Wilms tumor suppressor, WT1, suppresses epigenetic silencing of the β-catenin gene

Case series of adult Wilms' tumor and review of the literature

Background

Adult Wilms' tumor (AWT) is extremely rare in clinics and very difficult to diagnose preoperatively. However, a unified treatment plan of AWT is lacking and the prognosis is unfavorable. This study will present the follow-up data of AWT cases in Tongji Hospital and discuss the diagnosis, treatment, and prognosis of AWT.

Case Description

The clinical data of four AWT cases admitted to the Department of Urology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology from August 2010 to January 2019 were followed up and analyzed. The mean age of the three males and one female patients was 38 years old. One case was admitted due to lumbar and abdominal distension, one case due to renal occupancy found on routine physical examination, and the other two cases due to lumbar pain with painless gross hematuria. The tumors were 4-10 cm in size, three of which were confined to the kidney, and one case invaded the inferior vena cava. Four cases were treated surgically: three with radical nephrectomy and one with partial nephrectomy. Two cases were treated with postoperative adjuvant chemotherapy (one case received the actinomycin D + vincristine regimen and pirarubicin + vincristine regimen; another case was treated with etoposide + carboplatin and cyclophosphamide + vincristine + adriamycin), and the other two cases were received postoperative follow-up only. Similar cases were reviewed in the literature. According to the postoperative pathology, one case was AWT germ type, two cases were AWT epithelial type, and one case was AWT mixed type. Two cases were classified in stage I, one case in stage II, and one case in stage III. All cases were followed up over 5 years, with two deaths and two survivals and a mean progression-free survival of 39 months.

Conclusions

AWT is a relatively rare malignant tumor with a low preoperative diagnostic accuracy and a poorer prognosis than children. Early diagnosis, successful surgery, and standardized postoperative adjuvant therapy according to pathological typing and staging are the key points to improve the survival of AWT patients.

Wnt/β-Catenin Signaling Pathway in Pediatric Tumors: Implications for Diagnosis and Treatment

The evolutionarily conserved Wnt signaling has a significant and diverse role in maintaining cell homeostasis and tissue maintenance. It is necessary in the regulation of crucial biological functions such as embryonal development, proliferation, differentiation, cell fate, and stem cell pluripotency. The deregulation of Wnt/β-catenin signaling often leads to various diseases, including cancer and non-cancer diseases. The role of Wnt/β-catenin signaling in adult tumors has been extensively studied in literature. Although the Wnt signaling pathway has been well explored and recognized to play a role in the initiation and progression of cancer, there is still a lack of understanding on how it affects pediatric tumors. This review discusses the recent developments of this signaling pathway in pediatric tumors. We also focus on understanding how different types of variations in Wnt signaling pathway contribute to cancer development and provide an insight of tissue specific mutations that lead to clinical progression of these tumors.

Great potential of renal progenitor cells in kidney: From the development to clinic

The mammalian renal organ represents a pinnacle of complexity, housing functional filtering units known as nephrons. During embryogenesis, the depletion of niches containing renal progenitor cells (RPCs) and the subsequent incapacity of adult kidneys to generate new nephrons have prompted the formulation of protocols aimed at isolating residual RPCs from mature kidneys and inducing their generation from diverse cell sources, notably pluripotent stem cells. Recent strides in the realm of regenerative medicine and the repair of tissues using stem cells have unveiled critical signaling pathways essential for the maintenance and generation of human RPCs in vitro. These findings have ushered in a new era for exploring novel strategies for renal protection. The present investigation delves into potential transcription factors and signaling cascades implicated in the realm of renal progenitor cells, focusing on their protection and differentiation. The discourse herein elucidates contemporary research endeavors dedicated to the acquisition of progenitor cells, offering crucial insights into the developmental mechanisms of these cells within the renal milieu and paving the way for the formulation of innovative treatment modalities.

Advances in bi-directional relationships for EZH2 and oxidative stress

Over the past two decades, polycomb repressive complex 2(PRC2) has emerged as a vital repressive complex in overall cell fate determination. In mammals, enhancer of zeste homolog 2 (EHZ2), which is the core component of PRC2, has also been recognized as an important regulator of inflammatory, redox, tumorigenesis and damage repair signalling networks. To exert these effects, EZH2 must regulate target genes epigenetically or interact directly with other gene expression-regulating factors, such as LncRNAs and microRNAs. Our review provides a comprehensive summary of research advances, discoveries and trends regarding the regulatory mechanisms between EZH2 and reactive oxygen species (ROS). First, we outline novel findings about how EZH2 regulates the generation of ROS at the molecular level. Then, we summarize how oxidative stress controls EHZ2 alteration (upregulation, downregulation, or phosphorylation) via various molecules and signalling pathways. Finally, we address why EZH2 and oxidative stress have an undefined relationship and provide potential future research ideas.

Wilms' tumor gene 1: lessons from the interface between kidney development and cancer

In 1990, mutations of the Wilms' tumor-1 gene (WT1), encoding a transcription factor in the embryonic kidney, were found in 10-15% of Wilms' tumors; germline WT1 mutations were associated with hereditary syndromes involving glomerular and reproductive tract dysplasia. For more than three decades, these discoveries prompted investigators to explore the embryonic role of WT1 and the mechanisms by which loss of WT1 leads to malignant transformation. Here, we discuss how alternative splicing of WT1 generates isoforms that act in a context-specific manner to activate or repress target gene transcription. WT1 also regulates posttranscriptional regulation, alters the epigenetic landscape, and activates miRNA expression. WT1 functions at multiple stages of kidney development, including the transition from resting stem cells to committed nephron progenitor, which it primes to respond to WNT9b signals from the ureteric bud. WT1 then drives nephrogenesis by activating WNT4 expression and directing the development of glomerular podocytes. We review the WT1 mutations that account for Denys-Drash syndrome, Frasier syndrome, and WAGR syndrome. Although the WT1 story began with Wilms' tumors, an understanding of the pathways that link aberrant kidney development to malignant transformation still has some important gaps. Loss of WT1 in nephrogenic rests may leave these premalignant clones with inadequate DNA repair enzymes and may disturb the epigenetic landscape. Yet none of these observations provide a complete picture of Wilms' tumor pathogenesis. It appears that the WT1 odyssey is unfinished and still holds a great deal of untilled ground to be explored.

WT1 regulates expression of DNA repair gene Neil3 during nephrogenesis

Mammalian nephrons arise from a population of nephron progenitor cells (NPCs) expressing the master transcription factor Wilms tumor-1 (WT1), which is crucial for NPC proliferation, migration, and differentiation. In humans, biallelic loss of WT1 precludes nephrogenesis and leads to the formation of Wilms tumor precursor lesions. We hypothesize that WT1 normally primes the NPC for nephrogenesis by inducing expression of NPC-specific DNA repair genes that protect the genome. We analyzed transcript levels for a panel of DNA repair genes in embryonic day 17.5 (E17.5) versus adult mouse kidneys and noted seven genes that were increased >20-fold. We then isolated Cited1⁺ NPCs from E17.5 kidneys and found that only one gene, nei-like DNA glycosylase 3 (Neil3), was enriched. RNAscope in situ hybridization of E17.5 mouse kidneys showed increased Neil3 expression in the nephrogenic zone versus mature nephron structures. To determine whether Neil3 expression is WT1 dependent, we knocked down Wt1 in Cited1⁺ NPCs (60% knockdown efficiency) and noted a 58% reduction in Neil3 transcript levels. We showed that WT1 interacts with the Neil3 promoter and that activity of a Neil3 promoter-reporter vector was increased twofold in WT1⁺ versus WT1^- cells. We propose that Neil3 is a WT1-dependent DNA repair gene expressed at high levels in Cited1⁺ NPCs, where it repairs mutational injury to the genome during nephrogenesis. NEIL3 is likely just one of many such lineage-specific repair mechanisms that respond to genomic injury during kidney development.NEW & NOTEWORTHY We studied the molecular events leading to Wilms tumors as a model for the repair of genomic injury. Specifically, we showed that WT1 activates DNA repair gene Neil3 in nephron progenitor cells. However, our observations offer a much broader principle, demonstrating that the embryonic kidney invests in lineage-specific expression of DNA repair enzymes. Thus, it is conceivable that failure of these mechanisms could lead to a variety of "sporadic" congenital renal malformations and human disease.

WT1 regulates HOXB9 gene expression in a bidirectional way

The homeoboxB9 (HOXB9) gene is necessary for specification of the anterior-posterior body axis during embryonic development and expressed in various types of cancer. Here we show that the Wilms tumor transcription factor WT1 regulates the HOXB9 gene in a bidirectional manner. Silencing of WT1 activates HOXB9 in Wt1 expressing renal cell adenocarcinoma-derived 786-0 cells, mesonephric M15 cells and ex vivo cultured murine embryonic kidneys. In contrast, HOXB9 expression in U2OS osteosarcoma and human embryonic kidney (HEK) 293 cells, which lack endogenous WT1, is enhanced by overexpression of WT1. Consistently, Hoxb9 promoter activity is stimulated by WT1 in transiently transfected U2OS and HEK293 cells, but inhibited in M15 cells with CRISPR/Cas9-mediated Wt1 deletion. Electrophoretic mobility shift assay and chromatin immunoprecipitation demonstrate binding of WT1 to the HOXB9 promoter in WT1-overexpressing U2OS cells and M15 cells. BASP1, a transcriptional co-repressor of WT1, is associated with the HOXB9 promoter in the chromatin of these cell lines. Co-transfection of U2OS and HEK293 cells with BASP1 plus WT1 prevents the stimulatory effect of WT1 on the HOXB9 promoter. Our findings identify HOXB9 as a novel downstream target gene of WT1. Depending on the endogenous expression of WT1, forced changes in WT1 can either stimulate or repress HOXB9, and the inhibitory effect of WT1 on transcription of HOXB9 involves BASP1. Consistent with inhibition of Hoxb9 expression by WT1, both transcripts are distributed in an almost non-overlapping pattern in embryonic mouse kidneys. Regulation of HOXB9 expression by WT1 might become relevant during kidney development and cancer progression.

Identification of Basp1 as a novel angiogenesis-regulating gene by multi-model system studies

We have previously used the genetic diversity available in common inbred mouse strains to identify quantitative trait loci (QTLs) responsible for the differences in angiogenic response using the corneal micropocket neovascularization (CoNV) assay. Employing a mouse genome-wide association study (GWAS) approach, the region on chromosome 15 containing Basp1 was identified as being significantly associated with angiogenesis in inbred strains. Here, we developed a unique strategy to determine and verify the role of BASP1 in angiogenic pathways. Basp1 expression in cornea had a strong correlation with a haplotype shared by mouse strains with varied angiogenic phenotypes. In addition, inhibition of BASP1 demonstrated a dosage-dependent effect in both primary mouse brain endothelial and human microvascular endothelial cell (HMVEC) migration. To investigate its role in vivo, we knocked out basp1 in transgenic kdrl:zsGreen zebrafish embryos using a widely adopted CRISPR-Cas9 system. These embryos had severely disrupted vessel formation compared to control siblings. We further show that basp1 promotes angiogenesis by upregulating β-catenin gene and the Dll4/Notch1 signaling pathway. These results, to the best of our knowledge, provide the first in vivo evidence to indicate the role of Basp1 as an angiogenesis-regulating gene and opens the potential therapeutic avenues for a wide variety of systemic angiogenesis-dependent diseases.

An Overview on the Complexity of OCT4: at the Level of DNA, RNA and Protein

OCT4 plays critical roles in self-renewal and pluripotency maintenance of embryonic stem cells, and is considered as one of the main stemness markers. It also has pivotal roles in early stages of embryonic development. Most studies on OCT4 have focused on the expression and function of OCT4A, which is the biggest isoform of OCT4 known so far. Recently, many studies have shown that OCT4 has various transcript variants, protein isoforms, as well as pseudogenes. Distinguishing the expression and function of these variants and isoforms is a big challenge in expression profiling studies of OCT4. Understanding how OCT4 is functioning in different contexts, depends on knowing of where and when each of OCT4 transcripts, isoforms and pseudogenes are expressed. Here, we review OCT4 known transcripts, isoforms and pseudogenes, as well as its interactions with other proteins, and emphasize the importance of discriminating each of them in order to understand the exact function of OCT4 in stem cells, normal development and development of diseases.

LMO2 gene deletions significantly worsen the prognosis of Wilms’ tumor development in patients with WAGR syndrome

WAGR syndrome (OMIM #194072) is a rare genetic disorder that consists of development of Wilms’ tumor (nephroblastoma), aniridia, genitourinary anomalies and intellectual disability (mental retardation). It is associated with WAGR-region deletions in the 11p13 chromosome region. Our previous study of congenital aniridia patients revealed a noticeable number of aniridia patients with WAGR-region deletions but without Wilms’ tumor in their medical history. We assessed the involvement of other neighboring genes from affected chromosome regions in the patients with and without Wilms’ tumor. Reliable confidence was obtained for the LMO2 gene, which is significantly more often deleted in patients with nephroblastoma. Thus, our study presents genetic evidence that the development of Wilms tumors in WAGR syndrome patients should be attributed to the deletion of WT1 and LMO2 rather than WT1 only.

Molecular determinants of WNT9b responsiveness in nephron progenitor cells

Primed nephron progenitor cells (NPCs) appear in metanephric mesenchyme by E11.5 and differentiate in response to the inductive WNT9b signal from the ureteric bud. However, the NPC WNT-receptor complex is unknown. We obtained M15 cells from E10.5 mesonephric mesenchyme and systematically analyzed components required for canonical WNT9b-responsiveness. When M15 cells were transfected with a β-catenin luciferase reporter plasmid, exposure to recombinant WNT9b resulted in minimal luciferase activity. We then analyzed mRNA-expression of WNT-pathway components and identified Fzd1-6 and Lrp6 transcripts but not Rspo1. When M15 cells were treated with recombinant RSPO1 the response to transfected WNT9b was augmented 4.8-fold. Co-transfection of M15 cells with Fzd5 (but no other Fzd family member) further increased the WNT9b signal to 16.8-fold and siRNA knockdown of Fzd5 reduced the signal by 52%. Knockdown of Lrp6 resulted in 60% WNT9b signal reduction. We confirmed Fzd5, Lrp6 and Rspo1 mRNA expression in CITED1(+) NPCs from E15.5 embryonic mouse kidney. Thus, while many WNT signaling-pathway components are present by E10.5, optimum responsiveness of E11.5 cap mesenchyme requires that NPCs acquire RSPO1, FZD5 and LRP6.

Wilms' Tumor Protein 1 and Enzymatic Oxidation of 5-Methylcytosine in Brain Tumors: Potential Perspectives

The patterns of 5-methylcytosine (5mC) and its oxidized derivatives, 5-hydroxymethylcytosine, 5-formylcytosine, and 5-carboxylcytosine (5caC) are reportedly altered in a range of cancers. Likewise, Wilms' Tumor protein 1 (WT1), a transcription factor essential for urogenital, epicardium, and kidney development exhibits aberrant expression in multiple tumors. Interestingly, WT1 directly interacts with TET proteins that catalyze the enzymatic oxidation of 5mC and exhibits high affinity for 5caC-containing DNA substrates in vitro. Here we review recent developments in the fields of Tet-dependent 5mC oxidation and WT1 biology and explore potential perspectives for studying the interplay between TETs and WT1 in brain tumors.

Dormancy activation mechanism of tracheal stem cells

Accurate markers and molecular mechanisms of stem cell dormancy and activation are poorly understood. In this study, the anti-cancer drug, 5-fluorouracil, was used to selectively kill proliferating cells of human bronchial epithelial (HBE) cell line. This method can enrich and purify stem cell population. The dormant versus active status of stem cells was determined by phosphorylation of RNAp II Ser2. The surviving stem cells were cultured to form stem cell spheres expressing stem cell markers and transplanted into nude mice to form a teratoma. The results demonstrated the properties of stem cells and potential for multi-directional differentiation. Bisulfite sequencing polymerase chain reaction showed that demethylation of the Sox2 promoter by 5-FU resulted in Sox2 expression in the dormant stem cells. This study shows that the dormancy and activation of HBE stem cells is closely related to epigenetic modification.

Interaction of colon cancer cells with glycoconjugates triggers complex changes in gene expression, glucose transporters and cell invasion

Glycan metabolism balance is critical for cell prosperity, and macromolecule glycosylation is essential for cell communication, signaling and survival. Thus, glycotherapy may be a potential cancer treatment. The aim of the present study was to determine whether combined synthetic glycoconjugates (GCs) induce changes in gene expression that alter the survival of colon cancer cells. The current study evaluated the effect of the GCs N‑acetyl‑D‑glucosamine modified polyamidoamine dendrimer and calix[4]arene scaffold on cancer cell proliferation, apoptosis, invasion and sensitivity to immune cell‑mediated killing. Using reverse transcription‑quantitative polymerase chain reaction, the expression of genes involved in the aforementioned processes was measured. It was determined that GCs reduce the expression of the glucosaminyltransferases Mgat3 and Mgat5 responsible for surface glycosylation and employed components of the Wnt signaling pathway Wnt2B and Wnt9B. In addition, the calix[4]arene‑based GC reduced cell colony formation; this was accompanied by the downregulation of the metalloproteinase Mmp3. By contrast, the dendrimer‑based GC affected the expression of the glucose transporter components Sglt1 and Egfr1. Therefore, to the best of our knowledge, the present study is the first to reveal that N‑acetyl‑D‑glucosamine‑dendrimer/calix[4]arene GCs alter mRNA expression in a comprehensive way, resulting in the reduced malignant phenotype of the colon cancer cell line HT‑29.

EZH2 Impairs Human Dental Pulp Cell Mineralization via the Wnt/β-Catenin Pathway

The enhancer of zeste homolog 2 (EZH2) is a catalytic subunit of PRC2 (polycomb repressor complex 2). It mediates gene silencing via methyltransferase activity and is involved in the determination of cell lineage. However, the function of EZH2 and the underlying mechanisms by which it affects the differentiation of human dental pulp cell (hDPC) have remained underexplored. In this research, we found that EZH2 expression decreased during the mineralization of hDPCs, with attenuated H3K27me3 (trimethylation on lysine 27 in histone H3). Overexpression of EZH2 impaired the odontogenic differentiation of hDPCs, while EZH2 without methyltransferase activity mutation (mutation of suppressed variegation of 3 to 9, enhancer of zeste and trithorax domain, EZH2ΔSET) did not display this phenotype. In addition, siRNA knockdown studies showed that EZH2 negatively modulated hDPC differentiation in vitro and inhibited mineralized nodule formation in transplanted β-tricalcium phosphate / hDPC composites. To further investigate the underlying mechanisms, we explored the Wnt/β-catenin signaling pathway in view of the fact that previous research had documented the essential role that it plays during hDPC mineralization, as well as its links to EZH2 in other cells. We demonstrated for the first time that EZH2 depletion activated the Wnt/β-catenin signaling pathway and enhanced the accumulation of β-catenin in hDPCs. Chromatin immunoprecipitation analysis suggested that these effects are attributable to the level of the EZH2-regulated H3K27me3 on the β-catenin promoter. We conclude that EZH2 plays a negative role during the odontogenic differentiation of hDPCs. Suppression of EZH2 could promote hDPC mineralization by epigenetically regulating the expression of β-catenin and activating the Wnt canonical signaling pathway.

Identification of WT1 as determinant of heptatocellular carcinoma and its inhibition by Chinese herbal medicine Salvia chinensis Benth and its active ingredient protocatechualdehyde

Candidates from Chinese herbal Medicine might be preferable in drug discovery as the abundant experiences of traditional use usually hint the clinical efficacy. In this study, we screened the anti-tumour effect of several commonly used Chinese herbal Medicines on human hepatocellular carcinoma cells (HCC). We identified that Salvia chinensia Benth. (Shijianchuan in Chinese, SJC) exhibited prominent in vitro inhibition of HCC cells and suppressed the orthotopic growth of HCC in the liver of mice and repressed the lung metastasis of tumour cells. Using a pathway-specific PCR array and Gene Ontology analysis, we identified that Wnt/β-catenin pathway was associated with the suppressive effect of SJC on HCC cell proliferation and cell cycle progression. SJC repressed transcription activity of Wnt/β-catenin pathway and reduced expression of β-catenin in GSK-3β-independent but promoter-specific transcription inhibition mechanism. The suppressive effect of SJC on β-catenin expression and its transcription activity was associated with Wilms' tumor 1 (WT1) protein. WT1 was overexpressed in HCC tissues, and was negatively correlated to the overall survival of HCC patients. WT1 promoted proliferation and invasion of HCC cells, as well as β-catenin-dependent transcription activation of Wnt products, while knockdown of WT1 had the opposite effect. Docking experiment revealed that protocatechualdehyde (PCA) might be the active component of the herb. PCA suppressed transcription activity of Wnt/β-catenin pathway in WT1-dependent manner. Our study sheds light on the potential of PCA from commonly used anti-cancer Chinese herbal Medicine SJC as a lead compound targeting WT1 in the discovery of anti-HCC drugs.

WT1 ameliorates podocyte injury via repression of EZH2/β-catenin pathway in diabetic nephropathy

Epigenetic modulation of podocyte injury plays a pivotal role in diabetic nephropathy (DN). Wilm's tumor 1 (WT1) has been found to have opposing roles with β-catenin in podocyte biology. Herein, we asked whether the histone methyltransferase enzyme enhancer of zeste homolog 2 (EZH2) promotes WT1-induced podocyte injury via β-catenin activation and the underlying mechanisms. We found that WT1 antagonized EZH2 and ameliorated β-catenin-mediated podocyte injury as demonstrated by attenuated podocyte mesenchymal transition, maintenance of podocyte architectural integrity, decreased podocyte apoptosis and oxidative stress. Further, we provided mechanistical evidence that EZH2 was required in WT1-mediated β-catenin inactivation via repression of secreted frizzled-related protein 1 (SFRP-1), a Wnt antagonist. Moreover, EZH2-mediated silencing of SFRP-1 was due to increased histone 3 lysine 27 trimethylation (H3K27me3) on its promoter region. WT1 favored renal function and decreased podocyte injury in diabetic rats and DN patients. Notably, WT1 exhibited clinical and biological relevance as it was linked to dropped serum creatinine, decreased proteinuria and elevated estimated glomerular filtration rate (eGFR). We propose an epigenetic process via the WT1/EZH2/β-catenin axis in attenuating podocyte injury in DN. Targeting WT1 and EZH2 could be potential therapeutic approaches for DN.

Wilms' tumor in a 51-year-old patient: An extremely rare case and review of the literature

Wilms tumor or nephroblastoma is a common kidney malignant tumor in childhood, accounting for ~5% of all pediatric tumors. At present, reports on Wilms' tumor occurring in adults, particularly at ages >30 years, are extremely rare. The majority of the cases of adult Wilms' tumor are closely associated with chemotherapy. Furthermore, in rare cases, Wilms' tumor is characterized by three classic types of cells, namely blastemal, stromal and epithelial cells. We herein report a case of Wilms' tumor with three classic types of cells on histological examination in a 51 year-old male patient who had received prior chemotherapy. The patient promptly underwent radical nephrectomy and remains alive. A review of previously presented cases of adult Wilms' tumor from PubMed database was also performed.

WT1 targets Gas1 to maintain nephron progenitor cells by modulating FGF signals

Development of the metanephric kidney depends on tightly regulated interplay between self-renewal and differentiation of a nephron progenitor cell (NPC) pool. Several key factors required for the survival of NPCs have been identified, including fibroblast growth factor (FGF) signaling and the transcription factor Wilms' tumor suppressor 1 (WT1). Here, we present evidence that WT1 modulates FGF signaling by activating the expression of growth arrest-specific 1 (Gas1), a novel WT1 target gene and novel modulator of FGF signaling. We show that WT1 directly binds to a conserved DNA binding motif within the Gas1 promoter and activates Gas1 mRNA transcription in NPCs. We confirm that WT1 is required for Gas1 expression in kidneys in vivo. Loss of function of GAS1 in vivo results in hypoplastic kidneys with reduced nephron mass due to premature depletion of NPCs. Although kidney development in Gas1 knockout mice progresses normally until E15.5, NPCs show decreased rates of proliferation at this stage and are depleted as of E17.5. Lastly, we show that Gas1 is selectively required for FGF-stimulated AKT signaling in vitro. In summary, our data suggest a model in which WT1 modulates receptor tyrosine kinase signaling in NPCs by directing the expression of Gas1.

Emerging Transcriptional Mechanisms in the Regulation of Epithelial to Mesenchymal Transition and Cellular Plasticity in the Kidney

Notwithstanding controversies over the role of epithelial to mesenchymal transition in the pathogenesis of renal disease, the last decade has witnessed a revolution in our understanding of the regulation of renal cell plasticity. Significant parallels undoubtedly exist between ontogenic processes and the initiation and propagation of damage in the diseased kidney as evidenced by the reactivation of developmental programmes of gene expression, in particular with respect to TGFβ superfamily signaling. Indeed, multiple signaling pathways converge on a complex transcriptional regulatory nexus that additionally involves epigenetic activator and repressor mechanisms and microRNA regulatory networks that control renal cell plasticity. It is becoming increasingly apparent that differentiated cells can acquire an undifferentiated state akin to “stemness” which is leading us towards new models of complex cell behaviors and interactions. Here we discuss the latest findings that delineate new and novel interactions between this transcriptional regulatory network and highlight a hitherto poorly recognized role for the Polycomb Repressive Complex (PRC2) in the regulation of renal cell plasticity. A comprehensive understanding of how external stimuli interact with the epigenetic control of gene expression, in normal and diseased contexts, establishes a new therapeutic paradigm to promote the resolution of renal injury and regression of fibrosis.

Wilms Tumor Suppressor, WT1, Cooperates with MicroRNA-26a and MicroRNA-101 to Suppress Translation of the Polycomb Protein, EZH2, in Mesenchymal Stem Cells

Hereditary forms of Wilms arise from developmentally arrested clones of renal progenitor cells with biallelic mutations of WT1; recently, it has been found that Wilms tumors may also be associated with biallelic mutations in DICER1 or DROSHA, crucial for miRNA biogenesis. We have previously shown that a critical role for WT1 during normal nephrogenesis is to suppress transcription of the Polycomb group protein, EZH2, thereby de-repressing genes in the differentiation cascade. Here we show that WT1 also suppresses translation of EZH2. All major WT1 isoforms induce an array of miRNAs, which target the 3' UTR of EZH2 and other Polycomb-associated transcripts. We show that the WT1(+KTS) isoform binds to the 5' UTR of EZH2 and interacts directly with the miRNA-containing RISC to enhance post-transcriptional inhibition. These observations suggest a novel mechanism through which WT1 regulates the transition from resting stem cell to activated progenitor cell during nephrogenesis. Our findings also offer a plausible explanation for the fact that Wilms tumors can arise either from loss of WT1 or loss of miRNA processing enzymes.

HuR antagonizes the effect of an intronic pyrimidine-rich sequence in regulating WT1 +/-KTS isoforms

WT1 + KTS and -KTS isoforms only differ in 3 amino acids in protein sequence but show significant functional difference. The +/-KTS isoforms were generated by alternative usage of 2 adjacent 5' splice sites at RNA level, however, how these 2 isoforms are regulated is still elusive. Here we report the identification of an intronic pyrimidine-rich sequence that is critical for the ratio of +/-KTS isoforms, deletion or partial replacement of the sequence led to full/significant shift to -KTS isoform. To identify trans-factors that can regulate +/-KTS isoforms via the binding to the element, we performed RNP assembly using in vitro transcribed RNA with or without the pyrimidine-rich sequence. Mass spectrometry analysis of purified RNPs showed that the element associated with many splicing factors. Co-transfection of these factors with WT1 reporter revealed that HuR promoted the production of -KTS isoform at the reporter level. RNA immuno-precipitation experiment indicated that HuR interacted with the pyrimidine-rich element in WT1 intron 9. We further presented evidence that transient or stable over-expression of HuR led to enhanced expression of endogenous -KTS isoform. Moreover, knockdown of HuR resulted in decreased expression of endogenous -KTS isoform in 293T, SW620, SNU-387 and AGS cell lines. Together, these data indicate that HuR binds to the pyrimidine-rich sequence and antagonize its effect in regulating WT1 +/-KTS isoforms.