The transcriptional repressor Glis2 is a novel binding partner for p120 catenin

p120-catenin promotes innate antiviral immunity through stabilizing TBK1-IRF3 complex

TBK1-IRF3 complex plays vital roles in antiviral immune responses, its regulatory mechanisms are currently incompletely understood. p120-catenin (p120), an armadillo-repeat protein, mainly regulates the stability of classical cadherins and the development of epithelial-to-mesenchymal transitions (EMTs). Here we report that p120 is a positive regulator of type I IFN production. Ectopic expression of p120 enhanced Vesicular stomatitis virus and Sendai-virus-induced type I IFN production, whereas knockdown of p120 expression suppressed type I IFN production. Mechanistically, p120 promoted phosphorylation of IRF3 via stabilizing the TBK1-IRF3 complex. Consistently, p120 knock down mice are more susceptible to VSV infection as indicated by higher tissue viral titers, less IFN-I production and greater infiltration of immune cells. This study reveals p120 as an important positive regulator in innate immunity and identifies that p120 facilitates host antiviral response through stabilizing TBK1-IRF3 complex.

p120-catenin subfamily members have distinct as well as shared effects on dendrite morphology during neuron development in vitro

Dendritic arborization is essential for proper neuronal connectivity and function. Conversely, abnormal dendrite morphology is associated with several neurological pathologies like Alzheimer's disease and schizophrenia. Among major intrinsic mechanisms that determine the extent of the dendritic arbor is cytoskeletal remodeling. Here, we characterize and compare the impact of the four proteins involved in cytoskeletal remodeling-vertebrate members of the p120-catenin subfamily-on neuronal dendrite morphology. In relation to each of their own distributions, we find that p120-catenin and delta-catenin are expressed at relatively higher proportions in growth cones compared to ARVCF-catenin and p0071-catenin; ARVCF-catenin is expressed at relatively high proportions in the nucleus; and all catenins are expressed in dendritic processes and the soma. Through altering the expression of each p120-subfamily catenin in neurons, we find that exogenous expression of either p120-catenin or delta-catenin correlates with increased dendritic length and branching, whereas their respective depletion decreases dendritic length and branching. While increasing ARVCF-catenin expression also increases dendritic length and branching, decreasing expression has no grossly observable morphological effect. Finally, increasing p0071-catenin expression increases dendritic branching, but not length, while decreasing expression decreases dendritic length and branching. These distinct localization patterns and morphological effects during neuron development suggest that these catenins have both shared and distinct roles in the context of dendrite morphogenesis.

GLIS1-3: Links to Primary Cilium, Reprogramming, Stem Cell Renewal, and Disease

The GLI-Similar 1-3 (GLIS1-3) genes, in addition to encoding GLIS1-3 Krüppel-like zinc finger transcription factors, also generate circular GLIS (circGLIS) RNAs. GLIS1-3 regulate gene transcription by binding to GLIS binding sites in target genes, whereas circGLIS RNAs largely act as miRNA sponges. GLIS1-3 play a critical role in the regulation of many biological processes and have been implicated in various pathologies. GLIS protein activities appear to be regulated by primary cilium-dependent and -independent signaling pathways that via post-translational modifications may cause changes in the subcellular localization, proteolytic processing, and protein interactions. These modifications can affect the transcriptional activity of GLIS proteins and, consequently, the biological functions they regulate as well as their roles in disease. Recent studies have implicated GLIS1-3 proteins and circGLIS RNAs in the regulation of stemness, self-renewal, epithelial-mesenchymal transition (EMT), cell reprogramming, lineage determination, and differentiation. These biological processes are interconnected and play a critical role in embryonic development, tissue homeostasis, and cell plasticity. Dysregulation of these processes are part of many pathologies. This review provides an update on our current knowledge of the roles GLIS proteins and circGLIS RNAs in the control of these biological processes in relation to their regulation of normal physiological functions and disease.

GLIS2 promotes colorectal cancer through repressing enhancer activation

Gene transcription is coordinately regulated by multiple transcription factors. However, a systematic approach is still lacking to identify co-regulators for transcription factors. Here, we performed ChIP-Seq analysis and predicted the regulators for p53-mediated transcription process, from which we confirmed the roles of GLIS2, MAZ and MEF2A in regulating p53 target genes. We revealed that GLIS2 selectively regulates the transcription of PUMA but not p21. GLIS2 deficiency caused the elevation of H3K27ac and p53 binding on the PUMA enhancer, and promoted PUMA expression. It increased the rate of apoptosis, but not cell cycle. Moreover, GLIS2 represses H3K27ac level on enhancers, regulates the gene expression related with focal adhesion and promotes cell migration, through inhibiting p300. Big data analysis supports GLIS2 as an oncogene in colon cancer, and perhaps other cancers. Taken together, we have predicted candidates for p53 transcriptional regulators, and provided evidence for GLIS2 as an oncogene through repressing enhancer activation.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

Intracellular Signals Activated by Canonical Wnt Ligands Independent of GSK3 Inhibition and β-Catenin Stabilization

In contrast to non-canonical ligands, canonical Wnts promote the stabilization of β-catenin, which is a prerequisite for formation of the TCF4/β-catenin transcriptional complex and activation of its target genes. This pathway is initiated by binding of Wnt ligands to the Frizzled/LRP5/6 receptor complex, and it increases the half-life of β-catenin by precluding the phosphorylation of β-catenin by GSK3 and its binding to the βTrCP1 ubiquitin ligase. Other intercellular signals are also activated by Wnt ligands that do not inhibit GSK3 and increase β-catenin protein but that either facilitate β-catenin transcriptional activity or stimulate other transcriptional factors that cooperate with it. In this review, we describe the layers of complexity of these signals and discuss their crosstalk with β-catenin in activation of transcriptional targets.

GLIS1-3 transcription factors: critical roles in the regulation of multiple physiological processes and diseases

Krüppel-like zinc finger proteins form one of the largest families of transcription factors. They function as key regulators of embryonic development and a wide range of other physiological processes, and are implicated in a variety of pathologies. GLI-similar 1-3 (GLIS1-3) constitute a subfamily of Krüppel-like zinc finger proteins that act either as activators or repressors of gene transcription. GLIS3 plays a critical role in the regulation of multiple biological processes and is a key regulator of pancreatic β cell generation and maturation, insulin gene expression, thyroid hormone biosynthesis, spermatogenesis, and the maintenance of normal kidney functions. Loss of GLIS3 function in humans and mice leads to the development of several pathologies, including neonatal diabetes and congenital hypothyroidism, polycystic kidney disease, and infertility. Single nucleotide polymorphisms in GLIS3 genes have been associated with increased risk of several diseases, including type 1 and type 2 diabetes, glaucoma, and neurological disorders. GLIS2 plays a critical role in the kidney and GLIS2 dysfunction leads to nephronophthisis, an end-stage, cystic renal disease. In addition, GLIS1-3 have regulatory functions in several stem/progenitor cell populations. GLIS1 and GLIS3 greatly enhance reprogramming efficiency of somatic cells into induced embryonic stem cells, while GLIS2 inhibits reprogramming. Recent studies have obtained substantial mechanistic insights into several physiological processes regulated by GLIS2 and GLIS3, while a little is still known about the physiological functions of GLIS1. The localization of some GLIS proteins to the primary cilium suggests that their activity may be regulated by a downstream primary cilium-associated signaling pathway. Insights into the upstream GLIS signaling pathway may provide opportunities for the development of new therapeutic strategies for diabetes, hypothyroidism, and other diseases.

A central role for cadherin signaling in cancer

Cadherins are homophilic adhesion molecules with important functions in cell-cell adhesion, tissue morphogenesis, and cancer. In epithelial cells, E-cadherin accumulates at areas of cell-cell contact, coalesces into macromolecular complexes to form the adherens junctions (AJs), and associates via accessory partners with a subcortical ring of actin to form the apical zonula adherens (ZA). As a master regulator of the epithelial phenotype, E-cadherin is essential for the overall maintenance and homeostasis of polarized epithelial monolayers. Its expression is regulated by a host of genetic and epigenetic mechanisms related to cancer, and its function is modulated by mechanical forces at the junctions, by direct binding and phosphorylation of accessory proteins collectively termed catenins, by endocytosis, recycling and degradation, as well as, by multiple signaling pathways and developmental processes, like the epithelial to mesenchymal transition (EMT). Nuclear signaling mediated by the cadherin associated proteins β-catenin and p120 promotes growth, migration and pluripotency. Receptor tyrosine kinase, PI3K/AKT, Rho GTPase, and HIPPO signaling, are all regulated by E-cadherin mediated cell-cell adhesion. Finally, the recruitment of the microprocessor complex to the ZA by PLEKHA7, and the subsequent regulation of a small subset of miRNAs provide an additional mechanism by which the state of epithelial cell-cell adhesion affects translation of target genes to maintain the homeostasis of polarized epithelial monolayers. Collectively, the data indicate that loss of E-cadherin function, especially at the ZA, is a common and crucial step in cancer progression.

Structural characterization of CAS SH3 domain selectivity and regulation reveals new CAS interaction partners

CAS is a docking protein downstream of the proto-oncogene Src with a role in invasion and metastasis of cancer cells. The CAS SH3 domain is indispensable for CAS-mediated signaling, but structural aspects of CAS SH3 ligand binding and regulation are not well understood. Here, we identified the consensus CAS SH3 binding motif and structurally characterized the CAS SH3 domain in complex with ligand. We revealed the requirement for an uncommon centrally localized lysine residue at position +2 of CAS SH3 ligands and two rather dissimilar optional anchoring residues, leucine and arginine, at position +5. We further expanded the knowledge of CAS SH3 ligand binding regulation by manipulating tyrosine 12 phosphorylation and confirmed the negative role of this phosphorylation on CAS SH3 ligand binding. Finally, by exploiting the newly identified binding requirements of the CAS SH3 domain, we predicted and experimentally verified two novel CAS SH3 binding partners, DOK7 and GLIS2.

Functional roles of p120ctn family of proteins in central neurons

The cadherin-catenin complex in central neurons is associated with a variety of cytosolic partners, collectively called catenins. The p120ctn members are a family of catenins that are distinct from the more ubiquitously expressed α- and β-catenins. It is becoming increasingly clear that the functional roles of the p120ctn family of catenins in central neurons extend well beyond their functional roles in non-neuronal cells in partnering with cadherin to regulate adhesion. In this review, we will provide an overview of the p120ctn family in neurons and their varied functional roles in central neurons. Finally, we will examine the emerging roles of this family of proteins in neurodevelopmental disorders.

p120-catenin in canonical Wnt signaling

Canonical Wnt signaling controls β-catenin protein stabilization, its translocation to the nucleus and the activation of β-catenin/Tcf-4-dependent transcription. In this review, we revise and discuss the recent results describing actions of p120-catenin in different phases of this pathway. More specifically, we comment its involvement in four different steps: (i) the very early activation of CK1ɛ, essential for Dvl-2 binding to the Wnt receptor complex; (ii) the internalization of GSK3 and Axin into multivesicular bodies, necessary for a complete stabilization of β-catenin; (iii) the activation of Rac1 small GTPase, required for β-catenin translocation to the nucleus; and (iv) the release of the inhibitory action caused by Kaiso transcriptional repressor. We integrate these new results with the previously known action of other elements in this pathway, giving a particular relevance to the responses of the Wnt pathway not required for β-catenin stabilization but for β-catenin transcriptional activity. Moreover, we discuss the possible future implications, suggesting that the two cellular compartments where β-catenin is localized, thus, the adherens junction complex and the Wnt signalosome, are more physically connected that previously thought.

Beyond β-catenin: prospects for a larger catenin network in the nucleus

β-catenin is widely regarded as the primary transducer of canonical WNT signals to the nucleus. In most vertebrates, there are eight additional catenins that are structurally related to β-catenin, and three α-catenin genes encoding actin-binding proteins that are structurally related to vinculin. Although these catenins were initially identified in association with cadherins at cell-cell junctions, more recent evidence suggests that the majority of catenins also localize to the nucleus and regulate gene expression. Moreover, the number of catenins reported to be responsive to canonical WNT signals is increasing. Here, we posit that multiple catenins form a functional network in the nucleus, possibly engaging in conserved protein-protein interactions that are currently better characterized in the context of actin-based cell junctions.

Phosphorylation and isoform use in p120-catenin during development and tumorigenesis

P120-catenin is essential to vertebrate development, modulating cadherin and small-GTPase functions, and growing evidence points also to roles in the nucleus. A complexity in addressing p120-catenin's functions is its many isoforms, including optional splicing events, alternative points of translational initiation, and secondary modifications. In this review, we focus upon how choices in the initiation of protein translation, or the earlier splicing of the RNA transcript, relates to primary sequences that harbor established or putative regulatory phosphorylation sites. While certain p120 phosphorylation events arise via known kinases/phosphatases and have defined outcomes, in most cases the functional consequences are still to be established. In this review, we provide examples of p120-isoforms as they relate to phosphorylation events, and thereby to isoform dependent protein-protein associations and downstream functions. We also provide a view of upstream pathways that determine p120's phosphorylation state, and that have an impact upon development and disease. Because other members of the p120 subfamily undergo similar processing and phosphorylation, as well as related catenins of the plakophilin subfamily, what is learned regarding p120 will by extension have wide relevance in vertebrates.

SUMOylation Blocks the Ubiquitin-Mediated Degradation of the Nephronophthisis Gene Product Glis2/NPHP7

Glis2/NPHP7 is a transcriptional regulator mutated in type 7 nephronophthisis, an autosomal recessive ciliopathy associated with cystic and fibrotic kidney disease as well as characteristic extrarenal manifestations. While most ciliopathy-associated molecules are found in the cilium, Glis2/NPHP7 presumably localizes to the nucleus. However, the detection of endogenous Glis2/NPHP7 has remained unsuccessful, potentially due to its ubiquitylation-dependent rapid degradation. We report now that Glis2/NPHP7 is also SUMOylated, preferentially by PIAS4, which conjugates Glis2/NPHP7 to SUMO3. SUMOylation interferes with ubiquitylation and degradation of Glis2/NPHP7, suggesting that Glis2/NPHP7 protein levels are regulated by competing ubiquitylation/ SUMOylation. SUMOylation also alters the transcriptional activity of Glis2/NPHP7. While Glis2/NPHP7 activates the mouse insulin-2-promotor (mIns2), SUMOylated Glis2/NPHP7 lacks this property, and seems to act as a repressor. Taken together, our data reveal that Glis2/NPHP7 is extensively modified by post-translational modifications, suggesting that a tight control of this transcriptional regulator is required for normal development and tissue homeostasis.

Up-regulation of Glis2 involves in neuronal apoptosis after intracerebral hemorrhage in adult rats

The novel Krüppel-like zinc finger protein Gli-similar 2 (Glis2), one member of the transcription factors, is involved in controlling the flow of genetic information and the modulation of diverse cellular activities. Accumulating evidence has demonstrated its important roles in adult development and several diseases. However, information regarding the regulation and possible function of Glis2 in the central nervous system is still limited. In this study, we explored the roles of Glis2 during the pathophysiological process of intracerebral hemorrhage (ICH). An ICH rat model was established and assessed by behavioral tests. Expression of Glis2 was significantly up-regulated in brain areas surrounding the hematoma following ICH. Immunofluorescence showed that Glis2 was strikingly increased in neurons, but not astrocytes or microglia. Up-regulation of Glis2 was found to be accompanied by the increased expression of active caspase-3 and Bax and decreased expression of Bcl-2 in vivo and vitro studies. Moreover, knocking down Glis2 by RNA-interference in PC12 cells reduced active caspase-3 and Bax expression while increased Bcl-2. Collectively, we speculated that Glis2 might exert pro-apoptotic function in neurons following ICH.

An in vivo screen to identify candidate neurogenic genes in the developing Xenopus visual system

Neurogenesis in the brain of Xenopus laevis continues throughout larval stages of development. We developed a 2-tier screen to identify candidate genes controlling neurogenesis in Xenopus optic tectum in vivo. First, microarray and NanoString analyses were used to identify candidate genes that were differentially expressed in Sox2-expressing neural progenitor cells or their neuronal progeny. Then an in vivo, time-lapse imaging-based screen was used to test whether morpholinos against 34 candidate genes altered neural progenitor cell proliferation or neuronal differentiation over 3 days in the optic tectum of intact Xenopus tadpoles. We co-electroporated antisense morpholino oligonucleotides against each of the candidate genes with a plasmid that drives GFP expression in Sox2-expressing neural progenitor cells and quantified the effects of morpholinos on neurogenesis. Of the 34 morpholinos tested, 24 altered neural progenitor cell proliferation or neuronal differentiation. The candidates which were tagged as differentially expressed and validated by the in vivo imaging screen include: actn1, arl9, eif3a, elk4, ephb1, fmr1-a, fxr1-1, fbxw7, fgf2, gstp1, hat1, hspa5, lsm6, mecp2, mmp9, and prkaca. Several of these candidates, including fgf2 and elk4, have known or proposed neurogenic functions, thereby validating our strategy to identify candidates. Genes with no previously demonstrated neurogenic functions, gstp1, hspa5 and lsm6, were identified from the morpholino experiments, suggesting that our screen successfully revealed unknown candidates. Genes that are associated with human disease, such as such as mecp2 and fmr1-a, were identified by our screen, providing the groundwork for using Xenopus as an experimental system to probe conserved disease mechanisms. Together the data identify candidate neurogenic regulatory genes and demonstrate that Xenopus is an effective experimental animal to identify and characterize genes that regulate neural progenitor cell proliferation and differentiation in vivo.

Nuclear signaling from cadherin adhesion complexes

The arrival of multicellularity in evolution facilitated cell-cell signaling in conjunction with adhesion. As the ectodomains of cadherins interact with each other directly in trans (as well as in cis), spanning the plasma membrane and associating with multiple other entities, cadherins enable the transduction of "outside-in" or "inside-out" signals. We focus this review on signals that originate from the larger family of cadherins that are inwardly directed to the nucleus, and thus have roles in gene control or nuclear structure-function. The nature of cadherin complexes varies considerably depending on the type of cadherin and its context, and we will address some of these variables for classical cadherins versus other family members. Substantial but still fragmentary progress has been made in understanding the signaling mediators used by varied cadherin complexes to coordinate the state of cell-cell adhesion with gene expression. Evidence that cadherin intracellular binding partners also localize to the nucleus is a major point of interest. In some models, catenins show reduced binding to cadherin cytoplasmic tails favoring their engagement in gene control. When bound, cadherins may serve as stoichiometric competitors of nuclear signals. Cadherins also directly or indirectly affect numerous signaling pathways (e.g., Wnt, receptor tyrosine kinase, Hippo, NFκB, and JAK/STAT), enabling cell-cell contacts to touch upon multiple biological outcomes in embryonic development and tissue homeostasis.

From cell membrane to the nucleus: an emerging role of E-cadherin in gene transcriptional regulation

E-cadherin is a well-known mediator of cell–cell adherens junctions. However, many other functions of E-cadherin have been reported. Collectively, the available data suggest that E-cadherin may also act as a gene transcriptional regulator. Here, evidence supporting this claim is reviewed, and possible mechanisms of action are discussed. E-cadherin has been shown to modulate the activity of several notable cell signalling pathways, and given that most of these pathways in turn regulate gene expression, we proposed that E-cadherin may regulate gene transcription by affecting these pathways. Additionally, E-cadherin has been shown to accumulate in the nucleus where documentation of an E-cadherin fragment bound to DNA suggests that E-cadherin may directly regulate gene transcription. In summary, from the cell membrane to the nucleus, a role for E-cadherin in gene transcription may be emerging. Studies specifically focused on this potential role would allow for a more thorough understanding of this transmembrane glycoprotein in mediating intra- and intercellular activities.

p120-catenin regulates REST and CoREST, and modulates mouse embryonic stem cell differentiation

Although the canonical Wnt pathway and β-catenin have been extensively studied, less is known about the role of p120-catenin (also known as δ1-catenin) in the nuclear compartment. Here, we report that p120-catenin binds and negatively regulates REST and CoREST (also known as Rcor1), a repressive transcriptional complex that has diverse developmental and pathological roles. Using mouse embryonic stem cells (mESCs), mammalian cell lines, Xenopus embryos and in vitro systems, we find that p120-catenin directly binds the REST-CoREST complex, displacing it from established gene targets to permit their transcriptional activation. Importantly, p120-catenin levels further modulate the mRNA and protein levels of Oct4 (also known as POU5F1), Nanog and Sox2, and have an impact upon the differentiation of mESCs towards neural fates. In assessing potential upstream inputs to this new p120-catenin-REST-CoREST pathway, REST gene targets were found to respond to the level of E-cadherin, with evidence suggesting that p120-catenin transduces signals between E-cadherin and the nucleus. In summary, we provide the first evidence for a direct upstream modulator and/or pathway regulating REST-CoREST, and reveal a substantial role for p120-catenin in the modulation of stem cell differentiation.

DIPA-family coiled-coils bind conserved isoform-specific head domain of p120-catenin family: potential roles in hydrocephalus and heterotopia

Isoform-specific expression of p120 affects cell motility and migration during development and tumor progression. The DIPA coiled-coil protein is a novel binding partner to the conserved isoform 1–specific head domain of p120 family members. Zebrafish data suggest that DIPA is mechanistically linked to p120 isoform–specific function in development.

p120-catenin (p120) modulates adherens junction (AJ) dynamics by controlling the stability of classical cadherins. Among all p120 isoforms, p120-3A and p120-1A are the most prevalent. Both stabilize cadherins, but p120-3A is preferred in epithelia, whereas p120-1A takes precedence in neurons, fibroblasts, and macrophages. During epithelial-to-mesenchymal transition, E- to N-cadherin switching coincides with p120-3A to -1A alternative splicing. These isoforms differ by a 101–amino acid “head domain” comprising the p120-1A N-terminus. Although its exact role is unknown, the head domain likely mediates developmental and cancer-associated events linked to p120-1A expression (e.g., motility, invasion, metastasis). Here we identified delta-interacting protein A (DIPA) as the first head domain–specific binding partner and candidate mediator of isoform 1A activity. DIPA colocalizes with AJs in a p120-1A- but not 3A-dependent manner. Moreover, all DIPA family members (Ccdc85a, Ccdc85b/DIPA, and Ccdc85c) interact reciprocally with p120 family members (p120, δ-catenin, p0071, and ARVCF), suggesting significant functional overlap. During zebrafish neural tube development, both knockdown and overexpression of DIPA phenocopy N-cadherin mutations, an effect bearing functional ties to a reported mouse hydrocephalus phenotype associated with Ccdc85c. These studies identify a novel, highly conserved interaction between two protein families that may participate either individually or collectively in N-cadherin–mediated development.

p120-catenin in cancer - mechanisms, models and opportunities for intervention

The epithelial adherens junction is an E-cadherin-based complex that controls tissue integrity and is stabilized at the plasma membrane by p120-catenin (p120, also known as CTNND1). Mutational and epigenetic inactivation of E-cadherin has been strongly implicated in the development and progression of cancer. In this setting, p120 translocates to the cytosol where it exerts oncogenic properties through aberrant regulation of Rho GTPases, growth factor receptor signaling and derepression of Kaiso (also known as ZBTB33) target genes. In contrast, indirect inactivation of the adherens junction through conditional knockout of p120 in mice was recently linked to tumor formation, indicating that p120 can also function as a tumor suppressor. Supporting these opposing functions are findings in human cancer, which show that either loss or cytoplasmic localization of p120 is a common feature in the progression of several types of carcinoma. Underlying this dual biological phenomenon might be the context-dependent regulation of Rho GTPases in the cytosol and the derepression of Kaiso target genes. Here, we discuss past and present findings that implicate p120 in the regulation of cancer progression and highlight opportunities for clinical intervention.

Interaction with the Bardet-Biedl gene product TRIM32/BBS11 modifies the half-life and localization of Glis2/NPHP7

Although the two ciliopathies Bardet-Biedl syndrome and nephronophthisis share multiple clinical manifestations, the molecular basis for this overlap remains largely unknown. Both BBS11 and NPHP7 are unusual members of their respective gene families. Although BBS11/TRIM32 represents a RING finger E3 ubiquitin ligase also involved in hereditary forms of muscular dystrophy, NPHP7/Glis2 is a Gli-like transcriptional repressor that localizes to the nucleus, deviating from the ciliary localization of most other ciliopathy-associated gene products. We found that BBS11/TRIM32 and NPHP7/Glis2 can physically interact with each other, suggesting that both proteins form a functionally relevant protein complex in vivo. This hypothesis was further supported by the genetic interaction and synergist cyst formation in the zebrafish pronephros model. However, contrary to our expectation, the E3 ubiquitin ligase BBS11/TRIM32 was not responsible for the short half-life of NPHP7/Glis2 but instead promoted the accumulation of mixed Lys(48)/Lys(63)-polyubiquitylated NPHP7/Glis2 species. This modification not only prolonged the half-life of NPHP7/Glis2, but also altered the subnuclear localization and the transcriptional activity of NPHP7/Glis2. Thus, physical and functional interactions between NPHP and Bardet-Biedl syndrome gene products, demonstrated for Glis2 and TRIM32, may help to explain the phenotypic similarities between these two syndromes.

p120 catenin: an essential regulator of cadherin stability, adhesion-induced signaling, and cancer progression

p120 catenin is the best studied member of a subfamily of proteins that associate with the cadherin juxtamembrane domain to suppress cadherin endocytosis. p120 also recruits the minus ends of microtubules to the cadherin complex, leading to junction maturation. In addition, p120 regulates the activity of Rho family GTPases through multiple interactions with Rho GEFs, GAPs, Rho GTPases, and their effectors. Nuclear signaling is affected by the interaction of p120 with Kaiso, a transcription factor regulating Wnt-responsive genes as well as transcriptionally repressing methylated promoters. Multiple alternatively spliced p120 isoforms and complex phosphorylation events affect these p120 functions. In cancer, reduced p120 expression correlates with reduced E-cadherin function and with tumor progression. In contrast, in tumor cells that have lost E-cadherin expression, p120 promotes cell invasion and anchorage-independent growth. Furthermore, p120 is required for Src-induced oncogenic transformation and provides a potential target for future therapeutic interventions.

Beta-catenin versus the other armadillo catenins: assessing our current view of canonical Wnt signaling

The prevailing view of canonical Wnt signaling emphasizes the role of beta-catenin acting downstream of Wnt activation to regulate transcriptional activity. However, emerging evidence indicates that other armadillo catenins in vertebrates, such as members of the p120 subfamily, convey parallel signals to the nucleus downstream of canonical Wnt pathway activation. Their study is thus needed to appreciate the networked mechanisms of canonical Wnt pathway transduction, especially as they may assist in generating the diversity of Wnt effects observed in development and disease. In this chapter, we outline evidence of direct canonical Wnt effects on p120 subfamily members in vertebrates and speculate upon these catenins' roles in conjunction with or aside from beta-catenin.

A complex of BBS1 and NPHP7 is required for cilia motility in zebrafish

Bardet-Biedl syndrome (BBS) and nephronophthisis (NPH) are hereditary autosomal recessive disorders, encoded by two families of diverse genes. BBS and NPH display several overlapping phenotypes including cystic kidney disease, retinitis pigmentosa, liver fibrosis, situs inversus and cerebellar defects. Since most of the BBS and NPH proteins localize to cilia and/or their appendages, BBS and NPH are considered ciliopathies. In this study, we characterized the function of the transcription factor Nphp7 in zebrafish, and addressed the molecular connection between BBS and NPH. The knockdown of zebrafish bbs1 and nphp7.2 caused similar phenotypic changes including convergent extension defects, curvature of the body axis, hydrocephalus, abnormal heart looping and cystic pronephros, all consistent with an altered ciliary function. Immunoprecipitation assays revealed a physical interaction between BBS1 and NPHP7, and the simultaneous knockdown of zbbs1 and znphp7.2 enhanced the cystic pronephros phenotype synergistically, suggesting a genetic interaction between zbbs1 and znphp7.2 in vivo. Deletion of zBbs1 or zNphp7.2 did not compromise cilia formation, but disrupted cilia motility. Although NPHP7 has been shown to act as transcriptional repressor, our studies suggest a crosstalk between BBS1 and NPHP7 in regulating normal function of the cilium.

Gli-similar proteins: their mechanisms of action, physiological functions, and roles in disease

Gli-similar (Glis) 1-3 proteins constitute a subfamily of Krüppel-like zinc-finger proteins that are closely related to members of the Gli family. Glis proteins have been implicated in several pathologies, including cystic kidney disease, diabetes, hypothyroidism, fibrosis, osteoporosis, psoriasis, and cancer. In humans, a mutation in the Glis2 gene has been linked to the development of nephronophthisis (NPHP), a recessive cystic kidney disease, while mutations in Glis3 lead to an extended multisystem phenotype that includes the development of neonatal diabetes, polycystic kidneys, congenital hypothyroidism, and facial dysmorphism. Glis3 has also been identified as a risk locus for type-1 and type-2 diabetes and additional studies have revealed a role for Glis3 in pancreatic endocrine development, β-cell maintenance, and insulin regulation. Similar to Gli1-3, Glis2 and 3 have been reported to localize to the primary cilium. These studies appear to suggest that Glis proteins are part of a primary cilium-associated signaling pathway(s). It has been hypothesized that Glis proteins are activated through posttranslational modifications and subsequently translocate to the nucleus where they regulate transcription by interacting with Glis-binding sites in the promoter regions of target genes. This chapter summarizes the current state of knowledge regarding mechanisms of action of the Glis family of proteins, their physiological functions, as well as their roles in disease.

Loss of p120 catenin upregulates transcription of pro-inflammatory adhesion molecules in human endothelial cells

P120 catenin (p120ctn) is an adherens junction protein recognized to regulate barrier function, but emerging evidence indicates that p120ctn may also exert control on other cellular functions such as transcriptional suppression of genes. We investigated the hypothesis that loss of p120ctn in human endothelial cells activates transcription of pro-inflammatory adhesion molecules. For study, siRNA targeted to p120ctn was transfected into brain microvascular (HBMECs) or pulmonary artery endothelial cells (HPAECs) for 24-120h, which depleted 50-80% of endogenous p120ctn. This loss of p120ctn resulted in increased promoter reporter activity of transcription factors, NFκB, AP-1, and Kaiso, as well as of target genes, MMP-1 and ICAM-1. Real-time RT-PCR analysis indicated that the mRNA for ICAM-1, VCAM-1, and E- and P-selectins were all upregulated during the period of 24-120h of p120ctn depletion, although the time-course and extent of the expression profiles differed. The upregulated mRNA of adhesion molecules corresponded with increased PMN adhesion to the EC surface and elevated ICAM-1 protein expression. We further explored the role of ERK1/2 as a potential signaling mechanism responsible for regulation of transcriptional activities by p120ctn. Results indicated that loss of p120ctn increased phosphorylated ERK1/2, and a MEK1 inhibitor (PD98059) prevented NFκB nuclear translocation. This implicates ERK1/2 in signaling the NFκB activation induced by p120ctn loss. The findings provide strong evidence that deficiency in p120ctn expression in endothelial cells is a potent stimulus for transcriptional upregulation of multiple adhesion molecules. We conclude that p120ctn functions to suppress transcription, which is an important and novel regulation in vascular endothelium.

The evolutionary history of the catenin gene family during metazoan evolution

BACKGROUND

Catenin is a gene family composed of three subfamilies; p120, beta and alpha. Beta and p120 are homologous subfamilies based on sequence and structural comparisons, and are members of the armadillo repeat protein superfamily. Alpha does not appear to be homologous to either beta or p120 based on the lack of sequence and structural similarity, and the alpha subfamily belongs to the vinculin superfamily. Catenins link the transmembrane protein cadherin to the cytoskeleton and thus function in cell-cell adhesion. To date, only the beta subfamily has been evolutionarily analyzed and experimentally studied for its functions in signaling pathways, development and human diseases such as cancer. We present a detailed evolutionary study of the whole catenin family to provide a better understanding of how this family has evolved in metazoans, and by extension, the evolution of cell-cell adhesion.

RESULTS

All three catenin subfamilies have been detected in metazoans used in the present study by searching public databases and applying species-specific BLAST searches. Two monophyletic clades are formed between beta and p120 subfamilies using Bayesian phylogenetic inference. Phylogenetic analyses also reveal an array of duplication events throughout metazoan history. Furthermore, numerous annotation issues for the catenin family have been detected by our computational analyses.

CONCLUSIONS

Delta2/ARVCF catenin in the p120 subfamily, beta catenin in the beta subfamily, and alpha2 catenin in the alpha subfamily are present in all metazoans analyzed. This implies that the last common ancestor of metazoans had these three catenin subfamilies. However, not all members within each subfamily were detected in all metazoan species. Each subfamily has undergone duplications at different levels (species-specific, subphylum-specific or phylum-specific) and to different extents (in the case of the number of homologs). Extensive annotation problems have been resolved in each of the three catenin subfamilies. This resolution provides a more coherent description of catenin evolution.

Caspase-3 cleavage links delta-catenin to the novel nuclear protein ZIFCAT

δ-Catenin is an Armadillo protein of the p120-catenin subfamily capable of modulating cadherin stability, small GTPase activity, and nuclear transcription. From yeast two-hybrid screening of a human embryonic stem cell cDNA library, we identified δ-catenin as a potential interacting partner of the caspase-3 protease, which plays essential roles in apoptotic as well as non-apoptotic processes. Interaction of δ-catenin with caspase-3 was confirmed using cleavage assays conducted in vitro, in Xenopus apoptotic extracts, and in cell line chemically induced contexts. The cleavage site, a highly conserved caspase consensus motif (DELD) within Armadillo repeat 6 of δ-catenin, was identified through peptide sequencing. Cleavage thus generates an amino-terminal (residues 1-816) and carboxyl-terminal (residues 817-1314) fragment, each containing about half of the central Armadillo domain. We found that cleavage of δ-catenin both abolishes its association with cadherins and impairs its ability to modulate small GTPases. Interestingly, 817-1314 possesses a conserved putative nuclear localization signal that may facilitate the nuclear targeting of δ-catenin in defined contexts. To probe for novel nuclear roles of δ-catenin, we performed yeast two-hybrid screening of a mouse brain cDNA library, resolving and then validating interaction with an uncharacterized KRAB family zinc finger protein, ZIFCAT. Our results indicate that ZIFCAT is nuclear and suggest that it may associate with DNA as a transcriptional repressor. We further determined that other p120 subfamily catenins are similarly cleaved by caspase-3 and likewise bind ZIFCAT. Our findings potentially reveal a simple yet novel signaling pathway based upon caspase-3 cleavage of p120-catenin subfamily members, facilitating the coordinate modulation of cadherins, small GTPases, and nuclear functions.

Identification of nuclear localization, DNA binding, and transactivating mechanisms of Kruppel-like zinc finger protein Gli-similar 2 (Glis2)

Gli-similar 1-3 (Glis1-3) constitute a subfamily of Krüppel-like zinc finger (ZF) transcription factors that are closely related to the Gli protein family. Mutations in GLIS2 are linked to nephronophthisis, a chronic kidney disease characterized by renal fibrosis and atrophy in children and young adults. Currently, very little information exists about the mechanism of action of Glis2, its target genes, or the signaling pathways that regulate its activity. In this study, we show that a region within ZF3 is required for the nuclear localization of Glis2. Analysis of Glis2 DNA binding demonstrated that Glis2 binds effectively to the consensus Glis binding sequence (GlisBS) (G/C)TGGGGGGT(A/C). Although Glis2 was unable to induce transactivation of a GlisBS-dependent reporter, it effectively inhibited the GlisBS-mediated transactivation by Gli1. Mutations that disrupt the tetrahedral configuration of each ZF within Glis2 abolished Glis2 binding to GlisBS and also abrogated its inhibition of Gli1-mediated transactivation. In contrast, Glis2 was able to activate the murine insulin-2 (Ins2) promoter by binding directly to two GlisBS elements located at -263 and -99 within the Ins2 promoter. Phosphomimetic mutation of Ser(245) inhibited the binding of Glis2 to GlisBS and dramatically affected its transactivation of the Ins2 promoter and its ability to inhibit GlisBS-dependent transactivation by Gli1. In this study, we demonstrate that Glis2 can function as a transcriptional activator and that post-translational modification within its DNA-binding domain can regulate its transcriptional activity. This control may play a critical role in the Glis2-dependent regulation of target genes and renal function.

Nuclear localization of E-cadherin but not beta-catenin in human ovarian granulosa cell tumours and normal ovarian follicles and ovarian stroma

AIMS

The role of misregulated Wnt/beta-catenin signalling in human ovarian granulosa cell tumour (GCT) has not been well characterized. The aim of this study was to confirm subcellular localization of key molecules of Wnt signalling (beta-catenin and E-cadherin) in human ovarian GCTs.

METHODS AND RESULTS

Tissue samples taken from 32 human ovarian GCTs and 19 human normal ovaries containing 68 follicles were stained immunohistochemically using monoclonal anti-beta-catenin and anti-E-cadherin antibodies. None of the 32 GCTs and none of the 68 ovarian follicles showed beta-catenin nuclear expression (0%). On the other hand, 28 of 32 GCTs (88%) and 53 of 68 normal ovarian follicles (78%) showed nuclear expression of E-cadherin in granulosa cells. The ovarian stroma in all 19 normal ovaries showed nuclear expression of E-cadherin but not beta-catenin. Membranous and cytoplasmic expression was observed variously in ovarian GCT, follicles and stroma.

CONCLUSIONS

We have confirmed frequent nuclear localization of E-cadherin but not beta-catenin in human ovarian GCT, ovarian follicles and stroma. There is no evidence of misregulated Wnt/beta-catenin signalling (represented by nuclear expression of beta-catenin) in human ovarian GCT. Nuclear translocation of E-cadherin might contribute to ovarian folliculogenesis or granulosa/stromal cell differentiation.

Gli-similar (Glis) Krüppel-like zinc finger proteins: insights into their physiological functions and critical roles in neonatal diabetes and cystic renal disease

GLI-similar (Glis) 1-3 proteins constitute a subfamily of the Krüppel-like zinc finger transcription factors that are closely related to the Gli family. Glis1-3 play critical roles in the regulation of a number of physiological processes and have been implicated in several pathologies. Mutations in GLIS2 have been linked to nephronophthisis, an autosomal recessive cystic kidney disease. Loss of Glis2 function leads to renal atrophy and fibrosis that involves epithelial-mesenchymal transition (EMT) of renal tubule epithelial cells. Mutations in human GLIS3 have been implicated in a syndrome characterized by neonatal diabetes and congenital hypothyroidism (NDH) and in some patients accompanied by polycystic kidney disease, glaucoma, and liver fibrosis. In addition, the GLIS3 gene has been identified as a susceptibility locus for the risk of type 1 and 2 diabetes. Glis3 plays a key role in pancreatic development, particularly in the generation of ß-cells and in the regulation of insulin gene expression. Glis2 and Glis3 proteins have been demonstrated to localize to the primary cilium, a signaling organelle that has been implicated in several pathologies, including cystic renal diseases. This association suggests that Glis2/3 are part of primary cilium-associated signaling pathways that control the activity of Glis proteins. Upon activation in the primary cilium, Glis proteins may translocate to the nucleus where they subsequently regulate gene transcription by interacting with Glis-binding sites in the promoter regulatory region of target genes. In this review, we discuss the current knowledge of the Glis signaling pathways, their physiological functions, and their involvement in several human pathologies.

Junctional music that the nucleus hears: cell-cell contact signaling and the modulation of gene activity

Cell-cell junctions continue to capture the interest of cell and developmental biologists, with an emerging area being the molecular means by which junctional signals relate to gene activity in the nucleus. Although complexities often arise in determining the direct versus indirect nature of such signal transduction, it is clear that such pathways are essential for the function of tissues and that alterations may contribute to many pathological outcomes. This review assesses a variety of cell-cell junction-to-nuclear signaling pathways, and outlines interesting areas for further study.

P120 catenin represses transcriptional activity through Kaiso in endothelial cells

P120 catenin (p120ctn) belongs to the family of Armadillo repeat-containing proteins, which are believed to have dual functions of cell-cell adhesion and transcriptional regulation. In vascular endothelium, p120ctn is mostly recognized for its cell-cell adhesion function through its ability to regulate VE-cadherin. The current study investigated whether p120ctn in endothelial cells also has the capability to signal transcription events. Examination of several endothelial cell types indicated that Kaiso, a p120ctn-binding transcription factor, was abundantly expressed, with a predominant localization to the perinuclear region. Immunoprecipitation of endothelial cell lysates with a p120ctn antibody resulted in p120ctn-Kaiso complex formation, confirming the interactions of the two proteins. Transfection of the KBS (Kaiso-binding sequence) luciferase reporter plasmid into endothelial cells resulted in a 40% lower reporter activity compared to the mutant Kaiso-insensitive construct or empty vector pGL3, indicating that the suppressed reporter activity was attributed to endogenous Kaiso. The knock-down of p120ctn increased the KBS reporter activity 2-fold over control, but had no effects on the mutant KBS reporter activity. Furthermore, p120ctn knock-down also reduced Kaiso expression, suggesting that p120ctn functioned to stabilize Kaiso. Overall, the findings provide evidence that in endothelial cells, p120ctn has a transcription repression function through regulation of Kaiso, possibly as a cofactor with the transcription factor.

Gene array and fluorescence in situ hybridization biomarkers of activity of saracatinib (AZD0530), a Src inhibitor, in a preclinical model of colorectal cancer

PURPOSE

To evaluate the efficacy of saracatinib (AZD0530), an oral Src inhibitor, in colorectal cancer (CRC) and to identify biomarkers that predict antitumor activity.

EXPERIMENTAL DESIGN

Twenty-three CRC cell lines were exposed to saracatinib, and baseline gene expression profiles of three sensitive and eight resistant cell lines in vitro and in vivo were used to predict saracatinib sensitivity in an independent group of 10 human CRC explant tumors using the gene array K-Top Scoring Pairs (K-TSP) method. In addition, fluorescence in situ hybridization (FISH) and immunoblotting determined both Src gene copy number and activation of Src, respectively.

RESULTS

Two of 10 explant tumors were determined to be sensitive to saracatinib. The K-TSP classifier (TOX>GLIS2, TSPAN7>BCAS4, and PARD6G>NXN) achieved 70% (7 of 10) accuracy on the test set. Evaluation of Src gene copy number by FISH showed a trend toward significance (P = 0.066) with respect to an increase in Src gene copy and resistance to saracatinib. Tumors sensitive to saracatinib showed an increase in the activation of Src and FAK when compared with resistant tumors.

CONCLUSIONS

Saracatinib significantly decreased tumor growth in a subset of CRC cell lines and explants. A K-TSP classifier (TOX>GLIS2, TSPAN7>BCAS4, and PARD6G>NXN) was predictive for sensitivity to saracatinib. In addition, increased activation of the Src pathway was associated with sensitivity to saracatinib. These results suggest that FISH, a K-TSP classifier, and activation of the Src pathway have potential in identifying CRC patients that would potentially benefit from treatment with saracatinib.

Comparative proteomic analysis of plasma membrane proteins between human osteosarcoma and normal osteoblastic cell lines

BACKGROUND

Osteosarcoma (OS) is the most common primary malignant tumor of bone in children and adolescents. However, the knowledge in diagnostic modalities has progressed less. To identify new biomarkers for the early diagnosis of OS as well as for potential novel therapeutic candidates, we performed a sub-cellular comparative proteomic research.

METHODS

An osteosarcoma cell line (MG-63) and human osteoblastic cells (hFOB1.19) were used as our comparative model. Plasma membrane (PM) was obtained by aqueous two-phase partition. Proteins were analyzed through iTRAQ-based quantitative differential LC/MS/MS. The location and function of differential proteins were analyzed through GO database. Protein-protein interaction was examined through String software. One of differentially expressed proteins was verified by immunohistochemistry.

RESULTS

342 non-redundant proteins were identified, 68 of which were differentially expressed with 1.5-fold difference, with 25 up-regulated and 43 down-regulated. Among those differential proteins, 69% ware plasma membrane, which are related to the biological processes of binding, cell structure, signal transduction, cell adhesion, etc., and interaction with each other. One protein--CD151 located in net nodes was verified to be over-expressed in osteosarcoma tissue by immunohistochemistry.

CONCLUSION

It is the first time to use plasma membrane proteomics for studying the OS membrane proteins according to our knowledge. We generated preliminary but comprehensive data about membrane protein of osteosarcoma. Among these, CD151 was further validated in patient samples, and this small molecule membrane might be a new target for OS research. The plasma membrane proteins identified in this study may provide new insight into osteosarcoma biology and potential diagnostic and therapeutic biomarkers.

Out, in and back again: PtdIns(4,5)P(2) regulates cadherin trafficking in epithelial morphogenesis

The morphogenesis of epithelial cells in the tissue microenvironment depends on the regulation of the forces and structures that keep cells in contact with their neighbours. The formation of cell-cell contacts is integral to the establishment and maintenance of epithelial morphogenesis. In epithelial tissues, the misregulation of the signalling pathways that control epithelial polarization induces migratory and invasive cellular phenotypes. Many cellular processes influence cadherin targeting and function, including exocytosis, endocytosis and recycling. However, the localized generation of the lipid messenger PtdIns(4,5)P(2) is emerging as a fundamental signal controlling all of these processes. The PtdIns(4,5)P(2)-generating enzymes, PIPKs (phosphatidylinositol phosphate kinases) are therefore integral to these pathways. By the spatial and temporal targeting of PIPKs via the actions of its functional protein associates, PtdIns(4,5)P(2) is generated at discrete cellular locales to provide the cadherin-trafficking machinery with its required lipid messenger. In the present review, we discuss the involvement of PtdIns(4,5)P(2) and the PIPKs in the regulation of the E-cadherin (epithelial cadherin) exocytic and endocytic machinery, the modulation of actin structures at sites of adhesion, and the direction of cellular pathways which determine the fate of E-cadherin and cell-cell junctions. Recent work is also described that has defined phosphoinositide-mediated E-cadherin regulatory pathways by the use of organismal models.

Regulated adhesion as a driving force of gastrulation movements

Recent data have reinforced the fundamental role of regulated cell adhesion as a force that drives morphogenesis during gastrulation. As we discuss, cell adhesion is required for all modes of gastrulation movements in all organisms. It can even be instructive in nature, but it must be tightly and dynamically regulated. The picture that emerges from the recent findings that we review here is that different modes of gastrulation movements use the same principles of adhesion regulation, while adhesion molecules themselves coordinate the intra- and extracellular changes required for directed cell locomotion.

An oncogenomics-based in vivo RNAi screen identifies tumor suppressors in liver cancer

Cancers are highly heterogeneous and contain many passenger and driver mutations. To functionally identify tumor suppressor genes relevant to human cancer, we compiled pools of short hairpin RNAs (shRNAs) targeting the mouse orthologs of genes recurrently deleted in a series of human hepatocellular carcinomas and tested their ability to promote tumorigenesis in a mosaic mouse model. In contrast to randomly selected shRNA pools, many deletion-specific pools accelerated hepatocarcinogenesis in mice. Through further analysis, we identified and validated 13 tumor suppressor genes, 12 of which had not been linked to cancer before. One gene, XPO4, encodes a nuclear export protein whose substrate, EIF5A2, is amplified in human tumors, is required for proliferation of XPO4-deficient tumor cells, and promotes hepatocellular carcinoma in mice. Our results establish the feasibility of in vivo RNAi screens and illustrate how combining cancer genomics, RNA interference, and mosaic mouse models can facilitate the functional annotation of the cancer genome.

Anchoring junctions as drug targets: role in contraceptive development

In multicellular organisms, cell-cell interactions are mediated in part by cell junctions, which underlie tissue architecture. Throughout spermatogenesis, for instance, preleptotene leptotene spermatocytes residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier to enter the adluminal compartment for continued development. At the same time, germ cells must also remain attached to Sertoli cells, and numerous studies have reported extensive restructuring at the Sertoli-Sertoli and Sertoli-germ cell interface during germ cell movement across the seminiferous epithelium. Furthermore, the proteins and signaling cascades that regulate adhesion between testicular cells have been largely delineated. These findings have unveiled a number of potential "druggable" targets that can be used to induce premature release of germ cells from the seminiferous epithelium, resulting in transient infertility. Herein, we discuss a novel approach with the aim of developing a nonhormonal male contraceptive for future human use, one that involves perturbing adhesion between Sertoli and germ cells in the testis.

A role for the cleaved cytoplasmic domain of E-cadherin in the nucleus

Cell-cell contacts play a vital role in intracellular signaling, although the molecular mechanisms of these signaling pathways are not fully understood. E-cadherin, an important mediator of cell-cell adhesions, has been shown to be cleaved by gamma-secretase. This cleavage releases a fragment of E-cadherin, E-cadherin C-terminal fragment 2 (E-cad/CTF2), into the cytosol. Here, we study the fate and function of this fragment. First, we show that coexpression of the cadherin-binding protein, p120 catenin (p120), enhances the nuclear translocation of E-cad/CTF2. By knocking down p120 with short interfering RNA, we also demonstrate that p120 is necessary for the nuclear localization of E-cad/CTF2. Furthermore, p120 enhances and is required for the specific binding of E-cad/CTF2 to DNA. Finally, we show that E-cad/CTF2 can regulate the p120-Kaiso-mediated signaling pathway in the nucleus. These data indicate a novel role for cleaved E-cadherin in the nucleus.

Kruppel-like zinc finger protein Glis2 is essential for the maintenance of normal renal functions

To obtain insight into the physiological functions of the Krüppel-like zinc finger protein Gli-similar 2 (Glis2), mice deficient in Glis2 expression were generated. Glis2 mutant (Glis2(mut)) mice exhibit significantly shorter life spans than do littermate wild-type (WT) mice due to the development of progressive chronic kidney disease with features resembling nephronophthisis. Glis2(mut) mice develop severe renal atrophy involving increased cell death and basement membrane thickening in the proximal convoluted tubules. This development is accompanied by infiltration of lymphocytic inflammatory cells and interstitial/glomerular fibrosis. The severity of the fibrosis, inflammatory infiltrates, and glomerular and tubular changes progresses with age. Blood urea nitrogen and creatinine increase, and Glis2(mut) mice develop proteinuria and ultimately die prematurely of renal failure. A comparison of the gene expression profiles of kidneys from 25-day-old/60-day-old WT and Glis2(mut) mice by microarray analysis showed increased expressions of many genes involved in immune responses/inflammation and fibrosis/tissue remodeling in kidneys of Glis2(mut) mice, including several cytokines and adhesion and extracellular matrix proteins. Our data demonstrate that a deficiency in Glis2 expression leads to tubular atrophy and progressive fibrosis, similar to nephronophthisis, that ultimately results in renal failure. Our study indicates that Glis2 plays a critical role in the maintenance of normal kidney architecture and functions.