Wnt signaling inhibits cementoblast differentiation and promotes proliferation

Cementoblasts, tooth root lining cells, are responsible for laying down cementum on the root surface, a process that is indispensable for establishing a functional periodontal ligament. Cementoblasts share phenotypical features with osteoblasts. Wnt signaling has been implicated in increased bone formation by controlling mesenchymal stem cell or osteoblastic cell functions; however the role of Wnt signaling on cementogenesis has not been examined. In this study, we have identified a consistent expression profile of Wnt signaling molecules in cementoblasts, in vitro by RT-PCR. Exposure of cells to LiCl, which promotes canonical Wnt signaling by inhibiting GSK-3beta, increased beta-catenin nuclear translocation and up-regulated the transcriptional activity of a canonical Wnt-responsive promoters, suggesting that an endogenous canonical Wnt pathway functions in cementoblasts. Activation of endogenous canonical Wnt signaling with LiCl suppressed alkaline phosphatase (ALP) activity and expression of genes associated with cementum function; ALP, bone sialoprotein (BSP), and osteocalcin (OCN). Exposure to Wnt3a, as a representative canonical Wnt member, also inhibited the expression of ALP, BSP, and OCN gene. This effect was accompanied by decreased gene expression of Runx2 and Osterix and by increased gene expression of lymphoid enhancer factor-1. Pretreatment with Dickkopf (Dkk)-1, a potent canonical Wnt antagonist, which binds to a low-density lipoprotein-receptor-related protein (LRP)-5/6 co-receptor, attenuated the suppressive effects of Wnt3a on mRNA expression of Runx2 and OCN on cementoblasts. These findings suggest that canonical Wnt signaling inhibits cementoblast differentiation via regulation of expression of selective transcription factors. Wnt3a also increased the expression of cyclin D1, known as a cell cycle regulator, as well as cell proliferation. In conclusion, these observations suggest that Wnt signaling inhibits cementoblast differentiation and promotes cell proliferation. Elucidating the role of Wnt in controlling cementoblast function will provide new tools needed to improve on existing periodontal regeneration therapies.

Promotion of the self-renewal capacity of human acute leukemia cells by Wnt3A

BACKGROUND

Wnt/beta-catenin signaling is involved in the growth of various types of cancer cells. Wnt3A has been reported to promote the self-renewal of hematopoietic stem cells.

MATERIALS AND METHODS

The effects of recombinant Wnt3A protein on the in vitro growth of four acute myeloid leukemia (AML) and four acute T-lymphoblastic leukemia (T-ALL) cell lines was examined.

RESULTS

Wnt3A stimulation either had no effect on, or slightly suppressed, the short-term growth of these cell lines. In three cell lines, Wnt3A promoted clonogenic cell recovery after suspension culture, suggesting the promotion of the self-renewal capacity of leukemic stem or progenitor cells. Immunoblot analysis showed that Wnt3A stimulation reduced phosphorylated beta-catenin and increased beta-catenin in these cells, indicating that Wnt3A stimulation activated Wnt/beta-catenin signaling.

CONCLUSION

Wnt3A stimulation did not promote the growth of whole cell populations, but did promote the self-renewal of leukemic stem/progenitor cells in some AML and T-ALL cell lines.

Wnt-3a protein promote neuronal differentiation of neural stem cells derived from adult mouse spinal cord

BACKGROUND

Wnt proteins as growth factor have multiple functions in neural development, and especially serve key roles in differentiation and development. Wnt-3a is an intercellular signaling molecule that is involved in a variety of morphogenetic events. The purpose of this study was to investigate the effects of Wnt-3a signal protein on proliferation and differentiation of neural stem cells derived from adult mouse spinal cord.

METHODS

Adult mouse neural stem cells were cultured with serum free incubation. The recombined plasmid pSecTag2/Hygro B-Wnt3a for eukaryotic expression transfected adult neural stem cell, then the expression protein was detected by Western blot. The differentiation of adult neural stem cells was identified by the immunocytochemical technique.

RESULTS

The inducing differentiated rates of neurons were improved greatly by Wnt-3a protein compared with control (p<0.05).

CONCLUSION

Wnt-3a has obvious influence on the neuronal differentiation of adult neural stem cell.

Essential role of Wnt3a-mediated activation of mitogen-activated protein kinase p38 for the stimulation of alkaline phosphatase activity and matrix mineralization in C3H10T1/2 mesenchymal cells

Signaling pathways involved in the development of osteoprogenitors induced by Wnts remain poorly understood. In this study, we investigated the role of MAPKs in the development of mesenchymal cells into osteoprogenitors. In C3H10T1/2 mesenchymal cells, Wnt3a induced a rapid and transient activation of MAPKs p38 and ERK. Dickkopf 1, a selective antagonist of Wnt proteins binding to low-density lipoprotein-receptor-related protein-5/6 did not influence activation of p38 and ERK induced by Wnt3a. A MAPK kinase-1/2 (MEK1/2) inhibitor blocked, whereas a p38 inhibitor had no effect on, Wnt3a-induced cell proliferation. In contrast, both inhibitors significantly reduced alkaline phosphatase stimulation with a more pronounced effect of the p38 inhibitor. The p38 inhibitor also blunted nodule mineralization induced by Wnt3a. Associated with these effects, beta-catenin transcriptional activity, assessed with the TOPflash system, was dose-dependently decreased by the p38 but not by the ERK inhibitor. Both the reduced alkaline phosphatase stimulation and blunting of beta-catenin transcriptional activity were mimicked by expression of dominant-negative (dn) p38 and dnMEK 3/6. Inhibition of beta-catenin transcriptional activity by the p38 inhibitor as well as by dnp38 and dnMEK 3/6 molecules were not associated with changes in cytosolic and nuclear beta-catenin levels induced by Wnt3a. In conclusion, Wnt3a activates ERK and p38 in mesenchymal C3H10T1/2 cells by a low-density lipoprotein-receptor-related protein-5/6-independent mechanism. Activation of p38 regulates alkaline phosphatase activity and nodule mineralization induced by Wnt3a probably by interacting with beta-catenin transcriptional activity. These observations suggest that MAPKs ERK and p38 are probably essential pathways activated by Wnt proteins for the development of mesenchymal cells into osteoprogenitors.

Wnt3a signaling promotes proliferation, myogenic differentiation, and migration of rat bone marrow mesenchymal stem cells

AIM

To investigate the effects of the wingless-related MMTV integration site 3A (Wnt3a) signaling on the proliferation, migration, and the myogenic and adipogenic differentiation of rat bone marrow mesenchymal stem cells (rMSC).

METHODS

Primary MSC were isolated and cultured from Sprague-Dawley rats and characterized by flow cytometry. Mouse L cells were transfected with Wnt3a cDNA, and conditioned media containing active Wnt3a proteins were prepared. Cell proliferation was evaluated by cell count and 5-bromodeoxyuridine incorporation assay. The migration of rMSC was performed by using a transwell migration and wound healing assay. The myogenic and adipogenic differentiation in rMSC were examined by light microscopy, immunofluorescence, and RT-PCR at different time points after myogenic or adipogenic introduction.

RESULTS

Wnt3a signaling induced beta-catenin nuclear translocation and activated the Wnt pathway in rMSC. In the presence of Wnt3a, rMSC proliferated more rapidly than the control cells, keeping their differentiation potential. Moreover, Wnt3a signaling induced 2.62% and 3.76% of rMSC-expressed desmin and myosin heavy chain after being cultured in myogenic medium. The myogenic differentiation genes, including Pax7, MyoD, Myf5, Myf4, and myogenin, were activated after Wnt3a treatment. On the other hand, Wnt3a inhibited the adipogenic differentiation in rMSC through the downregulated expression of CCAAT/enhancer-binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma). Furthermore, Wnt3a promoted the migration capacity of rMSC.

CONCLUSION

The results indicate that Wnt3a signaling can induce myogenic differentiation in rMSC. Wnt3a signaling is also involved in the regulation of the proliferation and migration of rMSC. These results could provide a rational foundation for cell-based tissue repair in humans.

[Differentiation phenotypes of k562 cells induced by exogenous wnt5a]

This study was aimed to investigate the effect of exogenous Wnt5a on directional differentiation of K562 cells. Wnt5a and GFP condition mediums were prepared by recombinant adenoviral vector AdWnt5a and AdGFP transfecting CHO cells. K562 cells were treated with Wnt5a and the GFP condition mediums for 1 - 7 days as Wnt5a treated group and control group respectively. The morphological changes of K562 cells were observed by light microscope and electron microscope; the differentiation phenotypes of K562 cells were identified by the cytochemical staining of POX, PAS, alpha-NAE and immunocytochemistry of CD13, CD14, CD68, and the effect of Wnt5a on cell cycle distribution of K562 cells was detected by flow cytometry. The results showed that the morphology and ultrastructure of K562 cells treated by Wnt5a displayed differentiation mature feature; both POX and PAS staining showed higher positive ratio in Wnt5a treated group than that in control group; the alpha-NAE staining also was positive, but positive intensity in Wnt5a treated group could be inhibited up to 70% by NaF. The expressions of monocytic differentiation antigens of CD14, CD68 in Wnt5a treated group were higher than those in control group, but the expression differences of granulocytic differentiation antigen CD13 between Wnt5a treated group and control group were not significant. The cell cycle in treated group was blocked at G2 phase as compared with control group. It is concluded that exogenous Wnt5a can induce K562 cells to differentiate towards mature and K562 cells treated with Wnt5a displays features of differentiation towards monocytic lineage.

Transcriptional program induced by Wnt protein in human fibroblasts suggests mechanisms for cell cooperativity in defining tissue microenvironments

BACKGROUND

The Wnt signaling system plays key roles in development, regulation of stem cell self-renewal and differentiation, cell polarity, morphogenesis and cancer. Given the multifaceted roles of Wnt signaling in these processes, its transcriptional effects on the stromal cells that make up the scaffold and infrastructure of epithelial tissues are of great interest.

METHODS AND RESULTS

To begin to investigate these effects, we used DNA microarrays to identify transcriptional targets of the Wnt pathway in human lung fibroblasts. Cells were treated with active Wnt3a protein in culture, and RNA was harvested at 4 hours and 24 hours. Nuclear accumulation of ss-Catenin, as shown by immunofluorescence, and induction of AXIN2 demonstrate that fibroblasts are programmed to respond to extracellular Wnt signals. In addition to several known Wnt targets, we found many new Wnt induced genes, including many transcripts encoding regulatory proteins. Transcription factors with important developmental roles, including HOX genes, dominated the early transcriptional response. Furthermore, we found differential expression of several genes that play direct roles in the Wnt signaling pathway, as well as genes involved in other cell signaling pathways including fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) signaling. The gene most highly induced by Wnt3a was GREMLIN2, which encodes a secreted BMP antagonist.

CONCLUSIONS

Elevated expression of GREMLIN2 suggests a new role for Wnt signals in the maintenance of stem cell niches, whereby Wnt signals induce nearby fibroblasts to produce a BMP antagonist, inhibiting differentiation and promoting expansion of stem cells in their microenvironment. We suggest that Wnt-induced changes in the gene expression program of local stromal cells may play an important role in the establishment of specialized niches hospitable to the self-renewal of normal or malignant epithelial stem cells in vivo.

Quantitative phosphoproteome profiling of Wnt3a-mediated signaling network: indicating the involvement of ribonucleoside-diphosphate reductase M2 subunit phosphorylation at residue serine 20 in canonical Wnt signal transduction

The complexity of canonical Wnt signaling comes not only from the numerous components but also from multiple post-translational modifications. Protein phosphorylation is one of the most common modifications that propagates signals from extracellular stimuli to downstream effectors. To investigate the global phosphorylation regulation and uncover novel phosphoproteins at the early stages of canonical Wnt signaling, HEK293 cells were metabolically labeled with two stable isotopic forms of lysine and were stimulated for 0, 1, or 30 min with purified Wnt3a. After phosphoprotein enrichment and LC-MS/MS analysis, 1057 proteins were identified in all three time points. In total 287 proteins showed a 1.5-fold or greater change in at least one time point. In addition to many known Wnt signaling transducers, other phosphoproteins were identified and quantitated, implicating their involvement in canonical Wnt signaling. k-Means clustering analysis showed dynamic patterns for the differential phosphoproteins. Profile pattern and interaction network analysis of the differential phosphoproteins implicated the possible roles for those unreported components in Wnt signaling. Moreover 100 unique phosphorylation sites were identified, and 54 of them were quantitated in the three time points. Site-specific phosphopeptide quantitation revealed that Ser-20 phosphorylation on RRM2 increased upon 30-min Wnt3a stimulation. Further studies with mutagenesis, the Wnt reporter gene assay, and RNA interference indicated that RRM2 functioned downstream of beta-catenin as an inhibitor of Wnt signaling and that Ser-20 phosphorylation of RRM2 counteracted its inhibition effect. Our systematic profiling of dynamic phosphorylation changes responding to Wnt3a stimulation not only presented a comprehensive phosphorylation network regulated by canonical Wnt signaling but also found novel molecules and phosphorylation involved in Wnt signaling.

Wnt3a regulates survival, expansion, and maintenance of neural progenitors derived from human embryonic stem cells

Many reports describe the efficient derivation and expansion of neural progenitors (NP) from human embryonic stem cells (hESC). However, little is known about the signaling factors found within the neurosphere microenvironment that regulate NP maintenance and differentiation. We show that Wnt ligand and receptor transcripts are endogenously upregulated within neurospheres derived from noggin-primed hESC. In addition, neurosphere formation and size were significantly greater in the presence of exogenous Wnt3a compared to control conditions. Inhibition of endogenous Wnt signaling resulted in a significant reduction in the efficiency of neurosphere formation and overall size, due to effects on both NP proliferation and apoptosis. These findings demonstrate a requirement of Wnt signaling for maintenance, proliferation, and survival of NP when cultured in neurosphere conditions.

The interaction of the Wnt and Notch pathways modulates natural killer versus T cell differentiation

The Wnt and Notch signaling pathways have been independently shown to play a critical role in regulating hematopoietic cell fate decisions. We previously reported that induction of Notch signaling in human CD34(+)CD38(-) cord blood cells by culture with the Notch ligand Delta 1 resulted in more cells with T or natural killer (NK) lymphoid precursor phenotype. Here, we show that addition of Wnt3a to Delta 1 further increased the percentage of CD34(-)CD7(+) and CD34(-)CD7(+)cyCD3(+) cells with increased expression of CD3 epsilon and preT alpha. In contrast, culture with Wnt3a alone did not increase generation of CD34(-)CD7(+) precursors or expression of CD3 epsilon or preT alpha gene. Furthermore, Wnt3a increased the amount of activated Notch1, suggesting that Wnt modulates Notch signaling by affecting Notch protein levels. In contrast, addition of a Wnt signaling inhibitor to Delta 1 increased the percentage of CD56(+) NK cells. Overall, these results demonstrate that regulation of Notch signaling by the Wnt pathway plays a critical role in differentiation of precursors along the early T or NK differentiation pathways. Disclosure of potential conflicts of interest is found at the end of this article.

Wnt signaling and the regulation of bone mass

Human genetic studies have firmly established a link between bone mass in humans and gain-of-function or loss-of-function mutations in a Wnt coreceptor, low-density lipoprotein receptor-related protein 5 (LRP5), or in the Wnt antagonist sclerostin, and several molecular genetic studies in mice have consistently confirmed the critical importance of the Wnt signaling pathway in skeletal biology and disease. In what may be a novel paradigm, the ubiquitous nature of LRP5/6 and Wnt signaling is counterbalanced by the bone-restricted and regulated expression of Wnt antagonists such as sclerostin and Dickkopf-1 (Dkk1) in adult tissues, offering new and potentially safe therapeutic means of intervention to stimulate bone formation.

Wnt signaling enhances the activation and survival of human hepatic stellate cells

Wnt signaling was implicated in pulmonary and renal fibrosis. Since Wnt activity is enhanced in liver cirrhosis, Wnt signaling may also participate in hepatic fibrogenesis. Thus, we determined if Wnt signaling modulates hepatic stellate cell (HSC) activation and survival. Wnt3A treatment significantly activated human HSCs, while this was inhibited in secreted frizzled-related protein 1 (sFRP1) overexpressing cells. Wnt3A treatment significantly suppressed TRAIL-induced apoptosis in control HSCs versus sFRP1 over-expressing cells. Particularly, caspase 3 was more activated in sFRP1 over-expressing cells following TRAIL and Wnt3A treatment. These observations imply that Wnt signaling promotes hepatic fibrosis by enhancing HSC activation and survival.

Wnt inhibitory factor inhibits lung cancer cell growth

OBJECTIVE

Aberrant activation of the Wnt signaling pathway is associated with the pathogenesis of multiple cancers, including non-small cell lung cancer. Wnt inhibitory factor, a secreted Wnt antagonist, is downregulated in non-small cell lung cancer. We hypothesized that restoration of Wnt inhibitory factor function would inhibit lung cancer cell growth.

METHODS

The lung cancer cell lines A549 and H460 were transfected with an expression vector containing the Wnt inhibitory factor gene. Apoptosis rates and colony formation were measured after transfection. Recombinant Wnt inhibitory factor protein was used to treat H460 cells, and proliferation rates were measured with an MTS assay. Finally, Wnt inhibitory factor plasmid was peritumorally injected near H460 tumor xenografts in nude mice.

RESULTS

Wnt inhibitory factor-transfected cells had increased apoptosis and decreased colony formation than control cells. Recombinant human Wnt inhibitory factor protein was also able to inhibit H460 cell proliferation measured by using the MTS assay. Wnt inhibitory factor plasmid significantly inhibited the growth in vivo of H460 tumor xenografts in nude mice.

CONCLUSION

These data suggest that Wnt inhibitory factor is able to inhibit lung cancer cell growth both in vitro and in vivo and provides additional evidence that Wnt inhibitory factor plays an important role in Wnt pathway regulation in lung cancer.

EGF receptor is involved in WNT3a-mediated proliferation and motility of NIH3T3 cells via ERK pathway activation

WNT3a stimulates proliferation of NIH3T3 cells via activation of the extracellular signal-regulated kinase (ERK) pathway. The RAF-1-->MEK-->ERK cascade was immediately increased by WNT3a treatment, however, the upstream event triggering ERK pathway activation by WNT3a is not clear. WNT3a activated RAS and WNT3a-induced ERK activation was blocked by dominant-negative RAS, indicating that WNT3a might act upstream of RAS. WNT3a-induced ERK pathway activations were blocked by AG1478, the epidermal growth factor receptor (EGFR) inhibitor, and EGFR siRNA. The WNT3a-induced ERK pathway activation was not observed in fibroblasts retaining defective EGFR, but the WNT3a effect was restored by EGFR reconstitution. These results indicate involvement of EGFR in the WNT3a-induced ERK pathway activation. WNT3a-induced motility and cytoskeletal rearrangement as well as proliferation of NIH3T3 cells were blocked by AG1478 and EGFR siRNA or abolished in EGFR knock-out fibroblasts, indicating involvement of EGFR in those cellular processes. WNT3a-induced ERK pathway activation was not affected by Dickkoff-1 (DKK-1), although WNT3a-induced activations of the WNT/beta-catenin pathway and proliferation were reduced by DKK-1. EGFR is involved in WNT3a-induced proliferation via both routes dependent on and independent of the WNT/beta-catenin pathway. These results indicate that WNT3a stimulates proliferation and motility of NIH3T3 fibroblasts via EGFR-mediated ERK pathway activation.

Association of Dishevelled with the clathrin AP-2 adaptor is required for Frizzled endocytosis and planar cell polarity signaling

Upon activation by Wnt, the Frizzled receptor is internalized in a process that requires the recruitment of Dishevelled. We describe a novel interaction between Dishevelled2 (Dvl2) and micro2-adaptin, a subunit of the clathrin adaptor AP-2; this interaction is required to engage activated Frizzled4 with the endocytic machinery and for its internalization. The interaction of Dvl2 with AP-2 requires simultaneous association of the DEP domain and a peptide YHEL motif within Dvl2 with the C terminus of micro2. Dvl2 mutants in the YHEL motif fail to associate with micro2 and AP-2, and prevent Frizzled4 internalization. Corresponding Xenopus Dishevelled mutants show compromised ability to interfere with gastrulation mediated by the planar cell polarity (PCP) pathway. Conversely, a Dvl2 mutant in its DEP domain impaired in PCP signaling exhibits defective AP-2 interaction and prevents the internalization of Frizzled4. We suggest that the direct interaction of Dvl2 with AP-2 is important for Frizzled internalization and Frizzled/PCP signaling.

Wnt1 and Wnt5a affect endothelial proliferation and capillary length; Wnt2 does not

Blood vessel growth is critical for embryonic development and contributes to pathologies including cancer and diabetic retinopathy. A growing body of evidence suggests that signaling via the Wnt/beta-catenin pathway contributes to angiogenesis, and that paracrine Wnt signaling might alter endothelial cell function. To test the hypothesis that Wnt signaling promotes endothelial cell proliferation and vessel growth, we treated bovine aortic endothelial cells with Wnt1, Wnt2 and Wnt5a derived from coculture with Wnt-expressing fibroblasts. Endothelial cells cultured in the presence of Wnt1 displayed increased Wnt/beta-catenin signaling, proliferation and capillary stability in vitro. Wnt5a, which primarily signals via an alternate Wnt pathway, the Wnt/Ca(++) pathway, decreased both cell number and capillary length. Wnt2, which in other cell types activates the Wnt/beta-catenin pathway, did not activate signaling, affect cell number or increase capillary length. These results suggest that Wnt/beta-catenin and Wnt/Ca(++) signals might have opposing effects on angiogenesis.

Wnt-5a induces Dishevelled phosphorylation and dopaminergic differentiation via a CK1-dependent mechanism

Previously, we have shown that Wnt-5a strongly regulates dopaminergic neuron differentiation by inducing phosphorylation of Dishevelled (Dvl). Here, we identify additional components of the Wnt-5a-Dvl pathway in dopaminergic cells. Using in vitro gain-of-function and loss-of-function approaches, we reveal that casein kinase 1 (CK1) delta and CK1epsilon are crucial for Dvl phosphorylation by non-canonical Wnts. We show that in response to Wnt-5a, CK1epsilon binds Dvl and is subsequently phosphorylated. Moreover, in response to Wnt-5a or CK1epsilon, the distribution of Dvl changed from punctate to an even appearance within the cytoplasm. The opposite effect was induced by a CK1epsilon kinase-dead mutant or by CK1 inhibitors. As expected, Wnt-5a blocked the Wnt-3a-induced activation of beta-catenin. However, both Wnt-3a and Wnt-5a activated Dvl2 by a CK1-dependent mechanism in a cooperative manner. Finally, we show that CK1 kinase activity is necessary for Wnt-5a-induced differentiation of primary dopaminergic precursors. Thus, our data identify CK1 as a component of Wnt-5a-induced signalling machinery that regulates dopaminergic differentiation, and suggest that CK1delta/epsilon-mediated phosphorylation of Dvl is a common step in both canonical and non-canonical Wnt signalling.

Derivation of Motor Neurons from three Clonal Human Embryonic Stem Cell Lines

Human embryonic stem cells (hESC) demonstrate a remarkable proliferative and developmental potential and thus have huge therapeutic potential. To direct the differentiation of hESC to a specific lineage of high purity for cell transplantation is highly desirable. Here we describe a modified in vitro procedure to direct differentiation of three clonal hESC lines, hES 3.1, hES 3.2 and hES 3.3 efficiently to spinal motor neurons by using various differentiation factors namely retinoic acid (RA), sonic hedgehog (Shh), bone morphogenetic protein-2 (BMP-2) and Wnt3A. The highest number of motor neurons (58.0 +/- 7.6%) were obtained by an early treatment of embryoid bodies with a combination of RA + Shh from all the clonal hESC lines combined. The hES 3.1 line, however, produced relatively more motor neurons (69.5 +/- 11.8%) compared to other two hES clones, 3.2 (52.4 +/- 13.1%) and 3.3 (52.3 +/- 15.5%). Immunolocalisation studies revealed the expression of neuronal specific marker, beta omega-tubulin and motor neuron specific marker, HB9/HLXB9 in all the three hESC clones after 45 days of differentiation. The RT-PCR analyses showed the presence of the neuron-specific genes. This modified differentiation protocol provides a mean of obtaining an enriched population of motor neurons from hESC for possible use in studies of lineage development, drug discovery and also as a potential cell therapy for motor neuron disease.

Wnt3A activates canonical Wnt signalling in acute lymphoblastic leukaemia (ALL) cells and inhibits the proliferation of B-ALL cell lines

Acute lymphoblastic leukaemia (ALL) is the most common malignancy in children. Recently, there has been a growing interest in Wnt signalling in several aspects of cellular development, including cancer formation. Little is known about Wnt signalling in B-ALL. We investigated whether activation of canonical Wnt signalling could occur in B-ALL cells and thereby play a potential role in cellular growth and/or survival. This study found that Wnt3A induced beta-catenin accumulation in both primary B-ALL cells and B-ALL leukaemia cell lines. Further, Wnt3A was shown to induce nuclear translocation of beta-catenin and TCF/Lef-1 dependent transcriptions in the B-ALL cell line Nalm-6. Examination of the mRNA expression pattern of WNT ligands, FZD receptors and WNT antagonists in Nalm-6 cells identified a set of ligands and receptors available for signalling, as well as antagonists potentially available for modulating the response. Functional analyses showed that Wnt3A inhibited the proliferation of several, but not all, B-ALL cell lines studied. Finally, microarray analysis was used to identify several Wnt3A target genes involved in a diverse range of cellular activities, which are potential mediators of the Wnt3A-restrained proliferation.

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.

Wnt-3a utilizes a novel low dose and rapid pathway that does not require casein kinase 1-mediated phosphorylation of Dvl to activate beta-catenin

The current view of canonical Wnt signalling is that following Wnt binding to its receptors (Frizzled-Lrp5/6), dishevelled (Dvl) becomes hyperphosphorylated, and the signal is transduced to the APC-GSK3beta-axin-beta-catenin multiprotein complex, which subsequently dissociates. As a result beta-catenin is not phosphorylated, escapes proteosomal degradation and activates its target genes after translocation to the nucleus. Here, we analyzed the importance of the Wnt-3a-induced phosphorylation and shift in electrophoretic migration of Dvl (PS-Dvl) for the activation of beta-catenin. Analysis of Wnt-3a time- and dose-responses in a dopaminergic cell line showed that beta-catenin is activated rapidly (within minutes) and at a low dose of Wnt-3a (1 ng/ml). Surprisingly, PS-Dvl appeared only after 30 min and at greater doses (> or =20 ng/ml) of Wnt-3a. Moreover, we found that a casein kinase 1 inhibitor (D4476) or siRNA for casein kinase 1 delta/epsilon (CK1delta/epsilon) blocked the Wnt-3a-induced PS-Dvl. Interestingly, CK1 inhibition or siRNA for CK1delta/epsilon did not ablate the activation of beta-catenin by Wnt-3a, indicating that there is a PS-Dvl-independent path to activate beta-catenin. The increase in beta-catenin activation by Wnt-3a (PS-Dvl-dependent or -independent) were blocked by Dickkopf1 (Dkk1), suggesting that the effect of Wnt-3a is in both cases mediated by Lrp5/6 receptors. Thus, our results show that Wnt-3a rapidly induce a partial activation of beta-catenin in the absence of PS-Dvl at low doses, while at high doses induce a full activation of beta-catenin in a PS-Dvl-dependent manner.

The PI3 kinase-Akt pathway mediates Wnt3a-induced proliferation

Wnt3a activates proliferation of fibroblasts cells via activation of both extracellular signal-regulated kinase (ERK) and Wnt/beta-catenin signaling pathways. In this study, we show that the phosphatidyl inositol 3 kinases (PI3K)-Akt pathway is also involved in the Wnt3a-induced proliferation. Akt was activated within 30 min by Wnt3a in NIH3T3 cells. By Wnt3a treatment, activated Akt was transiently accumulated in nucleus although beta-catenin was accumulated in the nucleus of cells in a prolonged manner. The Wnt3a-induced Akt activation was not affected by siRNA-mediated reduction of beta-catenin, indicating that Wnt3a-induced Akt activation may occur independently of beta-catenin. The Wnt3a-induced Akt activation was abolished by pre-treatment with PI3K inhibitor, LY294002 and Wortmanin, but not by MEK inhibitor, U0126, indicating that Wnt3a activates Akt via PI3K. The growth and proliferation induced by Wnt3a were blocked by treatments of the PI3K inhibitors. Furthermore, Wnt3a-induced proliferation was blocked by Akt siRNA. These results reveal that the PI3K-Akt pathway mediates the Wnt3a-induced growth and proliferation of NIH3T3 cells.

A method for the selection of human embryonic stem cell sublines with high replating efficiency after single-cell dissociation

Human embryonic stem cells (hESCs) exhibit pluripotency and indefinite proliferation and are a potential source of cells for transplantation therapies and drug discovery. These applications will require large amounts of hESCs. However, hESCs are difficult to culture and maintain at larger scales, in part because of their low resistance to dissociation during passaging. To circumvent this, we developed a simple and easy method for establishing hESC sublines tolerant of complete dissociation. These cells exhibit high replating efficiency and also high cloning efficiency, and they maintain their ability to differentiate into the three germ layers. Several sublines have no detectable abnormalities in their karyotypes, and they retained their characteristics under feeder-free culture conditions and after freeze-thawing. Thus, these hESC sublines would be valuable for hESC applications.

Wnt expression and canonical Wnt signaling in human bone marrow B lymphopoiesis

BACKGROUND

The early B lymphopoiesis in mammals is regulated through close interactions with stromal cells and components of the intracellular matrix in the bone marrow (BM) microenvironment. Although B lymphopoiesis has been studied for decades, the factors that are implicated in this process, both autocrine and paracrine, are inadequately explored. Wnt signaling is known to be involved in embryonic development and growth regulation of tissues and cancer. Wnt molecules are produced in the BM, and we here ask whether canonical Wnt signaling has a role in regulating human BM B lymphopoiesis.

RESULTS

Examination of the mRNA expression pattern of Wnt ligands, Fzd receptors and Wnt antagonists revealed that BM B progenitor cells and stromal cells express a set of ligands and receptors available for induction of Wnt signaling as well as antagonists for fine tuning of this signaling. Furthermore, different B progenitor maturation stages showed differential expression of Wnt receptors and co-receptors, beta-catenin, plakoglobin, LEF-1 and TCF-4 mRNAs, suggesting canonical Wnt signaling as a regulator of early B lymphopoiesis. Exogenous Wnt3A induced stabilization and nuclear accumulation of beta-catenin in primary lineage restricted B progenitor cells. Also, Wnt3A inhibited B lymphopoiesis of CD133+CD10- hematopoietic progenitor cells and CD10+ B progenitor cells in coculture assays using a supportive layer of stromal cells. This effect was blocked by the Wnt antagonists sFRP1 or Dkk1. Examination of early events in the coculture showed that Wnt3A inhibits cell division of B progenitor cells.

CONCLUSION

These results indicate that canonical Wnt signaling is involved in human BM B lymphopoiesis where it acts as a negative regulator of cell proliferation in a direct or stroma dependent manner.

Differential inhibition of Wnt-3a by Sfrp-1, Sfrp-2, and Sfrp-3

Secreted frizzled related proteins (Sfrps) are extracellular attenuators of Wnt signaling that play important roles in both embryogenesis and oncogenesis. Although Sfrps are generally thought to bind and sequester Wnts away from active receptor complexes, very little is known about the specificity of Sfrp family members for various Wnts. In the developing chick neural tube, sfrp-1, 2, and 3 transcripts are expressed in and adjacent to the dorsal neural tube, where Wnt-1 and Wnt-3a are expressed. To better define the possible roles of Sfrp-1, 2, and 3 in the neural tube, we first tested the ability of purified Sfrps to inhibit Wnt-3a-induced accumulation of beta-catenin in L cells. We find that both Sfrp-1 and Sfrp-2 can inhibit Wnt-3a activity while Sfrp-3 cannot. To determine where Sfrp-1 and Sfrp-2 impinge on the Wnt signaling pathway, we tested the ability of these Sfrps to inhibit Wnt signaling induced by the addition of LiCl, an inhibitor of GSK-3. Sfrp-1 and Sfrp-2 are unable to inhibit the accumulation of beta-catenin in LiCl-treated cells, suggesting that the ability of Sfrps to inhibit the accumulation of beta-catenin is GSK-3 dependent. We have further shown that Sfrp-2 inhibits the ability of ectopic Wnt-3a to stimulate proliferation in the developing chick neural tube. These results provide the framework for understanding how Sfrps function to regulate Wnt-3a activity in developing embryos and in cancer.