VHL suppresses RAPTOR and inhibits mTORC1 signaling in clear cell renal cell carcinoma.

Inactivation of the tumor suppressor von Hippel-Lindau (VHL) gene is a key event in hereditary and sporadic clear cell renal cell carcinomas (ccRCC). The mechanistic target of rapamycin (mTOR) signaling pathway is a fundamental regulator of cell growth and proliferation, and hyperactivation of mTOR signaling is a common finding in VHL-dependent ccRCC. Deregulation of mTOR signaling correlates with tumor progression and poor outcome in patients with ccRCC. Here, we report that the regulatory-associated protein of mTOR (RAPTOR) is strikingly repressed by VHL. VHL interacts with RAPTOR and increases RAPTOR degradation by ubiquitination, thereby inhibiting mTORC1 signaling. Consistent with hyperactivation of mTORC1 signaling in VHL-deficient ccRCC, we observed that loss of vhl-1 function in C. elegans increased mTORC1 activity, supporting an evolutionary conserved mechanism. Our work reveals important new mechanistic insight into deregulation of mTORC1 signaling in ccRCC and links VHL directly to the control of RAPTOR/mTORC1. This may represent a novel mechanism whereby loss of VHL affects organ integrity and tumor behavior.

Therapeutic inhibition of HIF-2α reverses polycythemia and pulmonary hypertension in murine models of human diseases.

Polycythemia and pulmonary hypertension are 2 human diseases for which better therapies are needed. Upregulation of hypoxia-inducible factor-2α (HIF-2α) and its target genes, erythropoietin (EPO) and endothelin-1, causes polycythemia and pulmonary hypertension in patients with Chuvash polycythemia who are homozygous for the R200W mutation in the von Hippel Lindau (VHL) gene and in a murine mouse model of Chuvash polycythemia that bears the same homozygous VhlR200W mutation. Moreover, the aged VhlR200W mice developed pulmonary fibrosis, most likely due to the increased expression of Cxcl-12, another Hif-2α target. Patients with mutations in iron regulatory protein 1 (IRP1) also develop polycythemia, and Irp1-knockout (Irp1-KO) mice exhibit polycythemia, pulmonary hypertension, and cardiac fibrosis attributable to translational derepression of Hif-2α, and the resultant high expression of the Hif-2α targets EPO, endothelin-1, and Cxcl-12. In this study, we inactivated Hif-2α with the second-generation allosteric HIF-2α inhibitor MK-6482 in VhlR200W, Irp1-KO, and double-mutant VhlR200W;Irp1-KO mice. MK-6482 treatment decreased EPO production and reversed polycythemia in all 3 mouse models. Drug treatment also decreased right ventricular pressure and mitigated pulmonary hypertension in VhlR200W, Irp1-KO, and VhlR200W;Irp1-KO mice to near normal wild-type levels and normalized the movement of the cardiac interventricular septum in VhlR200Wmice. MK-6482 treatment reduced the increased expression of Cxcl-12, which, in association with CXCR4, mediates fibrocyte influx into the lungs, potentially causing pulmonary fibrosis. Our results suggest that oral intake of MK-6482 could represent a new approach to treatment of patients with polycythemia, pulmonary hypertension, pulmonary fibrosis, and complications caused by elevated expression of HIF-2α.

Ultrasound Microbubble-Mediated VHL Regulates the Biological Behavior of Ovarian Cancer Cells.

According to the literature, the von Hippel-Lindau (VHL) gene has a certain correlation with ovarian cancer. In this study, we investigated the effect and mechanism of ultrasound microbubble-mediated VHL on the biological function of ovarian cancer cells. Non-targeting lipid microbubbles and targeted lipid microbubbles were prepared. OVCAR-3 cells were treated with VHL mediated by ultrasound and microbubbles alone or together. Expressions of VHL, Akt, epithelial-mesenchymal-transition-related proteins and apoptosis-related proteins were detected by Western blot and quantitative real-time polymerase chain reaction as needed. The effect of ultrasound microbubble-mediated VHL on the proliferation, apoptosis, cell cycle, migration and invasion of OVCAR-3 cells was examined by Cell Counting Kit-8, flow cytometry, wound-healing assay and Transwell. Compared with other treatment methods, ultrasound microbubble mediation enhanced VHL expression in OVCAR-3 cells. Overexpression of liposome-mediated VHL inhibited the proliferation and migration; caused cell-cycle arrest; promoted apoptosis: downregulated the expressions of MMP2, MMP9, E-cadherin, Akt and Bcl-2; and upregulated the expressions of VHL and BCL2-associated X protein (BAX) in OVCAR-3 cells. The effect of microbubble-treated VHL was similar to liposome-mediated regulation, while ultrasound treatment enhanced the effect of VHL on OVCAR-3 cells. More interestingly, ultrasound microbubble-mediated VHL had the most obvious regulatory effect on OVCAR-3 cells. Ultrasound microbubble technology increases the transfection efficiency of VHL into OVCAR-3 cells and enhances the effect of VHL gene on the biological function of OVCAR-3 cells.

Identification of anti-tumoral feedback loop between VHLα and hnRNPA2B1 in renal cancer.

Our previous study identified a novel VHLα isoform which negatively modulated hnRNPA2B1 expression and therefore influenced pyruvate kinase transcript splicing in renal cancer, while the regulation and initiation of alternative translation are largely unknown. Here we unraveled the CUG-mediated translation start of VHLα, which was subjected to the regulation by both eukaryotic initiator factor eIF2A and RNA helicase eIF4A. Unexpectedly, we found hnRNPA2B1 promoted VHLα alternative translation as well via direct interaction with its octadic pentamer region of VHL transcript. The N-terminal of VHLα was indispensable in mediating ubiquitination of hnRNPA2B1 at lysine residues 274 and 305. We further identified aberrant overexpression of c-myc as upstream oncogenic signaling to positively regulate hnRNPA2B1 transcription in renal cancer. Therefore, our data suggested an anti-tumoral feedback loop between VHLα and hnRNPA2B1.

Ubiquitination of PPAR-gamma by pVHL inhibits ACLY expression and lipid metabolism, is implicated in tumor progression.

BACKGROUND: Intracellular lipid accumulation is associated with various diseases, particularly cancer. Mitochondrial dysfunction is considered as a cause of lipid accumulation; however, the related underlying mechanism remains unclear. FINDINGS: We found that Von Hippel-Lindau (VHL)-deficiency led to lipid accumulation and mitochondrial dysfunction in renal cell carcinoma cells. Moreover, VHL downregulated ATP-citrate lyase (ACLY), a key enzyme in de novo lipid synthesis, at the transcriptional level, which inhibited intracellular lipid accumulation in human renal carcinoma tissues. We identified PPARγ as the transcription factor regulating ACLY expression by binding to the cis-regulatory site PPRE on its promoter. VHL directly interacted with and promoted ubiquitination of PPARγ, leading to its degradation both in vitro and in vivo, resulting in the downregulation of ACLY. Furthermore, adenovirus-mediated VHL overexpression substantially ameliorated hepatic steatosis induced by a high-fat diet in db/db mice. Importantly, low VHL expression was associated with high ACLY expression and poor prognosis in human liver carcinoma in a dataset in The Cancer Genome Atlas. CONCLUSIONS: VHL plays role in cellular lipid metabolism via regulating mitochondria and targeting PPARγ, a transcription factor for ACLY independent of hypoxia-inducible factor 1α. A novel VHL-PPARγ-ACLY axis and its implication in fatty liver disease and cancer were uncovered.

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.

Von Hippel-Lindau Acts as a Metabolic Switch Controlling Nephron Progenitor Differentiation.

BACKGROUND: Nephron progenitors, the cell population that give rise to the functional unit of the kidney, are metabolically active and self-renew under glycolytic conditions. A switch from glycolysis to mitochondrial respiration drives these cells toward differentiation, but the mechanisms that control this switch are poorly defined. Studies have demonstrated that kidney formation is highly dependent on oxygen concentration, which is largely regulated by von Hippel-Lindau (VHL; a protein component of a ubiquitin ligase complex) and hypoxia-inducible factors (a family of transcription factors activated by hypoxia). METHODS: To explore VHL as a regulator defining nephron progenitor self-renewal versus differentiation, we bred Six2-TGCtg mice with VHLlox/lox mice to generate mice with a conditional deletion of VHL from Six2+ nephron progenitors. We used histologic, immunofluorescence, RNA sequencing, and metabolic assays to characterize kidneys from these mice and controls during development and up to postnatal day 21. RESULTS: By embryonic day 15.5, kidneys of nephron progenitor cell-specific VHL knockout mice begin to exhibit reduced maturation of nephron progenitors. Compared with controls, VHL knockout kidneys are smaller and developmentally delayed by postnatal day 1, and have about half the number of glomeruli at postnatal day 21. VHL knockout nephron progenitors also exhibit persistent Six2 and Wt1 expression, as well as decreased mitochondrial respiration and prolonged reliance on glycolysis. CONCLUSIONS: Our findings identify a novel role for VHL in mediating nephron progenitor differentiation through metabolic regulation, and suggest that VHL is required for normal kidney development.

The E3 ligase VHL promotes follicular helper T cell differentiation via glycolytic-epigenetic control.

Follicular helper T (Tfh) cells are essential for germinal center formation and effective humoral immunity, which undergo different stages of development to become fully polarized. However, the detailed mechanisms of their regulation remain unsolved. Here we found that the E3 ubiquitin ligase VHL was required for Tfh cell development and function upon acute virus infection or antigen immunization. VHL acted through the hypoxia-inducible factor 1α (HIF-1α)-dependent glycolysis pathway to positively regulate early Tfh cell initiation. The enhanced glycolytic activity due to VHL deficiency was involved in the epigenetic regulation of ICOS expression, a critical molecule for Tfh development. By using an RNA interference screen, we identified the glycolytic enzyme GAPDH as the key target for the reduced ICOS expression via m6A modification. Our results thus demonstrated that the VHL-HIF-1α axis played an important role during the initiation of Tfh cell development through glycolytic-epigenetic reprogramming.

The Lim1 oncogene as a new therapeutic target for metastatic human renal cell carcinoma.

Metastatic clear cell renal cell carcinoma (CCC) remains incurable despite advances in the development of anti-angiogenic targeted therapies and the emergence of immune checkpoint inhibitors. We have previously shown that the sonic hedgehog-Gli signaling pathway is oncogenic in CCC allowing us to identify the developmental Lim1 transcription factor as a Gli target and as a new oncogene in CCC regulating cell proliferation and apoptosis, and promoting tumor growth. In this previous study, preliminary in vitro results also suggested that Lim1 may be implicated in metastatic spread. Here we investigated the potential pro-metastatic role of Lim1 in advanced CCC (1) in vitro using a panel of CCC cell lines expressing or not the von Hippel-Lindau (VHL) tumor suppressor gene either naturally or by gene transfer and (2) ex vivo in 30 CCC metastatic tissues, including lymph nodes, lung, skin, bone, and adrenal metastases, and (3) in vivo, using a metastatic model by intravenous injection of siRNA-transfected cells into Balb/c nude. Our in vitro results reveal that Lim1 knockdown time-dependently decreased CCC cell motility, migration, invasion, and clonogenicity by up to 50% regardless of their VHL status. Investigating the molecular machinery involved in these processes, we identified a large panel of Lim1 targets known to be involved in cell adhesion (paxillin and fibronectin), epithelial-mesenchymal transition (Twist1/2 and snail), invasion (MMP1/2/3/8/9), and metastatic progression (CXCR4, SDF-1, and ANG-1). Importantly, Lim1 was found constitutively expressed in all metastatic tissues. The H-score in metastatic tissues being significantly superior to the score in the corresponding primary tumor tissues (P value = 0.009). Furthermore, we showed that Lim1 silencing decreases pulmonary metastasis development in terms of number and size in the in vivo metastatic model of human CCC. Taken together, these experiments strengthen the potential therapeutic value of Lim1 targeting as a promising novel approach for treating metastatic human CCC.

Immune regulation by protein ubiquitination: roles of the E3 ligases VHL and Itch.

Protein ubiquitination is an important means of post-translational modification which plays an essential role in the regulation of various aspects of leukocyte development and function. The specificity of ubiquitin tagging to a protein substrate is determined by E3 ubiquitin ligases via defined E3-substrate interactions. In this review, we will focus on two E3 ligases, VHL and Itch, to discuss the latest progress in understanding their roles in the differentiation and function of CD4+ T helper cell subsets, the stability of regulatory T cells, effector function of CD8+ T cells, as well as the development and maturation of innate lymphoid cells. The biological implications of these E3 ubiquitin ligases will be highlighted in the context of normal and dysregulated immune responses including the control of homeostasis, inflammation, auto-immune responses and anti-tumor immunity. Further elucidation of the ubiquitin system in immune cells will help in the design of new therapeutic interventions for human immunological diseases and cancer.

High Frequency of Ovarian Cyst Development in Vhl2B/+;Snf5+/- Mice.

The new paradigm of mutations in chromatin-modifying genes as driver events in the development of cancers has proved challenging to resolve the complex influences over disease phenotypes. In particular, impaired activities of members of the SWI/SNF chromatin remodeling complex have appeared in an increasing variety of tumors. Mutations in SNF5, a member of this ubiquitously expressed complex, arise in almost all cases of malignant rhabdoid tumor in the absence of additional genetic alterations. Therefore, we studied how activation of additional oncogenic pathways might shift the phenotype of disease driven by SNF5 loss. With the use of a genetically engineered mouse model, we examined the effects of a hypomorphic Vhl2B allele on disease phenotype, with a modest up-regulation of the hypoxia response pathway. Snf5+/-;Vhl2B/+ mice did not demonstrate a substantial difference in overall survival or a change in malignant rhabdoid tumor development. However, a high percentage of female mice showed complex hemorrhagic ovarian cysts, a phenotype rarely found in either parental mouse strain. These lesions also showed mosaic expression of SNF5 by immunohistochemistry. Therefore, our studies implicate that modest changes in angiogenic regulation interact with perturbations of SWI/SNF complex activity to modulate disease phenotypes.

E3 Ligase VHL Promotes Group 2 Innate Lymphoid Cell Maturation and Function via Glycolysis Inhibition and Induction of Interleukin-33 Receptor.

Group 2 innate lymphoid cells (ILC2s) are a specialized subset of lymphoid effector cells that are critically involved in allergic responses; however, the mechanisms of their regulation remain unclear. We report that conditional deletion of the E3 ubiquitin ligase VHL in innate lymphoid progenitors minimally affected early-stage bone marrow ILC2s but caused a selective and intrinsic decrease in mature ILC2 numbers in peripheral non-lymphoid tissues, resulting in reduced type 2 immune responses. VHL deficiency caused the accumulation of hypoxia-inducible factor 1α (HIF1α) and attenuated interleukin-33 (IL-33) receptor ST2 expression, which was rectified by HIF1α ablation or inhibition. HIF1α-driven expression of the glycolytic enzyme pyruvate kinase M2 downmodulated ST2 expression via epigenetic modification and inhibited IL-33-induced ILC2 development. Our study indicates that the VHL-HIF-glycolysis axis is essential for the late-stage maturation and function of ILC2s via targeting IL-33-ST2 pathway.

Deletion of the von Hippel-Lindau Gene in Hemangioblasts Causes Hemangioblastoma-like Lesions in Murine Retina.

von Hippel-Lindau (VHL) disease is an autosomal-dominant tumor predisposition syndrome characterized by the development of highly vascularized tumors and cysts. LOH of the VHL gene results in aberrant upregulation of hypoxia-inducible factors (HIF) and has been associated with tumor formation. Hemangioblastomas of the central nervous system and retina represent the most prevalent VHL-associated tumors, but no VHL animal model has reproduced retinal capillary hemangioblastomas (RCH), the hallmark lesion of ocular VHL. Here we report our work in developing a murine model of VHL-associated RCH by conditionally inactivating Vhl in a hemangioblast population using a Scl-Cre-ERT2 transgenic mouse line. In transgenic mice carrying the conditional allele and the Scl-Cre-ERT2 allele, 64% exhibited various retinal vascular anomalies following tamoxifen induction. Affected Vhl-mutant mice demonstrated retinal vascular lesions associated with prominent vasculature, anomalous capillary networks, hemorrhage, exudates, and localized fibrosis. Histologic analyses showed RCH-like lesions characterized by tortuous, dilated vasculature surrounded by "tumorlet" cell cluster and isolated foamy stromal cells, which are typically associated with RCH. Fluorescein angiography suggested increased vascular permeability of the irregular retinal vasculature and hemangioblastoma-like lesions. Vhl deletion was detected in "tumorlet" cells via microdissection. Our findings provide a phenotypic recapitulation of VHL-associated RCH in a murine model that may be useful to study RCH pathogenesis and therapeutics aimed at treating ocular VHL.Significance: This study describes a model that phenotypically recapitulates a form of retinal pathogenesis that is driven by genetic loss of the VHL tumor suppressor, providing a useful tool for its study and therapeutic intervention. Cancer Res; 78(5); 1266-74. ©2018 AACR.

Acidosis Acts through HSP90 in a PHD/VHL-Independent Manner to Promote HIF Function and Stem Cell Maintenance in Glioma.

Hypoxia is a common feature of solid tumors, which controls multiple aspects of cancer progression. One important function of hypoxia and the hypoxia-inducible factors (HIF) is the maintenance of cancer stem-like cells (CSC), a population of tumor cells that possess stem cell-like properties and drives tumor growth. Among the changes promoted by hypoxia is a metabolic shift resulting in acidification of the tumor microenvironment. Here, we show that glioma hypoxia and acidosis functionally cooperate in inducing HIF transcription factors and CSC maintenance. We found that these effects did not involve the classical PHD/VHL pathway for HIF upregulation, but instead involved the stress-induced chaperone protein HSP90. Genetic or pharmacologic inactivation of HSP90 inhibited the increase in HIF levels and abolished the self-renewal and tumorigenic properties of CSCs induced by acidosis. In clinical specimens of glioma, HSP90 was upregulated in the hypoxic niche and was correlated with a CSC phenotype. Our findings highlight the role of tumor acidification within the hypoxic niche in the regulation of HIF and CSC function through HSP90, with implications for therapeutic strategies to target CSC in gliomas and other hypoxic tumors. Cancer Res; 76(19); 5845-56. ©2016 AACR.

CRISPR-Mediated VHL Knockout Generates an Improved Model for Metastatic Renal Cell Carcinoma.

Metastatic renal cell carcinoma (mRCC) is nearly incurable and accounts for most of the mortality associated with RCC. Von Hippel Lindau (VHL) is a tumour suppressor that is lost in the majority of clear cell RCC (ccRCC) cases. Its role in regulating hypoxia-inducible factors-1α (HIF-1α) and -2α (HIF-2α) is well-studied. Recent work has demonstrated that VHL knock down induces an epithelial-mesenchymal transition (EMT) phenotype. In this study we showed that a CRISPR/Cas9-mediated knock out of VHL in the RENCA model leads to morphologic and molecular changes indicative of EMT, which in turn drives increased metastasis to the lungs. RENCA cells deficient in HIF-1α failed to undergo EMT changes upon VHL knockout. RNA-seq revealed several HIF-1α-regulated genes that are upregulated in our VHL knockout cells and whose overexpression signifies an aggressive form of ccRCC in the cancer genome atlas (TCGA) database. Independent validation in a new clinical dataset confirms the upregulation of these genes in ccRCC samples compared to adjacent normal tissue. Our findings indicate that loss of VHL could be driving tumour cell dissemination through stabilization of HIF-1α in RCC. A better understanding of the mechanisms involved in this phenomenon can guide the search for more effective treatments to combat mRCC.

Atlas on substrate recognition subunits of CRL2 E3 ligases.

The Cullin2-type ubiquitin ligases belong to the Cullin-Ring Ligase (CRL) family, which is a crucial determinant of proteasome-based degradation processes in eukaryotes. Because of the finding of von Hippel-Lindau tumor suppressor (VHL), the Cullin2-type ubiquitin ligases gain focusing in the research of many diseases, especially in tumors. These multisubunit enzymes are composed of the Ring finger protein, the Cullin2 scaffold protein, the Elongin B&C linker protein and the variant substrate recognition subunits (SRSs), among which the Cullin2 scaffold protein is the determining factor of the enzyme mechanism. Substrate recognition of Cullin2-type ubiquitin ligases depends on SRSs and results in the degradation of diseases associated substrates by intracellular signaling events. This review focuses on the diversity and the multifunctionality of SRSs in the Cullin2-type ubiquitin ligases, including VHL, LRR-1, FEM1b, PRAME and ZYG11. Recently, as more SRSs are being discovered and more aspects of substrate recognition have been illuminated, insight into the relationship between Cul2-dependent SRSs and substrates provides a new area for cancer research.

Melatonin and the von Hippel-Lindau/HIF-1 oxygen sensing mechanism: A review.

There are numerous reports that melatonin inhibits the hypoxia-inducible factor, HIF-1α, and the HIF-1α-inducible gene, VEGF, both in vivo and in vitro. Through the inhibition of the HIF-1-VEGF pathway, melatonin reduces hypoxia-induced angiogenesis. Herein we discuss the interaction of melatonin with HIF-1α and HIF-1α-inducible genes in terms of what is currently known concerning the HIF-1α hypoxia response element (HIF-1α-HRE) pathway. The von Hippel-Lindau protein (VHL), also known as the VHL tumor suppressor, functions as part of a ubiquitin ligase complex which recognizes HIF-1α as a substrate. As such, VHL is part of the oxygen sensing mechanism of the cell. Under conditions of hypoxia, HIF-1α stimulates the transcription of numerous HIF-1α-induced genes, including EPO, VEGF, and PFKFB3; the latter is an enzyme which regulates glycolysis. Data from several studies show that ROS generated in mitochondria under conditions of hypoxia stimulate HIF-1α. Since melatonin acts as an antioxidant and reduces ROS, these data suggest that the antioxidant action of melatonin could account for reduced HIF-1, less VEGF, and reduced glycolysis in cancer cells (Warburg effect). A direct or indirect inhibitory action (via the reduction in ROS) of melatonin on proteasome activity would account for much of the published data.

Translational Activation of HIF1α by YB-1 Promotes Sarcoma Metastasis.

Metastatic dissemination is the leading cause of death in cancer patients, which is particularly evident for high-risk sarcomas such as Ewing sarcoma, osteosarcoma, and rhabdomyosarcoma. Previous research identified a crucial role for YB-1 in the epithelial-to-mesenchymal transition (EMT) and metastasis of epithelial malignancies. Based on clinical data and two distinct animal models, we now report that YB-1 is also a major metastatic driver in high-risk sarcomas. Our data establish YB-1 as a critical regulator of hypoxia-inducible factor 1α (HIF1α) expression in sarcoma cells. YB-1 enhances HIF1α protein expression by directly binding to and activating translation of HIF1A messages. This leads to HIF1α-mediated sarcoma cell invasion and enhanced metastatic capacity in vivo, highlighting a translationally regulated YB-1-HIF1α axis in sarcoma metastasis.