanisms and relevance for human risk assessment

Pheochromocytomas are tumors originating from chromaffin cells of the adrenal medulla, which have been observed in numerous carcinogenicity studies. The authors have evaluated pheochromocytoma concurrence with other effects and the possible mechanisms, in order to assess the relevance of such data for the classification of carcinogenic effects and their relevance to humans. The evaluation revealed that pheochromocytomas occur with relatively higher frequency in male rats, especially when the following conditions are involved: hypoxia, uncoupling of oxidative phosphorylation, disturbance in calcium homeostasis, and disturbance of the hypothalamic endocrine axis. The underlying biochemical mechanisms suggest that other substances that interfere with these biochemical endpoints also produce pheochromocytomas. Such endpoints include enzymes involved in catecholamine synthesis, receptor tyrosine kinase (RET), hypoxia-inducible factor (HIF), succinate dehydrogenase, fumarate hydratase, and pyruvate dehydrogenase. To date, there is no indication that the substances inducing pheochromocytomas in animal experiments also induce corresponding tumors in humans. Because the mechanisms of action identified in rats are to be expected in humans, pheochromocytomas may be induced after exposure conditions similar to those used in the animal studies. Whether hereditary mutations represent a risk factor in humans is not clear. Pheochromocytomas that occur in animal experiments currently appear to have little relevance for conditions at the work place. When sufficiently documented and evaluated, such secondary pheochromocytomas are not relevant for classification and human risk assessment.

Identification of a microRNA panel for clear-cell kidney cancer

OBJECTIVES

To identify a robust panel of microRNA signatures that can classify tumor from normal kidney using microRNA expression levels. Mounting evidence suggests that microRNAs are key players in essential cellular processes and that their expression pattern can serve as diagnostic biomarkers for cancerous tissues.

METHODS

We selected 28 clear-cell type human renal cell carcinoma (ccRCC), samples from patient-matched specimens to perform high-throughput, quantitative real-time polymerase chain reaction analysis of microRNA expression levels. The data were subjected to rigorous statistical analyses and hierarchical clustering to produce a discrete set of microRNAs that can robustly distinguish ccRCC from their patient-matched normal kidney tissue samples with high confidence.

RESULTS

Thirty-five microRNAs were found that can robustly distinguish ccRCC from their patient-matched normal kidney tissue samples with high confidence. Among this set of 35 signature microRNAs, 26 were found to be consistently downregulated and 9 consistently upregulated in ccRCC relative to normal kidney samples. Two microRNAs, namely, MiR-155 and miR-21, commonly found to be upregulated in other cancers, and miR-210, induced by hypoxia, were also identified as overexpressed in ccRCC in our study. MicroRNAs identified as downregulated in our study can be correlated to common chromosome deletions in ccRCC.

CONCLUSIONS

Our analysis is a comprehensive, statistically relevant study that identifies the microRNAs dysregulated in ccRCC, which can serve as the basis of molecular markers for diagnosis.

PTEN suppression of YY1 induces HIF-2 activity in von-Hippel-Lindau-null renal-cell carcinoma

Despite recent advances in cancer therapies, metastatic renal cell carcinoma (RCC) remains difficult to treat. Most RCCs result from inactivation of the von Hippel Lindau (VHL) tumor suppressor, leading to stable expression of Hypoxia-Inducible Factor-alpha (HIF-1alpha, -2alpha, -3alpha) and the induction of downstream target genes, including those responsible for angiogenesis and metastasis. While VHL is inactivated in the majority of RCC cases, expression of the PTEN tumor suppressor is reduced in about 30% of cases. PTEN functions to antagonize PI3K/Akt/mTOR signaling, thereby controlling cell growth and survival. Activation of PI3K/Akt/mTOR leads to increased HIF-1alpha expression in certain cancer cells, supporting the rationale of using mTOR inhibitors as anti-cancer agents. Notably, HIF-2alpha, rather than HIF-1alpha, has been shown to play a critical role in renal tumorigenesis. To investigate whether HIF-2alpha is similarly regulated by the PI3K pathway in VHL(-/-)RCC cells, we manipulated PI3K signaling using PTEN overexpression and siRNA knockdown studies and pharmacologic inhibition of PI3K or Akt. Our data support a novel role for wild-type PTEN in promoting HIF-2alpha activity in VHL null RCC cells. This mechanism is unique to the cellular environment in which HIF-2alpha expression is deregulated, resulting from the loss of VHL function. Our data show that PTEN induces HIF-2alpha transcriptional activity by inhibiting expression of Yin Yang 1 (YY1), which acts as a novel corepressor of HIF-2alpha. Further, PTEN suppression of YY1 is mediated through antagonism of PI3K signaling. We conclude that wild-type PTEN relieves the repressive nature of YY1 at certain HIF-2alpha target promoters and that this mechanism may promote early renal tumorigenesis resulting from VHL inactivation by increasing HIF-2alpha activity.

Strong expression of chemokine receptor CXCR4 by renal cell carcinoma correlates with advanced disease

Diverse chemokines and their receptors have been associated with tumor growth, tumor dissemination, and local immune escape. In different tumor entities, the level of chemokine receptor CXCR4 expression has been linked with tumor progression and decreased survival. The aim of this study was to evaluate the influence of CXCR4 expression on the progression of human renal cell carcinoma. CXCR4 expression of renal cell carcinoma was assessed by immunohistochemistry in 113 patients. Intensity of CXCR4 expression was correlated with both tumor and patient characteristics. Human renal cell carcinoma revealed variable intensities of CXCR4 expression. Strong CXCR4 expression of renal cell carcinoma was significantly associated with advanced T-status (P = .039), tumor dedifferentiation (P = .0005), and low hemoglobin (P = .039). In summary, strong CXCR4 expression was significantly associated with advanced dedifferentiated renal cell carcinoma.

Differential dependence of hypoxia-inducible factors 1 alpha and 2 alpha on mTORC1 and mTORC2

Constitutive expression of hypoxia-inducible factor (HIF) has been implicated in several proliferative disorders. Constitutive expression of HIF1 alpha and HIF2 alpha has been linked to a number of human cancers, especially renal cell carcinoma (RCC), in which HIF2 alpha expression is the more important contributor. Expression of HIF1 alpha is dependent on the mammalian target of rapamycin (mTOR) and is sensitive to rapamycin. In contrast, there have been no reports linking HIF2 alpha expression with mTOR. mTOR exists in two complexes, mTORC1 and mTORC2, which are differentially sensitive to rapamycin. We report here that although there are clear differences in the sensitivity of HIF1 alpha and HIF2 alpha to rapamycin, both HIF1 alpha and HIF2 alpha expression is dependent on mTOR. HIF1 alpha expression was dependent on both Raptor (a constituent of mTORC1) and Rictor (a constitutive of mTORC2). In contrast, HIF2 alpha was dependent only on the mTORC2 constituent Rictor. These data indicate that although HIF1 alpha is dependent on both mTORC1 and mTORC2, HIF2 alpha is dependent only on mTORC2. We also examined the dependence of HIF alpha expression on the mTORC2 substrate Akt, which exists as three different isoforms, Akt1, Akt2, and Akt3. Interestingly, the expression of HIF2 alpha was dependent on Akt2, whereas that of HIF1 alpha was dependent on Akt3. Because HIF2 alpha is apparently more critical in RCC, this study underscores the importance of targeting mTORC2 and perhaps Akt2 signaling in RCC and other proliferative disorders in which HIF2 alpha has been implicated.