The von Hippel-Lindau tumour suppressor protein: new perspectives

pVHL-mediated regulation of the anti-angiogenic protein thrombospondin-1 decreases migration of Clear Cell Renal Carcinoma Cell Lines

Thrombospondin-1 (TSP-1) is a multifunctional matrix protein with antitumor activities due in part to its ability to inhibit angiogenesis, which in turn contributes to determine the fate of many tumours. Previous studies have shown that TSP-1 expression supports normal kidney angiostasis, and decreased TSP-1 levels contribute to the angiogenic phenotype of renal cell carcinomas (RCC). The loss of the von Hippel-Lindau tumour suppressor gene (VHL) in these tumours favours stabilization of the Hypoxia Inducible Factors (HIF), which in turn contribute to adapt tumour cells to hostile environments promoting tumour progression. However, HIF-independent regulation of certain genes might also be involved. We have previously shown that TSP-1 is regulated in hypoxia in clear cell RCC (ccRCC) in a HIF-independent manner; however, the effect of VHL protein (pVHL) on TSP-1 expression has not been evaluated. Our results proved that pVHL loss or mutation in its alpha or beta domain significantly decreased TSP-1 levels in ccRCC in a HIF-independent manner. Furthermore, this regulation proved to be important for ccRCC cells behaviour showing that decreased TSP-1 levels rendered ccRCC cells more migratory. This data substantiates a unique regulation pattern for TSP-1 in a pVHL-dependent manner, which may be relevant in the aggressiveness of ccRCC.

VHL Gene Alterations in Italian Patients with Isolated Renal Cell Carcinomas

Clear cell renal cell carcinoma (ccRCC) is the most common malignant neoplasm of the kidney and belongs to the few human tumors known to develop from mutations of the VHL tumor suppressor gene. VHL germline mutations are associated with hereditary ccRCCs in VHL disease. However, somatic VHL gene defects may also occur in sporadic ccRCCs. In this study, we analyzed the frequency and the spectrum of VHL gene alterations in 35 Italian patients with sporadic renal cell carcinoma (RCC). Tumor-specific intragenic VHL pathogenic mutations were detected in 38% (11/29) of the ccRCC patients and 33% (2/6) of the patients with other types of RCC. One novel 18-bp in-tandem duplication and 4 previously unreported nucleotide changes in the VHL gene were described. Microsatellite analysis showed loss of heterozygosity for at least 1 informative marker in 43% (9/21) of the ccRCCs and 50% (3/6) of the non-ccRCCs; 5 of the 13 tumors (38%) harboring VHL gene alterations also had loss of heterozygosity for at least 1 microsatellite marker. Our results confirm that somatic inactivation of the VHL gene may play a pivotal role in the tumorigenesis of sporadic ccRCCs in Italian patients and suggests that mutation analysis of the VHL gene may be helpful for discriminating sporadic, VHL-gene-related ccRCCs from those related to VHL disease.

Characterizing genomic differences of human cancer stratified by the TP53 mutation status

The key roles of the TP53 mutation in cancer have been well established. TP53 is the most frequently mutated gene, and its inactivation is widespread among human cancer types. However, the landscape of genomic alterations in human cancers stratified by the TP53 mutation has not yet been described. We obtained somatic mutation and copy number change data of 6551 regular-mutated samples from the Cancer Genome Atlas (TCGA) and compared significantly mutated genes (SMGs), copy number alterations, mutational signatures and mutational strand asymmetries between cancer samples with and without the TP53 mutation. We identified 126 SMGs, 30 of which were statistically significant in both the TP53 mutant and wild-type groups. Several SMGs, such as VHL, SMAD4 and PTEN, showed a mutation bias towards the TP53 wild-type group, whereas ATRX, IDH1 and RB1 were more prevalent in the TP53 mutant group. Five mutational signatures were extracted from the combined TCGA dataset on which mutational asymmetry analysis was performed, revealing that the TP53 mutant group exhibited substantially greater replication and transcription biases. Furthermore, we found that alterations of multiple genes in a merged mutually exclusive network composed of BRAF, EGFR, PAK1, PIK3CA, PTEN, APC and TERT were related to shortened survival in the TP53 wild-type group. In summary, we characterized the genomic differences and similarities underlying human cancers stratified by the TP53 mutation and identified multi-gene alterations of a merged mutually exclusive network to be a poor prognostic factor for the TP53 wild-type group.

Regulation of Bone Marrow Angiogenesis by Osteoblasts during Bone Development and Homeostasis

Bone marrow is a highly heterogeneous and vascularized tissue. The various cell types populating the bone marrow extensively communicate with each other, and cell-to-cell cross talk is likely to be essential for proper bone development and homeostasis. In particular, the existence of osteogenesis and angiogenesis coupling has been recently proposed. Despite its high degree of vascularization, a gradient of oxygenation is present in the bone marrow, and the endosteal surface of cortical bone appears to be among the most hypoxic areas in the body. Oxygen (O2) is both an essential metabolic substrate and a regulatory signal that is in charge of a specific genetic program. An important component of this program is the family of transcription factors known as hypoxia-inducible factors (HIFs). In this Perspective, we will summarize our current knowledge about the role of the HIF signaling pathway in controlling bone development and homeostasis, and especially in regulating the crosstalk between osteoblasts, progenitor cells, and bone marrow blood vessels.

Efficient generation of dopamine neuron-like cells from skin-derived precursors with a synthetic peptide derived from von Hippel-Lindau protein

Skin-derived precursors (SKPs) from mammalian dermis represent neural crest-related stem cells capable of differentiating into both neural and mesodermal progency. SKPs are of clinical interest because they serve as accessible autologous donor cells for neuronal repair for neuronal intractable diseases. However, little is known about the efficient generation of neurons from SKPs, and phenotypes of neurons generated from SKPs have been restricted. In addition, the neuronal repair using their generated neurons as donor cells has not been achieved. The von Hippel-Lindau protein (pVHL) is one of the proteins that play an important role during neuronal differentiation, and recently neuronal differentiation of neural progenitor cells by intracellular delivery of a synthetic VHL peptide derived from elongin BC-binding site has been demonstrated. In the present study, a synthetic VHL peptide derived from elongin BC-binding site was conjugated to the protein transduction domain (PTD) of HIV-TAT protein (TATVHL peptide) to facilitate entry into cells, and we demonstrate the efficient generation of cells with dopaminergic phenotype from SKPs with the intracellular delivery of TATVHL peptide, and characterized the generated cells. The TATVHL peptide-treated SKPs expressed neuronal marker proteins, particularly dopamine neuron markers, and also up-regulated mRNA levels of proneural basic helix-loop-helix factors. After the TATVHL peptide treatment, transplanted SKPs into Parkinson's disease (PD) model rats sufficiently differentiated into dopamine neuron-like cells in PD model rats, and partially but significantly corrected behavior of PD model rats. The generated dopamine neuron-like cells are expected to serve as donor cells for neuronal repair for PD.

Genetic and epigenetic analysis of the VHL gene in gastric cancers

The von Hippel-Lindau tumor suppressor gene (VHL), which is located on chromosome 3p25, plays an important role in tumorigenesis, particularly in tumor growth and vascularization. Mutations of the VHL gene have been observed in the hereditary VHL syndrome and a variety of other sporadic cancers. In this study, in order to investigate whether the VHL gene is involved in gastric carcinogenesis, we have examined the genetic alterations, including somatic mutations and allelic loss, with the two microsatellite markers, D3S1038 and D3S1110, as well as promoter hypermethylation of the VHL gene in 88 sporadic gastric adenocarcinomas. No mutation was detected in the coding region of the VHL gene. Allelic loss was found in 20 (33.9%) of 59 informative cancer cases at one or both markers. In addition, promoter hypermethylation was not detected in the gastric cancer samples. This is the first investigation of the genetic and epigenetic alterations of the VHL gene in gastric cancers. Our results suggest that genetic and epigenetic alterations of the VHL gene may be not involved in the development or progression of gastric cancers. The findings also provide evidence for the presence of another gastric cancer specific tumor suppressor gene at the 3p25 region.

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

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

Mosaicism in von Hippel-Lindau disease: an event important to recognize

von Hippel-Lindau disease (VHL) is an autosomal dominant, familial neoplastic disorder with variable interfamilial and intrafamilial expression. VHL is characterized by pre-disposition to development of a combination of benign and malignant tumours affecting multiple organs. We provide molecular evidence of somatic mosaicism in nearly asymptomatic man whose daughter had VHL. The mosaic subject was found to have a cyst of the kidney and an angioma of the glans penis and had had surgery for a mandibular cyst and epididymal cystadenomas. Mosaicism could provide a genetic explanation for the clinical heterogeneity and variable severity of VHL. The real incidence of mosaicism is still unclear and the identification of mosaicism has important consequences in genetic counseling of VHL patients who appear to have de novo VHL mutations and should be considered when evaluating patients with isolated VHL-related tumours. Our results strongly suggest a complete and extensive clinical examination in the parents of each patient affected by an apparently de novo VHL germline mutation. We recommend performing a mutation screening of both parents of a proband with techniques that permit detection of low percentages of mosaicism before concluding that the proband has a de novo VHL mutation.

Activation of non-ischemic, hypoxia-inducible signalling pathways up-regulate cytoprotective genes in the murine liver

BACKGROUND/AIMS

We investigated the molecular response of a non-ischemic hypoxic stress in the liver, in particular, to distinguish its hepatoprotective potential.

METHODS

The livers of mice were subjected to non-ischemic hypoxia by clamping the hepatic-artery (HA) for 2h while maintaining portal circulation. Hypoxia was defined by a decrease in oxygen saturation, the activation of hypoxia-inducible factor (HIF)-1 and the mRNA up-regulation of responsive genes. To demonstrate that the molecular response to hypoxia may in part be hepatoprotective, pre-conditioned animals were injected with an antibody against Fas (Jo2) to induce acute liver failure. Hepatocyte apoptosis was monitored by caspase-3 activity, cleavage of lamin A and animal survival.

RESULTS

Clamping the HA induced a hypoxic stress in the liver in the absence of severe metabolic distress or tissue damage. The hypoxic stimulus was sufficient to activate the HIF-1 signalling pathway and up-regulate hepatoprotective genes. Pre-conditioning the liver with hypoxia was able to delay the onset of Fas-mediated apoptosis and prolong animal survival.

CONCLUSIONS

Our data reveal that hepatic cells can sense and respond to a decrease in tissue oxygenation, and furthermore, that activation of hypoxia-inducible signalling pathways function in part to promote liver cell survival.

Central nervous system capillary haemangioblastoma: the pathologist's viewpoint

Haemangioblastomas are rare neoplasms of uncertain histogenesis. They represent 1.5-2.5% of intracranial tumours. While the cerebellum is by far the most frequent site, these lesions also tend to occur in the medulla and spinal cord. Most haemangioblastomas are sporadic but up to one quarter are associated with Von Hippel-Lindau disease (VHL). Although a fairly good number of haemangioblastomas were reported, a lack of side-by-side analysis of these reports has resulted in tentative conclusions that merely offer a first glimpse at their clinicopathologic diversity and histogenesis. To remedy this issue, this study presents a literature review concerning these lesions. Medline literature including both relevant monographs and clinicopathological case series. Haemangioblastomas occur either as a part of VHL disease (25-30%, inherited mutation of VHL gene on 3p25-26 chromosome) or as sporadic tumours (often with somatic mutation of VHL gene). They have diverse clinicopathologic presentations with cerebellar lesions having a better prognosis than their brainstem counterparts. Immunostaining is important for separation of haemangioblastomas from other tumours with similar histology. The rich vascularity of haemangioblastomas is due to overexpression of vascular endothelial growth factors. Moreover, 'stromal' cells represent the neoplastic cells of haemangioblastomas and are capable of forming blood islands with extramedullary haematopoiesis.

Hif-1alpha regulates differentiation of limb bud mesenchyme and joint development

Recent evidence suggests that low oxygen tension (hypoxia) may control fetal development and differentiation. A crucial mediator of the adaptive response of cells to hypoxia is the transcription factor Hif-1α. In this study, we provide evidence that mesenchymal condensations that give origin to endochondral bones are hypoxic during fetal development, and we demonstrate that Hif-1α is expressed and transcriptionally active in limb bud mesenchyme and in mesenchymal condensations. To investigate the role of Hif-1α in mesenchymal condensations and in early chondrogenesis, we conditionally inactivated Hif-1α in limb bud mesenchyme using a Prx1 promoter-driven Cre transgenic mouse. Conditional knockout of Hif-1α in limb bud mesenchyme does not impair mesenchyme condensation, but alters the formation of the cartilaginous primordia. Late hypertrophic differentiation is also affected as a result of the delay in early chondrogenesis. In addition, mutant mice show a striking impairment of joint development. Our study demonstrates a crucial, and previously unrecognized, role of Hif-1α in early chondrogenesis and joint formation.

Hypoxia increases cytoplasmic expression of NDRG1, but is insufficient for its membrane localization in human hepatocellular carcinoma

NDRG1 is a hypoxia-inducible protein, whose modulated expression is associated with the progression of human cancers. Here, we reveal that NDRG1 is markedly upregulated in the cytoplasm and on the membrane in human hepatocellular carcinoma (HCC). We demonstrate further that hypoxic stress increases the cytoplasmic expression of NDRG1 in vitro, but does not result in its localization on the plasma membrane. However, grown within an HCC-xenograft in vivo, cells express NDRG1 in the cytoplasm and on the plasma membrane. In conclusion, hypoxia is a potent inducer of NDRG1 in HCCs, albeit requiring additional stimuli within the tumour microenvironment for its recruitment to the membrane.

Germline mutation of von Hippel-Lindau (VHL) gene 695 G>A (R161Q) in a patient with a peculiar phenotype with type 2C VHL syndrome

Von Hippel-Lindau (VHL) disease is an autosomal dominant familial neoplastic disorder with an estimated birth incidence of approximately 1:36000 live. VHL has intrafamilial variability expression and it is characterized by the predisposition to develop hemangioblastomas of the central nervous system and retina, pheochromocytomas, clear-cell renal carcinoma, adenomas, and carcinomas of the pancreas, paragangliomas, renal and pancreatic cysts, papillary cystadenomas of the epididymis and, rarely, cystadenomas of the endolymphatic sac tumor and broad ligament. We describe a Sicilian girl with type 2C VHL who showed the apparently de novo mutation R161Q in association with an extra-axial supratentorial frontal meningioma, which can be included as a characteristic sign in VHL.

pVHL function is essential for endothelial extracellular matrix deposition

The tumor suppressor von Hippel-Lindau protein (pVHL) is critical for cellular molecular oxygen sensing, acting to target degradation of the hypoxia-inducible factor alpha transcription factor subunits under normoxic conditions. We have found that independent of its function in regulating hypoxic response, the VHL gene plays a critical role in embryonic endothelium development through regulation of vascular extracellular matrix assembly. We created mice lacking the VHL gene in endothelial cells; these conditional null mice died at the same stage as homozygous VHL-null mice, with similar vascular developmental defects. These included defective vasculogenesis in the placental labyrinth, a collapsed endocardium, and impaired vessel network patterning. The defects in embryonic vascularization were correlated with a diminished vascular fibronectin deposition in vivo and defective endothelial extracellular fibronectin assembly in vitro. We found that the impaired migration and adhesion of VHL-null endothelial cells can be partially rescued by the addition of back exogenous fibronectin, which indicates that pVHL regulation of fibronectin deposition plays an important functional role in vascular patterning and maintenance of vascular integrity.

Hypoxia and HIF-1 in Chondrogenesis

In endochondral bone development chondrocytes undergo proliferation, hypertrophic differentiation, mineralization of the surrounding matrix, death, blood vessel invasion, and finally replacement of cartilage with bone. The chondrocytic growth plate is a unique mesenchymal tissue, as it is avascular but it requires blood vessel invasion in order to be replaced by bone. We have recently provided evidence that the growth plate is hypoxic during fetal development. Adaptation to hypoxia is a critical event in numerous pathological settings, such as tumor progression and survival of tissues in which blood flow has been suddenly interrupted. One of the hallmarks of the response to hypoxia is activation of the transcription factor HIF-1alpha. The von Hippel-Lindau (VHL) tumor suppressor protein is a component of a ubiquitin ligase promoting proteolysis of HIF-1alpha. By using a genetic approach, we have demonstrated that VHL and HIF-1alpha are critical regulators of endochondral bone development.

Unusual ocular presentation of von Hippel-Lindau disease

CASE REPORT

We report a young girl who first presented with a unilateral total exudative retinal detachment diagnosed as Coats' disease. Eight years later, when she presented with classical retinal hemangioblastomas with reduced vision in the fellow eye, the diagnosis of von Hippel-Lindau (VHL) disease was confirmed.

COMMENTS

This case highlights the importance of considering the possibility of VHL in atypical cases of Coats' disease and unusual sporadic cases of unexplained unilateral exudative retinal detachment. The identification of VHL mutations and subsequent screening allows early diagnosis and treatment of asymptomatic retinal or central nervous system hemangioblastomas, as well as other malignancies associated with this syndrome.

Hypoxia and HIF-1α in chondrogenesis

In endochondral bone development chondrocytes undergo well-ordered and controlled phases of proliferation, hypertrophic differentiation, mineralization of the surrounding matrix, death, blood vessel invasion, and finally replacement of cartilage with bone. The chondrocytic growth plate is a unique mesenchymal tissue, as it is avascular but it requires blood vessel invasion, i.e. the angiogenic switch, in order to be replaced by bone. We have recently provided evidence that the growth plate is hypoxic during fetal development. Adaptation to hypoxia is a critical event in numerous pathological settings, such as tumor progression and survival of tissues in which blood flow has been suddenly interrupted. One of the hallmarks of the response to hypoxia is activation of the transcription factor HIF-1alpha. The von Hippel Lindau tumor suppressor protein VHL is a component of a ubiquitin ligase promoting proteolysis of HIF-1alpha. By using a genetic approach, we have demonstrated the essential role of the hypoxia/VHL/HIF-1alpha pathway in endochondral bone development. Hypoxia-dependent up regulation of HIF-1alpha transcriptional activity is critical for survival of hypoxic chondrocyte, and it shapes up the fetal growth plate by inhibiting chondrocyte proliferation, increasing matrix accumulation and probably modulating cell size. The findings overall highlight the usefulness of studying fetal growth plate development as a model to address issues such as adaptation of normal tissues to hypoxia, survival of hypoxic cells, and regulation of the angiogenic switch. They also demonstrate a crucial role of hypoxia and HIF-1alpha in development and differentiation.

Expression of von Hippel-Lindau tumor suppressor and tumor-associated carbonic anhydrases IX and XII in normal and neoplastic colorectal mucosa

AIM: To analyze possible relationships between CA IX/CA XII and pVHL expression in normal and neoplastic colorectal mucosa.

METHODS: Immunohistochemical staining of 42 tissue specimens obtained from 17 cancer patients was performed to evaluate the distribution and semi-quantitatively assess the levels of CA IX, CA XII and pVHL. VHL mRNAs from 14 fresh-frozen tumors was amplified by RT-PCR and subjected to sequencing. CA9 and CA12 mRNA levels were analyzed by semi-quantitative RT-PCR in comparison with VEGF as an indicator of hypoxia that uncouples the pVHL control.

RESULTS: Tumor tissues were associated with a borderline increase of CA IX staining signal and slight but significant decrease of CA XII immunoreactivity, whereas no association was found for pVHL. Sequence analysis of RT-PCR-amplified VHL mRNAs revealed no deletions/mutations, suggesting that they were VHL-competent. We did not observe any correlation between pVHL and CA IX/CA XII proteins as well as between VEGF and CA9 mRNAs, but the tumor-associated changes in mRNA levels of VEGF and CA12 showed a significant inverse relationship.

CONCLUSION: Our results indicate that CA9 and CA12 are regulated by different intratumoral factors and that lack of apparent relationship between the levels of CA IX/CA XII and pVHL cannot be fully assigned to uncoupling of negative regulatory function of pVHL by tumor hypoxia signified by induced VEGF transcription. The interplay between the functional pVHL and CA IX/CA XII in colorectal tumors seems rather complex and is not evident merely at the expression levels.

Gene expression profile identifies a rare epithelioid variant case of pleomorphic liposarcoma carrying FUS-CHOP transcript

AIMS

To describe a tumour with morphological and immunophenotypic characteristics of epithelioid variant of pleomorphic liposarcoma. Pleomorphic liposarcoma is a very rare variant of liposarcoma defined morphologically by the presence of pleomorphic lipoblasts showing peculiar epithelial-like features that can be confused with primary or metastatic carcinoma.

METHODS AND RESULTS

Molecular analysis demonstrated for the first time the presence of FUS-CHOP transcript in this liposarcoma variant. Microarray analysis revealed a gene expression profile related to a more aggressive tumour type when compared with other myxoid/round cell liposarcomas.

CONCLUSIONS

The present data show that the epithelioid variant of pleomorphic liposarcoma represents a further variant of myxoid liposarcoma sharing the FUS-CHOP fusion transcript but carrying a distinct expression profile, in keeping with its aggressive clinical course.

Expression profiles of a human pancreatic cancer cell line upon induction of apoptosis search for modulators in cancer therapy

We analyzed the differential gene expression in the pancreatic cancer cell line NP-18 upon induction of apoptosis caused by cyclin-dependent kinase inhibition triggered by either overexpression of the tumor suppressor gene p16(INK4A)using an adenoviral construction or incubation with the chemical inhibitors, roscovitine or olomoucine. Screening was performed using cDNA arrays from Clontech that allowed the determination of the expression of 1,176 genes specifically related with cancer. The analysis was carried out using the Atlas Image 2.01 (Clontech) and GeneSpring 4.2 (Silicon Genetics) softwares. Among the differentially expressed genes, we chose for further validation histone deacetylase 1 (HDAC1), von Hippel Lindau and decorin as upregulated genes, and Sp1, hypoxia-inducible factor-1 alpha and DNA primase as downregulated genes. The changes in the expression of these genes to mRNA were validated by quantitative RT-PCR and the final translation into protein by Western blot analysis. Inhibition of HDAC activity, Sp1 binding and DNA primase expression led to an increase in the level of apoptosis, both in parental cells and in doxorubicin-resistant cells. Therefore, these proteins could constitute possible targets to develop modulators in cancer chemotherapy that would increase or restore apoptosis.

Role of the C-terminal alpha-helical domain of the von Hippel-Lindau protein in its E3 ubiquitin ligase activity

In the present study, the role of the C-terminal alpha-helical domain (amino acid (aa) 195-208) of the von Hippel-Lindau (VHL) tumour suppressor was investigated. Deletions of the VHL C-terminus up to the naturally occurring 195-Gln-Term resulted in hypoxia-inducible factor (HIF)-1alpha downregulation in renal cell carcinoma (RCC)4 cells during normoxia, suggesting that this domain is not an absolute requirement for the ubiquitination of HIF-1alpha. However, detailed investigation of the ubiquitin protein isopeptide ligase ubiquitin ligase properties of VHL revealed C-terminal deletions to cause a significant impairment of HIF-1alpha ubiquitination, which is shown to be due to a loss in high-affinity binding to the target substrate. When VHL regulation of both HIF-1alpha N- and C-terminal oxygen-dependent degradation domains (HIF-ODDD) was investigated, it was found that only ubiquitination of the C-terminal HIF-ODDD was affected by the deletion of the VHL C-terminus. When RCC4 cells expressing C-terminal truncations of VHL were exposed to graded hypoxia, differences in the induction of HIF-1alpha were observed in comparison with full-length VHL, with a shift in the maximal induction of HIF-1alpha to a higher oxygen tension. These changes were accompanied by increased glucose transporter 1 expression, p300 CH1 domain binding and HIF-mediated reporter activity. We have thus defined a role for the C-terminal alpha-helical domain of VHL in the regulation of HIF-1alpha.

Fibronectin is a hypoxia-independent target of the tumor suppressor VHL

The von Hippel-Lindau (VHL) tumor suppressor gene regulates the extracellular matrix by controlling fibronectin deposition. To identify novel VHL target genes, we subjected mRNA from VHL-deficient RCC cells (786-0-pRC) and a transfectant re-expressing wildtype VHL (786-0-VHL) to differential expression profiling. Among the differentially expressed genes, we detected that fibronectin is upregulated in the presence of VHL, while it is not affected by hypoxia. Thus regulation of fibronectin deposition by VHL occurs at the transcriptional level, irrespective of oxygen levels.

The von Hippel-Lindau tumor suppressor protein is a molten globule under native conditions: implications for its physiological activities

The von-Hippel Lindau tumor suppressor protein (pVHL) is conserved throughout evolution, as its homologues are found in organisms ranging from mammals to the Drosophila melanogaster and Anopheles gambiae insects and the Caenorhabditis elegans nematode. Although the physiological role of pVHL is not fully understood, it has been shown to interact with a large number of unrelated proteins and was suggested to play a role in protein degradation as an E3 ubiquitin ligase component in the ubiquitin pathway. To gain insight into the molecular basis of pVHL activity, we analyzed its folding and stability in solution under physiologically relevant conditions. Dynamic light-scattering and gel filtration chromatography of the purified pVHL clearly indicated that the Stokes radius of the protein is larger than what would be expected from its crystal structure. However, under these conditions, the protein shows a clear secondary structure as determined by far-UV circular dichroism. Yet, the near-UV CD experiments show an absence of a tertiary structure. Upon the addition of urea, even at very low concentrations, the protein unfolds in a non-reversible manner, leading to the formation of amorphous aggregates. Furthermore, a large increase in fluorescence (>50-fold) is observed upon the addition of pVHL into a solution containing 8-anilino-1-naphthalene sulfonic acid. We therefore conclude that, under native conditions, the non-bound pVHL has a molten globule configuration with marginal stability. Although molten globular structures can be induced in many proteins under extreme conditions, this is one of the few reported cases of such a structure under the physiological conditions of pH, ionic strength, and temperature. The significance of the pVHL structural properties is being discussed in the context of its physiological activities.

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

The development of hereditary von Hippel-Lindau (VHL) disease and the majority of sporadic kidney cancers are due to the functional inactivation of the VHL gene. The product of the VHL gene, pVHL, in association with elongins B and C, cullin 2, and Rbx1 form an E3 ubiquitin-ligase complex VEC that targets the alpha subunits of hypoxia-inducible factor (HIF) for ubiquitination. Ubiquitin-tagged HIF-alpha proteins are subsequently degraded by the common 26S proteasome. pVHL functions as the substrate-docking interface that specifically recognizes prolyl-hydroxylated HIF-alpha. This hydroxylation occurs only in the presence of oxygen or normoxia. Thus, under hypoxia, HIF-alpha subunits are no longer subjected to degradation and are thereby able to dimerize with the common and constitutively stable beta subunits. The heterodimeric HIFs upregulate a myriad of hypoxia-inducible genes, triggering our physiologic response to hypoxia. Inappropriate accumulations of HIF-alpha in VHL disease are believed to contribute to the pathogenesis via the upregulation of several of these HIF target genes. Our current molecular understanding of the roles of HIF and pVHL in the development of VHL-associated clear-cell renal cell carcinoma (CC-RCC) is the focus of this review.

Molecular Cloning and Characterization of the von Hippel-Lindau-Like Protein

von Hippel-Lindau (VHL) tumor suppressor protein—inactivated in VHL disease and sporadic kidney cancer—is a component of an E3 ubiquitin ligase complex that selectively ubiquitinates the α subunit of the hypoxia-inducible factor (HIF) transcription factor for subsequent destruction by the 26S proteasome. Here, we report the identification and characterization of the first VHL homologue, VHL-like protein (VLP), located on chromosome 1q21.2. A 676-bp partial cDNA encoding a 139-amino acid protein that is 78% similar to VHL was isolated by reverse transcription-PCR from human brain cerebellum and several cancer cell lines. The expression of VLP transcript is most abundant in the placenta. Like VHL, VLP contains a β domain capable of binding HIFα. However, unlike VHL, it does not contain a recognizable α domain, which is required for nucleating the multiprotein E3 ubiquitin ligase complex. The increased expression of VLP in the presence of VHL attenuated the ubiquitination of HIFα and led to the accumulation of downstream HIF target genes. These results taken together indicate that VLP functions as a dominant-negative VHL to serve as a protector of HIFα.

Measurement of renal tumour and normal tissue perfusion using positron emission tomography in a phase II clinical trial of razoxane

Measurement of tumour and normal tissue perfusion in vivo in cancer patients will aid the clinical development of antiangiogenic and antivascular agents. We investigated the potential antiangiogenic effects of the drug razoxane by measuring the changes in parameters estimated from H(2)(15)O and C(15)O positron emission tomography (PET) to indicate alterations in vascular physiology. The study comprised 12 patients with primary or metastatic renal tumours >3 cm in diameter enrolled in a Phase II clinical trial of oral razoxane. Perfusion, fractional volume of distribution of water (VD) and blood volume (BV) were measured in tumour and normal tissue before and 4-8 weeks after treatment with 125 mg twice-daily razoxane. Renal tumour perfusion was variable but lower than normal tissue: mean 0.87 ml min(-1) ml(-1) (range 0.33-1.67) compared to renal parenchyma: mean 1.65 ml min(-1) ml(-1) (range 1.16-2.88). In eight patients, where parallel measurements were made during the same scan session, renal tumour perfusion was significantly lower than in normal kidney (P=0.0027). There was no statistically significant relationship between pretreatment perfusion and tumour size (r=0.32, n=13). In six patients scanned before and after razoxane administration, there was no statistically significant change in tumour perfusion: mean perfusion pretreatment was 0.81 ml min(-1) ml(-1) (range 0.46-1.26) and perfusion post-treatment was 0.72 ml min(-1) ml(-1) (range 0.51-1.15, P=0.15). Tumour VD and BV did not change significantly following treatment: mean pretreatment VD=0.66 (range 0.50-0.87), post-treatment VD=0.71 (range 0.63-0.82, P=0.22); pretreatment BV=0.18 ml ml(-1) (range 0.10-0.25), post-treatment BV=0.167 ml ml(-1) (range 0.091-0.24, P=0.55). Tumour perfusion, VD and BV did not change significantly with tumour progression. This study has shown that H(2)(15)O and C(15)O PET provide useful in vivo physiological measurements, that even highly angiogenic renal cancers have poor perfusion compared to surrounding normal tissue, and that PET can provide valuable information on the in vivo biology of angiogenesis in man and can assess the effects of antiangiogenic therapy.

Ubiquitinated deiodinase: not dead yet

Originating in the thyroid, the prohormone thyroxine is converted to triiodothyronine, which is essential in brain development, growth, and metabolism. A study in this issue reveals a novel mechanism for controlling triiodothyronine production that provides the first example of enzyme activity being restored by deubiquitination.

von Hippel-Lindau disease

von Hippel-Lindau disease is a heritable multisystem cancer syndrome that is associated with a germline mutation of the VHL tumour suppressor gene on the short arm of chromosome 3. This disorder is not rare (about one in 36000 livebirths) and is inherited as a highly penetrant autosomal dominant trait (ie, with a high individual risk of disease). Affected individuals are at risk of developing various benign and malignant tumours of the central nervous system, kidneys, adrenal glands, pancreas, and reproductive adnexal organs. Because of the complexities associated with management of the various types of tumours in this disease, treatment is multidisciplinary. We present an overview of the clinical aspects, management, and treatment options for von Hippel-Lindau disease.

Multiple splice variants of the human HIF-3 alpha locus are targets of the von Hippel-Lindau E3 ubiquitin ligase complex

Functional inactivation of the von Hippel-Lindau (VHL) tumor suppressor protein is the cause of familial VHL disease and sporadic kidney cancer. The VHL gene product (pVHL) is a component of an E3 ubiquitin ligase complex that targets the hypoxia-inducible factor (HIF) 1 and 2 alpha subunits for polyubiquitylation. This process is dependent on the hydroxylation of conserved proline residues on the alpha subunits of HIF-1/2 in the presence of oxygen. In our effort to identify orphan HIF-like proteins in the data base that are potential targets of the pVHL complex, we report multiple splice variants of the human HIF-3 alpha locus as follows: hHIF-3 alpha 1, hHIF-3 alpha 2 (also referred to as hIPAS; human inhibitory PAS domain protein), hHIF-3 alpha 3, hHIF-3 alpha 4, hHIF-3 alpha 5, and hHIF-3 alpha 6. We demonstrate that the common oxygen-dependent degradation domain of hHIF-3 alpha 1-3 splice variants is targeted for ubiquitylation by the pVHL complex in vitro and in vivo. This activity is enhanced in the presence of prolyl hydroxylase and is dependent on a proline residue at position 490. Furthermore, the ubiquitin conjugation occurs on lysine residues at position 465 and 568 within the oxygen-dependent degradation domain. These results demonstrate additional targets of the pVHL complex and suggest a growing complexity in the regulation of hypoxia-inducible genes by the HIF family of transcription factors.

Hereditary renal cancers

Hereditary renal cancer syndromes can lead to multiple bilateral kidney tumors that occur at a younger age than do nonhereditary renal cancers. Imaging plays an important role in the diagnosis and management of these syndromes. During the past decade, several new hereditary renal syndromes have been discovered but are not yet widely known. Whereas previously, the list of hereditary renal cancers in adults included von Hippel-Lindau disease and a rare form of chromosomal translocation, the list now includes the following syndromes: tuberous sclerosis, hereditary papillary renal cancer, Birt-Hogg-Dubé syndrome, hereditary leiomyoma renal cell carcinoma, familial renal oncocytoma, hereditary nonpolyposis colon cancer, and medullary carcinoma of the kidney. In addition, a number of newly described but poorly understood syndromes are under investigation. Even at this early stage, it is clear that elucidation of the underlying genetic mutations that cause hereditary renal cancer syndromes will have profound implications for understanding the origins of nonhereditary renal tumors. These studies will likely culminate in a better understanding of the causes of renal cancer, its prevention, and, ultimately, its cure.

Metastasis of renal cell carcinoma to haemangioblastoma of the spinal cord in von Hippel–Lindau disease: case report and review of the literature

A case is presented demonstrating the unusual phenomenon of a renal cell carcinoma metastasising to a spinal haemangioblastoma in a patient with von Hippel-Lindau (VHL) disease. Recent advances in the molecular biology of VHL disease relevant to possible mechanisms of tumour-to-tumour metastasis are briefly reviewed.

Mutations in the VHL gene from potassium bromate-induced rat clear cell renal tumors

Potassium bromate (KBrO(3)) is a rat renal carcinogen and a major drinking water disinfection by-product in water disinfected with ozone. Clear cell renal tumors, the most common form of human renal epithelial neoplasm, are rare in animals but are inducible by KBrO(3) in F344 rats. Detection of cytoplasmic periodic acid-Schiff-positive granules in clear cell tumors, indicative of glycogen accumulation, provides evidence of their biochemical similarity to human counterparts. Mutation in the coding region of the von Hippel-Lindau (VHL) gene is frequently detected in human clear cell renal carcinomas. Detection of VHL mutations in KBrO(3)-induced rat renal tumors could enhance the relevancy of these rat renal tumors for human health risk assessment. Formalin-fixed paraffin-embedded control tissues and renal tumors from male F344 rats exposed to KBrO(3) in the drinking water for 2 years were examined microscopically and were microdissected for DNA extraction. The coding sequence and a promoter region of the VHL gene were examined by polymerase chain reaction-single strand conformation polymorphism and/or DNA sequencing. Two of nine clear cell renal tumors carried the same C to T mutation at the core region of the Sp1 transcription factor binding motif in the VHL promoter and one of four untreated animals had C to T mutation outside the highly conserved core region. Mutation in the VHL coding sequence was only detected in one tumor. No VHL mutations were observed in three chromophilic tumors. KBrO(3)-induced rat renal tumors are morphologically similar to their human counterpart but the genetic basis of tumorigenesis is different.

Vascular permeability factor/vascular endothelial growth factor: a critical cytokine in tumor angiogenesis and a potential target for diagnosis and therapy

Vascular endothelial growth factor A (VEGF-A), the founding member of the vascular permeability factor (VPF)/VEGF family of proteins, is an important angiogenic cytokine with critical roles in tumor angiogenesis. This article reviews the literature with regard to VEGF-A's multiple functions, the mechanisms by which it induces angiogenesis, and its current and projected roles in clinical oncology. VEGF-A is a multifunctional cytokine that is widely expressed by tumor cells and that acts through receptors (VEGFR-1, VEGFR-2, and neuropilin) that are expressed on vascular endothelium and on some other cells. It increases microvascular permeability, induces endothelial cell migration and division, reprograms gene expression, promotes endothelial cell survival, prevents senescence, and induces angiogenesis. Recently, VEGF-A has also been shown to induce lymphangiogenesis. Measurements of circulating levels of VEGF-A may have value in estimating prognosis, and VEGF-A and its receptors are potential targets for therapy. Recognized as the single most important angiogenic cytokine, VEGF-A has a central role in tumor biology and will likely have an important role in future approaches designed to evaluate patient prognosis. It may also become an important target for cancer therapy.

Association of the P-glycoprotein transporter MDR1(C3435T) polymorphism with the susceptibility to renal epithelial tumors

Except for hereditary disease, genetic factors that contribute to the development of renal epithelial tumors are unknown. There is a possibility that the MDR1 encoded plasma membrane transporter P-glycoprotein (PGP) influences the risk of development of renal neoplasms. PGP is known to be involved in uptake, binding, transport, and distribution of xenobiotics. There is evidence that the MDR1(C3435T) polymorphism drives expression and modulates disease risk. In an explorational case-control study, constitutional genotype frequencies were established at MDR1(C3435T) of 537 healthy control subjects and compared with those of 212 patients with renal epithelial tumors. There were 179 clear cell renal cell carcinoma (CCRCC) and 33 tumors collectively assigned as non-CCRCC. In a second study, genotypes of another 150 healthy control subjects and 50 patients with three non-CCRCC types (26 papillary RCC, 11 chromophobe RCC, and 13 renal oncocytic adenoma) were compared. PCR-restriction fragment length polymorphism-based analysis of constitutional DNA, and statistical analysis were applied. PGP expression was analyzed by quantitative immunohistochemistry. The explorational study showed a significant association between T allele frequency and the occurrence of tumors (P = 0.007). When tumors were histopathologically distinguished into frequent CCRCC and less frequent non-CCRCC, both patient groups contributed to this effect with a seemingly strong influence by the latter (P = 0.0419). The second study established the T allele as a risk factor especially for non-CCRCC (P = 0.0005) with the highest risk for homozygote TT allele carriers (P < 0.0001). Independently, MDR1(C3435T) genotype associated variations in PGP expression were shown in normal renal parenchyma with a 1.5-fold difference of median values (TT, 1.9; CC, 2.8; P = 0.0065). The data provide evidence for PGP to influence the susceptibility to develop renal epithelial tumors by virtue of its MDR1(C3435T) polymorphism and changes in expression. Especially T and TT carriers are at risk for developing non-CCRCC, i.e., papillary and chromophobe RCC as well as oncocytic adenomas.

Recurrent polytopic chromaffin paragangliomas in a 9-year-old boy resulting from a novel germline mutation in the von Hippel-Lindau gene

Pheochromocytomas are frequently associated with inherited cancer syndromes such as von Hippel-Lindau disease (VHL). Retinal angioma and hemangioblastomas of the central nervous system are hallmarks of VHL, but its clinical variety is remarkably broad. Pheochromocytomas as the sole or first manifestation of VHL are rare but have been observed. In this case report, the authors describe an unusual case of initial collapse, seizures, and hypertensive crisis in a child who later was found to have multiple extraadrenal pheochromocytomas. Molecular diagnostics revealed a novel point mutation in the VHL gene (VHL nt. 406 T-->G). Only 7 months after the first lesions had been removed, a new paraganglioma developed in the contralateral periadrenal region. When encountering pheochromocytomas in children, the clinician should be aware that an associated tumor syndrome might be present, and appropriate molecular screening should be initiated. Molecular genetics aid in the clinical decision-making and clinical management of individual patients with pheochromocytoma.

Playing Tag with HIF: The VHL Story

Inactivation of the von Hippel-Lindau (VHL) tumour suppressor gene product pVHL is the cause of inherited VHL disease and is associated with sporadic kidney cancer. pVHL is found in a multiprotein complex with elongins B/C, Cul2, and Rbx1 forming an E3 ubiquitin ligase complex called VEC. This modular enzyme targets the alpha subunits of hypoxia-inducible factor (HIF) for ubiquitin-mediated destruction. Consequently, tumour cells lacking functional pVHL overproduce the products of HIF-target genes such as vascular endothelial growth factor (VEGF), which promotes angiogenesis. This likely accounts for the hypervascular nature of VHL-associated neoplasms. Although pVHL has been linked to the cell-cycle, differentiation, and the regulation of extracellular matrix assembly, microenvironment pH, and tissue invasiveness, this review will focus on the recent insights into the molecular mechanisms governing the E3 ubiquitin ligase function of VEC.

Fibrous meningioma in a patient with von Hippel-Lindau disease: a genetic analysis

Meningioma has been included in the constellation of tumors associated with von Hippel-Lindau (VHL) disease in previously published reports. It is unclear whether these tumors are an uncommon component of VHL disease or are more readily detected in these patients because of the frequency with which they undergo central nervous system imaging as part of the routine management of VHL disease. The authors report the case of a patient with VHL disease in whom a progressively enlarging supratentorial mass developed and was diagnosed as a hemangioblastoma because of its appearance on serial magnetic resonance images. At surgery the tumor displayed the typical features of a meningioma and was given the histological diagnosis of fibrous meningioma. Single-stranded conformational polymorphism analysis of the tumor DNA revealed a loss of heterozygosity at the neurofibromatosis Type 2 gene locus, known to be associated with sporadically occurring meningiomas. Despite this finding, the VHL gene locus on the allele from the patient's unaffected parent was normal. Thus it is unlikely that the occurrence of this patient's fibrous meningioma was associated with underlying VHL disease. Given the high frequency of neuroimaging sessions in patients with VHL disease, some supratentorial lesions that have been given radiological diagnoses of hemangioblastomas may be incidental meningiomas.

The von Hippel-Lindau protein interacts with heteronuclear ribonucleoprotein a2 and regulates its expression

The product of the von Hippel-Lindau (VHL) tumor suppressor gene, pVHL, functions as a ubiquitin-protein isopeptide ligase in regulating HIF-1 protein turnover, thus accounting for the increased transcription of hypoxia-inducible genes that accompanies VHL mutations. The increased vascular endothelial growth factor mRNA stability in cells lacking pVHL has been hypothesized to be due to a similar regulation of an RNA-binding protein. We report the expression of the GLUT-1 3'-untranslated region RNA-binding protein, heteronuclear ribonucleoprotein (hnRNP) A2, is specifically increased in pVHL-deficient cell lines. Enhanced hnRNP A2 expression was apparent in all cell fractions, including polysomes, where a similar modest effect on hnRNP L (a GLUT-1 and VEGF 3'-untranslated region-binding protein), was seen. Steady state levels of hnRNP A2 mRNA were unaffected. Regulation of hnRNP A2 levels correlated with the ability of pVHL to bind elongin C. Proteasome inhibition of cells expressing wild type pVHL selectively increased cytoplasmic hnRNP A2 levels to that seen in pVHL-deficient cells. Finally, an in vivo interaction between pVHL and hnRNP A2 was demonstrated in both the nucleus and the cytoplasm. Collectively, these data indicate that hnRNP A2 expression is regulated by pVHL in a manner that is dependent on elongin C interactions as well as functioning proteasomes.

Expression of hypoxia-inducible cell-surface transmembrane carbonic anhydrases in human cancer

An acidic extracellular pH is a fundamental property of the malignant phenotype. In von Hippel-Lindau (VHL)-defective tumors the cell surface transmembrane carbonic anhydrase (CA) CA9 and CA12 genes are overexpressed because of the absence of pVHL. We hypothesized that these enzymes might be involved in maintaining the extracellular acidic pH in tumors, thereby providing a conducive environment for tumor growth and spread. Using Northern blot analysis and immunostaining with specific antibodies we analyzed the expression of CA9 and CA12 genes and their products in a large sample of cancer cell lines, fresh and archival tumor specimens, and normal human tissues. Expression was also analyzed in cultured cells under hypoxic conditions. Expression of CA IX and CA XII in normal adult tissues was detected only in highly specialized cells and for most tissues their expression did not overlap. Analysis of RNA samples isolated from 87 cancer cell lines and 18 tumors revealed high-to-moderate levels of expression of CA9 and CA12 in multiple cancers. Immunohistochemistry revealed high-to-moderate expression of these enzymes in various normal tissues and multiple common epithelial tumor types. The immunostaining was seen predominantly on the cell surface membrane. The expression of both genes was markedly induced under hypoxic conditions in tumors and cultured tumor cells. We conclude that the cell surface trans-membrane carbonic anhydrases CA IX and CA XII are overexpressed in many tumors suggesting that this is a common feature of cancer cells that may be required for tumor progression. These enzymes may contribute to the tumor microenvironment by maintaining extracellular acidic pH and helping cancer cells grow and metastasize. Our studies show an important causal link between hypoxia, extracellular acidification, and induction or enhanced expression of these enzymes in human tumors.

Molecular-based therapies for renal cell carcinoma

The incidence of renal cell carcinoma (RCC) is rising steadily, but the ability to cure patients with metastatic RCC unfortunately remains limited. Emerging interest in gene therapy performance and safety is expressed by patients, medical institutes, and other agencies. It has become evident that better understanding of the genetic impairments and immune pathophysiology in RCC is essential for future improvement in patient care. Clinical trials now underway that are focusing on genetic and immune impairments will hopefully lead to future breakthroughs in RCC therapy. This paper reviews available gene therapies and other related therapeutic approaches for RCC and lists some of the current clinical trials focused on molecular-based therapies.

Do VHL and HIF-1 mirror p53 and Mdm-2? Degradation-transactivation loops of oncoproteins and tumor suppressors

Recently it has been shown that the VHL tumor suppressor targets the hypoxia-inducible transcription factor (HIF-1) for ubiquitin-dependent degradation by the proteasome. Past mysteries of the p53 tumor suppressor help to solve the present puzzles of the VHL tumor suppressor. Thus, Mdm-2 targets the p53 tumor suppressor for ubiquitin-dependent degradation by the proteasome, but, in addition, the p53 transcription factor induces Mdm-2, thus, establishing a feedback loop. Hypoxia or DNA damage by abrogating binding of HIF-1 with VHL and p53 with Mdm-2, respectively, leads to stabilization and accumulation transcriptionally active HIF-1 and p53. More detailed analysis depicts the VHL/HIF-1 pair as the p53/mdm-2 pair that is turned upside down, suggesting that VHL may be a HIF-1-inducible gene of the feedback loop. The extended model proposes that an oncoprotein and a tumor suppressor due to transactivation coupled with feedback protein degradation might form functional pairs (Rb/E7, E2F/Rb, E2F/Mdm-2, catenin/APC, p27, cyclin D1, Rb/gankyrin), thus, predicting missing links.

Ubiquitination of hypoxia-inducible factor requires direct binding to the beta-domain of the von Hippel-Lindau protein

von Hippel-Lindau (VHL) disease is a hereditary cancer syndrome that is characterized by the development of multiple vascular tumors and is caused by inactivation of the von Hippel-Lindau protein (pVHL). Here we show that pVHL, through its beta-domain, binds directly to hypoxia-inducible factor (HIF), thereby targeting HIF for ubiquitination in an alpha-domain-dependent manner. This is the first function to be ascribed to the pVHL beta-domain. Furthermore, we provide the first direct evidence that pVHL has a function analogous to that of an F-box protein, namely, to recruit substrates to a ubiquitination machine. These results strengthen the link between overaccumulation of HIF and development of VHL disease.

von Hippel-Lindau syndrome: target for anti-vascular endothelial growth factor (VEGF) receptor therapy

von Hippel-Lindau (VHL) syndrome is a familial cancer syndrome caused by germline mutations in the VHL tumor suppressor gene. Mutations in the VHL gene result in the constitutive stabilization of transcription factors hypoxia-inducible factors 1alpha and 2alpha, which bind to specific enhancer elements in the vascular endothelial growth factor (VEGF) gene and stimulate angiogenesis. This increase in angiogenesis under normoxic conditions in key target organs such as the brain, kidney, and eye leads to high morbidity and reduced life expectancy. Drugs designed to block the VEGF signaling pathway may prevent the long-term complications of the disease. To test this hypothesis, a clinical study was initiated to evaluate the effect of the VEGF tyrosine kinase receptor inhibitor SU5416 in patients with VHL syndrome. Preliminary data on SU5416 indicate that it is well tolerated when administered chronically in such patients. However, since little is known about the long-term use of such inhibitors, patients will need careful monitoring. Data obtained from monitoring these patients will provide valuable information for adjuvant treatment trials in cancer patients.

Renal toxicity and carcinogenicity of trichloroethylene: key results, mechanisms, and controversies

The discussion on renal carcinogenicity of trichloroethylene addresses epidemiological, mechanistic, and metabolic aspects. After trichloroethylene exposure of rats, renal cell tumors were found increased in males, and an increased incidence of interstitial cell tumors of the testes was reported. Studies on the metabolism of trichloroethylene in rodents and in humans support the role of bioactivation reactions for the development of tumors following exposure to trichloroethylene. Epidemiological cohort studies addressing the carcinogenicity of trichloroethylene with respect to the renal or urothelial target sites have been conducted, and no clear evidence for an elevated renal or urinary tract cancer risk in trichloroethylene-exposed groups was visible in exposed populations. However, a cohort study of 169 male workers having been exposed to unusually high levels of trichloroethylene in Germany within the period between 1956 and 1975 supported a nephrocarcinogenic effect of trichloroethylene in humans. The results of this study were discussed in the literature with considerable reserve; criticism was based mainly on the choice of the study group, which had been recruited from personnel of a company in which a cluster of four renal tumors was observed previously. Hence, a further case-control study was conducted in the same region. This study confirmed the results of the previous cohort study, supporting the concept of involvement of prolonged and high-dose trichloroethylene exposures in the development of renal cell cancer. Further investigations on patients with renal cell carcinoma and with histories of high trichloroethylene exposures, on the basis of excretion of marker proteins in the urine, pointed to toxic damage to the proximal renal tubules by trichloroethylene. The hypothesis of implication of a glutathione transferase-dependent bioactivating pathway of trichloroethylene, established in experimental animals, seems at least also plausible for humans. Apparently, the occurrence of renal cell carcinomas in man follows high-dose exposures to trichloroethylene that are also accompanied by damage to tubular renal cells. Development of renal cell carcinomas has been related to mutations in the vonHippel-Lindau (VHL) tumor suppressor gene. Renal cell carcinoma tissues of persons with histories of prolonged high-dose exposure to trichloroethylene were investigated for the occurrence of mutations of the vonHippel-Lindau (VHL) tumor suppressor gene. VHL gene mutations were found in the majority of renal cell tumors associated with high-level exposure to trichloroethylene. A specific mutational hot spot at the VHL nucleotide 454 was addressed as a unique mutation pattern of the VHL tumor suppressor gene. A synopsis of all experimental, clinical, and epidemiological data suggests that reactive metabolites of trichloroethylene, with likely involvement of dichlorovinyl-cysteine (DCVC), exert a genotoxic effect on the proximal tubule of the human kidney. This constitutes a tumor-initiating process of genotoxic nature, the initial genotoxic effect apparently being linked with mutational changes in the VHL tumor suppressor gene. However, there is compelling evidence that the full development of a malignant tumor requires continued promotional stimuli. Repetitive episodes of high peak exposures to trichloroethylene over a prolonged period of time apparently led to nephrotoxicity, visualized by the excretion of tubular marker proteins in the urine. This critical process of development of tubular damage by trichloroethylene must follow a "conventional" dose-dependence, implying a practical threshold. This view is much corroborated by the fact that the occurrence of human renal cell cancer is obviously confined to cases of unusually high trichloroethylene exposures in the past, with special characteristics of very high and repetitive peak exposures. Current instruments of regulation should be adjusted to allow adequate consideration of su