Pax6-dependent, but β-catenin-independent, function of Bcl9 proteins in mouse lens development

Novel biphasic mechanism of the canonical Wnt signalling component PYGO2 promotes cardiomyocyte differentiation from hUC-MSCs

Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) are used to regenerate the myocardium during cardiac repair after myocardial infarction. However, the regulatory mechanism underlying their ability to form mesodermal cells and differentiate into cardiomyocytes remains unclear. Here, we established a human-derived MSCs line isolated from healthy umbilical cords and established a cell model of the natural state to examine the differentiation of hUC-MSCs into cardiomyocytes. Quantitative RT-PCR, western blotting, immunofluorescence, flow cytometry, RNA Seq, and inhibitors of canonical Wnt signalling were used to detect the germ-layer markers T and MIXL1; the markers of cardiac progenitor cells MESP1, GATA4, and NKX2.5 and the cardiomyocyte-marker cTnT to identify the molecular mechanism associated with PYGO2, a key component of the canonical Wnt signalling pathway that regulates the formation of cardiomyocyte-like cells. We demonstrated that PYGO2 promotes the formation of mesodermal-like cells and their differentiation into cardiomyocytes through the hUC-MSC-dependent canonical Wnt signalling by promoting the early-stage entry of β-catenin into the nucleus. Surprisingly, PYGO2 did not alter the expression of the canonical-Wnt, NOTCH, or BMP signalling pathways during the middle-late stages. In contrast, PI3K-Akt signalling promoted hUC-MSCs formation and their differentiation into cardiomyocyte-like cells. To the best of our knowledge, this is the first study to demonstrate that PYGO2 uses a biphasic mechanism to promote cardiomyocyte formation from hUC-MSCs.

OMICS Analyses Unraveling Related Gene and Protein-Driven Molecular Mechanisms Underlying PACAP 38-Induced Neurite Outgrowth in PC12 Cells

The study aimed to understand mechanism/s of neuronal outgrowth in the rat adrenal-derived pheochromocytoma cell line (PC12) under pituitary adenylate cyclase-activating polypeptide (PACAP) treatment. Neurite projection elongation was suggested to be mediated via Pac1 receptor-mediated dephosphorylation of CRMP2, where GSK-3β, CDK5, and Rho/ROCK dephosphorylated CRMP2 within 3 h after addition of PACAP, but the dephosphorylation of CRMP2 by PACAP remained unclear. Thus, we attempted to identify the early factors in PACAP-induced neurite projection elongation via omics-based transcriptomic (whole genome DNA microarray) and proteomic (TMT-labeled liquid chromatography-tandem mass spectrometry) analyses of gene and protein expression profiles from 5-120 min after PACAP addition. The results revealed a number of key regulators involved in neurite outgrowth, including known ones, called 'Initial Early Factors', e.g., genes Inhba, Fst, Nr4a1,2,3, FAT4, Axin2, and proteins Mis12, Cdk13, Bcl91, CDC42, including categories of 'serotonergic synapse, neuropeptide and neurogenesis, and axon guidance'. cAMP signaling and PI3K-Akt signaling pathways and a calcium signaling pathway might be involved in CRMP2 dephosphorylation. Cross-referencing previous research, we tried to map these molecular components onto potential pathways, and we may provide important new information on molecular mechanisms of neuronal differentiation induced by PACAP. Gene and protein expression data are publicly available at NCBI GSE223333 and ProteomeXchange, identifier PXD039992.

Emerging Direct Targeting β-Catenin Agents

Aberrant accumulation of β-catenin in the cell nucleus as a result of deregulation of the Wnt/β-catenin pathway is found in various types of cancer. Direct β-catenin targeting agents are being researched despite obstacles; however, specific β-catenin drugs for clinical treatments have not been approved so far. We focused on direct β-catenin targeting of potential therapeutic value as anticancer agents. This review provides recent advances on small molecule β-catenin agents. Structure-activity relationships and biological activities of reported inhibitors are discussed. This work provides useful knowledge in the discovery of β-catenin agents.

Pygopus2 ameliorates mesenteric adipocyte poor differentiation to alleviate Crohn's disease -like colitis via the Axin2/GSK3β pathway

Objectives

Crohn's disease (CD) mesenteric adipose tissue (MAT) inflammation affects enteritis through the interaction between the mesentery and intestine, and we previously found that poorly differentiated mesenteric adipocytes were related to its inflammatory features. Pygopus2 (Pygo2) is a key negative regulator of adipocyte differentiation. We aimed to determine whether Pygo2 participates in CD mesenteric lesions and whether Pygo2 knockdown would be beneficial in a CD model (Il‐10^−/− mice).

Methods

Pygo2 expression in MAT from control and CD patients and Il‐10^−/− mice was measured by immunohistochemistry. Lentiviral transfection was used to regulate Pygo2 expression in Il‐10^−/− mice, and the effects on mesenteric adipocyte differentiation, inflammation, and dysfunction during spontaneous colitis, as well as the possible mechanism, were investigated.

Results

Pygo2 expression was increased in MAT from CD patients and Il‐10^−/− mice, and its expression correlated with poor adipocyte differentiation and inflammation. Pygo2 knockdown significantly ameliorated colitis in Il‐10^−/− mice. Moreover, the downregulation of Pygo2 gene expression could promote adipocyte differentiation and inhibit adipocyte inflammation in vivo and in vitro, and the effects were at least partly mediated by the Axis inhibition protein 2 (Axin2)/glycogen synthase kinase 3 beta (GSK3β) pathway.

Conclusions

The increase in Pygo2 may be related to mesenteric adipocyte poor differentiation and inflammatory features of CD, and Pygo2 inhibition could alleviate CD‐like colitis by improving mesenteric lesions by regulating the Axin2/GSK3β pathway.

Wnt/β-Catenin Signalling and Its Cofactor BCL9L Have an Oncogenic Effect in Bladder Cancer Cells

Bladder cancer (BC) is characterised by a high recurrence and progression rate. However, the molecular mechanisms of BC progression remain poorly understood. BCL9L, a coactivator of β-catenin was mutated in the 5′ and 3′ untranslated regions (UTRs). We assessed the influence of UTRs mutations on BCL9L, and the role of BCL9L and Wnt/β-catenin signalling in BC cells. UTR mutations were analysed by a luciferase reporter. BCL9L protein was assessed by immunohistochemistry in BC tissues. Cell proliferation was examined by crystal violet staining and by the spheroid model. Moreover, migration and invasion were analysed in real-time using the xCelligence RTCA system. The A > T mutation at 3′ UTR of BCL9L reduces the luciferase reporter mRNA expression and activity. BCL9L is predominantly increased in dysplastic urothelial cells and muscle-invasive BC. Knockdown of BCL9L and inhibition of Wnt/β-catenin signalling significantly repress the proliferation, migration and invasion of Cal29 and T24. In addition, BCL9L knockdown reduces mRNA level of Wnt/β-catenin target genes in Cal29 but not in T24 cells. BCL9L and Wnt/β-catenin signalling play an oncogenic role in bladder cancer cells and seems to be associated with BC progression. Nevertheless, the involvement of BCL9L in Wnt/β-catenin signalling is cell-line specific.

Changes in DNA methylation hallmark alterations in chromatin accessibility and gene expression for eye lens differentiation

Background

Methylation at cytosines (mCG) is a well-known regulator of gene expression, but its requirements for cellular differentiation have yet to be fully elucidated. A well-studied cellular differentiation model system is the eye lens, consisting of a single anterior layer of epithelial cells that migrate laterally and differentiate into a core of fiber cells. Here, we explore the genome-wide relationships between mCG methylation, chromatin accessibility and gene expression during differentiation of eye lens epithelial cells into fiber cells.

Results

Whole genome bisulfite sequencing identified 7621 genomic loci exhibiting significant differences in mCG levels between lens epithelial and fiber cells. Changes in mCG levels were inversely correlated with the differentiation state-specific expression of 1285 genes preferentially expressed in either lens fiber or lens epithelial cells (Pearson correlation r = − 0.37, p < 1 × 10^–42). mCG levels were inversely correlated with chromatin accessibility determined by assay for transposase-accessible sequencing (ATAC-seq) (Pearson correlation r = − 0.86, p < 1 × 10^–300). Many of the genes exhibiting altered regions of DNA methylation, chromatin accessibility and gene expression levels in fiber cells relative to epithelial cells are associated with lens fiber cell structure, homeostasis and transparency. These include lens crystallins (CRYBA4, CRYBB1, CRYGN, CRYBB2), lens beaded filament proteins (BFSP1, BFSP2), transcription factors (HSF4, SOX2, HIF1A), and Notch signaling pathway members (NOTCH1, NOTCH2, HEY1, HES5). Analysis of regions exhibiting cell-type specific alterations in DNA methylation revealed an overrepresentation of consensus sequences of multiple transcription factors known to play key roles in lens cell differentiation including HIF1A, SOX2, and the MAF family of transcription factors.

Conclusions

Collectively, these results link DNA methylation with control of chromatin accessibility and gene expression changes required for eye lens differentiation. The results also point to a role for DNA methylation in the regulation of transcription factors previously identified to be important for lens cell differentiation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13072-022-00440-z.

Hypoxia-inducible factor 1α induces osteo/odontoblast differentiation of human dental pulp stem cells via Wnt/β-catenin transcriptional cofactor BCL9

Accelerated dental pulp mineralization is a common complication in avulsed/luxated teeth, although the mechanisms underlying this remain unclear. We hypothesized that hypoxia due to vascular severance may induce osteo/odontoblast differentiation of dental pulp stem cells (DPSCs). This study examined the role of B-cell CLL/lymphoma 9 (BCL9), which is downstream of hypoxia-inducible factor 1α (HIF1α) and a Wnt/β-catenin transcriptional cofactor, in the osteo/odontoblastic differentiation of human DPSCs (hDPSCs) under hypoxic conditions. hDPSCs were isolated from extracted healthy wisdom teeth. Hypoxic conditions and HIF1α overexpression induced significant upregulation of mRNAs for osteo/odontoblast markers (RUNX2, ALP, OC), BCL9, and Wnt/β-catenin signaling target genes (AXIN2, TCF1) in hDPSCs. Overexpression and suppression of BCL9 in hDPSCs up- and downregulated, respectively, the mRNAs for AXIN2, TCF1, and the osteo/odontoblast markers. Hypoxic-cultured mouse pulp tissue explants showed the promotion of HIF1α, BCL9, and β-catenin expression and BCL9-β-catenin co-localization. In addition, BCL9 formed a complex with β-catenin in hDPSCs in vitro. This study demonstrated that hypoxia/HIF1α-induced osteo/odontoblast differentiation of hDPSCs was partially dependent on Wnt/β-catenin signaling, where BCL9 acted as a key mediator between HIF1α and Wnt/β-catenin signaling. These findings may reveal part of the mechanisms of dental pulp mineralization after traumatic dental injury.

Nuclear Expression of Pygo2 Correlates with Poorly Differentiated State Involving c-Myc, PCNA and Bcl9 in Myanmar Hepatocellular Carcinoma

In Myanmar, hepatocellular carcinoma (HCC) is commonly seen in young adult and associated with poor prognosis, while the molecular mechanisms that characterize HCC in Myanmar are unknown. As co-activation of Wnt/β-catenin signaling and c-Myc (Myc) are reported to associate with malignancy of HCC, we immunohistochemically investigated the expression of Pygo2 and Bcl9, the co-activators of the Wnt/β-catenin signaling, Myc and PCNA in 60 cases of Myanmar HCC. Pygo2 expression was confirmed by in situ hybridization. The signal intensity was measured by image analyzer and then statistically analyzed. As a result, the expression of Pygo2 was significantly higher in HCC compared to normal liver tissue and the nuclear signal was the most intense in poorly differentiated HCC. Cytoplasmic Bcl9 was expressed in the normal liver tissue but decreased in HCC with the progression of histopathological grade. Myc was significantly higher in poorly differentiated HCC, whereas PCNA labeling index increased with the progression of histopathological grade. Nuclear Pygo2 showed strong correlation with nuclear Myc (P < 0.01) and PCNA (P < 0.001), and inversely correlated with cytoplasmic Bcl9 (P < 0.01). Our results suggested Wnt/β-catenin and Myc signaling is commonly activated in Myanmar HCC and that the correlative upregulation of nuclear Pygo2 and Myc characterizes the malignant features of HCC in Myanmar.

The interactions of Bcl9/Bcl9L with β-catenin and Pygopus promote breast cancer growth, invasion, and metastasis

Canonical Wnt/β-catenin signaling is an established regulator of cellular state and its critical contributions to tumor initiation, malignant tumor progression and metastasis formation have been demonstrated in various cancer types. Here, we investigated how the binding of β-catenin to the transcriptional coactivators B-cell CLL/lymphoma 9 (Bcl9) and Bcl9-Like (Bcl9L) affected mammary gland carcinogenesis in the MMTV-PyMT transgenic mouse model of metastatic breast cancer. Conditional knockout of both Bcl9 and Bcl9L resulted into tumor cell death. In contrast, disrupting the interaction of Bcl9/Bcl9L with β-catenin, either by deletion of their HD2 domains or by a point mutation in the N-terminal domain of β-catenin (D164A), diminished primary tumor growth and tumor cell proliferation and reduced tumor cell invasion and lung metastasis. In comparison, the disruption of HD1 domain-mediated binding of Bcl9/Bcl9L to Pygopus had only moderate effects. Interestingly, interfering with the β-catenin-Bcl9/Bcl9L-Pygo chain of adapters only partially impaired the transcriptional response of mammary tumor cells to Wnt3a and TGFβ treatments. Together, the results indicate that Bcl9/Bcl9L modulate but are not critically required for canonical Wnt signaling in its contribution to breast cancer growth and malignant progression, a notion consistent with the “just-right” hypothesis of Wnt-driven tumor progression.

Differential regulation of β-catenin-mediated transcription via N- and C-terminal co-factors governs identity of murine intestinal epithelial stem cells

The homeostasis of the gut epithelium relies upon continuous renewal and proliferation of crypt-resident intestinal epithelial stem cells (IESCs). Wnt/β-catenin signaling is required for IESC maintenance, however, it remains unclear how this pathway selectively governs the identity and proliferative decisions of IESCs. Here, we took advantage of knock-in mice harboring transgenic β-catenin alleles with mutations that specifically impair the recruitment of N- or C-terminal transcriptional co-factors. We show that C-terminally-recruited transcriptional co-factors of β-catenin act as all-or-nothing regulators of Wnt-target gene expression. Blocking their interactions with β-catenin rapidly induces loss of IESCs and intestinal homeostasis. Conversely, N-terminally recruited co-factors fine-tune β-catenin's transcriptional output to ensure proper self-renewal and proliferative behaviour of IESCs. Impairment of N-terminal interactions triggers transient hyperproliferation of IESCs, eventually resulting in exhaustion of the self-renewing stem cell pool. IESC mis-differentiation, accompanied by unfolded protein response stress and immune infiltration, results in a process resembling aberrant "villisation" of intestinal crypts. Our data suggest that IESC-specific Wnt/β-catenin output requires selective modulation of gene expression by transcriptional co-factors.

The WNT/β‐catenin dependent transcription: A tissue‐specific business

β‐catenin‐mediated Wnt signaling is an ancient cell‐communication pathway in which β‐catenin drives the expression of certain genes as a consequence of the trigger given by extracellular WNT molecules. The events occurring from signal to transcription are evolutionarily conserved, and their final output orchestrates countless processes during embryonic development and tissue homeostasis. Importantly, a dysfunctional Wnt/β‐catenin pathway causes developmental malformations, and its aberrant activation is the root of several types of cancer. A rich literature describes the multitude of nuclear players that cooperate with β‐catenin to generate a transcriptional program. However, a unified theory of how β‐catenin drives target gene expression is still missing. We will discuss two types of β‐catenin interactors: transcription factors that allow β‐catenin to localize at target regions on the DNA, and transcriptional co‐factors that ultimately activate gene expression. In contrast to the presumed universality of β‐catenin's action, the ensemble of available evidence suggests a view in which β‐catenin drives a complex system of responses in different cells and tissues. A malleable armamentarium of players might interact with β‐catenin in order to activate the right “canonical” targets in each tissue, developmental stage, or disease context. Discovering the mechanism by which each tissue‐specific β‐catenin response is executed will be crucial to comprehend how a seemingly universal pathway fosters a wide spectrum of processes during development and homeostasis. Perhaps more importantly, this could ultimately inform us about which are the tumor‐specific components that need to be targeted to dampen the activity of oncogenic β‐catenin.

This article is categorized under:

Cancer > Molecular and Cellular Physiology

Cancer > Genetics/Genomics/Epigenetics

Cancer > Stem Cells and Development

Structure and function of Pygo in organ development dependent and independent Wnt signalling

Pygo is a nuclear protein containing two conserved domains, NHD and PHD, which play important roles in embryonic development and carcinogenesis. Pygo was first identified as a core component of the Wnt/β-catenin signalling pathway. However, it has also been reported that the function of Pygo is not always Wnt/β-catenin signalling dependent. In this review, we summarise the functions of both domains of Pygo and show that their functions are synergetic. The PHD domain mainly combines with transcription co-factors, including histone 3 and Bcl9/9l. The NHD domain mainly recruits histone methyltransferase/acetyltransferase (HMT/HAT) to modify lysine 4 of the histone 3 tail (H3K4) and interacts with Chip/LIM-domain DNA-binding proteins (ChiLS) to form enhanceosomes to regulate transcriptional activity. Furthermore, we summarised chromatin modification differences of Pygo in Drosophila (dPygo) and vertebrates, and found that Pygo displayes a chromatin silencing function in Drosophila, while in vertebates, Pygo has a chromatin-activating function due to the two substitution of two amino acid residues. Next, we confirmed the relationship between Pygo and Bcl9/9l and found that Pygo-Bcl/9l are specifically partnered both in the nucleus and in the cytoplasm. Finally, we discuss whether transcriptional activity of Pygo is Wnt/β-catenin dependent during embryonic development. Available information indications that the transcriptional activity of Pygo in embryonic development is either Wnt/β-catenin dependent or independent in both tissue-specific and cell-specific-modes.

TBX3 acts as tissue-specific component of the Wnt/β-catenin transcriptional complex

BCL9 and PYGO are β-catenin cofactors that enhance the transcription of Wnt target genes. They have been proposed as therapeutic targets to diminish Wnt signaling output in intestinal malignancies. Here we find that, in colorectal cancer cells and in developing mouse forelimbs, BCL9 proteins sustain the action of β-catenin in a largely PYGO-independent manner. Our genetic analyses implied that BCL9 necessitates other interaction partners in mediating its transcriptional output. We identified the transcription factor TBX3 as a candidate tissue-specific member of the β-catenin transcriptional complex. In developing forelimbs, both TBX3 and BCL9 occupy a large number of Wnt-responsive regulatory elements, genome-wide. Moreover, mutations in Bcl9 affect the expression of TBX3 targets in vivo, and modulation of TBX3 abundance impacts on Wnt target genes transcription in a β-catenin- and TCF/LEF-dependent manner. Finally, TBX3 overexpression exacerbates the metastatic potential of Wnt-dependent human colorectal cancer cells. Our work implicates TBX3 as context-dependent component of the Wnt/β-catenin-dependent transcriptional complex.

A Pygopus 2-Histone Interaction Is Critical for Cancer Cell Dedifferentiation and Progression in Malignant Breast Cancer

Pygopus 2 (Pygo2) is a coactivator of Wnt/β-catenin signaling that can bind bi- or trimethylated lysine 4 of histone-3 (H3K4me^2/3) and participate in chromatin reading and writing. It remains unknown whether the Pygo2-H3K4me^2/3 association has a functional relevance in breast cancer progression in vivo. To investigate the functional relevance of histone-binding activity of Pygo2 in malignant progression of breast cancer, we generated a knock-in mouse model where binding of Pygo2 to H3K4me^2/3 was rendered ineffective. Loss of Pygo2-histone interaction resulted in smaller, differentiated, and less metastatic tumors, due, in part, to decreased canonical Wnt/β-catenin signaling. RNA- and ATAC-sequencing analyses of tumor-derived cell lines revealed downregulation of TGFβ signaling and upregulation of differentiation pathways such as PDGFR signaling. Increased differentiation correlated with a luminal cell fate that could be reversed by inhibition of PDGFR activity. Mechanistically, the Pygo2-histone interaction potentiated Wnt/β-catenin signaling, in part, by repressing the expression of Wnt signaling antagonists. Furthermore, Pygo2 and β-catenin regulated the expression of miR-29 family members, which, in turn, repressed PDGFR expression to promote dedifferentiation of wild-type Pygo2 mammary epithelial tumor cells. Collectively, these results demonstrate that the histone binding function of Pygo2 is important for driving dedifferentiation and malignancy of breast tumors, and loss of this binding activates various differentiation pathways that attenuate primary tumor growth and metastasis formation. Interfering with the Pygo2-H3K4me^2/3 interaction may therefore serve as an attractive therapeutic target for metastatic breast cancer. SIGNIFICANCE: Pygo2 represents a potential therapeutic target in metastatic breast cancer, as its histone-binding capability promotes β-catenin-mediated Wnt signaling and transcriptional control in breast cancer cell dedifferentiation, EMT, and metastasis.

BCL9 provides multi-cellular communication properties in colorectal cancer by interacting with paraspeckle proteins

Colorectal cancer (CRC) is the third most commonly diagnosed cancer, which despite recent advances in treatment, remains incurable due to molecular heterogeneity of tumor cells. The B-cell lymphoma 9 (BCL9) oncogene functions as a transcriptional co-activator of the Wnt/β-catenin pathway, which plays critical roles in CRC pathogenesis. Here we have identified a β-catenin-independent function of BCL9 in a poor-prognosis subtype of CRC tumors characterized by expression of stromal and neural associated genes. In response to spontaneous calcium transients or cellular stress, BCL9 is recruited adjacent to the interchromosomal regions, where it stabilizes the mRNA of calcium signaling and neural associated genes by interacting with paraspeckle proteins. BCL9 subsequently promotes tumor progression and remodeling of the tumor microenvironment (TME) by sustaining the calcium transients and neurotransmitter-dependent communication among CRC cells. These data provide additional insights into the role of BCL9 in tumor pathogenesis and point towards additional avenues for therapeutic intervention.

Wnt status-dependent oncogenic role of BCL9 and BCL9L in hepatocellular carcinoma

Background

Activation of Wnt/β-catenin pathway is a frequent event in hepatocellular carcinoma and is associated with enhanced cell survival and proliferation. Therefore, targeting this signaling pathway is discussed as an attractive therapeutic approach for HCC treatment. BCL9 and BCL9L, two homologous coactivators of the β-catenin transcription factor complex, have not yet been comprehensively characterized in HCC. We aimed to elucidate the roles of BCL9 and BCL9L, especially regarding Wnt/β-catenin signaling and their prognostic value in HCC.

Methods

Expression of BCL9/BCL9L was determined in HCC cell lines (HLE, HLF, Huh7, HepG2, Hep3B, and Huh6) and normal liver cell lines (THLE-2 and THLE-3). To analyze proliferation and apoptosis, BCL9 and/or BCL9L were knocked down in Wnt-inactive HLE and Wnt-active HepG2 and Huh6 cells using siRNA. Subsequently, Wnt reporter assays were performed in HepG2 and Huh6 cells. BCL9 and BCL9L expression, clinicopathological and survival data of public HCC datasets were analyzed, taking the Wnt signaling status into account.

Results

Knockdown of BCL9L, but not of BCL9, reduced Wnt signaling activity. Knockdown of BCL9 and/or BCL9L reduced cell viability and increased apoptosis of Wnt-inactive HCC cells, but had no effect in Wnt-active cells. Expression of BCL9 and BCL9L was upregulated in human HCC and increased with progressing dedifferentiation. For BCL9L, higher expression was observed in tumors of larger size. Overexpression of BCL9 and BCL9L correlated with poor overall survival, especially in HCC without activated Wnt signaling.

Conclusion

Oncogenic BCL9 proteins represent promising targets for cancer therapy and inhibiting them may be particularly beneficial in Wnt-inactive HCCs.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s12072-019-09977-w) contains supplementary material, which is available to authorized users.

Profiling of chromatin accessibility and identification of general cis-regulatory mechanisms that control two ocular lens differentiation pathways

BACKGROUND

Promoters and enhancers are cis-regulatory DNA sequences that control specificity and quantity of transcription. Both are rich on clusters of cis-acting sites that interact with sequence-specific DNA-binding transcription factors (TFs). At the level of chromatin, these regions display increased nuclease sensitivity, reduced nucleosome density, including nucleosome-free regions, and specific combinations of posttranslational modifications of core histone proteins. Together, "open" and "closed" chromatins represent transcriptionally active and repressed states of individual genes, respectively. Cellular differentiation is marked by changes in local chromatin structure. Lens morphogenesis, regulated by TF Pax6, includes differentiation of epithelial precursor cells into lens fibers in parallel with differentiation of epithelial precursors into the mature lens epithelium.

RESULTS

Using ATAC-seq, we investigated dynamics of chromatin changes during mouse lens fibers and epithelium differentiation. Tissue-specific features of these processes are demonstrated via comparative studies of embryonic stem cells, forebrain, and liver chromatins. Unbiased analysis reveals cis-regulatory logic of lens differentiation through known (e.g., AP-1, Ets, Hsf4, Maf, and Pax6 sites) and novel (e.g., CTCF, Tead, and NF1) motifs. Twenty-six DNA-binding TFs, recognizing these cis-motifs, are markedly up-regulated in differentiating lens fibers. As specific examples, our ATAC-seq data uncovered both the regulatory regions and TF binding motifs in Foxe3, Prox1, and Mip loci that are consistent with previous, though incomplete, experimental data. A cross-examination of Pax6 binding with ATAC-seq data demonstrated that Pax6 bound to both open (H3K27ac and P300-enriched) and closed chromatin domains in lens and forebrain.

CONCLUSIONS

Our study has generated the first lens chromatin accessibility maps that support a general model of stage-specific chromatin changes associated with transcriptional activities of batteries of genes required for lens fiber cell formation. Analysis of active (or open) promoters and enhancers reveals important cis-DNA motifs that establish the molecular foundation for temporally and spatially regulated gene expression in lens. Together, our data and models open new avenues for the field to conduct mechanistic studies of transcriptional control regions, reconstruction of gene regulatory networks that govern lens morphogenesis, and identification of cataract-causing mutations in noncoding sequences.

Immunohistochemical Mapping of Bcl9 Using Two Antibodies that Recognize Different Epitopes Is Useful to Characterize Juvenile Development of Hepatocellular Carcinoma in Myanmar

B-cell lymphoma 9 (Bcl9) is the core component of Wnt/β-catenin signaling and overexpressed in nuclei of various tumors, including hepatocellular carcinoma (HCC). However, the extent of Bcl9 expression relative to HCC differentiation stage and its functional aspects are poorly understood. In this study, we examined the expression pattern of Bcl9 immunohistochemically, using two anti-Bcl9 antibodies; one was a conventional polyclonal-antibody (anti-Bcl9^ABC) against amino acid no.800-900 of human-Bcl9, while the other (anti-Bcl9^BIO) was against amino acid no.50-200, covering Pygopus-binding sites of Bcl9. Immunohistochemistry using anti-Bcl9^BIO demonstrated distinctive staining in the cytoplasm, while the anti-Bcl9^ABC signal was detected in both cytoplasm and nuclei of HCC cells, reflecting different states of Bcl9 function because Pygopus-binding to Bcl9 is essential to exert its function together with β-catenin in nucleus. Quantitative analysis revealed a significantly higher immunohistochemical-score by anti-Bcl9^BIO in normal liver comparing various differentiation grades of HCC (P < 0.004), whereas no significant difference was noted with anti-Bcl9^ABC. Interestingly, immunohistochemical-score of anti-Bcl9^BIO in patients aged < 40 years was significantly lower than that of ≥ 40 years group (P < 0.01). The results indicated that anti-Bcl9^BIO detected cytoplasmic Bcl9, which does not bind to Pygopus suggesting it could be a useful indicator for development of HCC in young Myanmar patients.

Mutations in Bcl9 and Pygo genes cause congenital heart defects by tissue-specific perturbation of Wnt/β-catenin signaling

Bcl9 and Pygopus (Pygo) are obligate Wnt/β-catenin cofactors in Drosophila, yet their contribution to Wnt signaling during vertebrate development remains unresolved. Combining zebrafish and mouse genetics, we document a conserved, β-catenin-associated function for BCL9 and Pygo proteins during vertebrate heart development. Disrupting the β-catenin-BCL9-Pygo complex results in a broadly maintained canonical Wnt response yet perturbs heart development and proper expression of key cardiac regulators. Our work highlights BCL9 and Pygo as selective β-catenin cofactors in a subset of canonical Wnt responses during vertebrate development. Moreover, our results implicate alterations in BCL9 and BCL9L in human congenital heart defects.

Molecular mechanisms of heart failure: insights from Drosophila

Heart failure places an enormous burden on health and economic systems worldwide. It is a complex disease that is profoundly influenced by both genetic and environmental factors. Neither the molecular mechanisms underlying heart failure nor effective prevention strategies are fully understood. Fortunately, relevant aspects of human heart failure can be experimentally studied in tractable model animals, including the fruit fly, Drosophila, allowing the in vivo application of powerful and sophisticated molecular genetic and physiological approaches. Heart failure in Drosophila, as in humans, can be classified into dilated cardiomyopathies and hypertrophic cardiomyopathies. Critically, many genes and cellular pathways directing heart development and function are evolutionarily conserved from Drosophila to humans. Studies of molecular mechanisms linking aging with heart failure have revealed that genes involved in aging-associated energy homeostasis and oxidative stress resistance influence cardiac dysfunction through perturbation of IGF and TOR pathways. Importantly, ion channel proteins, cytoskeletal proteins, and integrins implicated in aging of the mammalian heart have been shown to play significant roles in heart failure. A number of genes previously described having roles in development of the Drosophila heart, such as genes involved in Wnt signaling pathways, have recently been shown to play important roles in the adult fly heart. Moreover, the fly model presents opportunities for innovative studies that cannot currently be pursued in the mammalian heart because of technical limitations. In this review, we discuss progress in our understanding of genes, proteins, and molecular mechanisms that affect the Drosophila adult heart and heart failure.

Role of BCL9L in transforming growth factor-β (TGF-β)-induced epithelial-to-mesenchymal-transition (EMT) and metastasis of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has a low overall survival rate, which is approximately 20% during the first year and decreases to less than 6% within five years of the disease. This is due to premature dissemination accompanied by a lack of disease-specific symptoms during the initial stages. Additionally, to date there are no biomarkers for an early prognosis available.A growing number of studies indicate that epithelial to mesenchymal transition (EMT), triggered by WNT-, TGF-β- and other signaling pathways is crucial for the initiation of the metastatic process in PDAC. Here we show, that BCL9L is up-regulated in PDAC cell lines and patient tissue compared to non-cancer controls. RNAi-induced BCL9L knockdown negatively affected proliferation, migration and invasion of pancreatic cancer cells. On a molecular basis, BCL9L depletion provoked an increment of E-cadherin protein levels, with concomitant increase of β-catenin retention at the plasma membrane. This is linked to the induction of a strong epithelial phenotype in pancreatic cancer cells upon BCL9L knockdown even in the presence of the EMT-inducer TGF-β. Finally, xenograft mouse models of pancreatic cancer revealed a highly significant reduction in the number of liver metastases upon BCL9L knockdown. Taken together, our findings underline the key importance of BCL9L for EMT and thus progression and metastasis of pancreatic cancer cells. Direct targeting of this protein might be a valuable approach to effectively antagonize invasion and metastasis of PDAC.

The role of Pygo2 for Wnt/ß-catenin signaling activity during intestinal tumor initiation and progression

Pygo2 acts as a co-activator of Wnt signaling in a nuclear complex with ß-catenin/BCL9/BCL9-2 to increase target gene transcription. Previous studies showed that Pygo2 is upregulated in murine intestinal tumors and human colon cancer, but is apparently dispensable for normal intestinal homeostasis. Here, we have evaluated the in vivo role of Pygo2 during intestinal tumorigenesis using Pygo2 deficient mice. We analyzed chemically induced colon tumor development and conditional intestine specific mouse models harboring either Apc loss-of-function (LOF) or Ctnnb1 gain-of-function (ß-catenin GOF). Remarkably, the number and size of chemically induced tumors was significantly reduced in Pygo2 deficient mice, suggesting that Pygo2 has a tumor promoting function. Furthermore, loss of Pygo2 rescued early tumorigenesis of Ctnnb1 GOF mutants. In contrast, Pygo2 ablation was not sufficient to prevent tumor development of Apc LOF mice. The effect on tumor formation by Pygo2 knockout was linked to the repression of specific deregulated Wnt target genes, in particular of c-Myc. Moreover, the role of Pygo2 appears to be associated with the signaling output of deregulated Wnt signaling in the different tumor models. Thus, targeting Pygo2 might provide a novel strategy to suppress tumor formation in a context dependent manner.

New GJA8 variants and phenotypes highlight its critical role in a broad spectrum of eye anomalies

GJA8 encodes connexin 50 (Cx50), a transmembrane protein involved in the formation of lens gap junctions. GJA8 mutations have been linked to early onset cataracts in humans and animal models. In mice, missense mutations and homozygous Gja8 deletions lead to smaller lenses and microphthalmia in addition to cataract, suggesting that Gja8 may play a role in both lens development and ocular growth. Following screening of GJA8 in a cohort of 426 individuals with severe congenital eye anomalies, primarily anophthalmia, microphthalmia and coloboma, we identified four known [p.(Thr39Arg), p.(Trp45Leu), p.(Asp51Asn), and p.(Gly94Arg)] and two novel [p.(Phe70Leu) and p.(Val97Gly)] likely pathogenic variants in seven families. Five of these co-segregated with cataracts and microphthalmia, whereas the variant p.(Gly94Arg) was identified in an individual with congenital aphakia, sclerocornea, microphthalmia and coloboma. Four missense variants of unknown or unlikely clinical significance were also identified. Furthermore, the screening of GJA8 structural variants in a subgroup of 188 individuals identified heterozygous 1q21 microdeletions in five families with coloboma and other ocular and/or extraocular findings. However, the exact genotype-phenotype correlation of these structural variants remains to be established. Our data expand the spectrum of GJA8 variants and associated phenotypes, confirming the importance of this gene in early eye development.

Early Determination of the Periodontal Domain by the Wnt-Antagonist Frzb/Sfrp3

Odontogenesis results from the continuous and reciprocal interaction between cells of the oral epithelium and cranial neural crest-derived mesenchyme. The canonical Wnt signaling pathway plays a fundamental role in mediating these interactions from the earliest stages of tooth development. Here we analyze by in situ hybridization the expression patterns of the extracellular Wnt antagonist Frzb/Sfrp3. Although Frzb is expressed in dental mesenchymal cells from the earliest stages of odontogenesis, its expression is absent from a tiny population of mesenchymal cells immediately adjacent to the invaginating dental epithelium. Cell proliferation studies using BrdU showed that the Frzb expressing and Frzb non-expressing cell populations display different proliferative behavior during the initial stages of odontogenesis. DiI-mediated cell-fate tracing studies demonstrated that the Frzb expressing cells contribute to the formation of the dental follicle, the future periodontium. In contrast, the Frzb non-expressing cells give rise to the dental pulp. The present results indicate that Frzb is discriminating the presumptive periodontal territory from the rest of the dental mesenchyme from the very beginning of odontogenesis, where it might act as a barrier for the diffusion of Wnt molecules, thus regulating the activation of Wnt-dependent transcription within dental tissues.

Opposing roles of ICAT and Wnt/β-catenin signaling in NSC67657-induced monocytic differentiation

NSC67657 is a new steroid drug that induces monocytic differentiation of acute myeloid leukemia cells. Here, we demonstrate that NSC67657 has opposing effects on expression of downstream targets of inhibitor of β-catenin and TCF (ICAT) and Wnt signaling in HL60 cells. ICAT binds to β-catenin, and this interaction is further increased in NSC67657-differentiated cells. ICAT overexpression decreases expression of Wnt downstream targets and increases sensitivity of HL60 cells to NSC67657, while ICAT silencing increases Wnt signaling and delays the NSC67657-induced cell differentiation. In addition, pharmacological inhibition of Wnt/β-catenin signaling increases the NSC67657-induced cell differentiation, while activation of Wnt/β-catenin signaling inhibits the differentiation, indicating Wnt/β-catenin signaling inhibits NSC67657-induced monocytic differentiation of HL60 cells. Our data demonstrate the opposing roles of ICAT and Wnt signaling in the NSC67657-induced monocytic differentiation, and suggest that ICAT and Wnt signaling may serve as therapeutic targets for leukemia chemotherapy.

Pharmacological interventions in the Wnt pathway: inhibition of Wnt secretion versus disrupting the protein-protein interfaces of nuclear factors

Mutations in components of the Wnt pathways are a frequent cause of many human diseases, particularly cancer. Despite the fact that a causative link between aberrant Wnt signalling and many types of human cancers was established more than a decade ago, no Wnt signalling inhibitors have made it into the clinic so far. One reason for this is that no pathway-specific kinase is known. Additionally, targeting the protein-protein interactions needed to transduce the signal has not met with success so far. Complicating the search for and use of inhibitors is the complexity of the cascades triggered by the Wnts and their paramount biological importance. Wnt/β-catenin signalling is involved in virtually all aspects of embryonic development and in the control of the homeostasis of adult tissues. Encouragingly, however, in recent years, first successes with Wnt-pathway inhibitors have been reported in mouse models of disease. In this review, we summarize possible roads to follow during the quest to pharmacologically modulate the Wnt signalling pathway in cancer.

LINKED ARTICLES

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc.

A cytoplasmic role of Wnt/β-catenin transcriptional cofactors Bcl9, Bcl9l, and Pygopus in tooth enamel formation

Wnt-stimulated β-catenin transcriptional regulation is necessary for the development of most organs, including teeth. Bcl9 and Bcl9l are tissue-specific transcriptional cofactors that cooperate with β-catenin. In the nucleus, Bcl9 and Bcl9l simultaneously bind β-catenin and the transcriptional activator Pygo2 to promote the transcription of a subset of Wnt target genes. We showed that Bcl9 and Bcl9l function in the cytoplasm during tooth enamel formation in a manner that is independent of Wnt-stimulated β-catenin-dependent transcription. Bcl9, Bcl9l, and Pygo2 localized mainly to the cytoplasm of the epithelial-derived ameloblasts, the cells responsible for enamel production. In ameloblasts, Bcl9 interacted with proteins involved in enamel formation and proteins involved in exocytosis and vesicular trafficking. Conditional deletion of both Bcl9 and Bcl9l or both Pygo1 and Pygo2 in mice produced teeth with defective enamel that was bright white and deficient in iron, which is reminiscent of human tooth enamel pathologies. Overall, our data revealed that these proteins, originally defined through their function as β-catenin transcriptional cofactors, function in odontogenesis through a previously uncharacterized cytoplasmic mechanism, revealing that they have roles beyond that of transcriptional cofactors.

BCL9L Dysfunction Impairs Caspase-2 Expression Permitting Aneuploidy Tolerance in Colorectal Cancer

Chromosomal instability (CIN) contributes to cancer evolution, intratumor heterogeneity, and drug resistance. CIN is driven by chromosome segregation errors and a tolerance phenotype that permits the propagation of aneuploid genomes. Through genomic analysis of colorectal cancers and cell lines, we find frequent loss of heterozygosity and mutations in BCL9L in aneuploid tumors. BCL9L deficiency promoted tolerance of chromosome missegregation events, propagation of aneuploidy, and genetic heterogeneity in xenograft models likely through modulation of Wnt signaling. We find that BCL9L dysfunction contributes to aneuploidy tolerance in both TP53-WT and mutant cells by reducing basal caspase-2 levels and preventing cleavage of MDM2 and BID. Efforts to exploit aneuploidy tolerance mechanisms and the BCL9L/caspase-2/BID axis may limit cancer diversity and evolution.

BCL9/9L-β-catenin Signaling is Associated With Poor Outcome in Colorectal Cancer

BCL9/9L proteins enhance the transcriptional output of the β-catenin/TCF transcriptional complex and contribute critically to upholding the high WNT signaling level required for stemness maintenance in the intestinal epithelium. Here we show that a BCL9/9L-dependent gene signature derived from independent mouse colorectal cancer (CRC) models unprecedentedly separates patient subgroups with regard to progression free and overall survival. We found that this effect was by and large attributable to stemness related gene sets. Remarkably, this signature proved associated with recently described poor prognosis CRC subtypes exhibiting high stemness and/or epithelial-to-mesenchymal transition (EMT) traits. Consistent with the notion that high WNT signaling is required for stemness maintenance, ablating Bcl9/9l-β-catenin in murine oncogenic intestinal organoids provoked their differentiation and completely abrogated their tumorigenicity, while not affecting their proliferation. Therapeutic strategies aimed at targeting WNT responses may be limited by intestinal toxicity. Our findings suggest that attenuating WNT signaling to an extent that affects stemness maintenance without disturbing intestinal renewal might be well tolerated and prove sufficient to reduce CRC recurrence and dramatically improve disease outcome.

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Inhibiting BCL9/9L-β-catenin in CRC models reduces stemness and boosts differentiation traits

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CRC patients with low expression of BCL9/9L-β-catenin regulated genes have a better prognosis

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Tempering WNT signaling without affecting intestinal self renewal might be an attractive therapeutic strategy in CRC

Mutational activation of the WNT pathway is a key oncogenic event in colorectal cancer (CRC). Targeting the WNT pathway therefore appears as an attractive strategy, but the therapeutic window might be limited due to intestinal toxicity. Maximum WNT signaling strength is required for upholding stemness traits, which are linked to poor prognosis in CRC. Our data suggest that tempering WNT signaling through abrogating BCL9/9L-β-catenin signaling in CRC models is tolerable for intestinal homeostasis yet strongly diminishes stemness traits and may have a vast impact on CRC patient outcome.

Identification of in vivo DNA-binding mechanisms of Pax6 and reconstruction of Pax6-dependent gene regulatory networks during forebrain and lens development

The transcription factor Pax6 is comprised of the paired domain (PD) and homeodomain (HD). In the developing forebrain, Pax6 is expressed in ventricular zone precursor cells and in specific subpopulations of neurons; absence of Pax6 results in disrupted cell proliferation and cell fate specification. Pax6 also regulates the entire lens developmental program. To reconstruct Pax6-dependent gene regulatory networks (GRNs), ChIP-seq studies were performed using forebrain and lens chromatin from mice. A total of 3514 (forebrain) and 3723 (lens) Pax6-containing peaks were identified, with ∼70% of them found in both tissues and thereafter called 'common' peaks. Analysis of Pax6-bound peaks identified motifs that closely resemble Pax6-PD, Pax6-PD/HD and Pax6-HD established binding sequences. Mapping of H3K4me1, H3K4me3, H3K27ac, H3K27me3 and RNA polymerase II revealed distinct types of tissue-specific enhancers bound by Pax6. Pax6 directly regulates cortical neurogenesis through activation (e.g. Dmrta1 and Ngn2) and repression (e.g. Ascl1, Fezf2, and Gsx2) of transcription factors. In lens, Pax6 directly regulates cell cycle exit via components of FGF (Fgfr2, Prox1 and Ccnd1) and Wnt (Dkk3, Wnt7a, Lrp6, Bcl9l, and Ccnd1) signaling pathways. Collectively, these studies provide genome-wide analysis of Pax6-dependent GRNs in lens and forebrain and establish novel roles of Pax6 in organogenesis.