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

The endocannabinoid anandamide inhibits cholangiocarcinoma growth via activation of the noncanonical Wnt signaling pathway

Cholangiocarcinomas are cancers that have poor prognosis and limited treatment options. The noncanonical Wnt pathway is mediated predominantly by Wnt 5a, which activates a Ca(2+)-dependent pathway involving protein kinase C, or a Ca(2+)-independent pathway involving the orphan receptor Ror2 and subsequent activation of Jun NH(2)-terminal kinase (JNK). This pathway is associated with growth-suppressing effects in numerous cell types. We have shown that anandamide decreases cholangiocarcinoma growth in vitro. Therefore, we determined the effects of anandamide on cholangiocarcinoma tumor growth in vivo using a xenograft model and evaluated the effects of anandamide on the noncanonical Wnt signaling pathways. Chronic administration of anandamide decreased tumor growth and was associated with increased Wnt 5a expression in vitro and in vivo. Treatment of cholangiocarcinoma cells with recombinant Wnt 5a decreased cell proliferation in vitro. Neither anandamide nor Wnt 5a affected intracellular calcium release, but both increased the JNK phosphorylation. Stable knockdown of Wnt 5a or Ror2 expression in cholangiocarcinoma cells abolished the effects of anandamide on cell proliferation and JNK activation. Modulation of the endocannabinoid system may be important in cholangiocarcinoma treatment. The antiproliferative actions of the noncanonical Wnt signaling pathway warrants further investigation to dissect the mechanism by which this may occur.

Wnt5a regulates directional cell migration and cell proliferation via Ror2-mediated noncanonical pathway in mammalian palate development

Tissue and molecular heterogeneities are present in the developing secondary palate along the anteroposterior (AP) axis in mice. Here, we show that Wnt5a and its receptor Ror2 are expressed in a graded manner along the AP axis of the palate. Wnt5a deficiency leads to a complete cleft of the secondary palate, which exhibits distinct phenotypic alterations at histological, cellular and molecular levels in the anterior and posterior regions of the palate. We demonstrate that there is directional cell migration within the developing palate. In the absence of Wnt5a, this directional cell migration does not occur. Genetic studies and in vitro organ culture assays further demonstrate a role for Ror2 in mediating Wnt5a signaling in the regulation of cell proliferation and migration during palate development. Our results reveal distinct regulatory roles for Wnt5a in gene expression and cell proliferation along the AP axis of the developing palate, and an essential role for Wnt5a in the regulation of directional cell migration.

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.

CaSR stimulates secretion of Wnt5a from colonic myofibroblasts to stimulate CDX2 and sucrase-isomaltase using Ror2 on intestinal epithelia

To understand whether extracellular calcium-sensing receptor (CaSR) expression on colonic myofibroblast cells (18Co) contributed to epithelial homeostasis, we activated the CaSR with 5 mM Ca(2+), screened by RT-PCR Wnt family members, and measured their secretion. Transcripts for Wnt 1, 2, 2b, 3a, 4, and 7a were either absent or unchanged whereas Wnt3 decreased and Wnt5a increased. We assessed Wnt5a secretion by Western blot. High Ca(2+) (5 mM) substantially increased Wnt5a secretion; small interfering RNA (siRNA) against the CaSR reduced this to constitutive amounts. Expression of Wnt5a plasmid but not Wnt1 or Wnt3a increased caudal homeodomain factor CDX2 transcripts and protein in HT-29 adenocarcinoma cells. Wnt5a increased activity of a sucrase-isomaltase (SI) promoter in Caco-2BBE cells. Wnt5a protein stimulation of CDX2 transcripts and protein and SI reporter were increased by overexpression of wild-type Ror2, a Wnt5a receptor, and reduced with siRNA against Ror2. CaSR activation of HT-29 cells increased Ror2 protein expression. Ror2 protein was expressed in mouse jejunum from crypt base to villus tip and in the colon on surface epithelia. Our results show that activation of a G protein-coupled receptor, the CaSR, stimulates secretion of Wnt5a from myofibroblasts. Stimulation of epithelia by the CaSR increased the expression of a receptor for Wnt5a, the tyrosine kinase Ror2, suggesting existence of a unique paracrine relationship for CDX2 homoeostasis in the intestine and revealing new contributions of CaSR-activated myofibroblasts to intestinal stem cell niche microenvironments.

Cthrc1 selectively activates the planar cell polarity pathway of Wnt signaling by stabilizing the Wnt-receptor complex

Vertebrate Wnt proteins activate several distinct pathways. Intrinsic differences among Wnt ligands and Frizzled (Fzd) receptors, and the availability of pathway-specific coreceptors, LRP5/6, and Ror2, affect pathway selection. Here, we show that a secreted glycoprotein, Cthrc1, is involved in selective activation of the planar cell polarity (PCP) pathway by Wnt proteins. Although Cthrc1 null mutant mice appeared normal, the introduction of a heterozygous mutation of a PCP gene, Vangl2, resulted in abnormalities characteristic of PCP mutants. In HEK293T cells, Cthrc1 activated the PCP pathway but suppressed the canonical pathway. Cell-surface-anchored Cthrc1 bound to Wnt proteins, Fzd proteins, and Ror2 and enhanced the interaction of Wnt proteins and Fzd/Ror2 by forming the Cthrc1-Wnt-Fzd/Ror2 complex. Consistent with this, Ror2 mutant mice also showed PCP-related abnormalities in the inner ear. These results suggest that Cthrc1 is a Wnt cofactor protein that selectively activates the Wnt/PCP pathway by stabilizing ligand-receptor interaction.

Receptor tyrosine kinase Ror2 mediates Wnt5a-induced polarized cell migration by activating c-Jun N-terminal kinase via actin-binding protein filamin A

The receptor tyrosine kinase Ror2 has recently been shown to act as an alternative receptor or coreceptor for Wnt5a and to mediate Wnt5a-induced migration of cultured cells. However, little is known about the molecular mechanism underlying this migratory process. Here we show by wound-healing assays that Ror2 plays critical roles in Wnt5a-induced cell migration by regulating formation of lamellipodia and reorientation of microtubule-organizing center (MTOC). Wnt5a stimulation induces activation of the c-Jun N-terminal kinase JNK at the wound edge in a Ror2-dependent manner, and inhibiting JNK activity abrogates Wnt5a-induced lamellipodia formation and MTOC reorientation. Additionally, the association of Ror2 with the actin-binding protein filamin A is required for Wnt5a-induced JNK activation and polarized cell migration. We further show that Wnt5a-induced JNK activation and MTOC reorientation can be suppressed by inhibiting PKCzeta. Taken together, our findings indicate that Wnt5a/Ror2 activates JNK, through a process involving filamin A and PKCzeta, to regulate polarized cell migration.

Wnt5a is expressed in murine and human atherosclerotic lesions

Atherosclerosis is an inflammatory disease involving the accumulation of macrophages in the intima. Wnt5a is a noncanonical member of the Wnt family of secreted glycoproteins. Recently, human macrophages have been shown to express Wnt5a upon stimulation with bacterial pathogens in vitro and in granulomatous lesions in the lung of Mycobacterium tuberculosis-infected patients. Wnt5a expression has also been liked to Toll-like receptor-4 (TLR-4), an innate immune receptor implicated in atherosclerosis. These observations, along with the fact that Wnt5a is involved in cell migration and proliferation, led us to postulate that Wnt5a plays a role in atherosclerosis. To investigate this hypothesis, we characterized Wnt5a expression in murine and human atherosclerotic lesions. Tissue sections derived from the aortic sinus to the aortic arch of apolipoprotein E-deficient mice and sections derived from the carotid arteries of patients undergoing endarterectomy were subjected to immunohistochemical analysis. All samples were found to be positive for Wnt5a with predominant staining in the areas of macrophage accumulation within the intima. In parallel, we probed for the presence of TLR-4 and found coincident TLR-4 and Wnt5a expression. For both the Wnt5a and TLR-4 staining, consecutive tissue sections treated with an isotype- and species-matched Ig served as a negative control and exhibited little, if any, reactivity. Quantitative RT-PCR revealed that Wnt5a mRNA expression in RAW264.7 murine macrophages can be induced by stimulation with LPS, a known ligand for TLR-4. Combined, these findings demonstrate for the first time Wnt5a expression in human and murine atherosclerotic lesions and suggest that cross talk between TLR-4 and Wnt5a is operative in atherosclerosis.

Phosphatidylinositol-3-kinase-atypical protein kinase C signaling is required for Wnt attraction and anterior-posterior axon guidance

Wnt proteins are conserved axon guidance cues that control growth cone navigation. However, the intracellular signaling mechanisms that mediate growth cone turning in response to Wnts are unknown. We previously showed that Wnt-Frizzled signaling directs spinal cord commissural axons to turn anteriorly after midline crossing through an attractive mechanism. Here we show that atypical protein kinase C (aPKC), is required for Wnt-mediated attraction of commissural axons and proper anterior-posterior (A-P) pathfinding. A PKCzeta pseudosubstrate, a specific blocker of aPKC activity, and expression of a kinase-defective PKCzeta mutant in commissural neurons resulted in A-P randomization in "open-book" explants. Upstream of PKCzeta, heterotrimeric G-proteins and phosphatidylinositol-3-kinases (PI3Ks), are also required for A-P guidance, because pertussis toxin, wortmannin, and expression of a p110gamma kinase-defective construct all resulted in A-P randomization. Overexpression of p110gamma, the catalytic subunit of PI3Kgamma, caused precocious anterior turning of commissural axons before midline crossing in open-book explants and caused dissociated precrossing commissural axons, which are normally insensitive to Wnt attraction, to turn toward Wnt4-expressing cells. Therefore, we propose that atypical PKC signaling is required for Wnt-mediated A-P axon guidance and that PI3K can act as a switch to activate Wnt responsiveness during midline crossing.

The deleted in brachydactyly B domain of ROR2 is required for receptor activation by recruitment of Src

The transmembrane receptor 'ROR2' resembles members of the receptor tyrosine kinase family of signalling receptors in sequence but its' signal transduction mechanisms remain enigmatic. This problem has particular importance because mutations in ROR2 are associated with two human skeletal dysmorphology syndromes, recessive Robinow Syndrome (RS) and dominant acting Brachydactyly type B (BDB). Here we show, using a constitutive dimerisation approach, that ROR2 exhibits dimerisation-induced tyrosine kinase activity and the ROR2 C-terminal domain, which is deleted in BDB, is required for recruitment and activation of the non-receptor tyrosine kinase Src. Native ROR2 phosphorylation is induced by the ligand Wnt5a and is blocked by pharmacological inhibition of Src kinase activity. Eight sites of Src-mediated ROR2 phosphorylation have been identified by mass spectrometry. Activation via tyrosine phosphorylation of ROR2 receptor leads to its internalisation into Rab5 positive endosomes. These findings show that BDB mutant receptors are defective in kinase activation as a result of failure to recruit Src.

Tumor formation due to abnormalities in the beta-catenin-independent pathway of Wnt signaling

Wnt signaling is a complex pathway in which beta-catenin is typically viewed as a central mediator in regulating cell proliferation and differentiation. The significance of Wnt signaling in human cancer has been elucidated by the identification of mutations in genes coding for the beta-catenin-dependent pathway components, adenomatous polyposis coli gene product, beta-catenin, and Axin. Within the past 15 years, evidence has been growing of a beta-catenin-independent pathway in Wnt signaling. It is likely that this pathway activates several intracellular signaling systems to regulate cell migration, adhesion, and polarity. The beta-catenin-independent pathway has also been shown to play an important role in tumor biology. In contrast to the beta-catenin-dependent pathway, which is upregulated in many cancers and serves as a tumor promoter, the role of the beta-catenin-independent pathway is still controversial. Here we review recent developments in both the functions and mechanisms of the beta-catenin-independent pathway, with an emphasis on its functional contribution to human tumor progression.

Ror2 modulates the canonical Wnt signaling in lung epithelial cells through cooperation with Fzd2

Background

Wnt signaling is mediated through 1) the beta-catenin dependent canonical pathway and, 2) the beta-catenin independent pathways. Multiple receptors, including Fzds, Lrps, Ror2 and Ryk, are involved in Wnt signaling. Ror2 is a single-span transmembrane receptor-tyrosine kinase (RTK). The functions of Ror2 in mediating the non-canonical Wnt signaling have been well established. The role of Ror2 in canonical Wnt signaling is not fully understood.

Results

Here we report that Ror2 also positively modulates Wnt3a-activated canonical signaling in a lung carcinoma, H441 cell line. This activity of Ror2 is dependent on cooperative interactions with Fzd2 but not Fzd7. In addition, Ror2-mediated enhancement of canonical signaling requires the extracellular CRD, but not the intracellular PRD domain of Ror2. We further provide evidence that the positive effect of Ror2 on canonical Wnt signaling is inhibited by Dkk1 and Krm1 suggesting that Ror2 enhances an Lrp-dependent STF response.

Conclusion

The current study demonstrates the function of Ror2 in modulating canonical Wnt signaling. These findings support a functional scheme whereby regulation of Wnt signaling is achieved by cooperative functions of multiple mediators.

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.

Membrane type 1 matrix metalloproteinase induces epithelial-to-mesenchymal transition in prostate cancer

By mining DNA microarray data bases at GenBank, we identified up-regulation of membrane type 1 matrix metalloproteinase (MT1-MMP) in human primary and metastatic prostate cancer specimens as compared with nonmalignant prostate tissues. To explore the role of up-regulated MT1-MMP in early stage cancer progression, we have employed a three-dimensional cell culture model. Minimally invasive human prostate cancer cells (LNCaP) were transfected with MT1-green fluorescent protein (GFP) chimeric cDNA as compared with GFP cDNA, and morphologic and phenotypic changes were characterized. GFP-expressing LNCaP cells formed multicellular spheroids with cuboidal-like epithelial morphology, whereas MT1-GFP-expressing cells displayed a fibroblast-like morphology and a scattered growth pattern in type I collagen gels. Cell morphologic changes were accompanied by decreased epithelial markers and enhanced mesenchymal markers, consistent with epithelial-to-mesenchymal transition. MT1-MMP-induced morphologic change and cell scattering were abrogated by target inhibition of either the catalytic domain or the hemopexin domain. We further demonstrated that MT1-MMP-induced phenotypic changes were dependent upon up-regulation of Wnt5a, which has been implicated in epithelial-to-mesenchymal transition. We conclude that MT1-MMP plays an important role in early cancer dissemination by converting epithelial cells to migratory mesenchymal-like cells.

WNTers in La Jolla

A 'traditional' Wnt meeting, the first of which occurred over two decades ago as a meeting of the laboratories of Harold Varmus and Roel Nusse, was held at the University of California, San Diego, in June 2007. Organized by Karl Willert, Anthony Wynshaw-Boris and Katherine Jones, the meeting was attended by nearly 400 scientists interested in ;all things Wnt', including Wnt signal transduction mechanisms, and Wnt signaling in evolutionary and developmental biology, stem cell biology, regeneration and disease. Themes that dominated the meeting included the need for precise control over each step of the signal transduction mechanism and developing therapeutics for diseases caused by altered Wnt-signaling.

The complex pathways of Wnt 5a in cancer progression

In contrast to the transforming members of the Wnt family, shown to be upregulated in many cancers, the role of Wnt 5a is still controversial. While it has been attributed a tumour suppressor function in some malignancies, there is increasing evidence of promigratory and proinvasive effects in others, mediated predominantly through the planar cell polarity pathway and activation of protein kinase C. Obviously, the outcome of an individual Wnt 5a signal is dependent on a multitude of variables, ranging from availability of receptors, downstream effectors, and inhibitors to external influences coming from the tumour microenvironment and the extracellular matrix.

Wnt signaling and neurite outgrowth: insights and questions

Wnt signaling consists of a highly conserved set of biochemical pathways that have a multitude of functions during embryonic development and in the adult. The Wnt proteins are extracellular agents that often act as gradient morphogens, indicating that their distribution in tissues is tightly controlled. This attribute is also characteristic of factors that regulate neurite outgrowth and guide axons precisely to their specific destinations. Several studies in various species now have established that Wnts and their receptors have an important role in axonal guidance. Different ligand/receptor combinations have been identified that mediate this activity in many of the experimental models. Clues about downstream effector molecules have come from in vitro systems. In this article, the authors review the results from many of these models, evaluate what is known about the associated signaling pathways and speculate about the direction of future research.

Filopodia: the fingers that do the walking

Filopodia are actin-based structures composed of parallel bundles of actin filaments and various actin-associated proteins, and they play important roles in cell-cell signaling, guidance toward chemoattractants, and adhesion to the extracellular matrix. Two mechanisms for the formation of filopodia have been suggested, each using different sets of actin-regulating proteins, creating some controversy in the field. New molecules, some of unknown functions, have also been implicated in filopodium formation, suggesting that other possible mechanisms of filopodium formation exist. We discuss established and novel proteins that mediate the formation and dynamics of filopodia, different mechanisms of filopodium formation, and the various functions that distinct filopodia perform.

Synapse loss in cortex of agrin-deficient mice after genetic rescue of perinatal death

Agrin-deficient mice die at birth because of aberrant development of the neuromuscular junctions. Here, we examined the role of agrin at brain synapses. We show that agrin is associated with excitatory but not inhibitory synapses in the cerebral cortex. Most importantly, we examined the brains of agrin-deficient mice whose perinatal death was prevented by the selective expression of agrin in motor neurons. We find that the number of presynaptic and postsynaptic specializations is strongly reduced in the cortex of 5- to 7-week-old mice. Consistent with a reduction in the number of synapses, the frequency of miniature postsynaptic currents was greatly decreased. In accordance with the synaptic localization of agrin to excitatory synapses, changes in the frequency were only detected for excitatory but not inhibitory synapses. Moreover, we find that the muscle-specific receptor tyrosine kinase MuSK, which is known to be an essential component of agrin-induced signaling at the neuromuscular junction, is also localized to a subset of excitatory synapses. Finally, some components of the mitogen-activated protein (MAP) kinase pathway, which has been shown to be activated by agrin in cultured neurons, are deregulated in agrin-deficient mice. In summary, our results provide strong evidence that agrin plays an important role in the formation and/or the maintenance of excitatory synapses in the brain, and we provide evidence that this function involves MAP kinase signaling.

Cdc42 and noncanonical Wnt signal transduction pathways cooperate to promote cell polarity

Scratch-induced disruption of cultured monolayers induces polarity in front row cells that can be visualized by spatially localized polymerization of actin at the front of the cell and reorientation of the centrosome/Golgi to face the leading edge. We previously reported that centrosomal reorientation and microtubule polarization depend on a Cdc42-regulated signal transduction pathway involving activation of the Par6/aPKC complex followed by inhibition of GSK-3β and accumulation of the adenomatous polyposis coli (APC) protein at the plus ends of leading-edge microtubules. Using monolayers of primary rodent embryo fibroblasts, we show here that dishevelled (Dvl) and axin, two major components of the Wnt signaling pathway are required for centrosome reorientation and that Wnt5a is required for activation of this pathway. We conclude that disruption of cell–cell contacts leads to the activation of a noncanonical Wnt/dishevelled signal transduction pathway that cooperates with Cdc42/Par6/aPKC to promote polarized reorganization of the microtubule cytoskeleton.

Wnt-5A/Ror2 regulate expression of XPAPC through an alternative noncanonical signaling pathway

XWnt-5A, a member of the nontransforming Wnt-5A class of Wnt ligands, is required for convergent extension movements in Xenopus embryos. XWnt-5A knockdown phenocopies paraxial protocadherin (XPAPC) loss of function: involuted mesodermal cells fail to align mediolaterally, which results in aberrant movements and a selective inhibition of constriction. XWnt-5A depletion was rescued by coinjection of XPAPC RNA, indicating that XWnt-5A acts upstream of XPAPC. XWnt-5A, but not XWnt-11, stimulates XPAPC expression independent of the canonical Wnt/beta-catenin pathway. We show that transcriptional regulation of XPAPC by XWnt-5A requires the receptor tyrosine kinase Ror2. XWnt-5A/Xror2 signal through PI3 kinase and cdc42 to activate the JNK signaling cascade with the transcription factors ATF2 and c-jun. The Wnt-5A/Ror2 pathway represents an alternative, distinct branch of noncanonical Wnt signaling that controls gene expression and is required in the regulation of convergent extension movements in Xenopus gastrulation.

Multiplicity of the interactions of Wnt proteins and their receptors

Wnts are secreted proteins that are essential for a wide array of developmental and physiological processes. They signal across the plasma membranes by interacting with serpentine receptors of the Frizzled (Fz) family and members of the low-density-lipoprotein receptor-related protein (LRP) family. Recent advances in the Wnt signaling field have revealed that Wnt-unrelated proteins activate or suppress Wnt signaling by binding to Fzs or LRP5/6 and that atypical receptor tyrosine kinases mediate Wnt signaling independently of Fz and/or function as a Fz co-receptor. This review highlights recent progress in our understanding of the multiplicity of Wnts and their receptors. We discuss how the interaction between the ligands and receptors activate distinct intracellular signaling pathways. We also discuss how intracellular trafficking of Wnt signaling components can regulate the sensitivity of cells to Wnts.