Nuclear-cytoplasmic shuttling of Chibby controls beta-catenin signaling

MAP7 drives EMT and cisplatin resistance in ovarian cancer via wnt/β-catenin signaling

Methods

Our approach encompasses analyzing MAP7's expression levels across various datasets and clinical specimens, evaluating its association with patient outcomes, and probing its influence on ovarian cancer cell dynamics such as proliferation, migration, invasion, and apoptosis.

Results

We have identified significant upregulation of MAP7 in ovarian cancer tissues, which correlates with advanced disease stages, higher pathological grades, and unfavorable prognoses. Functionally, the inhibition of MAP7 suppresses cancer cell proliferation, migration, and invasion while promoting apoptosis. Notably, the silencing of MAP7 attenuates the epithelial-mesenchymal transition (EMT) and disrupts Wnt/β-catenin pathway signaling-two critical processes implicated in metastasis and chemoresistance. In cisplatin-resistant A2780-DDP cells, the downregulation of MAP7 effectively reverses their resistance to cisplatin. Furthermore, the nuclear localization of MAP7 in these cells underscores its pivotal role in driving cisplatin resistance by modulating the transcriptional regulation and interaction dynamics of β-catenin.

Conclusion

Our findings position MAP7 as a pivotal element in ovarian cancer advancement and cisplatin resistance, primarily through its modulation of EMT and the Wnt/β-catenin pathway. Its association with poor clinical outcomes underscores its potential as both a prognostic marker and a therapeutic target. Strategies aimed at MAP7 could represent a new frontier in combating chemotherapy resistance in ovarian cancer, emphasizing its significance in crafting complementary treatments for this disease.

The Cby3/ciBAR1 complex positions the annulus along the sperm flagellum during spermiogenesis

Proper compartmentalization of the sperm flagellum is essential for fertility. The annulus is a septin-based ring that demarcates the midpiece (MP) and the principal piece (PP). It is assembled at the flagellar base, migrates caudally, and halts upon arriving at the PP. However, the mechanisms governing annulus positioning remain unknown. We report that a Chibby3 (Cby3)/Cby1-interacting BAR domain-containing 1 (ciBAR1) complex is required for this process. Ablation of either gene in mice results in male fertility defects, caused by kinked sperm flagella with the annulus mispositioned in the PP. Cby3 and ciBAR1 interact and colocalize to the annulus near the curved membrane invagination at the flagellar pocket. In the absence of Cby3, periannular membranes appear to be deformed, allowing the annulus to migrate over the fibrous sheath into the PP. Collectively, our results suggest that the Cby3/ciBAR1 complex regulates local membrane properties to position the annulus at the MP/PP junction.

INPP5F translocates into cytoplasm and interacts with ASPH to promote tumor growth in hepatocellular carcinoma

Background

Increasing evidence has suggested inositol polyphosphate 5-phosphatase family contributes to tumorigenesis and tumor progression. However, the role of INPP5F in hepatocellular carcinoma (HCC) and its underlying mechanisms is unclear.

Methods

The expression of INPP5F in HCC was analyzed in public databases and our clinical specimens. The biological functions of INPP5F were investigated in vitro and vivo. The molecular mechanism of INPP5F in regulating tumor growth were studied by transcriptome-sequencing analysis, mass spectrometry analysis, immunoprecipitation assay and immunofluorescence assay.

Results

High expression of INPP5F was found in HCC tissues and was associated with poor prognosis in HCC patients. Overexpression of INPP5F promoted HCC cell proliferation, and vice versa. Knockdown of INPP5F suppressed tumor growth in vivo. Results from transcriptome-sequencing analysis showed INPP5F not only regulated a series of cell cycle related genes expression (c-MYC and cyclin E1), but also promoted many aerobic glycolysis related genes expression. Further studies confirmed that INPP5F could enhance lactate production and glucose consumption in HCC cell. Mechanistically, INPP5F activated Notch signaling pathway and upregulated c-MYC and cyclin E1 in HCC via interacting with ASPH. Interestingly, INPP5F was commonly nuclear-located in cells of adjacent non-tumor tissues, while in HCC, cytoplasm-located was more common. LMB (nuclear export inhibitor) treatment restricted INPP5F in nucleus and was associated with inhibition of Notch signaling and cell proliferation. Sequence of nuclear localization signals (NLSs) and nuclear export signals (NESs) in INPP5F aminoacidic sequence were then identified. Alteration of the NLSs or NESs influenced the localization of INPP5F and the expression of its downstream molecules. Furthermore, we found INPP5F interacted with both exportin and importin through NESs and NLSs, respectively, but the interaction with exportin was stronger, leading to cytoplasmic localization of INPP5F in HCC.

Conclusion

These findings indicate that INPP5F functions as an oncogene in HCC via a translocation mechanism and activating ASPH-mediated Notch signaling pathway. INPP5F may serve as a potential therapeutic target for HCC patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02216-x.

CEP164 is essential for efferent duct multiciliogenesis and male fertility

Cilia are evolutionarily conserved microtubule-based structures that perform diverse biological functions. Cilia are assembled on basal bodies and anchored to the plasma membrane via distal appendages. In the male reproductive tract, multicilia in efferent ducts (EDs) move in a whip-like motion to prevent sperm agglutination. Previously, we demonstrated that the distal appendage protein CEP164 recruits Chibby1 (Cby1) to basal bodies to facilitate basal body docking and ciliogenesis. Mice lacking CEP164 in multiciliated cells (MCCs) (FoxJ1-Cre;CEP164fl/fl) show a significant loss of multicilia in the trachea, oviduct, and ependyma. In addition, we observed male sterility; however, the precise role of CEP164 in male fertility remained unknown. Here, we report that the seminiferous tubules and rete testis of FoxJ1-Cre;CEP164fl/fl mice exhibit substantial dilation, indicative of dysfunctional multicilia in the EDs. We found that multicilia were hardly detectable in the EDs of FoxJ1-Cre;CEP164fl/fl mice although FoxJ1-positive immature cells were present. Sperm aggregation and agglutination were commonly noticeable in the lumen of the seminiferous tubules and EDs of FoxJ1-Cre;CEP164fl/fl mice. In FoxJ1-Cre;CEP164fl/fl mice, the apical localization of Cby1 and the transition zone marker NPHP1 was severely diminished, suggesting basal body docking defects. TEM analysis of EDs further confirmed basal body accumulation in the cytoplasm of MCCs. Collectively, we conclude that male infertility in FoxJ1-Cre;CEP164fl/fl mice is caused by sperm agglutination and obstruction of EDs due to loss of multicilia. Our study, therefore, unravels an essential role of the distal appendage protein CEP164 in male fertility.

Chibby is a weak regulator of β-catenin activity in gastric epithelium

The canonical Wnt-β-catenin pathway is important in normal development. Mutations in β-catenin or proteins involved with regulating its phosphorylation or localization result in its nuclear accumulation where it activates its target genes and stimulates cell proliferation. This pathway is dysregulated in many different types of cancer, including gastric cancer (GC). Chibby (Cby) is a 14-kDa protein that inhibits β-catenin localization to the nucleus and represses β-catenin-induced transcriptional activity. In the current study, we examined the expression and function of Cby in normal and cancerous human gastric tissue. Reverse-transcription polymerase chain reaction and immunohistochemistry revealed that Cby is expressed in human stomach and localized to glandular elements. Immunohistochemical staining intensity of Cby was decreased in GC tissue when compared with normal gastric epithelium. In AGS cells, a human gastric carcinoma cell line, Cby expression was low. Stable AGS cell transfectants overexpressing Cby were prepared. Cby overexpression did not affect proliferation rates or β-catenin levels. However, confocal microscopy and subcellular fractionation studies revealed that Cby overexpression resulted in a small decrease in nuclear β-catenin. Moreover, Cby overexpression caused a molecular weight shift in nuclear β-catenin and resulted in decreased β-catenin signaling in AGS cells as measured by the TopFlash assay. However, Cby overexpression did not affect c-Myc protein levels. To conclude, Cby expression was decreased in GC samples and Cby expression altered β-catenin localization in cultured GC cells. However, Cby did not affect cell proliferation rates or β-catenin-induced protein expression. Cby may be involved in the early events in the pathogenesis of GC.

Cloning, identification and function analysis of a Chibby homolog from Litopenaeus vannamei

Chibby, a vital inhibitor molecule of Wnt/β-catenin signaling pathway, participates in development and stem cell differentiation through the regulation of β-catenin. Our previous studies have demonstrated that Litopenaeus vannamei β-catenin (Lv-β-catenin) was involved in WSSV infection and could inhibit virus replication by modulating the host immune system. In the study, a Chibby homolog from L. vannamei (designed as Lv-Chibby) was isolated and its role in WSSV infection was investigated. Sequence analysis suggested that Lv-Chibby was a novel homolog of Chibby family. It could transcript in all examined tissues, including hemocyte, gill, intestine, hepatopancreas, muscle and heart. Real-time quantitative PCR demonstrated that Lv-Chibby could take part in WSSV infection and be down-regulated by WSSV. Further studies confirmed that Lv-Chibby was able to interact with Lv-β-catenin. Moreover, the relationship of Lv-β-catenin, Lv-Chibby and WSSV069 was investigated. It was shown that Lv-Chibby enhanced the interaction between Lv-β-catenin and WSSV069. Interestingly, WSSV069 promoted the interaction between Lv-β-catenin and Lv-Chibby under high concentration, while low concentration of WSSV069 inhibited their interaction. A subsequent immunofluorescence assay revealed that WSSV069 appeared to reduce the nuclear entry of Lv-β-catenin. In sum, these results implied that Wnt/β-catenin signal pathway plays an important role in the defense against virus, and Chibby could be modulated by WSSV to regulate the signal pathway.

New susceptibility loci for cutaneous melanoma risk and progression revealed using a porcine model

Despite major advances, it is estimated that a large part of melanoma predisposing genes remains to be discovered. Animal models of spontaneous diseases are valuable tools and experimental crosses can be used to identify and fine-map new susceptibility loci associated with melanoma. We performed a Genome-Wide Association Study (GWAS) of melanoma occurrence and progression (clinical ulceration and presence of metastasis) in a porcine model of spontaneous melanoma, the MeLiM pig. Five loci on chromosomes 2, 5, 7, 8 and 16 showed genome-wide significant associations (p < 5 × 10^–6) with either one of these phenotypes. Suggestive associations (p < 5 × 10^–5) were also found at 16 additional loci. Moreover, comparison of the porcine results to those reported by human melanoma GWAS indicated shared association signals notably at CDKAL1 and TERT loci but also nearby CCND1, FTO, PLA2G6 and TMEM38B-RAD23B loci. Extensive search of the literature revealed a potential key role of genes at the identified porcine loci in tumor invasion (DST, PLEKHA5, CBY1, LIMK2 and ETV5) and immune response modulation (ETV5, HERC3 and DICER1) of the progression phenotypes. These biological processes are consistent with the clinico-pathological features of MeLiM tumors and can open new routes for future melanoma research in humans.

Chibby suppresses aerobic glycolysis and proliferation of nasopharyngeal carcinoma via the Wnt/β-catenin-Lin28/let7-PDK1 cascade

BACKGROUND

Great progress has been achieved in the study of the aerobic glycolysis or the so-called Warburg effect in a variety of cancers; however, the regulation of the Warburg effect in Nasopharyngeal carcinoma (NPC) has not been completely defined.

METHODS

Gene expression pattern of NPC cells were used to test associations between Chibby and β-catenin expression. Chibby siRNAs and over-expression vector were transfected into NPC cells to down-regulate or up-regulate Chibby expression. Loss- and gain-of function assays were performed to investigate the role of Chibby in NPC cells. Western blot, cell proliferation, Glucose uptake, Lactate release, ATP level, and O2 consumption assays were used to determine the mechanism of Chibby regulation of underlying targets. Finally, immunohistochemistry assay of fresh NPC and nasopharyngeal normal tissue sample were used to detect the expression of Chibby, β-Catenin, and PDK1 by immunostaining.

RESULTS

We observed that Chibby, a β-catenin-associated antagonist, is down-regulated in nasopharyngeal carcinoma cell lines and inhibits Wnt/β-Catenin signaling induced Warburg effect. Mechanism study revealed that Chibby regulates aerobic glycolysis in NPC cells through pyruvate dehydrogenase kinase 1(PDK1), an important enzyme involved in glucose metabolism. Moreover, Chibby suppresses aerobic glycolysis of NPC via Wnt/β-Catenin-Lin28/let7-PDK1 cascade. Chibby and PDK1 are critical for Wnt/β-Catenin signaling induced NPC cell proliferation both in vitro and in vivo. Finally, immunostaining assay of tissue samples provides an important clinical relevance among Chibby, Wnt/β-Catenin signaling and PDK1.

CONCLUSIONS

Our study reveals an association between Chibby expression and cancer aerobic glycolysis, which highlights the importance of Wnt/β-catenin pathway in regulation of energy metabolism of NPC. These results indicate that Chibby and PDK1 are the potential target for NPC treatment.

Twa1/Gid8 is a β-catenin nuclear retention factor in Wnt signaling and colorectal tumorigenesis

Hyperactivation of Wnt/β-catenin signaling is one of the major causes of human colorectal cancer (CRC). A hallmark of Wnt signaling is the nuclear accumulation of β-catenin. Although β-catenin nuclear import and export have been widely investigated, the underlying mechanism of β-catenin's nuclear retention remains largely unknown. Here, we report that Twa1/Gid8 is a key nuclear retention factor for β-catenin during Wnt signaling and colorectal carcinogenesis. In the absence of Wnt, Twa1 exists together with β-catenin in the Axin complex and undergoes ubiquitination and degradation. Upon Wnt signaling, Twa1 translocates into the nucleus, where it binds and retains β-catenin. Depletion of Twa1 attenuates Wnt-stimulated gene expression, dorsal development of zebrafish embryos and xenograft tumor growth of CRC cells. Moreover, nuclear Twa1 is significantly upregulated in human CRC tissues, correlating with the nuclear accumulation of β-catenin and poor prognosis. Thus, our results identify Twa1 as a previously undescribed regulator of the Wnt pathway for promoting colorectal tumorigenesis by facilitating β-catenin nuclear retention.

Downregulation of nuclear and cytoplasmic Chibby is associated with advanced cervical cancer

Chibby has been identified as a putative tumor suppressor and antagonist to β-catenin, thereby controlling the Wnt signaling pathway. Chibby is typically downregulated in numerous types of cancer and may be associated with tumorigenesis. The present study aimed at clarifying the following: i) Whether Chibby antagonizes β-catenin in cervical cancer; ii) whether Chibby and β-catenin mRNA expression is associated with cancer progression; and iii) whether Chibby and β-catenin expression may be used as a biomarker. A total of 87 paraffin-embedded cervical sections with distinct cervical intraepithelial neoplasia (CIN) stages (chronic cervicitis, CIN 1, CIN 2, CIN 3 and invasive squamous cell carcinoma) were collected between June 2004 and October 2012 The mRNA expression level of Chibby and β-catenin was determined using the polymerase chain reaction. Protein expression and cellular localization of Chibby and β-catenin were determined using immunohistochemistry. Chibby and β-catenin were analyzed for possible association with the progression of cervical cancer. Chibby mRNA expression and the Chibby/β-catenin ratio were identified to be downregulated in invasive tumors. Positive cytoplasmic and nuclear staining for Chibby was associated with CIN staging and decreased as the CIN stage increased. In addition, the cytoplasmic and membrane intensity of β-catenin was associated with invasive tumors, in which a significantly increased level of protein expression was detected. Chibby may be a tumor suppressor in cervical cancer, since the dysregulation of Chibby expression is associated with tumorigenesis in cervical cancer. Chibby and β-catenin expression together may potentially to a biomarker for disease progression in cervical cancer.

Thyroid cancer 1 (C8orf4) shows high expression, no mutation and reduced methylation level in lung cancers, and its expression correlates with β-catenin and DNMT1 expression and poor prognosis

Thyroid cancer 1 (TC1, C8orf4) plays important roles in tumors. The aim of this study was to examine the protein expression levels, methylation status, and mutational status of TC1 (C8orf4) in lung cancers, and investigate the correlation between TC1, other members of the Wnt signaling pathway, and lung cancer. TC1 expression levels were assessed via immunohistochemical staining in 179 cases of lung cancer. β-catenin, TCF4, Axin, Disabled-2, Chibby, and DNA methyltransferase-1 (DNMT1) expressions were also examined. Bisulfite sequencing PCR analysis was used to examine the methylation status of the C8orf4 locus, while PCR analysis and direct sequencing were used to determine its mutational status. We found high TC1 expression correlated with poor differentiation, advanced TNM stage, lymphatic metastasis, and poor prognosis in lung cancer patients. TC1 expression also correlated with β-catenin and DNMT1 expressions. No mutations in C8orf4 were detected. However, methylation levels of C8orf4 in lung cancers were lower than in corresponding normal lung tissues. In conclusion, high TC1 expression is implicated in lung cancer progression and correlates with poor prognosis in lung cancer. Reduced methylation levels might be responsible for the elevated TC1 expression levels. TC1, β-catenin, and DNMT1 can synergistically activate Wnt/β-catenin signaling in lung cancers.

Nuclear roles for cilia-associated proteins

Cilia appear to be derived, evolutionarily, from structures present in the ancestral (pre-ciliary) eukaryote, such as microtubule-based vesicle trafficking and chromosome segregation systems. Experimental observations suggest that the ciliary gate, the molecular complex that mediates the selective molecular movement between cytoplasmic and ciliary compartments, shares features with nuclear pores. Our hypothesis is that this shared transport machinery is at least partially responsible for the observation that a number of ciliary and ciliogenesis-associated proteins are found within nuclei where they play roles in the regulation of gene expression, DNA repair, and nuclear import and export. Recognizing the potential for such nuclear roles is critical when considering the phenotypic effects that arise from the mutational modification of ciliary proteins.

Chibby1 knockdown promotes mesenchymal-to-epithelial transition-like changes

Chibby1 (Cby1) was originally isolated as a binding partner for β-catenin, a dual function protein in cell-cell adhesion and in canonical Wnt signaling. The canonical Wnt/β-catenin pathway is dysregulated in various diseases including cancer, most notably of the gastrointestinal origin. To investigate the role of Cby1 in colorectal tumorigenesis, we generated stable Cby1-knockdown (K_D) SW480 colon cancer cells. Unexpectedly, we found that Cby1 K_D induces mesenchymal-to-epithelial transition (MET)-like changes in SW480 as well as in HEK293 cells. Cby1-K_D cells displayed a cuboidal epithelial morphology with tight cell-cell contacts. In Cby1-K_D cells, the plasma membrane localization of E-cadherin and β-catenin was dramatically increased with formation of cortical actin rings, while the levels of the mesenchymal marker vimentin were decreased. Consistent with these changes, in wound healing assays, Cby1-K_D cells exhibited epithelial cell-like properties as they migrated collectively as epithelial sheets. Furthermore, the anchorage-independent growth of Cby1-K_D cells was reduced as determined by soft agar assays. These findings suggest that chronic Cby1 K_D in colon cancer cells may counteract tumor progression by promoting the MET process.

BAR Domain-Containing FAM92 Proteins Interact with Chibby1 To Facilitate Ciliogenesis

Chibby1 (Cby1) is a small, conserved coiled-coil protein that localizes to centrioles/basal bodies and plays a crucial role in the formation and function of cilia. During early stages of ciliogenesis, Cby1 is required for the efficient recruitment of small vesicles at the distal end of centrioles to facilitate basal body docking to the plasma membrane. Here, we identified family with sequence similarity 92, member A (FAM92A) and FAM92B, which harbor predicted lipid-binding BAR domains, as novel Cby1-interacting partners using tandem affinity purification and mass spectrometry. We found that in cultured cell lines, FAM92A colocalizes with Cby1 at the centrioles/basal bodies of primary cilia, while FAM92B is undetectable. In airway multiciliated cells, both FAM92A and -92B colocalize with Cby1 at the base of cilia. Notably, the centriolar localization of FAM92A and -92B depends largely on Cby1. Knockdown of FAM92A in RPE1 cells impairs ciliogenesis. Consistent with the membrane-remodeling properties of BAR domains, FAM92A and -92B in cooperation with Cby1 induce deformed membrane-like structures containing the small GTPase Rab8 in cultured cells. Our results therefore suggest that FAM92 proteins interact with Cby1 to promote ciliogenesis via regulation of membrane-remodeling processes.

Chibby functions to preserve normal ciliary morphology through the regulation of intraflagellar transport in airway ciliated cells

Airway cilia provide the coordinated motive force for mucociliary transport, which prevents the accumulation of mucus, debris, pollutants, and bacteria in our respiratory tracts. As airway cilia are constantly exposed to the environment and, hence, are an integral component of the pathogenesis of several congenital and chronic pulmonary disorders, it is necessary to understand the molecular mechanisms that control ciliated cell differentiation and ciliogenesis. We have previously reported that loss of the basal body protein Chibby (Cby) results in chronic upper airway infection in mice due to a significant reduction in the number of airway cilia. In the present work, we demonstrate that Cby is required for normal ciliary structure and proper distribution of proteins involved in the bidirectional intraflagellar transport (IFT) system, which consists of 2 distinct sub-complexes, IFT-A and IFT-B, and is essential for ciliary biogenesis and maintenance. In fully differentiated ciliated cells, abnormal paddle-like cilia with dilated ciliary tips are observed in Cby-/- airways and primary cultures of mouse tracheal epithelial cells (MTECs). In addition, IFT88, an IFT-B sub-complex protein, robustly accumulates within the dilated tips of both multicilia in Cby-/- MTECs and primary cilia in Cby-/- mouse embryonic fibroblasts (MEFs). Furthermore, we show that only IFT-B components, including IFT20 and IFT57, but not IFT-A and Bardet-Biedl syndrome (BBS) proteins, amass with IFT88 in these distended tips in Cby-/- ciliated cells. Taken together, our findings suggest that Cby plays a role in the proper distribution of IFT particles to preserve normal ciliary morphology in airway ciliated cells.

Conformational characterization of the intrinsically disordered protein Chibby: Interplay between structural elements in target recognition

The protein Chibby (Cby) is an antagonist of the Wnt signaling pathway, where it inhibits the binding between the transcriptional coactivator β-catenin and the Tcf/Lef transcription factors. The 126 residue Cby is partially disordered; its N-terminal half is unstructured while its C-terminal half comprises a coiled-coil domain. Previous structural analyses of Cby using NMR spectroscopy suffered from severe line broadening for residues within the protein's C-terminal half, hindering detailed characterization of the coiled-coil domain. Here, we use hydrogen/deuterium exchange-mass spectrometry (HDX-MS) to examine Cby's C-terminal half. Results reveal that Cby is divided into three structural elements: a disordered N-terminal half, a coiled-coil domain, and a C-terminal unstructured extension consisting of the last ∼ 25 residues (which we term C-terminal extension). A series of truncation constructs were designed to assess the roles of individual structural elements in protein stability and Cby binding to TC-1, a positive regulator of the Wnt signaling pathway. CD and NMR data show that Cby maintains coiled-coil structure upon deletion of either disordered region. NMR and ITC binding experiments between Cby and TC-1 illustrate that the interaction is retained upon deletion of either Cby's N-terminal half or its C-terminal extension. Intriguingly, Cby's C-terminal half alone binds to TC-1 with significantly greater affinity compared to full-length Cby, implying that target binding of the coiled-coil domain is affected by the flanking disordered regions.

Structural Analysis of the 14-3-3ζ/Chibby Interaction Involved in Wnt/β-Catenin Signaling

The partially disordered Chibby (Cby) is a conserved nuclear protein that antagonizes the Wnt/β-catenin signaling pathway. By competing with the Tcf/Lef family proteins for binding to β-catenin, Cby abrogates the β-catenin-mediated transcription of Wnt signaling genes. Additionally, upon phosphorylation on S20 by the kinase Akt, Cby forms a complex with 14-3-3 to facilitate the nuclear export of β-catenin, which represents another crucial mechanism for the regulation of Wnt signaling. To obtain a mechanistic understanding of the 14-3-3/Cby interaction, we have extensively characterized the complex using X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, and isothermal titration calorimetry (ITC). The crystal structure of the human 14-3-3ζ/Cby protein-peptide complex reveals a canonical binding mode; however the residue at the +2 position from the phosphorylated serine is shown to be uniquely oriented relative to other solved structures of 14-3-3 complexes. Our ITC results illustrate that although the phosphorylation of S20 is essential for Cby to recognize 14-3-3, residues flanking the phosphorylation site also contribute to the binding affinity. However, as is commonly observed in other 14-3-3/phosphopeptide crystal structures, residues of Cby flanking the 14-3-3 binding motif lack observable electron density. To obtain a more detailed binding interface, we have completed the backbone NMR resonance assignment of 14-3-3ζ. NMR titration experiments reveal that residues outside of the 14-3-3 conserved binding cleft, namely a flexible loop consisting of residues 203-210, are also involved in binding Cby. By using a combined X-ray and NMR approach, we have dissected the molecular basis of the 14-3-3/Cby interaction.

Diversification of importin-α isoforms in cellular trafficking and disease states

The human genome encodes seven isoforms of importin α which are grouped into three subfamilies known as α1, α2 and α3. All isoforms share a fundamentally conserved architecture that consists of an N-terminal, autoinhibitory, importin-β-binding (IBB) domain and a C-terminal Arm (Armadillo)-core that associates with nuclear localization signal (NLS) cargoes. Despite striking similarity in amino acid sequence and 3D structure, importin-α isoforms display remarkable substrate specificity in vivo. In the present review, we look at key differences among importin-α isoforms and provide a comprehensive inventory of known viral and cellular cargoes that have been shown to associate preferentially with specific isoforms. We illustrate how the diversification of the adaptor importin α into seven isoforms expands the dynamic range and regulatory control of nucleocytoplasmic transport, offering unexpected opportunities for pharmacological intervention. The emerging view of importin α is that of a key signalling molecule, with isoforms that confer preferential nuclear entry and spatiotemporal specificity on viral and cellular cargoes directly linked to human diseases.

Expression of CBY and methylation of CBY at promoter region in human laryngeal squamous cell carcinoma

AIMS AND BACKGROUND

Chibby (CBY), a β-catenin binding partner, inhibits Wnt/β-catenin-mediated transcriptional activation by competing with Tcf/Lef factors for β-catenin binding and promoting the export of β-catenin from nucleus to cytoplasm. The regulatory effect of CBY in this signaling pathway suggests its biological importance as a potential tumor suppressor gene. The purposes of this study were to determine whether the expression of CBY was downregulated in human laryngeal squamous cell carcinoma (LSCC) samples, the CpG sites of CBY at the promoter region were methylated in these tumor samples, and reduced expression of CBY was induced by methylation of CBY promoters.

METHODS

CBY expression was investigated by quantitative real-time PCR and immunohistochemistry in samples from 36 LSCC patients. The methylation status of the CBY promoter was detected by methylation-specific PCR.

RESULTS

Compared with normal laryngeal mucosa, the expression of CBY was downregulated in LSCC samples. The reduced CBY expression rate was 58.33% (21/36) at the mRNA and 66.67% (24/36) at the protein level. The promoters of CBY were methylated in 12/36 tumor samples, partially methylated in 5, and unmethylated in 19 samples. The methylation rate including incomplete methylation was 47.22% (17/36) in tumor samples, while no methylation was detected in normal laryngeal squamous epithelium. Compared with the unmethylated group, the expression of CBY was significantly different in the methylated group (p&lt;0.05) but similar in the partially methylated group (p&gt;0.05).

CONCLUSIONS

Our data indicate that CBY expression was downregulated in LSCC, which may be partially caused by methylation of CBY promoters.

Chibby promotes ciliary vesicle formation and basal body docking during airway cell differentiation

Airway multiciliated epithelial cells play crucial roles in the mucosal defense system, but their differentiation process remains poorly understood. Mice lacking the basal body component Chibby (Cby) exhibit impaired mucociliary transport caused by defective ciliogenesis, resulting in chronic airway infection. In this paper, using primary cultures of mouse tracheal epithelial cells, we show that Cby facilitates basal body docking to the apical cell membrane through proper formation of ciliary vesicles at the distal appendage during the early stages of ciliogenesis. Cby is recruited to the distal appendages of centrioles via physical interaction with the distal appendage protein CEP164. Cby then associates with the membrane trafficking machinery component Rabin8, a guanine nucleotide exchange factor for the small guanosine triphosphatase Rab8, to promote recruitment of Rab8 and efficient assembly of ciliary vesicles. Thus, our study identifies Cby as a key regulator of ciliary vesicle formation and basal body docking during the differentiation of airway ciliated cells.

Chibby functions in Xenopus ciliary assembly, embryonic development, and the regulation of gene expression

Wnt signaling and ciliogenesis are core features of embryonic development in a range of metazoans. Chibby (Cby), a basal-body associated protein, regulates β-catenin-mediated Wnt signaling in the mouse but not Drosophila. Here we present an analysis of Cby's embryonic expression and morphant phenotypes in Xenopus laevis. Cby RNA is supplied maternally, negatively regulated by Snail2 but not Twist1, preferentially expressed in the neuroectoderm, and regulates β-catenin-mediated gene expression. Reducing Cby levels reduced the density of multiciliated cells, the number of basal bodies per multiciliated cell, and the numbers of neural tube primary cilia; it also led to abnormal development of the neural crest, central nervous system, and pronephros, all defects that were rescued by a Cby-GFP chimera. Reduction of Cby led to an increase in Wnt8a and decreases in Gli2, Gli3, and Shh RNA levels. Many, but not all, morphant phenotypes were significantly reversed by the Wnt inhibitor SFRP2. These observations extend our understanding of Cby's role in mediating the network of interactions between ciliogenesis, signaling systems and tissue patterning.

Simplet/Fam53b is required for Wnt signal transduction by regulating β-catenin nuclear localization

Canonical β-catenin-dependent Wnt signal transduction is important for several biological phenomena, such as cell fate determination, cell proliferation, stem cell maintenance and anterior-posterior axis formation. The hallmark of canonical Wnt signaling is the translocation of β-catenin into the nucleus where it activates gene transcription. However, the mechanisms regulating β-catenin nuclear localization are poorly understood. We show that Simplet/Fam53B (Smp) is required for Wnt signaling by positively regulating β-catenin nuclear localization. In the zebrafish embryo, the loss of smp blocks the activity of two β-catenin-dependent reporters and the expression of Wnt target genes, and prevents nuclear accumulation of β-catenin. Conversely, overexpression of smp increases β-catenin nuclear localization and transcriptional activity in vitro and in vivo. Expression of mutant Smp proteins lacking either the nuclear localization signal or the β-catenin interaction domain reveal that the translocation of Smp into the nucleus is essential for β-catenin nuclear localization and Wnt signaling in vivo. We also provide evidence that mammalian Smp is involved in regulating β-catenin nuclear localization: the protein colocalizes with β-catenin-dependent gene expression in mouse intestinal crypts; siRNA knockdown of Smp reduces β-catenin nuclear localization and transcriptional activity; human SMP mediates β-catenin transcriptional activity in a dose-dependent manner; and the human SMP protein interacts with human β-catenin primarily in the nucleus. Thus, our findings identify the evolutionary conserved SMP protein as a regulator of β-catenin-dependent Wnt signal transduction.

Downregulated Chibby in laryngeal squamous cell carcinoma with increased expression in laryngeal carcinoma Hep-2 cells

Chibby (Cby) inhibits Wnt/β-catenin-mediated transcriptional activation by competing with Lef-1 (the transcription factor and target of β-catenin) to bind to β-catenin. This suggests that Cby could be a tumor suppressor protein. In the present study, we examined Cby expression in laryngeal squamous cell carcinoma (LSCC) and its function and mechanism in laryngeal carcinoma cell lines. Cby expression levels were investigated by immunohistochemistry in a panel of 36 LSCC patient cases. The expression of β-catenin, c-myc and cyclin D1 in Hep-2 were determined through RT-PCR and western blot analysis. Activity of Wnt/β-catenin signaling pathway after overexpression of Cby was measured by TCF/LEF luciferase reporter gene assay. Proliferation, clone forming ability, cell cycle distribution and cell apoptosis of Hep-2 cells were detected by MTT assay, plate colony forming assay, flow cytometry and TUNEL assay, respectively. This study showed that expression of Cby protein was strongly downregulated in LSCC tumor tissues in comparison to normal laryngeal mucosa samples. No significant correlation was found between the expression of Cby in tumor tissue and gender, age, clinical stage and tumor differentiation of laryngeal cancer patients. When Cby was overexpressed in Hep-2 cells, the expression of cyclin D1 was reduced and β-catenin activity was inhibited. Proliferation and plate colony forming assays revealed a significant inhibitory effect of Cby on growth and colony formation ability of Hep-2 cells after Cby overexpression in comparison to control and mock-infected cells. In addition, we also found that upregulated expression of Cby resulted in accumulation of numbers of cells in G0/G1 phase with concomitant decrease in S phase by cell cycle assay. TUNEL staining demonstrated that, compared with the control group, the rate of apoptosis in the plv-cs2.0-Cby group was significantly increased. Taken together, downregulation of Cby was observed in LSCC, but with no significant correlation to the clinicopathological features of LSCC patients. Overexpression of Cby effectively suppressed laryngeal carcinoma cell growth and promoted its apoptosis. A better understanding of the mechanisms of Cby gene activation in LSCC could provide potential novel therapeutic targets for human laryngeal carcinoma.

Cby1 promotes Ahi1 recruitment to a ring-shaped domain at the centriole-cilium interface and facilitates proper cilium formation and function

Cby1 localizes to centrioles and antagonizes canonical Wnt signaling. Cby1^−/− mice have cystic kidneys, and Cby1 facilitates primary cilium formation and ciliary recruitment of Arl13b. Cby1 localizes to a distal centriolar domain with Ofd1 and Ahi1, and the amount of Ahi1 at the transition zone is reduced in Cby1^−/− cells.

Defects in centrosome and cilium function are associated with phenotypically related syndromes called ciliopathies. Cby1, the mammalian orthologue of the Drosophila Chibby protein, localizes to mature centrioles, is important for ciliogenesis in multiciliated airway epithelia in mice, and antagonizes canonical Wnt signaling via direct regulation of β-catenin. We report that deletion of the mouse Cby1 gene results in cystic kidneys, a phenotype common to ciliopathies, and that Cby1 facilitates the formation of primary cilia and ciliary recruitment of the Joubert syndrome protein Arl13b. Localization of Cby1 to the distal end of mature centrioles depends on the centriole protein Ofd1. Superresolution microscopy using both three-dimensional SIM and STED reveals that Cby1 localizes to an ∼250-nm ring at the distal end of the mature centriole, in close proximity to Ofd1 and Ahi1, a component of the transition zone between centriole and cilium. The amount of centriole-localized Ahi1, but not Ofd1, is reduced in Cby1^−/− cells. This suggests that Cby1 is required for efficient recruitment of Ahi1, providing a possible molecular mechanism for the ciliogenesis defect in Cby1^−/− cells.

14-3-3 and β-catenin are secreted on extracellular vesicles to activate the oncogenic Wnt pathway

Aberrant activation of the canonical Wnt signal transduction pathway is involved in a large number of human diseases. β-catenin, the key effector protein of the canonical Wnt pathway, functions in the nucleus with T-cell factor/lymphoid enhancer factor (TCF/LEF) to activate expression of Wnt target genes. Here we show that members of the 14-3-3 protein family bind disheveled-2 (Dvl-2) and glycogen synthase-3β (GSK-3β) to attenuate the interaction between GSK-3β and β-catenin. Importantly, 14-3-3 and β-catenin form "bleb-like" structures and are secreted via extracellular vesicles to induce Wnt signaling activity in target cells. Our data suggest a novel way of transducing the oncogenic Wnt signal in which β-catenin is regulated by 14-3-3ζ through the formation of "oncosomes" that contain both the 14-3-3 and β-catenin proteins.

NBPF is a potential DNA-binding transcription factor that is directly regulated by NF-κB

The neuroblastoma breakpoint family (NBPF) has been reported to play potential roles in the development of neuroblastoma and human evolution. However, the exact regulation and function of this family is still unknown. In this study, the genes of NBPF family were found to be densely covered by many high-confidence ChIP-Seq peaks of NF-κB. The expressions of NBPF genes were thus deduced to be regulated by this transcription factor. The activities of NF-κB in HeLa, HepG2 and ECa109 cells were then manipulated with NF-κB activator (TNFα) and inhibitors (BAY11-7082 or p65 siRNA), and the expressions of NBPF genes in these cells were checked. As result, it was found that the expressions of NBPF genes were regulated by NF-κB in HeLa and HepG2 cells. Therefore, the genes of NBPF family were identified as new bona fide direct target genes of NF-κB. In addition, NBPF was also identified as a nuclear protein by in silico prediction and immunolocalization. Finally, the bioinformatics analysis revealed that most of NBPF proteins contained classical nuclear localization signals (NLSs) and a conserved DNA-binding domain similar to the transcription factor stat3b/dna complex or stat-1/dna complex in their N-terminals. Therefore, this study concluded that NBPF was nuclear protein that contained classical NLSs and conserved known DNA-binding domain, and its expression was regulated by another important transcription factor, NF-κB. These findings suggest that NBPF may function as DNA-binding transcription factor in nucleus, which provides important new insight into the functions of NBPF genes in the human cells.

The nuclear envelope LEM-domain protein emerin

Emerin, a conserved LEM-domain protein, is among the few nuclear membrane proteins for which extensive basic knowledge—biochemistry, partners, functions, localizations, posttranslational regulation, roles in development and links to human disease—is available. This review summarizes emerin and its emerging roles in nuclear “lamina” structure, chromatin tethering, gene regulation, mitosis, nuclear assembly, development, signaling and mechano-transduction. We also highlight many open questions, exploration of which will be critical to understand how this intriguing nuclear membrane protein and its “family” influence the genome.

Analysing the impact of nucleo-cytoplasmic shuttling of β-catenin and its antagonists APC, Axin and GSK3 on Wnt/β-catenin signalling

The canonical Wnt signalling pathway plays a critical role in development and disease. The key player of the pathway is β-catenin. Its activity is mainly regulated by the destruction complex consisting of APC, Axin and GSK3. In the nucleus, the complex formation of β-catenin and TCF initiates target gene expression. Our study provides a comprehensive analysis of the role of nucleo-cytoplasmic shuttling of APC, Axin, and GSK3 and the inactivation of β-catenin by the destruction complex in Wnt/β-catenin signalling. We address the following questions: Can nucleo-cytoplasmic shuttling of APC, Axin and GSK3 increase the [β-catenin/TCF] concentration? And, how is the [β-catenin/TCF] concentration influenced by phosphorylation and subsequent degradation of nuclear β-catenin? Based on experimental findings, we develop a compartmental model and conduct several simulation experiments. Our analysis reveals the following key findings: 1) nucleo-cytoplasmic shuttling of β-catenin and its antagonists can yield a spatial separation between the said proteins, which results in a breakdown of β-catenin degradation, followed by an accumulation of β-catenin and hence leads to an increase of the [β-catenin/TCF] concentration. Our results strongly suggest that Wnt signalling can benefit from nucleo-cytoplasmic shuttling of APC, Axin and GSK3, although they are in general β-catenin antagonising proteins. 2) The total robustness of the [β-catenin/TCF] output is closely linked to its absolute concentration levels. We demonstrate that the compartmental separation of β-catenin and the destruction complex does not only lead to a maximization, but additionally to an increased robustness of [β-catenin/TCF] signalling against perturbations in the cellular environment. 3) A nuclear accumulation of the destruction complex renders the pathway robust against fluctuations in Wnt signalling and against changes in the compartmental distribution of β-catenin. 4) Elucidating the impact of destruction complex inhibition, we show that the [β-catenin/TCF] concentration is more effectively enhanced by inhibition of the kinase GSK3 rather than the binding of β-catenin to the destruction complex.

TC-1 (C8orf4) expression is correlated with differentiation in ovarian carcinomas and might distinguish metastatic ovarian from metastatic colorectal carcinomas

Thyroid cancer 1 (TC-1, C8orf4) is involved in the development of many cancers. In this study, we investigated the correlation between the expression of TC-1 and the clinicopathological characteristics of ovarian and colorectal adenocarcinomas. We also explored the possible use of TC-1 as a marker to distinguish between metastatic tumors of the ovary and colorectum. We used immunohistochemistry to examine the expression level of TC-1 in 100 ovarian and 100 colorectal adenocarcinomas and 25 metastatic carcinomas with the ovary or colorectum as primary site. TC-1 was expressed in all ovarian carcinoma samples. The high expression rate of TC-1 was 84 % in ovarian carcinomas, which was much higher than that observed in colorectal adenocarcinomas (35 %, P < 0.001). High expression of TC-1 significantly correlated with poor differentiation of ovarian carcinomas (P = 0.013). To explore the value of TC-1 in distinguishing metastatic ovarian cancers from colorectal cancers, we found the area under the receiver operator characteristic curve of TC-1 to be 0.819 (95 % confidence interval, 0.760-0.878; P < 0.001). Furthermore, TC-1 was highly expressed in 100 % of nine metastatic ovarian cancers, but only in 31 % of 16 metastatic colorectal cancers. The higher expression of TC-1 in ovarian compared to colorectal adenocarcinomas suggests its potential use as a marker, to distinguish between metastatic ovarian and colorectal adenocarcinomas.

Maternal Mga is required for Wnt signaling and organizer formation in the early Xenopus embryo

Maternal Wnt11 is both necessary and sufficient for the formation of Spemann organizer in Xenopus embryo. Xnr3 and Siamois have been identified as the direct target genes of maternal Wnt11/β-catenin during organizer induction. The depletion of maternal XTcf3 resulted in the ectopic expression of Xnr3 and Siamois, suggesting the activity of β-catenin/XTcf3 is strictly regulated in the early Xenopus embryos. Here, we show that Xenopus mga (Xmga) is a maternal gene required for dorsal axis formation. Overexpression experiments indicate that mouse Mga potentiates the activity of β-catenin in the induction of organizer-specific genes. Depletion of maternal Xmga results in the dramatic decrease of the expression of organizer genes and ventralization phenotype, indicating that Xmga is required for β-catenin function and organizer formation. Depletion of XTcf3 cannot rescue organizer gene expression and axis formation in Xmga-depleted embryos, suggesting Xmga is downstream of XTcf3 during organizer induction. We conclude that maternal Xmga is critical for the function of β-catenin during organizer formation and dorsal development of Xenopus embryo. To our knowledge, this is a report for the first time to implicate Mga in regulating Wnt signaling.

A Wnt/beta-catenin pathway antagonist Chibby binds Cenexin at the distal end of mother centrioles and functions in primary cilia formation

The mother centriole of the centrosome is distinguished from immature daughter centrioles by the presence of accessory structures (distal and subdistal appendages), which play an important role in the organization of the primary cilium in quiescent cells. Primary cilia serve as sensory organelles, thus have been implicated in mediating intracellular signal transduction pathways. Here we report that Chibby (Cby), a highly conserved antagonist of the Wnt/β-catenin pathway, is a centriolar component specifically located at the distal end of the mother centriole and essential for assembly of the primary cilium. Cby appeared as a discrete dot in the middle of a ring-like structure revealed by staining with a distal appendage component of Cep164. Cby interacted with one of the appendage components, Cenexin (Cnx), which thereby abrogated the inhibitory effect of Cby on β-catenin-mediated transcriptional activation in a dose-dependent manner. Cby and Cnx did not precisely align, as Cby was detected at a more distal position than Cnx. Cnx emerged earlier than Cby during the cell cycle and was required for recruitment of Cby to the mother centriole. However, Cby was dispensable for Cnx localization to the centriole. During massive centriogenesis in in vitro cultured mouse tracheal epithelial cells, Cby and Cnx were expressed in a similar pattern, which was coincident with the expression of Foxj1. Our results suggest that Cby plays an important role in organization of both primary and motile cilia in collaboration with Cnx.

Drosophila chibby is required for basal body formation and ciliogenesis but not for Wg signaling

In contrast to vertebrate CBY, which functions in WNT signaling, Drosophila CBY is essential for normal basal body structure and function but dispensable for Wg signaling.

Centriole-to–basal body conversion, a complex process essential for ciliogenesis, involves the progressive addition of specific proteins to centrioles. CHIBBY (CBY) is a coiled-coil domain protein first described as interacting with β-catenin and involved in Wg-Int (WNT) signaling. We found that, in Drosophila melanogaster, CBY was exclusively expressed in cells that require functional basal bodies, i.e., sensory neurons and male germ cells. CBY was associated with the basal body transition zone (TZ) in these two cell types. Inactivation of cby led to defects in sensory transduction and in spermatogenesis. Loss of CBY resulted in altered ciliary trafficking into neuronal cilia, irregular deposition of proteins on spermatocyte basal bodies, and, consequently, distorted axonemal assembly. Importantly, cby^1/1 flies did not show Wingless signaling defects. Hence, CBY is essential for normal basal body structure and function in Drosophila, potentially through effects on the TZ. The function of CBY in WNT signaling in vertebrates has either been acquired during vertebrate evolution or lost in Drosophila.

Chibby suppresses growth of human SW480 colon adenocarcinoma cells through inhibition of β-catenin signaling

The canonical Wnt signaling pathway is crucial for embryonic development and adult tissue homeostasis. Activating mutations in the Wnt pathway are frequently associated with the pathogenesis of various types of cancer, particularly colon cancer. Upon Wnt stimulation, β-catenin plays a central role as a coactivator through direct interaction with Tcf/Lef transcription factors to stimulate target gene expression. We have previously shown that the evolutionarily conserved protein Chibby (Cby) physically binds to β-catenin to repress β-catenin-dependent gene activation by 1) competing with Tcf/Lef factors for binding to β-catenin and 2) facilitating nuclear export of β-catenin via interaction with 14-3-3 proteins. In this study, we employed human colon adenocarcinoma SW480 cells with high levels of endogenous β-catenin to address a potential tumor suppressor role of Cby. In SW480 stable cells expressing wild-type Cby (CbyWT), but not 14-3-3-binding- defective Cby mutant CbyS20A, a significant fraction of endogenous β-catenin was detected in the cytoplasm. Consistent with this, CbyWT-expressing cells showed low levels of β-catenin signaling activity, leading to reduced growth. Our results suggest that Cby, in collaboration with 14-3-3 proteins, can counteract oncogenic β-catenin signaling in colon cancer cells.

A role for primary cilia in glutamatergic synaptic integration of adult-born neurons

The sequential synaptic integration of adult-born neurons has been widely examined in rodents, but the mechanisms regulating the integration remain largely unknown. The primary cilium, a microtubule-based signaling center, is essential for vertebrate development, including the development of the CNS. We examined the assembly and function of the primary cilium in the synaptic integration of adult-born mouse hippocampal neurons. Primary cilia were absent in young adult-born neurons, but assembled precisely at the stage when newborn neurons approach their final destination, further extend dendrites and form synapses with entorhinal cortical projections. Conditional deletion of cilia from adult-born neurons induced severe defects in dendritic refinement and synapse formation. Deletion of primary cilia led to enhanced Wnt and β-catenin signaling, which may account for these developmental defects. Taken together, our findings identify the assembly of primary cilia as a critical regulatory event in the dendritic refinement and synaptic integration of adult-born neurons.

TCFs and Wnt/β-catenin signaling: more than one way to throw the switch

Wnts are conserved, secreted signaling proteins that can influence cell behavior by stabilizing β-catenin. Accumulated β-catenin enters the nucleus, where it physically associates with T-cell factor (TCF) family members to regulate target gene expression in many developmental and adult tissues. Recruitment of β-catenin to Wnt response element (WRE) chromatin converts TCFs from transcriptional repressors to activators. This review will outline the complex interplay between factors contributing to TCF repression and coactivators working with β-catenin to regulate Wnt targets. In addition, three variations of the standard transcriptional switch model will be discussed. One is the Wnt/β-catenin symmetry pathway in Caenorhabditis elegans, where Wnt-mediated nuclear efflux of TCF is crucial for activation of targets. Another occurs in vertebrates, where distinct TCF family members are associated with repression and activation, and recent evidence suggests that Wnt signaling facilitates a "TCF exchange" on WRE chromatin. Finally, a "reverse switch" mechanism for target genes that are directly repressed by Wnt/β-catenin signaling occurs in Drosophila cells. The diversity of TCF regulatory mechanisms may help to explain how a small group of transcription factors can function in so many different contexts to regulate target gene expression.

Generation and characterization of monoclonal antibodies against human Chibby protein

Chibby (Cby) was originally identified as an antagonist of the Wnt/β-catenin signaling pathway. It physically interacts with the key co-activator β-catenin and inhibits β-catenin-mediated transcriptional activation. More recently, we demonstrated that Cby protein localizes to the base of motile cilia and is required for ciliogenesis in the respiratory epithelium of mice. To gain further insight into the physiological function of Cby, we developed mouse monoclonal antibodies (MAbs) against human Cby protein and characterized two Cby MAbs, designated 8-2 and 27-11, in depth. Western blot analysis revealed that 8-2 reacts with both human and mouse Cby proteins, whereas 27-11 is specific to human Cby. The epitopes of 8-2 and 27-11 were narrowed down to the middle portion (aa 49-63) and N-terminal region (aa 1-31) of the protein, respectively. We also determined their isotypes and found that 8-2 and 27-11 belong to IgG2a and IgG1 with κ light chains, respectively. Both MAbs can be employed for immunoprecipitation assays. Moreover, 8-2 detects endogenous Cby protein on Western blots, and marks the ciliary base of motile cilia in the murine lung and trachea as shown by immunofluorescence staining. These Cby MAbs therefore hold promise as useful tools for the investigation of Wnt signaling and ciliogenesis.

Physiological inhibitors of Wnt signaling

Wnt signaling is crucial for cell proliferation and differentiation. It represents a complex network with mechanisms of self-regulation through positive and negative feedback. Recent increasing interest in this signaling pathway has led to the discovery of many new proteins that down-regulate Wnt activity. Here, we provide a short description of the most important and best-studied inhibitors, group them according to the target molecule within the Wnt cascade, and discuss their clinical potential. Although most of the inhibitors discussed here may also interact with proteins from other signaling pathways, we focus only on their ability to modulate Wnt signaling.

β-catenin dosage is a critical determinant of tracheal basal cell fate determination

The purpose of this study was to determine whether β-catenin regulates basal cell fate determination in the mouse trachea. Analysis of TOPGal transgene reporter activity and Wnt/β-catenin pathway gene expression suggested a role for β-catenin in basal cell proliferation and differentiation after naphthalene-mediated Clara-like and ciliated cell depletion. However, these basal cell activities occurred simultaneously, limiting precise determination of the role(s) played by β-catenin. This issue was overcome by analysis of β-catenin signaling in tracheal air-liquid interface cultures. The cultures could be divided into two phases: basal cell proliferation and basal cell differentiation. A role for β-catenin in basal cell proliferation was indicated by activation of the TOPGal transgene on proliferation days 3 to 5 and by transient expression of Myc (alias c-myc). Another peak of TOPGal transgene activity was detected on differentiation days 2 to 10 and was associated with the expression of Axin 2. These results suggest a role for β-catenin in basal to ciliated and basal to Clara-like cell differentiation. Genetic stabilization of β-catenin in basal cells shortened the period of basal cell proliferation but had a minor effect on this process. Persistent β-catenin signaling regulated basal cell fate by driving the generation of ciliated cells and preventing the production of Clara-like cells.

Strange as it may seem: the many links between Wnt signaling, planar cell polarity, and cilia

Cilia are important cellular structures that have been implicated in a variety of signaling cascades. In this review, we discuss the current evidence for and against a link between cilia and both the canonical Wnt/β-catenin pathway and the noncanonical Wnt/planar cell polarity (PCP) pathway. Furthermore, we address the evidence implicating a role for PCP components in ciliogenesis. Given the lack of consensus in the field, we use new data on the control of ciliary protein localization as a basis for proposing new models by which cell type-specific regulation of ciliary components via differential transport, regulated entry and exit, or diffusion barriers might generate context-dependent functions for cilia.

Structural characterization of partially disordered human Chibby: insights into its function in the Wnt-signaling pathway

The Wnt/β-catenin signaling pathway is critical to embryonic development as well as adult tissue regeneration. Dysregulation of this pathway can lead to a variety of human diseases, in particular cancers. Chibby (Cby), a small and highly conserved protein, plays an antagonistic role in Wnt signaling by inhibiting the binding of β-catenin to Tcf/Lef family proteins, a protein interaction that is essential for the transcriptional activation of Wnt target genes. Cby is also involved in regulating intracellular distribution of β-catenin. Phosphorylated Cby forms a ternary complex with 14-3-3 protein and β-catenin, facilitating the export of β-catenin from the nucleus. On the other hand, the antagonistic function of Cby is inhibited upon binding to thyroid cancer-1 (TC-1). To dissect the structure−function relationship of Cby, we have used NMR spectroscopy, ESI-MS, CD, and DLS to extensively characterize the structure of human Cby. Our results show that the 126-residue Cby is partially disordered under nondenaturing conditions. While the N-terminal portion of the protein is predominantly unstructured in solution, the C-terminal half of Cby adopts a coiled-coil structure through self-association. Initial data for the binding studies of Cby to 14-3-3ζ (one of the isoforms in the 14-3-3 family) and TC-1 via these two distinct structural modules have also been obtained. It is noteworthy that in a recent large-scale analysis of the intrinsically disordered proteome of mouse, a substantial number of disordered proteins are predicted to have coiled-coil motif presence in their sequences. The combination of these two molecular recognition features could facilitate disordered Cby in assembling protein complexes via different modes of interaction.

Altered lung morphogenesis, epithelial cell differentiation and mechanics in mice deficient in the Wnt/β-catenin antagonist Chibby

The canonical Wnt/β-catenin pathway plays crucial roles in various aspects of lung morphogenesis and regeneration/repair. Here, we examined the lung phenotype and function in mice lacking the Wnt/β-catenin antagonist Chibby (Cby). In support of its inhibitory role in canonical Wnt signaling, expression of β-catenin target genes is elevated in the Cby^−/− lung. Notably, Cby protein is prominently associated with the centrosome/basal body microtubule structures in embryonic lung epithelial progenitor cells, and later enriches as discrete foci at the base of motile cilia in airway ciliated cells. At birth, Cby^−/− lungs are grossly normal but spontaneously develop alveolar airspace enlargement with reduced proliferation and abnormal differentiation of lung epithelial cells, resulting in altered pulmonary function. Consistent with the Cby expression pattern, airway ciliated cells exhibit a marked paucity of motile cilia with apparent failure of basal body docking. Moreover, we demonstrate that Cby is a direct downstream target for the master ciliogenesis transcription factor Foxj1. Collectively, our results demonstrate that Cby facilitates proper postnatal lung development and function.