Collagen matrix assembly is driven by the interaction of von Hippel-Lindau tumor suppressor protein with hydroxylated collagen IV alpha 2

Hypoxia-inducible factor underlies von Hippel-Lindau disease stigmata

von Hippel-Lindau (VHL) disease is a rare hereditary cancer syndrome that causes a predisposition to renal clear-cell carcinoma, hemangioblastoma, pheochromocytoma, and autosomal-recessive familial polycythemia. pVHL is the substrate conferring subunit of an E3 ubiquitin ligase complex that binds to the three hypoxia-inducible factor alpha subunits (HIF1-3α) for polyubiquitylation under conditions of normoxia, targeting them for immediate degradation by the proteasome. Certain mutations in pVHL have been determined to be causative of VHL disease through the disruption of HIFα degradation. However, it remains a focus of investigation and debate whether the disruption of HIFα degradation alone is sufficient to explain the complex genotype-phenotype relationship of VHL disease or whether the other lesser or yet characterized substrates and functions of pVHL impact the development of the VHL disease stigmata; the elucidation of which would have a significant ramification to the direction of research efforts and future management and care of VHL patients and for those manifesting sporadic counterparts of VHL disease. Here, we examine the current literature including the other emergent pseudohypoxic diseases and propose that the VHL disease-phenotypic spectrum could be explained solely by the varied disruption of HIFα signaling upon the loss or mutation in pVHL.

The Extracellular Matrix Environment of Clear Cell Renal Cell Carcinoma

Simple Summary

The extracellular matrix (ECM) controls fundamental properties of tumors, including growth, blood vessel investment, and invasion. The ECM defines rigidity of tumor tissue and individual ECM proteins have distinct biological effects on tumor cells. This article reviews the composition and biological functions of the ECM of clear cell renal cell carcinoma (ccRCC). The most frequent initiating genetic mutation in ccRCC inactivates the VHL gene, which plays a direct role in organizing the ECM. This is predicted to result in local ECM modification, which promotes the growth of tumor cells and the invasion of blood vessels. Later in tumor growth, connective tissue cells are recruited, which are predicted to produce large amounts of ECM, affecting the growth and invasive behaviors of tumor cells. Strategies to therapeutically control the ECM are under active investigation and a better understanding of the ccRCC ECM will determine the applicability of ECM-modifying drugs to this type of cancer.

Abstract

The extracellular matrix (ECM) of tumors is a complex mix of components characteristic of the tissue of origin. In the majority of clear cell renal cell carcinomas (ccRCCs), the tumor suppressor VHL is inactivated. VHL controls matrix organization and its loss promotes a loosely organized and angiogenic matrix, predicted to be an early step in tumor formation. During tumor evolution, cancer-associated fibroblasts (CAFs) accumulate, and they are predicted to produce abundant ECM. The ccRCC ECM composition qualitatively resembles that of the healthy kidney cortex in which the tumor arises, but there are important differences. One is the quantitative difference between a healthy cortex ECM and a tumor ECM; a tumor ECM contains a higher proportion of interstitial matrix components and a lower proportion of basement membrane components. Another is the breakdown of tissue compartments in the tumor with mixing of ECM components that are physically separated in healthy kidney cortex. Numerous studies reviewed in this work reveal effects of specific ECM components on the growth and invasive behaviors of ccRCCs, and extrapolation from other work suggests an important role for ECM in controlling ccRCC tumor rigidity, which is predicted to be a key determinant of invasive behavior.

Developmentally Arrested Basket/Stellate Cells in Postnatal Human Brain as Potential Tumor Cells of Origin for Cerebellar Hemangioblastoma in von Hippel-Lindau Patients

von Hippel-Lindau (VHL) disease is an autosomal dominant hereditary cancer disorder caused by a germline mutation in the VHL tumor suppressor gene. Loss of the wild-type allele results in VHL deficiency and the potential formation of cerebellar hemangioblastomas, which resemble embryonic hemangioblast proliferation and differentiation processes. Multiple, microscopic, VHL-deficient precursors, termed developmentally arrested structural elements (DASEs), consistently involve the cerebellar molecular layer in VHL patients, indicating the tumor site of origin. Unlike hemangioblastomas, however, cerebellar DASEs do not express brachyury, a mesodermal marker for hemangioblasts. In this study, neuronal progenitors occupying the molecular layer were investigated as tumor cells of origin. By immunohistochemistry, cerebellar DASEs and hemangioblastomas lacked immunoreactivity with antibody ZIC1 (Zic family member 1), a granule cell progenitor marker with concordance from oligonucleotide RNA expression array analyses. Rather, cerebellar DASEs and hemangioblastomas were immunoreactive with antibody PAX2 (paired box 2), a marker of basket/stellate cell progenitors. VHL cerebellar cortices also revealed PAX2-positive cells in Purkinje and molecular layers, resembling the histological and molecular development of basket/stellate cells in postnatal non-VHL mouse and human cerebella. These data suggest that VHL deficiency can result in the developmental arrest of basket/stellate cells in the human cerebellum and that these PAX2-positive, initiated cells await another insult or signal to form DASEs and eventually, tumors.

Impaired oxygen-sensitive regulation of mitochondrial biogenesis within the von Hippel-Lindau syndrome

Mitochondria are the main consumers of oxygen within the cell. How mitochondria sense oxygen levels remains unknown. Here we show an oxygen-sensitive regulation of TFAM, an activator of mitochondrial transcription and replication, whose alteration is linked to tumours arising in the von Hippel-Lindau syndrome. TFAM is hydroxylated by EGLN3 and subsequently bound by the von Hippel-Lindau tumour-suppressor protein, which stabilizes TFAM by preventing mitochondrial proteolysis. Cells lacking wild-type VHL or in which EGLN3 is inactivated have reduced mitochondrial mass. Tumorigenic VHL variants leading to different clinical manifestations fail to bind hydroxylated TFAM. In contrast, cells harbouring the Chuvash polycythaemia VHL^R200W mutation, involved in hypoxia-sensing disorders without tumour development, are capable of binding hydroxylated TFAM. Accordingly, VHL-related tumours, such as pheochromocytoma and renal cell carcinoma cells, display low mitochondrial content, suggesting that impaired mitochondrial biogenesis is linked to VHL tumorigenesis. Finally, inhibiting proteolysis by targeting LONP1 increases mitochondrial content in VHL-deficient cells and sensitizes therapy-resistant tumours to sorafenib treatment. Our results offer pharmacological avenues to sensitize therapy-resistant VHL tumours by focusing on the mitochondria.

Multi-Omics Profiling to Assess Signaling Changes upon VHL Restoration and Identify Putative VHL Substrates in Clear Cell Renal Cell Carcinoma Cell Lines

The inactivation of von Hippel–Lindau (VHL) is critical for clear cell renal cell carcinoma (ccRCC) and VHL syndrome. VHL loss leads to the stabilization of hypoxia-inducible factor α (HIFα) and other substrate proteins, which, together, drive various tumor-promoting pathways. There is inadequate molecular characterization of VHL restoration in VHL-defective ccRCC cells. The identities of HIF-independent VHL substrates remain elusive. We reinstalled VHL expression in 786-O and performed transcriptome, proteome and ubiquitome profiling to assess the molecular impact. The transcriptome and proteome analysis revealed that VHL restoration caused the downregulation of hypoxia signaling, glycolysis, E2F targets, and mTORC1 signaling, and the upregulation of fatty acid metabolism. Proteome and ubiquitome co-analysis, together with the ccRCC CPTAC data, enlisted 57 proteins that were ubiquitinated and downregulated by VHL restoration and upregulated in human ccRCC. Among them, we confirmed the reduction of TGFBI (ubiquitinated at K676) and NFKB2 (ubiquitinated at K72 and K741) by VHL re-expression in 786-O. Immunoprecipitation assay showed the physical interaction between VHL and NFKB2. K72 of NFKB2 affected NFKB2 stability in a VHL-dependent manner. Taken together, our study generates a comprehensive molecular catalog of a VHL-restored 786-O model and provides a list of putative VHL-dependent ubiquitination substrates, including TGFBI and NFKB2, for future investigation.

Clear cell renal cell carcinoma ontogeny and mechanisms of lethality

The molecular features that define clear cell renal cell carcinoma (ccRCC) initiation and progression are being increasingly defined. The TRACERx Renal studies and others that have described the interaction between tumour genomics and remodelling of the tumour microenvironment provide important new insights into the molecular drivers underlying ccRCC ontogeny and progression. Our understanding of common genomic and chromosomal copy number abnormalities in ccRCC, including chromosome 3p loss, provides a mechanistic framework with which to organize these abnormalities into those that drive tumour initiation events, those that drive tumour progression and those that confer lethality. Truncal mutations in ccRCC, including those in VHL, SET2, PBRM1 and BAP1, may engender genomic instability and promote defects in DNA repair pathways. The molecular features that arise from these defects enable categorization of ccRCC into clinically and therapeutically relevant subtypes. Consideration of the interaction of these subtypes with the tumour microenvironment reveals that specific mutations seem to modulate immune cell populations in ccRCC tumours. These findings present opportunities for disease prevention, early detection, prognostication and treatment.

The pVHL neglected functions, a tale of hypoxia-dependent and -independent regulations in cancer

The von Hippel–Lindau protein (pVHL) is a tumour suppressor mainly known for its role as master regulator of hypoxia-inducible factor (HIF) activity. Functional inactivation of pVHL is causative of the von Hippel–Lindau disease, an inherited predisposition to develop different cancers. Due to its impact on human health, pVHL has been widely studied in the last few decades. However, investigations mostly focus on its role in degrading HIFs, whereas alternative pVHL protein–protein interactions and functions are insistently surfacing in the literature. In this review, we analyse these almost neglected functions by dissecting specific conditions in which pVHL is proposed to have differential roles in promoting cancer. We reviewed its role in regulating phosphorylation as a number of works suggest pVHL to act as an inhibitor by either degrading or promoting downregulation of specific kinases. Further, we summarize hypoxia-dependent and -independent pVHL interactions with multiple protein partners and discuss their implications in tumorigenesis.

MMPs, tyrosine kinase signaling and extracellular matrix proteolysis in kidney cancer

Patients diagnosed with metastatic renal cell carcinoma (RCC) have ∼12% chance for 5-year survival. The integrity of the extracellular matrix (ECM) that surrounds tumor cells influences their behavior and, when disturbed, it could facilitate local invasion and spread of tumor cells to distant sites. The interplay between von Hippel-Lindau/hypoxia inducible factor signaling axis and activated kinase networks results in aberrant ECM and tumor progression. Matrix metalloproteinases (MMPs) are proteolytic enzymes implicated in ECM remodeling, tumor angiogenesis, and immune cell infiltration. Understanding the cross-talk between kinase signaling and ECM proteolysis in RCC could provide insights into developing drugs that interfere specifically with the process of invasion. In this review, we discuss changes in the MMPs/ECM axis in RCC, prominent kinase signaling pathways implicated in MMPs induction, and comment on emerging extracellular regulatory networks that modulate MMPs activity.

The Roles of Cullin-2 E3 Ubiquitin Ligase Complex in Cancer

Posttranslational protein modifications play an important role in regulating protein stability and cellular function. There are at least eight Cullin family members. Among them, Cullin-2 forms a functional E3 ligase complex with elongin B, elongin C, RING-box protein 1 (RBX1, also called ROC1), as well as the substrate recognition subunit (SRS) to promote the substrate ubiquitination and degradation. In this book chapter, we will review Cullin-2 E3 ligase complexes that include various SRS proteins, including von Hippel Lindau (pVHL), leucine-rich repeat protein-1 (LRR-1), preferentially expressed antigen of melanoma (PRAME), sex-determining protein FEM-1 and early embryogenesis protein ZYG-11. We will focus on the VHL signaling pathway in clear cell renal cell carcinoma (ccRCC), which may reveal various therapeutic avenues in treating this lethal cancer.

Activation of Hypoxia-Inducible Factor Signaling Modulates the RNA Protein Interactome in Caenorhabditis elegans

The cellular response to hypoxia is crucial to organismal survival, and hypoxia-inducible factors (HIF) are the key mediators of this response. HIF-signaling is central to many human diseases and mediates longevity in the nematode. Despite the rapidly increasing knowledge on RNA-binding proteins (RBPs), little is known about their contribution to hypoxia-induced cellular adaptation. We used RNA interactome capture (RIC) in wild-type Caenorhabditis elegans and vhl-1 loss-of-function mutants to fill this gap. This approach identifies more than 1,300 nematode RBPs, 270 of which can be considered novel RBPs. Interestingly, loss of vhl-1 modulates the RBPome. This difference is not primarily explained by protein abundance suggesting differential RNA-binding. Taken together, our study provides a global view on the nematode RBPome and proteome as well as their modulation by HIF-signaling. The resulting RBP atlas is also provided as an interactive online data mining tool (http://shiny.cecad.uni-koeln.de:3838/celegans_rbpome).

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RNA interactome capture in wild-type C. elegans and vhl-1 loss-of-function mutants

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Identification of 1,354 nematode RBPs, 270 of which can be considered novel RBPs

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The modulation of the RBPome by vhl-1 is primary explained by differential RNA-binding

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The resulting RBP atlas is provided as an interactive online data mining tool

The role of collagen in cancer: from bench to bedside

Collagen is the major component of the tumor microenvironment and participates in cancer fibrosis. Collagen biosynthesis can be regulated by cancer cells through mutated genes, transcription factors, signaling pathways and receptors; furthermore, collagen can influence tumor cell behavior through integrins, discoidin domain receptors, tyrosine kinase receptors, and some signaling pathways. Exosomes and microRNAs are closely associated with collagen in cancer. Hypoxia, which is common in collagen-rich conditions, intensifies cancer progression, and other substances in the extracellular matrix, such as fibronectin, hyaluronic acid, laminin, and matrix metalloproteinases, interact with collagen to influence cancer cell activity. Macrophages, lymphocytes, and fibroblasts play a role with collagen in cancer immunity and progression. Microscopic changes in collagen content within cancer cells and matrix cells and in other molecules ultimately contribute to the mutual feedback loop that influences prognosis, recurrence, and resistance in cancer. Nanoparticles, nanoplatforms, and nanoenzymes exhibit the expected gratifying properties. The pathophysiological functions of collagen in diverse cancers illustrate the dual roles of collagen and provide promising therapeutic options that can be readily translated from bench to bedside. The emerging understanding of the structural properties and functions of collagen in cancer will guide the development of new strategies for anticancer therapy.

Mechanisms of hypoxia signalling: new implications for nephrology

Studies of the regulation of erythropoietin (EPO) production by the liver and kidneys, one of the classical physiological responses to hypoxia, led to the discovery of human oxygen-sensing mechanisms, which are now being targeted therapeutically. The oxygen-sensitive signal is generated by 2-oxoglutarate-dependent dioxygenases that deploy molecular oxygen as a co-substrate to catalyse the post-translational hydroxylation of specific prolyl and asparaginyl residues in hypoxia-inducible factor (HIF), a key transcription factor that regulates transcriptional responses to hypoxia. Hydroxylation of HIF at different sites promotes both its degradation and inactivation. Under hypoxic conditions, these processes are suppressed, enabling HIF to escape destruction and form active transcriptional complexes at thousands of loci across the human genome. Accordingly, HIF prolyl hydroxylase inhibitors stabilize HIF and stimulate expression of HIF target genes, including the EPO gene. These molecules activate endogenous EPO gene expression in diseased kidneys and are being developed, or are already in clinical use, for the treatment of renal anaemia. In this Review, we summarize information on the molecular circuitry of hypoxia signalling pathways underlying these new treatments and highlight some of the outstanding questions relevant to their clinical use.

EglN3 hydroxylase stabilizes BIM-EL linking VHL type 2C mutations to pheochromocytoma pathogenesis and chemotherapy resistance

Despite the discovery of the oxygen-sensitive regulation of HIFα by the von Hippel-Lindau (VHL) protein, the mechanisms underlying the complex genotype/phenotype correlations in VHL disease remain unknown. Some germline VHL mutations cause familial pheochromocytoma and encode proteins that preserve their ability to down-regulate HIFα. While type 1, 2A, and 2B VHL mutants are defective in regulating HIFα, type 2C mutants encode proteins that preserve their ability to down-regulate HIFα. Here, we identified an oxygen-sensitive function of VHL that is abolished by VHL type 2C mutations. We found that BIM-EL, a proapoptotic BH3-only protein, is hydroxylated by EglN3 and subsequently bound by VHL. VHL mutants fail to bind hydroxylated BIM-EL, regardless of whether they have the ability to bind hydroxylated HIFα or not. VHL binding inhibits BIM-EL phosphorylation by extracellular signal-related kinase (ERK) on serine 69. This causes BIM-EL to escape from proteasomal degradation, allowing it to enhance EglN3-induced apoptosis. BIM-EL was rapidly degraded in cells lacking wild-type VHL or in which EglN3 was inactivated genetically or by lack of oxygen, leading to enhanced cell survival and chemotherapy resistance. Combination therapy using ERK inhibitors, however, resensitizes VHL- and EglN3-deficient cells that are otherwise cisplatin-resistant.

A pan-cancer perspective of matrix metalloproteases (MMP) gene expression profile and their diagnostic/prognostic potential

Implication

By understanding Matrix Metalloprotease (MMP) dysregulation from a pan-cancer perspective, this study sheds light on the diagnostic potentials of MMPs across multiple neoplasms.

Background

MMPs are intriguing genes related to cancer disease progression, functional promotion of angiogenesis, invasion, metastasis, and avoidance of immune surveillance. Many studies have noted these genes are frequently upregulated in cancer. However, expression patterns of all MMPs and their diagnostic and prognostic potential have not been investigated in a pan-cancer perspective.

Methods

The Cancer Genome Atlas (TCGA) data were used to evaluate diagnostic and prognostic potential of 24 MMPs in fifteen different cancer types. Gene expression measured by RNA-seq was analyzed by differential expression, hierarchical clustering, and ROC analysis for individual genes and in combination.

Results

MMP1, MMP9, MMP10, MMP11, and MMP13 were almost universally upregulated across all cancers, with significant (p < 0.05) fold change (FC > 2) in ten of fifteen cancers. MMP3, MMP7, MMP12 and MMP14) are significantly up-regulated in at least 10 cancer types. Interestingly, MMP2, MMP7, MMP23B, MMP27 and MMP28) are significantly down-regulated in seven to nine cancer types. Multiple MMPs possess AUC’s > 0.9 in more than one cancer. However, survival analyses suggest that the prognostic value of MMPs is limited to clear cell renal carcinoma.

Conclusions

Most MMPs have consistently increased gene expression across cancers, while several MMPs have consistently decreased expression in several cancer types. Many MMPs have diagnostic value individually or in combination, while the prognostic value of MMPs is restricted to one subtype of kidney cancer.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5768-0) contains supplementary material, which is available to authorized users.

Genotype-phenotype relations of the von Hippel-Lindau tumor suppressor inferred from a large-scale analysis of disease mutations and interactors

Familiar cancers represent a privileged point of view for studying the complex cellular events inducing tumor transformation. Von Hippel-Lindau syndrome, a familiar predisposition to develop cancer is a clear example. Here, we present our efforts to decipher the role of von Hippel-Lindau tumor suppressor protein (pVHL) in cancer insurgence. We collected high quality information about both pVHL mutations and interactors to investigate the association between patient phenotypes, mutated protein surface and impaired interactions. Our data suggest that different phenotypes correlate with localized perturbations of the pVHL structure, with specific cell functions associated to different protein surfaces. We propose five different pVHL interfaces to be selectively involved in modulating proteins regulating gene expression, protein homeostasis as well as to address extracellular matrix (ECM) and ciliogenesis associated functions. These data were used to drive molecular docking of pVHL with its interactors and guide Petri net simulations of the most promising alterations. We predict that disruption of pVHL association with certain interactors can trigger tumor transformation, inducing metabolism imbalance and ECM remodeling. Collectively taken, our findings provide novel insights into VHL-associated tumorigenesis. This highly integrated in silico approach may help elucidate novel treatment paradigms for VHL disease.

Arginine refolds, stabilizes, and restores function of mutant pVHL proteins in animal model of the VHL cancer syndrome

The von Hippel-Lindau (VHL) syndrome is a rare inherited cancer, caused by mutations in the VHL gene, many of which render the VHL protein (pVHL) unstable. pVHL is a tumor-suppressor protein implicated in a variety of cellular processes, most notably in response to changes in oxygen availability, due to its role as part of an E3-ligase complex which targets the hypoxia-inducible factor (HIF) for degradation. Previously we reported, using in silico and in vitro analyses, that common oncogenic VHL mutations render pVHL less stable than the wild-type protein, distort its core domain and as a result reduce the ability of the protein to bind its target HIF-1α. Among various chemical chaperones tested, arginine was the most effective in refolding mutant of pVHL. Here we examined the consequences of administering L- or D-arginine to a Drosophila VHL model and to human renal carcinoma cells, both expressing misfolded versions of human pVHL. Arginine treatment increased pVHL solubility in both models and increased the half-life of the mutant pVHL proteins in the cell culture. In both models, L- as well as D-arginine enhanced the ability of wild-type pVHL and certain misfolded mutant versions of pVHL to bind ODD, the HIF-derived target peptide, reflecting restoration of pVHL function. Moreover, continuous feeding of Drosophila expressing misfolded versions of pVHL either L- or D-arginine rich diet rescued their lethal phenotype. Collectively, these in vivo results suggest that arginine supplementation should be examined as a potential novel treatment for VHL cancer syndrome.

The von Hippel–Lindau Tumor Suppressor Protein

The von Hippel–Lindau (VHL) gene is a two-hit tumor suppressor gene and is linked to the development of the most common form of kidney cancer, clear cell renal carcinoma; blood vessel tumors of the retina, cerebellum, and spinal cord called hemangioblastomas; and tumors of the sympathoadrenal nervous system called paragangliomas. The VHL gene product, pVHL, is the substrate recognition subunit of a cullin-dependent ubiquitin ligase that targets the α subunits of hypoxia-inducible factor (HIF) for destruction when oxygen is plentiful. Mounting evidence implicates HIF2 in the pathogenesis of pVHL-defective tumors and has provided a conceptual foundation for the development of drugs to treat them that inhibit HIF2-responsive gene products such as VEGF and, more recently, HIF2 itself. pVHL has additional, noncanonical functions that are cancer relevant, including roles related to the primary cilium, chromosome stability, extracellular matrix formation, and survival signaling.

Post-translational modification of type IV collagen with 3-hydroxyproline affects its interactions with glycoprotein VI and nidogens 1 and 2

Type IV collagen is a major component of the basement membrane and interacts with numerous other basement membrane proteins. Many of these interactions are poorly characterized. Type IV collagen is abundantly post-translationally modified with 3-hydroxyproline (3-Hyp), but 3-Hyp's biochemical role in type IV collagen's interactions with other proteins is not well established. In this work, we present binding data consistent with a major role of 3-Hyp in interactions of collagen IV with glycoprotein VI and nidogens 1 and 2. The increased binding interaction between type IV collagen without 3-Hyp and glycoprotein VI has been the subject of some controversy, which we sought to explore, whereas the lack of binding of nidogens to type IV collagen without 3-Hyp is novel. Using tandem MS, we show that the putative glycoprotein VI-binding site is 3-Hyp-modified in WT PFHR-9 type IV collagen, but not in PFHR-9 cells in which prolyl-3-hydroxylase 2 (P3H2) has been knocked out (KO). Moreover, we observed altered 3-Hyp occupancy across many other sites. Using amino acid analysis of type IV collagen from the WT and P3H2 KO cell lines, we confirm that P3H2 is the major, but not the only 3-Hyp-modifying enzyme of type IV collagen. These findings underscore the importance of post-translational modifications of type IV collagen for interactions with other proteins.

Boosting the hypoxic response in myeloid cells accelerates resolution of fibrosis and regeneration of the liver in mice

We have recently shown that targeting Vascular Endothelial Growth Factor (VEGF) specifically in scar-infiltrating myeloid cells prevented remodeling of the sinusoidal vasculature and abrogated the resolution of murine liver fibrosis, thereby unmasking an unanticipated link between angiogenesis and resolution of fibrosis. In a gain of function approach, we wanted to test the impact of VEGF overexpression in myeloid cells on fibrolysis. We observe that genetic inactivation of the von Hippel Lindau protein (VHL), a negative regulator of Hypoxia-inducible factors (HIF) in myeloid cells, leads to increased VEGF expression and most importantly, accelerated matrix degradation and reduced myofibroblast numbers after CCl₄ challenge. This is associated with enhanced expression of MMP-2 and -14 as well as lower expression of TIMP-2 in liver endothelial cells. In addition, we report increased expression of MMP-13 in scar-associated macrophages as well as improved liver regeneration upon ablation of VHL in myeloid cells. Finally, therapeutic infusion of macrophages nulli-zygous for VHL or treated with the pharmacologic hydroxylase inhibitor and HIF-inducer Dimethyloxalylglycine (DMOG) accelerates resolution of fibrosis. Hence, boosting the HIF-VEGF signaling axis in macrophages represents a promising therapeutic avenue for the treatment of liver fibrosis.

The HIF and other quandaries in VHL disease

Mutations in VHL underlie von Hippel-Lindau (VHL) disease, a hereditary cancer syndrome with several subtypes depending on the risk of developing certain combination of classic features, such as clear cell renal cell carcinoma (ccRCC), hemangioblastoma and pheochromocytoma. Although numerous potential substrates and functions of pVHL have been described over the past decade, the best-defined role of pVHL has remained as the negative regulator of the heterodimeric hypoxia-inducible factor (HIF) transcription factor via the oxygen-dependent ubiquitin-mediated degradation of HIF-α subunit. Despite the seminal discoveries that led to the molecular elucidation of the mammalian oxygen-sensing VHL-HIF axis, which have provided several rational therapies, the mechanisms underlying the complex genotype-phenotype correlation in VHL disease are unclear. This review will discuss and highlight the studies that have provided interesting insights as well as uncertainties to the underlying mechanisms governing VHL disease.

Epigenome Aberrations: Emerging Driving Factors of the Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma (ccRCC), the most common form of Kidney cancer, is characterized by frequent mutations of the von Hippel-Lindau (VHL) tumor suppressor gene in ~85% of sporadic cases. Loss of pVHL function affects multiple cellular processes, among which the activation of hypoxia inducible factor (HIF) pathway is the best-known function. Constitutive activation of HIF signaling in turn activates hundreds of genes involved in numerous oncogenic pathways, which contribute to the development or progression of ccRCC. Although VHL mutations are considered as drivers of ccRCC, they are not sufficient to cause the disease. Recent genome-wide sequencing studies of ccRCC have revealed that mutations of genes coding for epigenome modifiers and chromatin remodelers, including PBRM1, SETD2 and BAP1, are the most common somatic genetic abnormalities after VHL mutations in these tumors. Moreover, recent research has shed light on the extent of abnormal epigenome alterations in ccRCC tumors, including aberrant DNA methylation patterns, abnormal histone modifications and deregulated expression of non-coding RNAs. In this review, we discuss the epigenetic modifiers that are commonly mutated in ccRCC, and our growing knowledge of the cellular processes that are impacted by them. Furthermore, we explore new avenues for developing therapeutic approaches based on our knowledge of epigenome aberrations of ccRCC.

VHL deficiency augments anthracycline sensitivity of clear cell renal cell carcinomas by down-regulating ALDH2

The von Hippel-Lindau (VHL) is deficient in ∼70% of clear-cell renal cell carcinomas (ccRCC), which contributes to the carcinogenesis and drug resistance of ccRCC. Here we show that VHL-deficient ccRCC cells present enhanced cytotoxicity of anthracyclines in a hypoxia-inducible factor-independent manner. By subtractive proteomic analysis coupling with RNAi or overexpression verification, aldehyde dehydrogenase 2 (ALDH2) is found to be transcriptionally regulated by VHL and contributes to enhanced anthracyclines cytotoxicity in ccRCC cells. Furthermore, VHL regulates ALDH2 expression by directly binding the promoter of −130 bp to −160 bp to activate the transcription of hepatocyte nuclear factor 4 alpha (HNF-4α). In addition, a positive correlation is found among the protein expressions of VHL, HNF-4α and ALDH2 in ccRCC samples. These findings will deepen our understanding of VHL function and shed light on precise treatment for ccRCC patients.

The VHL tumour suppressor gene is lost in approximately 70% of clear cell renal cell carcinoma (ccRCC). In this study, the authors demonstrate that VHL loss in these tumours augments anthracyclines chemotherapy by down-regulation of ALDH2.

Von Hippel-Lindau Disease: Genetics and Role of Genetic Counseling in a Multiple Neoplasia Syndrome

Von Hippel-Lindau disease (VHL) is one of the most common inherited neoplasia syndromes and is characterized by highly vascular tumors of the eyes, brain, and spine, as well as benign and malignant tumors and/or cysts of the kidneys, adrenal medullae and sympathetic paraganglia, endolymphatic sac, epididymis, and broad ligament. Since the discovery of the VHL gene in 1993, more than 900 families with VHL have been identified and examined. Genetic testing for VHL is widely available and will detect a disease-causing mutation in rate 95% to 100% of individuals who have a clinical diagnosis of VHL, making it the standard of care for diagnosis of VHL. Furthermore, genetic testing for VHL is indicated in some individuals with seemingly sporadic VHL-related tumor types, as ≤ 10% of pheochromocytoma or early-onset renal cell carcinoma and ≤ 40% of CNS hemangioblastoma harbor germline VHL mutations without a family history or additional features of VHL disease. The majority of VHL mutations are private, but there are also well-characterized founder mutations. VHL is a complex, multiorgan disease that spans the breadth of oncology subspecialties, and, as such, providers in these subspecialties should be aware of when to consider a diagnosis of VHL, when to refer a patient to a genetics specialist for consideration of gene testing, and, perhaps most importantly, how to communicate this sensitive information in an age-appropriate manner to at-risk families. This review will provide state-of-the-art information regarding the genetics of VHL and will serve as a key reference for nongenetics professionals who encounter patients with VHL.

Modulation of the Hypoxic Response

Hypoxia stimulates a variety of adaptive responses, many mediated via the hypoxia inducible factors (HIF) family of transcriptional complexes. The balance of HIF-1, -2 and -3 controls a variety of genes, directly up-regulating transcription of genes involved in erythropoiesis, angiogenesis, vasomotor tone, metabolic pathways and processes related to cell multiplication and survival, and indirectly reducing the transcription of genes with other effects. HIF transcription factors are heterodimers consisting of an oxygen-regulated alpha chain bound to the constitutive aryl hydrocarbon receptor nuclear translocator. Under circumstances where oxygen is abundant the activity of the alpha chain is blocked by the actions of members of a family of oxygen-, iron- and oxoglutarate-dependent dioxygenase enzymes. Hydroxylation of two critical prolyl residues by the HIF prolyl hydroxylases (PHD1-3) leads to recognition by the von Hippel-Lindau E3 ubiquitin ligase complex, polyubiquitylation of the alpha chain and its consequent destruction by the proteasome. Hydroxylation of an asparaginyl residue by Factor Inhibiting HIF prevents any surviving HIF alpha chains from recruiting p300-CBP proteins, important for maximal transcriptional activation. Under conditions of acute hypoxia enzyme activity is suppressed, the HIF alpha chains are allowed to exist in their active form and target gene transcription is enhanced. In sustained hypoxia, adaptive responses mediated by the HIF pathway reduce oxygen demand and increase oxygen supply and thus ultimately down-regulate the pathway. However, a number of other processes also modulate HIF signalling and the balance between HIF-1 and HIF-2 actions. These include the generation of antisense HIF-1 and micro RNAs, up-regulation of HIF-3 alpha, antagonism of the HIF-p300 interaction by CITED2, increased PHD2 and PHD3 levels and effects on the pool of ankyrins within the cell which compete with HIF for the action of FIH. Additionally, effects on intermediary metabolism, reactive oxygen species, iron availability, nitric oxide levels and redox status within the cell may modulate HIF activity. Together, these effects lead to a reduction in the magnitude of the HIF response even if oxygenation is not restored and are predicted to alter the responsiveness of the system when oxygenation is restored.

Non-canonical GLI1/2 activation by PI3K/AKT signaling in renal cell carcinoma: A novel potential therapeutic target

Renal cell carcinoma (RCC) is the most lethal urologic malignancy; however, the molecular events supporting RCC carcinogenesis and progression remain poorly understood. In this study, based on the analysis of gene expression profile data from human clear cell RCC (ccRCC) and the corresponding normal tissues, we discovered that Hedgehog (HH) pathway component genes GLI1 and GLI2 were significantly elevated in ccRCC. Survival analysis of a large cohort of ccRCC samples demonstrated that the expression of GLI1 and GLI2 was negatively correlated with patient overall survival. Clinical sample-based VHL mutation and cell model-based VHL manipulation studies all indicated that the activation of GLI1 and GLI2 was not affected by VHL status. Further signaling pathway dissections demonstrated that GLI1 and GLI2 were activated by the phosphoinositide 3-kinase (PI3K)/AKT pathway, but not mediated by the canonical HH/SMO/GLI signaling. Up-regulation of GLI1 and GLI2 promoted RCC proliferation and clonogenic ability, whereas, a combination of GLIs inhibitor Gant61 and AKT inhibitor Perifosine synergistically suppressed RCC growth and induced apoptosis in vitro and in vivo. Therefore, this study identifies that GLI1 and GLI2 are critical for RCC carcinogenesis, and also provides an alternative therapeutic strategy for RCC.

Implications of Von Hippel-Lindau Syndrome and Renal Cell Carcinoma

Von Hippel-Lindau syndrome (VHLS) is a rare hereditary neoplastic disorder caused by mutations in the vhl gene leading to the development of tumors in several organs including the central nervous system, pancreas, kidneys, and reproductive organs. Manifestations of VHLS can present at different ages based on the affected organ and subclass of disease. In the subclasses of VHLS that cause renal disease, renal involvement typically begins closer to the end of the second decade of life and can present in different ways ranging from simple cystic lesions to solid tumors. Mutations in vhl are most often associated with clear cell renal carcinoma, the most common type of renal cancer, and also play a major role in sporadic cases of clear cell renal carcinoma. The recurrent, multifocal nature of this disease presents difficult challenges in the long-term management of patients with VHLS. Optimization of renal function warrants the use of several different approaches common to the management of renal carcinoma such as nephron sparing surgery, enucleation, ablation, and targeted therapies. In VHLS, renal lesions of 3 cm or bigger are considered to have metastatic potential and even small lesions often harbor malignancy. Many of the aspects of management revolve around optimizing both oncologic outcome and long-term renal function. As new surgical strategies and targeted therapies develop, the management of this complex disease evolves. This review will discuss the key aspects of the current management of VHLS.

VHL, the story of a tumour suppressor gene

Since the Von Hippel-Lindau (VHL) disease tumour suppressor gene VHL was identified in 1993 as the genetic basis for a rare disorder, it has proved to be of wide medical and scientific interest. VHL tumour suppressor protein (pVHL) plays a key part in cellular oxygen sensing by targeting hypoxia-inducible factors for ubiquitylation and proteasomal degradation. Early inactivation of VHL is commonly seen in clear-cell renal cell carcinoma (ccRCC), and insights gained from the functional analysis of pVHL have provided the foundation for the routine treatment of advanced-stage ccRCC with novel targeted therapies. However, recent sequencing studies have identified additional driver genes that are involved in the pathogenesis of ccRCC. As our understanding of the importance of VHL matures, it is timely to review progress from its initial description to current knowledge of VHL biology, as well as future prospects for novel medical treatments for VHL disease and ccRCC.

A clearer view of the molecular complexity of clear cell renal cell carcinoma

The von Hippel-Lindau (VHL) tumor suppressor gene is mutated as an early event in almost all cases of clear cell renal cell carcinoma (ccRCC), the most frequent form of kidney cancer. In this review we discuss recent advances in understanding how dysregulation of the many hypoxia-inducible factor α-dependent and -independent functions of the VHL tumor suppressor protein (pVHL) can contribute to tumor initiation and progression. Recent evidence showing extensive inter- and intratumoral genetic diversity has given rise to the idea that ccRCC should actually be considered as a series of molecularly related, yet distinct, diseases defined by the pattern of combinatorial genetic alterations present within the cells of the tumor. We highlight the range of genetic and epigenetic alterations that recur in ccRCC and discuss the mechanisms through which these events appear to function cooperatively with a loss of pVHL function in tumorigenesis.

The multifaceted von Hippel-Lindau tumour suppressor protein

Loss of von Hippel-Lindau protein (pVHL) is known to contribute to the initiation and progression of tumours associated with VHL disease as well as certain sporadic tumours including clear cell renal cell carcinoma (ccRCC). The VHL gene was first identified and cloned over 20 years ago and our understanding of its functions and effects has significantly increased since then. The best-known function of pVHL is its role in promoting the degradation of hypoxia-inducible factor α subunit (HIFα) as part of an E3 ubiquitin ligase complex. HIF stabilisation and transcriptional activation are also associated with various epigenetic alterations, indicating a potential role for VHL loss with changes in the epigenome. This review will highlight current knowledge regarding pVHL as well as discuss potentially novel roles of pVHL and how these may impact on cancer progression.

Von Hippel-Lindau protein and respiratory diseases

Von Hippel-Lindau protein (pVHL) was first identified as a tumor suppressor gene as mutations in the VHL gene predispose individuals to systemic benign or malignant tumors and cysts in many organs, including renal cell carcinoma of the clear-cell type and hemangioblastoma. Although pVHL is best known to act as a component of ubiquitin protein ligase for the proteasomal degradation of hypoxia inducible factor (HIF)-α, pVHL also interacts with extracellular matrix proteins and cytoskeleton, regulating extracellular matrix assembly, cell signaling, and many other cellular functions. Recent studies suggest that pVHL contributes to many lung diseases, including pulmonary arterial hypertension, lung cancer, pulmonary fibrosis, and acute respiratory distress syndrome. Mutation or loss of function of pVHL activates HIF and induced expression of vascular endothelial growth factor, endothelin-1, and FoxM1, leading to pulmonary arterial hypertension. Loss of pVHL in lung cancer cells promotes epithelial-mesenchymal transition and cancer migration and invasion while decreasing lung cancer cell proliferation and colonization. In patients of idiopathic pulmonary fibrosis, elevated expression of pVHL induces expression of fibronectin/integrin α5β1/focal adhesion kinase signaling, resulting in fibroproliferation and fibrosis. In alveolar epithelial cells, pVHL mediates Na-K-ATPase degradation in an HIF independent pathway, causing decreased edema clearance during hypoxia. These studies suggest that pVHL plays key roles in the pathogenesis of many lung diseases, and further investigations are warranted to elucidate the underlying molecular mechanisms.

Emblica officinalis extract induces autophagy and inhibits human ovarian cancer cell proliferation, angiogenesis, growth of mouse xenograft tumors

Patients with ovarian cancer (OC) may be treated with surgery, chemotherapy and/or radiation therapy, although none of these strategies are very effective. Several plant-based natural products/dietary supplements, including extracts from Emblicaofficinalis (Amla), have demonstrated potent anti-neoplastic properties. In this study we determined that Amla extract (AE) has anti-proliferative effects on OC cells under both in vitro and in vivo conditions. We also determined the anti-proliferative effects one of the components of AE, quercetin, on OC cells under in vitro conditions. AE did not induce apoptotic cell death, but did significantly increase the expression of the autophagic proteins beclin1 and LC3B-II under in vitro conditions. Quercetin also increased the expression of the autophagic proteins beclin1 and LC3B-II under in vitro conditions. AE also significantly reduced the expression of several angiogenic genes, including hypoxia-inducible factor 1α (HIF-1α) in OVCAR3 cells. AE acted synergistically with cisplatin to reduce cell proliferation and increase expression of the autophagic proteins beclin1 and LC3B-II under in vitro conditions. AE also had anti-proliferative effects and induced the expression of the autophagic proteins beclin1 and LC3B-II in mouse xenograft tumors. Additionally, AE reduced endothelial cell antigen – CD31 positive blood vessels and HIF-1α expression in mouse xenograft tumors. Together, these studies indicate that AE inhibits OC cell growth both in vitro and in vivo possibly via inhibition of angiogenesis and activation of autophagy in OC. Thus AE may prove useful as an alternative or adjunct therapeutic approach in helping to fight OC.

Genotype and tumor locus determine expression profile of pseudohypoxic pheochromocytomas and paragangliomas

Pheochromocytomas (PHEOs) and paragangliomas (PGLs) related to mutations in the mitochondrial succinate dehydrogenase (SDH) subunits A, B, C, and D, SDH complex assembly factor 2, and the von Hippel-Lindau (VHL) genes share a pseudohypoxic expression profile. However, genotype-specific differences in expression have been emerging. Development of effective new therapies for distinctive manifestations, e.g., a high rate of malignancy in SDHB- or predisposition to multifocal PGLs in SDHD patients, mandates improved stratification. To identify mutation/location-related characteristics among pseudohypoxic PHEOs/PGLs, we used comprehensive microarray profiling (SDHB: n = 18, SDHD-abdominal/thoracic (AT): n = 6, SDHD-head/neck (HN): n = 8, VHL: n = 13). To avoid location-specific bias, typical adrenal medulla genes were derived from matched normal medullas and cortices (n = 8) for data normalization. Unsupervised analysis identified two dominant clusters, separating SDHB and SDHD-AT PHEOs/PGLs (cluster A) from VHL PHEOs and SDHD-HN PGLs (cluster B). Supervised analysis yielded 6937 highly predictive genes (misclassification error rate of 0.175). Enrichment analysis revealed that energy metabolism and inflammation/fibrosis-related genes were most pronouncedly changed in clusters A and B, respectively. A minimum subset of 40 classifiers was validated by quantitative real-time polymerase chain reaction (quantitative real-time polymerase chain reaction vs. microarray: r = 0.87). Expression of several individual classifiers was identified as characteristic for VHL and SDHD-HN PHEOs and PGLs. In the present study, we show for the first time that SDHD-HN PGLs share more features with VHL PHEOs than with SDHD-AT PGLs. The presented data suggest novel subclassification of pseudohypoxic PHEOs/PGLs and implies cluster-specific pathogenic mechanisms and treatment strategies.

Pancreatic cyst development: insights from von Hippel-Lindau disease

Pancreatic cysts are a heterogeneous group of lesions, which can be benign or malignant. Due to improved imaging techniques, physicians are more often confronted with pancreatic cysts. Little is known about the origin of pancreatic cysts in general. Von Hippel-Lindau (VHL) disease is an atypical ciliopathy and inherited tumor syndrome, caused by a mutation in the VHL tumor suppressor gene encoding the VHL protein (pVHL). VHL patients are prone to develop cysts and neuroendocrine tumors in the pancreas in addition to several other benign and malignant neoplasms. Remarkably, pancreatic cysts occur in approximately 70% of VHL patients, making it the only hereditary tumor syndrome with such a discernible expression of pancreatic cysts. Cellular loss of pVHL due to biallelic mutation can model pancreatic cystogenesis in other organisms, suggesting a causal relationship. Here, we give a comprehensive overview of various pVHL functions, focusing on those that can potentially explain pancreatic cyst development in VHL disease. Based on preclinical studies, cilia loss in ductal cells is probably an important early event in pancreatic cyst development.

State of the science: an update on renal cell carcinoma

Renal cell carcinomas (RCC) are emerging as a complex set of diseases that are having a major socioeconomic impact and showing a continued rise in incidence throughout the world. As the field of urologic oncology faces these trends, several major genomic and mechanistic discoveries are altering our core understanding of this multitude of cancers, including several new rare subtypes of renal cancers. In this review, these new findings are examined and placed in the context of the well-established association of clear cell RCC (ccRCC) with mutations in the von Hippel-Lindau (VHL) gene and resultant aberrant hypoxia inducible factor (HIF) signaling. The impact of novel ccRCC-associated genetic lesions on chromatin remodeling and epigenetic regulation is explored. The effects of VHL mutation on primary ciliary function, extracellular matrix homeostasis, and tumor metabolism are discussed. Studies of VHL proteostasis, with the goal of harnessing the proteostatic machinery to refunctionalize mutant VHL, are reviewed. Translational efforts using molecular tools to elucidate discriminating features of ccRCC tumors and develop improved prognostic and predictive algorithms are presented, and new therapeutics arising from the earliest molecular discoveries in ccRCC are summarized. By creating an integrated review of the key genomic and molecular biological disease characteristics of ccRCC and placing these data in the context of the evolving therapeutic landscape, we intend to facilitate interaction among basic, translational, and clinical researchers involved in the treatment of this devastating disease, and accelerate progress toward its ultimate eradication.

Von Hippel-Lindau: how a rare disease illuminates cancer biology

Von Hippel-Lindau (VHL) disease is a rare autosomal dominant syndrome (1/36,000 live births) with highly penetrance that predispose to the development of a panel of highly vascularized tumors (model of tumoral angiogenesis). Main manifestations include central nervous system (CNS) and retinal haemangioblastomas, endolymphatic sac tumors, clear-cell renal cell carcinomas (RCC), phaeochromocytomas and pancreatic neuroendocrine tumors. RCC has become the first potential cause of mortality and VHL disease is the main cause of inherited RCC. The disease is caused by germline mutations in the VHL tumor-suppressor gene that plays a major role in regulation of the oxygen-sensing pathway by targeting the hypoxia-inducible factor HIF for degradation in proteasome. VHL has also major HIF-independent functions, specially in regulation of primary cilium, extracellular matrix and apoptosis. Somatic inactivation of the VHL gene is the main molecular event in most sporadic RCC and the treatment of advanced RCC has been revolutionized by targeted therapy with drugs that block angiogenesis. These drugs are now in first line in metastatic sporadic RCC and have shown promising results for RCC, pancreatic neuroendocrine tumors and malignant pheochromocytomas in VHL patients.

Renal cancer: oxygen meets metabolism

Over the last two decades molecular studies of inherited tumor syndromes that are associated with the development of kidney cancer have led to the identification of genes and biochemical pathways, which play key roles in the malignant transformation of renal epithelial cells. Some of these findings have broad biological impact and extend beyond renal cancer. This review's focus is on the von Hippel-Lindau (VHL)/hypoxia-inducible factor (HIF) oxygen-sensing pathway and its role in physiology, energy metabolism and tumorigenesis.

Two sides to every story: the HIF-dependent and HIF-independent functions of pVHL

von Hippel–Lindau (VHL) disease is a hereditary cancer syndrome caused by inherited mutations that inactivate the VHL tumour suppressor gene. The VHL locus encodes pVHL, whose best studied function is to bind to and down-regulate the hypoxia-inducible factor (HIF) family of oxygen-dependent transcription factors. Early efforts have established the fundamental role of HIF in VHL-defective tumorigenesis and in particular renal cell carcinoma. However, recent findings have revealed an alternate side to the story, the HIF-independenttumour suppressor functions of pVHL. These include pVHL's ability to regulate apoptosis and senescence as well as its role in the maintenance of primary cilium and orchestrating the deposition of the extracellular matrix. To what extent these HIF-dependent and HIF-independent functions cooperate in VHL-defective tumorigenesis remains to be determined.

JunB promotes cell invasion and angiogenesis in VHL-defective renal cell carcinoma

Inactivation of the von Hippel-Lindau (VHL) tumor-suppressor gene causes both hereditary and sporadic clear-cell renal-cell carcinoma (ccRCC). Although the best-characterized function of the VHL protein (pVHL) is regulation of hypoxia-inducible factor-α (HIFα), pVHL also controls the development of pheochromocytoma through HIF-independent pathways by regulating JunB. However, it is largely unknown how these pathways contribute to the development and progression of ccRCC. In the present study, we confirmed that JunB was upregulated in VHL-defective ccRCC specimens by immunostaining. Short-hairpin RNA (shRNA)-mediated knockdown of JunB in 786-O and A498 VHL null ccRCC cells suppressed their invasiveness. In addition, JunB knockdown significantly repressed tumor growth and microvessel density in xenograft tumor assays. Conversely, forced expression of wild-type, but not dimerization-defective, JunB in a VHL-restored 786-O subclone promoted invasion in vitro and tumor growth and vessel formation in vivo. Quantitative PCR array analysis revealed that JunB regulated multiple genes relating to tumor invasion and angiogenesis such as matrix metalloproteinase-2 (MMP-2), MMP-9 and chemokine (C-C motif) ligand-2 (CCL2) in 786-O cells. JunB knockdown in these cells reduced the proteolytic activity of both MMPs in gelatin zymography and the amount of CCL2 in the culture supernatant. Moreover, shRNA-mediated knockdown of MMP-2 or inhibition of CCL2 activity with a neutralizing antibody repressed xenograft tumor growth and angiogenesis. Collectively, these results suggest that JunB promotes tumor invasiveness and enhances angiogenesis in VHL-defective ccRCCs.

Proteomic dissection of the von Hippel-Lindau (VHL) interactome

The von Hippel-Lindau (VHL) tumor suppressor gene encodes a component of a ubiquitin ligase complex containing elongin B, elongin C, cullin 2, and Rbx1, which acts as a negative regulator of hypoxia inducible factor (HIF). VHL ubiquitinates and degrades the alpha subunits of HIF, and this is proposed to suppress tumorigenesis and tumor angiogenesis. Several lines of evidence also suggest important roles for HIF-independent VHL functions in the maintenance of primary cilium, extracellular matrix formation, and tumor suppression. We undertook a series of proteomic analyses to gain a comprehensive picture of the VHL-interacting proteins. We found that the ARF tumor suppressor interacts with VHL30, a longer VHL isoform, but not with VHL19, a shorter VHL isoform. ARF was found to release VHL30 from the E3 ligase complex, promoting the binding of VHL30 to a protein arginine methyltransferase, PRMT3. Our analysis of the VHL19 interactome also uncovered that VHL19 displays an affinity to collagens and their biosynthesis enzymes.

Complex cellular functions of the von Hippel-Lindau tumor suppressor gene: insights from model organisms

The von Hippel-Lindau tumor suppressor gene (VHL) has attracted intensive interest not only because its mutations predispose carriers to devastating tumors, but also because it is involved in oxygen sensing under physiological conditions. VHL loss-of-function mutations result in organ-specific tumors, such as hemangioblastoma of the central nervous system and renal cell carcinoma, both untreatable with conventional chemotherapies. The VHL protein is best known as an E3 ubiquitin ligase that targets hypoxia-inducible factor-α (HIF-α), but many diverse, non-canonical cellular functions have also been assigned to VHL, mainly based on studies in cell culture systems. As such, although the HIF-dependent role of VHL is critical, the full spectrum of pathophysiological functions of VHL is still unresolved. Such understanding requires careful cross-referencing with physiologically relevant experimental models. Studies in model systems, such as Caenorhabditis elegans, Drosophila, zebrafish and mouse have provided critical in vivo confirmation of the VHL-HIF pathway, and verification of potentially important cellular functions including microtubule stabilization and epithelial morphogenesis. More recently, animal models have also suggested systemic roles of VHL in hematopoiesis, metabolic homeostasis and inflammation. In this review, the studies performed in model organisms will be summarized and placed in context with existing clinical and in vitro data.

Targeting the tumor microenvironment: focus on angiogenesis

Tumorigenesis is a complex multistep process involving not only genetic and epigenetic changes in the tumor cell but also selective supportive conditions of the deregulated tumor microenvironment. One key compartment of the microenvironment is the vascular niche. The role of angiogenesis in solid tumors but also in hematologic malignancies is now well established. Research on angiogenesis in general, and vascular endothelial growth factor in particular, is a major focus in biomedicine and has led to the clinical approval of several antiangiogenic agents including thalidomide, bevacizumab, sorafenib, sunitinib, pazopanib, temesirolimus, and everolimus. Indeed, antiangiogenic agents have significantly changed treatment strategies in solid tumors (colorectal cancer, renal cell carcinoma, and breast cancer) and multiple myeloma. Here we illustrate important aspects in the interrelationship between tumor cells and the microenvironment leading to tumor progression, with focus on angiogenesis, and summarize derived targeted therapies.

Type IV collagen-initiated signals provide survival and growth cues required for liver metastasis

The liver is a major site of metastasis for human malignancies, yet the factors that regulate tumor cell survival and growth in this organ remain elusive. Previously, we reported that M-27(IGF-IR) murine lung carcinoma cells with ectopic insulin-like growth factor-1 (IGF-I) receptor overexpression acquired a site-specific, liver-metastasizing potential. Gene expression profiling and subsequent RNA and protein analyses revealed that this was associated with major changes to the expression of extracellular matrix (ECM) protein-encoding genes including type III, IV and XVIII collagen genes, and these changes were also observed in the respective tumors in vivo. Because type IV collagen was the most prominently altered ECM protein in this model, we further analyzed its functional relevance to liver metastasis. M-27 cells stably overexpressing type IV collagen α1 and α2 chains were generated and their growth and metastatic properties investigated. We found that these cells acquired a site-selective growth advantage in the liver and this was associated with cell rescue from anoikis in a collagen IV/α2 integrin/FAK-dependent manner and increased responsiveness to IGF-I. Conversely, collagen IV or focal adhesion kinase (FAK) silencing by small-interfering RNA in highly metastatic tumor cells enhanced anoikis and decreased liver metastases formation. Moreover, analysis of human surgical specimens revealed uniformly high collagen IV expression in 65/65 hepatic metastases analyzed, regardless of tissue of origin, whereas it was variable and generally low in 50/50 primary colorectal carcinoma specimens examined. The results suggest that collagen IV-conveyed signals are essential cues for liver metastasis in diverse tumor types and identify mediators of collagen IV signaling as potential therapeutic targets in the management of hepatic metastases.

Mapping structural landmarks, ligand binding sites, and missense mutations to the collagen IV heterotrimers predicts major functional domains, novel interactions, and variation in phenotypes in inherited diseases affecting basement membranes

Collagen IV is the major protein found in basement membranes. It comprises three heterotrimers (α1α1α2, α3α4α5, and α5α5α6) that form distinct networks, and are responsible for membrane strength and integrity.We constructed linear maps of the collagen IV heterotrimers ("interactomes") that indicated major structural landmarks, known and predicted ligand-binding sites, and missense mutations, in order to identify functional and disease-associated domains, potential interactions between ligands, and genotype–phenotype relationships. The maps documented more than 30 known ligand-binding sites as well as motifs for integrins, heparin, von Willebrand factor (VWF), decorin, and bone morphogenetic protein (BMP). They predicted functional domains for angiogenesis and haemostasis, and disease domains for autoimmunity, tumor growth and inhibition, infection, and glycation. Cooperative ligand interactions were indicated by binding site proximity, for example, between integrins, matrix metalloproteinases, and heparin. The maps indicated that mutations affecting major ligand-binding sites, for example, for Von Hippel Lindau (VHL) protein in the α1 chain or integrins in the α5 chain, resulted in distinctive phenotypes (Hereditary Angiopathy, Nephropathy, Aneurysms, and muscle Cramps [HANAC] syndrome, and early-onset Alport syndrome, respectively). These maps further our understanding of basement membrane biology and disease, and suggest novel membrane interactions, functions, and therapeutic targets.

VHL and HIF signalling in renal cell carcinogenesis

Hypoxia-inducible factor (HIF) plays an important role in renal tumourigenesis. In the majority of clear cell RCC (ccRCC), the most frequent and highly vascularized RCC subtype, HIF is constitutively activated by inactivation of the von Hippel-Lindau gene. Of the HIF subunits, HIF-2alpha appears to be more oncogenic than HIF-1alpha, in that HIF-2alpha activates pro-tumourigenic target genes. In addition, recent studies indicate that HIF-1alpha, more than HIF-2alpha, can undergo proteasomal degradation in VHL - /- RCC cells. A more detailed understanding of the molecular basis of hypoxia and angiogenesis in renal carcinogenesis has set the stage for the development of targeted therapies, inhibiting multiple HIF-related pathways, such as the phosphatidylinositol 3-kinase-AKT-mTOR, RAS/RAF/MAP, and VEGF signalling routes. However, despite the positive results of these targeting agents in progression-free survival, clinical resistance remains an issue. Recent pre-clinical studies have suggested new targeting approaches such as inhibition of HIF-driven key metabolic enzymes and have introduced new HIF targeting agents, such as histone deacetylase inhibitors, with successful anti-neoplastic effects. In this review, we discuss existing and novel findings about RCC carcinogenesis, with subsequent clinical implications.

Deletion of von Hippel-Lindau in glomerular podocytes results in glomerular basement membrane thickening, ectopic subepithelial deposition of collagen {alpha}1{alpha}2{alpha}1(IV), expression of neuroglobin, and proteinuria

Vascular endothelial growth factor, which is critical for blood vessel formation, is regulated by hypoxia inducible transcription factors (HIFs). A component of the E3 ubiquitin ligase complex, von Hippel-Lindau (VHL) facilitates oxygen-dependent polyubiquitination and proteasomal degradation of HIFalpha subunits. Hypothesizing that deletion of podocyte VHL would result in HIFalpha hyperstabilization, we crossed podocin promoter-Cre transgenic mice, which express Cre recombinase in podocytes beginning at the capillary loop stage of glomerular development, with floxed VHL mice. Vascular patterning and glomerular development appeared unaltered in progeny lacking podocyte VHL. However, urinalysis showed increased albumin excretion by 4 weeks when compared with wild-type littermates with several sever cases (>1000 microg/ml). Many glomerular ultrastructural changes were seen in mutants, including focal subendothelial delamination and widespread podocyte foot process broadening, and glomerular basement membranes (GBMs) were significantly thicker in 16-week-old mutants compared with controls. Moreover, immunoelectron microscopy showed ectopic deposition of collagen alpha1alpha2alpha1(IV) in GBM humps beneath podocytes. Significant increases in the number of Ki-67-positive mesangial cells were also found, but glomerular WT1 expression was significantly decreased, signifying podocyte death and/or de-differentiation. Indeed, expression profiling of mutant glomeruli suggested a negative regulatory feedback loop involving the HIFalpha prolyl hydroxylase, Egln3. In addition, the brain oxygen-binding protein, Neuroglobin, was induced in mutant podocytes. We conclude that podocyte VHL is required for normal maintenance of podocytes, GBM composition and ultrastructure, and glomerular barrier properties.