Negative Regulator Of Β-catenin Research Articles

Disrupting CCDC137-mediated LZTS2 and β-TrCP interaction in the nucleus inhibits hepatocellular carcinoma development via β-catenin and AKT.

Hepatocellular carcinoma (HCC) is a highly heterogeneous solid tumor, with its biological characteristics intricately linked to the activation of oncogenes. This research specifically explored CCDC137, a molecule within the CCDC family exhibiting the closest association with HCC. Our investigation aimed to unravel the role, underlying mechanisms, and potential therapeutic implications of CCDC137 in the context of HCC. We observed a close correlation between elevated CCDC137 expression and poor prognosis in HCC patients, along with a promotive effect on HCC progression in vitro and in vivo. Mechanistically, we identified LZTS2, a negative regulator of β-catenin, as the binding protein of CCDC137. CCDC137 facilitated K48-linked poly-ubiquitination of LZTS2 at lysine 467 via recruiting E3 ubiquitin ligase β-TrCP in the nucleus, triggering AKT phosphorylation and activation of β-catenin pathway. Moreover, the 1-75 domain of CCDC137 was responsible for the formation of the CCDC137-LZTS2-β-TrCP complex. Subsequently, designed peptides targeting the 1-75 domain of CCDC137 to disrupt CCDC137-LZTS2 interaction demonstrated efficacy in inhibiting HCC progression. This promising outcome was further supported by HCC organoids and patient-derived xenograft (PDX) models, underscoring the potential clinical utility of the peptides. This study elucidated the mechanism of the CCDC137-LZTS2-β-TrCP protein complex in HCC and offered clinically significant therapeutic strategies targeting this complex.

ICBP90, an epigenetic regulator, induces DKK3 promoter methylation, promotes glioma progression, and reduces sensitivity to cis-platinum

Glioma is the most common brain malignancy, characterized by high morbidity, high mortality, and treatment-resistance. Inverted CCAAT box Binding Protein of 90 kDa (ICBP90) has been reported to be involved in tumor progression and the maintenance of DNA methylation. Herein, we constructed ICBP90 over-expression and knockdown glioma cell lines, and found that ICBP90 knockdown inhibited glioma cell proliferation, migration, and invasion. ICBP90 silencing potentially enhanced cellular sensitivity to cis-platinum (DDP) and exacerbated DDP-induced pyroptosis, manifested by the elevated levels of gasdermin D-N-terminal and cleaved caspase 1; whereas, ICBP90 over-expression exhibited the opposite effects. Consistently, ICBP90 knockdown inhibited tumor growth in an in vivo mouse xenograft study using U251 cells stably expressing sh-ICBP90 and oe-ICBP90. Further experiments found that ICBP90 reduced the expression of Dickkopf 3 homolog (DKK3), a negative regulator of β-catenin, by binding its promoter and inducing DNA methylation. ICBP90 knockdown prevented the nuclear translocation of β‐catenin and suppressed the expression of c-Myc and cyclin D1. Besides, DKK3 over-expression restored the effects of ICBP90 over-expression on cell proliferation, migration, invasion, and DDP sensitivity. Our findings suggest that ICBP90 inhibits the expression of DKK3 in glioma by maintaining DKK3 promoter methylation, thereby conducing to ICBP90-mediated carcinogenesis and drug insensitivity.

Glutamine transporter SLC38A3 promotes breast cancer metastasis via Gsk3β/β-catenin/EMT pathway

Breast cancer is the leading cancer-related cause of death in women. Here we show that solute carrier family 38-member 3 (SLC38A3) is overexpressed in breast cancer, particularly in triple-negative breast cancer (TNBC) cells and tissues. Our study reveals that SLC38A3 regulates cellular glutamine, glutamate, asparagine, aspartate, alanine, and glutathione (GSH) levels in breast cancer cells. Our data demonstrate that SLC38A3 enhances cell viability, cell migration and invasion in vitro, and promotes tumor growth and metastasis in vivo, while reducing apoptosis and oxidative stress. Mechanistically, we show that SLC38A3 suppresses the activity of glycogen synthase kinase 3-β (Gsk3β), a negative regulator of β-catenin, and increases protein levels of β-catenin, leading to the upregulation of epithelial-to-mesenchymal-transition (EMT)-inducing transcription factors and EMT markers in breast cancer. In summary, we show that SLC38A3 is overexpressed in breast cancer and promotes breast cancer metastasis via the GSK3β/β-catenin/EMT pathway, presenting a novel therapeutic target to explore for breast cancer.

Pharmacologic inhibition of PARP5, but not that of PARP1 or 2, promotes cytokine production and osteoclastogenesis through different pathways.

PARPs, which are members of the poly(ADP-ribose) polymerase superfamily, promote tumorigenesis and tumour-associated inflammation and are thus therapeutic targets for several cancers. The aim of the present study is to investigate the mechanistic insight into the roles PARPs for inflammation. Primary murine macrophages were cultured in the presence or absence of the PARP5 inhibitor NVP-TNKS656 to examine the role of PARP5 for cytokine production. In contrast to the roles of other PARPs for induction of inflammation, we found in the present study that pharmacologic inhibition of PARP5 induces production of inflammatory cytokines in primary murine macrophages. We found that treatment with the PARP5 inhibitor NVP-TNKS656 in macrophages enhanced steady-state and LPS-mediated cytokine production through degradation of IκBα and subsequent nuclear translocation of NF-κB. We also found that pharmacologic inhibition of PARP5 stabilises the adaptor protein 3BP2, a substrate of PARP5, and that accelerated cytokine production induced by PARP5 inhibition was rescued in 3BP2-deleted macrophages. Additionally, we found that LPS increases the expression of 3BP2 and AXIN1, a negative regulator of β-catenin, through suppression of PARP5 transcripts in macrophages, leading to further activation of cytokine production and inhibition of β-catenin-mediated cell proliferation, respectively. Lastly, we found that PARP5 inhibition in macrophages promotes osteoclastogenesis through stabilisation of 3BP2 and AXIN1, leading to activation of SRC and suppression of β-catenin, respectively. Our results show that pharmacologic inhibition of PARP5 against cancers unexpectedly induces adverse autoinflammatory side effects through activation of innate immunity, unlike inhibition of other PARPs.

Tumor necrosis factor-inducible gene 6 interacts with CD44, which is involved in fate-change of hepatic stellate cells

Tumor necrosis factor-inducible gene 6 protein (TSG-6) is a cytokine secreted by mesenchymal stem cells (MSCs) and regulates MSC stemness. We previously reported that TSG-6 changes primary human hepatic stellate cells (pHSCs) into stem-like cells by activating yes-associated protein-1 (YAP-1). However, the molecular mechanism behind the reprogramming action of TSG-6 in pHSCs remains unknown. Cluster of differentiation 44 (CD44) is a transmembrane protein that has multiple functions depending on the ligand it is binding, and it is involved in various signaling pathways, including the Wnt/β-catenin path-way. Given that β-catenin influences stemness and acts down-stream of CD44, we hypothesized that TSG-6 interacts with the CD44 receptor and stimulates β-catenin to activate YAP-1 during TSG-6-mediated transdifferentiation of HSCs. Immuno-precipitation assays showed the interaction of TSG-6 with CD44, and immunofluorescence staining analyses revealed the colocalization of TSG-6 and CD44 at the plasma membrane of TSG-6-treated pHSCs. In addition, TSG-6 treatment upregulated the inactive form of phosphorylated glycogen synthase kinase (GSK)-3β, which is a negative regulator of β-catenin, and promoted nuclear accumulation of active/nonphosphorylated β-catenin, eventually leading to the activation of YAP-1. However, CD44 suppression in pHSCs following CD44 siRNA treatment blocked the activation of β-catenin and YAP-1, which inhibited the transition of TSG-6-treated HSCs into stem-like cells. Therefore, these findings demonstrate that TSG-6 interacts with CD44 and activates β-catenin and YAP-1 during the conversion of TSG-6-treated pHSCs into stem-like cells, suggesting that this novel pathway is an effective therapeutic target for control-ling liver disease.

ALDHHIGH Population Is Regulated by the AKT/β-Catenin Pathway in a Cervical Cancer Model.

ALDH is an enzyme involved in different cellular processes, including cancer. It has been shown that a cellular subpopulation with high ALDH activity (ALDHHIGH) within a tumor is related to functional capabilities such as stemness, chemoresistance, and tumorigenicity. However, few studies have focused on determining the mechanisms behind ALDH activity within the cells. Previously, our group reported that ALDHHIGH cells have higher tumorigenicity in Cervical Cancer (CC) cell lines. Based on this, we were interested to know the molecular mediators of the ALDHHIGH cells, specifically β-catenin, inasmuch as β-catenin is regulated through different pathways, such as Wnt signaling, and that it acts as a transcriptional co-activator involved in cancer progression. In this work, we show that the increase in ALDHHIGH cell percentage is reverted by β-catenin knockdown. Consistently, upon GSK3-β inactivation, a negative regulator of β-catenin, we observed an increase in ALDHHIGH cells. Additionally, we observed a low percentage of cells positive for Fzd receptor, suggesting that in our model there is a low capacity to respond to Wnt ligands. The analysis of ALDHHIGH cells in a sphere formation model demonstrated the active state of AKT. In accordance with this, impairment of AKT activity not only reduced β-catenin active state, but also the percentage of ALDHHIGH cells. This corroborates that AKT acts upstream of β-catenin, thus affecting the percentage of ALDHHIGH cells. In conclusion, our results show that ALDHHIGH cells are dependent on β-catenin, in spite of the Wnt pathway seems to be dispensable, while AKT emerges as central player supporting a mechanism in this important axis that is not yet well known but its analysis improves our understanding of ALDH activity on CC.

Tankyrase Inhibitors Target Colorectal Cancer Stem Cells via AXIN-Dependent Downregulation of c-KIT Tyrosine Kinase.

Cancer stem cells (CSC) constitute heterogeneous cell subpopulations of a tumor. Although targeting CSCs is important for cancer eradication, no clinically approved drugs that target CSCs have been established. Tankyrase poly(ADP-ribosyl)ates and destabilizes AXIN, a negative regulator of β-catenin, and promotes β-catenin signaling. Here, we report that tankyrase inhibitors downregulate c-KIT tyrosine kinase and inhibit the growth of CD44-positive colorectal CSCs. c-KIT expression in CD44-positive subpopulations of colorectal cancer COLO-320DM cells is associated with their tumor-initiating potential in vivo Tankyrase inhibitors downregulate c-KIT expression in established cell lines, such as COLO-320DM and DLD-1, and colorectal cancer patient-derived cells. These effects of tankyrase inhibitors are caused by reducing the recruitment of SP1 transcription factor to the c-KIT gene promoter and depend on AXIN2 stabilization but not β-catenin downregulation. Whereas c-KIT knockdown inhibits the growth of CD44-positive COLO-320DM cells, c-KIT overexpression in DLD-1 cells confers resistance to tankyrase inhibitors. Combination of a low-dose tankyrase inhibitor and irinotecan significantly inhibited the growth of COLO-320DM tumors in a mouse xenograft model. These observations suggest that tankyrase inhibitors target c-KIT-positive colorectal CSCs and provide a novel therapeutic strategy for cancer.

Abstract B68: EGFR signaling mediated modulation of transcription and probable crosstalk with components of Wnt signaling

Abstract Introduction: The purpose of the study is to examine the crosstalk between HER2/EGFR and Wnt signaling in HER2-positive (HER2+) breast cancer cells. Human epidermal growth factor receptors (HER) constitute a family of four transmembrane receptors (HER1-HER4). Ligand binding to HER1 (EGFR), HER3, and HER4 results in heterodimerization with other HER family members, including HER2. HER2+ breast cancer is characterized by an amplification of the HER2 gene, resulting in an increase in HER2 protein presence on the surface of cells, magnification of downstream intracellular signaling, and enhanced responsiveness to ligand stimulation (e.g., EGF). Approximately 20-30% of breast cancers have HER2 amplifications. The Wnt pathway is highly conserved in mammals and overexpression of some Wnt family members results in cancer. Wnts are ligands that bind to Frizzled/LRP receptors to initiate downstream signaling that results in the stabilization and nuclear translocation of β-catenin. Once in the nucleus, β-catenin associates with activators such as TCF/LEF, SMADs, ATF2, and KLF4 to promote the transcription of many target genes. EGFR and Wnt crosstalk has been observed in various cell types following EGF treatment. As an example, EGF treatment of human epidermoid carcinoma cells results in β-catenin nuclear translocation and activation of TCF/LEF dependent reporters. Mitogen-Activated Protein Kinases (MAPKs), which are activated following EGF stimulation, have been demonstrated to inhibit GSK3β, a negative regulator of β-catenin. However, no genome-wide analysis has been conducted to determine what genes are regulated by β-catenin following EGF treatment in HER2+ breast cancer cells. We sought to determine the modulation of gene expression following the stimulation of HER2+ breast cancer cells with EGF and to investigate the mechanisms that underlie the changes observed in gene expression. Our studies have revealed exciting and novel findings that elucidate the effects of EGFR signaling on the epigenetic landscape. Specifically, we have identified putative β-catenin targets that become activated following EGFR stimulation. We hypothesize that EGFR signaling promotes the activation of specific β-catenin genes in order to alter cellular identity. Methods: RNA-seq and ChIP-seq for H3K18ac and H3K27ac was conducted following an EGF treatment time course in SKBR3 cells. The levels of several proteins of interest were determined by Western blot analysis. The cellular localization of proteins of interest was examined using biochemically fractionated lysates followed by Western blot analysis. Results: RNA-seq analysis following an EGF treatment time course revealed that approximately 2,200 genes are either upregulated or downregulated compared to untreated cells. Moreover, the expression profiles clearly demonstrated waves of transcription. Next, we determined the status of H3K18ac and H3K27ac using ChIP-seq following an EGF time course. We found that H3K18ac and H3K27ac increased globally within 1h post-EGF treatment compared to untreated cells. We conducted a motif discovery search for transcription factor binding sites contained from -1000bp to +200bp for all activated genes and determined that each wave of transcription had some unique putative regulators. As expected, the genes activated at 1h and 2h post-EGF treatment contained c-Jun and JunD binding sites. Surprisingly, TCF3, TCF5, and LEF1 motifs were enriched in some genes that peaked in expression at 6h, 16h, and 24h post EGF treatment. Lastly, we biochemically fractionated the cellular compartments and detected an increase in chromatin associated β-catenin following EGF treatment, suggesting a crosstalk between EGFR and Wnt signaling components. We plan to determine the genome-wide localization of β-catenin following EGF treatment. Conclusions: Our data suggest that a crosstalk between EGFR and Wnt signaling components may regulate β-catenin target genes and lead HER2+ cells' resistance to therapeutic treatment. Citation Format: Miguel Nava, Nwamaka Amobi, Nathan Zemke, Arnold Berk, Robin Farias-Eisner, Jay Vadgama, Yanyuan Wu. EGFR signaling mediated modulation of transcription and probable crosstalk with components of Wnt signaling [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr B68.

In Vitro Transcriptome Response to a Mixture of Lactobacilli Strains in Intestinal Porcine Epithelial Cell Line.

Background: Food and feed supplements containing microorganisms with probiotic potential are of increasing interest due to their healthy promoting effect on human and animals. Their mechanism of action is still unknown. Using a microarray approach, the aim of this study was to investigate the differences in genome-wide gene expression induced by a mixture of three Lactobacillus strains (L. rhamnosus, L. plantarum, and L. paracasei) in intestinal porcine epithelial cells (IPEC-1) and to identify the genes and pathways involved in intestinal barrier functions. Methods: Undifferentiated IPEC-1 cells seeded at a density of 2.0 × 105/mL in 24-wells culture plates were cultivated at 37 °C and 5% CO2 until they reached confluence (2–3 days). Confluent cells monolayer were then cultivated with 1 mL of fresh lactobacilli (LB) mixture suspension prepared for a concentration of approximately 3.3 × 107 CFU/mL for each strain (1 × 108 CFU/mL in total) for 3 h and analyzed by microarray using Gene Spring GX v.11.5. Results: The functional analysis showed that 1811 of the genes modulated by LB treatment are involved in signaling (95% up-regulation, 121 genes with a fold change higher than 10). The most enhanced expression was registered for AXIN2 (axis inhibition protein 2-AXIN2) gene (13.93 Fc, p = 0.043), a negative regulator of β-catenin with a key role in human cancer. LB affected the cellular proliferation by increasing 10 times (Fc) the NF1 gene encoding for the neurofibromin protein, a tumor suppressor that prevent cells from uncontrolled proliferation. The induction of genes like serpin peptidase inhibitor, clade A member 3 (SERPINA 3), interleukin-20 (IL-20), oncostatin M (OSM), granulocyte-macrophage colony-stimulating factor (GM-CSF), and the suppression of chemokine (C-X-C motif) ligand 2/macrophage inflammatory protein 2-alpha (CXCL-2/MIP-2), regulator of G-protein signaling 2 (RGS2), and of pro-inflammatory interleukin-18 (IL-18) genes highlights the protective role of lactobacilli in epithelial barrier function against inflammation and in the activation of immune response. Conclusion: Gene overexpression was the predominant effect produced by lactobacilli treatment in IPEC-1 cells, genes related to signaling pathways being the most affected. The protective role of lactobacilli in epithelial barrier function against inflammation and in the activation of immune response was also noticed.

Methylation of DACT2 contributes to the progression of breast cancer through activating WNT signaling pathway.

The activation of the Wnt/β-catenin signaling pathway has been demonstrated to play important roles in breast carcinogenesis and to be associated with a poorer prognosis in breast cancer patients. However, genetic mutation is not the major reason for Wnt/β-catenin activation in breast cancer. Dishevelled-associated antagonist of β-catenin homolog 2 (DACT2) is a negative regulator of β-catenin and acts as a tumor suppressor in numerous cancer types; however, the expression change and potential role of DACT2 in breast cancer is unknown. The present study detected the expression and function of DACT2 in breast cancer progression. It was identified that the expression of DACT2 significantly decreased in breast cancer tissues compared with paired adjacent normal breast tissues. Additional investigation demonstrated that the hypermethylation of DACT2 gene promoter contributes to the loss of the gene in breast cancer. It was also demonstrated that DACT2 is a tumor suppressor in breast cancer and inhibits the proliferation and invasion of breast cancer cells by repressing the expression of β-catenin target genes associated with tumor growth and metastasis. The present study indicates that the loss of DACT2 may contribute to breast cancer progression and provides a promising therapeutic target for the treatment of breast cancer.

APC Mutations as a Potential Biomarker for Sensitivity to Tankyrase Inhibitors in Colorectal Cancer.

In most colorectal cancers, Wnt/β-catenin signaling is activated by loss-of-function mutations in the adenomatous polyposis coli (APC) gene and plays a critical role in tumorigenesis. Tankyrases poly(ADP-ribosyl)ate and destabilize Axins, a negative regulator of β-catenin, and upregulate β-catenin signaling. Tankyrase inhibitors downregulate β-catenin and are expected to be promising therapeutics for colorectal cancer. However, colorectal cancer cells are not always sensitive to tankyrase inhibitors, and predictive biomarkers for the drug sensitivity remain elusive. Here we demonstrate that the short-form APC mutations predict the sensitivity of colorectal cancer cells to tankyrase inhibitors. By using well-established colorectal cancer cell lines, we found that tankyrase inhibitors downregulated β-catenin in the drug-sensitive, but not resistant, colorectal cancer cells. The drug-sensitive cells showed higher Tcf/LEF transcriptional activity than the resistant cells and possessed "short" truncated APCs lacking all seven β-catenin-binding 20-amino acid repeats (20-AARs). In contrast, the drug-resistant cells possessed "long" APC retaining two or more 20-AARs. Knockdown of the long APCs with two 20-AARs increased β-catenin, Tcf/LEF transcriptional activity and its target gene AXIN2 expression. Under these conditions, tankyrase inhibitors were able to downregulate β-catenin in the resistant cells. These results indicate that the long APCs are hypomorphic mutants, whereas they exert a dominant-negative effect on Axin-dependent β-catenin degradation caused by tankyrase inhibitors. Finally, we established 16 patient-derived colorectal cancer cells and confirmed that the tankyrase inhibitor-responsive cells harbor the short-form APC mutations. These observations exemplify the predictive importance of APC mutations, the most common genetic alteration in colorectal cancers, for molecular targeted therapeutics. Mol Cancer Ther; 16(4); 752-62. ©2017 AACR.

Extensive metabolic disorders are present in APCmin tumorigenesis mice

Wnt signaling plays essential role in mesenchymal stem cell (MSC) differentiation. Activation of Wnt signaling suppresses adipogenesis, but promotes osteogenesis in MSC. Adenomatous polyposis coli (APC) is a negative regulator of β-catenin and Wnt signaling activity. The mutation of APC gene leads to the activation of Wnt signaling and is responsible for tumorigenesis in APCmin mouse; however, very few studies focused on its metabolic abnormalities. The present study reports a widespread metabolic disorder phenotype in APCmin mice. The old APCmin mice have decreased body weight and impaired adipogenesis, but severe hyperlipidemia, which mimic the phenotypes of Familial Adenomatous Polyposis (FAP), an inherited disease also caused by APC gene mutation in human. We found that the expression of lipid metabolism and free fat acids (FA) use genes in the white adipose tissue (WAT) of the APCmin mice is much lower than those of control. The changed gene expression pattern may lead to the disability of circulatory lipid transportation and storage at WAT. Moreover, the APCmin mice could not maintain the core body temperature in cold condition. PET–CT determination revealed that the BAT of APCmin mice has significantly impaired ability to take up 18FDG from the blood. Morphological studies identified that the brown adipocytes of APCmin mice were filled with lipid droplets but fewer mitochondria. These results matched with the findings of impaired BAT function in APCmin mice. Collectively, our study explores a new mechanism that explains abnormal metabolism in APCmin mice and provides insights into studying the metabolic disorders of FAP patients.

Tumor promotion and inhibition by phenobarbital in livers of conditional Apc-deficient mice.

Activation of Wnt/β-catenin signaling is important for human and rodent hepatocarcinogenesis. In mice, the tumor promoter phenobarbital (PB) selects for hepatocellular tumors with activating β-catenin mutations via constitutive androstane receptor activation. PB-dependent tumor promotion was studied in mice with genetic inactivation of Apc, a negative regulator of β-catenin, to circumvent the problem of randomly induced mutations by chemical initiators and to allow monitoring of PB- and Wnt/β-catenin-dependent tumorigenesis in the absence of unknown genomic alterations. Moreover, the study was designed to investigate PB-induced proliferation of liver cells with activated β-catenin. PB treatment provided Apc-deficient hepatocytes with only a minor proliferative advantage, and additional connexin 32 deficiency did not affect the proliferative response. PB significantly promoted the outgrowth of Apc-deficient hepatocellular adenoma (HCA), but simultaneously inhibited the formation of Apc-deficient hepatocellular carcinoma (HCC). The probability of tumor promotion by PB was calculated to be much lower for hepatocytes with loss of Apc, as compared to mutational β-catenin activation. Comprehensive transcriptomic and phosphoproteomic characterization of HCA and HCC revealed molecular details of the two tumor types. HCC were characterized by a loss of differentiated hepatocellular gene expression, enhanced proliferative signaling, and massive over-activation of Wnt/β-catenin signaling. In conclusion, PB exerts a dual role in liver tumor formation by promoting the growth of HCA but inhibiting the growth of HCC. Data demonstrate that one and the same compound can produce opposite effects on hepatocarcinogenesis, depending on context, highlighting the necessity to develop a more differentiated view on the tumorigenicity of this model compound.

Loss of axin2 in murine aortic valves leads to myxomatous disease

In the older population, calcific and myxomatous valve diseases are the two main heart valve diseases. Mechanisms involved in aortic valve calcification are similar to bone formation while myxomatous valves display cartilaginous features with proteoglycan accumulation and increased chondrogenic markers; Sox9, Hapln1 and aggrecan. Similarly, increased Wnt/β‐catenin signaling is measured in calcific aortic valve while loss of Wnt/β‐catenin signaling promotes chondrogenic differentiation in aortic valves. This indicates a major role of Wnt/β‐catenin signaling in heart valve homeostasis although underlying mechanisms are still poorly understood. To further investigate the role of Wnt/β‐catenin signaling, we analyzed heart valves from mice deficient in axin2, a negative regulator of β‐catenin. X‐gal staining performed on Axin2‐lacZ knockout mice (KO) indicates that axin2 is expressed in endothelial and interstitial cells in adult heart valves. At 2 months, KO mice demonstrate thickened proteoglycan‐rich aortic valves with increased Sox9 and Hapln1 expression while focal aggrecan‐rich areas are observed in 4 months old KO mice. Surprisingly thickened aortic valves do not calcify as indicated by lack of alizarin red staining in 1 year old KO mice. These markers are consistent with increased chondrogenic features observed in human myxomatous mitral valves. Interestingly, melanocyte accumulation also is observed in thickened aortic valve, suggesting that axin2 regulates neural crest cells contribution to heart valves. Altogether these data indicate a role for axin2 in heart valve homeostasis and in myxomatous disease. Ongoing in vivo and in vitro studies are investigating the specific functions of axin2 in valve diseases mechanisms.

Glycogen Synthase Kinase 3β Promotes Osteogenic Differentiation of Murine Adipose-Derived Stromal Cells

Although the role of glycogen synthase kinase 3β (GSK3β) in osteogenic differentiation of bone marrow-derived mesenchymal stromal cells (BMSCs) is well-characterized as a negative regulator of β-catenin, its effect on osteogenesis of adipose-derived stromal cells (ADSCs) is poorly understood. Here, we show that GSK3β positively regulates osteogenic differentiation of murine ADSCs. Gain-of-function studies showed that GSK3β promotes in vitro osteogenesis of ADSCs. Regulation of GSK3β activity in ADSCs, either by small interfering RNA (siRNA)-mediated GSK3β silencing or by pharmacological inhibitors, blunted osteogenesis and the expression of osteogenic markers. Importantly, we demonstrated that transgenic mice, engineered to overexpress the constitutively active GSK3β (GSK3β-S9A) mutant, exhibited a marked increase in osteogenesis, whereas expression of the catalytically inactive GSK3β (GSK3β-K85A) in mice inhibits osteogenic differentiation. Molecular analyses showed that the enhanced osteoblast differentiation induced by GSK3β was mediated by downregulation of β-catenin. Remarkably, β-catenin silencing enhances osteogenesis and osteoblast marker gene expression such as alkaline phosphatase (ALP) and osterix. Taken together, these findings demonstrate a novel role for GSK3β in the regulation of osteogenic differentiation in ADSCs.

Inactivation of Glycogen Synthase Kinase-3β Is Required for Osteoclast Differentiation

Glycogen synthase kinase-3β (GSK-3β) is a serine/threonine kinase originally identified as a regulator of glycogen deposition. Although the role of GSK-3β in osteoblasts is well characterized as a negative regulator of β-catenin, its effect on osteoclast formation remains largely unidentified. Here, we show that the GSK-3β inactivation upon receptor activator of NF-κB ligand (RANKL) stimulation is crucial for osteoclast differentiation. Regulation of GSK-3β activity in bone marrow macrophages by retroviral expression of the constitutively active GSK-3β (GSK3β-S9A) mutant inhibits RANKL-induced osteoclastogenesis, whereas expression of the catalytically inactive GSK-3β (GSK3β-K85R) or small interfering RNA (siRNA)-mediated GSK-3β silencing enhances osteoclast formation. Pharmacological inhibition of GSK-3β further confirmed the negative role of GSK-3β in osteoclast formation. We also show that overexpression of the GSK3β-S9A mutant in bone marrow macrophages inhibits RANKL-mediated NFATc1 induction and Ca(2+) oscillations. Remarkably, transgenic mice expressing the GSK3β-S9A mutant show an osteopetrotic phenotype due to impaired osteoclast differentiation. Further, osteoclast precursor cells from the transgenic mice show defects in expression and nuclear localization of NFATc1. These findings demonstrate a novel role for GSK-3β in the regulation of bone remodeling through modulation of NFATc1 in RANKL signaling.

Resveratrol modulates angiogenesis through the GSK3β/β-catenin/TCF-dependent pathway in human endothelial cells

Vascular endothelial growth factor (VEGF) plays a critical role in angiogenesis due to its potent and specific ability to promote the proliferation and migration of endothelial cells. Resveratrol has been shown to have many health-benefiting effects, including the protection of cardiovascular system. In this study we examined the effect of resveratrol on angiogenesis in human umbilical vein endothelial cells (HUVECs). We observed that resveratrol was able to modulate the expression of VEGF and the formation of vascular network in a biphasic pattern. While resveratrol at low concentrations, from 1 to 10 μM, up-regulated the expression of VEGF and promoted angiogenesis, it had opposite effect at high concentrations (20 μM and higher). The biphasic effect of resveratrol on angiogenesis was confirmed by chick chorioallantoic membrane assay. Up-regulation of VEGF expression depended on the nuclear accumulation and transcriptional activity of β-catenin. Correspondingly, GSK3β, a negative regulator of β-catenin, turned into a less active state (phosphorylated at Ser9) in cells exposed to 5 μM of resveratrol, but became more active at 20 μM. We demonstrated that both Akt and ERK signaling pathways, which are known to be critical for angiogenesis, became activated in response to 5 μM of resveratrol and functioned to inactivate GSK3β. Our findings may have implications in the management of cardiovascular diseases and other conditions such as cancer by the use of resveratrol.

Homeodomain-interacting protein kinase 2 (HIPK2) targets β-catenin for phosphorylation and proteasomal degradation

The regulation of intracellular β-catenin levels is central in the Wnt/β-catenin signaling cascade and the activation of the Wnt target genes. Here, we show that homeodomain-interacting protein kinase 2 (HIPK2) acts as a negative regulator of the Wnt/β-catenin pathway. Knock-down of endogenous HIPK2 increases the stability of β-catenin and results in the accumulation of β-catenin in the nucleus, consequently enhancing the expression of Wnt target genes and cell proliferation both in vivo and in cultured cells. HIPK2 inhibits TCF/LEF-mediated target gene activation via degradation of β-catenin. HIPK2 phosphorylates β-catenin at its Ser33 and Ser37 residues without the aid of a priming kinase. Substitutions of Ser33 and Ser37 for alanines abolished the degradation of β-catenin associated with HIPK2. In ex vivo mouse model, HIPK2 knock-down resulted in accumulation of β-catenin, thereby potentiated β-catenin-mediated cell proliferation and tumor formation. Furthermore, the axis duplication induced by the ectopic expression of β-catenin was blocked by co-injection of HIPK2 mRNAs into Xenopus embryos. Taken together, HIPK2 appears to function as a novel negative regulator of β-catenin through its phosphorylation and proteasomal degradation.

Pancreatic β Cell Proliferation Is Stimulated by Wnt Signaling

Both type 1 and type 2 diabetes result from a loss of pancreatic β cell mass. There is considerable interest, therefore, in understanding the mechanisms responsible for β cell proliferation. Previous studies have shown that various components of the Wnt signaling pathway are found in the pancreas and that dysregulation of this pathway can result in reduced islet mass, but the exact mechanisms involved are unknown. Wnts are small proteins that signal though cell surface receptors called Frizzleds, leading to the stabilization and accumulation of β-catenin. This protein then translocates to the nucleus, where it interacts with transcription factors to control the transcription of target genes. Rulifson et al . investigated this link between the Wnt pathway and β cell proliferation by treating cultured mouse pancreatic islets with purified Wnt3a. Immunohistochemical analysis demonstrated increased amounts of Ki67, a marker of cell proliferation. Treatment of islets with Wnt3a also increased the abundance of the mRNAs for the transcription factor Pitx2, a known downstream target of β-catenin, and cyclin D2, a protein involved in control of the cell cycle. Chromatin immunoprecipitation assays revealed that Wnt3a directed the association of Pitx2 with the cyclin D2 gene. Mice with pancreas-specific expression of a constitutively active form of β-catenin had increased β cell proliferation and higher serum insulin levels than did wild-type mice. In contrast, transgenic mice with pancreas-specific inducible expression of Axin, a negative regulator of β-catenin, had reduced islet mass, lower insulin production, and lower abundance of Pitx2 and cyclin D2 than did wild-type mice. This study provides mechanistic evidence of the importance of Wnt signaling for β cell proliferation. I. C. Rulifson, S. K. Karnik, P. W. Heiser, D. ten Berge, H. Chen, X. Gu, M. M. Taketo, R. Nusse, M. Hebrok, S. K. Kim, Wnt signaling regulates pancreatic β cell proliferation. Proc. Natl. Acad. Sci. USA 104 , 6247-6252 (2007). [Abstract] [Full Text]

The latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus manipulates the activity of glycogen synthase kinase-3beta.

The latency-associated nuclear antigen (LANA) of Kaposi's sarcoma-associated herpesvirus (KSHV) is expressed in all KSHV-associated malignancies. LANA is essential for replication and maintenance of the viral episomes during latent infection. However, LANA also has a transcriptional regulatory role and can affect gene expression both positively and negatively. A previously performed yeast two-hybrid screen identified glycogen synthase kinase 3 (GSK-3) as a LANA-interacting protein. Interaction with both GSK-3alpha and GSK-3beta was confirmed in transfected cells with coprecipitation assays. GSK-3beta also interacted with the herpesvirus saimiri homolog ORF73. GSK-3beta is an intermediate in the Wnt signaling pathway and a negative regulator of beta-catenin. In transfected cells, LANA was shown to overcome GSK-3beta-mediated degradation of beta-catenin. Examination of primary effusion lymphoma (PEL) cells found increased levels of beta-catenin relative to KSHV-negative B cells, and this translated into increased activity of a beta-catenin-responsive reporter containing Tcf/Lef binding sites. In tetradecanoyl phorbol acetate-treated PEL cells, loss of LANA expression correlated temporally with loss of detectable beta-catenin. LANA was found to alter the intracellular distribution of GSK-3beta so that nuclear GSK-3beta was more readily detectable in the presence of LANA. Mapping experiments with coimmunoprecipitation assays revealed that both N-terminal and C-terminal LANA sequences were required for efficient GSK-3beta interaction. LANA mutants that were defective for GSK-3beta interaction were unable to mediate GSK-3beta relocalization or activate a beta-catenin-responsive Tcf-luciferase reporter. This study identified manipulation of GSK-3beta activity as a mechanism by which LANA may modify transcriptional activity and contribute to the phenotype of primary effusion lymphoma.