Endogenous Wnt/β-Catenin Signaling Is Required for Cardiac Differentiation in Human Embryonic Stem Cells

Wnt/beta-catenin signaling is an important regulator of differentiation and morphogenesis that can also control stem cell fates. Our group has developed an efficient protocol to generate cardiomyocytes from human embryonic stem (ES) cells via induction with activin A and BMP4.We tested the hypothesis that Wnt/beta-catenin signals control both early mesoderm induction and later cardiac differentiation in this system. Addition of exogenous Wnt3a at the time of induction enhanced cardiac differentiation, while early inhibition of endogenous Wnt/beta-catenin signaling with Dkk1 inhibited cardiac differentiation, as indicated by quantitative RT-PCR analysis for beta-myosin heavy chain (beta-MHC), cardiac troponin T (cTnT), Nkx2.5, and flow cytometry analysis for sarcomeric myosin heavy chain (sMHC). Conversely, late antagonism of endogenously produced Wnts enhanced cardiogenesis, indicating a biphasic role for the pathway in human cardiac differentiation. Using quantitative RT-PCR, we show that canonical Wnt ligand expression is induced by activin A/BMP4 treatment, and the extent of early Wnt ligand expression can predict the subsequent efficiency of cardiogenesis. Measurement of Brachyury expression showed that addition of Wnt3a enhances mesoderm induction, whereas blockade of endogenously produced Wnts markedly inhibits mesoderm formation. Finally, we show that Wnt/beta-catenin signaling is required for Smad1 activation by BMP4.Our data indicate that induction of mesoderm and subsequent cardiac differentiation from human ES cells requires fine-tuned cross talk between activin A/BMP4 and Wnt/beta-catenin pathways. Controlling these pathways permits efficient generation of cardiomyocytes for basic studies or cardiac repair applications

γ-Catenin is overexpressed in acute myeloid leukemia and promotes the stabilization and nuclear localization of β-catenin

Canonical Wnt signaling regulates the transcription of T-cell factor (TCF)-responsive genes through the stabilization and nuclear translocation of the transcriptional co-activator, β-catenin. Overexpression of β-catenin features prominently in acute myeloid leukemia (AML) and has previously been associated with poor clinical outcome. Overexpression of γ-catenin mRNA (a close homologue of β-catenin) has also been reported in AML and has been linked to the pathogenesis of this disease, however, the relative roles of these catenins in leukemia remains unclear. Here we report that overexpression and aberrant nuclear localization of γ-catenin is frequent in AML. Significantly, γ-catenin expression was associated with β-catenin stabilization and nuclear localization. Consistent with this, we found that ectopic γ-catenin expression promoted the stabilization and nuclear translocation of β-catenin in leukemia cells. β-Catenin knockdown demonstrated that both γ- and β-catenin contribute to TCF-dependent transcription in leukemia cells. These data indicate that γ-catenin expression is a significant factor in the stabilization of β-catenin in AML. We also show that although normal cells exclude nuclear translocation of both γ- and β-catenin, this level of regulation is lost in the majority of AML patients and cell lines, which allow nuclear accumulation of these catenins and inappropriate TCF-dependent transcription

Inhibition of Melanogenesis by the Pyridinyl Imidazole Class of Compounds: Possible Involvement of the Wnt/β-Catenin Signaling Pathway

While investigating the role of p38 MAPK in regulating melanogenesis, we found that pyridinyl imidazole inhibitors class compounds as well as the analog compound SB202474, which does not inhibit p38 MAPK, suppressed both α-MSH-induced melanogenesis and spontaneous melanin synthesis. In this study, we demonstrated that the inhibitory activity of the pyridinyl imidazoles correlates with inhibition of the canonical Wnt/β-catenin pathway activity. Imidazole-treated cells showed a reduction in the level of Tcf/Lef target genes involved in the β-catenin signaling network, including ubiquitous genes such as Axin2, Lef1, and Wisp1 as well as cell lineage-restricted genes such as microphthalmia-associated transcription factor and dopachrome tautomerase. Although over-expression of the Wnt signaling pathway effector β-catenin slightly restored the melanogenic program, the lack of complete reversion suggested that the imidazoles interfered with β-catenin-dependent transcriptional activity rather than with β-catenin expression. Accordingly, we did not observe any significant change in β-catenin protein expression. The independence of p38 MAPK activity from the repression of Wnt/β-catenin signaling pathway was confirmed by small interfering RNA knockdown of p38 MAPK expression, which by contrast, stimulated β-catenin-driven gene expression. Our data demonstrate that the small molecule pyridinyl imidazoles possess two distinct and opposite mechanisms that modulate β-catenin dependent transcription: a p38 inhibition-dependent effect that stimulates the Wnt pathway by increasing β-catenin protein expression and an off-target mechanism that inhibits the pathway by repressing β-catenin protein functionality. The p38-independent effect seems to be dominant and, at least in B16-F0 cells, results in a strong block of the Wnt/β-catenin signaling pathway

Völkisch und sozial? : Neonazistische Agitation gegen die neue EU-Freizügigkeit für Arbeitnehmerinnen

Wnt/β-catenin signalling pathway is crucial for the formation of many tissues and organs during development. In recent years, this pathway has also been found to regulate the biology of stem cells in the intestine and probably in other organs in adult life. Abnormal activation of Wnt/β-catenin signalling, which controls the expression of a high number of genes, is critical for the initiation and progression of most colorectal cancers. In line with this, the gene expression signature induced by activation of the Wnt/β-catenin pathway defines the intestinal stem cells present at the bottom of the crypts and also colon cancer stem cells. This supports the importance of inhibitors of the Wnt/β-catenin pathway as potential agents in colorectal cancer therapy. However, the complexity, wide activity in the organism modulating the biology of several cell types, and characteristics of this pathway have delayed the identification of suitable targets and so, the development of such inhibitors that are only now reaching the clinic.Peer reviewe

WIKI4, a Novel Inhibitor of Tankyrase and Wnt/beta-Catenin Signaling

The Wnt/ß-catenin signaling pathway controls important cellular events during development and often contributes to disease when dysregulated. Using high throughput screening we have identified a new small molecule inhibitor of Wnt/ß-catenin signaling, WIKI4. WIKI4 inhibits expression of ß-catenin target genes and cellular responses to Wnt/ß-catenin signaling in cancer cell lines as well as in human embryonic stem cells. Furthermore, we demonstrate that WIKI4 mediates its effects on Wnt/ß-catenin signaling by inhibiting the enzymatic activity of TNKS2, a regulator of AXIN ubiquitylation and degradation. While TNKS has previously been shown to be the target of small molecule inhibitors of Wnt/ß-catenin signaling, WIKI4 is structurally distinct from previously identified TNKS inhibitors

AKT Kinase Activity Is Required for Lithium to Modulate Mood-Related Behaviors in Mice

Bipolar disorder (BP) is a debilitating psychiatric disorder, affecting ∼2% of the worldwide population, for which the etiological basis, pathogenesis, and neurocircuitry remain poorly understood. Individuals with BP suffer from recurrent episodes of mania and depression, which are commonly treated with the mood stabilizer lithium. However, nearly half of BP patients do not respond adequately to lithium therapy and the clinically relevant mechanisms of lithium for mood stabilization remain elusive. Here, we modeled lithium responsiveness using cellular assays of glycogen synthase kinase 3 (GSK-3) signaling and mood-related behavioral assays in inbred strains of mice that differ in their response to lithium. We found that activating AKT through phosphosrylation of a key regulatory site (Thr308) was associated with lithium response—activation of signaling pathways downstream of GSK-3 in cells and attenuation of mood-related behaviors in mice—and this response was attenuated by selective and direct inhibition of AKT kinase activity. Conversely, the expression of constitutively active AKT1 in both the cellular and behavioral assays conferred lithium sensitivity. In contrast, selective and direct GSK-3 inhibition by the ATP-competitive inhibitor CHIR99021 bypassed the requirement for AKT activation and modulated behavior in both lithium-responsive and non-responsive mouse strains. These results distinguish the mechanism of action of lithium from direct GSK-3 inhibition both in vivo and in vitro, and highlight the therapeutic potential for selective GSK-3 inhibitors in BP treatment