The receptor tyrosine kinase Ror2 associates with the melanoma-associated antigen (MAGE) family protein Dlxin-1 and regulates its intracellular distribution

Genomic and transcriptomic landscape to decipher the genetic basis of hyperpigmentation in Lanping black-boned sheep (Ovis aries)

BACKGROUND

Lanping black-boned sheep (LPB) represent a distinctive mammalian species characterized by hyperpigmentation, resulting in black bone and muscle features, in contrast to their conventional counterparts exhibiting red muscle and white bone. The genetic basis underlying LPB hyperpigmentation has remained enigmatic.

METHODS

In this study, we conducted whole-genome sequencing of 100 LPB and 50 Lanping normal sheep (LPN), and integrated this data with 421 sequenced datasets from wild and domestic sheep, shedding light on the genetic backdrop and genomic variations associated with LPB. Furthermore, we performed comparative RNA-Seq analysis using liver sample to pinpoint genes implicated in the pigmentation process. We generated a comprehensive dataset comprising 97,944,357 SNPs from 571 sheep, facilitating an in-depth exploration of genetic factors.

RESULTS

Population genetic structure analysis revealed that the LPB breed traces its origin back to LPN, having evolved into a distinct breed. The integration of positively selected genes with differentially expressed genes identified two candidates, ERBB4 and ROR1, potentially linked to LPB hyperpigmentation. Comparative analysis of ERBB4 and ROR1 mRNA relative expression levels in liver, spleen, and kidney tissues of LPB, in comparison to Diqing sheep, revealed significant upregulation, except for ERBB4 in the liver. Gene expression heatmaps further underscored marked allelic frequency disparities in different populations.

CONCLUSION

Our findings establish the evolutionary lineage of the LPB breed from LPN and underscore the involvement of ERBB4 and ROR1 genes in melanin synthesis. These results enhance our comprehension of the molecular basis of hyperpigmentation and contribute to a more comprehensive depiction of sheep diversity.

ROR2 promotes cell cycle progression and cell proliferation through the PI3K/AKT signaling pathway in gastric cancer

Proliferation is a critical characteristic of the progression of gastric cancer (GC). Receptor tyrosine kinase-like orphan receptor 2 (ROR2), the orphan receptor tyrosine kinase-like receptor, exhibits effects on tumor growth due to its abnormal expression in cancer. The goal of our study was to assess the potential regulatory role exerted by the ROR2 on GC cells. Through previous bioinformatics analysis, we discovered an association between ROR2 and the G2/M phase of the GC cell cycle. However, little is known about the link between ROR2 and the G2/M phase cell cycle in GC. Here, the findings of our study indicate that ROR2, after transcribed expression by Twist1, activates the PI3K/AKT/mTOR/S6K signal transduction pathway, thus leading to the acceleration of the G2/M phase and subsequent promotion of cell proliferation in GC. Furthermore, the functional link among ROR2, Twist1, and G2/M phase of cell cycle was also confirmed in mouse xenograft tissues and human tissues. ROR2 expression was correlated with Twist expression and lower survival in vivo. Notably, our suggestion is that focusing on ROR2 as a potential therapeutic approach could show potential for the management of GC.

Role of the Ror family receptors in Wnt5a signaling

Ror-family receptors, Ror1 and Ror2, are type I transmembrane proteins that possess an extracellular cysteine-rich domain, which is conserved throughout the Frizzled-family receptors and is a binding site for Wnt ligands. Both Ror1 and Ror2 function primarily as receptors or co-receptors for Wnt5a to activate the β-catenin-independent, non-canonical Wnt signaling, thereby regulating cell polarity, migration, proliferation, and differentiation depending on the context. Ror1 and Ror2 are expressed highly in many tissues during embryogenesis but minimally or scarcely in adult tissues, with some exceptions. In contrast, Ror1 and Ror2 are expressed in many types of cancers, and their high expression often contributes to the progression of the disease. Therefore, Ror1 and Ror2 have been proposed as potential targets for the treatment of the malignancies. In this review, we provide an overview of the regulatory mechanisms of Ror1/Ror2 expression and discuss how Wnt5a-Ror1/Ror2 signaling is mediated and regulated by their interacting proteins.

The non-canonical Wnt receptor Ror2 is required for cartilage cell polarity and morphogenesis of the craniofacial skeleton in zebrafish

Non-canonical/β-catenin-independent Wnt signaling plays crucial roles in tissue/cell polarity in epithelia, but its functions have been less well studied in mesenchymal tissues, such as the skeleton. Mutations in non-canonical Wnt signaling pathway genes cause human skeletal diseases such as Robinow syndrome and Brachydactyly Type B1, which disrupt bone growth throughout the endochondral skeleton. Ror2 is one of several non-canonical Wnt receptor/co-receptors. Here, we show that ror2-/- mutant zebrafish have craniofacial skeletal defects, including disruptions of chondrocyte polarity. ror1-/- mutants appear to be phenotypically wild type, but loss of both ror1 and ror2 leads to more severe cartilage defects, indicating partial redundancy. Skeletal defects in ror1/2 double mutants resemble those of wnt5b-/- mutants, suggesting that Wnt5b is the primary Ror ligand in zebrafish. Surprisingly, the proline-rich domain of Ror2, but not its kinase domain, is required to rescue its function in mosaic transgenic experiments in ror2-/- mutants. These results suggest that endochondral bone defects in ROR-related human syndromes reflect defects in cartilage polarity and morphogenesis.

[Mage-D1 binding to activated p75NTR positively regulates mineralization of rat ectomesenchymal stem cells in vitro]

OBJECTIVE

To detect the binding of Mage-D1 with activated p75NTR and explore their role in regulating mineralization of ectomesenchymal stem cells (EMSCs).

METHODS

EMSCs were isolated from the tooth germs of embryonic SD rats (19.5 days of gestation) by tissue explant culture and were identified for surface markers using flow cytometry. The cultured cells were divided into blank control group, 100 ng/mL nerve growth factor (NGF) stimulation group, and lentivirus-mediated Mage-D1 interference (SH-Mage-D1) group. Proximity ligation assay was used to detect the binding of Mage-D1 with activated p75NTR in the EMSCs, and the binding strength was compared among the 3 groups. Alizarin red staining and ALP staining were used to observe mineralization of the induced cells. The expressions of ALP, Runx2, OCN, BSP, OPN, Msx1 and Dlx1 at both the mRNA and protein levels were detected using RT-PCR and Western blotting.

RESULTS

The isolated EMSCs expressed high levels of cell surface markers CD44, CD90, CD29, CD146, and CD105 with a low expression of CD45. The results of proximity ligation assay showed that the binding of Mage-D1 with activated p75NTR in the cells increased over time, and the binding strength was significantly greater in NFG-treated cells than in the cells in the other two groups (P < 0.05). Alizarin red staining and ALP staining of the induced cells showed that the changes in the mineralization nodules were consistent with those of ALP activity. The cells treated with 100 ng/mL NGF exhibited significantly increased expressions of ALP, Runx2, OCN, BSP, OPN, Col1, Msx1 and Dlx1 as compared with the cells in the other two groups (P < 0.05).

CONCLUSION

Mage-D1 directly binds to activated p75NTR in embryonic rat EMSCs to positively regulate the mineralization of the EMSCs.

Emerging roles of the MAGE protein family in stress response pathways

The melanoma antigen (MAGE) proteins all contain a MAGE homology domain. MAGE genes are conserved in all eukaryotes and have expanded from a single gene in lower eukaryotes to ∼40 genes in humans and mice. Whereas some MAGEs are ubiquitously expressed in tissues, others are expressed in only germ cells with aberrant reactivation in multiple cancers. Much of the initial research on MAGEs focused on exploiting their antigenicity and restricted expression pattern to target them with cancer immunotherapy. Beyond their potential clinical application and role in tumorigenesis, recent studies have shown that MAGE proteins regulate diverse cellular and developmental pathways, implicating them in many diseases besides cancer, including lung, renal, and neurodevelopmental disorders. At the molecular level, many MAGEs bind to E3 RING ubiquitin ligases and, thus, regulate their substrate specificity, ligase activity, and subcellular localization. On a broader scale, the MAGE genes likely expanded in eutherian mammals to protect the germline from environmental stress and aid in stress adaptation, and this stress tolerance may explain why many cancers aberrantly express MAGEs Here, we present an updated, comprehensive review on the MAGE family that highlights general characteristics, emphasizes recent comparative studies in mice, and describes the diverse functions exerted by individual MAGEs.

ROR2 knockdown suppresses breast cancer growth through PI3K/ATK signaling

The receptor tyrosine kinase like orphan receptor 2 (ROR2) has been implicated in the pathogenesis of a variety of human cancers, including breast cancer. Here, we analyzed the clinical significance of ROR2 in breast cancer (BC) progression, and its function in the regulation of BC cell proliferation and growth. Analysis of ROR2 mRNA levels in 45 BC tissues and adjacent non-tumor tissues revealed that ROR2 expression was significantly increased in BC tissues, and that it correlated with tumor diameter. Kaplan-Meier disease-free survival (DFS) analysis demonstrated that BC patients with higher ROR2 expression had lower DFS. Knockdown of ROR2 suppressed in vitro proliferation of BC cells and promoted apoptosis, while ROR2 overexpression induced BC cell proliferation and suppressed apoptosis. Importantly, ROR2 suppression also reduced the tumor growth in mouse BC xenografts, indicating that ROR2 promotes BC tumorigenesis in vivo. In addition, our data revealed that ROR2 promotes proliferation of BC cells by activating the PI3K/AKT signaling pathway. Together, our results indicate that ROR2 acts as an oncogenic gene in breast cancer, and suggest that the ROR2/PI3K/AKT regulatory network contributes to breast cancer progression.

Genetic interactions between Ror2 and Wnt9a, Ror1 and Wnt9a and Ror2 and Ror1: Phenotypic analysis of the limb skeleton and palate in compound mutants

Mutations in the human receptor tyrosine kinase ROR2 are associated with Robinow syndrome (RRS) and brachydactyly type B1. Amongst others, the shortened limb phenotype associated with RRS is recapitulated in Ror2^-/- mutant mice. In contrast, Ror1^-/- mutant mice are viable and show no limb phenotype. Ror1^-/- ;Ror2^-/- double mutants are embryonic lethal, whereas double mutants containing a hypomorphic Ror1 allele (Ror1^hyp ) survive up to birth and display a more severe shortened limb phenotype. Both orphan receptors have been shown to act as possible Wnt coreceptors and to mediate the Wnt5a signal. Here, we analyzed genetic interactions between the Wnt ligand, Wnt9a, and Ror2 or Ror1, as Wnt9a has also been implicated in skeletal development. Wnt9a^-/- single mutants display a mild shortening of the long bones, whereas these are severely shortened in Ror2^-/- mutants. Ror2^-/- ;Wnt9a^-/- double mutants displayed even more severely shortened long bones, and intermediate phenotypes were observed in compound Ror2;Wnt9a mutants. Long bones were also shorter in Ror1^hyp/hyp ;Wnt9a^-/- double mutants. In addition, Ror1^hyp/hyp ;Wnt9a^-/- double mutants displayed a secondary palate cleft phenotype, which was not present in the respective single mutants. Interestingly, 50% of compound mutant pups heterozygous for Ror2 and homozygous mutant for Ror1 also developed a secondary palate cleft phenotype.

Knockdown of NRAGE induces odontogenic differentiation by activating NF-κB signaling in mouse odontoblast-like cells

PURPOSE

Neurotrophin receptor-interacting MAGE homologue (Nrage) plays an important role in bone development and the metabolism of normal skeletal structures. Our previous study showed that Nrage inhibited the odontogenic differentiation of mouse dental pulp cells. However, the potential roles and mechanism of Nrage in regulating odontogenic differentiation are unknown. The aim of this study was to investigate the molecular mechanism of Nrage in odontogenic differentiation of mouse odontoblast-like cells.

MATERIALS AND METHODS

Endogenous expression of Nrage was stably downregulated by lentivirus-mediated shRNA. Mineralized nodules formation was detected by alizarin red S staining. Dmp-1, Dspp, and ALP mRNA and protein levels were detected by qRT-PCR and western blotting, respectively. In addition, ALPase activity was detected. Confocal microscopy and co-immunoprecipitation (co-IP) were used to analyze the interactions between NRAGE and NF-κB signaling molecules. An IKK inhibitor was also used in the study.

RESULTS

NRAGE expression in odontoblasts was downregulated during mouse first maxillary molar development. Moreover, NRAGE expression was downregulated during odontogenic differentiation of odontoblast-like cells. NRAGE knockdown significantly upregulated DMP1 and DSP expression, increased ALPase activity, and promoted mineralized nodule formation. In addition, NRAGE knockdown increased the translocation of NF-κB1 to the nucleus and phosphorylation levels of p65. Co-IP results showed that NRAGE bound to IKKβ. Most importantly, the promoting effect of Nrage knockdown on odontoblastic differentiation was reduced after treatment with an IKK inhibitor.

CONCLUSIONS

Our data confirmed that NRAGE is an important regulator of odontogenic differentiation of odontoblasts by inhibiting the NF-κB signaling pathway through binding to IKKβ.

ABBREVIATIONS

Nrage: neurotrophin receptor-interacting MAGE homologue; DSP: dentin sialophospho protein; DMP-1: dentin matrix protein-1; BMP: bone morphogenetic protein; Wnt: wingless; NF-κB: nuclear factor of activated B cells; DAPI: 4',6-diamidino-2-phenylindole; KO: knockout; DPCs: dental pulp cells; AA: ascorbic acid; β-Gly: β-glycerophosphate; Dex: dexamethasone; co-IP: co-immunoprecipitation; IκB: inhibitor of NF-κB; IKK: IκB kinase.

Inhibition of PPARγ, adipogenesis and insulin sensitivity by MAGED1

Peroxisome proliferator-activated receptor-γ (PPARγ) is a master regulator of adipogenesis and a target of the thiazolidinedione (TZD) class of antidiabetic drugs; therefore, identifying novel regulators of PPARγ action in adipocytes is essential for the future development of therapeutics for diabetes. MAGE family member D1 (MAGED1), by acting as an adaptor for ubiquitin-dependent degradation pathways and a co-factor for transcription, plays an important role in neural development, cell differentiation and circadian rhythm. Here, we showed that MAGED1 expression was downregulated during adipogenesis and loss of MAGED1 promoted preadipocyte proliferation and differentiation in vitro. MAGED1 bound to PPARγ and suppressed the stability and transcriptional activity of PPARγ. Compared to WT littermates, MAGED1-deficient mice showed increased levels of PPARγ protein and its target genes, more CD29+CD34+Sca-1+ adipocyte precursors and hyperplasia of white adipose tissues (WATs). Moreover, MAGED1-deficient mice developed late-onset obesity as a result of decreased energy expenditure and physical activity. However, these mice were metabolically healthy as shown by improved glucose clearance and insulin sensitivity, normal levels of serum lipids and enhanced secretion of adipokines such as leptin and adiponectin. Taken together, our data identify MAGED1 as a novel negative regulator of PPARγ activity, adipogenesis and insulin sensitivity in mice. MAGED1 might therefore serve as a novel pharmaceutical target to treat obesity-associated insulin resistance.

The biochemistry, signalling and disease relevance of RYK and other WNT-binding receptor tyrosine kinases

The receptor tyrosine kinases (RTKs) are a well-characterized family of growth factor receptors that have central roles in human disease and are frequently therapeutically targeted. The RYK, ROR, PTK7 and MuSK subfamilies make up an understudied subset of WNT-binding RTKs. Numerous developmental, stem cell and pathological roles of WNTs, in particular WNT5A, involve signalling via these WNT receptors. The WNT-binding RTKs have highly context-dependent signalling outputs and stimulate the β-catenin-dependent, planar cell polarity and/or WNT/Ca²⁺ pathways. RYK, ROR and PTK7 members have a pseudokinase domain in their intracellular regions. Alternative signalling mechanisms, including proteolytic cleavage and protein scaffolding functions, have been identified for these receptors. This review explores the structure, signalling, physiological and pathological roles of RYK, with particular attention paid to cancer and the possibility of therapeutically targeting RYK. The other WNT-binding RTKs are compared with RYK throughout to highlight the similarities and differences within this subset of WNT receptors.

Diverse roles for the ror-family receptor tyrosine kinases in neurons and glial cells during development and repair of the nervous system

The Ror-family of receptor tyrosine kinases (RTKs) are involved critically in tissue genesis and organogenesis during development. In mammals, Ror1 and Ror2, members of the Ror-family RTKs, have been shown to mediate cell polarity, migration, proliferation, and differentiation through the activation of noncanonical Wnt signaling by acting as receptors or co-receptors for Wnt5a. Nematodes bearing mutations within the cam-1 gene, encoding a Ror2 ortholog, exhibit defects in various developmental processes of the nervous system, including neuronal cell migration, polarization, axonal extension, and synaptic transmission. In mice, Ror2 and/or Ror1 are also shown to play roles in regulating neurite extension, synapse formation, and synaptic transmission of hippocampal neurons, indicating that the Ror-family RTKs have evolutionarily conserved functions at least in part in neurons during development. Furthermore, Ror2 and/or Ror1 are expressed in neural stem/progenitor cells of the developing brain and in astrocytes of the adult brain after injury, and they play important roles in regulating cell proliferation under these different contexts. In this article, we overview recent advances in our understanding of the roles of the Ror-family RTKs in the development and repair of the nervous system and discuss their potential for therapeutic targets to neurodegenerative diseases. Developmental Dynamics 247:24-32, 2018. © 2017 Wiley Periodicals, Inc.

ROR-Family Receptor Tyrosine Kinases

ROR-family receptor tyrosine kinases form a small subfamily of receptor tyrosine kinases (RTKs), characterized by a conserved, unique domain architecture. ROR RTKs are evolutionary conserved throughout the animal kingdom and act as alternative receptors and coreceptors of WNT ligands. The intracellular signaling cascades activated downstream of ROR receptors are diverse, including but not limited to ROR-Frizzled-mediated activation of planar cell polarity signaling, RTK-like signaling, and antagonistic regulation of WNT/β-Catenin signaling. In line with their diverse repertoire of signaling functions, ROR receptors are involved in the regulation of multiple processes in embryonic development such as development of the axial and paraxial mesoderm, the nervous system and the neural crest, the axial and appendicular skeleton, and the kidney. In humans, mutations in the ROR2 gene cause two distinct developmental syndromes, recessive Robinow syndrome (RRS; MIM 268310) and dominant brachydactyly type B1 (BDB1; MIM 113000). In Robinow syndrome patients and animal models, the development of multiple organs is affected, whereas BDB1 results only in shortening of the distal phalanges of fingers and toes, reflecting the diversity of functions and signaling activities of ROR-family RTKs. In this chapter, we give an overview on ROR receptor structure and function. We discuss their signaling functions and role in vertebrate embryonic development with a focus on those developmental processes that are affected by mutations in the ROR2 gene in human patients.

p75 neurotrophin receptor regulates differential mineralization of rat ectomesenchymal stem cells

OBJECTIVES

The aim of this study was to investigate whether p75NTR (p75 neurotrophin receptor) regulates differential mineralization capacity of rEMSCs (rat ectomesenchymal stem cells) and underlying mechanisms associated with Mage-D1 (melanoma-associated antigens-D1).

MATERIALS AND METHODS

Immunohistochemical staining of p75NTR in developing tooth germs was performed on E12.5d (embryonic 12.5 days) and E19.5d (embryonic 19.5 days). E12.5d EMSCs and E19.5d EMSCs were isolated in the same pregnant Sprague-Dawley rats from embryonic maxillofacial processes and tooth germs. p75NTR small-interfering RNA, p75NTR overexpression plasmid, Mage-D1 small-interfering RNA and recombined rat NGF were used to transfect cells.

RESULTS

p75NTR was expressed in epithelial-mesenchymal interaction areas at E12.5d and E19.5d tooth germ development stages. E19.5d EMSCs had higher p75NTR expression levels and differential mineralization capacity but lower levels of cell proliferation. Under induction by mineralized culture medium, the potential of differential mineralization had identical trends in regulation of p75NTR in EMSCs; Mage-D1 did not fluctuate and TrkA was not expressed. Binding of p75NTR and Mage-D1 were detected. Mage-D1 knockdown significantly down-regulated expression of related genes, which NGF could not rescue.

CONCLUSION

p75NTR participated in tooth germ development stages and mediated differential mineralization of EMSCs. p75NTR played a critical role in regulating the potential of differential mineralization of EMSCs. Mage-D1 seemed to act as a bridge in the underlying mechanism of effects of p75NTR.

Complex roles of NRAGE on tumor

NRAGE, also known as Dlxin-1or MAGE-D1, is a member of type II melanoma-associated antigen (MAGE) and plays an essential role in life activities, including differentiation, apoptosis, and cell cycle. Studies increasingly found that NRAGE is closely related to the tumor events, such as tumor occurrence, invasion, and metastasis. However, complex and contradictory functions of NRAGE in different circumstances are observed, suggesting that NRAGE is unique from other MAGE gene family members. This review summarizes recent findings concerning the structure and biological functions of NRAGE, which may provide a basis for a more comprehensive understanding of and further research on NRAGE.

Essential role of Wnt5a-Ror1/Ror2 signaling in metanephric mesenchyme and ureteric bud formation

Spatiotemporally regulated interaction between the metanephric mesenchyme (MM) and Wolffian duct (WD) is essential for the induction of a single ureteric bud (UB). The MM then interacts with the tip of the UB to induce outgrowth and branching of the UB, which in turn promotes growth of the adjacent MM. The Ror family receptor tyrosine kinases, Ror1 and Ror2, have been shown to act as receptors for Wnt5a to mediate noncanonical Wnt signaling. Previous studies have shown that Ror2-mutant mice exhibit ectopic formation of the UB, due to abnormal juxtaposition of the MM to the WD. We show here that both Ror1 and Ror2 are expressed in the mesenchyme between the MM and WD during UB formation. Although Ror1-mutant mice show no apparent defects in UB formation, Ror1;Ror2-double-mutant mice exhibit either defects in UB outgrowth and branching morphogenesis, associated with the loss of the MM from the UB domain, or ectopic formation of the UB. We also show genetic interactions between Ror1 and Wnt5a during UB formation. These findings suggest that Wnt5a-Ror1/Ror2 signaling regulates cooperatively the formation of the MM at the proper position to ensure normal development of the UB.

Identification of novel NRAGE involved in the radioresistance of esophageal cancer cells

Radiotherapy (RT) is one main method for the treatment of esophageal squamous cell carcinoma (ESCC), and the radioresistance is the predominant cause of patients with local recurrence. The previous results of gene microarray and subsequent verification showed that NRAGE might be involved in radiation resistance of ESCC cells. In this study, we reestablished human esophageal carcinoma radioresistant cell lines TE13R120 and ECA109R60 with gradient dose irradiation as previously reported, respectively. NRAGE expression was high in TE13R120 and ECA109R60 cells and was correlative with ionizing radiation (IR) resistance in clinic. However, the radiosensitivity of TE13R120 cells had a remarkable increase detected by colony formation assays after siRNA against NRAGE (siNRG) transfection into TE13R120 cells. Compared with TE13 cells, an increasing number of TE13R120 cells with NRAGE overexpression in S phase and a lower ratio in G2/M were observed by flow cytometry method (FCM). Intriguingly, the above changes were partially reversed in TE13R120 cells treated with siNRG. More importantly, the ectopic subcellular localization of NRAGE mediated nuclear translocation of β-catenin which may be one reason of IR resistance of esophageal carcinoma cell. These data indicate that NRAGE extremely may be a pivotal factor involved in Wnt/β-catenin signal pathway, mediating nuclear translocation of β-catenin and then facilitating the formation of radioresistance of ESCC.

NRAGE promotes cell proliferation by stabilizing PCNA in a ubiquitin-proteasome pathway in esophageal carcinomas

Neurotrophin receptor-interacting melanoma antigen-encoding gene homolog (NRAGE) is generally recognized as a tumor suppressor as it induces cell apoptosis and suppresses cell metastasis. However, it has recently been reported that NRAGE is overexpressed in lung cancer, melanoma and colon cancer, implicating a complicated role of NRAGE as we have expected. In the study, we aim to elucidate the functional roles and molecular mechanisms of NRAGE in esophageal carcinoma. We found that both NRAGE mRNA and protein were significantly overexpressed in esophageal tumor tissues. Consistently, both in vivo and in vitro analyses demonstrated that knockdown of NRAGE apparently inhibited cell growth, and cell cycle analysis further demonstrated that NRAGE knockdown cells were mainly arrested in G2M cell phase, accompanied with an apparent reduction of S phase. In the process of exploring molecular mechanisms, we found that either knockdown in vitro or knockout in vivo of NRAGE reduced proliferating cell nuclear antigen (PCNA) protein, expression of which could completely rescue the inhibited proliferation in NRAGE defective cells. Furthermore, NRAGE physically interacted with PCNA in esophageal cancer cells through DNA polymerase III subunit, and knockdown of NRAGE facilitated PCNA K48-linked polyubiquitination, leading PCNA to the proteasome-dependent degradation and a ubiquitin-specific protease USP10 was identified to be a key regulator in the process of K48 polyubiquitination in NRAGE-deleted cells. In conclusion, our study highlights a unique role of NRAGE and implies that NRAGE is likely to be an attractive oncotarget in developing novel genetic anticancer therapeutic strategies for esophageal squamous cell carcinomas.

Maged1 co-interacting with CREB through a hexapeptide repeat domain regulates learning and memory in mice

Maged1 is a member of the type II melanoma antigen (MAGE) family of proteins, which is highly conserved in the brain between mouse and human. Recently, Maged1 has been reported to be involved in depression and impaired sexual behavior. However, the role of Maged1 in learning and memory remains unknown. The aim of the present study was therefore to investigate whether Maged1 deficiency can impair learning and memory formation. By behavioral tests and electrophysiological recording, we observed that 5-6-month-old Maged1 knockout mice displayed the reduced basal synaptic transmission, pronounced hippocampal dysfunction, impaired spatial learning, and a deficit in long-term potentiation induction. Data from immunohistochemical and Western blot showed the reduced dendritic spine density and the number of synapses in the hippocampus of the Maged1 knockout mice, and Maged1 deficiency prevented the interaction of Maged1 with cAMP response element-binding protein (CREB). Furthermore, by chromatin immunoprecipitation and luciferase assay, we observed the downregulated activity of CREB and the suppressed CREB-dependent transcription after deficiency of Maged1, which lead to the decreased levels of brain-derived neurotrophic factor. Taken together, our results provide the evidence that Maged1 is involved in synaptic transmission and hippocampus-dependent learning and memory formation.

The role of Ryk and Ror receptor tyrosine kinases in Wnt signal transduction

Receptor tyrosine kinases of the Ryk and Ror families were initially classified as orphan receptors because their ligands were unknown. They are now known to contain functional extracellular Wnt-binding domains and are implicated in Wnt-signal transduction in multiple species. Although their signaling mechanisms still remain to be resolved in detail, both Ryk and Ror control important developmental processes in different tissues. However, whereas many other Wnt-signaling responses affect cell proliferation and differentiation, Ryk and Ror are mostly associated with controlling processes that rely on the polarized migration of cells. Here we discuss what is currently known about the involvement of this exciting class of receptors in development and disease.

Ror2-Src signaling in metastasis of mouse melanoma cells is inhibited by NRAGE

The receptor tyrosine kinase (RTK) Ror2 plays important roles in developmental morphogenesis and mediates the filopodia formation in Wnt5a-induced cell migration. However, the function of Ror2 in noncanonical Wnt signaling resulting in cancer metastasis is largely unknown. Here, we show that Ror2 expression is higher in the highly metastatic murine B16-BL6 melanoma cells than in the low metastatic variant B16 cells. Overexpression of Ror2 increases the metastasis ability of B16 cells, and knockdown of Ror2 reduces the migration ability of B16-BL6 cells. Furthermore, the inhibition of Src kinase activity is critical for the Ror2-mediated cell migration upon Wnt5a treatment. The C-terminus of Ror2, which is deleted in brachydactyly type B (BDB), is essential for the mutual interaction with the SH1 domain of Src. Intriguingly, the Neurotrophin receptor-interacting MAGE homologue (NRAGE), which, as we previously reported, can remodel the cellular skeleton and inhibit cell-cell adhesion and metastasis of melanoma and pancreatic cancer, sharply blocks the interaction between Src and Ror2 and inhibits Ror2-mediated B16 cell migration by decreasing the activity of Src and focal adhesion kinase (FAK). Our data show that Ror2 is a potential factor in the tumorigenesis and metastasis in a Src-dependent manner that is negatively regulated by NRAGE.

Alternative Wnt pathways and receptors

In addition to activating β-catenin/TCF transcriptional complexes, Wnt proteins can elicit a variety of other responses. These are often lumped together under the denominator "alternative" or "non-canonical" Wnt signaling, but they likely comprise distinct signaling events. In this article, I discuss how the use of different ligand and receptor combinations is thought to give rise to these alternative Wnt-signaling responses. Although many of the biochemical details remain to be resolved, it is evident that alternative Wnt signaling plays important roles in regulating tissue morphogenesis during embryonic development.

MAGE-D1 regulates expression of depression-like behavior through serotonin transporter ubiquitylation

The ubiquitin-proteasome system (UPS) controls the stability of most cellular proteins. The polymorphism of UPS-related genes is associated with major depression disorder, but less is known about the molecule that plays a role in depression by modulating the UPS. Melanoma antigen gene-D1 (MAGE-D1) interacts with RING E3 ubiquitin ligase and is implicated in protein degradation. MAGE-D1 may thus play an important role in the CNS via ubiquitylation. Here, we clarified a novel role of MAGE-D1 in emotional functions, namely its modulation of ubiquitylation to the serotonin transporter (SERT). The MAGE-D1 knock-out and knockdown by small interfering RNA (siRNA) in the prefrontal cortex showed depression-like behavior, such as a decrease in exploratory behavior in both the home cage and novel apparatus, a decrease in social interaction, increased immobility time during forced swimming and tail suspension, and a decrease in sucrose preference without any anxiety, or cognitive or motor dysfunction. Acute and chronic (28 d) administration of sertraline (10 mg/kg) and imipramine (20 mg/kg) reversed all or part of depression-like behavior in knock-out mice. In these mice, the serotonergic function in the prefrontal cortex and hippocampus was hypoactive, accompanied by hyperexpression of SERT attributable to a decrease in ubiquitylation. Furthermore, MAGE-D1 binds to SERT via the necdin homology domain. MAGE-D1 overexpression in cells resulted in a decrease in serotonin uptake activity and the protein level of SERT but an increase in ubiquitylated SERT. Together, the present findings suggest a novel role for MAGE-D1 in depressive behaviors: modulating SERT ubiquitylation.

Ror-family receptor tyrosine kinases regulate maintenance of neural progenitor cells in the developing neocortex

The Ror-family of receptor tyrosine kinases (RTKs), Ror1 and Ror2, have been shown to play crucial roles in the developmental morphogenesis by acting as receptors or co-receptors to mediate Wnt5a-induced signaling. Although Ror1, Ror2, and Wnt5a are expressed in the developing brain, little is known about their roles in the neural development. Here we show that Ror1, Ror2, and their ligand Wnt5a are highly expressed in neocortical neural progenitor cells (NPCs). siRNA-mediated suppression of Ror1, Ror2, or Wnt5a in cultured NPCs isolated from embryonic neocortex results in the reduction of βIII-tubulin-positive neurons that are produced from NPCs possibly through the generation of T-box brain 2 (Tbr2)-positive intermediate progenitors. BrdU-labeling experiments further reveal that proportion of proliferative and neurogenic NPCs, that are positive for neural progenitor cell marker (Pax6), but negative for glial cell marker (glial fibrillary acidic protein; GFAP), is reduced within a few days in culture following knockdown of these molecules, suggesting that Ror1, Ror2, and Wnt5a regulate neurogenesis through the maintenance of NPCs. Moreover, we show that Dishevelled2 (Dvl2) is involved in Wnt5a–Ror1 and Wnt5a–Ror2 signalings in NPCs, and that suppressed expression of Dvl2 indeed reduces the proportion of proliferative and neurogenic NPCs. Interestingly, suppressed or forced expression of either Ror1 or Ror2 in NPCs in the developing neocortex results in their precocious or delayed differentiation into neurons, respectively. Collectively, these results indicate that Wnt5a–Ror1 and Wnt5a–Ror2 signalings play roles in maintaining proliferative and neurogenic NPCs during neurogenesis of the developing neocortex.

Conditional deletion of Msx homeobox genes in the uterus inhibits blastocyst implantation by altering uterine receptivity

An effective bidirectional communication between an implantation-competent blastocyst and the receptive uterus is a prerequisite for mammalian reproduction. The blastocyst will implant only when this molecular cross-talk is established. Here we show that the muscle segment homeobox gene (Msh) family members Msx1 and Msx2, which are two highly conserved genes critical for epithelial-mesenchymal interactions during development, also play crucial roles in embryo implantation. Loss of Msx1/Msx2 expression correlates with altered uterine luminal epithelial cell polarity and affects E-cadherin/β-catenin complex formation through the control of Wnt5a expression. Application of Wnt5a in vitro compromised blastocyst invasion and trophoblast outgrowth on cultured uterine epithelial cells. The finding that Msx1/Msx2 genes are critical for conferring uterine receptivity and readiness to implantation could have clinical significance, because compromised uterine receptivity is a major cause of pregnancy failure in IVF programs.

Maged1, a new regulator of skeletal myogenic differentiation and muscle regeneration

BACKGROUND

In normal adult skeletal muscle, cell turnover is very slow. However, after an acute lesion or in chronic pathological conditions, such as primary myopathies, muscle stem cells, called satellite cells, are induced to proliferate, then withdraw definitively from the cell cycle and fuse to reconstitute functional myofibers.

RESULTS

We show that Maged1 is expressed at very low levels in normal adult muscle but is strongly induced after injury, during the early phase of myoblast differentiation. By comparing in vitro differentiation of myoblasts derived from wild-type or Maged1 knockout mice, we observed that Maged1 deficiency results in reduced levels of p21CIP1/WAF1, defective cell cycle exit and impaired myotube maturation. In vivo, this defect results in delayed regeneration of injured muscle.

CONCLUSIONS

These data demonstrate for the first time that Maged1 is an important factor required for proper skeletal myoblast differentiation and muscle healing.

NRAGE is a negative regulator of nerve growth factor-stimulated neurite outgrowth in PC12 cells mediated through TrkA-ERK signaling

NRAGE, also denominated as MAGE-D1 or Dlxin-1, is firstly identified as a molecule interacting with NGF low affinity receptor p75NTR. It facilitates cell cycle arrest and NGF-dependent neuronal apoptosis. Here we report that NRAGE is downregulated while p75NTR is upregulated during the process of NGF-induced neuronal differentiation of PC12 cells. Knockdown of NRAGE by RNA interference accelerates NGF-mediated neurite outgrowth. In addition, in the NRAGE-suppressed cells, NGF-induced ERK activation is increased and this activation is MEK-dependent. Conversely, NRAGE overexpression significantly represses NGF-induced ERK activation. Further studies revealed that NRAGE downregulates TrkA expression through a post-transcriptional manner and thereby blocks NGF-induced TrkA phosphrylation at tyrosine-490. Altogether, these data indicate for the first time that NRAGE is an endogenous inhibitor for NGF-induced neuronal differentiation of PC12 cells by regulating TrkA-ERK signaling.

Ror2/Frizzled complex mediates Wnt5a-induced AP-1 activation by regulating Dishevelled polymerization

The receptor tyrosine kinase Ror2 acts as a receptor or coreceptor for Wnt5a to mediate Wnt5a-induced activation of the Wnt/JNK pathway and inhibition of the beta-catenin-dependent canonical Wnt pathway. However, little is known about how Ror2 cooperates with another receptor component(s) to mediate Wnt5a signaling. We show here that Ror2 regulates Wnt5a-induced polymerization of Dishevelled (Dvl) and that this Ror2-mediated regulation of Dvl is independent of the cytoplasmic region of Ror2. Ror2 can associate with Frizzled7 (Fz7) via its extracellular cysteine-rich domain to form a receptor complex that is required for the regulation of Dvl and activation of the AP-1 promoter after Wnt5a stimulation. Suppressed expression of Fz7 indeed results in the inhibition of Wnt5a-induced polymerization of Dvl and AP-1 activation. Interestingly, both the DIX and the DEP domains of Dvl are indispensable for Dvl polymerization and subsequent AP-1 activation after Wnt5a stimulation. We further show that polymerized Dvl is colocalized with Rac1 and that suppressed expression of Rac1 inhibits Wnt5a-induced AP-1 activation. Collectively, our results indicate that Ror2/Fz receptor complex plays an important role in the Wnt5a/Rac1/AP-1 pathway by regulating the polymerization of Dvl.

Interaction of MAGED1 with nuclear receptors affects circadian clock function

The circadian clock has a central role in physiological adaption and anticipation of day/night changes. In a genetic screen for novel regulators of circadian rhythms, we found that mice lacking MAGED1 (Melanoma Antigen Family D1) exhibit a shortened period and altered rest-activity bouts. These circadian phenotypes are proposed to be caused by a direct effect on the core molecular clock network that reduces the robustness of the circadian clock. We provide in vitro and in vivo evidence indicating that MAGED1 binds to RORalpha to bring about positive and negative effects on core clock genes of Bmal1, Rev-erbalpha and E4bp4 expression through the Rev-Erbalpha/ROR responsive elements (RORE). Maged1 is a non-rhythmic gene that, by binding RORalpha in non-circadian way, enhances rhythmic input and buffers the circadian system from irrelevant, perturbing stimuli or noise. We have thus identified and defined a novel circadian regulator, Maged1, which is indispensable for the robustness of the circadian clock to better serve the organism.

Ror-family receptor tyrosine kinases in noncanonical Wnt signaling: their implications in developmental morphogenesis and human diseases

The Ror-family receptor tyrosine kinases (RTKs) play crucial roles in the development of various organs and tissues. In mammals, Ror2, a member of the Ror-family RTKs, has been shown to act as a receptor or coreceptor for Wnt5a to mediate noncanonical Wnt signaling. Ror2- and Wnt5a-deficient mice exhibit similar abnormalities during developmental morphogenesis, reflecting their defects in convergent extension movements and planar cell polarity, characteristic features mediated by noncanonical Wnt signaling. Furthermore, mutations within the human Ror2 gene are responsible for the genetic skeletal disorders dominant brachydactyly type B and recessive Robinow syndrome. Accumulating evidence demonstrate that Ror2 mediates noncanonical Wnt5a signaling by inhibiting the beta-catenin-TCF pathway and activating the Wnt/JNK pathway that results in polarized cell migration. In this article, we review recent progress in understanding the roles of noncanonical Wnt5a/Ror2 signaling in developmental morphogenesis and in human diseases, including heritable skeletal disorders and tumor invasion.

Orphan receptor kinase ROR2 is expressed in the mouse uterus

OBJECTIVE

Wingless-type mouse mammary tumor virus integration site family, member 5A (WNT5A), is expressed in mouse decidua and is thought to play an important role in decidualization. We examined expression of the receptor for WNT5A, receptor tyrosine kinase-like orphan receptor 2 (ROR2), in the uteri of cycling and pregnant mice.

STUDY DESIGN

Reverse transcription (RT)-PCR and immunohistochemistry were performed.

RESULTS

RT-PCR revealed that transcripts for Ror2, Wnt3a, Wnt5a and inhibitor of WNT signaling, Dickkopf homolog 1 (Dkk1), were present in the pregnant uterus. Immunohistochemistry revealed that in the virgin uterus, ROR2 is expressed in stromal cells and on the basal side of uterine gland and endometrial epithelial cells. During pregnancy, both the luminal and basal side of uterine gland epithelial cells expressed ROR2, stromal cell expression of ROR2 became more frequent and ROR2 expressing uterine Natural Killer (NK) cells and cells lining the maternal vascular space emerged. Immunofluorescence imaging and flow cytometry revealed that although uterine NK cells expressed ROR2, NK cells of the spleen were ROR2 negative.

CONCLUSION

The expression of ROR2 by endometrial epithelial cells may suggest WNT signaling has roles in uterine epithelial cell polarity or implantation. Expression of ROR2 by uterine NK cells may suggest WNT signaling regulates uterine NK cell functions such angiogenesis and regulation of trophoblast migration. In summary, our results show that ROR2 expression by maternal uterine cells is influenced by pregnancy.

Melanoma-Associated Antigen Family Protein-D1 Regulation of Tumor Cell Migration, Adhesion to Endothelium, and Actin Structures Reorganization in Response to Hypoxic Stress

Melanoma-associated antigen family protein-D1 (MAGE-D1) is a recently identified p75 neurotrophin receptor intracellular binding protein and functions as an adaptor that mediates multiple signaling pathways, including Dlx/Msx-mediated transcription. Here, a new regulatory function for MAGE-D1 in tumor cell motility and adhesion to endothelium is described. MAGE-D1 over-expression suppressed HeLa cell and BEL7402 cell migration, invasion, and adhesion to the monolayer of ECV304 cells. We also report that MAGE-D1 over-expression disrupted actin cytoskeleton rearrangement induced by hypoxia and down-regulated hypoxia inducible factor 1-dependent luciferase gene expression. These findings provide new insight into the ability of MAGE-D1 to suppress the motility and adhesion response of tumor cells by interfering with actin cytoskeleton reorganization and hypoxia inducible factor 1-dependent gene expression.

EBNA3C can modulate the activities of the transcription factor Necdin in association with metastasis suppressor protein Nm23-H1

Previous studies have demonstrated the interaction between the Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) and the metastatic suppressor Nm23-H1 both in vitro and in vivo (C. Subramanian, M. A. Cotter II, and E. S. Robertson, Nat. Med. 7:350-355, 2001). Importantly EBNA3C can reverse the ability of Nm23-H1 to suppress migration of human cells in vitro. EBNA3C contributes to EBV-associated human cancers by regulating transcription of a number of cellular and viral promoters as well as targeting and altering the transcription activities of the metastasis suppressor Nm23-H1. Furthermore, Necdin is a cellular protein which is highly induced in terminally differentiated cells; it contributes to the regulation of cell growth and is also known to interact with viral oncoproteins. In this report, we show that Nm23-H1 and EBNA3C can modulate the biological functions of Necdin in the context of EBV infection and transformation. The levels of Necdin were consistently lower in EBV-positive cells, and EBNA3C could change the subcellular localization of Necdin as well as rescue cells from the antiangiogenic and antiproliferative effects mediated by Necdin. We also show that Necdin directly interacts with Nm23-H1, resulting in modulation of the biochemical function of Nm23-H1 as well as the biological function of Necdin. Both EBNA3C and Nm23-H1 were able to rescue not only Necdin-mediated transcriptional repression of the downstream vascular endothelial growth factor promoter but also Necdin-mediated growth suppression and antiangiogenic effects on cancer cells. The majority of this response was mediated through amino acid residues 191 to 222 of Necdin, which are also known to be important for nuclear matrix targeting. These studies suggest a role for Necdin in the regulation of downstream cellular targets in a hypoxic environment in virus-associated human cancers.

Necdin, a Prader-Willi syndrome candidate gene, regulates gonadotropin-releasing hormone neurons during development

Prader-Willi syndrome (PWS) is a complex genetic disorder characterized by hyperphagia, obesity and hypogonadotrophic hypogonadism, all highly suggestive of hypothalamic dysfunction. The NDN gene, encoding the MAGE family protein, necdin, maps to the PWS chromosome region and is highly expressed in mature hypothalamic neurons. Adult mice lacking necdin have reduced numbers of gonadotropin-releasing hormone (GnRH) neurons, but the mechanism for this reduction is unknown. Herein, we show that, although necdin is not expressed in an immature, migratory GnRH neuronal cell line (GN11), high levels are present in a mature GnRH neuronal cell line (GT1-7). Furthermore, overexpression of necdin activates GnRH transcription through cis elements bound by the homeodomain repressor Msx that are located in the enhancer and promoter of the GnRH gene, and knock-down of necdin expression reduces GnRH gene expression. In fact, overexpression of Necdin relieves Msx repression of GnRH transcription through these elements and necdin co-immunoprecipitates with Msx from GnRH neuronal cells, indicating that necdin may activate GnRH gene expression by preventing repression of GnRH gene expression by Msx. Finally, necdin is necessary for generation of the full complement of GnRH neurons during mouse development and extension of GnRH axons to the median eminence. Together, these results indicate that lack of necdin during development likely contributes to the hypogonadotrophic hypogonadal phenotype in individuals with PWS.

RumMAGE-D the Members: Structure and Function of a New Adaptor Family of MAGE-D Proteins

MAGE genes were first described as cancer-testis antigens, which are silenced in normal adult tissues but aberrantly expressed in tumor cells. The short peptides, derived from the degradation of MAGE transcripts, are the source of antigens that cause tumor rejection reactions when presented in the context of major histocompatibility complex. The recent discovery of a subset of genes that contain the structurally conserved MAGE homology domain (MHD) has accelerated the investigation into the normal function of MAGE genes. This new type of MAGE gene is normally expressed in embryonal and adult tissue, especially the brain. MAGE-D1, also known as NRAGE or Dlxin-1, functions as an adaptor protein that mediates multiple signaling pathways, including NGFR (p75NTR) and UNC5H1-induced apoptosis and Dlx/Msx-mediated transcription. Loss of a different MAGE family member, Necdin, which works as a cell cycle regulator, may play a role in the pathogenesis of Prader-Willi syndrome, a neurobehavioral disorder. In this article, the authors discuss recent findings concerning the structure and function of new MAGE genes, primarily focusing on MAGE-D1. Because some MAGE-D subfamily proteins share significant homology within the MHD, these recent discoveries on MAGE-D1 may give insight into the function of other MAGE-D proteins.

Ror receptor tyrosine kinases: orphans no more

Receptor tyrosine kinase-like orphan receptor (Ror) proteins are a conserved family of tyrosine kinase receptors that function in developmental processes including skeletal and neuronal development, cell movement and cell polarity. Although Ror proteins were originally named because the associated ligand and signaling pathway were unknown, recent studies in multiple species have now established that Ror proteins are Wnt receptors. Depending on the cellular context, Ror proteins can either activate or repress transcription of Wnt target genes and can modulate Wnt signaling by sequestering Wnt ligands. New evidence implicates Ror proteins in planar cell polarity, an alternative Wnt pathway. Here, we review the progress made in understanding these mysterious proteins and, in particular, we focus on their function as Wnt receptors.

Wnt5a modulates glycogen synthase kinase 3 to induce phosphorylation of receptor tyrosine kinase Ror2

The receptor tyrosine kinase Ror2 plays important roles in mediating non-canonical Wnt5a signaling by activating the Wnt-JNK pathway and inhibiting the beta-catenin-TCF pathway. It has been shown that Ror2 is phosphorylated and activated by casein kinase Iepsilon when both molecules are over-expressed in cultured cells. However, it remains unknown whether or not Ror2 is phosphorylated upon Wnt5a stimulation. Here we show that Ror2 is phosphorylated on serine/threonine residues upon stimulation of cultured cells, expressing Ror2 endogenously, with Wnt5a, but not Wnt3a. It was found that treatment of cells with glycogen synthase kinase-3 (GSK-3) inhibitors (LiCl and SB216763) or small interfering RNAs (siRNAs) for GSK-3 (mainly GSK-3alpha) can inhibit Wnt5a-induced phosphorylation of Ror2. Immunoprecipitated Ror2 can also be phosphorylated by purified GSK-3alpha or GSK-3betain vitro, and ectopic co-expression of Ror2 and GSK-3 (mainly GSK-3alpha) in cultured cells results in Ror2 phosphorylation, irrespective of Wnt5a, that is sensitive to SB216763. These results indicate that GSK-3 is involved in Wnt5a-induced phosphorylation of Ror2. Moreover, it was found that Wnt5a-induced cell migration can be inhibited by SB216763 or by siRNA-mediated suppression of GSK-3alpha (and GSK-3beta) expression, further emphasizing the role(s) of GSK-3 in Wnt5a-induced signaling.

Novel Robinow syndrome causing mutations in the proximal region of the frizzled-like domain of ROR2 are retained in the endoplasmic reticulum

ROR2 is a member of the cell surface receptor tyrosine kinase (RTKs) family of proteins and is involved in the developmental morphogenesis of the skeletal, cardiovascular and genital systems. Mutations in ROR2 have been shown to cause two distinct human disorders, autosomal recessive Robinow syndrome and dominantly inherited Brachydactyly type B. The recessive form of Robinow syndrome is a disorder caused by loss-of-function mutations whereas Brachydactyly type B is a dominant disease and is presumably caused by gain-of-function mutations in the same gene. We have previously established that all the missense mutations causing Robinow syndrome in ROR2 are retained in the endoplasmic reticulum and therefore concluded that their loss of function is due to a defect in their intracellular trafficking. These mutations were in the distal portion of the frizzled-like cysteine rich domain and kringle domain. Here we report the identification of two novel mutations in the frizzled-like cysteine-rich domain of ROR2 causing Robinow syndrome. We establish the retention of the mutated proteins in the endoplasmic reticulum of HeLa cells and therefore failure to reach the plasma membrane. The clustering of Robinow-causing mutations in the extracellular frizzled-like cysteine-rich domain of ROR2 suggests a stringent requirement for the correct folding of this domain prior to export of ROR2 from the endoplasmic reticulum to the plasma membrane.

Inhibition of adenovirus-mediated human MAGE-D1 on angiogenesis in vitro and in vivo

MAGE-D1 is a member of the MAGE family of proteins, and functions as an adaptor that mediates multiple signaling pathways. The current study for the first time provides evidence for a role of MAGE-D1 in the negative regulation of angiogenic activity in vitro and in vivo models. Our findings showed that MAGE-D1 over-expression significantly suppressed the angiogenic key events such as endothelial cell migration and invasion, adhesion on collagen I substrate, and in vitro differentiation into tube-like structures under both normoxic and hypoxic conditions. MAGE-D1 over-expression also inhibited in vivo angiogenesis in Matrigel plugs that were implanted subcutaneously in mice. With further experiments, we revealed that MAGE-D1 over-expression disrupted actin cytoskeleton organization and lamellipodia formation, and down-regulated HIF-1-dependent gene expression in endothelial cells under hypoxic conditions. These findings demonstrate a new function of MAGE-D1 in the regulation of angiogenesis and provide new insight into the ability of MAGE-D1 to suppress the growth and angiogenic response of endothelial cells by interfering with HIF-1-dependent gene expression, and actin cytoskeleton reorganization, suggesting that MAGE-D1 might be a novel inhibitor of angiogenesis in vitro and in vivo.

Filopodia formation mediated by receptor tyrosine kinase Ror2 is required for Wnt5a-induced cell migration

The receptor tyrosine kinase Ror2 plays important roles in developmental morphogenesis. It has recently been shown that Ror2 mediates Wnt5a-induced noncanonical Wnt signaling by activating the Wnt–JNK pathway and inhibiting the β-catenin–TCF pathway. However, the function of Ror2 in noncanonical Wnt signaling leading to cell migration is largely unknown. We show, using genetically different or manipulated cultured cells, that Ror2 is critical for Wnt5a-induced, but not Wnt3a-induced, cell migration. Ror2-mediated cell migration requires the extracellular cysteine-rich domain (CRD), which is the binding site for Wnt5a, and the cytoplasmic proline-rich domain (PRD) of Ror2. Furthermore, Ror2 can mediate filopodia formation via actin reorganization, irrespective of Wnt5a, and this Ror2-mediated filopodia formation requires the actin-binding protein filamin A, which associates with the PRD of Ror2. Intriguingly, disruption of filopodia formation by suppressing the expression of either Ror2 or filamin A inhibits Wnt5a-induced cell migration, indicating that Ror2-mediated filopodia formation is essential for Wnt5a-induced cell migration.

ER-associated protein degradation is a common mechanism underpinning numerous monogenic diseases including Robinow syndrome

Correct folding of nascent polypeptide chains within the ER is critical for function, assembly into multi-subunit complexes and trafficking through the exocytic pathway for secretory and cell surface proteins. This process is rather inefficient, and a substantial proportion of nascent polypeptides is rejected by an ER quality control system and targeted for degradation. In some cases, only a minor fraction of nascent chains is correctly folded, and the smallest alteration to polypeptide primary structure (i.e. point mutation) can result in the complete loss of function with inherent pathological consequences; cystic fibrosis and emphysema result from such mutations. We have taken a bioinformatic approach to parse a large database of known disease susceptibility genes for candidates whose disease-associated alleles are likely prone to misfolding in the ER. Surprisingly, we find that proteins with ER-targeting signals are over represented in this database when compared with all predicted proteins in the human genome (45 versus 30%). We selected a subgroup of proteins that were positive for both an ER-targeting signal and a membrane-anchoring domain and thereby identified several ER-associated degradation diseases candidates. To determine whether our analysis had identified new ER-degradation substrates, we established that ER retention is indeed the mechanism underlying Robinow syndrome (RRS), one of the identified candidates. Specifically, mutant alleles of ROR2 that are associated with RRS are retained within the ER, whereas wild-type and non-pathogenic alleles are exported to the plasma membrane. These data both uncover a major pathogenic factor for RRS and indicate that misfolding of secretory proteins is likely to significantly contribute to human disease and morbidity.

BRCA2 suppresses cell proliferation via stabilizing MAGE-D1

Germ line mutations in BRCA2 gene predispose women to early-onset familial breast and ovarian cancer. BRCA2 is a protein of multiple functions. In addition to its role in DNA double-strand break repair, BRCA2 also plays a role in stabilization of stalled DNA replication forks, cytokinesis, transcription regulation, mammalian gametogenesis, centrosome duplication, and suppression of cell proliferation. However, how BRCA2 mutations predispose women specifically to breast and ovarian cancer remains undefined. Here we found that BRCA2 binds and stabilizes MAGE-D1, a member of the MAGE gene family of proteins. Expression of BRCA2 and MAGE-D1 synergistically suppresses cell proliferation independently of the p53 pathway. Using two MAGE-D1 RNA interferences and two cell lines expressing low or undetectable levels of MAGE-D1, we further showed that the expression of MAGE-D1 is required for BRCA2-mediated suppression of cell proliferation, indicating that MAGE-D1 is a downstream target of BRCA2 and that BRCA2 suppresses cell proliferation via stabilizing MAGE-D1. Importantly, MAGE-D1 protein expression was reduced in 6 of 16 breast carcinoma cell lines tested as compared with untransformed immortal mammary epithelial cell lines, suggesting that suppression of MAGE-D1 expression may be involved in the tumorigenesis of a subset of sporadic breast cancers.

Silymarin protects pancreatic beta-cells against cytokine-mediated toxicity: implication of c-Jun NH2-terminal kinase and janus kinase/signal transducer and activator of transcription pathways

Silymarin is a polyphenolic flavonoid that has a strong antioxidant activity and exhibits anticarcinogenic, antiinflammatory, and cytoprotective effects. Although its hepatoprotective effect has been well documented, the effect of silymarin on pancreatic beta-cells is largely unknown. In this study, the effect of silymarin on IL-1beta and/or interferon (IFN)-gamma-induced beta-cell damage was investigated using RINm5F cells and human islets. IL-1beta and/or IFN-gamma induced cell death in a time-dependent manner in RINm5F cells. The time-dependent increase in cytokine-induced cell death appeared to correlate with the time-dependent nitric oxide (NO) production. Silymarin dose-dependently inhibited both cytokine-induced NO production and cell death in RINm5F cells. Treatment of human islets with a combination of IL-1beta and IFN-gamma (IL-1beta+IFN-gamma), for 48 h and 5 d, resulted in an increase of NO production and the impairment of glucose-stimulated insulin secretion, respectively. Silymarin prevented IL-1beta+IFN-gamma-induced NO production and beta-cell dysfunction in human islets. These cytoprotective effects of silymarin appeared to be mediated through the suppression of c-Jun NH2-terminal kinase and Janus kinase/signal transducer and activator of transcription pathways. Our data show a direct cytoprotective effect of silymarin in pancreatic beta-cells and suggest that silymarin may be therapeutically beneficial for type 1 diabetes.

Modulation of GDF5/BRI-b signalling through interaction with the tyrosine kinase receptor Ror2

The brachydactylies are a group of inherited disorders of the hands characterized by shortened digits. Mutations in the tyrosine kinase receptor Ror2 cause brachydactyly type B (BDB). Mutations in GDF5, a member of the BMP/TGF-beta ligand family, cause brachydactyly type C (BDC) whereas mutations in the receptor for GDF5, BRI-b, cause brachydactyly type A2 (BDA2). There is considerable degree of phenotypic overlap between the subtypes BDB, BDC and BDA2. Here we demonstrate that all three components are involved in GDF5 induced regulation of chondrogenesis. We show that Ror2 (tyrosine kinase receptor) and BRI-b (serine/threonine kinase receptor) form a ligand independent heteromeric complex. The frizzled-like-CRD domain of Ror2 is required for this complex. Within that complex Ror2 gets transphosphorylated by BRI-b. We show that Ror2 modulates GDF5 signalling by inhibition of Smad1/5 signalling and by activating a Smad-independent pathway. Both pathways however, are needed for chondrogenic differentiation as demonstrated in ATDC5 cells. The functional interaction of Ror2 with GDF5 and BRI-b was genetically confirmed by the presence of epistatic effects in crosses of Ror2, BRI-b and Gdf5 deficient mice. These results indicate for the first time a direct interaction of Ser/Thr- and Tyr-Kinase receptors and provide evidence for modulation of the Smad-pathway and GDF5 triggered chondrogenesis.

The orphan receptor tyrosine kinase Ror2 modulates canonical Wnt signaling in osteoblastic cells

Ror2 is an orphan receptor tyrosine kinase that plays crucial roles in developmental morphogenesis, particularly of the skeleton. We have identified human Ror2 as a novel regulator of canonical Wnt signaling in osteoblastic (bone-forming) cells with selective activities, enhancing Wnt1 but antagonizing Wnt3. Immunoprecipitation studies demonstrated physical interactions between human Ror2 and mammalian Wnt1 and Wnt3. Functionally, Ror2 antagonized Wnt1- and Wnt3-mediated stabilization of cytosolic beta-catenin in osteoblastic cells. However, Ror2 had opposing effects on a more distal step of canonical Wnt signaling: it potentiated Wnt1 activity but inhibited Wnt3 function as assessed by changes in Wnt-responsive reporter gene activity. Despite binding to Ror2, neither Wnt1 nor Wnt3 altered receptor activity as assessed by levels of Ror2 autophosphorylation. The ability of Ror2 to regulate canonical Wnt signaling in osteoblastic cells should have physiological consequences in bone, because Wnt signaling is known to modulate osteoblast survival and differentiation. Expression of Ror2 mRNA was highly regulated in a biphasic manner during human osteoblast differentiation, being virtually undetectable in pluripotent stem cells, increasing 300-fold in committed preosteoblasts, and disappearing again in osteocytes. Furthermore, Ror2 expression in osteoblasts was suppressed by the Wnt antagonist, secreted frizzled-related protein 1. The regulated expression of Ror2 during osteoblast differentiation, its inverse expression pattern with secreted frizzled-related protein 1, and its ability to modulate Wnt signaling in osteoblastic cells suggest that Ror2 may regulate bone formation.

The receptor tyrosine kinase Ror2 associates with and is activated by casein kinase Iepsilon

Ror2, a member of the mammalian Ror family of receptor tyrosine kinases, plays important roles in developmental morphogenesis, although the mechanism underlying activation of Ror2 remains largely elusive. We show that when expressed in mammalian cells, Ror2 associates with casein kinase Iepsilon (CKIepsilon), a crucial regulator of Wnt signaling. This association occurs primarily via the cytoplasmic C-terminal proline-rich domain of Ror2. We also show that Ror2 is phosphorylated by CKIepsilon on serine/threonine residues, in its C-terminal serine/threonine-rich 2 domain, resulting in autophosphorylation of Ror2 on tyrosine residues. Furthermore, it was found that association of Ror2 with CKIepsilon is required for its serine/threonine phosphorylation by CKIepsilon. Site-directed mutagenesis of tyrosine residues in Ror2 reveals that the sites of phosphorylation are contained among the five tyrosine residues in the proline-rich domain but not among the four tyrosine residues in the tyrosine kinase domain. Moreover, we show that in mammalian cells, CKIepsilon-mediated phosphorylation of Ror2 on serine/threonine and tyrosine residues is followed by the tyrosine phosphorylation of G protein-coupled receptor kinase 2, a kinase with a developmental expression pattern that is remarkably similar to that of Ror2. Intriguingly, a mutant of Ror2 lacking five tyrosine residues, including the autophosphorylation sites, fails to tyrosine phosphorylate G protein-coupled receptor kinase 2. This indicates that autophosphorylation of Ror2 is required for full activation of its tyrosine kinase activity. These findings demonstrate a novel role for CKIepsilon in the regulation of Ror2 tyrosine kinase.