AMER1 regulates the distribution of the tumor suppressor APC between microtubules and the plasma membrane

Osteopathia striata with cranial sclerosis as a cancer predisposition syndrome: The first report of neuroblastoma and review of all cancers in OSCS

Osteopathia Striata with Cranial Sclerosis (OSCS) is a rare genetic condition primarily characterized by metaphyseal striations of long bones, bone sclerosis, macrocephaly, and other congenital anomalies. It is caused by pathogenic variants in AMER1, a tumor suppressor and a WNT signaling repressor gene with key roles in tissue regeneration, neurodevelopment, tumorigenesis, and other developmental processes. While somatic AMER1 pathogenic variants have frequently been identified in several tumor types (e.g., Wilms tumor and colorectal cancer), whether OSCS (i.e., with AMER1 germline variants) is a tumor predisposition syndrome is not clear, with only nine cases reported with tumors. We here report the first case of neuroblastoma diagnosed in a male child with OSCS, review all previously reported tumors diagnosed in individuals with OSCS, and discuss potential tumorigenic mechanisms of AMER1. Our report adds to the accumulating evidence suggesting OSCS is a tumor predisposition condition, highlighting the importance of maintaining a high index of suspicion for the associated tumors when evaluating patients with OSCS. Importantly, Wilms tumor stands out as the most commonly observed tumor in OSCS patients, underscoring the need for regular surveillance.

A Mosaic Variant in CTNNB1/β-catenin as a Novel Cause for Osteopathia Striata With Cranial Sclerosis

CONTEXT

Osteopathia striata with cranial sclerosis (OSCS) is a rare bone disorder with X-linked dominant inheritance, characterized by a generalized hyperostosis in the skull and long bones and typical metaphyseal striations in the long bones. So far, loss-of-function variants in AMER1 (also known as WTX or FAM123B), encoding the APC membrane recruitment protein 1 (AMER1), have been described as the only molecular cause for OSCS. AMER1 promotes the degradation of β-catenin via AXIN stabilization, acting as a negative regulator of the WNT/β-catenin signaling pathway, a central pathway in bone formation.

OBJECTIVE

In this study, we describe a Dutch adult woman with an OSCS-like phenotype, namely, generalized high bone mass and characteristic metaphyseal striations, but no genetic variant affecting AMER1.

RESULTS

Whole exome sequencing led to the identification of a mosaic missense variant (c.876A > C; p.Lys292Asn) in CTNNB1, coding for β-catenin. The variant disrupts an amino acid known to be crucial for interaction with AXIN, a key factor in the β-catenin destruction complex. Western blotting experiments demonstrate that the p.Lys292Asn variant does not significantly affect the β-catenin phosphorylation status, and hence stability in the cytoplasm. Additionally, luciferase reporter assays were performed to investigate the effect of p.Lys292Asn β-catenin on canonical WNT signaling. These studies indicate an average 70-fold increase in canonical WNT signaling activity by p.Lys292Asn β-catenin.

CONCLUSION

In conclusion, this study indicates that somatic variants in the CTNNB1 gene could explain the pathogenesis of unsolved cases of osteopathia striata.

Oncogenes and tumor suppressor genes: functions and roles in cancers

Cancer, being the most formidable ailment, has had a profound impact on the human health. The disease is primarily associated with genetic mutations that impact oncogenes and tumor suppressor genes (TSGs). Recently, growing evidence have shown that X-linked TSGs have specific role in cancer progression and metastasis as well. Interestingly, our genome harbors around substantial portion of genes that function as tumor suppressors, and the X chromosome alone harbors a considerable number of TSGs. The scenario becomes even more compelling as X-linked TSGs are adaptive to key epigenetic processes such as X chromosome inactivation. Therefore, delineating the new paradigm related to X-linked TSGs, for instance, their crosstalk with autosome and involvement in cancer initiation, progression, and metastasis becomes utmost importance. Considering this, herein, we present a comprehensive discussion of X-linked TSG dysregulation in various cancers as a consequence of genetic variations and epigenetic alterations. In addition, the dynamic role of X-linked TSGs in sex chromosome-autosome crosstalk in cancer genome remodeling is being explored thoroughly. Besides, the functional roles of ncRNAs, role of X-linked TSG in immunomodulation and in gender-based cancer disparities has also been highlighted. Overall, the focal idea of the present article is to recapitulate the findings on X-linked TSG regulation in the cancer landscape and to redefine their role toward improving cancer treatment strategies.

Recurrent Wnt Pathway and ARID1A Alterations in Sinonasal Olfactory Carcinoma

Sinonasal tumors with neuroepithelial differentiation, defined by neuroectodermal elements reminiscent of olfactory neuroblastoma (ONB) and epithelial features such as keratin expression or gland formation, are a diagnostically challenging group that has never been formally included in sinonasal tumor classifications. Recently, we documented that most of these neuroepithelial neoplasms have distinctive histologic and immunohistochemical findings and proposed the term "olfactory carcinoma" to describe these tumors. However, the molecular characteristics of olfactory carcinoma have not yet been evaluated. In this study, we performed targeted molecular profiling of 23 sinonasal olfactory carcinomas to further clarify their pathogenesis and classification. All tumors included in this study were composed of high-grade neuroectodermal cells that were positive for pankeratin and at least 1 specific neuroendocrine marker. A significant subset of cases also displayed rosettes and neurofibrillary matrix, intermixed glands with variable cilia, peripheral p63/p40 expression, and S100 protein-positive sustentacular cells. Recurrent oncogenic molecular alterations were identified in 20 tumors, including Wnt pathway alterations affecting CTNNB1 (n = 8) and PPP2R1A (n = 2), ARID1A inactivation (n = 5), RUNX1 mutations (n = 3), and IDH2 hotspot mutations (n = 2). Overall, these findings do demonstrate the presence of recurrent molecular alterations in olfactory carcinoma, although this group of tumors does not appear to be defined by any single mutation. Minimal overlap with alterations previously reported in ONB also adds to histologic and immunohistochemical separation between ONB and olfactory carcinoma. Conversely, these molecular findings enhance the overlap between olfactory carcinoma and sinonasal neuroendocrine carcinomas. A small subset of neuroepithelial tumors might better fit into the superseding molecular category of IDH2-mutant sinonasal carcinoma. At this point, sinonasal neuroendocrine and neuroepithelial tumors may best be regarded as a histologic and molecular spectrum that includes core groups of ONB, olfactory carcinoma, neuroendocrine carcinoma, and IDH2-mutant sinonasal carcinoma.

IRF-2 inhibits cancer proliferation by promoting AMER-1 transcription in human gastric cancer

BACKGROUND

Interferon regulatory factor 2 (IRF-2) acts as an anti-oncogene in gastric cancer (GC); however, the underlying mechanism remains unknown.

METHODS

This study determined the expression of IRF-2 in GC tissues and adjacent non-tumor tissues using immunohistochemistry (IHC) and explored the predictive value of IRF-2 for the prognoses of GC patients. Cell function and xenograft tumor growth experiments in nude mice were performed to test tumor proliferation ability, both in vitro and in vivo. Chromatin immunoprecipitation sequencing (ChIP-Seq) assay was used to verify the direct target of IRF-2.

RESULTS

We found that IRF-2 expression was downregulated in GC tissues and was negatively correlated with the prognoses of GC patients. IRF-2 negatively affected GC cell proliferation both in vitro and in vivo. ChIP-Seq assay showed that IRF-2 could directly activate AMER-1 transcription and regulate the Wnt/β-catenin signaling pathway, which was validated using IHC, in both tissue microarray and xenografted tumor tissues, western blot analysis, and cell function experiments.

CONCLUSIONS

Increased expression of IRF-2 can inhibit tumor growth and affect the prognoses of patients by directly regulating AMER-1 transcription in GC and inhibiting the Wnt/β-catenin signaling pathway.

The Adenoviral E1B-55k Protein Present in HEK293 Cells Mediates Abnormal Accumulation of Key WNT Signaling Proteins in Large Cytoplasmic Aggregates

HEK293 cells are one of the most widely used cell lines in research, and HEK293 cells are frequently used as an in vitro model for studying the WNT signaling pathway. The HEK293 cell line was originally established by transfection of human embryonic kidney cells with sheared adenovirus 5 DNA, and it is known that that HEK293 cells stably express the adenoviral E1A and E1B-55k proteins. Here, we show that HEK293 cells display an unexpected distribution of key components of the WNT/β-catenin signaling pathway where AXIN1, APC, DVL2 and tankyrase are all co-localized in large spherical cytoplasmic aggregates. The cytoplasmic aggregates are enclosed by a narrow layer of the adenoviral E1B-55k protein. The reduction of E1B-55k protein levels leads to the disappearance of the cytoplasmic aggregates thus corroborating an essential role of the E1B-55k protein in mediating the formation of the aggregates. Furthermore, HEK293 cells with reduced E1B-55k protein levels display reduced levels of transcriptional activation of WNT/β-catenin signaling upon stimulation by the Wnt3A agonist. The demonstrated influence of the E1B-55k protein on the cellular localization of WNT/β-catenin signaling components and on transcriptional regulation of WNT/β-catenin signaling asks for caution in the interpretation of data derived from the HEK293 cell line.

The cytoskeleton in phagocytosis and macropinocytosis

Cells of the innate immune system, notably macrophages, neutrophils and dendritic cells, perform essential antimicrobial and homeostatic functions. These functions rely on the dynamic surveillance of the environment supported by the formation of elaborate membrane protrusions. Such protrusions - pseudopodia, lamellipodia and filopodia - facilitate the sampling of the surrounding fluid by macropinocytosis, as well as the engulfment of particulates by phagocytosis. Both processes entail extreme plasma membrane deformations that require the coordinated rearrangement of cytoskeletal polymers, which exert protrusive force and drive membrane coalescence and scission. The resulting vacuolar compartments undergo pronounced remodeling and ultimate resolution by mechanisms that also involve the cytoskeleton. Here, we describe the regulation and functions of cytoskeletal assembly and remodeling during macropinocytosis and phagocytosis.

Advances and Insights of APC-Asef Inhibitors for Metastatic Colorectal Cancer Therapy

In Colorectal cancer (CRC), adenomatous polyposis coli (APC) directly interacts with the Rho guanine nucleotide exchange factor 4 (Asef) and releases its GEF activity. Activated Asef promotes the aberrant migration and invasion of CRC cell through a CDC42-mediated pathway. Knockdown of either APC or Asef significantly decreases the migration of CRC cells. Therefore, disrupting the APC-Asef interaction is a promising strategy for the treatment of invasive CRC. With the growth of structural information, APC-Asef inhibitors have been designed, providing hope for CRC therapy. Here, we will review the APC-Asef interaction in cancer biology, the structural complex of APC-Asef, two generations of peptide inhibitors of APC-Asef, and small molecule inhibitors of APC-Asef, focusing on research articles over the past 30 years. We posit that these advances in the discovery of APC-Asef inhibitors establish the protein-protein interaction (PPI) as targetable and provide a framework for other PPI programs.

The origins and genetic interactions of KRAS mutations are allele- and tissue-specific

Mutational activation of KRAS promotes the initiation and progression of cancers, especially in the colorectum, pancreas, lung, and blood plasma, with varying prevalence of specific activating missense mutations. Although epidemiological studies connect specific alleles to clinical outcomes, the mechanisms underlying the distinct clinical characteristics of mutant KRAS alleles are unclear. Here, we analyze 13,492 samples from these four tumor types to examine allele- and tissue-specific genetic properties associated with oncogenic KRAS mutations. The prevalence of known mutagenic mechanisms partially explains the observed spectrum of KRAS activating mutations. However, there are substantial differences between the observed and predicted frequencies for many alleles, suggesting that biological selection underlies the tissue-specific frequencies of mutant alleles. Consistent with experimental studies that have identified distinct signaling properties associated with each mutant form of KRAS, our genetic analysis reveals that each KRAS allele is associated with a distinct tissue-specific comutation network. Moreover, we identify tissue-specific genetic dependencies associated with specific mutant KRAS alleles. Overall, this analysis demonstrates that the genetic interactions of oncogenic KRAS mutations are allele- and tissue-specific, underscoring the complexity that drives their clinical consequences.

KIF23 activated Wnt/β-catenin signaling pathway through direct interaction with Amer1 in gastric cancer

Increased expression of the kinesin family member 23 (KIF23) has been verified in gastric cancer (GC) and its upregulation contributes to cell proliferation. Even though, the role of KIF23 has not been fully elucidated in GC, and the mechanisms of KIF23 as an oncogene remain unknown. To further identify its potential role in GC, we analyzed gene expression data from GC patients in GEO and TCGA datasets. KIF23 was upregulated in GC, and increased expression of KIF23 correlated with poor prognosis. Importantly, KIF23 inhibition not only suppressed GC cell proliferation, tumorigenesis, but also migration and invasion, and arrested the cell cycle in the G2/M phase. Mechanistic investigations confirmed that KIF23 activated the Wnt/β-catenin signaling pathway by directly interacting with APC membrane recruitment 1 (Amer1). Furthermore, KIF23 exhibited competitive binding with Amer1 to block the association of Amer1 with adenomatous polyposis coli (APC), thus relocating Amer1 from the membrane and cytoplasm to the nucleus and attenuating the ability of Amer1 to negatively regulate Wnt/β-catenin signaling, resulting in activation of this signaling pathway. Collectively, our findings demonstrated that KIF23 promoted GC cell proliferation by directly interacting with Amer1 and activating the Wnt/β-catenin signaling pathway.

Whole Exome Sequencing Provides the Correct Diagnosis in a Case of Osteopathia Striata with Cranial Sclerosis: Case Report of a Novel Frameshift Mutation in AMER1

The diagnosis of rare diseases with multisystem manifestations can constitute a difficult process that delays the determination of the underlying cause. Whole exome sequencing (WES) provides a suitable option to examine multiple target genes associated with several disorders that display common features. In this study, we report the case of a female patient suspected of having Sotos syndrome. Screening for the initially selected genes, considering Sotos syndrome and Sotos-like disorders, did not identify any pathogenic variants that could explain the phenotype. The extended analysis, which considered all genes in the exome associated with features consistent with those shown by the studied patient, revealed a novel frameshift variant in the AMER1 gene, responsible for osteopathia striata with cranial sclerosis. WES analysis and an updated revision of previously reported disease-causing mutations, proved useful to reach an accurate diagnosis and guide further examination to identify critical abnormalities.

Can the microbiota predict response to systemic cancer therapy, surgical outcomes, and survival? The answer is in the gut

INTRODUCTION

The gut microbiota seems to play a key role in tumorigenesis, across various hallmarks of cancer. Recent evidence suggests its potential use as a biomarker predicting drug response and adding prognostic information, generally in the context of immuno-oncology.

AREAS COVERED

In this review, we focus on the modulating effects of gut microbiota dysbiosis on various anticancer molecules used in practice, including cytotoxic and immune-modulating agents, primarily immune-checkpoint inhibitors (ICI). Pubmed/Medline-based literature search was conducted to find potential original studies that discuss gut microbiota as a prognostic and predictive biomarker for cancer therapy. We also looked at the US ClinicalTrials.gov website to find additional studies particularly ongoing human clinical trials.

EXPERT COMMENTARY

Sequencing of stool-derived materials and tissue samples from cancer patients and animal models has shown a significant enrichment of various bacteria such as Fusobacterium nucleatum and Bacteroides fragilis were associated with resistant disease and poorer outcomes. Gut microbiota was also found to be associated with surgical outcomes and seems to play a significant role in anastomotic leak (ATL) after surgery mainly by collagen breakdown. However, this research field is just at the beginning and the current findings are not yet ready to change clinical practice.

Affinity proteomics identifies novel functional modules related to adhesion GPCRs

Adhesion G protein-coupled receptors (ADGRs) have recently become a target of intense research. Their unique protein structure, which consists of a G protein-coupled receptor combined with long adhesive extracellular domains, suggests a dual role in cell signaling and adhesion. Despite considerable progress in the understanding of ADGR signaling over the past years, the knowledge about ADGR protein networks is still limited. For most receptors, only a few interaction partners are known thus far. We aimed to identify novel ADGR-interacting partners to shed light on cellular protein networks that rely on ADGR function. For this, we applied affinity proteomics, utilizing tandem affinity purifications combined with mass spectrometry. Analysis of the acquired proteomics data provides evidence that ADGRs not only have functional roles at synapses but also at intracellular membranes, namely at the endoplasmic reticulum, the Golgi apparatus, mitochondria, and mitochondria-associated membranes (MAMs). Specifically, we found an association of ADGRs with several scaffold proteins of the membrane-associated guanylate kinases family, elementary units of the γ-secretase complex, the outer/inner mitochondrial membrane, MAMs, and regulators of the Wnt signaling pathways. Furthermore, the nuclear localization of ADGR domains together with their physical interaction with nuclear proteins and several transcription factors suggests a role of ADGRs in gene regulation.

A Case Study on the Keap1 Interaction with Peptide Sequence Epitopes Selected by the Peptidomic mRNA Display

Many protein-protein and peptide-protein interactions (PPIs) play key roles in the regulation of biological functions, and therefore, the modulation of PPIs has become an attractive target of new drug development. Although a number of PPIs have already been identified, over 100 000 unknown PPIs are predicted to exist. To uncover such unknown PPIs, it is important to devise a conceptually distinct method from that of currently available methods. Herein, an mRNA display by using a total RNA library derived from various human tissues, which serves as a unique method to physically isolate peptide epitopes that potentially bind to a target protein of interest, is reported. In this study, selection was performed against Kelch-like ECH-associated protein (Keap1) as a model target protein, leading to a peptide epitope originating from astrotactin-1 (ASTN1). It turned out that this ASTN1 peptide was able to interact with Keap1 more strongly than that with a known peptide derived from Nrf2; a well-known, naturally occurring Keap1 binder. This case study demonstrates the applicability of peptidomic mRNA display for the rapid exploration of consensus binding peptide motifs and the potential for the discovery of unknown PPIs with other proteins of interest.

Zebrafish Wtx is a negative regulator of Wnt signaling but is dispensable for embryonic development and organ homeostasis

BACKGROUND

The X-chromosomally linked gene WTX is a human disease gene and a member of the AMER family. Mutations in WTX are found in Wilms tumor, a form of pediatric kidney cancer and in patients suffering from OSCS (Osteopathia striata with cranial sclerosis), a sclerosing bone disorder. Functional data suggest WTX to be an inhibitor of the Wnt/β-catenin signaling pathway. Deletion of Wtx in mouse leads to perinatal death, impeding the analysis of its physiological role.

RESULTS

To gain insights into the function of Wtx in development and homeostasis we have used zebrafish as a model and performed both knockdown and knockout studies using morpholinos and transcription activator-like effector nucleases (TALENs), respectively. Wtx knockdown led to increased Wnt activity and embryonic dorsalization. Also, wtx mutants showed a transient upregulation of Wnt target genes in the context of caudal fin regeneration. Surprisingly, however, wtx as well as wtx/amer2/amer3 triple mutants developed normally, were fertile and did not show any anomalies in organ maintenance.

CONCLUSIONS

Our data show that members of the zebrafish wtx/amer gene family, while sharing a partially overlapping expression pattern do not compensate for each other. This observation demonstrates a remarkable robustness during development and regeneration in zebrafish.

Driver genes exome sequencing reveals distinct variants in African Americans with colorectal neoplasia

BACKGROUND

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in the United States. African Americans are disproportionately affected by CRC. Our hypothesis is that driver genes with known and novel mutations have an impact on CRC outcome in this population. Therefore, we investigated the variants' profiles in a panel of 15 CRC genes.

PATIENTS & METHODS

Colorectal specimens (n=140) were analyzed by targeted exome sequencing using an Ion Torrent platform. Detected variants were validated in 36 samples by Illumina sequencing. The novel status of the validated variants was determined by comparison to publicly available databases. Annotated using ANNOVAR and in-silico functional analysis of these variants were performed to determine likely pathogenic variants.

RESULTS

Overall, 121 known and novel variants were validated: APC (27%), AMER1 (3%), ARID1 (7%), MSH3 (12%), MSH6 (10%), BRAF (4%), KRAS (6%), FBXW7 (4%), PIK3CA (6%), SMAD4 (5%), SOX9 (2%), TCF7L2 (2%), TGFBR2 (5%), TP53 (7%). From these validated variants, 12% were novel in 8 genes (AMER1, APC, ARID1A, BRAF, MSH6, PIK3CA, SMAD4, and TCF7L2). Of the validated variants, 23% were non-synonymous, 14% were stopgains, 24% were synonymous and 39% were intronic variants.

CONCLUSION

We here report the specifics of variants' profiles of African Americans with colorectal lesions. Validated variants showed that Tumor Suppressor Genes (TSGs) APC and ARID1 and DNA Mismatch repair (MMR) genes MSH3 and MSH6 are the genes with the highest numbers of validated variants. Oncogenes KRAS and PIK3CA are also altered and likely participate in the increased proliferative potential of the mutated colonic epithelial cells in this population.

MiR-4524b-5p/WTX/β-catenin axis functions as a regulator of metastasis in cervical cancer

Cervical cancer is the second most deadly gynecological tumor worldwide. MicroRNAs (miRNAs) play very important roles in tumor oncogenesis and progression. The mechanism of post-transcription regulation of WTX gene is still unknown. A series of differential miRNAs were discovered by microarray analysis comparing three pairs of primary cervical cancer specimens and their relapsed tumors from three patients. Quantitative reverse transcriptase PCR (qRT-PCR), Western Blot (WB) and Immunohistochemistry (IHC) was used to detect the expression of miR-4524b-5p and WTX in cervical cell lines and tissues. The biological function of miR-4524b-5p and WTX was investigated through knockdown and overexpression with inhibitor/siRNA and mimic/plasmid in vitro and in vivo. In this study, we found that miR-4524b-5p is highly expressed in relapsed cervical cancer specimens. Combined in vitro and in vivo experiments, showed that miR-4524b-5p could regulate the migration and invasion ability of cervical cancer. Furthermore, we also found that miR-4524b-5p could regulate the migration and invasion of cervical cancer by targeting WTX and that WTX could regulate the expression of β-catenin. Taken together, our data identified a miR-4524b-5p/WTX/β-catenin regulatory axis for cervical cancer, and miR-4524b-5p may be a potential target for cervical cancer therapy.

Striatin is a novel modulator of cell adhesion

The adherens junctions (AJs) and tight junctions (TJs) provide critical adhesive contacts between neighboring epithelial cells and are crucial for epithelial adhesion, integrity, and barrier functions in a wide variety of tissues and organisms. The striatin protein family, which are part of the striatin interaction phosphatases and kinases complex, are multidomain scaffolding proteins that play important biologic roles. We have previously shown that striatin colocalizes with the tumor suppressor protein adenomatous polyposis coli in the TJs of epithelial cells. Here we show that striatin affects junction integrity and cell migration, probably through a mechanism that involves the adhesion molecule E-cadherin. Cells engaged in cell-cell adhesion expressed a high MW-modified form of striatin that forms stable associations with detergent-insoluble, membrane-bound cellular fractions. In addition, striatin has recently been suggested to be a target of the poly (ADP-ribose) polymerases Tankyrase 1, and we have found that striatin interacts with Tankyrase 1 and is subsequently poly-ADP-ribosylated. Taken together, our results suggest that striatin is a novel cell-cell junctional protein that functions to maintain correct cell adhesion and may have a role in establishing the relationship between AJs and TJs that is fundamental for epithelial cell-cell adhesion.-Lahav-Ariel, L., Caspi, M., Nadar-Ponniah, P. T., Zelikson, N., Hofmann, I., Hanson, K. K., Franke, W. W., Sklan, E. H., Avraham, K. B., Rosin-Arbesfeld, R. Striatin is a novel modulator of cell adhesion.

Genetic and Molecular Insights Into Genotype-Phenotype Relationships in Osteopathia Striata With Cranial Sclerosis (OSCS) Through the Analysis of Novel Mouse Wtx Mutant Alleles

The X-linked WTX/AMER1 protein constitutes an important component of the β-catenin destruction complex that can both enhance and suppress canonical β-catenin signaling. Somatic mutations in WTX/AMER1 have been found in a proportion of the pediatric kidney cancer Wilms' tumor. By contrast, germline mutations cause the severe sclerosing bone dysplasia osteopathia striata congenita with cranial sclerosis (OSCS), a condition usually associated with fetal or perinatal lethality in male patients. Here we address the developmental and molecular function of WTX by generating two novel mouse alleles. We show that in addition to the previously reported skeletal abnormalities, loss of Wtx causes severe midline fusion defects including cleft palate and ectopic synostosis at the base of the skull. By contrast, deletion of the C-terminal part of the protein results in only mild developmental abnormalities permitting survival beyond birth. Adult analysis, however, revealed skeletal defects including changed skull morphology and an increased whole-body bone density, resembling a subgroup of male patients carrying a milder, survivable phenotype. Molecular analysis in vitro showed that while β-catenin fails to co-immunoprecipitate with the truncated protein, partial recruitment appears to be achieved in an indirect manner using AXIN/AXIN2 as a molecular bridge. Taken together our analysis provides a novel model for WTX-caused bone diseases and explains on the molecular level how truncation mutations in this gene may retain some of WTX-protein functions. © 2018 American Society for Bone and Mineral Research.

A knock-in mouse line conditionally expressing the tumor suppressor WTX/AMER1

WTX/AMER1 is an important developmental regulator, mutations in which have been identified in a proportion of patients suffering from the renal neoplasm Wilms' tumor and in the bone malformation syndrome Osteopathia Striata with Cranial Sclerosis (OSCS). Its cellular functions appear complex and the protein can be found at the membrane, within the cytoplasm and the nucleus. To understand its developmental and cellular function an allelic series for Wtx in the mouse is crucial. Whereas mice carrying a conditional knock out allele for Wtx have been previously reported, a gain-of-function mouse model that would allow studying the molecular, cellular and developmental role of Wtx is still missing. Here we describe the generation of a novel mouse strain that permits the conditional activation of WTX expression. Wtx fused to GFP was introduced downstream a stop cassette flanked by loxP sites into the Rosa26 locus by gene targeting. Ectopic WTX expression is reported after crosses with several Cre transgenic mice in different embryonic tissues. Further, functionality of the fusion protein was demonstrated in the context of a Wtx null allele.

Insulin signaling regulates a functional interaction between adenomatous polyposis coli and cytoplasmic dynein

Diabetes is linked to an increased risk for colorectal cancer, but the mechanistic underpinnings of this clinically important effect are unclear. Here we describe an interaction between the microtubule motor cytoplasmic dynein, the adenomatous polyposis coli tumor suppressor protein (APC), and glycogen synthase kinase-3β (GSK-3β), which could shed light on this issue. GSK-3β is perhaps best known for glycogen regulation, being inhibited downstream in an insulin-signaling pathway. However, the kinase is also important in many other processes. Mutations in APC that disrupt the regulation of β-catenin by GSK-3β cause colorectal cancer in humans. Of interest, both APC and GSK-3β interact with microtubules and cellular membranes. We recently demonstrated that dynein is a GSK-3β substrate and that inhibition of GSK-3β promotes dynein-dependent transport. We now report that dynein stimulation in intestinal cells in response to acute insulin exposure (or GSK-3β inhibition) is blocked by tumor-promoting isoforms of APC that reduce an interaction between wild-type APC and dynein. We propose that under normal conditions, insulin decreases dynein binding to APC to stimulate minus end-directed transport, which could modulate endocytic and secretory systems in intestinal cells. Mutations in APC likely impair the ability to respond appropriately to insulin signaling. This is exciting because it has the potential to be a contributing factor in the development of colorectal cancer in patients with diabetes.

Establishment of Par-Polarized Cortical Domains via Phosphoregulated Membrane Motifs

The Par polarity complex creates mutually exclusive cortical domains in diverse animal cells. Activity of the atypical protein kinase C (aPKC) is a key output of the Par complex as phosphorylation removes substrates from the Par domain. Here, we investigate how diverse, apparently unrelated Par substrates couple phosphorylation to cortical displacement. Each protein contains a basic and hydrophobic (BH) motif that interacts directly with phospholipids and also overlaps with aPKC phosphorylation sites. Phosphorylation alters the electrostatic character of the sequence, inhibiting interaction with phospholipids and the cell cortex. We searched for overlapping BH and aPKC phosphorylation site motifs (i.e., putative phosphoregulated BH motifs) in several animal proteomes. Candidate proteins with strong PRBH signals associated with the cell cortex but were displaced into the cytoplasm by aPKC. These findings demonstrate a potentially general mechanism for exclusion of proteins from the Par cortical domain in polarized cells.

Structures of the APC-ARM domain in complexes with discrete Amer1/WTX fragments reveal that it uses a consensus mode to recognize its binding partners

The tumor suppressor APC employs its conserved armadillo repeat (ARM) domain to recognize many of its binding partners, including Amer1/WTX, which is mutated in Wilms' tumor and bone overgrowth syndrome. The APC–Amer1 complex has important roles in regulating Wnt signaling and cell adhesion. Three sites A1, A2, and A3 of Amer1 have been reported to mediate its interaction with APC-ARM. In this study, crystal structures of APC–ARM in complexes with Amer1-A1, -A2, and -A4, which is newly identified in this work, were determined. Combined with our GST pull-down, yeast two-hybrid, and isothermal titration calorimetry (ITC) assay results using mutants of APC and Amer1 interface residues, our structures demonstrate that Amer1-A1, -A2, and -A4, as well as other APC-binding proteins such as Asef and Sam68, all employ a common recognition pattern to associate with APC–ARM. In contrast, Amer1-A3 binds to the C-terminal side of APC–ARM through a bipartite interaction mode. Composite mutations on either APC or Amer1 disrupting all four interfaces abrogated their association in cultured cells and impaired the membrane recruitment of APC by Amer1. Our study thus comprehensively elucidated the recognition mechanism between APC and Amer1, and revealed a consensus recognition sequence employed by various APC–ARM binding partners.

Exome Sequencing Reveals AMER1 as a Frequently Mutated Gene in Colorectal Cancer

PURPOSE

Somatic mutations occur at early stages of adenoma and accumulate throughout colorectal cancer progression. The aim of this study was to characterize the mutational landscape of stage II tumors and to search for novel recurrent mutations likely implicated in colorectal cancer tumorigenesis.

EXPERIMENTAL DESIGN

The exomic DNA of 42 stage II, microsatellite-stable colon tumors and their paired mucosae were sequenced. Other molecular data available in the discovery dataset [gene expression, methylation, and copy number variations (CNV)] were used to further characterize these tumors. Additional datasets comprising 553 colorectal cancer samples were used to validate the discovered mutations.

RESULTS

As a result, 4,886 somatic single-nucleotide variants (SNV) were found. Almost all SNVs were private changes, with few mutations shared by more than one tumor, thus revealing tumor-specific mutational landscapes. Nevertheless, these diverse mutations converged into common cellular pathways, such as cell cycle or apoptosis. Among this mutational heterogeneity, variants resulting in early stop codons in the AMER1 (also known as FAM123B or WTX) gene emerged as recurrent mutations in colorectal cancer. Losses of AMER1 by other mechanisms apart from mutations such as methylation and copy number aberrations were also found. Tumors lacking this tumor suppressor gene exhibited a mesenchymal phenotype characterized by inhibition of the canonical Wnt pathway.

CONCLUSIONS

In silico and experimental validation in independent datasets confirmed the existence of functional mutations in AMER1 in approximately 10% of analyzed colorectal cancer tumors. Moreover, these tumors exhibited a characteristic phenotype.

Microtubule plus-end tracking proteins and their roles in cell division

Microtubules are cellular components that are required for a variety of essential processes such as cell motility, mitosis, and intracellular transport. This is possible because of the inherent dynamic properties of microtubules. Many of these properties are tightly regulated by a number of microtubule plus-end-binding proteins or +TIPs. These proteins recognize the distal end of microtubules and are thus in the right context to control microtubule dynamics. In this review, we address how microtubule dynamics are regulated by different +TIP families, focusing on how functionally diverse +TIPs spatially and temporally regulate microtubule dynamics during animal cell division.

Osteopathia striata with cranial sclerosis, Wilms’ tumor and the WTX gene

Osteopathia striata with cranial sclerosis (OSCS, OMIM#300373) is an X-linked dominant sclerosing bone dysplasia that shows a distinct phenotype in females and males. In 2009, Zandra Jenkins et al found that germline mutations in the FAM123B/WTX/AMER1 gene, mapped to chromosome Xq11.2, cause both the familial and sporadic forms of OSCS. Intriguingly, the WTX gene was already known as a putative tumor suppressor gene, since in 2007 Rivera et al had reported inactivating WTX mutations in Wilms’ tumor (WT), the most frequent renal tumor of childhood. Here we review the heterogeneous clinical presentation of OSCS patients and the involvement of WTX anomalies in OSCS and in WT.

different Roles for the axin interactions with the SAMP versus the second twenty amino acid repeat of adenomatous polyposis coli

Wnt signalling is prevented by the proteosomal degradation of β-catenin, which occurs in a destruction complex containing adenomatous polyposis coli (APC), APC-like (APCL), Axin and Axin2. Truncating mutations of the APC gene result in the constitutive stabilisation of β-catenin and the initiation of colon cancer, although tumour cells tolerate the expression of wild-type APCL. Using the colocalisation of overexpressed Axin, APC and APCL constructs as a readout of interaction, we found that Axin interacted with the second twenty amino acid repeat (20R2) of APC and APCL. This interaction involved a domain adjacent to the C-terminal DIX domain of Axin. We identified serine residues within the 20R2 of APCL that were involved in Axin colocalisation, the phosphorylation of truncated APCL and the down-regulation of β-catenin. Our results indicated that Axin, but not Axin2, displaced APC, but not APCL, from the cytoskeleton and stimulated its incorporation into bright cytoplasmic dots that others have recognised as β-catenin destruction complexes. The SAMP repeats in APC interact with the N-terminal RGS domain of Axin. Our data showed that a short domain containing the first SAMP repeat in truncated APC was required to stimulate Axin oligomerisation. This was independent of Axin colocalisation with 20R2. Our data also suggested that the RGS domain exerted an internal inhibitory constraint on Axin oligomerisation. Considering our data and those from others, we discuss a working model whereby β-catenin phosphorylation involves Axin and the 20R2 of APC or APCL and further processing of phospho-β-catenin occurs upon the oligomerisation of Axin that is induced by binding the SAMP repeats in APC.

Adenomatous polyposis coli (APC) membrane recruitment 3, a member of the APC membrane recruitment family of APC-binding proteins, is a positive regulator of Wnt-β-catenin signalling

The adenomatous polyposis coli (APC) membrane recruitment (Amer) family proteins Amer1/Wilms tumour gene on the X chromosome and Amer2 are binding partners of the APC tumour suppressor protein, and act as negative regulators in the Wnt signalling cascade. So far, nothing has been known about the third member of the family, Amer3. Here we show that Amer3 binds to the armadillo repeat domain of APC, similarly to Amer1 and Amer2. Amer3 also binds to the Wnt pathway regulator conductin/axin2. Furthermore, we identified Amer1 as binding partner of Amer3. Whereas Amer1 and Amer2 are linked to the plasma membrane by an N-terminal membrane localization domain, Amer3 lacks this domain. Amer3 localizes to the cytoplasm and nucleus of epithelial cells, and this is dependent on specific nuclear import and export sequences. Functionally, exogenous Amer3 enhances the expression of a β-catenin/T-cell factor-dependent reporter gene, and knockdown of endogenous Amer3 reduces Wnt target gene expression in colorectal cancer cells. Thus, Amer3 acts as an activator of Wnt signalling, in contrast to Amer1 and Amer2, which are inhibitors, suggesting a nonredundant role of Amer proteins in the regulation of this pathway. Our data, together with those of previous studies, provide a comprehensive picture of similarities and differences within the Amer protein family.

β-arrestin promotes Wnt-induced low density lipoprotein receptor-related protein 6 (Lrp6) phosphorylation via increased membrane recruitment of Amer1 protein

β-Arrestin is a scaffold protein that regulates signal transduction by seven transmembrane-spanning receptors. Among other functions it is also critically required for Wnt/β-catenin signal transduction. In the present study we provide for the first time a mechanistic basis for the β-arrestin function in Wnt/β-catenin signaling. We demonstrate that β-arrestin is required for efficient Wnt3a-induced Lrp6 phosphorylation, a key event in downstream signaling. β-Arrestin regulates Lrp6 phosphorylation via a novel interaction with phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2)-binding protein Amer1/WTX/Fam123b. Amer1 has been shown very recently to bridge Wnt-induced and Dishevelled-associated PtdIns(4,5)P2 production to the phosphorylation of Lrp6. Using fluorescence recovery after photobleaching we show here that β-arrestin is required for the Wnt3a-induced Amer1 membrane dynamics and downstream signaling. Finally, we show that β-arrestin interacts with PtdIns kinases PI4KIIα and PIP5KIβ. Importantly, cells lacking β-arrestin showed higher steady-state levels of the relevant PtdInsP and were unable to increase levels of these PtdInsP in response to Wnt3a. In summary, our data show that β-arrestins regulate Wnt3a-induced Lrp6 phosphorylation by the regulation of the membrane dynamics of Amer1. We propose that β-arrestins via their scaffolding function facilitate Amer1 interaction with PtdIns(4,5)P2, which is produced locally upon Wnt3a stimulation by β-arrestin- and Dishevelled-associated kinases.

Stat3 inhibits WTX expression through up-regulation of microRNA-370 in Wilms tumor

Wilms tumor (WT) is a genetically heterogeneous childhood kidney tumor. Several genetic mutations have been identified in WT patients, including inactivation of WTX, somatic stabilizing CTNNB1, and p53 mutations. However, the molecular mechanisms in tumorigenesis remain largely unexplored. Stat3 is a transcription factor that can promote oncogenesis. Stat3 activation is commonly viewed as crucial for multiple tumor proliferation and metastasis. We show that Stat3 is highly activated in Wilms tumor tissues compared to those in adjacent tissues. IL-6 treatment or transfection of a constitutively activated Stat3 in G401 cells promotes cell proliferation. At the molecular level, we further elucidate that Stat3 inhibits WTX expression through up-regulation of microRNA-370. Our results suggest that Stat3/miR-370/WTX regulatory axis might be a critical mechanism in Wilms tumor cells.

The β-catenin destruction complex

The Wnt/β-catenin pathway is highly regulated to insure the correct temporal and spatial activation of its target genes. In the absence of a Wnt stimulus, the transcriptional coactivator β-catenin is degraded by a multiprotein "destruction complex" that includes the tumor suppressors Axin and adenomatous polyposis coli (APC), the Ser/Thr kinases GSK-3 and CK1, protein phosphatase 2A (PP2A), and the E3-ubiquitin ligase β-TrCP. The complex generates a β-TrCP recognition site by phosphorylation of a conserved Ser/Thr-rich sequence near the β-catenin amino terminus, a process that requires scaffolding of the kinases and β-catenin by Axin. Ubiquitinated β-catenin is degraded by the proteasome. The molecular mechanisms that underlie several aspects of destruction complex function are poorly understood, particularly the role of APC. Here we review the molecular mechanisms of destruction complex function and discuss several potential roles of APC in β-catenin destruction.

FAM123A binds to microtubules and inhibits the guanine nucleotide exchange factor ARHGEF2 to decrease actomyosin contractility

The FAM123 gene family comprises three members: FAM123A, the tumor suppressor WTX (also known as FAM123B), and FAM123C. WTX is required for normal development and causally contributes to human disease, in part through its regulation of β-catenin-dependent WNT signaling. The roles of FAM123A and FAM123C in signaling, cell behavior, and human disease remain less understood. We defined and compared the protein-protein interaction networks for each member of the FAM123 family by affinity purification and mass spectrometry. Protein localization and functional studies suggest that the FAM123 family members have conserved and divergent cellular roles. In contrast to WTX and FAM123C, we found that microtubule-associated proteins were enriched in the FAM123A protein interaction network. FAM123A interacted with and tracked with the plus end of dynamic microtubules. Domain interaction experiments revealed a "SKIP" amino acid motif in FAM123A that mediated interaction with the microtubule tip tracking proteins end-binding protein 1 (EB1) and EB3--and therefore with microtubules. Cells depleted of FAM123A showed compartment-specific effects on microtubule dynamics, increased actomyosin contractility, larger focal adhesions, and decreased cell migration. These effects required binding of FAM123A to and inhibition of the guanine nucleotide exchange factor ARHGEF2, a microtubule-associated activator of RhoA. Together, these data suggest that the SKIP motif enables FAM123A, but not the other FAM123 family members, to bind to EB proteins, localize to microtubules, and coordinate microtubule dynamics and actomyosin contractility.

Amer2 protein interacts with EB1 protein and adenomatous polyposis coli (APC) and controls microtubule stability and cell migration

EB1 is key factor in the organization of the microtubule cytoskeleton by binding to the plus-ends of microtubules and serving as a platform for a number of interacting proteins (termed +TIPs) that control microtubule dynamics. Together with its direct binding partner adenomatous polyposis coli (APC), EB1 can stabilize microtubules. Here, we show that Amer2 (APC membrane recruitment 2), a previously identified membrane-associated APC-binding protein, is a direct interaction partner of EB1 and acts as regulator of microtubule stability together with EB1. Amer2 binds to EB1 via specific (S/T)xIP motifs and recruits it to the plasma membrane. Coexpression of Amer2 and EB1 generates stabilized microtubules at the plasma membrane, whereas knockdown of Amer2 leads to destabilization of microtubules. Knockdown of Amer2, APC, or EB1 reduces cell migration, and morpholino-mediated down-regulation of Xenopus Amer2 blocks convergent extension cell movements, suggesting that the Amer2-EB1-APC complex regulates cell migration by altering microtubule stability.

A Proteome-wide screen for mammalian SxIP motif-containing microtubule plus-end tracking proteins

Microtubule plus-end tracking proteins (+TIPs) are structurally and functionally diverse factors that accumulate at the growing microtubule plus-ends, connect them to various cellular structures, and control microtubule dynamics [1, 2]. EB1 and its homologs are +TIPs that can autonomously recognize growing microtubule ends and recruit to them a variety of other proteins. Numerous +TIPs bind to end binding (EB) proteins through natively unstructured basic and serine-rich polypeptide regions containing a core SxIP motif (serine-any amino acid-isoleucine-proline) [3]. The SxIP consensus sequence is short, and the surrounding sequences show high variability, raising the possibility that undiscovered SxIP containing +TIPs are encoded in mammalian genomes. Here, we performed a proteome-wide search for mammalian SxIP-containing +TIPs by combining biochemical and bioinformatics approaches. We have identified a set of previously uncharacterized EB partners that have the capacity to accumulate at the growing microtubule ends, including protein kinases, a small GTPase, centriole-, membrane-, and actin-associated proteins. We show that one of the newly identified +TIPs, CEP104, interacts with CP110 and CEP97 at the centriole and is required for ciliogenesis. Our study reveals the complexity of the mammalian +TIP interactome and provides a basis for investigating the molecular crosstalk between microtubule ends and other cellular structures.

WTX R353X mutation in a family with osteopathia striata and cranial sclerosis (OS-CS): case report and literature review of the disease clinical, genetic and radiological features

Osteopathia striata with cranial sclerosis (OS-CS) or Horan-Beighton syndrome is a rare X-linked dominant inherited bone dysplasia, characterized by longitudinal striations of long bones and cranial sclerosis. Patients can be asymptomatic or present with typical facial dysmorphism, sensory defects, internal organs anomalies, growth and mental retardation, depending on the severity of the disease. WTX gene (Xq11) has been recently identified as the disease causing gene. Aim of this article is to present the case of a 6 year old girl initially evaluated for bilateral hearing loss. Patient's head CT scan pointed out sclerosis of skull base and mastoid cells, and abnormal middle-ear ossification. Clinical examination of the patient and her mother were suspicious for OS-CS. The diagnosis was confirmed by X-rays examination showing typical longitudinal striation. Genetic analysis allowed the identification of maternally transmitted heterozygous nonsense c.1057C>T (p.R353X) WTX gene mutation. We also provide a systematic review of currently available knowledge about clinical, radiologic and genetic features typical of the OS-CS.

Regulation of Wnt signaling by the tumor suppressor adenomatous polyposis coli does not require the ability to enter the nucleus or a particular cytoplasmic localization

Wnt signaling plays key roles in development and disease. The tumor suppressor adenomatous polyposis coli (APC) is an essential negative regulator of Wnt signaling. Its best-characterized role is as part of the destruction complex, targeting the Wnt effector β-catenin (βcat) for phosphorylation and ultimate destruction, but several studies suggested APC also may act in the nucleus at promoters of Wnt-responsive genes or to shuttle βcat out for destruction. Even in its role in the destruction complex, APC's mechanism of action remains mysterious. We have suggested APC positions the destruction complex at the appropriate subcellular location, facilitating βcat destruction. In this study, we directly tested APC's proposed roles in the nucleus or in precisely localizing the destruction complex by generating a series of APC2 variants to which we added tags relocalizing otherwise wild-type APC to different cytoplasmic locations. We tested these for function in human colon cancer cells and Drosophila embryos. Strikingly, all rescue Wnt regulation and down-regulate Wnt target genes in colon cancer cells, and most restore Wnt regulation in Drosophila embryos null for both fly APCs. These data suggest that APC2 does not have to shuttle into the nucleus or localize to a particular subcellular location to regulate Wnt signaling.

Regulation of Wnt signaling by the tumor suppressor adenomatous polyposis coli does not require the ability to enter the nucleus or a particular cytoplasmic localization

Wnt signaling plays key roles in development and disease. The tumor suppressor adenomatous polyposis coli (APC) is an essential negative regulator of Wnt signaling. Its best-characterized role is as part of the destruction complex, targeting the Wnt effector β-catenin (βcat) for phosphorylation and ultimate destruction, but several studies suggested APC also may act in the nucleus at promoters of Wnt-responsive genes or to shuttle βcat out for destruction. Even in its role in the destruction complex, APC's mechanism of action remains mysterious. We have suggested APC positions the destruction complex at the appropriate subcellular location, facilitating βcat destruction. In this study, we directly tested APC's proposed roles in the nucleus or in precisely localizing the destruction complex by generating a series of APC2 variants to which we added tags relocalizing otherwise wild-type APC to different cytoplasmic locations. We tested these for function in human colon cancer cells and Drosophila embryos. Strikingly, all rescue Wnt regulation and down-regulate Wnt target genes in colon cancer cells, and most restore Wnt regulation in Drosophila embryos null for both fly APCs. These data suggest that APC2 does not have to shuttle into the nucleus or localize to a particular subcellular location to regulate Wnt signaling.

The WTX tumor suppressor enhances p53 acetylation by CBP/p300

WTX encodes a tumor suppressor, frequently inactivated in Wilms tumor, with both plasma membrane and nuclear localization. WTX has been implicated in β-catenin turnover, but its effect on nuclear proteins is unknown. We report an interaction between WTX and p53, derived from the unexpected observation of WTX, p53, and E1B 55K colocalization within the characteristic cytoplasmic body of adenovirus-transformed kidney cells. In other cells without adenovirus expression, the C-terminal domain of WTX binds to the DNA-binding domain of p53, enhances its binding to CBP, and increases CBP/p300-mediated acetylation of p53 at Lys 373/382. WTX knockdown accelerates CBP/p300 protein turnover and attenuates this modification of p53. In p53-reconstitution experiments, cell-cycle arrest, apoptosis, and p53 target-gene expression are suppressed by depletion of WTX. Together, these results suggest that WTX modulates p53 function, in part through regulation of its activator CBP/p300.

Crystal structures of the armadillo repeat domain of adenomatous polyposis coli and its complex with the tyrosine-rich domain of Sam68

Adenomatous polyposis coli (APC) is a tumor suppressor protein commonly mutated in colorectal tumors. APC plays important roles in Wnt signaling and other cellular processes. Here, we present the crystal structure of the armadillo repeat (Arm) domain of APC, which facilitates the binding of APC to various proteins. APC-Arm forms a superhelix with a positively charged groove. We also determined the structure of the complex of APC-Arm with the tyrosine-rich (YY) domain of the Src-associated in mitosis, 68 kDa protein (Sam68), which regulates TCF-1 alternative splicing. Sam68-YY forms numerous interactions with the residues on the groove and is thereby fixed in a bent conformation. We assessed the effects of mutations and phosphorylation on complex formation between APC-Arm and Sam68-YY. Structural comparisons revealed different modes of ligand recognition between the Arm domains of APC and other Arm-containing proteins.

The male phenotype in osteopathia striata congenita with cranial sclerosis

Osteopathia striata with cranial sclerosis (OSCS) is an X-linked disease caused by truncating mutations in WTX. Females exhibit sclerotic striations on the long bones, cranial sclerosis, and craniofacial dysmorphism. Males with OSCS have significant skeletal sclerosis, do not have striations but do display a more severe phenotype commonly associated with gross structural malformations, patterning defects, and significant pre- and postnatal lethality. The recent description of mutations in WTX underlying OSCS has led to the identification of a milder, survivable phenotype in males. Individuals with this presentation can have, in addition to skeletal sclerosis, Hirschsprung disease, joint contractures, cardiomyopathy, and neuromuscular anomalies. A diagnosis of OSCS should be considered in males with macrocephaly, skeletal sclerosis that is most marked in the cranium and the absence of metaphyseal striations. The observation of striations in males may be indicative of a WTX mutation in a mosaic state supporting the contention that this sign in females is indicative of the differential lyonization of cells in the osteoblastic lineage.

Wilms tumor gene on X chromosome (WTX) inhibits degradation of NRF2 protein through competitive binding to KEAP1 protein

WTX is a tumor suppressor protein that is lost or mutated in up to 30% of cases of Wilms tumor. Among its known functions, WTX interacts with the β-transducin repeat containing family of ubiquitin ligase adaptors and promotes the ubiquitination and degradation of the transcription factor β-catenin, a key control point in the WNT/β-catenin signaling pathway. Here, we report that WTX interacts with a second ubiquitin ligase adaptor, KEAP1, which functions to regulate the ubiquitination of the transcription factor NRF2, a key control point in the antioxidant response. Surprisingly, we find that unlike its ability to promote the ubiquitination of β-catenin, WTX inhibits the ubiquitination of NRF2. WTX and NRF2 compete for binding to KEAP1, and thus loss of WTX leads to rapid ubiquitination and degradation of NRF2 and a reduced response to cytotoxic insult. These results expand our understanding of the molecular mechanisms of WTX and reveal a novel regulatory mechanism governing the antioxidant response.

Amer2 protein is a novel negative regulator of Wnt/β-catenin signaling involved in neuroectodermal patterning

Wnt/β-catenin signaling is negatively controlled by the adenomatous polyposis coli (APC) tumor suppressor, which induces proteasomal degradation of β-catenin as part of the β-catenin destruction complex. Amer2 (APC membrane recruitment 2; FAM123A) is a direct interaction partner of APC, related to the tumor suppressor Amer1/WTX, but its function in Wnt signaling is not known. Here, we show that Amer2 recruits APC to the plasma membrane by binding to phosphatidylinositol 4,5-bisphosphate lipids via lysine-rich motifs and that APC links β-catenin and the destruction complex components axin and conductin to Amer2. Knockdown of Amer2 increased Wnt target gene expression and reporter activity in cell lines, and overexpression reduced reporter activity, which required membrane association of Amer2. In Xenopus embryos, Amer2 is expressed mainly in the dorsal neuroectoderm and neural tissues. Down-regulation of Amer2 by specific morpholino oligonucleotides altered neuroectodermal patterning, which could be rescued by expression of a dominant-negative mutant of Lef1 that interferes with β-catenin-dependent transcription. Our data characterize Amer2 for the first time as a negative regulator of Wnt signaling both in cell lines and in vivo and define Amer proteins as a novel family of Wnt pathway regulators.

Shaping microtubules into diverse patterns: molecular connections for setting up both ends

Microtubules serve as rails for intracellular trafficking and their appropriate organization is critical for the generation of cell polarity, which is a foundation of cell differentiation, tissue morphogenesis, ontogenesis and the maintenance of homeostasis. The microtubule array is not just a static railway network; it undergoes repeated collapse and reassembly in diverse patterns during cell morphogenesis. In the last decade much progress has been made toward understanding the molecular mechanisms governing complex microtubule patterning. This review first revisits the basic principle of microtubule dynamics, and then provides an overview of how microtubules are arranged in highly shaped and functional patterns in cells changing their morphology by factors controlling the fate of microtubule ends.

Pathology, genetics and cytogenetics of Wilms' tumour

Wilms' tumour (WT) is an embryonal cancer of childhood and is thought to be derived from embryonic kidney precursor cells. The Knudson two hit model was initially thought to occur in WT, but findings emerging from genetic and cytogenetic studies in the past two decades have implicated several genetic events. Recent techniques in genetic analysis have improved our ability to characterise changes in genes involved in WT which include WT1, CTNNB1, IGF2 and WTX. These genetic events have not only provided insight into the pathobiology of this malignancy, but the recognition of these candidate genes may offer potential targets for novel therapies. In this review, we will provide an overview of the pathological, genetic and cytogenetic characteristics of WT.