Crossroads of Wnt and Hippo in epithelial tissues

Wnt signalling facilitates neuronal differentiation of cochlear Frizzled10-positive cells in mouse cochlea via glypican 6 modulation

Degeneration of cochlear spiral ganglion neurons (SGNs) leads to irreversible sensorineural hearing loss (SNHL), as SGNs lack regenerative capacity. Although cochlear glial cells (GCs) have some neuronal differentiation potential, their specific identities remain unclear. This study identifies a distinct subpopulation, Frizzled10 positive (FZD10+) cells, as an important type of GC responsible for neuronal differentiation in mouse cochlea. FZD10 + cells can differentiate into various SGN subtypes in vivo, adhering to natural proportions. Wnt signaling enhances the ability of FZD10 + cells to function as neural progenitors and increases the neuronal excitability of the FZD10-derived neurons. Single-cell RNA sequencing analysis characterizes FZD10-derived differentiating cell populations, while crosstalk network analysis identifies multiple signaling pathways and target genes influenced by Wnt signaling that contribute to the function of FZD10 + cells as neural progenitors. Pseudotime analysis maps the differentiation trajectory from proliferated GCs to differentiating neurons. Further experiments indicate that glypican 6 (GPC6) may regulate this neuronal lineage, while GPC6 deficiency diminishes the effects of Wnt signaling on FZD10-derived neuronal differentiation and synapse formation. These findings suggest the critical role of Wnt signaling in the neuronal differentiation derived from cochlear FZD10 + cells and provide insights into the mechanisms potentially involved in this process.

Wnt/β-Catenin Signaling Regulates Yap/Taz Activity during Embryonic Development in Zebrafish

Hippo-YAP/TAZ and Wnt/β-catenin signaling pathways, by controlling proliferation, migration, cell fate, stemness, and apoptosis, are crucial regulators of development and tissue homeostasis. We employed zebrafish embryos as a model system to elucidate in living reporter organisms the crosstalk between the two signaling pathways. Co-expression analysis between the Wnt/β-catenin Tg(7xTCF-Xla.Siam:GFP)ia4 and the Hippo-Yap/Taz Tg(Hsa.CTGF:nlsmCherry)ia49 zebrafish reporter lines revealed shared spatiotemporal expression profiles. These patterns were particularly evident in key developmental regions such as the midbrain-hindbrain boundary (MHB), epidermis, muscles, neural tube, notochord, floorplate, and otic vesicle. To investigate the relationship between the Wnt/β-catenin pathway and Hippo-Yap/Taz signaling in vivo, we conducted a series of experiments employing both pharmacological and genetic strategies. Modulation of the Wnt/β-catenin pathway with IWR-1, XAV939, or BIO resulted in a significant regulation of the Yap/Taz reporter signal, highlighting a clear correlation between β-catenin and Yap/Taz activities. Furthermore, genetic perturbation of the Wnt/β-catenin pathway, by APC inhibition or DKK1 upregulation, elicited evident and robust alteration of Yap/Taz activity. These findings revealed the intricate regulatory mechanisms underlying the crosstalk between the Wnt/β-catenin and Hippo-Yap/Taz signaling, shedding light on their roles in orchestrating developmental processes in vivo.

The Hippo signalling pathway and its impact on eye diseases

The Hippo signalling pathway, an evolutionarily conserved kinase cascade, has been shown to be crucial for cell fate determination, homeostasis and tissue regeneration. Recent experimental and clinical studies have demonstrated that the Hippo signalling pathway is involved in the pathophysiology of ocular diseases. This article provides the first systematic review of studies on the regulatory and functional roles of mammalian Hippo signalling systems in eye diseases. More comprehensive studies on this pathway are required for a better understanding of the pathophysiology of eye diseases and the development of effective therapies.

MUC13 drives cancer aggressiveness and metastasis through the YAP1-dependent pathway

Anchorage-independent survival after intravasation of cancer cells from the primary tumor site represents a critical step in metastasis. Here, we reveal new insights into how MUC13-mediated anoikis resistance, coupled with survival of colorectal tumor cells, leads to distant metastasis. We found that MUC13 targets a potent transcriptional coactivator, YAP1, and drives its nuclear translocation via forming a novel survival complex, which in turn augments the levels of pro-survival and metastasis-associated genes. High expression of MUC13 is correlated well with extensive macrometastasis of colon cancer cells with elevated nuclear YAP1 in physiologically relevant whole animal model systems. Interestingly, a positive correlation of MUC13 and YAP1 expression was observed in human colorectal cancer tissues. In brief, the results presented here broaden the significance of MCU13 in cancer metastasis via targeting YAP1 for the first time and provide new avenues for developing novel strategies for targeting cancer metastasis.

HPV E6 inhibits E6AP to regulate epithelial homeostasis by modulating keratinocyte differentiation commitment and YAP1 activation

Human papillomaviruses (HPV) cause persistent infections by modulating epithelial homeostasis in cells of the infected basal layer. Using FUCCI and cell-cell competition assays, we have identifed regulatory roles for E6AP and NHERF1, which are the primary HPV11 E6 cellular targets, as well as being targets of the high-risk E6 proteins, in processes governing epithelial homeostasis (i.e. cell density, cell cycle entry, commitment to differentiation and basal layer delamination). Depletion of E6AP, or expression of HPV11 or 16E6 increased keratinocyte cell density and cell cycle activity, and delayed the onset of differentiation; phenotypes which were conspicuously present in HPV11 and 16 infected patient tissue. In line with proposed E6 functions, in HPV11 condyloma tissue, E6AP and NHERF1 were significantly reduced when compared to uninfected epithelium. In experimental systems, loss of HPV11 E6/E6AP binding abolished 11E6's homeostasis regulatory functions, while loss of E6/NHERF1 binding reduced the cell density threshold at which differentiation was triggered. By contrast, a NHERF1-binding mutant of 16E6 was not compromised in its homeostasis functions, while E6AP appeared essential. RNA sequencing revealed similar transcriptional profiles in both 11 and 16E6-expressing cells and E6AP-/- cells, with YAP target genes induced, and keratinocyte differentiation genes being downregulated. HPV11 E6-mediated Yap activation was observed in 2D and 3D (organotypic raft) cell culture systems and HPV-infected lesions, with both NHERF1, which is a regulator of the Hippo and Wnt pathways, and E6AP, playing an important role. As the conserved binding partner of Alpha group HPV E6 proteins, the precise role of E6AP in modulating keratinocyte phenotype and associated signalling pathways has not previously been defined. Our study suggests a model in which the preserved functions of the low and high-risk Alpha E6 proteins modulate epithelial homeostasis via E6AP activity, and lead to alteration of multiple downstream pathways, including those involving NHERF1 and YAP.

Yes-associated protein regulates glutamate homeostasis through promoting the expression of excitatory amino acid transporter-2 in astrocytes via β-catenin signaling

The homeostasis of glutamate is mainly regulated by the excitatory amino acid transporters (EAATs), especially by EAAT2 in astrocytes. Excessive glutamate in the synaptic cleft caused by dysfunction or dysregulation of EAAT2 can lead to excitotoxicity, neuronal death and cognitive dysfunction. However, it remains unclear about the detailed regulation mechanism of expression and function of astrocytic EAAT2. In this study, first, we found increased neuronal death and impairment of cognitive function in YAP^GFAP -CKO mice (conditionally knock out Yes-associated protein [YAP] in astrocytes), and identified EAAT2 as a downstream target of YAP through RNA sequencing. Second, the expression of EAAT2 was decreased in cultured YAP^-/- astrocytes and the hippocampus of YAP^GFAP -CKO mice, and glutamate uptake was reduced in YAP^-/- astrocytes, but increased in YAP-upregulated astrocytes. Third, further investigation of the mechanism showed that the mRNA and protein levels of β-catenin were decreased in YAP^-/- astrocytes and increased in YAP-upregulated astrocytes. Wnt3a activated YAP signaling and up-regulated EAAT2 through β-catenin. Furthermore, over-expression or activation of β-catenin partially restored the downregulation of EAAT2, the impairment of glutamate uptake, neuronal death and cognitive decline that caused by YAP deletion. Finally, activation of EAAT2 also rescued neuronal death and cognitive decline in YAP^GFAP -CKO mice. Taken together, our study identifies an unrecognized role of YAP signaling in the regulation of glutamate homeostasis through the β-catenin/EAAT2 pathway in astrocytes, which may provide novel insights into the pathogenesis of brain diseases that closely related to the dysfunction or dysregulation of EAAT2, and promote the development of clinical strategy.

Epithelial tissue geometry directs emergence of bioelectric field and pattern of proliferation

Patterns of proliferation are templated by both gradients of mechanical stress as well as by gradients in membrane voltage (Vm), which is defined as the electric potential difference between the cytoplasm and the extracellular medium. Either gradient could regulate the emergence of the other, or they could arise independently and synergistically affect proliferation within a tissue. Here, we examined the relationship between endogenous patterns of mechanical stress and the generation of bioelectric gradients in mammary epithelial tissues. We observed that the mechanical stress gradients in the tissues presaged gradients in both proliferation and depolarization, consistent with previous reports correlating depolarization with proliferation. Furthermore, disrupting the Vm gradient blocked the emergence of patterned proliferation. We found that the bioelectric gradient formed downstream of mechanical stresses within the tissues and depended on connexin-43 (Cx43) hemichannels, which opened preferentially in cells located in regions of high mechanical stress. Activation of Cx43 hemichannels was necessary for nuclear localization of Yap/Taz and induction of proliferation. Together, these results suggest that mechanotransduction triggers the formation of bioelectric gradients across a tissue, which are further translated into transcriptional changes that template patterns of growth.

Knockdown of YAP inhibits growth in Hep-2 laryngeal cancer cells via epithelial-mesenchymal transition and the Wnt/β-catenin pathway

BACKGROUND

Yes-associated protein (YAP) plays a crucial role in tumour development and it is the main effector of the Hippo signalling pathway. However, the mechanism underlying YAP downregulation in laryngeal cancer is still unclear. In our previous study, we found that YAP, compared with adjacent tissues, was expressed higher in laryngeal cancer and was also closely associated with histological differentiation, TNM stage and poor prognosis.

METHODS

In this study, we attempted to determine whether silenced YAP could downregulate human laryngeal carcinoma Hep-2 cells progression. YAP was downregulated in Hep-2 cells by shRNA, and the malignant ability of Hep-2 was assessed in vitro and in vivo.

RESULTS

In vitro, CCK-8, colony formation and wound healing assays showed that downregulation of YAP significantly reduced the rates of proliferation, migration, and invasion in Hep-2 cells. Downregulation of YAP distinctly induced G2/M cycle arrest and increased the rate of apoptosis. Accordingly, western blot assay suggested that the expression of DKK1, vimentin and β-catenin was significantly decreased after YAP downregulated treatment, thereby indicating that YAP mediated the EMT programme and the Wnt/β-catenin signalling pathway in carcinoma of the larynx. Furthermore, silencing of YAP suppressed Hep-2 cell tumourigenesis and metastasis in vivo.

CONCLUSION

In summary, our findings demonstrated the proliferation of YAP downregulation and the invasion of Hep-2 cells via downregulating the Wnt/β-catenin pathway in vitro and in vivo, suggesting that YAP may provide a potential therapeutic strategy for the treatment of laryngeal cancer.

The Iroquois homeobox proteins IRX3 and IRX5 have distinct roles in Wilms tumour development and human nephrogenesis

Wilms tumour is a paediatric malignancy with features of halted kidney development. Here, we demonstrate that the Iroquois homeobox genes IRX3 and IRX5 are essential for mammalian nephrogenesis and govern the differentiation of Wilms tumour. Knock‐out Irx3⁻/Irx5⁻ mice showed a strongly reduced embryonic nephron formation. In human foetal kidney and Wilms tumour, IRX5 expression was already activated in early proliferative blastema, whereas IRX3 protein levels peaked at tubular differentiation. Accordingly, an orthotopic xenograft mouse model of Wilms tumour showed that IRX3^−/− cells formed bulky renal tumours dominated by immature mesenchyme and active canonical WNT/β‐catenin‐signalling. In contrast, IRX5^−/− cells displayed activation of Hippo and non‐canonical WNT‐signalling and generated small tumours with abundant tubulogenesis. Our findings suggest that promotion of IRX3 signalling or inhibition of IRX5 signalling could be a route towards differentiation therapy for Wilms tumour, in which WNT5A is a candidate molecule for enforced tubular maturation. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Hippo-YAP/TAZ signaling in angiogenesis

Angiogenesis is a complex, multistep process involving dynamic changes in endothelial cell (EC) shapes and behaviors, especially in specialized cell types such as tip cells (with active filopodial extensions), stalk cells (with less motility) and phalanx cells (with stable junction connections). The Hippo-Yes-associated protein (YAP)/ transcription activator with PDZ binding motif (TAZ) signaling plays a critical role in development, regeneration and organ size by regulating cell-cell contact and actin cytoskeleton dynamics. Recently, with the finding that YAP is expressed in the front edge of the developing retinal vessels, Hippo-YAP/TAZ signaling has emerged as a new pathway for blood vessel development. Intriguingly, the LATS1/2-mediated angiomotin (AMOT) family and YAP/TAZ activities contribute to EC shapes and behaviors by spatiotemporally modulating actin cytoskeleton dynamics and EC junction stability. Herein, we summarize the recent understanding of the role of Hippo-YAP/TAZ signaling in the processes of EC sprouting and junction maturation in angiogenesis.

Substratum stiffness tunes proliferation downstream of Wnt3a in part by regulating integrin-linked kinase and frizzled-1

The Wnt/β-catenin pathway controls a variety of cellular behaviors, aberrant activation of which are associated with tumor progression in several types of cancer. The same cellular behaviors are also affected by the mechanical properties of the extracellular matrix (ECM) substratum, which induces signaling through integrins and integrin-linked kinase (ILK). Here, we examined the role of substratum stiffness in the regulation of cell proliferation downstream of Wnt3a. We found that treatment with Wnt3a increased proliferation of cells cultured on stiff substrata, with compliances characteristic of breast tumors, but not of cells on soft substrata, with compliances comparable to that of normal mammary tissue. Depleting ILK rendered cells unresponsive to Wnt3a on both substrata. Ectopic expression of ILK permitted Wnt3a to induce proliferation of cells on both microenvironments, although proliferation on soft substrata remained lower than that on stiff substrata. We further showed that ILK regulates expression of the Wnt receptor frizzled-1 (Fzd1), suggesting the presence of a positive feedback loop between Wnt3a, ILK and Fzd1. These findings suggest that tissue mechanics regulates the cellular response to Wnt under physiological and pathological microenvironmental conditions.This article has an associated First Person interview with the first author of the paper.

WNT receptor signalling in lung physiology and pathology

The WNT signalling cascades have emerged as critical regulators of a wide variety of biological aspects involved in lung development as well as in physiological and pathophysiological processes in the adult lung. WNTs (secreted glycoproteins) interact with various transmembrane receptors and co-receptors to activate signalling pathways that regulate transcriptional as well as non-transcriptional responses within cells. In physiological conditions, the majority of WNT receptors and co-receptors can be detected in the adult lung. However, dysregulation of WNT signalling pathways contributes to the development and progression of chronic lung pathologies, including idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), asthma and lung cancer. The interaction between a WNT and the (co-)receptor(s) present at the cell surface is the initial step in transducing an extracellular signal into an intracellular response. This proximal event in WNT signal transduction with (cell-specific) ligand-receptor interactions is of great interest as a potential target for pharmacological intervention. In this review we highlight the diverse expression of various WNT receptors and co-receptors in the aforementioned chronic lung diseases and discuss the currently available biologicals and pharmacological tools to modify proximal WNT signalling.

A genetic variant in Rassf1a predicts outcome in mCRC patients treated with cetuximab plus chemotherapy: results from FIRE-3 and JACCRO 05 and 06 trials

The Hippo pathway is involved in colorectal cancer (CRC) development and progression. The Hippo regulator Rassf1a is also involved in the Ras signaling cascade. In this work, we tested single nucleotide polymorphisms within Hippo components and their association with outcome in CRC patients treated with cetuximab. Two cohorts treated with cetuximab plus chemotherapy were evaluated (198 RAS wild-type (WT) patients treated with first-line FOLFIRI plus Cetuximab within the FIRE-3 trial and 67 Ras WT patients treated either with first-line mFOLFOX6 or SOX plus Cetuximab). In these two populations, Rassf1a rs2236947 was associated with overall survival (OS), as patients with a CC genotype had significantly longer OS compared with those with CA or AA genotypes. This association was stronger in patients with left-side CRC (hazard ratio (HR): 1.79 (1.01-3.14); P=0.044 and HR: 2.83 (1.14-7.03); P=0.025, for Fire 3 and JACCRO cohorts, respectively). Rassf1a rs2236947 is a promising biomarker for patients treated with cetuximab plus chemotherapy.

Ascl2 activation by YAP1/KLF5 ensures the self-renewability of colon cancer progenitor cells

Achaete scute-like 2 (Ascl2) is the Wnt signaling target, its regulation by other signaling is undefined. Now we demonstrated that CD133⁺/CD44⁺ cell population from HT-29 or Caco-2 cells exhibited cancer stem cell (CSC) properties with highly expressed Ascl2, which is related to the Hippo signaling pathway. YAP1 interference in CD133⁺/CD44⁺ HT-29 or Caco-2 cells reduced their proliferation, colony-forming ability and tumorsphere formation in vitro and inhibited the ‘stemness’-associated genes and Ascl2 expression. Enforcing YAP1 expression in HT-29 or Caco-2 cells triggered the opposite changes. Ascl2 interference reversed the phenotype of YAP1-enforced expressed HT-29 or Caco-2 cells. Krüppel-like factor 5 (KLF5) protein, not KLF5 mRNA levels, were increased due to YAP1 overexpression which is reported to prevent KLF5 degradation. Co-immunoprecipitation (Co-IP) assays demonstrated that YAP1 bound with KLF5 in HT-29 and Caco-2 cells. Luciferase and chromatin immunoprecipitation (ChIP) assays indicated that both YAP1 and KLF5 bound to the first two loci with GC-boxes in Ascl2 promoter and induced Ascl2 transcription. The decreased Ascl2 transcription by YAP1 interference required an intact KLF5 binding site (GC-box) within Ascl2 promoter, KLF5 knockdown reduced YAP1 binding and Ascl2 luciferase reporter activity upon YAP1 overexpression. Positive correlation among YAP1 and Ascl2 mRNA levels was observed in colorectal cancer (CRC) samples. Thus, our study demonstrated that Ascl2, a fate decider of CRC progenitor cells can be activated by the Hippo signaling pathway in CRC progenitor cells, and ensured their self-renewability.

β-catenin-mediated YAP signaling promotes human glioma growth

Background

Hippo/YAP pathway is known to be important for development, growth and organogenesis, and dysregulation of this pathway leads to tumor progression.We and others find that YAP is up-regulated in human gliomas and associated with worse prognosis of patients. However, the role and mechanism of YAP in glioma progression is largely unknown.

Methods

The expression of YAP in glioma tissues was detected by quantitative polymerase chain reaction (qPCR) and immunoblotting. The effect of YAP on glioma progression was examined using cell growth assays and intracranial glioma model. The effect of YAP on β-catenin protein level, subcellular location and transcription activity was examined by immunoblotting, immunofluorescence and RT-PCR.

Results

Firstly, knockdown of YAP inhibited glioma cell proliferation in vitro and tumor growth in vivo. In addition, YAP modulated the protein level, subcellular location and transcription activity of β-catenin via regulating the activity of GSK3β. Lastly, β-catenin partially mediated the effect of YAP on glioma cell proliferation.

Conclusion

Our findings identify that YAP promotes human glioma growth through enhancing Wnt/β-catenin signaling. In addition, this study provides a new crosstalk mechanism between Hippo/YAP and Wnt/β-catenin pathways, which suggests a new strategy for human glioma treatment.

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0606-1) contains supplementary material, which is available to authorized users.

Hippo Pathway: An Emerging Regulator of Craniofacial and Dental Development

The evolutionarily conserved Hippo signaling pathway is a vital regulator of organ size that fine-tunes cell proliferation, apoptosis, and differentiation. A number of important studies have revealed critical roles of Hippo signaling and its effectors Yap (Yes-associated protein) and Taz (transcriptional coactivator with PDZ binding motif) in tissue development, homeostasis, and regeneration, as well as in tumorigenesis. In addition, recent studies have shown evidence of crosstalk between the Hippo pathway and other key signaling pathways, such as Wnt signaling, that not only regulates developmental processes but also contributes to disease pathogenesis. In this review, we summarize the major discoveries in the field of Hippo signaling and what has been learned about its regulation and crosstalk with other signaling pathways, with a particular focus on recent findings involving the Hippo-Yap pathway in craniofacial and tooth development. New and exciting studies of the Hippo pathway are anticipated that will significantly improve our understanding of the molecular mechanisms of human craniofacial and tooth development and disease and will ultimately lead to the development of new therapies.

Primary Cilia and Coordination of Receptor Tyrosine Kinase (RTK) and Transforming Growth Factor β (TGF-β) Signaling

Since the beginning of the millennium, research in primary cilia has revolutionized our way of understanding how cells integrate and organize diverse signaling pathways during vertebrate development and in tissue homeostasis. Primary cilia are unique sensory organelles that detect changes in their extracellular environment and integrate and transmit signaling information to the cell to regulate various cellular, developmental, and physiological processes. Many different signaling pathways have now been shown to rely on primary cilia to function properly, and mutations that lead to ciliary dysfunction are at the root of a pleiotropic group of diseases and syndromic disorders called ciliopathies. In this review, we present an overview of primary cilia-mediated regulation of receptor tyrosine kinase (RTK) and transforming growth factor β (TGF-β) signaling. Further, we discuss how defects in the coordination of these pathways may be linked to ciliopathies.

Spatial regulation of ARAF controls the MST2-Hippo pathway

The RAF-MAPK signaling pathway regulates several very diverse cellular processes such as proliferation, differentiation, apoptosis, and transformation. While the canonical function of RAF kinases within the MAPK pathway is the activation of MEK, our group could demonstrate an important crosstalk between RAF signaling and the pro-apoptotic mammalian sterile 20-like kinase (MST2) tumor suppressor pathway in several cancer entities, including head and neck, colon, and breast. Here, the RAF kinases CRAF and ARAF sequester and inhibit the pro-apoptotic kinase MST2 independently of their own kinase activity. In our recent study, we showed that the ARAF-MST2 complex is regulated by subcellular compartmentalization during epithelial differentiation. Proliferating cells of the basal cell layer in squamous epithelia and tumor cells express ARAF at the mitochondria thus allowing for efficient sequestration of MST2. In contrast, non-malignant squamous epithelia have ARAF localized at the plasma membrane, where the control of MST2-mediated apoptosis is compromised. This re-distribution is regulated by the scaffold protein kinase suppressor of Ras 2 (KSR2). Here, we summarize how spatial and temporal regulation of RAF signaling complexes affect cellular signaling and functions.

Pals1 Haploinsufficiency Results in Proteinuria and Cyst Formation

The nephron is the basic physiologic subunit of the mammalian kidney and is made up of several apicobasally polarized epithelial cell types. The process of apicobasal polarization in animal cells is controlled by the evolutionarily conserved Crumbs (CRB), Partitioning-defective, and Scribble protein complexes. Here, we investigated the role of protein associated with LIN-7 1 (Pals1, also known as Mpp5), a core component of the apical membrane-determining CRB complex in the nephron. Pals1 interacting proteins, including Crb3 and Wwtr1/Taz, have been linked to renal cyst formation in mice before. Immunohistologic analysis revealed Pals1 expression in renal tubular cells and podocytes of human kidneys. Mice lacking one Pals1 allele (functionally haploid for Pals1) in nephrons developed a fully penetrant phenotype, characterized by cyst formation and severe defects in renal barrier function, which led to death within 6-8 weeks. In Drosophila nephrocytes, deficiency of the Pals1 ortholog caused alterations in slit-diaphragm-like structures. Additional studies in epithelial cell culture models revealed that Pals1 functions as a dose-dependent upstream regulator of the crosstalk between Hippo- and TGF-β-mediated signaling. Furthermore, Pals1 haploinsufficiency in mouse kidneys associated with the upregulation of Hippo pathway target genes and marker genes of TGF-β signaling, including biomarkers of renal diseases. These findings support a link between apical polarity proteins and renal diseases, especially renal cyst diseases. Further investigation of the Pals1-linked networks is required to decipher the mechanisms underlying the pathogenesis of these diseases.

Wnt activated β-catenin and YAP proteins enhance the expression of non-coding RNA component of RNase MRP in colon cancer cells

RMRP, the RNA component of mitochondrial RNA processing endoribonuclease, is a non-coding RNA (ncRNA) part of the RNase MRP complex functioning in mitochondrial and ribosomal RNA processing. Even though various mutations in the RMRP gene are linked to developmental defects and pathogenesis, its relevance to cancer etiology has not been well established. Here we examined the expression of RMRP and found a significant increase in colorectal and breast cancer patient tissues. So we tested whether the oncogenic signaling pathways, Wnt/β-catenin and Hippo/YAP pathways, are relevant to the enhanced expression of RMRP in cancer cells because of the predicted β-catenin/TCF and YAP/TBX5 elements in the upstream regions of the RMRP gene. As expected, Wnt signal activation significantly induced the RMRP transcription thru β-catenin and YAP transcription factors. More importantly, YAP protein was critical for RMRP transcription by association to the proximal site near the transcription start site of the RMRP gene, a Pol III promoter, along with β-catenin and TBX5 proteins. We propose that the interplay of Wnt and Hippo signaling pathways could regulate target genes, coding or non-coding, by the β-catenin/YAP/TBX5 transcription complex in cancer cells.

Serum dickkopf-1 is a novel serological biomarker for the diagnosis and prognosis of pancreatic cancer

Purpose

To identify whether Dickkopf-1 (DKK1) could be a potential biomarker for early detection and prognosis in patients with pancreatic cancer (PC).

Methods

Serum was collected from 140 patients with pancreatic adenocarcinoma and 92 control patients without pancreatic adenocarcinoma. Serological levels of DKK1 were examined by enzyme-linked immunosorbent assay (ELISA). The sensitivity and specificity was compared with carbohydrate antigen 19-9 (CA19-9). A 2-year follow-up was monitored to evaluate the correlation between DKK1 serum levels and overall survival. The expression of DKK1 in PC tumor tissues was also evaluated using immunohistochemistry staining.

Results

Serum levels of DKK1 and CA19-9 were elevated in PC patients in the early-stage cases. These levels increased with the advancement of clinical stage. There was significant difference in DKK1 serum levels between early and advanced PC stages. Receiver operating characteristic curve (ROCC) analysis showed that DKK1 was significantly better than CA19-9 in differentiating patients with PC from the controls (area under the curve (AUC) 0.919 versus 0.853, respectively), especially in distinguishing early-stage cancer from chronic pancreatitis (CP). The expression of DKK1 in PC tissues correlated with its expression in serum samples. The overall survival rate was 24.4% in the group with higher DKK1 levels and was found to be significantly different from the group with lower DKK1 levels (33.3%).

Conclusion

DKK1 may be a novel diagnostic/prognostic biomarker for PC.

Differential localization of A-Raf regulates MST2-mediated apoptosis during epithelial differentiation

A-Raf belongs to the family of oncogenic Raf kinases that are involved in mitogenic signaling by activating the MEK-ERK pathway. Low kinase activity of A-Raf toward MEK suggested that A-Raf might have alternative functions. We recently identified A-Raf as a potent inhibitor of the proapoptotic mammalian sterile 20-like kinase (MST2) tumor suppressor pathway in several cancer entities including head and neck, colon, and breast. Independent of kinase activity, A-Raf binds to MST2 thereby efficiently inhibiting apoptosis. Here, we show that the interaction of A-Raf with the MST2 pathway is regulated by subcellular compartmentalization. Although in proliferating normal cells and tumor cells A-Raf localizes to the mitochondria, differentiated non-carcinogenic cells of head and neck epithelia, which express A-Raf at the plasma membrane. The constitutive or induced re-localization of A-Raf to the plasma membrane compromises its ability to efficiently sequester and inactivate MST2, thus rendering cells susceptible to apoptosis. Physiologically, A-Raf re-localizes to the plasma membrane upon epithelial differentiation in vivo. This re-distribution is regulated by the scaffold protein kinase suppressor of Ras 2 (KSR2). Downregulation of KSR2 during mammary epithelial cell differentiation or siRNA-mediated knockdown re-localizes A-Raf to the plasma membrane causing the release of MST2. By using the MCF7 cell differentiation system, we could demonstrate that overexpression of A-Raf in MCF7 cells, which induces differentiation. Our findings offer a new paradigm to understand how differential localization of Raf complexes affects diverse signaling functions in normal cells and carcinomas.

Non-coding RNAs in Mammary Gland Development and Disease

Non-coding RNAs (ncRNAs) are untranslated RNA molecules that function to regulate the expression of numerous genes and associated biochemical pathways and cellular functions. NcRNAs include small interfering RNAs (siRNAs), microRNAs (miRNAs), PIWI-interacting RNAs (piRNAs), small nucleolar RNAs (snoRNAs) and long non-coding RNAs (lncRNAs). They participate in the regulation of all developmental processes and are frequently aberrantly expressed or functionally defective in disease. This Chapter will focus on the role of ncRNAs, in particular miRNAs and lncRNAs, in mammary gland development and disease.

Two-signal requirement for growth-promoting function of Yap in hepatocytes

The transcriptional coactivator Yes-associated protein (Yap) promotes proliferation and inhibits apoptosis, suggesting that Yap functions as an oncogene. Most oncogenes, however, require a combination of at least two signals to promote proliferation. In this study, we present evidence that Yap activation is insufficient to promote growth in the otherwise normal tissue. Using a mosaic mouse model, we demonstrate that Yap overexpression in a fraction of hepatocytes does not lead to their clonal expansion, as proliferation is counterbalanced by increased apoptosis. To shift the activity of Yap towards growth, a second signal provided by tissue damage or inflammation is required. In response to liver injury, Yap drives clonal expansion, suppresses hepatocyte differentiation, and promotes a progenitor phenotype. These results suggest that Yap activation is insufficient to promote growth in the absence of a second signal thus coordinating tissue homeostasis and repair.

Structural dissection of Hippo signaling

The Hippo pathway controls cell number and organ size by restricting cell proliferation and promoting apoptosis, and thus is a key regulator in development and homeostasis. Dysfunction of the Hippo pathway correlates with many pathological conditions, especially cancer. Hippo signaling also plays important roles in tissue regeneration and stem cell biology. Therefore, the Hippo pathway is recognized as a crucial target for cancer therapy and regeneration medicine. To date, structures of several key components in Hippo signaling have been determined. In this review, we summarize current available structural studies of the Hippo pathway, which may help to improve our understanding of its regulatory mechanisms, as well as to facilitate further functional studies and potential therapeutic interventions.

Lung epithelial stem cells and their niches: Fgf10 takes center stage

Throughout life adult animals crucially depend on stem cell populations to maintain and repair their tissues to ensure life-long organ function. Stem cells are characterized by their capacity to extensively self-renew and give rise to one or more differentiated cell types. These powerful stem cell properties are key to meet the changing demand for tissue replacement during normal lung homeostasis and regeneration after lung injury. Great strides have been made over the last few years to identify and characterize lung epithelial stem cells as well as their lineage relationships. Unfortunately, knowledge on what regulates the behavior and fate specification of lung epithelial stem cells is still limited, but involves communication with their microenvironment or niche, a local tissue environment that hosts and influences the behaviors or characteristics of stem cells and that comprises other cell types and extracellular matrix. As such, an intimate and dynamic epithelial-mesenchymal cross-talk, which is also essential during lung development, is required for normal homeostasis and to mount an appropriate regenerative response after lung injury. Fibroblast growth factor 10 (Fgf10) signaling in particular seems to be a well-conserved signaling pathway governing epithelial-mesenchymal interactions during lung development as well as between different adult lung epithelial stem cells and their niches. On the other hand, disruption of these reciprocal interactions leads to a dysfunctional epithelial stem cell-niche unit, which may culminate in chronic lung diseases such as chronic obstructive pulmonary disease (COPD), chronic asthma and idiopathic pulmonary fibrosis (IPF).

A combination of Wnt and growth factor signaling induces Arl4c expression to form epithelial tubular structures

Growth factor-dependent epithelial morphological changes and proliferation are essential for the formation of tubular structures, but the underlying molecular mechanisms are poorly understood. Co-stimulation with Wnt3a and epidermal growth factor (Wnt3a/EGF) induced development of tubes consisting of intestinal epithelial cells by inducing expression of Arl4c, an Arf-like small GTP-binding protein, in three-dimensional culture, while stimulation with Wnt3a or EGF alone did not. Arl4c expression resulted in rearrangement of the cytoskeleton through activation of Rac and inactivation of Rho properly, which promoted cell growth by inducing nuclear translocation of Yes-associated protein and transcriptional co-activator with PDZ-binding motif (YAP/TAZ) in leading cells. Arl4c was expressed in ureteric bud tips and pretubular structures in the embryonic kidney. In an organoid culture assay, Wnt and fibroblast growth factor signaling simultaneously induced elongation and budding of kidney ureteric buds through Arl4c expression. YAP/TAZ was observed in the nucleus of extending ureteric bud tips. Thus, Arl4c expression induced by a combination of growth factor signaling mechanisms is involved in tube formation.

Bisphenol A exposure alters developmental gene expression in the fetal rhesus macaque uterus

Bisphenol A (BPA) exposure results in numerous developmental and functional abnormalities in reproductive organs in rodent models, but limited data are available regarding BPA effects in the primate uterus. To determine if maternal oral BPA exposure affects fetal uterine development in a non-human primate model, pregnant rhesus macaques carrying female fetuses were exposed orally to 400 µg/kg BPA or vehicle control daily from gestation day (GD) 50-100 or GD100-165. Fetal uteri were collected at the completion of treatment (GD100 or GD165); tissue histology, cell proliferation, and expression of estrogen receptor alpha (ERα) and progesterone receptor (PR) were compared to that of controls. Gene expression analysis was conducted using rhesus macaque microarrays. There were no significant differences in histology or in the percentage of cells expressing the proliferation marker Ki-67, ERα, or PR in BPA-exposed uteri compared to controls at GD100 or GD165. Minimal differences in gene expression were observed between BPA-exposed and control GD100 uteri. However, at GD165, BPA-exposed uteri had significant differences in gene expression compared to controls. Several of the altered genes, including HOXA13, WNT4, and WNT5A, are critical for reproductive organ development and/or adult function. We conclude that second or third trimester BPA exposure does not significantly affect fetal uterus development based on morphological, proliferation, and steroid hormone receptor assessments. However, differences in expression of key developmental genes after third trimester exposure suggest that BPA could alter transcriptional signals influencing uterine function later in life.

Wnt signaling in adult intestinal stem cells and cancer

Signaling initiated by secreted glycoproteins of the Wnt family regulates many aspects of embryonic development and it is involved in homeostasis of adult tissues. In the gastrointestinal (GI) tract the Wnt pathway maintains the self-renewal capacity of epithelial stem cells. The stem cell attributes are conferred by mutual interactions of the stem cell with its local microenvironment, the stem cell niche. The niche ensures that the threshold of Wnt signaling in the stem cell is kept in physiological range. In addition, the Wnt pathway involves various feedback loops that balance the opposing processes of cell proliferation and differentiation. Today, we have compelling evidence that mutations causing aberrant activation of the Wnt pathway promote expansion of undifferentiated progenitors and lead to cancer. The review summarizes recent advances in characterization of adult epithelial stem cells in the gut. We mainly focus on discoveries related to molecular mechanisms regulating the output of the Wnt pathway. Moreover, we present novel experimental approaches utilized to investigate the epithelial cell signaling circuitry in vivo and in vitro. Pivotal aspects of tissue homeostasis are often deduced from studies of tumor cells; therefore, we also discuss some latest results gleaned from the deep genome sequencing studies of human carcinomas of the colon and rectum.

Polyploidization and cell fusion contribute to wound healing in the adult Drosophila epithelium

BACKGROUND

Reestablishing epithelial integrity and biosynthetic capacity is critically important following tissue damage. The adult Drosophila abdominal epithelium provides an attractive new system to address how postmitotic diploid cells contribute to repair.

RESULTS

Puncture wounds to the adult Drosophila epidermis close initially by forming a melanized scab. We found that epithelial cells near the wound site fuse to form a giant syncytium, which sends lamellae under the scab to re-epithelialize the damaged site. Other large cells arise more peripherally by initiating endocycles and becoming polyploid, or by cell fusion. Rac GTPase activity is needed for syncytium formation, while the Hippo signaling effector Yorkie modulates both polyploidization and cell fusion. Large cell formation is functionally important because when both polyploidization and fusion are blocked, wounds do not re-epithelialize.

CONCLUSIONS

Our observations indicate that cell mass lost upon wounding can be replaced by polyploidization instead of mitotic proliferation. We propose that large cells generated by polyploidization or cell fusion are essential because they are better able than diploid cells to mechanically stabilize wounds, especially those containing permanent acellular structures, such as scar tissue.