Jade-1 inhibits Wnt signalling by ubiquitylating beta-catenin and mediates Wnt pathway inhibition by pVHL

ARHGAP24 inhibits cell cycle progression, induces apoptosis and suppresses invasion in renal cell carcinoma

Renal cell carcinoma (RCC) is the major cause of kidney malignancy-related deaths. Rho GTPases are key regulators in cancer cell metastasis. ARHGAP24, a Rac-specific member of the Rho GTPase-activating protein family, acts as a functional target of cancer cell migration and invasion. In the present study, we identified ARHGAP24 expression is downregulated in renal cancer tissues and is highly correlated with long-term survival in RCC patients. Therefore, we investigated the biological functions of ARHGAP24 in renal cancer cells. Ectopic expression of ARHGAP24 resulted in inhibited cell proliferation and arrested cell cycle in two renal cancer cell lines (786-0 and Caki-2); the results were confirmed by ARHGAP24 knocking down. In addition, ARHGAP24 significantly reduced the cell invasion ability and induced apoptosis in renal cancer cells. In addition, overexpressing ARHGAP24 impaired tumor formation in vivo. In summary, our results illustrated that ARHGAP24 plays a unique role in RCC progression as a tumor repressor.

Forkhead Box F2 Suppresses Gastric Cancer through a Novel FOXF2-IRF2BPL-β-Catenin Signaling Axis

DNA methylation has been identified as a hallmark of gastric cancer (GC). Identifying genes that are repressed by DNA promoter methylation is essential in providing insights into the molecular pathogenesis of gastric cancer. Using genome-wide methylation studies, we identified that transcription factor forkhead box F2 (FOXF2) was preferentially methylated in gastric cancer. We then investigated the functional significance and clinical implication of FOXF2 in gastric cancer. FOXF2 was silenced in gastric cancer cell lines and cancer tissues by promoter methylation, which was negatively associated with mRNA expression. Ectopic expression of FOXF2 inhibited proliferation, colony formation, G₁-S cell-cycle transition, induced apoptosis of gastric cancer cell lines, and suppressed growth of xenograft tumors in nude mice; knockdown of FOXF2 elicited opposing effects. FOXF2 inhibited Wnt signaling by inducing β-catenin protein ubiquitination and degradation independently of GSK-3β. FOXF2 directly bound the promoter of E3 ligase interferon regulatory factor 2-binding protein-like (IRF2BPL) and induced its transcriptional expression. IRF2BPL in turn interacted with β-catenin, increasing its ubiquitination and degradation. Multivariate Cox regression analysis identified FOXF2 hypermethylation as an independent prognostic factor of poor survival in early-stage gastric cancer patients. In conclusion, FOXF2 is a critical tumor suppressor in gastric carcinogenesis whose methylation status serves as an independent prognostic factor for gastric cancer patients.Significance: FOXF2-mediated upregulation of the E3 ligase IRF2BPL drives ubiquitylation and degradation of β-catenin in gastric cancer, blunting Wnt signaling and suppressing carcinogenesis. Cancer Res; 78(7); 1643-56. ©2018 AACR.

The role of ubiquitination and deubiquitination in the regulation of cell junctions

Maintenance of cell junctions plays a crucial role in the regulation of cellular functions including cell proliferation, permeability, and cell death. Disruption of cell junctions is implicated in a variety of human disorders, such as inflammatory diseases and cancers. Understanding molecular regulation of cell junctions is important for development of therapeutic strategies for intervention of human diseases. Ubiquitination is an important type of post-translational modification that primarily regulates endogenous protein stability, receptor internalization, enzyme activity, and protein-protein interactions. Ubiquitination is tightly regulated by ubiquitin E3 ligases and can be reversed by deubiquitinating enzymes. Recent studies have been focusing on investigating the effect of protein stability in the regulation of cell-cell junctions. Ubiquitination and degradation of cadherins, claudins, and their interacting proteins are implicated in epithelial and endothelial barrier disruption. Recent studies have revealed that ubiquitination is involved in regulation of Rho GTPases’ biological activities. Taken together these studies, ubiquitination plays a critical role in modulating cell junctions and motility. In this review, we will discuss the effects of ubiquitination and deubiquitination on protein stability and expression of key proteins in the cell-cell junctions, including junction proteins, their interacting proteins, and small Rho GTPases. We provide an overview of protein stability in modulation of epithelial and endothelial barrier integrity and introduce potential future search directions to better understand the effects of ubiquitination on human disorders caused by dysfunction of cell junctions.

The natural agent rhein induces β-catenin degradation and tumour growth arrest

The natural agent rhein is an ananthraquinone derivative of rhubarb, which has anticancer effects. To determine the mechanisms underlying the anticancer effects of rhein, we detected the effect of rhein on several oncoproteins. Here, we show that rhein induces β‐catenin degradation in both hepatoma cell HepG2 and cervical cancer cell Hela. Treatment of HepG2 and Hela cells with rhein shortens the half‐life of β‐catenin. The proteasome inhibitor MG132 blunts the downregulation of β‐catenin by rhein. The induction of β‐catenin degradation by rhein is dependent on GSK3 but independent of Akt. Treatment of HepG2 and Hela cells with GSK3 inhibitor or GSK3β knockdown abrogates the effect of rhein on β‐catenin. GSK3β knockdown compromises the inhibition of HepG2 and Hela cell growth by rhein. Furthermore, rhein dose not downregulate β‐catenin mutant that is deficient of phosphorylation at multiple residues including Ser33, Ser37, Thr41 and Ser45. Moreover, rhein induces cell cycle arrest at S phase in both HepG2 and Hela cells. Intraperitoneal administration of rhein suppresses tumour cells proliferation and tumour growth in HepG2 xenografts model. Finally, the levels of β‐catenin are reduced in rhein‐treated tumours. These data demonstrate that rhein can induce β‐catenin degradation and inhibit tumour growth.

The roles of ubiquitin modifying enzymes in neoplastic disease

The initial experiments performed by Rose, Hershko, and Ciechanover describing the identification of a specific degradation signal in short-lived proteins paved the way to the discovery of the ubiquitin mediated regulation of numerous physiological functions required for cellular homeostasis. Since their discovery of ubiquitin and ubiquitin function over 30years ago it has become wholly apparent that ubiquitin and their respective ubiquitin modifying enzymes are key players in tumorigenesis. The human genome encodes approximately 600 putative E3 ligases and 80 deubiquitinating enzymes and in the majority of cases these enzymes exhibit specificity in sustaining either pro-tumorigenic or tumour repressive responses. In this review, we highlight the known oncogenic and tumour suppressive effects of ubiquitin modifying enzymes in cancer relevant pathways with specific focus on PI3K, MAPK, TGFβ, WNT, and YAP pathways. Moreover, we discuss the capacity of targeting DUBs as a novel anticancer therapeutic strategy.

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

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

The connections of Wnt pathway components with cell cycle and centrosome: side effects or a hidden logic?

Wnt signaling cascade has developed together with multicellularity to orchestrate the development and homeostasis of complex structures. Wnt pathway components - such as β-catenin, Dishevelled (DVL), Lrp6, and Axin-- are often dedicated proteins that emerged in evolution together with the Wnt signaling cascade and are believed to function primarily in the Wnt cascade. It is interesting to see that in recent literature many of these proteins are connected with cellular functions that are more ancient and not limited to multicellular organisms - such as cell cycle regulation, centrosome biology, or cell division. In this review, we summarize the recent literature describing this crosstalk. Specifically, we attempt to find the answers to the following questions: Is the response to Wnt ligands regulated by the cell cycle? Is the centrosome and/or cilium required to activate the Wnt pathway? How do Wnt pathway components regulate the centrosomal cycle and cilia formation and function? We critically review the evidence that describes how these connections are regulated and how they help to integrate cell-to-cell communication with the cell and the centrosomal cycle in order to achieve a fine-tuned, physiological response.

The regulation of β-catenin activity and function in cancer: therapeutic opportunities

Wnt/β-catenin signaling is an evolutionarily conserved and versatile pathway that is known to be involved in embryonic development, tissue homeostasis and a wide variety of human diseases. Aberrant activation of this pathway gives rise to the accumulation of β-catenin in the nucleus and promotes the transcription of many oncogenes such as c-Myc and CyclinD-1. As a result, it contributes to carcinogenesis and tumor progression of several cancers, including colon cancer, hepatocellular carcinoma, pancreatic cancer, lung cancer and ovarian cancer. β-Catenin is a pivotal component of the Wnt signaling pathway and it is tightly regulated at three hierarchical levels: protein stability, subcellular localization and transcriptional activity. Uncovering the regulatory mechanisms of β-catenin will provide new insights into the pathogenesis of cancer and other diseases, as well as new therapeutic strategies against these diseases. In this review we dissect the concrete regulatory mechanisms of β-catenin from three aspects mentioned above. Then we focus on the role of β-catenin in cancer initiation, progression, dormancy, immunity and cancer stem cell maintenance. At last, we summarize the recent progress in the development of agents for the pharmacological modulation of β-catenin activity in cancer therapy.

USP7 inhibitor P5091 inhibits Wnt signaling and colorectal tumor growth

Aberrant activation of Wnt/β-catenin signaling is closely associated with the development of various human cancers, especially colorectal cancers (CRC). The ubiquitin proteasome system (UPS) is essential in the regulation of Wnt signaling and inhibitors targeting the UPS could have great potential in CRC therapy. Ubiquitin-specific protease 7 (USP7), a deubiquitinating enzyme, plays a significant role in neoplastic diseases due to its well-known function of regulating the MDM2-p53 complex. Inspired by our recent study identifying the positive role of USP7 in the Wnt signaling, we report here that USP7 is overexpressed in colorectal carcinoma cell lines and tissues, which is closely related with the poor prognosis. USP7 knockdown inhibits the proliferation of CRC cells with different p53 status, and USP7 inhibition by its inhibitor P5091 attenuates the activity of Wnt signaling via enhanced ubiquitination and the subsequent degradation of β-catenin. In vitro, P5091 inhibited the proliferation and induced apoptosis of CRC cells. P5091 also suppressed in vivo tumor growth in the HCT116 xenograft mouse model, which is consistently associated with reduced expression of β-catenin and Wnt target genes. In conclusion, our preclinical study indicated that USP7 could be a potential drug target and its inhibitor P5091 deserves further development as anticancer agent for Wnt hyper-activated CRC therapy.

The epigenetic landscape of renal cancer

The majority of kidney cancers are associated with mutations in the von Hippel-Lindau gene and a small proportion are associated with infrequent mutations in other well characterized tumour-suppressor genes. In the past 15 years, efforts to uncover other key genes involved in renal cancer have identified many genes that are dysregulated or silenced via epigenetic mechanisms, mainly through methylation of promoter CpG islands or dysregulation of specific microRNAs. In addition, the advent of next-generation sequencing has led to the identification of several novel genes that are mutated in renal cancer, such as PBRM1, BAP1 and SETD2, which are all involved in histone modification and nucleosome and chromatin remodelling. In this Review, we discuss how altered DNA methylation, microRNA dysregulation and mutations in histone-modifying enzymes disrupt cellular pathways in renal cancers.

Forkhead Transcription Factor 3a (FOXO3a) Modulates Hypoxia Signaling via Up-regulation of the von Hippel-Lindau Gene (VHL)

FOXO3a, a member of the forkhead homeobox type O (FOXO) family of transcriptional factors, regulates cell survival in response to DNA damage, caloric restriction, and oxidative stress. The von Hippel-Lindau (VHL) tumor suppressor gene encodes a component of the E3 ubiquitin ligase complex that mediates hypoxia-inducible factor α degradation under aerobic conditions, thus acting as one of the key regulators of hypoxia signaling. However, whether FOXO3a impacts cellular hypoxia stress remains unknown. Here we show that FOXO3a directly binds to the VHL promoter and up-regulates VHL expression. Using a zebrafish model, we confirmed the up-regulation of vhl by foxo3b, an ortholog of mammalian FOXO3a Furthermore, by employing the clustered regularly interspaced short palindromic repeats (CRISPR)-associated RNA-guided endonuclease Cas9 (CRISPR/Cas9) technology, we deleted foxo3b in zebrafish and determined that expression of hypoxia-inducible genes was affected under hypoxia. Moreover, foxo3b-null zebrafish exhibited impaired acute hypoxic tolerance, resulting in death. In conclusion, our findings suggest that, by modulating hypoxia-inducible factor activity via up-regulation of VHL, FOXO3a (foxo3b) plays an important role in survival in response to hypoxic stress.

Renal Carcinogenesis, Tumor Heterogeneity, and Reactive Oxygen Species: Tactics Evolved

SIGNIFICANCE

The number of kidney cancers is growing 3-5% each year due to unknown etiologies. Intra- and inter-tumor mediators increase oxidative stress and drive tumor heterogeneity. Recent Advances: Technology advancement in state-of-the-art instrumentation and methodologies allows researchers to detect and characterize global landscaping modifications in genes, proteins, and pathophysiology patterns at the single-cell level.

CRITICAL ISSUES

We postulate that the sources of reactive oxygen species (ROS) and their activation within subcellular compartments will change over a timeline of tumor evolvement and contribute to tumor heterogeneity. Therefore, the complexity of intracellular changes within a tumor and ROS-induced tumor heterogeneity coupled to the advancement of detecting these events globally are limited at the level of data collection, organization, and interpretation using software algorithms and bioinformatics.

FUTURE DIRECTIONS

Integrative and collaborative research, combining the power of numbers with careful experimental design, protocol development, and data interpretation, will translate cancer biology and therapeutics to a heightened level or leave the abundant raw data as stagnant and underutilized. Antioxid. Redox Signal. 25, 685-701.

Blocking peptides and molecular mimicry as treatment for kidney disease

Protein mimotopes, or blocking peptides, are small therapeutic peptides that prevent protein-protein interactions by selectively mimicking a native binding domain. Inexpensive technology facilitates straightforward design and production of blocking peptides in sufficient quantities to allow preventive and therapeutic trials in both in vitro and in vivo experimental disease models. The kidney is an ideal peptide target, since small molecules undergo rapid filtration and efficient bulk absorption by tubular epithelial cells. Because the half-life of peptides is markedly prolonged in the kidneys compared with the bloodstream, blocking peptides are an attractive tool for treating diverse renal diseases, including ischemia, proteinuric states, such as membranous nephropathy and focal and segmental glomerulosclerosis, and renal cell carcinoma. Therapeutic peptides represent one of the fastest-growing reagent classes for novel drug development in human disease, partly because of their ease of administration, high binding affinity, and minimal off-target effects. This review introduces the concepts of blocking peptide design, production, and administration and highlights the potential use of therapeutic peptides to prevent or treat specific renal diseases.

Control of Hedgehog Signalling by the Cilia-Regulated Proteasome

The Hedgehog signalling pathway is evolutionarily highly conserved and essential for embryonic development of invertebrates and vertebrates. Consequently, impaired Hedgehog signalling results in very severe human diseases, ranging from holoprosencephaly to Pallister-Hall syndrome. Due to this great importance for human health, the focus of numerous research groups is placed on the investigation of the detailed mechanisms underlying Hedgehog signalling. Today, it is known that tiny cell protrusions, known as primary cilia, are necessary to mediate Hedgehog signalling in vertebrates. Although the Hedgehog pathway is one of the best studied signalling pathways, many questions remain. One of these questions is: How do primary cilia control Hedgehog signalling in vertebrates? Recently, it was shown that primary cilia regulate a special kind of proteasome which is essential for proper Hedgehog signalling. This review article will cover this novel cilia-proteasome association in embryonic Hedgehog signalling and discuss the possibilities provided by future investigations on this topic.

Correlation analysis of VHL and Jade-1 gene expression in human renal cell carcinoma

Objective

The aim of this study was to investigate the correlation of von Hippel-Lindau tumor suppressor (VHL) mRNA expression and jade family PHD finger 1 (Jade-1) gene expression in patients with renal cell carcinoma (RCC). Another aim of this study was to analyze the relationship of these two genes with clinicalpathological features of the RCC patients.

Methods

A total of 75 RCC patients who received surgically therapy in our hospital were included. All patients had complete pathological data. The expression of VHL/Jade-1 was determined by real-time polymerase chain reaction (RT-PCR).

Results

VHL and Jade-1 were both obviously downregulated in RCC tissues than that of the matched normal tissues, and both negatively correlated with tumor size as well as tumor grade. And we found a fine association of VHL gene expression with Jade-1.

Conclusion

VHL/Jade-1 exhibited significantly decreased expression in RCC tissues and was closely related to the clinical prognosis of patients. The finding of VHL expression positively correlated with Jade-1 expression shed light and provided crucial evidence on the connection of VHL protein with Wnt/b-catenin pathway.

Structure, function and regulation of jade family PHD finger 1 (JADE1)

The family of JADE proteins includes three paralogues encoded by individual genes and designated PHF17 (JADE1), PHF16 (JADE2), and PHF15 (JADE3). All three JADE proteins bear in tandem two Plant Homeo-domains (PHD) which are zinc finger domains. This review focuses on one member of the JADE family, JADE1. Studies addressing the biochemical, cellular and biological role of JADE1 are discussed. Recent discoveries of JADE1 function in the regulation of the epithelial cell cycle with potential relevance to disease are presented. Unresolved questions and future directions are formulated.

WDR26 is a new partner of Axin1 in the canonical Wnt signaling pathway

The stability of β‐catenin is very important for canonical Wnt signaling. A protein complex including Axin/APC/GSK3β phosphorylates β‐catenin to be degraded by ubiquitination with β‐TrCP. In the recent study, we isolated WDR26, a protein that binds to Axin. Here, we found that WDR26 is a negative regulator of the canonical Wnt signaling pathway, and that WDR26 affected β‐catenin levels. In addition, WDR26/Axin binding is involved in the ubiquitination of β‐catenin. These results suggest that WDR26 plays a negative role in β‐catenin degradation in the Wnt signaling pathway.

An oxygen-insensitive Hif-3α isoform inhibits Wnt signaling by destabilizing the nuclear β-catenin complex

Hypoxia-inducible factors (HIFs), while best known for their roles in the hypoxic response, have oxygen-independent roles in early development with poorly defined mechanisms. Here, we report a novel Hif-3α variant, Hif-3α2, in zebrafish. Hif-3α2 lacks the bHLH, PAS, PAC, and ODD domains, and is expressed in embryonic and adult tissues independently of oxygen availability. Hif-3α2 is a nuclear protein with significant hypoxia response element (HRE)-dependent transcriptional activity. Hif-3α2 overexpression not only decreases embryonic growth and developmental timing but also causes left-right asymmetry defects. Genetic deletion of Hif-3α2 by CRISPR/Cas9 genome editing increases, while Hif-3α2 overexpression decreases, Wnt/β-catenin signaling. This action is independent of its HRE-dependent transcriptional activity. Mechanistically, Hif-3α2 binds to β-catenin and destabilizes the nuclear β-catenin complex. This mechanism is distinct from GSK3β-mediated β-catenin degradation and is conserved in humans. These findings provide new insights into the oxygen-independent actions of HIFs and uncover a novel mechanism regulating Wnt/β-catenin signaling.

Jade-1S phosphorylation induced by CK1α contributes to cell cycle progression

The PHD zinc finger protein Jade-1S is a component of the HBO1 histone acetyltransferase complex and binds chromatin in a cell cycle-dependent manner. Jade-1S also acts as an E3 ubiquitin ligase for the canonical Wnt effector protein β-catenin and is influenced by CK1α-mediated phosphorylation. To further elucidate the functional impact of this phosphorylation, we used a stable, low-level expression system to express either wild-type or mutant Jade-1S lacking the N-terminal CK1α phosphorylation motif. Interactome analyses revealed that the Jade-1S mutant unable to be phosphorylated by CK1α has an increased binding affinity to proteins involved in chromatin remodelling, histone deacetylation, transcriptional repression, and ribosome biogenesis. Interestingly, cells expressing the mutant displayed an elongated cell shape and a delay in cell cycle progression. Finally, phosphoproteomic analyses allowed identification of a Jade-1S site phosphorylated in the presence of CK1α but closely resembling a PLK1 phosphorylation motif. Our data suggest that Jade-1S phosphorylation at an N-terminal CK1α motif creates a PLK1 phospho-binding domain. We propose CK1α phosphorylation of Jade 1S to serve as a molecular switch, turning off chromatin remodelling functions of Jade-1S and allowing timely cell cycle progression. As Jade-1S protein expression in the kidney is altered upon renal injury, this could contribute to understanding mechanisms underlying epithelial injury repair.

The novel function of JADE1S in cytokinesis of epithelial cells

JADE1 belongs to a small family of PHD zinc finger proteins that interacts with histone acetyl transferase (HAT) HBO1 and is associated with chromatin. We recently reported JADE1 chromatin shuttling and phosphorylation during G2/M to G1 transition, which was sensitive to Aurora A inhibition. In the current study we examined mechanisms of the cell cycle regulation by the small isoform of JADE1 protein, JADE1S, and report data showing that JADE1S has a novel function in the regulation of cytokinesis. Using FACS assays, we show that, JADE1S depletion facilitated rates of G1-cells accumulation in synchronously dividing HeLa cell cultures. Depletion of JADE1S protein in asynchronously dividing cells decreased the proportion of cytokinetic cells, and increased the proportion of multi-nuclear cells, indicative of premature and failed cytokinesis. In contrast, moderate overexpression of JADE1S increased the number of cytokinetic cells in time- and dose- dependent manner, indicating cytokinetic delay. Pharmacological inhibition of Aurora B kinase resulted in the release of JADE1S-mediated cytokinetic delay and allowed progression of abscission in cells over-expressing JADE1S. Finally, we show that JADE1S protein localized to centrosomes in interphase and mitotic cells, while during cytokinesis JADE1S localized to the midbody. Neither JADE1L nor partner of JADE1, HAT HBO1 was localized to the centrosomes or midbodies. Our study identifies the novel role for JADE1S in regulation of cytokinesis and suggests function in Aurora B kinase-mediated cytokinesis checkpoint.

The c-Cbl ubiquitin ligase regulates nuclear β-catenin and angiogenesis by its tyrosine phosphorylation mediated through the Wnt signaling pathway

Wnt signaling plays important roles in both the tumor-induced angiogenesis and tumorigenesis through the transcriptionally active nuclear β-catenin. Recently, c-Cbl was identified as a unique E3 ubiquitin ligase targeting the active nuclear β-catenin. However, little is known about the molecular mechanisms by which c-Cbl regulates ubiquitination and degradation of active β-catenin. Here, we demonstrate that Wnt activation promotes the phosphorylation of c-Cbl at tyrosine 731(Tyr-731), which increases c-Cbl dimerization and binding to β-catenin. Tyr-731 phosphorylation and dimerization mediate c-Cbl nuclear translocation and lead to the degradation of nuclearly active β-catenin in the Wnt-on phase. c-Cbl activation also inhibits expression of the pro-angiogenic Wnt targets, IL-8 and VEGF. Phospho-Tyr-731-inactive mutant c-Cbl (Y731F) enhances and phosphomimetic mutant c-Cbl (Y731E) suppresses angiogenesis in zebrafish. Taken together, we have identified a novel mechanism for the regulation of active nuclear β-catenin by c-Cbl and its critical role in angiogenesis. This mechanism can be further explored to modulate both the pathological angiogenesis and the tumorigenesis.

Synergistic signaling of tumor cell invasiveness by hepatocyte growth factor and hypoxia

Hepatocyte growth factor (HGF) signaling promotes tumor invasiveness in renal cell carcinoma (RCC) and other cancers. In clear cell RCC, VHL loss generates pseudohypoxia that exacerbates HGF-driven invasion through β-catenin deregulation. Hypoxia also enhances HGF-driven invasiveness by papillary RCC cells, but in the absence of VHL, loss signaling integration involves three parallel routes: 1) hypoxia-induced reactive oxygen species production and decreased DUSP2 expression, leading to enhanced mitogen-activated protein kinase (MAPK) cascade activation; 2) reactive oxygen species-induced diacylglycerol production by phospholipase Cγ, leading to protein kinase C activation and increased protein phosphatase- 2A activity, thereby suppressing HGF-induced Akt activation; and 3) a profound shift from HGF-enhanced, proliferation- oriented metabolism to autophagy-dependent invasion and suppression of proliferation. This tripartite signaling integration was not unique to RCC or HGF; in RCC cells, invasive synergy induced by the combination of hypoxia and epidermal growth factor occurred through the same mechanism, and in estrogen receptor-positive breast cancer cells, this mechanism was suppressed in the absence of estrogen. These results define the molecular basis of growth factor and hypoxia invasive synergy in VHL-competent papillary RCC cells, illustrate the plasticity of invasive and proliferative tumor cell states, and provide signaling profiles by which they may be predicted.

Tumour suppressor TRIM33 targets nuclear β-catenin degradation

Aberrant activation of β-catenin in the nucleus has been implicated in a variety of human cancers but the fate of nuclear β-catenin is unknown. Here we demonstrate that tripartite motif-containing protein 33 (TRIM33), acting as an E3 ubiquitin ligase, reduces the abundance of nuclear β-catenin protein. TRIM33-mediated β-catenin is destabilized and is GSK-3β or β-TrCP independent. TRIM33 interacts with and ubiquitylates nuclear β-catenin. Moreover, protein kinase Cδ, which directly phosphorylates β-catenin at Ser715, is required for the TRIM33–β-catenin interaction. The function of TRIM33 in suppressing tumour cell proliferation and brain tumour development depends on TRIM33-promoted β-catenin degradation. In human glioblastoma specimens, endogenous TRIM33 levels are inversely correlated with β-catenin. In summary, our findings identify TRIM33 as a tumour suppressor that can abolish tumour cell proliferation and tumorigenesis by degrading nuclear β-catenin. This work suggests a new therapeutic strategy against human cancers caused by aberrant activation of β-catenin.

Gramicidin A: A New Mission for an Old Antibiotic

Gramicidin A (GA) is a channel-forming ionophore that renders biological membranes permeable to specific cations which disrupts cellular ionic homeostasis. It is a well-known antibiotic, however it’s potential as a therapeutic agent for cancer has not been widely evaluated. In two recently published studies, we showed that GA treatment is toxic to cell lines and tumor xenografts derived from renal cell carcinoma (RCC), a devastating disease that is highly resistant to conventional therapy. GA was found to possess the qualities of both a cytotoxic drug and a targeted angiogenesis inhibitor, and this combination significantly compromised RCC growth in vitro and in vivo. In this review, we summarize our recent research on GA, discuss the possible mechanisms whereby it exerts its anti-tumor effects, and share our perspectives on the future opportunities and challenges to the use of GA as a new anticancer agent.

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

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

β-catenin links von Hippel-Lindau to aurora kinase A and loss of primary cilia in renal cell carcinoma

von Hippel-Lindau (VHL) gene mutations are associated with clear cell renal cell carcinoma (ccRCC). A hallmark of ccRCC is loss of the primary cilium. Loss of this key organelle in ccRCC is caused by loss of VHL and associated with increased Aurora kinase A (AURKA) and histone deacetylase 6 (HDAC6) activities, which drive disassembly of the primary cilium. However, the underlying mechanism by which VHL loss increases AURKA levels has not been clearly elucidated, although it has been suggested that hypoxia-inducible factor-1α (HIF-1α) mediates increased AURKA expression in VHL-null cells. By contrast, we found that elevated AURKA expression is not increased by HIF-1α, suggesting an alternate mechanism for AURKA dysregulation in VHL-null cells. We report here that AURKA expression is driven by β-catenin transcription in VHL-null cells. In a panel of RCC cell lines, we observed nuclear accumulation of β-catenin and increased AURKA signaling to HDAC6. Moreover, HIF-1α inhibited AURKA expression by inhibiting β-catenin transcription. VHL knockdown activated β-catenin and elevated AURKA expression, decreased primary cilia formation, and caused significant shortening of cilia length in cells that did form cilia. The β-catenin responsive transcription inhibitor iCRT14 reduced AURKA levels and rescued ciliary defects, inducing a significant increase in primary cilia formation in VHL-deficient cells. These data define a role for β-catenin in regulating AURKA and formation of primary cilia in the setting of VHL deficiency, opening new avenues for treatment with β-catenin inhibitors to rescue ciliogenesis in ccRCC.

The ubiquitin ligase RNF220 enhances canonical Wnt signaling through USP7-mediated deubiquitination of β-catenin

Wnt/β-catenin signaling plays critical roles in embryonic development and disease. Here, we identify RNF220, a RING domain E3 ubiquitin ligase, as a new regulator of β-catenin. RNF220 physically interacts with β-catenin, but instead of promoting its ubiquitination and proteasomal degradation, it stabilizes β-catenin and promotes canonical Wnt signaling. Our analysis showed that RNF220 interacts with USP7, a ubiquitin-specific peptidase, which is required for RNF220 to stabilize β-catenin. The RNF220/USP7 complex deubiquitinates β-catenin and enhances canonical Wnt signaling. Interestingly, the stability of RNF220 itself is negatively regulated by Gsk3β, which is a key component of the β-catenin destruction complex and is inhibited upon Wnt stimulation. Accordingly, the RNF220/USP7 complex works as a positive feedback regulator of β-catenin signaling. In colon cancer cells with stimulated Wnt signaling, knockdown of RNF220 or USP7 impairs Wnt signaling and expression of Wnt target genes, suggesting a potentially novel role of RNF220 in Wnt-related tumorigenesis.

Casein kinase 1 α phosphorylates the Wnt regulator Jade-1 and modulates its activity

Tight regulation of Wnt/β-catenin signaling is critical for vertebrate development and tissue maintenance, and deregulation can lead to a host of disease phenotypes, including developmental disorders and cancer. Proteins associated with primary cilia and centrosomes have been demonstrated to negatively regulate canonical Wnt signaling in interphase cells. The plant homeodomain zinc finger protein Jade-1 can act as an E3 ubiquitin ligase-targeting β-catenin for proteasomal degradation and concentrates at the centrosome and ciliary basal body in addition to the nucleus in interphase cells. We demonstrate that the destruction complex component casein kinase 1α (CK1α) phosphorylates Jade-1 at a conserved SLS motif and reduces the ability of Jade-1 to inhibit β-catenin signaling. Consistently, Jade-1 lacking the SLS motif is more effective than wild-type Jade-1 in reducing β-catenin-induced secondary axis formation in Xenopus laevis embryos in vivo. Interestingly, CK1α also phosphorylates β-catenin and the destruction complex component adenomatous polyposis coli at a similar SLS motif to the effect that β-catenin is targeted for degradation. The opposing effect of Jade-1 phosphorylation by CK1α suggests a novel example of the dual functions of CK1α activity to either oppose or promote canonical Wnt signaling in a context-dependent manner.

Destabilizing LSD1 by Jade-2 promotes neurogenesis: an antibraking system in neural development

Histone H3K4 demethylase LSD1 plays an important role in stem cell biology, especially in the maintenance of the silencing of differentiation genes. However, how the function of LSD1 is regulated and the differentiation genes are derepressed are not understood. Here, we report that elimination of LSD1 promotes embryonic stem cell (ESC) differentiation toward neural lineage. We showed that the destabilization of LSD1 occurs posttranscriptionally via the ubiquitin-proteasome pathway by an E3 ubiquitin ligase, Jade-2. We demonstrated that Jade-2 is a major LSD1 negative regulator during neurogenesis in vitro and in vivo in both mouse developing cerebral cortices and zebra fish embryos. Apparently, Jade-2-mediated degradation of LSD1 acts as an antibraking system and serves as a quick adaptive mechanism for re-establishing epigenetic landscape without more laborious transcriptional regulations. As a potential anticancer strategy, Jade-2-mediated LSD1 degradation could potentially be used in neuroblastoma cells to induce differentiation toward postmitotic neurons.

Loss of VHL expression contributes to epithelial-mesenchymal transition in oral squamous cell carcinoma

OBJECTIVE

Loss of Von Hippel-Lindau (VHL) gene expression has been implicated in the development of human cancers. However, its function in oral squamous cell carcinoma (OSCC) remains undefined. The aim of this study was to clarify the VHL expression in OSCC and to explore the underlying mechanisms of VHL in modulating the epithelial-mesenchymal transition (EMT) in OSCC.

MATERIALS AND METHODS

The expression of VHL, HIF-1α and EMT related proteins in OSCC tissues were evaluated by immunohistochemistry. The correlation of VHL with clinico-pathological characteristics, prognosis and EMT related proteins were analyzed. The roles of VHL on the cell morphology, proliferation, migration, and invasion were determined by MTT, scratch and transwell invasion assay in Tscca and Tca8113P160 cells. The EMT related proteins were determined by Western blot and immunofluorescence (IF) methods.

RESULTS

Loss of VHL expression was closely associated with pathologic grading, lymph node metastasis, poor prognosis, and EMT in OSCC. After re-expression of VHL, there was a cell morphologic change and motivation, proliferation, invasion of the cells were inhibited. The expression of Snail, N-cadherin and MMP-2/9, HIF-1α and VEGF were down-regulated in both the cell lines after transfection with VHL plasmid, while E-cadherin was up-regulated. Moreover, the effect of VHL suppressing β-catenin accumulation in nucleus was proved by Western blot and IF.

CONCLUSION

VHL was significantly correlated with EMT process of OSCC. β-Catenin was an important downstream gene of VHL besides HIF-1α, which could induce the EMT process in OSCC.

Interaction between Nm23 and the tumor suppressor VHL

Among the anti-tumor genes (tumor suppressors and metastasis suppressors), the von-Hippel Lindau gene and the Nm23 family of genes are among the more intriguing ones. Both are small (long and short forms of VHL are 30 and 19 kD, respectively, and Nm23 is ~17 kD), and both possess diverse molecular and cellular functions. Despite extensive studies, the entire spectra of functions and the molecular function-phenotype correlation of these two proteins have not been completely elucidated. In this report, we present data showing these two proteins interact physically. We also summarize and confirm the previous studies that demonstrated the endocytic function of these two genes and further show that the endocytic function of VHL is mediated through the activity of Nm23. These functional and molecular interactions are evolutionarily conserved from Drosophila to human.

Regulation of Wnt/β-catenin signaling by posttranslational modifications

The canonical Wnt signaling pathway (or Wnt/β-catenin pathway) plays a pivotal role in embryonic development and adult homeostasis; deregulation of the Wnt pathway contributes to the initiation and progression of human diseases including cancer. Despite its importance in human biology and disease, how regulation of the Wnt/β-catenin pathway is achieved remains largely undefined. Increasing evidence suggests that post-translational modifications (PTMs) of Wnt pathway components are essential for the activation of the Wnt/β-catenin pathway. PTMs create a highly dynamic relay system that responds to Wnt stimulation without requiring de novo protein synthesis and offer a platform for non-Wnt pathway components to be involved in the regulation of Wnt signaling, hence providing alternative opportunities for targeting the Wnt pathway. This review highlights the current status of PTM-mediated regulation of the Wnt/β-catenin pathway with a focus on factors involved in Wnt-mediated stabilization of β-catenin.

Regulation of the transcriptional activation of the androgen receptor by the UXT-binding protein VHL

Loss and/or inactivation of the VHL (von Hippel-Lindau) tumour suppressor causes various tumours. Using a yeast two-hybrid system, we have identified the AR (androgen receptor) co-activator UXT (ubiquitously expressed transcript), as a VHL-interacting protein. GST pull-down and co-immunoprecipitation assays show that UXT interacts with VHL. In addition, UXT recruits VHL to the nucleus. VHL associates with the DBD (DNA-binding domain) and hinge domains of the AR and induces AR ubiquitination. Moreover, VHL interaction with the AR activates AR transactivation upon DHT (dihydrotestosterone) treatment. VHL knockdown inhibits AR ubiquitination and decreases transcriptional activation of the AR. Our data suggest that the VHL-UXT interaction and VHL-induced ubiquitination of AR regulate transcriptional activation of the AR.

Histone acetyltransferase Hbo1 destabilizes estrogen receptor α by ubiquitination and modulates proliferation of breast cancers

The estrogen receptor (ER) is a key molecule for growth of breast cancers. It has been a successful target for treatment of breast cancers. Elucidation of the ER expression mechanism is of importance for designing therapeutics for ER-positive breast cancers. However, the detailed mechanism of ER stability is still unclear. Here, we report that histone acetyltransferase Hbo1 promotes destabilization of estrogen receptor α (ERα) in breast cancers through lysine 48-linked ubiquitination. The acetyltransferase activity of Hbo1 is linked to its activity for ERα ubiquitination. Depletion of Hbo1 and anti-estrogen treatment displayed a potent growth suppression of breast cancer cell line. Hbo1 modulated transcription by ERα. Mutually exclusive expression of Hbo1 and ERα was observed in roughly half of the human breast tumors examined in the present study. Modulation of ER stability by Hbo1 in breast cancers may provide a novel therapeutic possibility.

A novel non-coding RNA lncRNA-JADE connects DNA damage signalling to histone H4 acetylation

A prompt and efficient DNA damage response (DDR) eliminates the detrimental effects of DNA lesions in eukaryotic cells. Basic and preclinical studies suggest that the DDR is one of the primary anti-cancer barriers during tumorigenesis. The DDR involves a complex network of processes that detect and repair DNA damage, in which long non-coding RNAs (lncRNAs), a new class of regulatory RNAs, may play an important role. In the current study, we identified a novel lncRNA, lncRNA-JADE, that is induced after DNA damage in an ataxia-telangiectasia mutated (ATM)-dependent manner. LncRNA-JADE transcriptionally activates Jade1, a key component in the HBO1 (human acetylase binding to ORC1) histone acetylation complex. Consequently, lncRNA-JADE induces histone H4 acetylation in the DDR. Markedly higher levels of lncRNA-JADE were observed in human breast tumours in comparison with normal breast tissues. Knockdown of lncRNA-JADE significantly inhibited breast tumour growth in vivo. On the basis of these results, we propose that lncRNA-JADE is a key functional link that connects the DDR to histone H4 acetylation, and that dysregulation of lncRNA-JADE may contribute to breast tumorigenesis.

Receptor tyrosine kinase-like orphan receptor 2 (Ror2) expression creates a poised state of Wnt signaling in renal cancer

Expression of the receptor tyrosine kinase-like orphan receptor 2 (Ror2) has been identified in an increasing array of tumor types and is known to play a role as an important mediator of Wnt signaling cascades. In this study, we aimed to clarify Ror2 interactions with the Wnt pathways within the context of renal cell carcinoma (RCC). An examination of Ror2 expression in primary human RCC tumors showed a significant correlation with several Wnt signaling genes, including the classical feedback target gene Axin2. We provide evidence that Ror2 expression results in a partially activated state for canonical Wnt signaling through an increased signaling pool of β-catenin, leading to an enhancement of downstream target genes following Wnt3a stimulation in both renal and renal carcinoma-derived cells. Additionally, inhibition of low-density lipoprotein receptor-related protein 6 (LRP6) with either siRNA or dickkopf decreased the response to Wnt3a stimulation, but no change was seen in the increased β-catenin pool associated with Ror2 expression, suggesting that LRP6 cofactor recruitment is necessary for a Wnt3a-induced signal but that it does not participate in the Ror2 effect on β-catenin signaling. These results highlight a new role for Ror2 in conveying a tonic signal to stabilize soluble β-catenin and create a poised state of enhanced responsiveness to Wnt3a exogenous signals in RCC.

Candidate tumor suppressor and pVHL partner Jade-1 binds and inhibits AKT in renal cell carcinoma

The von Hippel-Lindau (VHL) tumor suppressor pVHL is lost in the majority of clear-cell renal cell carcinomas (RCC). Activation of the PI3K/AKT/mTOR pathway is also common in RCC, with PTEN loss occurring in approximately 30% of the cases, but other mechanisms responsible for activating AKT at a wider level in this setting are undefined. Plant homeodomain protein Jade-1 (PHF17) is a candidate renal tumor suppressor stabilized by pVHL. Here, using kinase arrays, we identified phospho-AKT1 as an important target of Jade-1. Overexpressing or silencing Jade-1 in RCC cells increased or decreased levels of endogenous phospho-AKT/AKT1. Furthermore, reintroducing pVHL into RCC cells increased endogenous Jade-1 and suppressed endogenous levels of phospho-AKT, which colocalized with and bound to Jade-1. The N-terminus of Jade-1 bound both the catalytic domain and the C-terminal regulatory tail of AKT, suggesting a mechanism through which Jade-1 inhibited AKT kinase activity. Intriguingly, RCC precursor cells where Jade-1 was silenced exhibited an increased capacity for AKT-dependent anchorage-independent growth, in support of a tumor suppressor function for Jade-1 in RCC. In support of this concept, an in silico expression analysis suggested that reduced Jade-1 expression is a poor prognostic factor in clear-cell RCC that is associated with activation of an AKT1 target gene signature. Taken together, our results identify 2 mechanisms for Jade-1 fine control of AKT/AKT1 in RCC, through loss of pVHL, which decreases Jade-1 protein, or through attenuation in Jade-1 expression. These findings help explain the pathologic cooperativity in clear-cell RCC between PTEN inactivation and pVHL loss, which leads to decreased Jade-1 levels that superactivate AKT. In addition, they prompt further investigation of Jade-1 as a candidate biomarker and tumor suppressor in clear-cell RCC.

c-Cbl, a ubiquitin E3 ligase that targets active β-catenin: a novel layer of Wnt signaling regulation

Regulation of transcriptionally active nuclear β-catenin during the Wnt-on phase is crucial to ensure controlled induction of Wnt target genes. Several ubiquitin E3 ligases are known to regulate cytosolic β-catenin during the Wnt-off phase, but little is known about the fate of active nuclear β-catenin in the Wnt-on phase. We now describe ubiquitination of active β-catenin in the Wnt-on phase by a RING finger ubiquitin E3 ligase, Casitas B-lineage lymphoma (c-Cbl) in endothelial cells. c-Cbl binds preferentially to nuclearly active β-catenin in the Wnt-on phase via the armadillo repeat region. Wild-type c-Cbl suppresses and E3 ligase-deficient c-Cbl-70Z increases Wnt signaling. Wnt induces nuclear translocation of c-Cbl where it ubiquitinates nuclear β-catenin. Deletion of the c-Cbl UBA domain abrogates its dimerization, binding to β-catenin, Wnt-induced c-Cbl nuclear translocation, and ubiquitination of nuclear β-catenin. c-Cbl activity inhibits pro-angiogenic Wnt targets IL-8 and VEGF levels and angiogenesis in a β-catenin-dependent manner. This study defines for the first time c-Cbl as a ubiquitin E3 ligase that targets nuclearly active β-catenin in the Wnt-on phase and uncovers a novel layer of regulation of Wnt signaling.

The von Hippel-Lindau protein pVHL inhibits ribosome biogenesis and protein synthesis

pVHL, the product of von Hippel-Lindau (VHL) tumor suppressor gene, functions as the substrate recognition component of an E3-ubiquitin ligase complex that targets hypoxia inducible factor α (HIF-α) for ubiquitination and degradation. Besides HIF-α, pVHL also interacts with other proteins and has multiple functions. Here, we report that pVHL inhibits ribosome biogenesis and protein synthesis. We find that pVHL associates with the 40S ribosomal protein S3 (RPS3) but does not target it for destruction. Rather, the pVHL-RPS3 association interferes with the interaction between RPS3 and RPS2. Expression of pVHL also leads to nuclear retention of pre-40S ribosomal subunits, diminishing polysomes and 18S rRNA levels. We also demonstrate that pVHL suppresses both cap-dependent and cap-independent protein synthesis. Our findings unravel a novel function of pVHL and provide insight into the regulation of ribosome biogenesis by the tumor suppressor pVHL.

Wnt/β-catenin signalling: from plasma membrane to nucleus

Wnt/β-catenin signalling plays essential roles in embryonic development as well as tissue homoeostasis in adults. Thus abnormal regulation of Wnt/β-catenin signalling is linked to a variety of human diseases, including cancer, osteoporosis and Alzheimer's disease. Owing to the importance of Wnt signalling in a wide range of biological fields, a better understanding of its precise mechanisms could provide fundamental insights for therapeutic applications. Although many studies have investigated the regulation of Wnt/β-catenin signalling, our knowledge remains insufficient due to the complexity and diversity of Wnt signalling. It is generally accepted that the identification of novel regulators and their functions is a prerequisite to fully elucidating the regulation of Wnt/β-catenin signalling. Recently, several novel modulators of Wnt signalling have been determined through multiple genetic and proteomic approaches. In the present review, we discuss the mechanistic regulation of Wnt/β-catenin signalling by focusing on the roles of these novel regulators.

In vivo HIF-mediated reductive carboxylation is regulated by citrate levels and sensitizes VHL-deficient cells to glutamine deprivation

Hypoxic and VHL-deficient cells use glutamine to generate citrate and lipids through reductive carboxylation (RC) of α-ketoglutarate. To gain insights into the role of HIF and the molecular mechanisms underlying RC, we took advantage of a panel of disease-associated VHL mutants and showed that HIF expression is necessary and sufficient for the induction of RC in human renal cell carcinoma (RCC) cells. HIF expression drastically reduced intracellular citrate levels. Feeding VHL-deficient RCC cells with acetate or citrate or knocking down PDK-1 and ACLY restored citrate levels and suppressed RC. These data suggest that HIF-induced low intracellular citrate levels promote the reductive flux by mass action to maintain lipogenesis. Using [(1-13)C]glutamine, we demonstrated in vivo RC activity in VHL-deficient tumors growing as xenografts in mice. Lastly, HIF rendered VHL-deficient cells sensitive to glutamine deprivation in vitro, and systemic administration of glutaminase inhibitors suppressed the growth of RCC cells as mice xenografts.

HectD1 E3 ligase modifies adenomatous polyposis coli (APC) with polyubiquitin to promote the APC-axin interaction

The adenomatous polyposis coli (APC) protein functions as a negative regulator of the Wnt signaling pathway. In this capacity, APC forms a "destruction complex" with Axin, CK1α, and GSK3β to foster phosphorylation of the Wnt effector β-catenin earmarking it for Lys-48-linked polyubiquitylation and proteasomal degradation. APC is conjugated with Lys-63-linked ubiquitin chains when it is bound to Axin, but it is unclear whether this modification promotes the APC-Axin interaction or confers upon APC an alternative function in the destruction complex. Here we identify HectD1 as a candidate E3 ubiquitin ligase that modifies APC with Lys-63 polyubiquitin. Knockdown of HectD1 diminished APC ubiquitylation, disrupted the APC-Axin interaction, and augmented Wnt3a-induced β-catenin stabilization and signaling. These results indicate that HectD1 promotes the APC-Axin interaction to negatively regulate Wnt signaling.

Uremic serum and solutes increase post-vascular interventional thrombotic risk through altered stability of smooth muscle cell tissue factor

BACKGROUND

Stent thrombosis (ST), a postinterventional complication with a mortality rate of 50%, has an incidence that rises precipitously in patients at risk. Chronic renal failure and end-stage renal disease have emerged as particularly strong ST risk factors, yet the mechanism remains elusive. Tissue factor (TF) is a crucial mediator of injury-related thrombosis and has been implicated for ST. We posit that uremia modulates TF in the local vessel wall to induce postinterventional thrombosis in patients with end-stage renal disease.

METHODS AND RESULTS

As a model of the de-endothelialized, postinterventional state, we exposed primary human vascular smooth muscle cells (vSMCs) pretreated with uremic serum (obtained from ESRD patients on hemodialysis) to coronary-like blood flow. vSMC TF expression, activity, stability, and posttranslational modification were examined after vSMCs were treated with uremic serum or solutes. We found significantly greater clot formation after uremic serum exposure, which was substantially reduced with the prior treatment with anti-TF neutralizing antibody. Uremic sera induced 2- to 3-fold higher TF expression and activity in vSMCs independent of diabetes mellitus. Relevant concentrations of isolated uremic solutes such as indole-3-acetic acid (3.5 μg/mL), indoxyl sulfate (25 μg/mL), and uric acid (80 μg/mL) recapitulated these effects in cell culture and the flow loop model. We show further that TF undergoes ubiquitination at baseline and that uremic serum, indole-3-acetic acid, and indoxyl sulfate significantly prolong TF half-life by inhibiting its ubiquitination.

CONCLUSIONS

The uremic milieu is profoundly thrombogenic and upregulates vSMC TF levels by increasing TF stability and decreasing its ubiquitination. Together, these data demonstrate for the first time that the posttranslational regulation of TF in uremia may have a causative role in the increased ST risk observed in uremic patients. These data suggest that interventions that reduce vSMC TF may help to prevent ST and that uremic solutes should be considered as novel risk factors for ST in patients with chronic renal failure.

Polycystin-1 regulates the stability and ubiquitination of transcription factor Jade-1

Autosomal-dominant polycystic kidney disease (ADPKD) and von Hippel-Lindau (VHL) disease lead to large kidney cysts that share pathogenetic features. The polycystin-1 (PC1) and pVHL proteins may therefore participate in the same key signaling pathways. Jade-1 is a pro-apoptotic and growth suppressive ubiquitin ligase for beta-catenin and transcriptional coactivator associated with histone acetyltransferase activity that is stabilized by pVHL in a manner that correlates with risk of VHL renal disease. Thus, a relationship between Jade-1 and PC1 was sought. Full-length PC1 bound, stabilized and colocalized with Jade-1 and inhibited Jade-1 ubiquitination. In contrast, the cytoplasmic tail or the naturally occurring C-terminal fragment of PC1 (PC1-CTF) promoted Jade-1 ubiquitination and degradation, suggesting a dominant-negative mechanism. ADPKD-associated PC1 mutants failed to regulate Jade-1, indicating a potential disease link. Jade-1 ubiquitination was mediated by Siah-1, an E3 ligase that binds PC1. By controlling Jade-1 abundance, PC1 and the PC1-CTF differentially regulate Jade-1-mediated transcriptional activity. A key target of PC1, the cyclin-dependent kinase inhibitor p21, is also up-regulated by Jade-1. Through Jade-1, PC1 and PC1 cleaved forms may exert fine control of beta-catenin and canonical Wnt signaling, a critical pathway in cystic renal disease. Thus, Jade-1 is a transcription factor and ubiquitin ligase whose activity is regulated by PC1 in a manner that is physiologic and may correlate with disease. Jade-1 may be an important therapeutic target in renal cystogenesis.

Genetic variation in hippocampal microRNA expression differences in C57BL/6 J X DBA/2 J (BXD) recombinant inbred mouse strains

BACKGROUND

miRNAs are short single-stranded non-coding RNAs involved in post-transcriptional gene regulation that play a major role in normal biological functions and diseases. Little is currently known about how expression of miRNAs is regulated. We surveyed variation in miRNA abundance in the hippocampus of mouse inbred strains, allowing us to take a genetic approach to the study of miRNA regulation, which is novel for miRNAs. The BXD recombinant inbred panel is a very well characterized genetic reference panel which allows quantitative trait locus (QTL) analysis of miRNA abundance and detection of correlates in a large store of brain and behavioural phenotypes.

RESULTS

We found five suggestive trans QTLs for the regulation of miRNAs investigated. Further analysis of these QTLs revealed two genes, Tnik and Phf17, under the miR-212 regulatory QTLs, whose expression levels were significantly correlated with miR-212 expression. We found that miR-212 expression is correlated with cocaine-related behaviour, consistent with a reported role for this miRNA in the control of cocaine consumption. miR-31 is correlated with anxiety and alcohol related behaviours. KEGG pathway analysis of each miRNA's expression correlates revealed enrichment of pathways including MAP kinase, cancer, long-term potentiation, axonal guidance and WNT signalling.

CONCLUSIONS

The BXD reference panel allowed us to establish genetic regulation and characterize biological function of specific miRNAs. QTL analysis enabled detection of genetic loci that regulate the expression of these miRNAs. eQTLs that regulate miRNA abundance are a new mechanism by which genetic variation influences brain and behaviour. Analysis of one of these QTLs revealed a gene, Tnik, which may regulate the expression of a miRNA, a molecular pathway and a behavioural phenotype. Evidence of genetic covariation of miR-212 abundance and cocaine related behaviours is strongly supported by previous functional studies, demonstrating the value of this approach for discovery of new functional roles and downstream processes regulated by miRNA.

Epigenetic stability, adaptability, and reversibility in human embryonic stem cells

The stability of human embryonic stem cells (hESCs) is of critical importance for both experimental and clinical applications. We find that as an initial response to altered culture conditions, hESCs change their transcription profile for hundreds of genes and their DNA methylation profiles for several genes outside the core pluripotency network. After adaption to conditions of feeder-free defined and/or xeno-free culture systems, expression and DNA methylation profiles are quite stable for additional passaging. However, upon reversion to the original feeder-based culture conditions, numerous transcription changes are not reversible. Similarly, although the majority of DNA methylation changes are reversible, highlighting the plasticity of DNA methylation, a few are persistent. Collectively, this indicates these cells harbor a memory of culture history. For culture-induced DNA methylation changes, we also note an intriguing correlation: hypomethylation of regions 500-2440 bp upstream of promoters correlates with decreased expression, opposite to that commonly seen at promoter-proximal regions. Lastly, changes in regulation of G-coupled protein receptor pathways provide a partial explanation for many of the unique transcriptional changes observed during hESC adaptation and reverse adaptation.

FIP200 inhibits β-catenin-mediated transcription by promoting APC-independent β-catenin ubiquitination

Focal adhesion kinase-family-interacting protein of 200 kDa (FIP200) has been shown to regulate multiple cellular functions, including cell adhesion, autophagy, development and proliferation. Furthermore, FIP200 is considered to have tumor-suppressive activity, which may be correlated with its inactivation in human breast cancers, in addition to its role as an important signal transduction node. Herein, we report that FIP200 interacts with the oncoprotein β-catenin. Moreover, FIP200 promotes destabilization of wild-type β-catenin, but not a cancer-causing form of β-catenin, and as a result represses the β-catenin-mediated transcription. FIP200-induced degradation of β-catenin is independent of adenomatous polyposis coli (APC) of the well-established β-catenin destruction complex (glycogen synthase kinase-3β/axin/APC), in a component of β-catenin E3 ubiquitin ligase, β-TrCP-dependent manner. Thus, the APC-independent β-catenin degradation by FIP200 suggests a role for FIP200 in tumor suppression in the presence of APC dysfunction. These findings reveal a new and important function of FIP200 in regulation of the Wnt/β-catenin pathway.

FANCL ubiquitinates β-catenin and enhances its nuclear function

Bone marrow failure is a nearly universal complication of Fanconi anemia. The proteins encoded by FANC genes are involved in DNA damage responses through the formation of a multisubunit nuclear complex that facilitates the E3 ubiquitin ligase activity of FANCL. However, it is not known whether loss of E3 ubiquitin ligase activity accounts for the hematopoietic stem cell defects characteristic of Fanconi anemia. Here we provide evidence that FANCL increases the activity and expression of β-catenin, a key pluripotency factor in hematopoietic stem cells. We show that FANCL ubiquitinates β-catenin with atypical ubiquitin chain extension known to have nonproteolytic functions. Specifically, β-catenin modified with lysine-11 ubiquitin chain extension efficiently activates a lymphocyte enhancer-binding factor-T cell factor reporter. We also show that FANCL-deficient cells display diminished capacity to activate β-catenin leading to reduced transcription of Wnt-responsive targets c-Myc and Cyclin D1. Suppression of FANCL expression in normal human CD34(+) stem and progenitor cells results in fewer β-catenin active cells and inhibits expansion of multilineage progenitors. Together, these results suggest that diminished Wnt/β-catenin signaling may be an underlying molecular defect in FANCL-deficient hematopoietic stem cells leading to their accelerated loss.