Metastatic Clear-cell Renal Cell Carcinoma With a Long-term Response to Sunitinib: A Distinct Phenotype Independently Associated With Low PD-L1 Expression

BACKGROUND

Long-term responders (LTRs) are defined by at least 18 months of response to sunitinib in metastatic clear-cell renal cell carcinoma (ccRCC). Well-described by clinical studies, the phenotype of these tumors has never been explored.

PATIENTS AND METHODS

In a retrospective and multicenter study, 90 ccRCCs of patients with metastatic disease were analyzed. Immunohistochemistry (carbonic anhydrase IX, vascular endothelial growth factor, c-MET, programmed death-ligand 1 [PD-L1], and PD-1) and VHL status were performed. Progression-free survival and overall survival were calculated from sunitinib introduction and from progression. LTRs and their corresponding tumors were compared with others using univariate and multivariate analysis.

RESULTS

Twenty-eight patients were LTRs. They had a median progression-free survival of 28 months versus 4 months for other patients (P < .001). Similarly, LTRs had a median overall survival of 49 months versus 14 months (P < .001), even from progression (median, 21 vs. 7 months; P = .029). They were associated with a favorable or intermediate risk (International Metastatic Renal Cell Carcinoma Database Consortium model) (P = .007) and less liver metastasis (P = .036). They experienced more frequent complete or partial responses at the first radiologic evaluation (P = .035). The corresponding ccRCCs were associated with less nucleolar International Society for Urological Pathology grade 4 (P = .037) and hilar fat infiltration (P = .006). They were also associated with low PD-L1 expression (P = .02). Only the International Metastatic Renal Cell Carcinoma Database Consortium model and PD-L1 expression remained significant after multivariate analysis (P = .014 and P = .029, respectively).

CONCLUSION

Primary tumor characteristics of LTRs were studied for the first time and demonstrated a different phenotype. Interestingly, they were characterized by low expression of PD-L1, suggesting a potentially lower impact of targeted immunotherapy in these patients.

Disturbed Flow Increases UBE2C (Ubiquitin E2 Ligase C) via Loss of miR-483-3p, Inducing Aortic Valve Calcification by the pVHL (von Hippel-Lindau Protein) and HIF-1α (Hypoxia-Inducible Factor-1α) Pathway in Endothelial Cells

Objective- Calcific aortic valve (AV) disease, characterized by AV sclerosis and calcification, is a major cause of death in the aging population; however, there are no effective medical therapies other than valve replacement. AV calcification preferentially occurs on the fibrosa side, exposed to disturbed flow (d-flow), whereas the ventricularis side exposed to predominantly stable flow remains protected by unclear mechanisms. Here, we tested the role of novel flow-sensitive UBE2C (ubiquitin E2 ligase C) and microRNA-483-3p (miR-483) in flow-dependent AV endothelial function and AV calcification. Approach and Results- Human AV endothelial cells and fresh porcine AV leaflets were exposed to stable flow or d-flow. We found that UBE2C was upregulated by d-flow in human AV endothelial cells in the miR-483-dependent manner. UBE2C mediated OS-induced endothelial inflammation and endothelial-mesenchymal transition by increasing the HIF-1α (hypoxia-inducible factor-1α) level. UBE2C increased HIF-1α by ubiquitinating and degrading its upstream regulator pVHL (von Hippel-Lindau protein). These in vitro findings were corroborated by immunostaining studies using diseased human AV leaflets. In addition, we found that reduction of miR-483 by d-flow led to increased UBE2C expression in human AV endothelial cells. The miR-483 mimic protected against endothelial inflammation and endothelial-mesenchymal transition in human AV endothelial cells and calcification of porcine AV leaflets by downregulating UBE2C. Moreover, treatment with the HIF-1α inhibitor (PX478) significantly reduced porcine AV calcification in static and d-flow conditions. Conclusions- These results suggest that miR-483 and UBE2C and pVHL are novel flow-sensitive anti- and pro-calcific AV disease molecules, respectively, that regulate the HIF-1α pathway in AV. The miR-483 mimic and HIF-1α pathway inhibitors may serve as potential therapeutics of calcific AV disease.

Vhl deficiency in osteocytes produces high bone mass and hematopoietic defects

Tissue oxygen (O₂) levels vary during development and disease; adaptations to decreased O₂ (hypoxia) are mediated by hypoxia-inducible factor (HIF) transcription factors. HIFs are active in the skeleton, and stabilizing HIF-α isoforms cause high bone mass (HBM) phenotypes. A fundamental limitation of previous studies examining the obligate role for HIF-α isoforms in the skeleton involves the persistence of gene deletion as osteolineage cells differentiate into osteocytes. Because osteocytes orchestrate skeletal development and homeostasis, we evaluated the influence of Vhl or Hif1a disruption in osteocytes. Osteocytic Vhl deletion caused HBM phenotype, but Hif1a was dispensable in osteocytes. Vhl cKO mice revealed enhanced canonical Wnt signaling. B cell development was reduced while myelopoiesis increased in osteocytic Vhl cKO, revealing a novel influence of Vhl/HIF-α function in osteocytes on maintenance of bone microarchitecture via canonical Wnt signaling and effects on hematopoiesis.

The Protein Phosphatase PPM1G Destabilizes HIF-1α Expression

Hypoxia-inducible factors (HIFs) are key regulators of hypoxic responses, and their stability and transcriptional activity are controlled by several kinases. However, the regulation of HIF by protein phosphatases has not been thoroughly investigated. Here, we found that overexpression of Mg²⁺/Mn²⁺-dependent protein phosphatase 1 gamma (PPM1G), one of Ser/Thr protein phosphatases, downregulated protein expression of ectopic HIF-1α under normoxic or acute hypoxic conditions. In addition, the deficiency of PPM1G upregulated protein expression of endogenous HIF-1α under normoxic or acute oxidative stress conditions. PPM1G decreased expression of HIF-1α via the proteasomal pathway. PPM1G-mediated HIF-1α degradation was dependent on prolyl hydroxylase (PHD), but independent of von Hippel-Lindau (VHL). These data suggest that PPM1G is critical for the control of HIF-1α-dependent responses.

Phosphorylation and Ubiquitination Regulate Protein Phosphatase 5 Activity and Its Prosurvival Role in Kidney Cancer

The serine/threonine protein phosphatase 5 (PP5) regulates multiple cellular signaling networks. A number of cellular factors, including heat shock protein 90 (Hsp90), promote the activation of PP5. However, it is unclear whether post-translational modifications also influence PP5 phosphatase activity. Here, we show an "on/off switch" mechanism for PP5 regulation. The casein kinase 1δ (CK1δ) phosphorylates T362 in the catalytic domain of PP5, which activates and enhances phosphatase activity independent of Hsp90. Overexpression of the phosphomimetic T362E-PP5 mutant hyper-dephosphorylates substrates such as the co-chaperone Cdc37 and glucocorticoid receptor in cells. Our proteomic approach revealed that the tumor suppressor von Hippel-Lindau protein (VHL) interacts with and ubiquitinates K185/K199-PP5 for proteasomal degradation in a hypoxia- and prolyl-hydroxylation-independent manner. Finally, VHL-deficient clear cell renal cell carcinoma (ccRCC) cell lines and patient tumors exhibit elevated PP5 levels. Downregulation of PP5 causes ccRCC cells to undergo apoptosis, suggesting a prosurvival role for PP5 in kidney cancer.

[Expression, purification and binding activity analysis of von Hippel-Lindau (VHL)]

Objective To purify recombinant protein of human von Hippel-Lindau (VHL) and identify its function. Methods VHL gene sequence was amplified from human mammary cDNA using PCR and inserted into the prokaryotic expression vector pGEX-KG. Glutathione S-transferase-VHL (GST-VHL) recombinant plasmid we obtained was converted into BL21(DE3) sensitive bacteria to induce a small amount of GST-VHL protein. The expressed product was detected by SDS-PAGE and Western blot analysis. The recombinant protein was purified by GST beads and its function was verified by GST pull-down assay. Results The obtained recombinant plasmid could be successfully digested by double enzymes. Gene sequencing showed that the VHL sequence was correct and there was no mutation. The recombinant protein with approximately relative molecular mass (M_r) 56 000 was purified by converting recombinant plasmid to BL21(DE3) sensitive bacteria and inducing it in small quantities. GST pull-down assay verified that GST-VHL recombinant protein had the function of binding hypoxia inducible factor-1 α (HIF-1 α) in vitro. Conclusion GST-VHL recombinant protein is purified and can combine with HIF-1α protein in vitro.

Deregulation of LIMD1-VHL-HIF-1α-VEGF pathway is associated with different stages of cervical cancer

To understand the mechanism of cellular stress in basal-parabasal layers of normal cervical epithelium and during different stages of cervical carcinoma, we analyzed the alterations (expression/methylation/copy number variation/mutation) of HIF-1α and its associated genes LIMD1, VHL and VEGF in disease-free normal cervix (n = 9), adjacent normal cervix of tumors (n = 70), cervical intraepithelial neoplasia (CIN; n = 32), cancer of uterine cervix (CACX; n = 174) samples and two CACX cell lines. In basal-parabasal layers of normal cervical epithelium, LIMD1 showed high protein expression, while low protein expression of VHL was concordant with high expression of HIF-1α and VEGF irrespective of HPV-16 (human papillomavirus 16) infection. This was in concordance with the low promoter methylation of LIMD1 and high in VHL in the basal-parabasal layers of normal cervix. LIMD1 expression was significantly reduced while VHL expression was unchanged during different stages of cervical carcinoma. This was in concordance with their frequent methylation during different stages of this tumor. In different stages of cervical carcinoma, the expression pattern of HIF-1α and VEGF was high as seen in basal-parabasal layers and inversely correlated with the expression of LIMD1 and VHL. This was validated by demethylation experiments using 5-aza-2'-deoxycytidine in CACX cell lines. Additional deletion of LIMD1 and VHL in CIN/CACX provided an additional growth advantage during cervical carcinogenesis through reduced expression of genes and associated with poor prognosis of patients. Our data showed that overexpression of HIF-1α and its target gene VEGF in the basal-parabasal layers of normal cervix was due to frequent inactivation of VHL by its promoter methylation. This profile was maintained during different stages of cervical carcinoma with additional methylation/deletion of VHL and LIMD1.

Compromised JMJD6 Histone Demethylase Activity Affects VHL Gene Repression in Preeclampsia

CONTEXT

The von Hippel Lindau (VHL) protein is a key executor of the cellular hypoxic response that is compromised in preeclampsia, a serious disorder complicating 5% to 7% of pregnancies. To date, the mechanisms controlling VHL gene expression in the human placenta remain elusive.

OBJECTIVE

We examined VHL epigenetic regulation in normal pregnancy and in preeclampsia, a pathology characterized by placental hypoxia.

DESIGN, SETTING, AND PARTICIPANTS

Placentae were obtained from early-onset preeclampsia (n = 56; <34 weeks of gestation) and late-onset preeclampsia (n = 19; ≥34 weeks of gestation). Placentae from healthy normotensive age-matched preterm control (n = 43) and term control (n = 23) pregnancies were included as controls.

MAIN OUTCOME MEASURE(S)

We measured the activity of Jumonji domain containing protein 6 (JMJD6), a ferrous iron (Fe2+)- and oxygen-dependent histone demethylase, and examined its function in the epigenetic control of VHL.

RESULTS

JMJD6 regulates VHL gene expression in the human placenta. VHL downregulation in preeclampsia is dependent on decreased JMJD6 demethylase activity due to hypoxia and reduced Fe2+ bioavailability. Chromatin immunoprecipitation assays revealed decreased association of JMJD6 and its histone targets with the VHL promoter. Findings in preeclampsia were corroborated in a murine model of pharmacological hypoxia using FG-4592. Placentae from FG-4592-treated mice exhibited reduced VHL levels, accompanied by placental morphological alterations and reduced pup weights. Notably, Fe2+ supplementation rescued JMJD6 histone demethylase activity in histone from E-PE and FG-4592-treated mice.

CONCLUSIONS

Our study uncovers epigenetic regulation of VHL and its functional consequences for altered oxygen and iron homeostasis in preeclampsia.

Sonic Hedgehog Agonist Protects Against Complex Neonatal Cerebellar Injury

The cerebellum undergoes rapid growth during the third trimester and is vulnerable to injury and deficient growth in infants born prematurely. Factors associated with preterm cerebellar hypoplasia include chronic lung disease and postnatal glucocorticoid administration. We modeled chronic hypoxemia and glucocorticoid administration in neonatal mice to study whole cerebellar and cell type-specific effects of dual exposure. Chronic neonatal hypoxia resulted in permanent cerebellar hypoplasia. This was compounded by administration of prednisolone as shown by greater volume loss and Purkinje cell death. In the setting of hypoxia and prednisolone, administration of a small molecule Smoothened-Hedgehog agonist (SAG) preserved cerebellar volume and protected against Purkinje cell death. Such protective effects were observed even when SAG was given as a one-time dose after dual insult. To model complex injury and determine cell type-specific roles for the hypoxia inducible factor (HIF) pathway, we performed conditional knockout of von Hippel Lindau (VHL) to hyperactivate HIF1α in cerebellar granule neuron precursors (CGNP) or Purkinje cells. Surprisingly, HIF activation in either cell type resulted in no cerebellar deficit. However, in mice administered prednisolone, HIF overactivation in CGNPs resulted in significant cerebellar hypoplasia, whereas HIF overactivation in Purkinje cells caused cell death. Together, these findings indicate that HIF primes both cell types for injury via glucocorticoids, and that hypoxia/HIF + postnatal glucocorticoid administration act on distinct cellular pathways to cause cerebellar injury. They further suggest that SAG is neuroprotective in the setting of complex neonatal cerebellar injury.

Epigenetic regulators: multifunctional proteins modulating hypoxia-inducible factor-α protein stability and activity

The hypoxia-inducible factor (HIF) is a heterodimeric transcription factor governing a transcriptional program in response to reduced O2 availability in metazoans. It contributes to physiology and pathogenesis of many human diseases through its downstream target genes. Emerging studies have shown that the transcriptional activity of HIF is highly regulated at multiple levels and the epigenetic regulators are essential for HIF-mediated transactivation. In this review, we will discuss the comprehensive regulation of HIF transcriptional activity by different types of epigenetic regulators.

A "Click Chemistry Platform" for the Rapid Synthesis of Bispecific Molecules for Inducing Protein Degradation

Proteolysis targeting chimeras (PROTACs) are bispecific molecules containing a target protein binder and an ubiquitin ligase binder connected by a linker. By recruiting an ubiquitin ligase to a target protein, PROTACs promote ubiquitination and proteasomal degradation of the target protein. The generation of effective PROTACs depends on the nature of the protein/ligase ligand pair, linkage site, linker length, and linker composition, all of which have been difficult to address in a systematic way. Herein, we describe a "click chemistry" approach for the synthesis of PROTACs. We demonstrate the utility of this approach with the bromodomain and extraterminal domain-4 (BRD4) ligand JQ-1 (3) and ligase binders targeting cereblon (CRBN) and Von Hippel-Lindau (VHL) proteins. An AlphaScreen proximity assay was used to determine the ability of PROTACs to form the ternary ligase-PROTAC-target protein complex and a MSD assay to measure cellular degradation of the target protein promoted by PROTACs.

18F-FDG Uptake in Well-Differentiated Neuroendocrine Tumors Correlates with Both Ki-67 and VHL Pathway Inactivation

BACKGROUND

18F-FDG-PET scan positivity correlates with poor prognosis in neuroendocrine neoplasms (NEN). Glucose transporter 1 (GLUT1) and carbonic anhydrase 9 (CA9) are markers of aggressiveness in tumors. Together with von Hippel-Lindau protein (pVHL), they are involved in tumor cell metabolism via the hypoxia-inducible factor signaling pathway. The aim of this study was to compare, in a series of well-differentiated neuroendocrine tumors (NET), the 18F-FDG uptake and expression of the proliferation markers Ki-67, GLUT1, CA9, and pVHL.

PATIENTS AND METHODS

This retrospective study included 27 patients with well-differentiated NET. 18F-FDG-PET images were evaluated by the maximum standardized uptake value (SUVmax). GLUT1, CA9, and pVHL were analyzed by immunohistochemistry.

RESULTS

The NET were of pancreatic (n = 19), midgut (n = 4), duodenal (n = 1), esophageal (n = 1), rectal (n = 1), and pulmonary (n = 1) origin. Eight, 11, and 8 tumors were grade 1, 2, and 3, respectively. The mean/median Ki-67 index was 15/10% (1-60). The mean/median SUVmax was 6.2/5.2 (1.4-18.7). SUVmax correlated with greater tumor size (p = 0.03), higher expression of Ki-67 (p = 0.04), and lower expression of pVHL (p = 0.008). In the group of 16 NET with a low proliferative index (Ki-67 index <10%), 5/6 (83%) of the tumors with a high SUVmax had decreased pVHL expression (p = 0.0013).

CONCLUSION

This study confirms that 18F-FDG-PET uptake correlates with both tumor size and proliferation in well-differentiated NET, and it highlights a subset of low-grade but 18F-FDG-PET-positive NET related to sporadic inactivation of the VHL pathway.

MicroRNAs Associated with Von Hippel-Lindau Pathway in Renal Cell Carcinoma: A Comprehensive Review

Renal cell carcinoma (RCC) are the most common renal neoplasia and can be divided into three main histologic subtypes, among which clear cell RCC is by far the most common form of kidney cancer. Despite substantial advances over the last decade in the understanding of RCC biology, surgical treatments, and targeted and immuno-therapies in the metastatic setting, the prognosis for advanced RCC patients remains poor. One of the major problems with RCC treatment strategies is inherent or acquired resistance towards therapeutic agents over time. The discovery of microRNAs (miRNAs), a class of small, non-coding, single-stranded RNAs that play a crucial role in post-transcriptional regulation, has added new dimensions to the development of novel diagnostic and treatment tools. Because of an association between Von Hippel–Lindau (VHL) genes with chromosomal loss in 3p25-26 and clear cell RCC, miRNAs have attracted considerable scientific interest over the last years. The loss of VHL function leads to constitutional activation of the hypoxia inducible factor (HIF) pathway and to consequent expression of numerous angiogenic and carcinogenic factors. Since miRNAs represent key players of carcinogenesis, tumor cell invasion, angiogenesis, as well as in development of metastases in RCC, they might serve as potential therapeutic targets. Several miRNAs are already known to be dysregulated in RCC and have been linked to biological processes involved in tumor angiogenesis and response to anti-cancer therapies. This review summarizes the role of different miRNAs in RCC angiogenesis and their association with the VHL gene, highlighting their potential role as novel drug targets.

HIF activation causes synthetic lethality between the VHL tumor suppressor and the EZH1 histone methyltransferase

Inactivation of the von Hippel-Lindau tumor suppressor protein (pVHL) is the signature lesion in the most common form of kidney cancer, clear cell renal cell carcinoma (ccRCC). pVHL loss causes the transcriptional activation of hypoxia-inducible factor (HIF) target genes, including many genes that encode histone lysine demethylases. Moreover, chromatin regulators are frequently mutated in this disease. We found that ccRCC displays increased H3K27 acetylation and a shift toward mono- or unmethylated H3K27 caused by an HIF-dependent increase in H3K27 demethylase activity. Using a focused short hairpin RNA library, as well as CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein 9) and a pharmacological inhibitor, we discovered that pVHL-defective ccRCC cells are hyperdependent on the H3K27 methyltransferase EZH1 for survival. Therefore, targeting EZH1 could be therapeutically useful in ccRCC.

VHL-TGFBI signaling is involved in the synergy between 5-aza-2'-deoxycytidine and paclitaxel against human renal cell carcinoma

PURPOSE

To analyse the role of von Hippel-Lindau (VHL) and transforming growth factor β-induced (TGFBI) in synergistic mechanisms of 5-aza-2'-deoxycytidine (DAC) and paclitaxel (PTX) against renal cell carcinoma (RCC).

METHODS

To elucidate the role in the synergy between DAC and PTX against RCC cells, TGFBI expression was regulated using siRNA technology and an expression vector containing the full-length cDNA for TGFBI was also transfected into RCC cells. The proliferation of RCC cells was evaluated using the WST-1 assay and TGFBI expression was detected by real-time PCR (RT-PCR), and Western blot.

RESULTS

The results indicated that the expression of TGFBI was significantly decreased by DAC or PTX alone in vitro and in vivo. Moreover, the combination of DAC and PTX caused a synergistic decrease in the expression of TGFBI in RCC cells. We also investigated the effect of VHL-TGFBI signaling on the synergy between DAC and PTX, although the synergy between the two medications was not abolished by interfering with VHL activity or TGFBI expression. RCC cells without VHL activity and RCC cells expressing high levels of TGFBI displayed an increased synergistic effect compared to control cells.

CONCLUSION

Our study suggests that VHL-TGFBI signaling is involved in the synergy between DAC and PTX against RCC cells. In addition, the synergy between DAC and PTX is more effective in VHL inactive RCC cells.

Action of YM155 on clear cell renal cell carcinoma does not depend on survivin expression levels

The dioxonapthoimidazolium YM155 is a survivin suppressant which has been investigated as an anticancer agent in clinical trials. Here, we investigated its growth inhibitory properties on a panel of immortalized and patient derived renal cell carcinoma (RCC) cell lines which were either deficient in the tumour suppressor von Hippel-Lindau (VHL) protein or possessed a functional copy. Neither the VHL status nor the survivin expression levels of these cell lines influenced their susceptibility to growth inhibition by YM155. Of the various RCC lines, the papillary subtype was more resistant to YM155, suggesting that the therapeutic efficacy of YM155 may be restricted to clear cell subtypes. YM155 was equally potent in cells (RCC786.0) in which survivin expression had been stably silenced or overexpressed, implicating a limited reliance on survivin in the mode of action of YM155. A follow-up in-vitro high throughput RNA microarray identified possible targets of YM155 apart from survivin. Selected genes (ID1, FOXO1, CYLD) that were differentially expressed in YM155-sensitive RCC cells and relevant to RCC pathology were validated with real-time PCR and western immunoblotting analyses. Thus, there is corroboratory evidence that the growth inhibitory activity of YM155 in RCC cell lines is not exclusively mediated by its suppression of survivin. In view of the growing importance of combination therapy in oncology, we showed that a combination of YM155 and sorafenib at ½ x IC50 concentrations was synergistic on RCC786.0 cells. However, when tested intraperitoneally on a murine xenograft model derived from a nephrectomised patient with clear cell RCC, a combination of suboptimal doses of both drugs failed to arrest tumour progression. The absence of synergy in vivo highlighted the need to further optimize the dosing schedules of YM155 and sorafenib, as well as their routes of administration. It also implied that the expression of other oncogenic proteins which YM155 may target is either low or absent in this clear cell RCC.

Targeting endogenous proteins for degradation through the affinity-directed protein missile system

Targeted proteolysis of endogenous proteins is desirable as a research toolkit and in therapeutics. CRISPR/Cas9-mediated gene knockouts are irreversible and often not feasible for many genes. Similarly, RNA interference approaches necessitate prolonged treatments, can lead to incomplete knockdowns and are often associated with off-target effects. Targeted proteolysis can overcome these limitations. In this report, we describe an affinity-directed protein missile (AdPROM) system that harbours the von Hippel-Lindau (VHL) protein, the substrate receptor of the Cullin2 (CUL2) E3 ligase complex, tethered to polypeptide binders that selectively bind and recruit endogenous target proteins to the CUL2-E3 ligase complex for ubiquitination and proteasomal degradation. By using synthetic monobodies that selectively bind the protein tyrosine phosphatase SHP2 and a camelid-derived VHH nanobody that selectively binds the human ASC protein, we demonstrate highly efficient AdPROM-mediated degradation of endogenous SHP2 and ASC in human cell lines. We show that AdPROM-mediated loss of SHP2 in cells impacts SHP2 biology. This study demonstrates for the first time that small polypeptide binders that selectively recognize endogenous target proteins can be exploited for AdPROM-mediated destruction of the target proteins.

Hypoxia-inducible factor-2α stabilizes the von Hippel-Lindau (VHL) disease suppressor, Myb-related protein 2

Ubiquitin ligase von Hippel–Lindau tumor suppressor (pVHL) negatively regulates protein levels of hypoxia-inducible factor-α (HIF-α). Loss of pVHL causes HIF-α accumulation, which contributes to the pathogenesis of von Hippel-Lindau (VHL) disease. In contrast, v-Myb avian myeloblastosis viral oncogene homolog–like 2 (MYBL2; B-Myb), a transcription factor, prevents VHL pathogenesis by regulating gene expression of HIF-independent pathways. Both HIF-α and B-Myb are targets of pVHL-mediated polyubiquitination and proteasomal degradation. Here, we show that knockdown of HIF-2α induces downregulation of B-Myb in 786-O cells, which are deficient in pVHL, and this downregulation is prevented by proteasome inhibition. In the presence of pVHL and under hypoxia-like conditions, B-Myb and HIF-2α are both upregulated, and the upregulation of B-Myb requires expression of HIF-2α. We also show that HIF-2α and B-Myb interact in the nucleus, and this interaction is mediated by the central region of HIF-2α and the C-terminal region of B-Myb. These data indicate that oncogenic HIF-2α stabilizes B-Myb to suppress VHL pathogenesis.

Glutaminase and poly(ADP-ribose) polymerase inhibitors suppress pyrimidine synthesis and VHL-deficient renal cancers

Many cancer-associated mutations that deregulate cellular metabolic responses to hypoxia also reprogram carbon metabolism to promote utilization of glutamine. In renal cell carcinoma (RCC), cells deficient in the von Hippel-Lindau (VHL) tumor suppressor gene use glutamine to generate citrate and lipids through reductive carboxylation (RC) of α-ketoglutarate (αKG). Glutamine can also generate aspartate, the carbon source for pyrimidine biosynthesis, and glutathione for redox balance. Here we have shown that VHL-/- RCC cells rely on RC-derived aspartate to maintain de novo pyrimidine biosynthesis. Glutaminase 1 (GLS1) inhibitors depleted pyrimidines and increased ROS in VHL-/- cells but not in VHL+/+ cells, which utilized glucose oxidation for glutamate and aspartate production. GLS1 inhibitor-induced nucleoside depletion and ROS enhancement led to DNA replication stress and activation of an intra-S phase checkpoint, and suppressed the growth of VHL-/- RCC cells. These effects were rescued by administration of glutamate, αKG, or nucleobases with N-acetylcysteine. Further, we observed that the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib synergizes with GLS1 inhibitors to suppress the growth of VHL-/- cells in vitro and in vivo. This work describes a mechanism that explains the sensitivity of RCC tumor growth to GLS1 inhibitors and supports the development of therapeutic strategies for targeting VHL-deficient RCC.

Chemical approaches to targeted protein degradation through modulation of the ubiquitin-proteasome pathway

Manipulation of the ubiquitin-proteasome system to achieve targeted degradation of proteins within cells using chemical tools and drugs has the potential to transform pharmacological and therapeutic approaches in cancer and other diseases. An increased understanding of the molecular mechanism of thalidomide and its analogues following their clinical use has unlocked small-molecule modulation of the substrate specificity of the E3 ligase cereblon (CRBN), which in turn has resulted in the advancement of new immunomodulatory drugs (IMiDs) into the clinic. The degradation of multiple context-specific proteins by these pleiotropic small molecules provides a means to uncover new cell biology and to generate future drug molecules against currently undruggable targets. In parallel, the development of larger bifunctional molecules that bring together highly specific protein targets in complexes with CRBN, von Hippel-Lindau, or other E3 ligases to promote ubiquitin-dependent degradation has progressed to generate selective chemical compounds with potent effects in cells and in vivo models, providing valuable tools for biological target validation and with future potential for therapeutic use. In this review, we survey recent breakthroughs achieved in these two complementary methods and the discovery of new modes of direct and indirect engagement of target proteins with the proteasome. We discuss the experimental characterisation that validates the use of molecules that promote protein degradation as chemical tools, the preclinical and clinical examples disclosed to date, and the future prospects for this exciting area of chemical biology.

Deregulated expression of VHL mRNA variants in papillary thyroid cancer

Recent findings demonstrated that a subset of papillary thyroid cancers (PTCs) is characterized by reduced expression of the von Hippel-Lindau (VHL) tumor suppressor gene, and that lowest levels associated with more aggressive PTCs. In the present study, the levels of the two VHL mRNA splicing variants, VHL-213 (V1) and VHL-172 (V2), were measured in a series of 96 PTC and corresponding normal matched tissues by means of quantitative RT-PCR. Variations in the mRNA levels were correlated with patients' clinicopathological parameters and disease-free interval (DFI). The analysis of VHL mRNA in tumor tissues, compared to normal matched tissues, revealed that its expression was either up- or down-regulated in the majority of PTC. In particular, V1 and V2 mRNA levels were altered, respectively, in 78 (81.3%) and 65 (67.7%) out of the 96 PTCs analyzed. A significant positive correlation between the two mRNA variants was observed (p < 0.001). Univariate analysis documented the lack of association between each variant and clinicopathological parameters such as age, tumor size, histology, TNM stage, lymph node metastases, and BRAF mutational status. However, a strong correlation was found between altered V1 or V2 mRNA levels and DFI. Multivariate regression analysis indicated higher V1 mRNA values, along with lymph node metastases at diagnosis, as independent prognostic factors predicting DFI. In conclusion, the data reported demonstrate that VHL gene expression is deregulated in the majority of PTC tissues. Of particular interest is the apparent protective role exerted by VHL transcripts against PTC recurrences.

VHL-TGFBI signaling is involved in the synergy between 5-aza-2'-deoxycytidine and paclitaxel against human renal cell carcinoma

PURPOSE

To analyse the role of von Hippel-Lindau (VHL) and transforming growth factor β-induced (TGFBI) in synergistic mechanisms of 5-aza-2'-deoxycytidine (DAC) and paclitaxel (PTX) against renal cell carcinoma (RCC).

METHODS

To elucidate the role in the synergy between DAC and PTX against RCC cells, TGFBI expression was regulated using siRNA technology and an expression vector containing the full-length cDNA for TGFBI was also transfected into RCC cells. The proliferation of RCC cells was evaluated using the WST-1 assay and TGFBI expression was detected by real-time PCR (RT-PCR), and Western blot.

RESULTS

The results indicated that the expression of TGFBI was significantly decreased by DAC or PTX alone in vitro and in vivo. Moreover, the combination of DAC and PTX caused a synergistic decrease in the expression of TGFBI in RCC cells. We also investigated the effect of VHL-TGFBI signaling on the synergy between DAC and PTX, although the synergy between the two medications was not abolished by interfering with VHL activity or TGFBI expression. RCC cells without VHL activity and RCC cells expressing high levels of TGFBI displayed an increased synergistic effect compared to control cells.

CONCLUSIONS

Our study suggests that VHL-TGFBI signaling is involved in the synergy between DAC and PTX against RCC cells. In addition, the synergy between DAC and PTX is more effective in VHL inactive RCC cells.

Pseudohypoxia induced by miR-126 deactivation promotes migration and therapeutic resistance in renal cell carcinoma

Pseudohypoxia plays a central role in the progression and therapeutic resistance of clear cell renal cell carcinoma (ccRCC); however, the underlying mechanisms are poorly understood. MicroRNA miR-126 has decreased expression in metastatic or relapsed ccRCC as compared to primary tumors, but the mechanisms by which miR-126 is implicated in RCC remain unknown. Through RNA-seq profiling to evaluate the impact of overexpression or CRISPR knockout of miR-126, we have identified SERPINE1 as a miR-126-5p target regulating cell motility, and SLC7A5 as a miR-126-3p target regulating the mTOR/HIF pathway. Specifically, miR-126 inhibits HIFα protein expression independent of von Hippel-Lindau tumor suppressor (VHL). On the other hand, deactivation of miR-126 induces a pseudohypoxia state due to increased HIFα expression, which further enhances therapeutic resistance and cell motility mediated by SLC7A5 and SERPINE1, respectively. Finally, the clinical relevance of miR-126 modulated gene regulation in ccRCC has been confirmed with profiling data from The Cancer Genome Atlas.

S-2-hydroxyglutarate regulates CD8+ T-lymphocyte fate

R-2-hydroxyglutarate accumulates to millimolar levels in cancer cells with gain-of-function isocitrate dehydrogenase 1/2 mutations. These levels of R-2-hydroxyglutarate affect 2-oxoglutarate-dependent dioxygenases. Both metabolite enantiomers, R- and S-2-hydroxyglutarate, are detectible in healthy individuals, yet their physiological function remains elusive. Here we show that 2-hydroxyglutarate accumulates in mouse CD8+ T cells in response to T-cell receptor triggering, and accumulates to millimolar levels in physiological oxygen conditions through a hypoxia-inducible factor 1-alpha (HIF-1α)-dependent mechanism. S-2-hydroxyglutarate predominates over R-2-hydroxyglutarate in activated T cells, and we demonstrate alterations in markers of CD8+ T-cell differentiation in response to this metabolite. Modulation of histone and DNA demethylation, as well as HIF-1α stability, mediate these effects. S-2-hydroxyglutarate treatment greatly enhances the in vivo proliferation, persistence and anti-tumour capacity of adoptively transferred CD8+ T cells. Thus, S-2-hydroxyglutarate acts as an immunometabolite that links environmental context, through a metabolic-epigenetic axis, to immune fate and function.

SENP1 promotes proliferation of clear cell renal cell carcinoma through activation of glycolysis

Metabolic shift toward aerobic glycolysis is a fundamental element contributing to the development and progression of clear cell renal cell carcinoma (ccRCC). We and others previously observed enhanced glycolysis and diminished tricarboxylic acid (TCA) cycle activity in ccRCC tissue. Here, by integrated gene expression and metabolomic analyses of 36 matched pairs of tumor and adjacent normal tissues, we showed that expression of Sentrin/SUMO-specific protease 1 (SENP1) is positively associated with glycolysis levels in ccRCC. Moreover, SENP1 knockdown in RCC4/VHL cells downregulated expression of key glycolytic enzymes under normoxic and hypoxic conditions and inhibited cell proliferation under hypoxic conditions, possibly due to ineffective deSUMOylation and stablization of Hif-1α related to the SENP-1 deficiency. Finally, SENP1 expression correlated positively with tumor pathological grade and was an indicator of poor overall survival and advanced tumor progression in ccRCC. Altered VHL gene function is found in 60-90% ccRCC cases of ccRCC, but therapies targeting VHL-related signaling pathways have been ineffective, spurring exploration of alternative pathological signaling events. Our results provide a possible mechanistic explanation for the role of SENP1 in the initiation and development of ccRCC with normal VHL activity, and identifies SENP1 as a potential treatment target for the disease.