Molecular basis of the VHL hereditary cancer syndrome

Interferon-α enhances the susceptibility of renal cell carcinoma to rapamycin by suppressing mTOR activity

The aim of the present study was to investigate the antiproliferative effects of interferon (IFN)-α and rapamycin (RPM) on renal cell carcinoma (RCC) cells and examine the synergistic growth suppression conferred by IFN-α and RPM. The effects of IFN-α and/or RPM on RCC cells were determined using a WST-1 assay and the synergy of IFN-α and RPM against three RCC cell lines was analyzed with isobolographic analysis. The expression of mammalian target of rapamycin (mTOR) was downregulated by RNAi, and the expression and phosphorylation of proteins in the mTOR pathway following treatment with IFN-α and/or RPM was examined by western blot analysis. The observations indicated that IFN-α significantly increased the susceptibility of RCC cells to RPM and the synergistic effect of IFN-α and RPM against RCC cells was confirmed in all three RCC cell lines. The mTOR pathway was shown to be associated with the synergistic effect of IFN-α and RPM against RCC. IFN-α and RPM alone decreased the phosphorylation of mTOR, p70 S6 kinase, S6 and 4E binding protein 1, and IFN-α significantly enhanced the RPM-induced suppression of the mTOR pathway. However, in RCC cells with low mTOR activity, the synergy of IFN-α and RPM was eliminated. Therefore, the results of the present study indicate that the mTOR pathway plays an important role in the synergistic effect of IFN-α and RPM against RCC cells. Thus, mTOR may serve as an effective therapeutic target in the treatment of advanced RCC.

Nuclear ARRB1 induces pseudohypoxia and cellular metabolism reprogramming in prostate cancer

Tumour cells sustain their high proliferation rate through metabolic reprogramming, whereby cellular metabolism shifts from oxidative phosphorylation to aerobic glycolysis, even under normal oxygen levels. Hypoxia-inducible factor 1A (HIF1A) is a major regulator of this process, but its activation under normoxic conditions, termed pseudohypoxia, is not well documented. Here, using an integrative approach combining the first genome-wide mapping of chromatin binding for an endocytic adaptor, ARRB1, both in vitro and in vivo with gene expression profiling, we demonstrate that nuclear ARRB1 contributes to this metabolic shift in prostate cancer cells via regulation of HIF1A transcriptional activity under normoxic conditions through regulation of succinate dehydrogenase A (SDHA) and fumarate hydratase (FH) expression. ARRB1-induced pseudohypoxia may facilitate adaptation of cancer cells to growth in the harsh conditions that are frequently encountered within solid tumours. Our study is the first example of an endocytic adaptor protein regulating metabolic pathways. It implicates ARRB1 as a potential tumour promoter in prostate cancer and highlights the importance of metabolic alterations in prostate cancer.

Mitohormesis: Promoting Health and Lifespan by Increased Levels of Reactive Oxygen Species (ROS)

Increasing evidence indicates that reactive oxygen species (ROS), consisting of superoxide, hydrogen peroxide, and multiple others, do not only cause oxidative stress, but rather may function as signaling molecules that promote health by preventing or delaying a number of chronic diseases, and ultimately extend lifespan. While high levels of ROS are generally accepted to cause cellular damage and to promote aging, low levels of these may rather improve systemic defense mechanisms by inducing an adaptive response. This concept has been named mitochondrial hormesis or mitohormesis. We here evaluate and summarize more than 500 publications from current literature regarding such ROS-mediated low-dose signaling events, including calorie restriction, hypoxia, temperature stress, and physical activity, as well as signaling events downstream of insulin/IGF-1 receptors, AMP-dependent kinase (AMPK), target-of-rapamycin (TOR), and lastly sirtuins to culminate in control of proteostasis, unfolded protein response (UPR), stem cell maintenance and stress resistance. Additionally, consequences of interfering with such ROS signals by pharmacological or natural compounds are being discussed, concluding that particularly antioxidants are useless or even harmful.

Enhancement of proliferation and invasion by MicroRNA-590-5p via targeting PBRM1 in clear cell renal carcinoma cells

MicroRNAs (miRNAs) play an important role in cancer development. In our study, miR-590-5p is found to be upregulated in the examined renal cell carcinoma (RCC) cell lines. PBRM1 acts as tumor suppressor in RCC, and its downregulation is associated with increased proliferation and aggressive behavior in RCC. We confirmed that PBRM1 was a direct target of miR-590-5p. miR-590-5p could regulate PBRM1 mRNA and protein expressions in clear cell renal carcinoma (ccRCC) ACHN and 786-O cells. Downregulation of miR-590-5p, which resulted in increased PBRM1, inhibited proliferation and invasion of ccRCC cells. Upregulation of miR-590-5p, which resulted in decreased PBRM1, promoted proliferation and invasion of ccRCC cells. The process of miR-590-5p promoting proliferation was found to be implicated in its inhibition of G1/S transition of ccRCC cells, and the action mechanisms were involved in its downregulation of PBRM1/p21(WAF1/CIP1) expression. In conclusion, we identified the role of miR-590-5p, serving as an oncomir in ccRCC, and our findings provide a potential target for the treatment of ccRCC.

SPOP promotes tumorigenesis by acting as a key regulatory hub in kidney cancer

Hypoxic stress and hypoxia-inducible factors (HIFs) play important roles in a wide range of tumors. We demonstrate that SPOP, which encodes an E3 ubiquitin ligase component, is a direct transcriptional target of HIFs in clear cell renal cell carcinoma (ccRCC). Furthermore, hypoxia results in cytoplasmic accumulation of SPOP, which is sufficient to induce tumorigenesis. This tumorigenic activity occurs through the ubiquitination and degradation of multiple regulators of cellular proliferation and apoptosis, including the tumor suppressor PTEN, ERK phosphatases, the proapoptotic molecule Daxx, and the Hedgehog pathway transcription factor Gli2. Knockdown of SPOP specifically kills ccRCC cells, indicating that it may be a promising therapeutic target. Collectively, our results indicate that SPOP serves as a regulatory hub to promote ccRCC tumorigenesis.

Identification of erythropoietin receptor-derived peptides having the potential to induce cancer-reactive cytotoxic T lymphocytes from HLA-A24(+) patients with renal cell carcinoma

Molecular targeting therapy with anti-angiogenic agents, including sunitinib and sorafenib, has been proven to be the first- and second-line standard treatments for metastatic renal cell carcinoma (mRCC) worldwide. Despite their significant antitumor effects, most of the patients with mRCC have not been cured. Under such circumstances, anti-cancer immunotherapy has been considered as a promising treatment modality for mRCC, and cytotoxic T lymphocytes (CTLs) are the most powerful effectors among several immune cells and molecules. Therefore, we previously conducted anti-cancer vaccine therapy with peptides derived from carbonic anhydrase-9 and vascular endothelial growth factor receptor-1 as phase-I/II trials for mRCC patients and reported their clinical benefits. Alternatively, up-regulated expression of erythropoietin (Epo) and its receptor (EpoR) in RCC has been reported, and their co-expression is involved in tumorigenesis. In order to increase options for peptide-based vaccination therapy, we searched for novel EpoR-peptides for HLA-A24(+) RCC patients. Among 5 peptides derived from EpoR, which were prepared based on the binding motif to the HLA-A24 allele, EpoR52-60 peptide had the potential to induce peptide-specific CTLs from peripheral blood mononuclear cells of HLA-A24(+) RCC patients. Cytotoxicity toward HLA-A24(+) and EpoR-expressing RCC cells was ascribed to peptide-specific CD8(+) T cells. These results indicate that the EpoR52-60 peptide could be a promising candidate for a peptide-based anti-cancer vaccine for HLA-A24(+) mRCC patients.

Tumor derived vasculogenesis in von Hippel-Lindau disease-associated tumors

von Hippel-Lindau disease (VHL) patients develop highly vascular tumors, including central nervous system hemangioblastomas. It has been hypothesized that the vascular nature of these tumors is the product of reactive angiogenesis. However, recent data indicate that VHL-associated hemangioblastoma neoplastic cells originate from embryologically-arrested hemangioblasts capable of blood and endothelial cell differentiation. To determine the origin of tumor vasculature in VHL-associated hemangioblastomas, we analyzed the vascular elements in tumors from VHL patients. We demonstrate that isolated vascular structures and blood vessels within VHL-associated hemangioblastomas are a result of tumor-derived vasculogenesis. Further, similar to hemangioblastomas, we demonstrate that other VHL-associated lesions possess vascular tissue of tumor origin and that tumor-derived endothelial cells emerge within implanted VHL deficient UMRC6 RCC murine xenografts. These findings further establish the embryologic, developmentally arrested, hemangioblast as the tumor cell of origin for VHL-associated hemangioblastomas and indicate that it is also the progenitor cell for other VHL-associated tumors.

PP6C hotspot mutations in melanoma display sensitivity to Aurora kinase inhibition

Recent whole genome melanoma sequencing studies have identified recurrent mutations in the gene encoding the catalytic subunit of serine/threonine phosphatase 6 (PPP6C/PP6C). However, the biochemical, functional, and clinical ramifications of these mutations are unknown. Sequencing PP6C from patients with melanoma (233 primary and 77 metastatic specimens) with extended prospective clinical outcome revealed a large number of hotspot mutations in patients with both primary and metastatic melanoma. Despite minimal association between stage and presence of PP6C mutations in patients with primary melanoma, a subpopulation of cells within each tumor did contain PP6C mutations, suggesting PP6C mutation is an early, but non-tumor-initiating event in melanoma. Among patients with primary melanoma with PP6C mutations, patients with stop mutations had significantly shorter recurrence-free survival compared with patients without stop mutations. In addition, PP6C mutations were independent of commonly observed BRAF and NRAS mutations. Biochemically, PP6C mutations could be classified as those that interact with PP6C regulatory subunits and those that do not. Mutations that did not bind to PP6C regulatory subunits were associated with increased phosphorylation of Aurora kinase, a PP6C substrate, and mitotic defects. However, both classes of PP6C mutations led to increased sensitivity to Aurora kinase inhibition. Together, these data support for the first time that PP6C mutations are molecularly, biochemically, and clinically heterogeneous.

IMPLICATIONS

PP6C mutations have distinct functional and clinical consequences in melanoma, and confer sensitivity to Aurora A kinase inhibitors.

The contributions of HIF-target genes to tumor growth in RCC

Somatic mutations or loss of expression of tumor suppressor VHL happen in the vast majority of clear cell Renal Cell Carcinoma, and it’s causal for kidney cancer development. Without VHL, constitutively active transcription factor HIF is strongly oncogenic and is essential for tumor growth. However, the contribution of individual HIF-responsive genes to tumor growth is not well understood. In this study we examined the contribution of important HIF-responsive genes such as VEGF, CCND1, ANGPTL4, EGLN3, ENO2, GLUT1 and IGFBP3 to tumor growth in a xenograft model using immune-compromised nude mice. We found that the suppression of VEGF or CCND1 impaired tumor growth, suggesting that they are tumor-promoting genes. We further discovered that the lack of ANGPTL4, EGLN3 or ENO2 expression did not change tumor growth. Surprisingly, depletion of GLUT1 or IGFBP3 significantly increased tumor growth, suggesting that they have tumor-inhibitory functions. Depletion of IGFBP3 did not lead to obvious activation of IGFIR. Unexpectedly, the depletion of IGFIR protein led to significant increase of IGFBP3 at both the protein and mRNA levels. Concomitantly, the tumor growth was greatly impaired, suggesting that IGFBP3 might suppress tumor growth in an IGFIR-independent manner. In summary, although the overall transcriptional activity of HIF is strongly tumor-promoting, the expression of each individual HIF-responsive gene could either enhance, reduce or do nothing to the kidney cancer tumor growth.

Hypoxia-inducible factors enhance the effector responses of CD8(+) T cells to persistent antigen

Cytolytic activity by CD8(+) cytotoxic T lymphocytes (CTLs) is a powerful strategy for the elimination of intracellular pathogens and tumor cells. The destructive capacity of CTLs is progressively dampened during chronic infection, yet the environmental cues and molecular pathways that influence immunological 'exhaustion' remain unclear. Here we found that CTL immunity was regulated by the central transcriptional response to hypoxia, which is controlled in part by hypoxia-inducible factors (HIFs) and the von Hippel-Lindau tumor suppressor VHL. Loss of VHL, the main negative regulator of HIFs, led to lethal CTL-mediated immunopathology during chronic infection, and VHL-deficient CTLs displayed enhanced control of persistent viral infection and neoplastic growth. We found that HIFs and oxygen influenced the expression of pivotal transcription, effector and costimulatory-inhibitory molecules of CTLs, which was relevant to strategies that promote the clearance of viruses and tumors.

ATF4 promotes bone angiogenesis by increasing VEGF expression and release in the bone environment

Activating transcription factor 4 (ATF4) is a critical transcription factor for bone remodeling; however, its role in bone angiogenesis has not been established. Here we show that ablation of the Atf4 gene expression in mice severely impaired skeletal vasculature and reduced microvascular density of the bone associated with dramatically decreased expression of hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF) in osteoblasts located on bone surfaces. Results from in vivo studies revealed that hypoxia/reoxygenation induction of HIF-1α and VEGF expression leading to bone angiogenesis, a key adaptive response to hypoxic conditions, was severely compromised in mice lacking the Atf4 gene. Loss of ATF4 completely prevented endothelial sprouting from embryonic metatarsals, which was restored by addition of recombinant human VEGF protein. In vitro studies revealed that ATF4 promotion of HIF-1α and VEGF expression in osteoblasts was highly dependent upon the presence of hypoxia. ATF4 interacted with HIF-1α in hypoxic osteoblasts, and loss of ATF4 increased HIF-1α ubiquitination and reduced its protein stability without affecting HIF-1α mRNA stability and protein translation. Loss of ATF4 increased the binding of HIF-1α to prolyl hydroxylases, the enzymes that hydroxylate HIF-1a protein and promote its proteasomal degradation via the pVHL pathway. Furthermore, parathyroid hormone-related protein (PTHrP) and receptor activator of NF-κB ligand (RANKL), both well-known activators of osteoclasts, increased release of VEGF from the bone matrix and promoted angiogenesis through the protein kinase C- and ATF4-dependent activation of osteoclast differentiation and bone resorption. Thus, ATF4 is a new key regulator of the HIF/VEGF axis in osteoblasts in response to hypoxia and of VEGF release from bone matrix, two critical steps for bone angiogenesis.

HIFs, angiogenesis, and cancer

Tumor hypoxia was first described in the 1950s by radiation oncologists as a frequent cause of failure to radiotherapy in solid tumors. Today, it is evident that tumor hypoxia is a common feature of many cancers and the master regulator of hypoxia, hypoxia-inducible factor-1 (HIF-1), regulates multiple aspects of tumorigenesis, including angiogenesis, proliferation, metabolism, metastasis, differentiation, and response to radiation therapy. Although the tumor hypoxia response mechanism leads to a multitude of downstream effects, it is angiogenesis that is most crucial and also most susceptible to molecular manipulation. The delineation of molecular mechanisms of angiogenesis has revealed a critical role for HIF-1 in the regulation of angiogenic growth factors. In this article, we review what has been described about HIF-1: its structure, its regulation, and its implication for cancer therapy and we focus on its role in angiogenesis and cancer.

Targeting HIF2α translation with Tempol in VHL-deficient clear cell renal cell carcinoma

The tumor suppressor gene, Von Hippel-Lindau (VHL), is frequently mutated in the most common form of kidney cancer, clear cell renal cell carcinoma (CCRCC). In hypoxic conditions, or when there is a VHL mutation, the hypoxia inducible factors, HIF1α and HIF2α, are stabilized and transcribe a panel of genes associated with cancer such as vascular endothelial growth factor receptor (VEGFR), platelet derived growth factor (PDGF), and glucose transporter 1 (GLUT1). Recent studies in clear cell kidney cancer have suggested that HIF2α, but not HIF1α, is the critical oncoprotein in the VHL pathway. Therefore, targeting HIF2α could provide a potential therapeutic approach for patients with advanced CCRCC. Since iron regulatory protein 1 (IRP1) is known to inhibit the translation of HIF2α, we investigated whether Tempol, a stable nitroxide that activates IRP1 towards IRE-binding, might have a therapeutic effect on a panel of human CCRCC cells expressing both HIF1α and HIF2α. We first evaluated the protein expression of HIF1α and HIF2α in 15 different clear cell renal carcinoma cell lines established from patient tumors in our laboratory. Tempol decreased the expression of HIF2α, and its downstream targets in all the cell lines of the panel. This effect was attributed to a dramatic increase of IRE-binding activity of IRP1. Several cell lines were found to have an increased IRP1 basal activity at 20% O₂ compared to 5% O₂, which may lower HIF2α expression in some of the cell lines in a VHL-independent manner. Taken together our data identify Tempol as an agent with potential therapeutic activity targeting expression of HIF2α in VHL-deficient clear cell kidney cancer and illustrate the importance of studying biochemical processes at relevant physiological O2 levels.

Tumor-suppressive microRNA-1291 directly regulates glucose transporter 1 in renal cell carcinoma

Our recent studies of microRNA (miRNA) expression signatures demonstrated that microRNA-1291 (miR-1291) was significantly downregulated in renal cell carcinoma (RCC) clinical specimens and was a putative tumor-suppressive miRNA in RCC. The aim of the present study was to investigate the functional significance of miR-1291 in cancer cells and to identify novel miR-1291-mediated cancer pathways and target genes in RCC. Expression of miR-1291 was significantly downregulated in RCC tissues compared with adjacent non-cancerous tissues. Restoration of mature miR-1291 in RCC cell lines (A498 and 786-O) revealed significant inhibition of cell proliferation, migration and invasion, suggesting that miR-1291 functioned as a tumor suppressor. To identify miR-1291-mediated molecular pathways and targets, we used gene expression analysis (expression of RCC clinical specimens and miR-1291-transfected A498 cells) and in silico database analysis. Our data demonstrated that 79 signaling pathways were significantly regulated by tumor-suppressive miR-1291 in RCC cells. Moreover, solute career family 2 member 1 (SLC2A1) was a candidate target of miR-1291 regulation. The SLC2A1 gene provides instructions for producing glucose transporter protein type 1 (GLUT1). Luciferase reporter assays showed that miR-1291 directly regulated SLC2A1/GLUT1. In RCC clinical specimens, the expression of SLC2A1/GLUT1 mRNA was significantly higher in cancer tissues than in non-cancerous tissues. A significant inverse correlation was recognized between SLC2A1/GLUT1 and miR-1291 expression (r = -0.55, P < 0.0001). Loss of tumor-suppressive miR-1291 enhanced RCC cell proliferation, migration and invasion through targeting SLC2A1/GLUT1. The identification of novel tumor-suppressive miR-1291-mediated molecular pathways and targets has provided new insights into RCC oncogenesis and metastasis.

Loss of the Birt-Hogg-Dubé gene product folliculin induces longevity in a hypoxia-inducible factor-dependent manner

Signaling through the hypoxia-inducible factor hif-1 controls longevity, metabolism, and stress resistance in Caenorhabditis elegans. Hypoxia-inducible factor (HIF) protein levels are regulated through an evolutionarily conserved ubiquitin ligase complex. Mutations in the VHL gene, encoding a core component of this complex, cause a multitumor syndrome and renal cell carcinoma in humans. In the nematode, deficiency in vhl-1 promotes longevity mediated through HIF-1 stabilization. However, this longevity assurance pathway is not yet understood. Here, we identify folliculin (FLCN) as a novel interactor of the hif-1/vhl-1 longevity pathway. FLCN mutations cause Birt-Hogg-Dubé syndrome in humans, another tumor syndrome with renal tumorigenesis reminiscent of the VHL disease. Loss of the C. elegans ortholog of FLCN F22D3.2 significantly increased lifespan and enhanced stress resistance in a hif-1-dependent manner. F22D3.2, vhl-1, and hif-1 control longevity by a mechanism distinct from insulin-like signaling. Daf-16 deficiency did not abrogate the increase in lifespan mediated by flcn-1. These findings define FLCN as a player in HIF-dependent longevity signaling and connect organismal aging, stress resistance, and regulation of longevity with the formation of renal cell carcinoma.

Renal cancer in von Hippel-Lindau disease and related syndromes

Sporadic and hereditary forms of renal cell carcinoma (RCC), von Hippel-Lindau (VHL) disease and the familial paraganglioma syndromes are closely related in terms of their clinical, molecular, and genetic aspects. Most RCCs occur sporadically and the heritable fraction of RCC is estimated to be just 2-4%. An understanding of the molecular genetic basis, the disease-specific and gene-specific biology and the clinical characteristics of these cancer syndromes is of utmost importance for effective genetic diagnosis and appropriate treatment. In addition, such insight will improve our understanding of sporadic RCCs. To date, 10 different heritable RCC syndromes have been described. VHL syndrome is the oldest known hereditary RCC syndrome. Similar to VHL disease, phaeochromocytoma is a major manifestation of the paraganglioma syndromes types 1, 3 and 4 in which RCCs have been reported. These syndromes are therefore regarded as VHL-related disorders and are included in this Review. Multifocal tumours, bilateral occurrence, a young age at diagnosis and/or family history are clinical red flags suggestive of hereditary disease and should trigger referral for genetic and molecular analysis. The identification of an underlying genetic alteration enables gene-specific risk assessment and opens up the possibility of a tailored follow-up strategy and specific surveillance protocols as the basis of effective preventive medicine. The important goals of preventive medicine are to increase the life expectancy of affected patients and to improve their quality of life. The study of seemingly rare hereditary syndromes and their susceptibility genes has consistently revealed clues regarding the aetiology and pathogenesis of these diseases, and can aid diagnosis and the development of therapeutics for patients affected by much more common sporadic counterparts.

Identification of pVHL as a novel substrate for Aurora-A in clear cell renal cell carcinoma (ccRCC)

Clear cell renal cell carcinoma (ccRCC) is the most common histological subtype of kidney cancer and is often characterized by mutations or deletions of the Von Hippel Lindau (VHL) tumour suppressor gene. Aurora gene family members are implicated in proper mitotic progression and spindle checkpoint function and play a crucial role in cancer progression. In the present study, we assessed the expression of Aurora-A in a cohort of 30 ccRCC with fully characterized VHL status (wt/wt or mut/del) and Fuhrman grade. Aurora-A transcript and protein levels were significantly increased in high Fuhrman grade tumours and in VHLwt/wt tumours. These results suggest that Aurora-A and VHL interact in the ccRCC. We demonstrated that the two proteins interact in vivo and identified the Ser72 on the sequence of VHL as the unique site phosphorylated by Aurora-A.

HIF expression and the role of hypoxic microenvironments within primary tumours as protective sites driving cancer stem cell renewal and metastatic progression

Hypoxic microenvironments frequently exist in many solid tumours with oxygen levels fluctuating temporally and spatially from normoxia to hypoxia. The response to hypoxia in human cells is mainly regulated by hypoxia-inducible factors (HIFs), a family of transcription factors which orchestrate signalling events leading to angiogenesis and tumorigenesis. Several events conspire together to lead to the stabilization of HIF-α, commonly expressed in many cancer cell types. These events can result from low oxygen tensions occurring within the expanding tumour mass to produce hypoxic microenvironments or from mutations whereby the HIFs cause changes in expression of genes involved in several cellular functions. Hypoxia-mediated HIF-α regulation has gained significant prominence in tumour biology over recent years, and the hypoxic microenvironments have been shown to facilitate and trigger major molecular and immunological processes necessary to drive the progression of tumours to malignancy. More recently, it has been realized that the hypoxic microenvironments also play significant roles in shielding tumour cells from immune attack by promoting immune suppression. In addition, the hypoxic microenvironment promotes many other oncogenic events, such as the metabolic reconfiguration of tumour cells, neovascularization, epithelial to mesenchymal transition (EMT), and cancer stem cell renewal and accumulation. This article reviews the molecular mechanisms underlying tumour hypoxia and their pro-tumour contributions, such as immune suppression, development of nascent and more permeable tumour vasculature, selective cancer stem cell renewal, accumulation, mobilization and promotion of EMT leading to tumour cell metastasis.

Signal transducer and activator of transcription 3 (STAT3) degradation by proteasome controls a developmental switch in neurotrophin dependence

Neonatal brains develop through a program that eliminates about half of the neurons. During this period, neurons depend on neurotrophins for their survival. Recently, we reported that, at the conclusion of the naturally occurring death period, neurons become neurotrophin-independent and, further, that this developmental switch is achieved by the emergence of a second survival pathway mediated by signal transducer and activator of transcription 3 (STAT3). Here I show that calcineurin plays a key role in controlling the developmental switch in mouse hippocampal neurons. Calcineurin promotes the degradation of STAT3 via the ubiquitin-proteasome pathway. Inhibition of calcineurin acutely increases total levels of STAT3 as well as its activated forms, resulting in decreased levels of the tumor suppressor p53 and its proapoptotic target, Bax. In vivo and in vitro, calcineurin regulates levels of STAT3 and neurotrophin dependence. TMF/ARA 160 (TATA element modulatory factor/androgen receptor co-activator 160), the key mediator of STAT3 ubiquitination, is required for calcineurin-dependent STAT3 degradation. Thus, these results show that the ubiquitin-proteasome pathway controls the critical developmental switch of neurotrophin dependence in the newborn hippocampus.

First report of bilateral pheochromocytoma in the clinical spectrum of HIF2A-related polycythemia-paraganglioma syndrome

CONTEXT

Molecular genetic research has so far resulted in the identification of 10 well-characterized susceptibility genes for hereditary pheochromocytoma (PHEO) or paraganglioma (PGL). Recently, a new syndrome characterized by multiple PGLs and somatostatinomas associated with congenital polycythemia due to somatic mutations in HIF2A has been reported.

OBJECTIVE

The aim of the study was to define the genetic defect in a new case of bilateral PHEO and multiple PGLs associated with congenital polycythemia.

PATIENT

A female patient presented with neonatal polycythemia (treated by phlebotomies, 1 session approximately every 4 mo), mildly enlarged cerebral ventricles, and bilateral PHEO and multiple PGLs. There was no family history of any neuroendocrine tumor or polycythemia. Surgical removal of the tumors only temporarily normalized plasma erythropoietin (Epo) levels and discontinued phlebotomies. No germline mutations were initially detected in the SDHB, SDHC, SDHD, VHL, and PHD2 genes, known to be associated with polycythemia. The PHEOs presented with a typical noradrenergic biochemical phenotype.

RESULTS

A heterozygous missense mutation (c.1589C>T) was identified in exon 12 of HIF2A, resulting in an alanine 530 substitution in the HIF-2α protein with valine (A530V). This somatic mutation was detected in the tissue from 1 PHEO and 1 PGL, with no HIF2A germline mutation found. This mutation led to stabilization of HIF-2α and hence a gain-of-function phenotype, as in previously published studies.

CONCLUSION

This case represents the first association of a somatic HIF2A gain-of-function mutation with PHEO and congenital polycythemia, and it alerts physicians to perform proper genetic screening in patients presenting with multiple norepinephrine-producing PHEOs and polycythemia. This report also extends the previous findings of a new syndrome of only multiple PGLs, somatostatinomas, and polycythemia to multiple PHEOs.

Functional aspects of primary cilia in signaling, cell cycle and tumorigenesis

Dysfunctional cilia underlie a broad range of cellular and tissue phenotypes and can eventually result in the development of ciliopathies: pathologically diverse diseases that range from clinically mild to highly complex and severe multi-organ failure syndromes incompatible with neonatal life. Given that virtually all cells of the human body have the capacity to generate cilia, it is likely that clinical manifestations attributed to ciliary dysfunction will increase in the years to come. Disputed but nevertheless enigmatic is the notion that at least a subset of tumor phenotypes fit within the ciliopathy disease spectrum and that cilia loss may be required for tumor progression. Contending for the centrosome renders ciliation and cell division mutually exclusive; a regulated tipping of balance promotes either process. The mechanisms involved, however, are complex. If the hypothesis that tumorigenesis results from dysfunctional cilia is true, then why do the classic ciliopathies only show limited hyperplasia at best? Although disassembly of the cilium is a prerequisite for cell proliferation, it does not intrinsically drive tumorigenesis per se. Alternatively, we will explore the emerging evidence suggesting that some tumors depend on ciliary signaling. After reviewing the structure, genesis and signaling of cilia, the various ciliopathy syndromes and their genetics, we discuss the current debate of tumorigenesis as a ciliopathy spectrum defect, and describe recent advances in this fascinating field.

Combined mutation of Vhl and Trp53 causes renal cysts and tumours in mice

The combinations of genetic alterations that cooperate with von Hippel–Lindau (VHL) mutation to cause clear cell renal cell carcinoma (ccRCC) remain poorly understood. We show that the TP53 tumour suppressor gene is mutated in approximately 9% of human ccRCCs. Combined deletion of Vhl and Trp53 in primary mouse embryo fibroblasts causes proliferative dysregulation and high rates of aneuploidy. Deletion of these genes in the epithelium of the kidney induces the formation of simple cysts, atypical cysts and neoplasms, and deletion in the epithelia of the genital urinary tract leads to dysplasia and tumour formation. Kidney cysts display a reduced frequency of primary cilia and atypical cysts and neoplasms exhibit a pro-proliferative signature including activation of mTORC1 and high expression of Myc, mimicking several cellular and molecular alterations seen in human ccRCC and its precursor lesions. As the majority of ccRCC is associated with functional inactivation of VHL, our findings suggest that for a subset of ccRCC, loss of p53 function represents a critical event in tumour development.

Protein tyrosine phosphatase ζ enhances proliferation by increasing β-catenin nuclear expression in VHL-inactive human renal cell carcinoma cells

OBJECTIVE

We investigated the role of protein tyrosine phosphatase ζ (Ptprz1) in human renal cell carcinoma (RCC) cells' proliferation and associations between Ptprz1 expression and von Hippel-Lindau (VHL) activation.

METHODS

A normal human renal cell line and four human RCC cell lines were used in this study. VHL or Ptprz1 expression in RCC cells was increased by transfection with a VHL or Ptprz1 vector. VHL or Ptprz1 expression was decreased in these cells by siRNA using Lipofectamine 2000. Cells' proliferative activity was assessed by WST-1 assay.

RESULTS

Our results suggested that Ptprz1 was a target of VHL, and a loss of VHL activation increased Ptprz1 expression in RCC cells. Ptprz1 enhanced β-catenin protein expressions in the nuclear fractions of RCC cells and participated in regulating proliferation by activating β-catenin and its downstream genes. In addition, a loss of VHL activity may enhance the proliferative activity of RCC cells by increasing Ptprz1 expression.

CONCLUSION

Ptprz1-enhanced RCC cells' proliferation depends on VHL inactivation, and the Ptprz1/β-catenin pathway may be a potential target for treating RCC with inactive VHL.

Induction of erythropoietin increases the cell proliferation rate in a hypoxia-inducible factor-1-dependent and -independent manner in renal cell carcinoma cell lines

Erythropoietin (Epo) is a potent inducer of erythropoiesis that is mainly produced in the kidney. Epo is expressed not only in the normal kidney, but also in renal cell carcinomas (RCCs). The aim of the present study was to gain insights into the roles of Epo and its receptor (EpoR) in RCC cells. The study used two RCC cell lines, Caki-1 and SKRC44, in which Epo and EpoR are known to be highly expressed. The proliferation rate and expression level of hypoxia-inducible factor-1α (HIF-1α) were measured prior to and following Epo treatment and under normoxic and hypoxic conditions. To examine whether HIF-1α or Epo were involved in cellular proliferation during hypoxia, these proteins were knocked down using small interfering RNA (siRNA) in Caki-1 and SKRC44 cells. The results demonstrated that Epo enhanced the proliferation of the Caki-1 and SKRC44 cells. HIF-1α expression was increased upon the induction of hypoxia in the Caki-1 cells, but remained unaffected in the SKRC44 cells. The proliferation rate was increased under hypoxic conditions in the Caki-1 cells, but was decreased in the SKRC44 cells. Under hypoxic conditions, the proliferation of the Caki-1 cells was significantly reduced by the knock-down of HIF-1α or Epo, while the proliferation of the SKRC44 cells was significantly suppressed by the knock-down of Epo, but not HIF-1α. In conclusion, these data suggest that the induction of Epo may accelerate the proliferation of the RCC cell lines in either a HIF-1α-dependent or -independent manner.

mTOR inhibitors in advanced renal cell carcinomas: from biology to clinical practice

To date, oral everolimus is indicated for the treatment of patients with advanced renal cell carcinoma, whose disease has progressed on or after treatment with vascular endothelial growth factor-targeted therapy, and intravenous temsirolimus for the first-line treatment of patients with poor prognosis metastatic renal cell carcinoma. However, some factors could guide the treatment choice aiming to individualize a treatment plan. Besides the crucial issue of treatment efficacy, other factors are to be considered such as disease status, histological subtype, extent of the disease, patient-specific factors, and agent-specific factors. All of these considerations have to stay in the frame of guideline recommendations which represent evidence-based medicine. The purpose of this article is to summarize the main pharmacological and pharmacokinetic characteristics of mTOR inhibitors, and to define targeted populations according to prognostic indexes.

New syndrome of paraganglioma and somatostatinoma associated with polycythemia

PURPOSE

The occurrence of ≥ two distinct types of tumors, one of them paraganglioma (PGL), is unusual in an individual patient, except in hereditary cancer syndromes.

PATIENTS AND METHODS

Four unrelated patients were investigated, with thorough clinical evaluation. Plasma and tissue catecholamines and metanephrines were measured by high-performance liquid chromatography. Anatomic and functional imaging were performed for tumor visualization. Germline and tumor tissue DNA were analyzed for hypoxia-inducible factor 2 alpha (HIF2A) mutations. The prolyl hydroxylation and stability of the mutant HIF2α protein, transcriptional activity of mutant HIF2A, and expression of hypoxia-related genes were also investigated. Immunohistochemical staining for HIF1/2α was performed on formalin-fixed, paraffin-embedded tumor tissue.

RESULTS

Patients were found to have polycythemia, multiple PGLs, and duodenal somatostatinomas by imaging or biochemistry with somatic gain-of-function HIF2A mutations. Each patient carried an identical unique mutation in both types of tumors but not in germline DNA. The HIF2A mutations in these patients were clustered adjacent to an oxygen-sensing proline residue, affecting HIF2α interaction with the prolyl hydroxylase domain 2-containing protein, decreasing the hydroxylation of HIF2α, and reducing HIF2α affinity for the von Hippel-Lindau protein and its degradation. An increase in the half-life of HIF2α was associated with upregulation of the hypoxia-related genes EPO, VEGFA, GLUT1, and END1 in tumors.

CONCLUSION

Our findings indicate the existence of a new syndrome with multiple PGLs and somatostatinomas associated with polycythemia. This new syndrome results from somatic gain-of-function HIF2A mutations, which cause an upregulation of hypoxia-related genes, including EPO and genes important in cancer biology.

Nervous system involvement in von Hippel-Lindau disease: pathology and mechanisms

Patients with von Hippel-Lindau disease carry a germline mutation of the Von Hippel-Lindau (VHL) tumor-suppressor gene. We discuss the molecular consequences of loss of VHL gene function and their impact on the nervous system. Dysfunction of the VHL protein causes accumulation and activation of hypoxia inducible factor (HIF) which can be demonstrated in earliest stages of tumorigenesis and is followed by expression of VEGF, erythropoietin, nitric oxide synthase and glucose transporter 1 in VHL-deficient tumor cells. HIF-independent functions of VHL, epigenetic inactivation of VHL, pVHL proteostasis, and links between loss of VHL function and developmental arrest are also described. A most intriguing feature in VHL disease is the occurrence of primary hemangioblastic tumors in the nervous system, the origin of which has not yet been entirely clarified, and current hypotheses are discussed. Endolymphatic sac tumors may extend into the brain, but originally arise from proliferation of endolymphatic duct/sac epithelium; the exact nature of the proliferating epithelial cell, however, also has remained unclear, as well as the question why tumors almost consistently develop in the intraosseous portion of the endolymphatic sac/duct only. The epitheloid clear cell morphology of both advanced hemangioblastoma and renal clear cell carcinoma can make the differential diagnosis challenging, recent developments in immunohistochemical differentiation are discussed. Finally, metastasis to brain may not only be caused by renal carcinoma, but may derive from VHL disease-associated pheochromocytoma/paraganglioma, or pancreatic neuroendocrine tumor.

Life-span extension from hypoxia in Caenorhabditis elegans requires both HIF-1 and DAF-16 and is antagonized by SKN-1

Stabilization of the hypoxia-inducible factor (HIF-1) protein extends longevity in Caenorhabditis elegans. However, stabilization of mammalian HIF-1α has been implicated in tumor growth and cancer development. Consequently, for the hypoxic response to benefit mammalian health, we must determine the components of the response that contribute to longevity, and separate them from those that cause harm in mammals. Here, we subject adult worms to low oxygen environments. We find that growth in hypoxia increases longevity in wild-type worms but not in animals lacking HIF-1 or DAF-16. Conversely, hypoxia shortens life span in combination with overexpression of the antioxidant stress response protein SKN-1. When combined with mutations in other longevity pathways or dietary restriction, hypoxia extends life span but to varying extents. Collectively, our results show that hypoxia modulates longevity in a complex manner, likely involving components in addition to HIF-1.

Genetics and molecular pathogenesis of pheochromocytoma and paraganglioma

Although most pheochromocytomas (PCCs) and paragangliomas (PGLs) are sporadic, molecular genetic medicine has revealed that a considerable number of patients with apparently sporadic PCC actually have a genetic predisposition to the development of these tumors. After decades of intensive research, several genes are now known to play an important role in the pathogenesis of PCC. At present, these are RET proto-oncogene, von Hippel-Lindau disease tumor suppressor gene (VHL), neurofibromatosis type 1 tumor suppressor gene (NF1), genes encoding the succinate dehydrogenase (SDH) complex subunits SDHB, SDHC, and SDHD, but also SDHA, the gene encoding the enzyme responsible for the flavination of SDHA (SDHAF2 or hSDH5), and the newly described TMEM127 and MAX tumor suppressor genes. In addition to these ten PCC susceptibility genes, two other genes, KIF1B and PHD2, have also been associated with PCC. Studying the pathogenesis and the molecular correlation of these mutations has revealed the existence of two main transcription signatures: a pseudohypoxic cluster (VHL and SDH mutations) and a cluster rich in kinase receptor signaling and their downstream pathways (RET, NF1, TMEM127, and MAX mutations). However, the general mechanism in the pathogenesis of a syndrome does not entirely apply in the particular pathogenesis of PCC as a manifestation of that syndrome. A better understanding of the complexity and high genetic diversity of PCC and PGL may lead to more efficient diagnosis and management of the disease.

Reduced cilia frequencies in human renal cell carcinomas versus neighboring parenchymal tissue

Background

Cilia are essential organelles in multiple organ systems, including the kidney where they serve as important regulators of renal homeostasis. Renal nephron cilia emanate from the apical membrane of epithelia, extending into the lumen where they function in flow-sensing and ligand-dependent signaling cascades. Ciliary dysfunction underlies renal cyst formation that is in part caused by deregulation of planar cell polarity and canonical Wnt signaling. Renal cancer pathologies occur sporadically or in heritable syndromes caused by germline mutations in tumor suppressor genes including VHL. Importantly, Von Hippel-Lindau (VHL) patients frequently develop complex renal cysts that can be considered a premalignant stage. One of the well-characterized molecular functions of VHL is its requirement for the maintenance of cilia. In this study, tissue from 110 renal cancer patients who underwent nephrectomy was analyzed to determine if lower ciliary frequency is a common hallmark of renal tumorigenesis by comparing cilia frequencies in both tumor and adjacent parenchymal tissue biopsies from the same kidney.

Methods

We stained sections of human renal material using markers for cilia. Preliminary staining was performed using an immunofluorescent approach and a combination of acetylated-α-tubulin and pericentrin antibodies and DAPI. After validation of an alternative, higher throughput approach using acetylated-α-tubulin immunohistochemistry, we continued to manually quantify cilia in all tissues. Nuclei were separately counted in an automated fashion in order to determine ciliary frequencies. Similar staining and scoring for Ki67 positive cells was performed to exclude that proliferation obscures cilia formation potential.

Results

Samples from renal cell carcinoma patients deposited in our hospital tissue bank were previously used to compose a tissue microarray containing three cores of both tumor and parenchymal tissue per patient. Cilia frequencies in a total of eighty-nine clear cell, eight papillary, five chromophobe renal cell carcinomas, two sarcomatoid renal tumors and six oncocytomas were determined. A marked decrease of primary cilia across renal cell carcinoma subtypes was observed compared to adjacent nontumorigenic tissue.

Conclusions

Our study shows that cilia are predominantly lost in renal cell carcinomas compared to tissue of the tumor parenchyma. These results suggest that ciliary loss is common in renal tumorigenesis, possibly participating in the sequence of cellular events leading to malignant tumor development. Future therapies aimed at restoring or circumventing cilia signaling might therefore aid in current treatment efficacy.

Vasoactive intestinal peptide induces oxidative stress and suppresses metastatic potential in human clear cell renal cell carcinoma

Molecular mechanisms involved in progression of clear-cell renal-cell carcinomas (ccRCCs) are poorly understood. A common genetic mutation found in ccRCC is the loss of the von Hippel-Lindau (VHL) gene, which contributes to cancer progression and metastasis. We investigated VIP effects on metastatic and angiogenic factors in human VHL-null A498 ccRCC and HK2 renal cells. VIP increased adhesion but decreased expression of metalloproteinases, MMP2 and MMP9, as well as cell migration and VEGF expression and secretion in A498 but not in HK2 cells. VIP enhanced ROS levels and decreased nuclear levels of β-catenin and NFκB p50-subunit in A498 cells, suggesting neuropeptide involvement in the observed decrease of metastatic ability in clear-cell carcinoma. VIP effects in A498 cells were blocked by the VPAC(1/2)-receptor antagonist JV-1-53. In conclusion, present data point to a role of VIP in preventing invasion and metastasis in ccRCCs and support its potential therapeutic usefulness in this disease.

[Energy metabolism pathway related genes and adaptive evolution of tumor cells]

The proliferation of tumor cells is an extremely energy-consuming process. However, different from normal cells, tumor cells generate energy via glycolysis even under aerobic conditions, which is one of the ten hallmarks of tumor cells. The switch of energy metabolism results in a series of physiological changes in tumor cells, including rapid generation of ATP and abundant biomass for cell proliferation, which form the basis of tumor cells to successfully adapt to their extreme microenvironment (e.g. lack of oxygen). In this review, we will introduce recent progress in studying somatic mutations on the energy metabolism related genes in tumors, with special focus on the potential factors involving in the "switch" and to decipher the genetic adaptive footprint of the "switch" from the angle of molecular evolution.

Pancreatic neuroendocrine tumors: biology, diagnosis,and treatment

Pancreatic neuroendocrine tumors (PNETs), a group of endocrine tumors arising in the pancreas, are among the most common neuroendocrine tumors. The genetic causes of familial and sporadic PNETs are somewhat understood, but their molecular pathogenesis remains unknown. Most PNETs are indolent but have malignant potential. The biological behavior of an individual PNET is unpredictable; higher tumor grade, lymph node and liver metastasis, and larger tumor size generally indicate a less favorable prognosis. Endocrine testing, imaging, and histological evidence are necessary to accurately diagnose PNETs. A 4-pronged aggressive treatment approach consisting of surgery, locoregional therapy, systemic therapy, and complication control has become popular in academic centers around the world. The optimal application of the multiple systemic therapeutic modalities is under development; efficacy, safety, availability, and cost should be considered when treating a specific patient. The clinical presentation, diagnosis, and treatment of specific types of PNETs and familial PNET syndromes, including the novel Mahvash disease, are summarized.

Estrogen receptor α is a novel target of the Von Hippel-Lindau protein and is responsible for the proliferation of VHL-deficient cells under hypoxic conditions

The Von Hippel-Lindau gene (VHL) is frequently deleted or mutated in human renal cell carcinoma (RCC) at the early stage. According to the well-established theory, pVHL acts as a tumor suppressor through its E3 ligase activity, which targets hypoxia-inducing factor-1α (HIF-1α). However, the elevated expression of HIF-1α did not promote cell proliferation, indicating that there would be another target, which could promote cell proliferation at the early cancer stage of RCC. In this study, we show that estrogen receptor-α (ER-α) is a novel proteasomal degradation target of the pVHL E3 ligase. Indeed, the overexpression of VHL suppresses exo- and endogenous ER-α expression, whereas si-pVHL can increase ER-α expression. The negative regulation of pVHL on ER-α expression is achieved by its E3 ligase activity. Thus, pVHL can promote the ER-α ubiquitinylation. In addition, we revealed that ER-α and HIF-1α are competitive substrates of pVHL. Thus, under normal conditions, ER-α overexpression can increase the transcription factor activity of HIF-1α. Under the hypoxic condition, where HIF-1α is not a suitable target of pVHL, ER-α is more rapidly degraded by pVHL. However, in VHL-deficient cells, the expression of ER-α and HIF-1α is retained, so that the hypoxic condition did not suppress cell proliferation obviously compared with cells that are expressing pVHL. Thus, blocking of ER-α using its inhibitor could suppress the proliferation of VHL-deficient cells as effectively as hypoxia-induced growth suppression. Considering our results, blocking of ER-α signaling in VHL-deficient cancer cells would be beneficial for cancer suppression. Indeed, we showed the anti-proliferative effect of Faslodex in VHL-deficient cells.

Integrative analysis of neuroblastoma and pheochromocytoma genomics data

Background

Pheochromocytoma and neuroblastoma are the most common neural crest-derived tumors in adults and children, respectively. We have performed a large-scale in silico analysis of altogether 1784 neuroblastoma and 531 pheochromocytoma samples to establish similarities and differences using analysis of mRNA and microRNA expression, chromosome aberrations and a novel bioinformatics analysis based on cooperative game theory.

Methods

Datasets obtained from Gene Expression Omnibus and ArrayExpress have been subjected to a complex bioinformatics analysis using GeneSpring, Gene Set Enrichment Analysis, Ingenuity Pathway Analysis and own software.

Results

Comparison of neuroblastoma and pheochromocytoma with other tumors revealed the overexpression of genes involved in development of noradrenergic cells. Among these, the significance of paired-like homeobox 2b in pheochromocytoma has not been reported previously. The analysis of similar expression patterns in neuroblastoma and pheochromocytoma revealed the same anti-apoptotic strategies in these tumors. Cancer regulation by stathmin turned out to be the major difference between pheochromocytoma and neuroblastoma. Underexpression of genes involved in neuronal cell-cell interactions was observed in unfavorable neuroblastoma. By the comparison of hypoxia- and Ras-associated pheochromocytoma, we have found that enhanced insulin like growth factor 1 signaling may be responsible for the activation of Src homology 2 domain containing transforming protein 1, the main co-factor of RET. Hypoxia induced factor 1α and vascular endothelial growth factor signaling included the most prominent gene expression changes between von Hippel-Lindau- and multiple endocrine neoplasia type 2A-associated pheochromocytoma.

Conclusions

These pathways include previously undescribed pathomechanisms of neuroblastoma and pheochromocytoma and associated gene products may serve as diagnostic markers and therapeutic targets.

Hemangioblastoma stromal cells show committed stem cell phenotype

BACKGROUND

Hemangioblastomas are benign vascular tumors of the central nervous system that occur sporadically or in association with von Hippel-Lindau disease. These tumors are characteristically composed of a dense capillary network with intervening stromal/interstitial cells. To date, the histogenesis of hemangioblastoma remains unclear. We hypothesize that hemangioblastomas arise from a defective mesodermal stem cell, which gives rise to the atypical vasculature.

METHODS

To test our hypothesis, we have characterized the cellular composition of hemangioblastomas by immunophenotyping pluripotent and committed stem cells and vascular endothelial cells.

RESULTS

Our findings show that hemangioblastoma endothelial cells are positive for CD133, a stem and progenitor cell marker. Vascular endothelial cells also expressed nuclear Oct4. In addition to the endothelium, both CD133 and Oct4 were present in stromal and perivascular cells. Interestingly, neither the endothelium nor the stromal cells expressed Sox2 or Nanog suggesting a committed stem cell phenotype.

CONCLUSIONS

From these findings, we believe that hemangioblastoma stromal cells are committed stem cells producing both vascular cell types. The findings also show an unusual CD133-positive endothelial phenotype in hemangioblastoma.

Warburg effect's manifestation in aggressive pheochromocytomas and paragangliomas: insights from a mouse cell model applied to human tumor tissue

A glycolytic profile unifies a group of pheochromocytomas and paragangliomas (PHEOs/PGLs) with distinct underlying gene defects, including von Hippel-Lindau (VHL) and succinate dehydrogenase B (SDHB) mutations. Nevertheless, their tumor aggressiveness is distinct: PHEOs/PGLs metastasize rarely in VHL-, but frequently in SDHB-patients. To date, the molecular mechanisms causing the more aggressive phenotype in SDHB-PHEOs/PGLs remain largely unknown. Recently, however, an excellent model to study aggressive PHEOs (mouse tumor tissue (MTT) cells) has been developed from mouse PHEO cells (MPC). We employed this model for a proteomics based approach to identify changes characteristic for tumor aggressiveness, which we then explored in a homogeneous set of human SDHB- and VHL-PHEOs/PGLs. The increase of glucose transporter 1 in VHL, and of hexokinase 2 in VHL and SDHB, confirmed their glycolytic profile. In agreement with the cell model and in support of decoupling of glycolysis, the Krebs cycle and oxidative phosphorylation (OXPHOS), SDHB tumors showed increased lactate dehydrogenase levels. In SDHB-PGLs OXPHOS complex activity was increased at complex III and, as expected, decreased at complex II. Moreover, protein and mRNA expression of all tested OXPHOS-related genes were higher in SDHB- than in VHL-derived tumors. Although there was no direct evidence for increased reactive oxygen species production, elevated superoxide dismutase 2 expression may reflect elevated oxidative stress in SDHB-derived PHEOs/PGLs. For the first time, we show that despite dysfunction in complex II and evidence for a glycolytic phenotype, the Warburg effect does not seem to fully apply to SDHB-PHEOs/PGLs with respect to decreased OXPHOS. In addition, we present evidence for increased LDHA and SOD2 expression in SDHB-PHEOs/PGLs, proteins that have been proposed as promising therapeutic targets in other cancers. This study provides new insight into pathogenic mechanisms in aggressive human PHEOs/PGLs, which may lead to identifying new diagnostic and prognostic markers in the near future.

Identification of 3 novel VHL germ-line mutations in Danish VHL patients

BACKGROUND

von Hippel-Lindau (VHL) disease is a hereditary cancer syndrome in which the patients develop retinal and central nervous system hemangioblastomas, pheochromocytomas and clear-cell renal tumors. The autosomal dominant disease is caused by mutations in the VHL gene.

METHODS

VHL mutational analysis was carried out by sequencing of the coding sequence and by multiplex ligation-dependent probe amplification analysis. The functional consequence of the variants was investigated using in silico prediction tools.

RESULTS

A total of 289 probands suspected of having VHL syndrome have been screened for mutations in the VHL gene. Twenty-six different VHL mutations were identified in 36 families including one in-frame duplication, two frame-shift mutations, four nonsense mutations, twelve missense mutations, three intronic mutations and four large genomic rearrangements. Three of these mutations (c.319 C > T, c.342_343dupGGT and c.520_521dupAA) were novel.

CONCLUSIONS

In this study we report the VHL germ-line mutations found in Danish families. We found three novel VHL mutations where two were classified as pathogenic and the latter was classified as a variant of unknown significance. Together, our findings contribute to the interpretation of the potential pathogenicity of VHL germ-line mutations.

CD31 angiogenesis and combined expression of HIF-1α and HIF-2α are prognostic in primary clear-cell renal cell carcinoma (CC-RCC), but HIFα transcriptional products are not: implications for antiangiogenic trials and HIFα biomarker studies in primary CC-RCC

Hypoxia-inducible factors, HIF-1α and HIF-2α, are expressed in the majority of clear-cell renal cell carcinoma (CC-RCC). In vitro, HIFα isoforms regulate a differential set of genes, and their effects in vivo within CC-RCC tumours may affect outcome. The role of angiogenesis and HIFα transcriptional products, including those involved in cell metabolism and morphological dedifferentiation have not been extensively investigated and might have relevance to the development of antiangiogenic or anti-HIFα trials in primary CC-RCC, either before or after radical nephrectomy. We analysed 168 consecutive clear-cell renal tumours from 1983 to 1999 within tissue microarrays and assessed expression of HIF-1α and HIF-2α together with the protein expression of seven of their target genes (BNIP3, CA9, Cyclin D1, GLUT-1, LDH5, Oct-4 and VEGF). The expression of these factors was compared with patient overall survival and CD31 angiogenesis. We found that HIFα antigenicity deteriorated with the age of the paraffin block (P < 0.0001) and in tumours from 1983 to 1992 was deemed not to be reliable. Similar findings were found in aged archival osteosarcoma samples. This might have important implications for retrospective biomarker studies that rely on archival tissue material. HIF-1α(HIGH)/HIF-2α(LOW) tumours had a worse overall survival compared with HIF-1α(LOW)/HIF-2α(LOW) tumours (P = 0.04). Surprisingly, on multivariate analysis, high levels of CD31(+) angiogenesis was shown to be an independent prognostic marker of increased overall survival (P = 0.003). We propose that better differentiation of vascular endothelium may be a reflection of a greater production of vessel stabilization factors versus pro-angiogenic factors, and therefore a less aggressive phenotype.

Genomic copy number alterations in clear cell renal carcinoma: associations with case characteristics and mechanisms of VHL gene inactivation

Array comparative genomic hybridization was used to identify copy number alterations in clear cell renal cell carcinoma (ccRCC) patient tumors to identify associations with patient/clinical characteristics. Of 763 ccRCC patients, 412 (54%) provided frozen biopsies. Clones were analyzed for significant copy number differences, adjusting for multiple comparisons and covariates in multivariate analyses. Frequent alterations included losses on: 3p (92.2%), 14q (46.8%), 8p (38.1%), 4q (35.4%), 9p (32.3%), 9q (31.8%), 6q (30.8%), 3q (29.4%), 10q (25.7%), 13q (24.5%), 1p (23.5%) and gains on 5q (60.2%), 7q (39.6%), 7p (30.6%), 5p (26.5%), 20q (25.5%), 12q (24.8%), 12p (22.8%). Stage and grade were associated with 1p, 9p, 9q, 13q and 14q loss and 12q gain. Males had more alterations compared with females, independent of stage and grade. Significant differences in the number/types of alterations were observed by family cancer history, age at diagnosis and smoking status. Von Hippel-Lindau (VHL) gene inactivation was associated with 3p loss (P Collapse

Key Words

• renal cancer
• epidemiology
• vhl

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MESH Headings Collapse

Grants

• HHSN261200800001C NCI NIH HHS
• HHSN261200800001E NCI NIH HHS

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Affiliation(s)

L E Moore Division of Cancer Epidemiology and Genetics (DCEG), National Cancer Institute (NCI), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Bethesda, MD, USA
E Jaeger University of California San Francisco, San Francisco, CA, USA
M L Nickerson Cancer and Inflammation Program, NCI, NIH, DHHS, Frederick, MD, USA
P Brennan International Agency for Research on Cancer, Lyon, France
S De Vries University of California San Francisco, San Francisco, CA, USA
R Roy University of California San Francisco, San Francisco, CA, USA
J Toro Division of Cancer Epidemiology and Genetics (DCEG), National Cancer Institute (NCI), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Bethesda, MD, USA
H Li Division of Biostatistics, Department of Environmental Medicine, New York University, New York, NY, USA
S Karami Division of Cancer Epidemiology and Genetics (DCEG), National Cancer Institute (NCI), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Bethesda, MD, USA
P Lenz DCEG, Science Applications International Corporation-Frederick, Inc., NCI-Frederick, Frederick, MD, USA
D Zaridze Institute of Carcinogenesis, Cancer Research Centre, Moscow, Russia
V Janout Department of Preventive Medicine, Faculty of Medicine, Palacky University, Olomouc, Czech Republic
V Bencko Institute of Hygiene and Epidemiology, Charles University, Prague, Czech Republic
M Navratilova Department of Cancer Epidemiology and Genetics, Masaryk Memorial Cancer Institute, Brno, Czech Republic
N Szeszenia-Dabrowska Department of Epidemiology, Institute of Occupational Medicine, Lodz, Poland
D Mates Institue of Public Health, Bucharest, Romania
W M Linehan Urologic Oncology Branch, NCI, NIH, DHHS, Bethesda, MD, USA
M Merino Laboratory of Pathology, NCI, NIH, DHHS, Bethesda, MD, USA
J Simko University of California San Francisco, San Francisco, CA, USA
R Pfeiffer Division of Cancer Epidemiology and Genetics (DCEG), National Cancer Institute (NCI), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Bethesda, MD, USA
P Boffetta The Tisch Cancer Institute, Mount Sinai School of Medicine, New York, NY, USA International Cancer Prevention Research Institute, Lyon, France
S Hewitt Applied Molecular Pathology Laboratory, NCI, NIH, DHHS, Bethesda, MD, USA
N Rothman Division of Cancer Epidemiology and Genetics (DCEG), National Cancer Institute (NCI), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Bethesda, MD, USA
W-H Chow Division of Cancer Epidemiology and Genetics (DCEG), National Cancer Institute (NCI), National Institutes of Health (NIH), Department of Health and Human Services (DHHS), Bethesda, MD, USA
F M Waldman University of California San Francisco, San Francisco, CA, USA

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The VHL/HIF axis in clear cell renal carcinoma

Inactivation of the VHL tumor suppressor protein (pVHL) is a common event in clear cell renal carcinoma, which is the most common form of kidney cancer. pVHL performs many functions, including serving as the substrate recognition module of an ubiquitin ligase complex that targets the alpha subunits of the heterodimeric HIF transcription factor for proteasomal degradation. Deregulation of HIF2α appears to be a driving force in pVHL-defective clear cell renal carcinomas. In contrast, genetic and functional studies suggest that HIF1α serves as a tumor suppressor and is a likely target of the 14q deletions that are characteristic of this tumor type. Drugs that inhibit HIF2α, or its downstream targets such as VEGF, are in various stages of clinical testing. Indeed, clear cell renal carcinomas are exquisitely sensitive to VEGF deprivation and four VEGF inhibitors have now been approved for the treatment of this disease.