Stage- and subunit-specific functions of polycomb repressive complex 2 in bladder urothelial formation and regeneration

EZH2 specifically regulates ISL1 during embryonic urinary tract formation

Isl1 has been described as an embryonic master control gene expressed in the pericloacal mesenchyme. Deletion of Isl1 from the genital mesenchyme in mice leads to an ectopic urethral opening and epispadias-like phenotype. Using genome wide association methods, we identified ISL1 as the key susceptibility gene for classic bladder exstrophy (CBE), comprising epispadias and exstrophy of the urinary bladder. The most significant marker (rs6874700) identified in our recent GWAS meta-analysis achieved a p value of 1.48 × 10- 24 within the ISL1 region. In silico analysis of rs6874700 and all other genome-wide significant markers in Linkage Disequilibrium (LD) with rs6874700 (D' = 1.0; R2 > 0.90) revealed marker rs2303751 (p value 8.12 × 10- 20) as the marker with the highest regulatory effect predicted. Here, we describe a novel 1.2 kb intragenic promoter residing between 6.2 and 7.4 kb downstream of the ISL1 transcription starting site, which is located in the reverse DNA strand and harbors a binding site for EZH2 at the exact region of marker rs2303751. We show, that EZH2 silencing in HEK cells reduces ISL1 expression. We show that ezh2-/- knockout (KO) zebrafish larvae display tissues specificity of ISL1 regulation with reduced expression of Isl1 in the pronephric region of zebrafish larvae. In addition, a shorter and malformed nephric duct is observed in ezh2-/- ko zebrafish Tg(wt1ß:eGFP) reporter lines. Our study shows, that Ezh2 is a key regulator of Isl1 during urinary tract formation and suggests tissue specific ISL1 dysregulation as an underlying mechanism for CBE formation.

EZH2 and matrix co-regulate phenotype and KCNB2 expression in bladder smooth muscle cells

BACKGROUND

Partial bladder outlet obstruction (PBO) is a widespread cause of urinary dysfunction and patient discomfort, resulting in immense health care costs. Previously, we found that obstruction is associated with altered regulation of epigenetic machinery and altered function. Here we examined if PBO and chronic bladder obstructive disease (COBD) affect epigenetic marks in a proof of principle gene and explored mechanisms of its epigenetic regulation using in vitro models.

METHODS

Archival obstruction tissues from COBD had been created in 200-250 g female Sprague-Dawley rats by surgical ligation of the urethra for 6 weeks, followed by removal of the suture and following animals for 6 more weeks. Obstruction (PBO) is the 6-week ligation only. Sham ligations comprise passing the suture behind the urethra. Histone3 lysine27 trimethylation (H3K27me3) was studied by immunostaining and Chromatin immunoprecipitation (ChIP)/PCR. The interaction of matrix with KCNB2 regulation was studied in human bladder SMC plated on damaged matrix and native collagen and treated with vehicle or UNC1999. Cells were analyzed by immunostaining for cell phenotype, and western blotting for KCNB2, H3K27me3 and EZH2. Effects of conditioned media from these cells were also examined on cell phenotype. siRNA against KCNB2 was examined for effects on cell phenotype and gene expression by RT-qPCR.

RESULTS

H3K27me3 increased by immunofluorescence during PBO, and by ChIP/PCR during COBD in the CpG Island (CGI) as well as 350 bp upstream. Obstruction vs. sham also showed an increase in H3K27me3 deposition. In SMC in vitro, EZH2 inhibition restored KCNB2 expression and partially restored SMC phenotype.

CONCLUSIONS

Regulation of KCNB2 at the promoter demonstrated dynamic changes in H3K27me3 during COBD and obstruction. In vitro models suggest that matrix plays a role in regulation of EZH2, H3K27me3 and KCNB2, which may play a role in the regulation of smooth muscle phenotype in vivo.

Targeting the PRC2-dependent epigenetic program alleviates urinary tract infections

Urinary tract infection (UTI) is a pervasive health problem worldwide. Patients with a history of UTIs suffer increased risk of recurrent infections, a major risk of antibiotic resistance. Here, we show that bladder infections induce expression of Ezh2 in bladder urothelial cells. Ezh2 is the methyltransferase of polycomb repressor complex 2 (PRC2)-a potent epigenetic regulator. Urothelium-specific inactivation of PRC2 results in reduced urine bacterial burden, muted inflammatory response, and decreased activity of the NF-κB signaling pathway. PRC2 inactivation also facilitates proper regeneration after urothelial damage from UTIs, by attenuating basal cell hyperplasia and increasing urothelial differentiation. In addition, treatment with Ezh2-specific small-molecule inhibitors improves outcomes of the chronic and severe bladder infections in mice. These findings collectively suggest that the PRC2-dependent epigenetic reprograming controls the amplitude of inflammation and severity of UTIs and that Ezh2 inhibitors may be a viable non-antibiotic strategy to manage chronic and severe UTIs.

Development, regeneration and tumorigenesis of the urothelium

The urothelium of the bladder functions as a waterproof barrier between tissue and outflowing urine. Largely quiescent during homeostasis, this unique epithelium rapidly regenerates in response to bacterial or chemical injury. The specification of the proper cell types during development and injury repair is crucial for tissue function. This Review surveys the current understanding of urothelial progenitor populations in the contexts of organogenesis, regeneration and tumorigenesis. Furthermore, we discuss pathways and signaling mechanisms involved in urothelial differentiation, and consider the relevance of this knowledge to stem cell biology and tissue regeneration.

Male Lower Urinary Tract Dysfunction: An Underrepresented Endpoint in Toxicology Research

Lower urinary tract dysfunction (LUTD) is nearly ubiquitous in men of advancing age and exerts substantial physical, mental, social, and financial costs to society. While a large body of research is focused on the molecular, genetic, and epigenetic underpinnings of the disease, little research has been dedicated to the influence of environmental chemicals on disease initiation, progression, or severity. Despite a few recent studies indicating a potential developmental origin of male LUTD linked to chemical exposures in the womb, it remains a grossly understudied endpoint in toxicology research. Therefore, we direct this review to toxicologists who are considering male LUTD as a new aspect of chemical toxicity studies. We focus on the LUTD disease process in men, as well as in the male mouse as a leading research model. To introduce the disease process, we describe the physiology of the male lower urinary tract and the cellular composition of lower urinary tract tissues. We discuss known and suspected mechanisms of male LUTD and examples of environmental chemicals acting through these mechanisms to contribute to LUTD. We also describe mouse models of LUTD and endpoints to diagnose, characterize, and quantify LUTD in men and mice.

Alterations of Chromatin Regulators in the Pathogenesis of Urinary Bladder Urothelial Carcinoma

Simple Summary

Urinary bladder cancer is one of the ten major cancers worldwide, with higher incidences in males, in smokers, and in highly industrialized countries. New therapies beyond cytotoxic chemotherapy are urgently needed to improve treatment of these tumors. A better understanding of the mechanisms underlying their development may help in this regard. Recently, it was discovered that a group of proteins regulating the state of chromatin and thus gene expression is exceptionally and frequently affected by gene mutations in bladder cancers. Altered function of these mutated chromatin regulators must therefore be fundamental in their development, but how and why is poorly understood. Here we review the current knowledge on changes in chromatin regulators and discuss their possible consequences for bladder cancer development and options for new therapies.

Abstract

Urothelial carcinoma (UC) is the most frequent histological type of cancer in the urinary bladder. Genomic changes in UC activate MAPK and PI3K/AKT signal transduction pathways, which increase cell proliferation and survival, interfere with cell cycle and checkpoint control, and prevent senescence. A more recently discovered additional category of genetic changes in UC affects chromatin regulators, including histone-modifying enzymes (KMT2C, KMT2D, KDM6A, EZH2), transcription cofactors (CREBBP, EP300), and components of the chromatin remodeling complex SWI/SNF (ARID1A, SMARCA4). It is not yet well understood how these changes contribute to the development and progression of UC. Therefore, we review here the emerging knowledge on genomic and gene expression alterations of chromatin regulators and their consequences for cell differentiation, cellular plasticity, and clonal expansion during UC pathogenesis. Our analysis identifies additional relevant chromatin regulators and suggests a model for urothelial carcinogenesis as a basis for further mechanistic studies and targeted therapy development.

Posttranslational regulation of FOXA1 by Polycomb and BUB3/USP7 deubiquitin complex in prostate cancer

Forkhead box protein A1 (FOXA1) is essential for androgen-dependent prostate cancer (PCa) growth. However, how FOXA1 levels are regulated remains elusive and its therapeutic targeting proven challenging. Here, we report FOXA1 as a nonhistone substrate of enhancer of zeste homolog 2 (EZH2), which methylates FOXA1 at lysine-295. This methylation is recognized by WD40 repeat protein BUB3, which subsequently recruits ubiquitin-specific protease 7 (USP7) to remove ubiquitination and enhance FOXA1 protein stability. They functionally converge in regulating cell cycle genes and promoting PCa growth. FOXA1 is a major therapeutic target of the inhibitors of EZH2 methyltransferase activities in PCa. FOXA1-driven PCa growth can be effectively mitigated by EZH2 enzymatic inhibitors, either alone or in combination with USP7 inhibitors. Together, our study reports EZH2-catalyzed methylation as a key mechanism to FOXA1 protein stability, which may be leveraged to enhance therapeutic targeting of PCa using enzymatic EZH2 inhibitors.

Enhancer of Zeste 2 Polycomb Repressive Complex 2 Subunit Is Required for Uterine Epithelial Integrity

Normal proliferation and differentiation of uterine epithelial cells are critical for uterine development and function. Enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), a core component of polycomb repressive complexes 2, possesses histone methyltransferase activity that catalyzes the trimethylation of lysine 27 of histone H3. EZH2 has been involved in epithelial-mesenchymal transition, a key event in development and carcinogenesis. However, its role in uterine epithelial cell function remains unknown. To determine the role of uterine EZH2, Ezh2 was conditionally deleted using progesterone receptor Cre recombinase, which is expressed in both epithelial and mesenchymal compartments of the uterus. Loss of EZH2 promoted stratification of uterine epithelium, an uncommon and detrimental event in the uterus. The abnormal epithelium expressed basal cell markers, including tumor protein 63, cytokeratin 5 (KRT5), KRT6A, and KRT14. These results suggest that EZH2 serves as a guardian of uterine epithelial integrity, partially via inhibiting the differentiation of basal-like cells and preventing epithelial stratification. The observed epithelial abnormality was accompanied by fertility defects, altered uterine growth and function, and the development of endometrial hyperplasia. Thus, the Ezh2 conditional knockout mouse model may be useful to explore mechanisms that regulate endometrial homeostasis and uterine function.

In vivo replacement of damaged bladder urothelium by Wolffian duct epithelial cells

The bladder's remarkable regenerative capacity had been thought to derive exclusively from its own progenitors. While examining consequences of DNA methyltransferase 1 (Dnmt1) inactivation in mouse embryonic bladder epithelium, we made the surprising discovery that Wolffian duct epithelial cells can support bladder regeneration. Conditional Dnmt1 inactivation in mouse urethral and bladder epithelium triggers widespread apoptosis, depletes basal and intermediate bladder cells, and disrupts uroplakin protein expression. These events coincide with Wolffian duct epithelial cell recruitment into Dnmt1 mutant urethra and bladder where they are reprogrammed to express bladder markers, including FOXA1, keratin 5, P63, and uroplakin. This is evidence that Wolffian duct epithelial cells are summoned in vivo to replace damaged bladder epithelium and function as a reservoir of cells for bladder regeneration.

X chromosome protects against bladder cancer in females via a KDM6A-dependent epigenetic mechanism

Men are much more likely than women to develop bladder cancer (BCa), but the underlying cause of this gender disparity remains poorly defined. Using sex-reversed mice, we show that the sex chromosome complement is an independent cause and, moreover, amplifies the biasing effects of sex hormones. We also show that the X-linked lysine demethylase 6A (KDM6A) is a sexually dimorphic gene. Wild-type but not catalytically dead KDM6A confers sustained tumor suppressor activity in vitro. Knockout of mouse Kdm6a reduces expression of Cdkn1a and Perp, canonical gene targets of the tumor suppressor p53. Consistently, loss of Kdm6a increases BCa risk in female mice, and mutations or reduced expression of human KDM6A predicts poor prognosis of female BCa patients. Collectively, the study reveals that the X chromosome protects against BCa among females via a KDM6A-dependent epigenetic mechanism and further suggests that KDM6A is a prototypical sex-biasing tumor suppressor with both demethylase-dependent and demethylase-independent activities.

Sleeping beauty: awakening urothelium from its slumber

The bladder urothelium is essentially quiescent but regenerates readily upon injury. The process of urothelial regeneration harkens back to the process of urothelial development whereby urothelial stem/progenitor cells must proliferate and terminally differentiate to establish all three urothelial layers. How the urothelium regulates the level of proliferation and the timing of differentiation to ensure the precise degree of regeneration is of significant interest in the field. Without a carefully-orchestrated process, urothelial regeneration may be inadequate, thereby exposing the host to toxins or pathogens. Alternatively, regeneration may be excessive, thereby setting the stage for tumor development. This review describes our current understanding of urothelial regeneration. The current controversies surrounding the identity and location of urothelial progenitor cells that mediate urothelial regeneration are discussed and evidence for each model is provided. We emphasize the factors that have been shown to be crucial for urothelial regeneration, including local growth factors that stimulate repair, and epithelial-mesenchymal cross talk, which ensures feedback regulation. Also highlighted is the emerging concept of epigenetic regulation of urothelial regeneration, which additionally fine tunes the process through transcriptional regulation of cell cycle genes and growth and differentiation factors. Finally, we emphasize how several of these pathways and/or programs are often dysregulated during malignant transformation, further corroborating their importance in directing normal urothelial regeneration. Together, evidence in the field suggests that any attempt to exploit regenerative programs for the purposes of enhanced urothelial repair or replacement must take into account this delicate balance.