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

Catalytic inhibitor of Protein Phosphatase 5 activates the extrinsic apoptotic pathway by disrupting complex II in kidney cancer

Serine/threonine protein phosphatase-5 (PP5) is involved in tumor progression and survival, making it an attractive therapeutic target. Specific inhibition of protein phosphatases has remained challenging because of their conserved catalytic sites. PP5 contains its regulatory domains within a single polypeptide chain, making it a more desirable target. Here we used an in silico approach to screen and develop a selective inhibitor of PP5. Compound P053 is a competitive inhibitor of PP5 that binds to its catalytic domain and causes apoptosis in renal cancer. We further demonstrated that PP5 interacts with FADD, RIPK1, and caspase 8, components of the extrinsic apoptotic pathway complex II. Specifically, PP5 dephosphorylates and inactivates the death effector protein FADD, preserving complex II integrity and regulating extrinsic apoptosis. Our data suggests that PP5 promotes renal cancer survival by suppressing the extrinsic apoptotic pathway. Pharmacologic inhibition of PP5 activates this pathway, presenting a viable therapeutic strategy for renal cancer.

Fibronectin Promotes Cell Growth and Migration in Human Renal Cell Carcinoma Cells

The prognostic and therapeutic values of fibronectin have been reported in patients with renal cell carcinoma (RCC). However, the underlying mechanisms of malignancy in RCC are not completely understood. We found that silencing of fibronectin expression attenuated human RCC 786-O and Caki-1 cell growth and migration. Silencing of potential fibronectin receptor integrin α5 and integrin β1 decreased 786-O cell ability in movement and chemotactic migration. Biochemical examination revealed a reduction of cyclin D1 and vimentin expression, transforming growth factor-β1 (TGF-β1) production, as well as Src and Smad phosphorylation in fibronectin-silenced 786-O and Caki-1 cells. Pharmacological inhibition of Src decreased 786-O cell growth and migration accompanied by a reduction of cyclin D1, fibronectin, vimentin, and TGF-β1 expression, as well as Src and Smad phosphorylation. In 786-O cells, higher activities in cell growth and migration than in Caki-1 cells were noted, along with elevated fibronectin and TGF-β1 expression. The additions of exogenous fibronectin and TGF-β1 promoted Caki-1 cell growth and migration, and increased cyclin D1, fibronectin, vimentin, and TGF-β1 expression, as well as Src and Smad phosphorylation. These findings highlight the role of fibronectin in RCC cell growth and migration involving Src and TGF-β1 signaling.

Aberrant expressions of miRNA-206 target, FN1, in multifactorial Hirschsprung disease

Background

MicroRNAs (miRNAs) have been associated with the Hirschsprung disease (HSCR) pathogenesis, however, the findings are still inconclusive. We aimed to investigate the effect of miRNA-206 and its targets, fibronectin 1 (FN1), serum deprivation response (SDPR), and paired box 3 (PAX3) expressions on multifactorial HSCR in Indonesia, a genetically distinct group within Asia.

Methods

We determined the miRNA-206, FN1, SDPR and PAX3 expressions in both the ganglionic and aganglionic colon of HSCR patients and control colon by quantitative real-time polymerase chain reaction (qRT-PCR).

Results

Twenty-one sporadic HSCR patients and thirteen controls were ascertained in this study. The miRNA-206 expression was up-regulated (2-fold) in the ganglionic colon and down-regulated (0.5-fold) in the aganglionic colon compared to the control group (ΔC_T 12.4 ± 3.0 vs. 14.1 ± 3.9 vs. 13.1 ± 2.7), but these differences did not reach significant levels (p = 0.48 and p = 0.46, respectively). Interestingly, the FN1 expression was significantly increased in both the ganglionic (38-fold) and aganglionic colon (18-fold) groups compared to the control group ΔC_T 5.7 ± 3.0 vs. 6.8 ± 2.3 vs. 11.0 ± 5.0; p = 0.001 and p = 0.038, respectively). Furthermore, the expressions of SDPR were similar in the ganglionic, aganglionic and control colon groups (ΔC_T 2.4 ± 0.6 vs. 2.2 ± 0.4 vs. 2.1 ± 0.6; p = 0.16 and p = 0.39, respectively), while no change was observed in the PAX3 expression between the ganglionic, aganglionic, and control colon groups (ΔC_T 3.8 ± 0.8 vs. 4.1 ± 0.8 vs. 3.7 ± 1.1; p = 0.83 and p = 0.44, respectively).

Conclusion

Our study is the first report of aberrant FN1 expressions in the colon of patients with HSCR and supplies further insights into the contribution of aberrant FN1 expression in the HSCR pathogenesis.

Bilateral Pheochromocytomas in a Patient with Y175C Von Hippel-Lindau Mutation

Von Hippel-Lindau (VHL) disease, caused by germline mutations in the VHL gene, is characterized by metachronously occurring tumors including pheochromocytoma, renal cell carcinoma (RCC), and hemangioblastoma. Although VHL disease leads to reduced life expectancy, its diagnosis is often missed and tumor screening guidelines are sparse. VHL protein acts as a tumor suppressor by targeting hypoxia-inducible factors (HIFs) for degradation through an oxygen-dependent mechanism. VHL mutants with more severely reduced HIF degrading function carry a high risk of RCC, while mutants with preserved HIF degrading capacity do not cause RCC but still lead to other tumors. VHL disease is classified into clinical types (1 and 2A-2C) based on this genotype-phenotype relationship. We report a case of bilateral pheochromocytomas and no other VHL-related tumors in a patient with Y175C VHL and show that this mutant preserves the ability to degrade HIF in normal oxygen conditions but, similar to the wild-type VHL protein, loses its ability to degrade HIF under hypoxic conditions. This study adds to the current understanding of the structure-function relationship of VHL mutations, which is important for risk stratification of future tumor development in the patients.

VHL-dependent alterations in the secretome of renal cell carcinoma: Association with immune cell response?

Secreted proteins could modulate the interaction between tumor, stroma and immune cells within the tumor microenvironment thereby mounting an immunosuppressive tumor microenvironment. In order to determine the secretome-mediated, von Hippel Lindau (VHL)-regulated cross-talk between tumor cells and T lymphocytes peripheral blood mononuclear cells (PBMC) from healthy donors were either cultured in conditioned media obtained from normoxic and hypoxic human VHL-deficient renal cell carcinoma (RCC) cell line (786-0^VHL−) and its wild type (wt) VHL-transfected counterpart (786-0^VHL+) or directly co-cultured with both cell lines. An increased T cell proliferation was detected in the presence of 786-0^VHL+-conditioned medium. By applying a quantitative proteomic-based approach using differential gel electrophoresis followed by mass spectrometry fourteen proteins were identified to be differentially expressed within the secretome of 786-0^VHL− cells when compared to that of 786-0^VHL+ cells. All proteins identified were involved in multiple tumor-associated biological functions including immune responses. Functional studies on manganese superoxide dismutase 2 (MnSOD2) demonstrated that it was a regulator of T cell activation-induced oxidative signaling and cell death. Direct effects of soluble MnSOD2 on the growth properties and interleukin 2 (IL-2) secretion of T cells could be demonstrated underlining the critical role of extracellular MnSOD2 levels for T cell proliferation and activation.

Towards a new classification of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) constitute a heterogeneous group of tumours associated with variable clinical presentations, growth rates, and prognoses. To improve the management of GEP-NENs, the WHO developed a classification system that enables tumours to be graded based on markers of cell proliferation in biopsy specimens. Indeed, histopathology has been a mainstay in the diagnosis of GEP-NENs, and the WHO grading system facilitates therapeutic decision-making; however, considerable intratumoural heterogeneity, predominantly comprising regional variations in proliferation rates, complicates the evaluation of tumour biology. The use of molecular imaging modalities to delineate the most-aggressive cell populations is becoming more widespread. In addition, molecular profiling is increasingly undertaken in the clinical setting, and genomic studies have revealed a number of chromosomal alterations in GEP-NENs, although the 'drivers' of neoplastic development have not been identified. Thus, our molecular understanding of GEP-NENs remains insufficient to inform on patient prognosis or selection for treatments, and the WHO classification continues to form the basis for management of this disease. Nevertheless, our increasing understanding of the molecular genetics and biology of GEP-NENs has begun to expose flaws in the WHO classification. We describe the current understanding of the molecular characteristics of GEP-NENs, and discuss how advances in molecular profiling measurements, including assays of circulating mRNAs, are likely to influence the management of these tumours.

Decoding the Molecular and Mutational Ambiguities of Gastroenteropancreatic Neuroendocrine Neoplasm Pathobiology

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN), considered a heterogeneous neoplasia, exhibit ill-defined pathobiology and protean symptomatology and are ubiquitous in location. They are difficult to diagnose, challenging to manage, and outcome depends on cell type, secretory product, histopathologic grading, and organ of origin. A morphologic and molecular genomic review of these lesions highlights tumor characteristics that can be used clinically, such as somatostatin-receptor expression, and confirms features that set them outside the standard neoplasia paradigm. Their unique pathobiology is useful for developing diagnostics using somatostatin-receptor targeted imaging or uptake of radiolabeled amino acids specific to secretory products or metabolism. Therapy has evolved via targeting of protein kinase B signaling or somatostatin receptors with drugs or isotopes (peptide-receptor radiotherapy). With DNA sequencing, rarely identified activating mutations confirm that tumor suppressor genes are relevant. Genomic approaches focusing on cancer-associated genes and signaling pathways likely will remain uninformative. Their uniquely dissimilar molecular profiles mean individual tumors are unlikely to be easily or uniformly targeted by therapeutics currently linked to standard cancer genetic paradigms. The prevalence of menin mutations in pancreatic NEN and P27^KIP1 mutations in small intestinal NEN represents initial steps to identifying a regulatory commonality in GEP-NEN. Transcriptional profiling and network-based analyses may define the cellular toolkit. Multianalyte diagnostic tools facilitate more accurate molecular pathologic delineations of NEN for assessing prognosis and identifying strategies for individualized patient treatment. GEP-NEN remain unique, poorly understood entities, and insight into their pathobiology and molecular mechanisms of growth and metastasis will help identify the diagnostic and therapeutic weaknesses of this neoplasia.

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.

Low VHL mRNA expression is associated with more aggressive tumor features of papillary thyroid carcinoma

Alterations of the von Hippel–Lindau (VHL) tumor suppressor gene can cause different hereditary tumors associated with VHL syndrome, but the potential role of the VHL gene in papillary thyroid carcinoma (PTC) has not been characterized. This study set out to investigate the relationship of VHL expression level with clinicopathological features of PTC in an ethnically and geographically homogenous group of 264 patients from Serbia, for the first time. Multivariate logistic regression analysis showed a strong correlation between low level of VHL expression and advanced clinical stage (OR = 5.78, 95% CI 3.17–10.53, P<0.0001), classical papillary morphology of the tumor (OR = 2.92, 95% CI 1.33–6.44, P = 0.008) and multifocality (OR = 1.96, 95% CI 1.06–3.62, P = 0.031). In disease-free survival analysis, low VHL expression had marginal significance (P = 0.0502 by the log-rank test) but did not appear to be an independent predictor of the risk for chance of faster recurrence in a proportion hazards model. No somatic mutations or evidence of VHL downregulation via promoter hypermethylation in PTC were found. The results indicate that the decrease of VHL expression associates with tumor progression but the mechanism of downregulation remains to be elucidated.

Genomics and epigenomics of clear cell renal cell carcinoma: recent developments and potential applications

Majority of clear cell renal cell carcinomas (ccRCCs) are diagnosed in the advanced metastatic stage resulting in dramatic decrease of patient survival. Thereby, early detection and monitoring of the disease may improve prognosis and treatment results. Recent technological advances enable the identification of genetic events associated with ccRCC and reveal significant molecular heterogeneity of ccRCC tumors. This review summarizes recent findings in ccRCC genomics and epigenomics derived from chromosomal aberrations, DNA sequencing and methylation, mRNA, miRNA expression profiling experiments. We provide a molecular insight into ccRCC pathology and recapitulate possible clinical applications of genomic alterations as predictive and prognostic biomarkers.

K63-ubiquitylation of VHL by SOCS1 mediates DNA double-strand break repair

DNA repair is essential for maintaining genomic stability, and defects in this process significantly increase the risk of cancer. Clear-cell renal cell carcinoma (CCRCC) caused by inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene is characterized by high genomic instability. However, the molecular mechanism underlying the association between the loss of VHL and genomic instability remains unclear. Here, we show that suppressor of cytokine signaling 1 (SOCS1) promotes nuclear redistribution and K63-ubiquitylation of VHL in response to DNA double-strand breaks (DSBs). Loss of VHL or VHL mutations that compromise its K63-ubiquitylation attenuates the DNA-damage response (DDR), resulting in decreased homologous recombination repair and persistence of DSBs. These results identify VHL as a component of the DDR network, inactivation of which contributes to the genomic instability associated with CCRCC.

The protein tyrosine phosphatase receptor type J is regulated by the pVHL-HIF axis in clear cell renal cell carcinoma

Mass spectrometry analysis of renal cancer cell lines recently suggested that the protein-tyrosine phosphatase receptor type J (PTPRJ), an important regulator of tyrosine kinase receptors, is tightly linked to the von Hippel-Lindau protein (pVHL). Therefore, we aimed to characterize the biological relevance of PTPRJ for clear cell renal cell carcinoma (ccRCC). In pVHL-negative ccRCC cell lines, both RNA and protein expression levels of PTPRJ were lower than those in the corresponding pVHL reconstituted cells. Quantitative RT-PCR and western blot analysis of ccRCC with known VHL mutation status and normal matched tissues as well as RNA in situ hybridization on a tissue microarray (TMA) confirmed a decrease of PTPRJ expression in more than 80% of ccRCCs, but in only 12% of papillary RCCs. ccRCC patients with no or reduced PTPRJ mRNA expression had a less favourable outcome than those with a normal expression status (p = 0.05). Sequence analysis of 32 PTPRJ mRNA-negative ccRCC samples showed five known polymorphisms but no mutations, implying other mechanisms leading to PTPRJ's down-regulation. Selective silencing of HIF-α by siRNA and reporter gene assays demonstrated that pVHL inactivation reduces PTPRJ expression through a HIF-dependent mechanism, which is mainly driven by HIF-2α stabilization. Our results suggest PTPRJ as a member of a pVHL-controlled pathway whose suppression by HIF is critical for ccRCC development.

The p53 inhibitor pifithrin-α can stimulate fibrosis in a rat model of ischemic acute kidney injury

Inhibition of the tumor suppressor p53 diminishes tubular cell apoptosis and protects renal function in animal models of acute kidney injury (AKI). Therefore, targeting p53 has become an attractive therapeutic strategy in the approach to AKI. Although the acute protective effects of p53 inhibition in AKI have been examined, there is still relatively little known regarding the impact of acute p53 inhibition on the chronic sequelae of AKI. Consequently, we utilized the p53 inhibitor pifithrin-α to examine the long-term effects of p53 inhibition in a rodent model of ischemic AKI. Male Sprague-Dawley rats were subjected to bilateral renal artery clamping for 30 min followed by reperfusion for up to 8 wk. Pifithrin-α or vehicle control was administered at the time of surgery and then daily for 2 days [brief acute administration (BA)] or 7 days [prolonged acute administration (PA)]. Despite the acute protective effect of pifithrin-α in models of ischemic AKI, we found no protection in the microvascular rarefaction at 4 wk or development fibrosis at 8 wk with pifithrin-α administered on the BA schedule compared with vehicle control-treated animals. Furthermore, pifithrin-α administered on a PA schedule actually produced worse fibrosis compared with vehicle control animals after ischemic injury [21%/area (SD4.4) vs.16%/area (SD3.6)] as well as under sham conditions [2.6%/area (SD1.8) vs. 4.7%/area (SD1.3)]. The development of fibrosis with PA administration was independent of microvascular rarefaction. We identified enhanced extracellular matrix production, epithelial-to-mesenchymal transition, and amplified inflammatory responses as potential contributors to the augmented fibrosis observed with PA administration of pifithrin-α.

Molecular targeted therapy in advanced renal cell carcinoma: A review of its recent past and a glimpse into the near future

Renal cell carcinoma (RCC) is the most lethal of all urologic malignancies. Recent translational research in RCC has led to the discovery of a new class of therapeutics that specifically target important signaling molecules critical in the pathogenesis of the disease. It is now clear that these new molecular targeted agents have revolutionized the management of patients with metastatic RCC. However, the exact molecular mechanism accounting for their clinical effect is largely unknown and a significant proportion of patients with metastatic RCC do not respond to these therapeutics. This review presents the relevant background leading to the development of molecular targeted therapy for patients with advanced RCC and summarizes current management issues in particular relating to the emerging problem of treatment resistance and the need for clinical and laboratory biomarkers to predict treatment outcomes in these patients. In addition, this paper will also address surgical issues in the era of molecular targeted therapy including the role of cytoreductive surgery and surgical safety issues post-molecular therapy. Lastly, this review will also address the need to explore new molecular treatment targets in RCC and briefly present our work on one of the promising molecular targets - the type 1 insulin-like growth factor receptor (IGF1R), which may in the near future lead to the development of anti-IGF1R therapy for patients with advanced RCC.

von Hippel-Lindau protein adjusts oxygen sensing of the FIH asparaginyl hydroxylase

Hypoxia inevitably develops in rapidly growing tumors and acts as an important microenvironment that forces changes in tumor behavior. Hypoxia-inducible factor 1α (HIF-1α) is activated during hypoxia and promotes the progression of malignancy by stimulating angiogenesis and by augmenting the ability of tumors to survive. In aerobic conditions, HIF-1α is destabilized by the PHD prolyl-hydroxylases that target HIF-1α for proteolysis via the von Hippel-Lindau protein (pVHL) and further inactivated by the FIH asparaginyl-hydroxylase that precludes the recruitment of transcription coactivators. Although HIF-1α degradation is well understood, little is known about how its transcriptional activity increases gradually in response to decreasing oxygen. In particular, it has been questioned how FIH having a high affinity for oxygen regulates the HIF-1α activity in moderate hypoxia. We here found that the HIF-1α-FIH interaction is disrupted in 1-5% oxygen. Both in vitro and in vivo binding analyses revealed that pVHL acts as an adaptor for FIH to bind HIF-1α. Furthermore, because the pVHL-FIH interaction depends on oxygen tension, the FIH-mediated inactivation of HIF-1α can be exquisitely regulated according to the severity of hypoxia. Based on these findings, we propose that pVHL fine-tunes the transcriptional activity of HIF-1α in graded oxygen tensions.

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.

von Hippel-Lindau tumor suppressor mutants faithfully model pathological hypoxia-driven angiogenesis and vascular retinopathies in zebrafish

Biallelic inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene predisposes human patients to the development of highly vascularized neoplasms in multiple organ systems. We show that zebrafish vhl mutants display a marked increase in blood vessel formation throughout the embryo, starting at 2 days post-fertilization. The most severe neovascularization is observed in distinct areas that overlap with high vegfa mRNA expression, including the vhl mutant brain and eye. Real-time quantitative PCR revealed increased expression of the duplicated VEGFA orthologs vegfaa and vegfab, and of vegfb and its receptors flt1, kdr and kdr-like, indicating increased vascular endothelial growth factor (Vegf) signaling in vhl mutants. Similar to VHL-associated retinal neoplasms, diabetic retinopathy and age-related macular degeneration, we show, by tetramethyl rhodamine-dextran angiography, that vascular abnormalities in the vhl−/− retina lead to vascular leakage, severe macular edema and retinal detachment. Significantly, vessels in the brain and eye express cxcr4a, a marker gene expressed by tumor and vascular cells in VHL-associated hemangioblastomas and renal cell carcinomas. VEGF receptor (VEGFR) tyrosine kinase inhibition (through exposure to sunitinib and 676475) blocked vhl−/−-induced angiogenesis in all affected tissues, demonstrating that Vegfaa, Vegfab and Vegfb are key effectors of the vhl−/− angiogenic phenotype through Flt1, Kdr and Kdr-like signaling. Since we show that the vhl−/− angiogenic phenotype shares distinct characteristics with VHL-associated vascular neoplasms, zebrafish vhl mutants provide a valuable in vivo vertebrate model to elucidate underlying mechanisms contributing to the development of these lesions. Furthermore, vhl mutant zebrafish embryos carrying blood vessel-specific transgenes represent a unique and clinically relevant model for tissue-specific, hypoxia-induced pathological angiogenesis and vascular retinopathies. Importantly, they will allow for a cost-effective, non-invasive and efficient way to screen for novel pharmacological agents and combinatorial treatments.

Human nephrosclerosis triggers a hypoxia-related glomerulopathy

In the kidney, hypoxia contributes to tubulointerstitial fibrosis, but little is known about its implications for glomerular damage and glomerulosclerosis. Chronic hypoxia was hypothesized to be involved in nephrosclerosis (NSC) or "hypertensive nephropathy." In the present study genome-wide expression data from microdissected glomeruli were studied to examine the role of hypoxia in glomerulosclerosis of human NSC. Functional annotation analysis revealed prominent regulation of hypoxia-associated biological processes in NSC, including angiogenesis, fibrosis, and inflammation. Glomerular expression levels of a majority of genes regulated by the hypoxia-inducible factors (HIFs) were significantly altered in NSC. Among these HIF targets, chemokine C-X-C motif receptor 4 (CXCR4) was prominently induced. Glomerular CXCR4 mRNA induction was confirmed by quantitative RT-PCR in an independent cohort with NSC but not in those with other glomerulopathies. By immunohistological analysis, CXCR4 showed enhanced positivity in podocytes in NSC biopsy specimens. This CXCR4 positivity was associated with nuclear localization of HIF1alpha only in podocytes of NSC, indicating transcriptional activity of HIF. As the CXCR4 ligand CXCL12/SDF-1 is constitutively expressed in podocytes, autocrine signaling may contribute to NSC. In addition, a blocking CXCR4 antibody caused significant inhibition of wound closure by podocytes in an in vitro scratch assay. These data support a role for CXCR4/CXCL12 in human NSC and indicate that hypoxia not only is involved in tubulointerstitial fibrosis but also contributes to glomerular damage in NSC.

Differences in regulation of tight junctions and cell morphology between VHL mutations from disease subtypes

Background

In von Hippel-Lindau (VHL) disease, germline mutations in the VHL tumor suppressor gene cause clear cell renal carcinomas, hemangioblastomas, and pheochromocytomas. The VHL gene product is part of an ubiquitin E3 ligase complex and hypoxia-inducible factor alpha (HIF-α) is a key substrate, although additional VHL functions have been described. A genotype-phenotype relationship exists in VHL disease such that specific VHL mutations elicit certain subsets of these tumors. Here, we examine VHL genotype-phenotype correlations at the cellular level, focusing on the regulation of tight junctions and cell morphology.

Methods

Wild-type and various mutant VHL proteins representing VHL disease subtypes were stably expressed in 3 VHL-negative renal carcinoma cell lines. Using these cell lines, the roles of various VHL-associated cellular functions in regulation of cell morphology were investigated.

Results

As a whole, type 1 mutants varied greatly from type 2 mutants, demonstrating high levels of HIF-2α, cyclin D1 and α5 integrin, lower p27 levels, and a spindly, fibroblastic cellular appearance. Type 2 mutations demonstrated an epithelial morphology similar to wild-type VHL in the majority of the renal cell lines used. Knockdown of p27 in cells with wild-type VHL led to perturbations of both epithelial morphology and ZO-1 localization to tight junctions. ZO-1 localization correlated well with VHL disease subtypes, with greater mislocalization observed for genotypes associated with a higher risk of renal carcinoma. HIF-2α knockdown in 786-O partially restored ZO-1 localization, but did not restore an epithelial morphology.

Conclusion

VHL has both HIF-α dependent and HIF-α independent functions in regulating tight junctions and cell morphology that likely impact the clinical phenotypes seen in VHL disease.

Zebrafish mutants in the von Hippel-Lindau tumor suppressor display a hypoxic response and recapitulate key aspects of Chuvash polycythemia

We have generated 2 zebrafish lines carrying inactivating germline mutations in the von Hippel-Lindau (VHL) tumor suppressor gene ortholog vhl. Mutant embryos display a general systemic hypoxic response, including the up-regulation of hypoxia-induced genes by 1 day after fertilization and a severe hyperventilation and cardiophysiologic response. The vhl mutants develop polycythemia with concomitantly increased epo/epor mRNA levels and erythropoietin signaling. In situ hybridizations reveal global up-regulation of both red and white hematopoietic lineages. Hematopoietic tissues are highly proliferative, with enlarged populations of c-myb(+) hematopoietic stem cells and circulating erythroid precursors. Chemical activation of hypoxia-inducible factor signaling recapitulated aspects of the vhl(-/-) phenotype. Furthermore, microarray expression analysis confirms the hypoxic response and hematopoietic phenotype observed in vhl(-/-) embryos. We conclude that VHL participates in regulating hematopoiesis and erythroid differentiation. Injections with human VHLp30 and R200W mutant mRNA demonstrate functional conservation of VHL between mammals and zebrafish at the amino acid level, indicating that vhl mutants are a powerful new tool to study genotype-phenotype correlations in human disease. Zebrafish vhl mutants are the first congenital embryonic viable systemic vertebrate animal model for VHL, representing the most accurate model for VHL-associated polycythemia to date. They will contribute to our understanding of hypoxic signaling, hematopoiesis, and VHL-associated disease progression.

Inadequate activation of the GTPase RhoA contributes to the lack of fibronectin matrix assembly in von Hippel-Lindau protein-defective renal cancer cells

The von Hippel-Lindau (VHL) tumor suppressor gene regulates extracellular matrix deposition. In VHL negative renal cancer cells, VHL(-), the lack of fibronectin matrix assembly is thought to promote and maintain tumor angiogenesis allowing vessels to infiltrate tumors. Therefore, and considering the importance of this process in tumor growth, we aimed to study why VHL(-) renal cancer cells fail to form a proper extracellular matrix. Our results showed that VHL(-) cells were not defective in fibronectin production and that the fibronectin produced by these cells was equally functional in promoting cell adhesion and matrix assembly as that produced by VHL+ cells. We have previously reported that VHL(-) cells fail to form beta1 integrin fibrillar adhesions and have a diminished organization of actin stress fibers; therefore, we aimed to study if the small GTPase family is involved in this process. We found that activation of the RhoA GTPase was defective in VHL(-) cells, and this was possibly mediated by an increased activation of its inhibitor, p190RhoGAP. Additionally, the expression of constitutively active RhoA in VHL(-) cells resulted in formation of a fibronectin matrix. These results strongly suggest an important role for RhoA in some of the defects observed in renal cancer cells.

Downregulation of integrins by von Hippel-Lindau (VHL) tumor suppressor protein is independent of VHL-directed hypoxia-inducible factor alpha degradation

Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene occurs in the majority of clear-cell renal cell carcinomas (RCCs). It was previously shown that VHL decreased the abundance of integrins alpha2, alpha5, and beta1, which is consistent with VHL-associated changes in cell-cell and cell - extracellular matrix adhesions. We investigated the mechanism by which VHL downregulates integrins. Although VHL can target hypoxia-inducible factor alpha (HIFalpha) subunits for degradation, VHL-dependent reduction of integrins was independent of O2 concentration and HIFalpha levels. VHL reduced the half-lives of integrins, and this activity was blocked by proteasomal inhibition. Although ectopically expressed FLAG-VHL retained HIFalpha degradation activity, it neither downregulated integrins nor promoted adherens and tight intercellular junctions, in contrast to expressed wild-type VHL. Moreover, integrins co-immunoprecipitated with wild-type VHL, but not FLAG-VHL. These data indicate that the downregulation of integrins by VHL is distinct from the regulation of HIFalpha subunits by VHL, and suggests that the loss of this activity contributes to VHL-associated RCC development through disruption of adherens and tight junctions.

Two novel VHL targets, TGFBI (BIGH3) and its transactivator KLF10, are up-regulated in renal clear cell carcinoma and other tumors

Mutations in the VHL gene are associated with highly vascular tumors of kidney, brain, retina, and adrenal gland. The inability of the mutant VHL protein to destabilize HIF-1 plays a crucial role in malignant angiogenesis. VHL is also associated with ECM assembly but the molecular mechanisms of this activity remain unclear. We used expression arrays and cell lines with different VHL status to identify ECM-associated genes controlled by VHL. One of them, adhesion-associated TGFBI, was repressed by VHL and overexpressed in renal, gastrointestinal, brain, and other tumors. Analyzing the mechanism of TGFBI up-regulation in clear cell carcinoma, we identified a novel VHL target, a Kruppel-like transcriptional factor 10 (KLF10). The TGFBI promoter, which we isolated and studied in Luc-reporter assay, was induced by KLF10 but not hypoxia. These data provide the molecular basis for the observed VHL effect on TGFBI and stimulate further research into the KLF10 and TGFBI roles in cancer.

Ser80Ile mutation and a concurrent Pro25Leu variant of the VHL gene in an extended Hungarian von Hippel-Lindau family

Von Hippel-Lindau disease (VHL) is a rare autosomal dominant disease characterized by development of cystic and tumorous lesions at multiple sites, including the brain, spinal cord, kidneys, adrenals, pancreas, epididymis and eyes. The clinical phenotype results from molecular abnormalities of the VHL tumor suppressor gene, mapped to human chromosome 3p25-26. The VHL gene encodes two functionally active VHL proteins due to the presence of two translational initiation sites separated by 53 codons. The majority of disease-causing mutations have been detected downstream of the second translational initiation site, but there are conflicting data as to whether few mutations located in the first 53 codons, such as the Pro25Leu could have a pathogenic role. In this paper we report a large Hungarian VHL type 2 family consisting of 32 members in whom a disease-causing AGT80AAT (Ser80Ile) c.239G>A, p.Ser80Ile mutation, but not the concurrent CCT25CTT (Pro25Leu) c.74C>T, p.Pro25Leu variant co-segregated with the disease. To our knowledge, the Ser80Ile mutation has not been previously described in VHL type 2 patients with high risk of pheochromocytoma and renal cell cancer. Therefore, this finding represents a novel genotype-phenotype association and VHL kindreds with Ser80Ile mutation will require careful surveillance for pheochromocytoma. We concluded that the Pro25Leu variant is a rare, neutral variant, but the presence such a rare gene variant may make genetic counseling difficult.

Loss of PL6 protein expression in renal clear cell carcinomas and other VHL-deficient tumours

Mutations in the von Hippel-Lindau tumour suppressor gene (VHL) cause the VHL hereditary cancer syndrome and occur in most sporadic clear cell renal cell cancers (CC-RCCs). The mechanisms by which VHL loss of function promotes tumour development in the kidney are not fully elucidated. Here, we analyse expression of PL6, one of the potential tumour suppressor genes from the critical 3p21.3 region involved in multiple common cancers. We classify PL6 as a Golgi-resident protein based on its perinuclear co-localization with GPP130 in all cells and tissues analysed. We show that PL6 RNA and protein expression is completely or partially lost in all analysed CC-RCCs and other VHL-deficient tumours studied, including the early precancerous lesions in VHL disease. The restoration of VHL function in vitro in the VHL-deficient CC-RCC cell lines was found to reinstate PL6 expression, thus establishing a direct link between VHL and PL6. Insensitivity of PL6 to hypoxia suggested that PL6 is regulated by VHL via a HIF-1-independent pathway. We ruled out mutations and promoter methylation as possible causes of PL6 down-regulation in CC-RCC. We hypothesize that loss of a putative PL6 secretory function due to VHL deficiency is an early and important event that may promote tumour initiation and growth.

Over expression of insulin-like growth factor binding protein 3 in clear cell renal cell carcinoma

PURPOSE

We recently reported that IGFBP-3 (insulin-like growth factor binding protein 3) is one of the top genes that are over expressed in clear cell renal cell carcinoma. We further investigated IGFBP-3 expression in renal tumors using gene expression microarrays, immunohistochemistry and Western blotting.

MATERIALS AND METHODS

A total of 70 renal neoplasms were subjected to gene expression microarrays using gene chips containing 21,632 cDNA clones. IGFBP-3 expression was measured in each renal epithelial neoplasm. In addition, we performed immunohistochemistry for IGFBP-3 in 127 renal epithelial tumors, including 58 clear cell renal cell carcinomas. Moreover, IGFBP-3 staining intensity was evaluated to determine whether there was a correlation with Fuhrman grade. Lastly, Western blot was performed to confirm IGFBP-3 levels.

RESULTS

On microarray analysis of 70 renal neoplasms IGFBP-3 mRNA was increased in 63% of clear cell renal cell carcinomas (27 of 43) but in only 4% of other renal tumors (1 of 24). On immunohistochemistry 74% of clear cell renal cell carcinomas (43 of 58) showed IGFBP-3 immunoreactivity compared to only 9% of other renal neoplasms (6 of 69). High grade (Fuhrman grades 3 and 4) clear cell renal cell carcinomas showed higher IGFBP-3 staining intensity than low grade ones (15 of 17 vs 8 of 41). Western blot confirmed immunohistochemistry findings with the detection of high IGFBP-3 in clear cell renal cell carcinoma but not in other types of kidney tumors.

CONCLUSIONS

With a combination of cDNA microarrays, Western blot and immunohistochemistry we confirmed that IGFBP-3 is a marker for clear cell renal cell carcinoma. Furthermore, higher IGFBP-3 expression was associated with higher Fuhrman grade.

Hypoxia-inducible factors and cancer

Decreased oxygen availability is a common feature during embryonic development as well of malignant tumours. Hypoxia regulates many transcription factors, and one of the most studied is the hypoxia-inducible factor (HIF). As a consequence of HIF stabilisation, the cell constitutively upregulates the hypoxic programme resulting in the expression of genes responsible for global changes in cell proliferation, angiogenesis, metastasis, invasion, de-differentiation and energy metabolism. Of the three known alpha subunits of HIF transcription factors, HIF-1alpha and HIF-2alpha have been the most studied. Their differential expression and function have been widely discussed, however no clear picture has been drawn on how these two transcription factors differently regulate common and unique target genes. Their role as oncogenes has also been suggested in several studies. In this review we provide an overview of the current knowledge on some of the most important aspects of HIFalpha regulation, its role in tumour angiogenesis and energetic metabolism. We also give an overview of how the modulation of HIF regulating pathways is a potential therapeutic target that may have benefits in the treatment of cancer.

Overexpression of von Hippel-Lindau tumor suppressor protein and antisense HIF-1alpha eradicates gliomas

The von Hippel-Lindau tumor suppressor protein (pVHL) suppresses tumor formation by binding the alpha subunits of hypoxia-inducible-factors responsible for stimulating tumor angiogenesis and glycolysis, and targeting them for ubiquitination and proteasomal destruction. Loss of pVHL leads to tumorigenesis and development of sporadic renal cell carcinomas and central nervous system hemangioblastomas. In the present study, we investigated whether engineered overexpression of pVHL in C6 glioma cells, which already express endogenous pVHL, would suppress the tumorigenicity of this particular tumor cell type. C6 cells overexpressing VHL displayed a reduced growth rate (70% inhibition) compared to the parental cell line when subcutaneously implanted in athymic (nu/nu) mice. Growth inhibition was associated with a 50% reduction in the number of tumor vessels and a 60% increase in tumor cell apoptosis, due in part to downregulation of HIF-1, VEGF, and the antiapoptotic factor Bcl-2, respectively. Gene transfer of VHL suppressed the growth of established C6 gliomas, and synergized with antisense HIF-1 to completely eradicate tumors. The data suggest that VHL gene therapy and/or agents that increase VHL expression could have utility in the treatment of gliomas, particularly when combined with agents that inhibit the expression or function of HIF-1.

Tumor cell invasion of von Hippel Lindau renal cell carcinoma cells is mediated by membrane type-1 matrix metalloproteinase

Background

Metastatic renal cell carcinoma (RCC) remains the leading cause of mortality in patients with clear cell RCC arising from mutations in the von Hippel Lindau (VHL) tumor suppressor. Successful RCC tumor suppression by VHL requires the negative regulation of hypoxia inducible factor alpha (HIF alpha) protein and its downstream targets. Thus, identification of HIF target genes responsible for RCC tumor progression will aid in the development of therapies for this disease. We previously identified membrane type-1 matrix metalloproteinase (MT1-MMP) as a transcriptional target of HIF-2alpha in RCC cells null for VHL and showed that MT1-MMP is overexpressed in these cells. MT1-MMP is a key regulator of tumor progression through its functions as a matrix-degrading enzyme, as well as its ability to cleave factors, such as adhesion molecules and other MMPs. The aim of this study was to investigate the contribution of MT1-MMP to the invasive potential of RCC cells using in vitro type I collagen degradation and invasion assays.

Results

We evaluated RCC cells wild-type (WT8) and null (pRc-9) for VHL for invasive characteristics and showed that the pRc-9 cells demonstrated a greater propensity for both invasion and degradation of a type I collagen matrix. Furthermore, overexpression of either HIF-2alpha or MT1-MMP in the poorly invasive cell line, WT8, promoted collagen degradation and invasion of these cells. Finally, using RNAi, we show that inhibition of MT1-MMP suppresses tumor cell invasion of RCC cells.

Conclusion

Our results suggest that MT1-MMP is a major mediator of tumor cell invasiveness and type I collagen degradation by VHL RCC cells that express either MT1-MMP or HIF-2alpha. As such, MT1-MMP may represent a novel target for anti-invasion therapy for this disease.

Physiological oxygenation status is required for fully differentiated phenotype in kidney cortex proximal tubules

Hypoxia has been suspected to trigger transdifferentiation of renal tubular cells into myofibroblasts in an epithelial-to-mesenchymal transition (EMT) process. To determine the functional networks potentially altered by hypoxia, rat renal tubule suspensions were incubated under three conditions of oxygenation ranging from normoxia (lactate uptake) to severe hypoxia (lactate production). Transcriptome changes after 4 h were analyzed on a high scale by restriction fragment differential display. Among 1,533 transcripts found, 42% were maximally expressed under severe hypoxia and 8% under mild hypoxia (Po2 = 48 mmHg), suggesting two different levels of oxygen sensing. Normoxia was required for full expression of the proximal tubule-specific transcripts 25-hydroxyvitamin D 1-hydroxylase ( Cyp27b1) and l-pyruvate kinase ( Pklr), transcripts involved in tissue cohesion such as fibronectin ( Fn1) and N-cadherin ( Cdh2), and non-muscle-type myosin transcripts. Mild hypoxia increased myogenin transcript level. Conversely, severe hypoxia increased transcripts involved in extracellular matrix remodeling, those of muscle-type myosins, and others involved in creatine phosphate synthesis and lactate transport ( Slc16a7). Accordingly, microscopy showed loss of tubule aggregation under hypoxia, without tubular disruption. Hypoxia also increased the levels of kidney-specific transcripts normally restricted to the less oxygenated medullary zone and others specific for the distal part of the nephron. We conclude that extensive oxygen supply to the kidney tubule favors expression of its differentiated functions specifically in the proximal tubule, whose embryonic origin is mesenchymal. The phenotype changes could potentially permit transient adaptation to hypoxia but also favor pathological processes such as tissue invasion.

Differential gene expression identifies subgroups of renal cell carcinoma

Clear cell carcinoma of the kidney, the most common subtype of renal cell cancer, displays different biological behavior in different patients. This heterogeneity cannot be recognized by light microscopy. In this study, gene expression in 16 clear cell renal cell carcinoma samples and 17 non-malignant tissue types comprising 539 samples was determined using oligonucleotide microarrays representing approximately 40,000 known genes and ESTs. Differences in gene expression were quantified as the fold change in gene expression between the various sets of samples. A set of genes was identified that was overexpressed in the renal cell carcinoma samples compared with the normal kidney samples. Principle component analysis of the set of renal cell carcinomas using this set of genes overexpressed in renal cell cancer revealed the existence of 2 major subgroups among the renal carcinomas. A series of principle component analyses of the set of renal cell carcinomas using different gene sets composed of genes involved in different metabolic pathways also revealed the same 2 major subgroups of the renal cell cancers. Eisen clustering using the same genes also revealed the same 2 major renal cell cancer subsets. Review of the pathology suggested that these 2 subgroups differed in pathologic grade. Genes differentially expressed between the 2 renal cell cancer subsets were identified. Examination of gene expression in each renal cell cancer subset and the pool of renal cell carcinoma samples compared with that in 17 different normal tissues revealed genes specifically overexpressed in renal cell cancer compared with these normal tissues. The authors conclude that gene expression patterns may be useful in helping to further classify subtypes of renal cell carcinoma that may have clinical significance. In addition, the genes identified as overexpressed in each set of clear cell renal cell carcinomas compared with normal tissues may represent useful targets for therapy.

Extracellular matrix alterations in conventional renal cell carcinomas by tissue microarray profiling influenced by the persistent, long-term, low-dose ionizing radiation exposure in humans

The present study was carried out in order to examine molecular alterations of extracellular matrix (ECM), associated with cell-cell communication in conventional (clear-cell) renal cell carcinomas (cRCCs) influenced by persistent long-term, low-dose ionizing radiation (IR) exposure to patients living more than 19 years after the Chernobyl accident in Cesium 137 (137Cs)-contaminated areas of Ukraine. The ECM major components such as fibronectin, laminin, E-cadherin/beta-catenin complexes and p53 tumor suppressor gene protein, and transforming growth factor beta 1 (TGF-beta1) were immunohistochemically (IHC) evaluated in cRCCs from 59 Ukrainian patients, which represented 18 patients living in non-contaminated areas and 41 patients from 137Cs-contaminated areas. In contrast, a control group of 19 Spanish patients with analogue tumors were also investigated. For IHC evaluation, a tissue microarray technique was used. Decrease or loss and abnormal distribution of fibronectin, laminin, E-cadherin/beta-catenin complexes accompanied by elevated levels of p53 and TGF-beta1 were detected in the Ukrainian cRCCs from 137Cs-contaminated areas with statistically significant differences. Thus, our study suggests that chronic long-term, low-dose IR exposure might result in global remodeling of ECM components of the cRCCs with disruption in peri-epithelial stroma and epithelial basement membranes.

von Hippel-Lindau Tumor Suppressor Protein Regulates the Assembly of Intercellular Junctions in Renal Cancer Cells through Hypoxia-Inducible Factor–Independent Mechanisms

Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene is responsible for the development of renal cell cancers (RCC), pheochromocytomas, and tumors in other organs. The best known function of VHL protein (VHL) is to target the hypoxia-inducible factor (HIF) for proteasome degradation. VHL is also required for the establishment of an epithelial-like cell shape in otherwise fibroblastic-like RCC cell lines. However, the underlying mechanisms and whether this is linked to HIF remain undetermined. Because the breakage of intercellular junctions induces a fibroblastic-like phenotype in multiple cancer cell models, we hypothesized that VHL may be required for the assembly of intercellular junctions in RCC cells. Our experiments showed that VHL in RCC cell lines is necessary for the normal organization of adherens and tight intercellular junctions, the maintenance of cell polarity, and control of paracellular permeability. Additionally, 786-O cells reconstituted with wild-type VHL and with a constitutively active form of HIF-2alpha did not reproduce any of the phenotypic alterations of VHL-negative cells. In summary, we show that VHL inactivation in RCC cells disrupts intercellular junctions and cell shape through HIF-independent events, supporting the concept that VHL has additional functions beside its role in the regulation of HIF.

Interplay between VHL/HIF1α and Wnt/β-catenin pathways during colorectal tumorigenesis

Activation of the Wnt signaling pathway initiates the transformation of colorectal epithelial cells, although the transition to metastatic cancer requires angiogenesis. We have investigated the expression of the von Hippel-Lindau (VHL) tumor suppressor in the intestines from humans and mice. Here, we show that VHL expression is regulated by TCF4 and is restricted to the proliferative compartment at the bottom of intestinal crypts. Accordingly, VHL is completely absent from the proliferative intestinal pockets of Tcf4(-/-) perinatal mice. We observed complementary staining of the hypoxia-inducible factor (HIF) 1alpha to VHL in normal intestinal epithelium as well as in all stages of colorectal cancer (CRC). To the best of our knowledge, this is the first report demonstrating the presence of nuclear HIF1alpha in normoxic healthy adult tissue. Although we observed upregulated levels of VHL in very early CRC lesions from sporadic and familial adenomatous polyposis patients - presumably due to activated Wnt signaling - a clear reduction of VHL expression is observed in later stages of CRC progression, coinciding with stabilization of HIF1alpha. As loss of VHL in later stages of CRC progression results in stabilization of HIF, these data provide evidence that selection for VHL downregulation provides a proangiogenic impulse for CRC progression.

Loss of the von Hippel Lindau Tumor Suppressor Disrupts Iron Homeostasis in Renal Carcinoma Cells

Given the modulation of iron metabolism by hypoxia and the high iron requirement of neoplastic cells, we investigated iron metabolism in a human renal cancer cell line with a mutated von Hippel Lindau (VHL) tumor suppressor gene (RCC10) and in a transfectant clone with wild-type VHL (RCC63). The loss of VHL strongly up-regulated transferrin receptor expression in RCC10 cells as a result of hypoxia inducible factor-1 (HIF-1)-mediated transcriptional activation, leading to an increased uptake of transferrin-bound 55Fe. Increased iron availability did not compromise the resistance of VHL-defective cells to oxidative stress or promote faster cell multiplication. Surprisingly, the content of ferritin H and L subunits and ferritin mRNA levels were considerably lower in the RCC10 than in the RCC63 cells. Despite the similarities between HIF-1 and iron regulatory protein 2 (IRP2), we found no evidence of specific regulation of IRP2 by VHL. However, both IRP2 and IRP1 were slightly activated in RCC10 cells, thus indicating that this cell line has a somewhat reduced labile iron pool (LIP). The finding that RCC10 cells had a lower ferritin content but more ferritin-associated 55Fe than RCC63 explains why VHL-lacking cells may have a smaller LIP despite increased iron uptake. We also found a correlation between cytoprotection from iron-mediated damage and efficient incorporation into ferritin of both transferrin and non-transferrin-bound 55Fe. This study shows that, like oncogene activation, the loss of an oncosuppressor rearranges the expression pattern of the genes of iron metabolism to increase iron availability. However, in the case of VHL loss, mechanisms affecting iron handling by ferritin somehow counteract the effects that the reduced content of this protective protein may have on proliferation and oxidant sensitivity.

Tumor Suppression by the von Hippel-Lindau Protein Requires Phosphorylation of the Acidic Domain

The tumor suppressor function of the von Hippel-Lindau protein (pVHL) has previously been linked to its role in regulating hypoxia-inducible factor levels. However, VHL gene mutations suggest a hypoxia-inducible factor-independent function for the N-terminal acidic domain in tumor suppression. Here, we report that phosphorylation of the N-terminal acidic domain of pVHL by casein kinase-2 is essential for its tumor suppressor function. This post-translational modification did not affect the levels of hypoxia-inducible factor; however, it did change the binding of pVHL to another known binding partner, fibronectin. Cells expressing phospho-defective mutants caused improper fibronectin matrix deposition and demonstrated retarded tumor formation in mice. We propose that phosphorylation of the acidic domain plays a role in the regulation of proper fibronectin matrix deposition and that this may be relevant for the development of VHL-associated malignancies.

Gene expression profiling of renal cell carcinoma

Renal cell carcinoma (RCC) is a histologically diverse disease, with variable and often unpredictable clinical behavior. The prognosis worsens dramatically with the onset of clinical metastasis, and current regimens of systemic therapy yield only modest benefits for metastatic RCC. Gene expression profiling is a promising technique for refining the diagnosis and staging of RCC, as well as for highlighting potential therapeutic targets. We review the recent advances in expression profiling of RCC and discuss the clinical and biological insights obtained from these studies.