Nuclear localization of beta-catenin by interaction with transcription factor LEF-1

Akt is negatively regulated by the MULAN E3 ligase

The serine/threonine kinase Akt functions in multiple cellular processes, including cell survival and tumor development. Studies of the mechanisms that negatively regulate Akt have focused on dephosphorylation-mediated inactivation. In this study, we identified a negative regulator of Akt, MULAN, which possesses both a RING finger domain and E3 ubiquitin ligase activity. Akt was found to directly interact with MULAN and to be ubiquitinated by MULAN in vitro and in vivo. Other molecular assays demonstrated that phosphorylated Akt is a substantive target for both interaction with MULAN and ubiquitination by MULAN. The results of the functional studies suggest that the degradation of Akt by MULAN suppresses cell proliferation and viability. These data provide insight into the Akt ubiquitination signaling network.

Crystal structures of the armadillo repeat domain of adenomatous polyposis coli and its complex with the tyrosine-rich domain of Sam68

Adenomatous polyposis coli (APC) is a tumor suppressor protein commonly mutated in colorectal tumors. APC plays important roles in Wnt signaling and other cellular processes. Here, we present the crystal structure of the armadillo repeat (Arm) domain of APC, which facilitates the binding of APC to various proteins. APC-Arm forms a superhelix with a positively charged groove. We also determined the structure of the complex of APC-Arm with the tyrosine-rich (YY) domain of the Src-associated in mitosis, 68 kDa protein (Sam68), which regulates TCF-1 alternative splicing. Sam68-YY forms numerous interactions with the residues on the groove and is thereby fixed in a bent conformation. We assessed the effects of mutations and phosphorylation on complex formation between APC-Arm and Sam68-YY. Structural comparisons revealed different modes of ligand recognition between the Arm domains of APC and other Arm-containing proteins.

Mouse Tcf3 represses canonical Wnt signaling by either competing for β-catenin binding or through occupation of DNA-binding sites

Tcf3 acts as a transcription factor controlling gene expression in canonical Wnt signaling. In this study we show that mouse Tcf3 represses canonical Wnt signaling in mouse neural stem cells and in human HEK 293 cells. We demonstrate that mouse Tcf3 mediates repression of both moderate and high levels of canonical Wnt signaling, by either competing with other members of the Tcf/Lef family for binding to β-catenin, or for binding to DNA. We observed that the repressor activity of mouse Tcf3 was only relieved effectively upon simultaneous disruption of both mechanisms. Immunofluorescence of transfected HEK 293 cells showed co-localization of β-catenin and Tcf3 in the nucleus of cells transfected with full-length Tcf3, but not in cells transfected with N-terminal deleted versions. A direct physical interaction between β-catenin and Tcf3 in the nucleus was confirmed by co-immunoprecipitation studies. The inhibitory β-catenin/Tcf3 interface was independent of the ability of Tcf3 to directly interact with DNA.

LRP5 and bone mass regulation: Where are we now?

The discovery of causal mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene underlying conditions of altered bone mass ushered in a new era in bone research. Since those original publications, the role of Lrp5 and the Wnt/β-catenin signaling pathway controlled by Lrp5 and its homologs, Lrp6 and Lrp4, in bone mass regulation has been an intense area of investigation. Studies to date have implicated this pathway in skeletal development, osteoblast differentiation and proliferation, osteoblast/osteocyte apoptosis, regulation of the balance between osteogenesis-chondrogenesis-adipogenesis, regulation of osteoclastogenesis and the response of bone to mechanical loading. Interestingly, the data from knockout and transgenic mice involving Lrp4/5/6 and/or their regulators, as well as β-catenin signaling pathway components, and in vitro studies have sometimes yielded conflicting results. Adding to the complexity of the system are the studies that suggested Lrp5 regulated bone mass through a gut-bone endocrine signaling system involving Lrp5 mediated control of gut serotonin synthesis. However, recent studies have called this into question and so this provocative concept remains an open question. Clearly, the manipulation of Lrp5/Wnt/β-catenin pathway presents as a major target for drug development to treat diseases of low bone mass such as osteoporosis and these new therapies are in full progress. At present, although it is clear that Lrp5 has a role in bone mass regulation, much of the details remain to be elucidated and this is a major and exciting challenge for future studies.

Normal morphogenesis of epithelial tissues and progression of epithelial tumors

Epithelial cells organize into various tissue architectures that largely maintain their structure throughout the life of an organism. For decades, the morphogenesis of epithelial tissues has fascinated scientists at the interface of cell, developmental, and molecular biology. Systems biology offers ways to combine knowledge from these disciplines by building integrative models that are quantitative and predictive. Can such models be useful for gaining a deeper understanding of epithelial morphogenesis? Here, we take inventory of some recurring themes in epithelial morphogenesis that systems approaches could strive to capture. Predictive understanding of morphogenesis at the systems level would prove especially valuable for diseases such as cancer, where epithelial tissue architecture is profoundly disrupted.

How do they do Wnt they do?: regulation of transcription by the Wnt/β-catenin pathway

Wnt/β-catenin signalling is known to play many roles in metazoan development and tissue homeostasis. Misregulation of the pathway has also been linked to many human diseases. In this review, specific aspects of the pathway's involvement in these processes are discussed, with an emphasis on how Wnt/β-catenin signalling regulates gene expression in a cell and temporally specific manner. The T-cell factor (TCF) family of transcription factors, which mediate a large portion of Wnt/β-catenin signalling, will be discussed in detail. Invertebrates contain a single TCF gene that contains two DNA-binding domains, the high mobility group (HMG) domain and the C-clamp, which increases the specificity of DNA binding. In vertebrates, the situation is more complex, with four TCF genes producing many isoforms that contain the HMG domain, but only some of which possess a C-clamp. Vertebrate TCFs have been reported to act in concert with many other transcription factors, which may explain how they obtain sufficient specificity for specific DNA sequences, as well as how they achieve a wide diversity of transcriptional outputs in different cells.

Long-distance signaling from synapse to nucleus via protein messengers

The communication between synapses and the cell nucleus has attracted considerable interest for many years. This interest is largely fueled by the idea that synapse-to-nucleus signaling might specifically induce the expression of genes that make long-term memory "stick." However, despite many years of research, it is still essentially unclear how synaptic signals are conveyed to the nucleus, and it remains to a large degree enigmatic how activity-induced gene expression feeds back to synaptic function. In this chapter, we will focus on the activity-dependent synapto-nuclear trafficking of protein messengers and discuss the underlying mechanisms of their retrograde transport and their supposed functional role in neuronal plasticity.

Signaling from the adherens junction

The cadherin/catenin complex organizes to form a structural Velcro that joins the cytoskeletal networks of adjacent cells. Functional loss of this complex arrests the development of normal tissue organization, and years of research have gone into teasing out how the physical structure of adhesions conveys information to the cell interior. Evidence that most cadherin-binding partners also localize to the nucleus to regulate transcription supports the view that cadherins serve as simple stoichiometric inhibitors of nuclear signals. However, it is also clear that cadherin-based adhesion initiates a variety of molecular events that can ultimately impact nuclear signaling. This chapter discusses these two modes of cadherin signaling in the context of tissue growth and differentiation.

Proteasome and cancer

Cancer is one of the most frightful diseases mostly resulting in mortality; it has recently become more possible to overcome with the help of new therapies. In this direction, carcinogenesis is defined as a complicated process that can include several different factors that contribute to its progress. Proteasome is implicated in cancer studies as it is the main degradation system for oxidatively damaged proteins and also for several proteins playing a role in the cell cycle and transcription, which are important for cancer improvement. Because of this crucial role of proteasome in cancer development, myriad in vitro and in vivo studies have focused on the proteasome in different cancer cases. In this chapter, the involvement of proteasome in the degradation of cancer-related proteins is explained with the results of representative studies. Related to these proteins, the use of proteasome inhibitors in cancer treatment is reviewed.

Wnt signaling and telomerase activation of hepatoblastoma: correlation with chemosensitivity and surgical resectability

PURPOSE

Recently, it became apparent that telomerase directly modulated Wnt signaling as a cofactor in a β-catenin transcriptional complex. In this study, we investigated Wnt/β-catenin signaling and telomerase activation in hepatoblastoma (HBL).

METHODS

Tumors derived from 56 HBL cases treated with the Japanese Study Group for Pediatric Liver Tumors (JPLT) Protocol-2 were analyzed for oncogenic mutations (missense mutations and interstitial deletions in the third exon) of the CTNNB1 gene-encoding β-catenin and for the expression levels of telomerase reverse transcriptase (TERT).

RESULTS

Oncogenic mutations of CTNNB1 were detected in 42 cases (75%). The expression levels of TERT were significantly higher in 14 cases without mutation (P < .05) and in 8 cases with metastasis (P < .01). Interestingly, Wnt/β-catenin target genes were significantly activated in the tumors without mutations (P = .013). In cases with mutations, preoperative chemotherapy was more effective (P = .008), and complete resection rate was higher (P = .034). Consequently, 2 patients with mutations and 4 patients without mutations died of disease (P = .013). High expression of TERT was detected in all tumors of these dead patients.

CONCLUSIONS

Wnt/β-catenin signaling in the HBLs without CTNNB1 mutations was activated by high expression of TERT. The clinical courses in HBLs without CTNNB1 mutations seemed to be unfavorable because of chemoresistance and low rates of resectability.

Silymarin targets β-catenin signaling in blocking migration/invasion of human melanoma cells

Metastatic melanoma is a leading cause of death from skin diseases, and is often associated with activation of Wnt/β-catenin signaling pathway. We have examined the inhibitory effect of silymarin, a plant flavanoid from Silybum marianum, on cell migration of metastasis-specific human melanoma cell lines (A375 and Hs294t) and assessed whether Wnt/β-catenin signaling is the target of silymarin. Using an in vitro invasion assay, we found that treatment of human melanoma cell lines with silymarin resulted in concentration-dependent inhibition of cell migration, which was associated with accumulation of cytosolic β-catenin, while reducing the nuclear accumulation of β-catenin (i.e., β-catenin inactivation) and reducing the levels of matrix metalloproteinase (MMP) -2 and MMP-9 which are the down-stream targets of β-catenin. Silymarin enhanced: (i) the levels of casein kinase 1α, glycogen synthase kinase-3β and phosphorylated-β-catenin on critical residues Ser(45), Ser(33/37) and Thr(41), and (ii) the binding of β-transducin repeat-containing proteins (β-TrCP) with phospho forms of β-catenin in melanoma cells. These events play important roles in degradation or inactivation of β-catenin. To verify whether β-catenin is a potent molecular target of silymarin, the effect of silymarin was determined on β-catenin-activated (Mel 1241) and β-catenin-inactivated (Mel 1011) melanoma cells. Treatment of Mel 1241 cells with silymarin or FH535, an inhibitor of Wnt/β-catenin pathway, significantly inhibited cell migration of Mel 1241 cells, which was associated with the elevated levels of casein kinase 1α and glycogen synthase kinase-3β, and decreased accumulation of nuclear β-catenin and inhibition of MMP-2 and MMP-9 levels. However, this effect of silymarin and FH535 was not found in Mel 1011 melanoma cells. These results indicate for the first time that silymarin inhibits melanoma cell migration by targeting β-catenin signaling pathway.

Wnt/Β-catenin and sex hormone signaling in endometrial homeostasis and cancer

A delicate balance between estrogen and progestagen signaling underlies proper functioning of the female reproductive tract and, in particular, the monthly re- and degenerative phases characteristic of the menstrual cycle. Here, we propose that the canonical Wnt/β-catenin signaling pathway may underlie this finely tuned hormonal equilibrium in endometrial homeostasis and, upon its constitutive activation, lead to neoplastic transformation of the endometrium. During the menstrual cycle, estradiol will enhance Wnt/β-catenin signaling in the proliferative phase, while progesterone inhibits Wnt/β-catenin signaling, thus restraining estrogens' proliferative actions, during the secretory phase. In case of enhanced or unopposed estrogen signaling, constitutive activation of Wnt/β-catenin signaling will trigger endometrial hyperplasia, which may develop further into endometrial cancer.

Inhibition of glycogen synthase kinase-3 increases the cytotoxicity of enzastaurin

Cutaneous T cell lymphomas (CTCL) represent a spectrum of several distinct non-Hodgkin's lymphomas that are characterized by an invasion of the skin by malignant, clonal lymphocytes. Our lab has previously demonstrated that the Protein Kinase C (PKC) β inhibitor Enzastaurin increases apoptosis in malignant lymphocytes of CTCL. These results directly led to a clinical trial for Enzastaurin in CTCL where it was well tolerated and showed modest activity. To ascertain a means of improving the efficacy of Enzastaurin, we investigated complimentary signaling pathways and identified Glycogen Synthase Kinase 3 (GSK3) as important in survival signaling in CTCL. Enzastaurin combined with GSK3 inhibitors demonstrated anenhancement of cytotoxicity. Treatment with a combination of Enzastaurin and the GSK3 inhibitor AR-A014418 resulted in up-regulation of β catenin total protein and β catenin-mediated transcription. Inhibition of β catenin-mediated transcription or shRNA knockdown of β catenin decreased the cytotoxic effects of Enzastaurin plus AR-A014418. In addition, treatment with Enzastaurin and AR-A014418 decreased the mRNA levels and surface expression of CD44. shRNA knockdown of β catenin also restored CD44 surface expression. Our observations provide a rationale for the combined targeting of PKC and GSK3 signaling pathways in CTCL to enhance the therapeutic outcome.

Regulation of β-catenin by t-DARPP in upper gastrointestinal cancer cells

Background

Truncated dopamine and cyclic-AMP-regulated phosphoprotein (t-DARPP) is frequently overexpressed in gastrointestinal malignancies. In this study, we examined the role of t-DARPP in regulating β-catenin.

Results

The pTopFlash construct that contains multiple TCF/LEF-binding sites was used as a measure of β-catenin/TCF transcription activity. Gastric (AGS, MKN28) and esophageal (FLO-1) adenocarcinoma cancer cell lines that lack t-DARPP expression were utilized to establish stable and transient in vitro expression models of t-DARPP. The expression of t-DARPP led to a significant induction of the pTOP reporter activity, indicative of activation of β-catenin/TCF nuclear signaling. Immunofluorescence assays supported this finding and showed accumulation and nuclear translocation of β-catenin in cells expressing t-DARPP. These cells had a significant increase in their proliferative capacity and demonstrated up-regulation of two transcription targets of β-catenin/TCF: Cyclin D1 and c-MYC. Because phosphorylated GSK-3β is inactive and loses its ability to phosphorylate β-catenin and target it towards degradation by the proteasome, we next examined the levels of phospho-GSK-3β. These results demonstrated an increase in phospho-GSK-3β and phospho-AKT. The knockdown of endogenous t-DARPP in MKN45 cancer cells demonstrated a reversal of the signaling events. To examine whether t-DARPP mediated GSK-3β phosphorylation in an AKT-dependent manner, we used a pharmacologic inhibitor of PI3K/AKT, LY294002, in cancer cells expressing t-DARPP. This treatment abolished the phosphorylation of AKT and GSK-3β leading to a reduction in β-catenin, Cyclin D1, and c-MYC protein levels.

Conclusions

Our findings demonstrate, for the first time, that t-DARPP regulates β-catenin/TCF activity, thereby implicating a novel oncogenic signaling in upper gastrointestinal cancers.

The Notch-2 gene is regulated by Wnt signaling in cultured colorectal cancer cells

Background

Notch and Wnt pathways are key regulators of intestinal homeostasis and alterations in these pathways may lead to the development of colorectal cancer (CRC). In CRC the Apc/β-catenin genes in the Wnt signaling pathway are frequently mutated and active Notch signaling contributes to tumorigenesis by keeping the epithelial cells in a proliferative state. These pathways are simultaneously active in proliferative adenoma cells and a crosstalk between them has previously been suggested in normal development as well as in cancer.

Principal Findings

In this study, in silico analysis of putative promoters involved in transcriptional regulation of genes coding for proteins in the Notch signaling pathway revealed several putative LEF-1/TCF sites as potential targets for β-catenin and canonical Wnt signaling. Further results from competitive electrophoretic mobility-shift assay (EMSA) studies suggest binding of several putative sites in Notch pathway gene promoters to in vitro translated β-catenin/Lef-1. Wild type (wt)-Apc negatively regulates β-catenin. By induction of wt-Apc or β-catenin silencing in HT29 cells, we observed that several genes in the Notch pathway, including Notch-2, were downregulated. Finally, active Notch signaling was verified in the Apc^Min/+ mouse model where Hes-1 mRNA levels were found significantly upregulated in intestinal tumors compared to normal intestinal mucosa. Luciferase assays showed an increased activity for the core and proximal Notch-2 promoter upon co-transfection of HCT116 cells with high expression recombinant Tcf-4, Lef-1 or β-catenin.

Conclusions

In this paper, we identified Notch-2 as a novel target for β-catenin-dependent Wnt signaling. Furthermore our data supports the notion that additional genes in the Notch pathway might be transcriptionally regulated by Wnt signaling in colorectal cancer.

Postgenomic technologies targeting the Wnt signaling network

The recent development of high-throughput sequencing technologies and the availability of whole genome sequences of a variety of living organisms, including that of humans, have led to an enormous push in the quest for a comprehensive inquiry for the function of each and every gene discovered in different model organisms. A major conclusion from the sequencing projects was that while forward genetics had been extremely successful in identifying key genes/components of many biological processes, such as signal transduction cascades, the function(s) of the majority of genes in the genome remains a mystery. In this article, we discuss the use of a variety of high-throughput postgenomic tools, including functional genomics, proteomics, and chemical genetics that are being implemented in an exhaustive molecular dissection of a key evolutionarily conserved signal transduction pathway, namely the Wnt/wingless (wg) pathway and its associated signaling network.

VentX trans-activates p53 and p16ink4a to regulate cellular senescence

Cell senescence is a process of irreversible arrest of cell proliferation and plays an important role in tumor suppression. Recent studies showed that Wnt inhibition is a trigger of cellular senescence. Using methods of reverse genetics, we recently identified VentX, a human homolog of the vertebrate Xenopus Vent family of homeobox genes, as a novel Wnt repressor and a putative tumor suppressor in lymphocytic leukemia. Here, we show that VentX is a direct transcriptional activator of p53-p21 and p16ink4a-Rb tumor suppression pathways. Ectopic expression of VentX in cancer cells caused an irreversible cell cycle arrest with a typical senescence-like phenotype. Conversely, inhibition of VentX expression by RNA interference ameliorated chemotherapeutic agent-induced senescence in lymphocytic leukemia cells. The results of our study further reveal the mechanisms underlying tumor suppression function of VentX and suggest a role of VentX as a potential target in cancer prevention and treatment.

Bicuspid aortic valve disease: the role of oxidative stress in Lrp5 bone formation

The bicuspid aortic valve is a common congenital cardiac anomaly, having a prevalence of 0.9% to 1.37% in the general population and a male preponderance ratio of 2:1. The recognition of a bicuspid aortic valve is clinically relevant because of its association with aortic stenosis or regurgitation, aortic aneurysm or dissection, and infective endocarditis. Although some patients with a bicuspid aortic valve may go undetected without clinical complications for a lifetime, the vast majority will require intervention, most often surgery, at some point. In fact, the natural history of bicuspid aortic valve is that of valve calcification and progressive stenosis that typically occur at a faster rate than in tricuspid aortic valves. This pattern of presentation supports the hypothesis that shear stress in patients with congenitally abnormal aortic valves may contribute to an earlier leaflet calcification. However, there is emerging research data showing that the valve calcification process might have a similar pathophysiologic process to that of vascular atherosclerosis. This review focuses on the current knowledge of the cellular mechanisms of bicuspid aortic valve.

Evolution of the parathyroid hormone family and skeletal formation pathways

Bone is considered to be a feature of higher vertebrates and one of the features that was required for the movement from water onto land. But there are a number of evolutionarily important species that have cartilaginous skeletons, including sharks. Both bony and cartilaginous fish are believed to have a common ancestor who had a bony skeleton. A number of factors and pathways have been shown to be involved in the development and maintenance of bony skeleton including the Wnt pathway and the parathyroid hormone gene family. The study of these pathways and factors in cartilaginous animals may shed light on the evolution of the vertebrate skeleton.

Possible involvement of NEDD4 in keloid formation; its critical role in fibroblast proliferation and collagen production

Keloid represents overgrowth of granulation tissue, which is characterized by collection of atypical fibroblasts with excessive deposition of extracellular matrix components, after skin injury, but its etiology is still largely unknown. We recently performed genome-wide association study (GWAS) of keloid and identified NEDD4 to be one of candidate molecules associated with keloid susceptibility. Here we demonstrate a possible mechanism of NEDD4 involvement in keloid formation through enhancement of the proliferation and invasiveness of fibroblasts as well as upregulation of type 1 collagen expression. Activation of NEDD4 affected subcellular localization and protein stability of p27 which was implied its critical role in contact inhibition. It also induced accumulation of β-catenin in the cytoplasm and activated the TCF/β-catenin transcriptional activity. Furthermore, NEDD4 upregulated expressions of fibronectin and type 1 collagen and contributed to the excessive accumulation of extracellular matrix. Our findings provide new insights into mechanism developing keloid and can be applied for development of a novel treatment for keloid.

Beta-catenin signaling in hepatic development and progenitors: which way does the WNT blow?

The Wnt/β-catenin pathway is an evolutionarily conserved signaling cascade that plays key roles in development and adult tissue homeostasis and is aberrantly activated in many tumors. Over a decade of work in mouse, chick, xenopus, and zebrafish models has uncovered multiple functions of this pathway in hepatic pathophysiology. Specifically, beta-catenin, the central component of the canonical Wnt pathway, is implicated in the regulation of liver regeneration, development, and carcinogenesis. Wnt-independent activation of beta-catenin by receptor tyrosine kinases has also been observed in the liver. In liver development across various species, through regulation of cell proliferation, differentiation, and maturation, beta-catenin directs foregut endoderm specification, hepatic specification of the foregut, and hepatic morphogenesis. Its role has also been defined in adult hepatic progenitors or oval cells especially in their expansion and differentiation. Thus, beta-catenin undergoes tight temporal regulation to exhibit pleiotropic effects during hepatic development and in hepatic progenitor biology.

Beta-catenin signaling, liver regeneration and hepatocellular cancer: sorting the good from the bad

Among the adult organs, liver is unique for its ability to regenerate. A concerted signaling cascade enables optimum initiation of the regeneration process following insults brought about by surgery or a toxicant. Additionally, there exists a cellular redundancy, whereby a transiently amplifying progenitor population appears and expands to ensure regeneration, when differentiated cells of the liver are unable to proliferate in both experimental and clinical scenarios. One such pathway of relevance in these phenomena is Wnt/β-catenin signaling, which is activated relatively early during regeneration mostly through post-translational modifications. Once activated, β-catenin signaling drives the expression of target genes that are critical for cell cycle progression and contribute to initiation of the regeneration process. The role and regulation of Wnt/β-catenin signaling is now documented in rats, mice, zebrafish and patients. More recently, a regenerative advantage of the livers in β-catenin overexpressing mice was reported, as was also the case after exogenous Wnt-1 delivery to the liver paving the way for assessing means to stimulate the pathway for therapeutics in liver failure. β-Catenin is also pertinent in hepatic oval cell activation and differentiation. However, aberrant activation of the Wnt/β-catenin signaling is reported in a significant subset of hepatocellular cancers (HCC). While many mechanisms of such activation have been reported, the most functional means of aberrant and sustained activation is through mutations in the β-catenin gene or in AXIN1/2, which encodes for a scaffolding protein critical for β-catenin degradation. Intriguingly, in experimental models hepatic overexpression of normal or mutant β-catenin is insufficient for tumorigenesis. In fact β-catenin loss promoted chemical carcinogenesis in the liver due to alternate mechanisms. Since most HCC occur in the backdrop of chronic hepatic injury, where hepatic regeneration is necessary for maintenance of liver function, but at the same time serves as the basis of dysplastic changes, this Promethean attribute exhibits a Jekyll and Hyde behavior that makes distinguishing good regeneration from bad regeneration essential for targeting selective molecular pathways as personalized medicine becomes a norm in clinical practice. Could β-catenin signaling be one such pathway that may be redundant in regeneration and indispensible in HCC in a subset of cases?

Targeting the oncogenic protein beta-catenin to enhance chemotherapy outcome against solid human cancers

Background

Beta-catenin is a multifunctional oncogenic protein that contributes fundamentally to cell development and biology. Elevation in expression and activity of β-catenin has been implicated in many cancers and associated with poor prognosis. Beta-catenin is degraded in the cytoplasm by glycogen synthase kinase 3 beta (GSK-3β) through phosphorylation. Cell growth and proliferation is associated with β-catenin translocation from the cytoplasm into the nucleus.

This laboratory was the first to demonstrate that selenium-containing compounds can enhance the efficacy and cytotoxicity of anticancer drugs in several preclinical xenograft models. These data provided the basis to identify mechanism of selenium action focusing on β-catenin as a target. This study was designed to: (1) determine whether pharmacological doses of methylseleninic acid (MSeA) have inhibitory effects on the level and the oncogenic activity of β-catenin, (2) investigate the kinetics and the mechanism of β-catenin inhibition, and (3) confirm that inhibition of β-catenin would lead to enhanced cytotoxicity of standard chemotherapeutic drugs.

Results

In six human cancer cell lines, the inhibition of total and nuclear expression of β-catenin by MSeA was dose and time dependent. The involvement of GSK-3β in the degradation of β-catenin was cell type dependent (GSK-3β-dependent in HT-29, whereas GSK-3β-independent in HCT-8). However, the pronounced inhibition of β-catenin by MSeA was independent of various drug treatments and was not reversed after combination therapy.

Knockout of β-catenin by ShRNA and its inhibition by MSeA yielded similar enhancement of cytotoxicity of anticancer drugs.

Collectively, the generated data demonstrate that β-catenin is a target of MSeA and its inhibition resulted in enhanced cytotoxicity of chemotherapeutic drugs.

Conclusions

This study demonstrates that β-catenin, a molecule associated with drug resistance, is a target of selenium and its inhibition is associated with increased multiple drugs cytotoxicity in various human cancers. Further, degradation of β-catenin by GSK-3β is not a general mechanism but is cell type dependent.

The leukemia-associated Mllt10/Af10-Dot1l are Tcf4/β-catenin coactivators essential for intestinal homeostasis

Wnt signaling maintains the undifferentiated state of intestinal crypt progenitor cells by inducing the formation of nuclear TCF4/β-catenin complexes. In colorectal cancer, activating mutations in Wnt pathway components cause inappropriate activation of TCF4/β-catenin-driven transcription. Despite the passage of a decade after the discovery of TCF4 and β-catenin as the molecular effectors of the Wnt signal, few transcriptional activators essential and unique to the regulation of this transcription program have been found. Using proteomics, we identified the leukemia-associated Mllt10/Af10 and the methyltransferase Dot1l as Tcf4/β-catenin interactors in mouse small intestinal crypts. Mllt10/Af10-Dot1l, essential for transcription elongation, are recruited to Wnt target genes in a β-catenin-dependent manner, resulting in H3K79 methylation over their coding regions in vivo in proliferative crypts of mouse small intestine in colorectal cancer and Wnt-inducible HEK293T cells. Depletion of MLLT10/AF10 in colorectal cancer and Wnt-inducible HEK293T cells followed by expression array analysis identifies MLLT10/AF10 and DOT1L as essential activators to a large extent dedicated to Wnt target gene regulation. In contrast, previously published β-catenin coactivators p300 and BRG1 displayed a more pleiotropic target gene expression profile controlling Wnt and other pathways. tcf4, mllt10/af10, and dot1l are co-expressed in Wnt-driven tissues in zebrafish and essential for Wnt-reporter activity. Intestinal differentiation defects in apc-mutant zebrafish can be rescued by depletion of Mllt10 and Dot1l, establishing these genes as activators downstream of Apc in Wnt target gene activation in vivo. Morpholino-depletion of mllt10/af10-dot1l in zebrafish results in defects in intestinal homeostasis and a significant reduction in the in vivo expression of direct Wnt target genes and in the number of proliferative intestinal epithelial cells. We conclude that Mllt10/Af10-Dot1l are essential, largely dedicated activators of Wnt-dependent transcription, critical for maintenance of intestinal proliferation and homeostasis. The methyltransferase DOT1L may present an attractive candidate for drug targeting in colorectal cancer.

The Wnt /β-catenin signaling pathway in the adult neurogenesis

The Wnt/β-catenin signaling pathway plays an important role in neural development, β-catenin is a central component of the Wnt/β-catenin signaling pathway, which not only performs the function of transmitting information in the cytoplasm, but also translocates to the nucleus-activating target gene transcription. The target genes in neural tissues have not been fully revealed, but the effects of the Wnt/β-catenin signaling pathway in adult neurogenesis have been demonstrated by ongoing research, which are significative to the basic research and treatment of neuronal degeneration diseases. Here, we review key findings to show the characteristics of β-catenin and its pivotal nature in the Wnt/β-catenin signaling pathway in a number of molecular studies. We also review current literature on the role of β-catenin in adult neurogenesis, which consists of an active process encompassing the proliferation, migration, differentiation and final synaptogenesis.

Cell-autonomous integrin control of Wnt and Notch signalling during somitogenesis

Integrins act at signalling crossroads, and their interactions with other signal transduction pathways are key to the regulation of normal and pathological cell cytoarchitecture and behaviour. Here, we describe a signalling cascade that acts during the formation of the defining segmental features of the vertebrate body – the somites – in which β1-integrin activity regulates epithelialisation by controlling downstream Wnt and Notch activity crucial for somite border formation. Using in vivo transcriptional inhibition in the developing chick embryo, we show that β1-integrin in the anterior presomitic mesoderm activates canonical Wnt signalling in a cell-autonomous, `outside-inside' manner. Signalling is mediated by integrin-linked kinase (ILK), leading to modulation of glycogen synthase kinase 3β (GSK3β) phosphorylation, and activates Notch signalling in the anterior presomitic mesoderm. The two signalling pathways then cooperate to promote somite formation via cMESO1/Mesp2. Our results show that β1-integrin can regulate cell shape and tissue morphogenesis indirectly, by regulation of downstream signalling cascades.

Wnt/Β-catenin and sex hormone signaling in endometrial homeostasis and cancer

A delicate balance between estrogen and progestagen signaling underlies proper functioning of the female reproductive tract and, in particular, the monthly re- and degenerative phases characteristic of the menstrual cycle. Here, we propose that the canonical Wnt/β-catenin signaling pathway may underlie this finely tuned hormonal equilibrium in endometrial homeostasis and, upon its constitutive activation, lead to neoplastic transformation of the endometrium. During the menstrual cycle, estradiol will enhance Wnt/β-catenin signaling in the proliferative phase, while progesterone inhibits Wnt/β-catenin signaling, thus restraining estrogens' proliferative actions, during the secretory phase. In case of enhanced or unopposed estrogen signaling, constitutive activation of Wnt/β-catenin signaling will trigger endometrial hyperplasia, which may develop further into endometrial cancer.

Delta-catenin/NPRAP: A new member of the glycogen synthase kinase-3beta signaling complex that promotes beta-catenin turnover in neurons

Through a multiprotein complex, glycogen synthase kinase-3beta (GSK-3beta) phosphorylates and destabilizes beta-catenin, an important signaling event for neuronal growth and proper synaptic function. delta-Catenin, or NPRAP (CTNND2), is a neural enriched member of the beta-catenin superfamily and is also known to modulate neurite outgrowth and synaptic activity. In this study, we investigated the possibility that delta-catenin expression is also affected by GSK-3beta signaling and participates in the molecular complex regulating beta-catenin turnover in neurons. Immunofluorescent light microscopy revealed colocalization of delta-catenin with members of the molecular destruction complex: GSK-3beta, beta-catenin, and adenomatous polyposis coli proteins in rat primary neurons. GSK-3beta formed a complex with delta-catenin, and its inhibition resulted in increased delta-catenin and beta-catenin expression levels. LY294002 and amyloid peptide, known activators of GSK-3beta signaling, reduced delta-catenin expression levels. Furthermore, delta-catenin immunoreactivity increased and protein turnover decreased when neurons were treated with proteasome inhibitors, suggesting that the stability of delta-catenin, like that of beta-catenin, is regulated by proteasome-mediated degradation. Coimmunoprecipitation experiments showed that delta-catenin overexpression promoted GSK-3beta and beta-catenin interactions. Primary cortical neurons and PC12 cells expressing delta-catenin treated with proteasome inhibitors showed increased ubiquitinated beta-catenin forms. Consistent with the hypothesis that delta-catenin promotes the interaction of the destruction complex molecules, cycloheximide treatment of cells overexpressing delta-catenin showed enhanced beta-catenin turnover. These studies identify delta-catenin as a new member of the GSK-3beta signaling pathway and further suggest that delta-catenin is potentially involved in facilitating the interaction, ubiquitination, and subsequent turnover of beta-catenin in neuronal cells.

O2 regulates stem cells through Wnt/β-catenin signalling

Stem cells reside in specialized microenvironments or 'niches' that regulate their function. In vitro studies using hypoxic culture conditions (<5% O2) have revealed strong regulatory links between O2 availability and functions of stem and precursor cells. Although some stem cells are perivascular, others may occupy hypoxic niches and be regulated by O2 gradients. However, the underlying mechanisms remain unclear. Here, we show that hypoxia inducible factor-1α (HIF-1α), a principal mediator of hypoxic adaptations, modulates Wnt/β-catenin signalling in hypoxic embryonic stem (ES) cells by enhancing β-catenin activation and expression of the downstream effectors LEF-1 and TCF-1. This regulation extends to primary cells, including isolated neural stem cells (NSCs), and is not observed in differentiated cells. In vivo, Wnt/β-catenin activity is closely associated with low O2 regions in the subgranular zone of the hippocampus, a key NSC niche. Hif-1α deletion impairs hippocampal Wnt-dependent processes, including NSC proliferation, differentiation and neuronal maturation. This decline correlates with reduced Wnt/β-catenin signalling in the subgranular zone. O2 availability, therefore, may have a direct role in stem cell regulation through HIF-1α modulation of Wnt/β-catenin signalling.

Interplay of cadherin-mediated cell adhesion and canonical Wnt signaling

The epithelial-mesenchymal transition is essential in both embryonic development and the progression of carcinomas. Wnt signaling and cadherin-mediated adhesion have been implicated in both processes; clarifying their role will depend on linking them to rearrangements of cellular structure and behavior. beta-Catenin is an essential molecule both in cadherin-mediated cell adhesion and in canonical Wnt signaling. Numerous experiments have shown that the loss of cadherin-mediated cell adhesion can promote beta-catenin release and signaling; this is accomplished by proteases, protein kinases and other molecules. Cadherin loss can also signal to several other regulatory pathways. Additionally, many target genes of Wnt signaling influence cadherin adhesion. The most conspicuous of these Wnt target genes encode the transcription factors Twist and Slug, which directly inhibit the E-cadherin gene promoter. Other Wnt/beta-catenin target genes encode metalloproteases or the cell adhesion molecule L1, which favor the degradation of E-cadherin. These factors provide a mechanism whereby cadherin loss and increased Wnt signaling induce epithelial-mesenchymal transition in both carcinomas and development.

Claudin family of proteins and cancer: an overview

Tight junctions are the apical cell-cell adhesion that regulate paracellular permeability and are critical for epithelial cell polarity. Molecular architecture of tight junction has been studied extensively, which has confirmed that claudin family of proteins is integral component of tight junction. Loss of cell-cell adhesion is central to the cellular transformation and acquisition of metastatic potential; however, the role of claudin family of proteins play in a series of pathophysiological events, including human carcinoma development, is only now beginning to be understood. Several claudin mouse knockout models have been generated and the diversity of phenotypes observed clearly demonstrates their important roles in the maintenance of tissue integrity in various organs and suggest that claudins also participate in cellular contexts other than tight junctions. The mechanisms of claudin regulation and their exact roles in normal physiology and disease are being elucidated, but much work remains to be done. In this review, we have discussed the conceptual framework concerning claudins and their potential implication in cancer. We predict that next several years will likely witness a boom in our understanding of the potential role of claudins in the regulation of tumorigenesis, which may, in turn, provide new approaches for the targeted therapy.

Cytoplasmic beta-catenin accumulation is a good prognostic marker in upper and lower gastrointestinal adenocarcinomas

AIMS

beta-Catenin is an important molecule in cancer biology. Membranous beta-catenin enhances cellular differentiation and inhibits invasion by its action on E-cadherin. The aim was to ascertain whether the cellular expression of these molecules in colorectal and oesophageal cancer specimens is associated with survival in patients with gastrointestinal cancer.

METHODS AND RESULTS

Tumour samples from 149 patients undergoing resection for colorectal adenocarcinoma and 147 patients undergoing resection for oesophageal adenocarcinoma were retrospectively analysed using immunohistochemical techniques to assess beta-catenin expression. Increasing beta-catenin expression in the cytoplasm was associated with improved survival for colorectal cancer cases on both univariate (P = 0.003) and multivariate (P = 0.01) analysis. In addition, increased expression in the most recent cohort of oesophageal adenocarcinoma patients was associated with improved TNM staging (P = 0.007). Membrane expression was weakly associated with survival in colorectal cancer on univariate analysis (P = 0.09), but not on multivariate analysis (P = 0.21). Complete absence of beta-catenin expression at all three sites was associated with reduced 5-year survival in colorectal cancer.

CONCLUSIONS

This is one of the largest prognostic studies of beta-catenin in gastrointestinal adenocarcinoma. It shows that low levels of cytoplasmic beta-catenin expression are associated with reduced survival in patients with colorectal cancer as well as worse TNM staging in oesophageal adenocarcinoma (a recognized surrogate end-point for survival). We believe this is the first time that this has been reported. This finding should be tested prospectively in oncological trials to validate whether the presence of cytoplasmic beta-catenin could be used as a prognostic marker for less aggressive disease.

Traf2- and Nck-interacting kinase is essential for Wnt signaling and colorectal cancer growth

T-cell factor-4 (TCF4) is a transcription factor essential for maintaining the undifferentiated status and self-renewal of intestinal epithelial cells. It has therefore been considered that constitutive activation of TCF4 by aberrant Wnt signaling is a major force driving colorectal carcinogenesis. We previously identified Traf2- and Nck-interacting kinase (TNIK) as one of the proteins that interact with TCF4 in colorectal cancer cells, but its functional significance has not been elucidated. Here, we report that TNIK is an activating kinase for TCF4 and essential for colorectal cancer growth. TNIK, but not its catalytically inactive mutant, phosphorylated the conserved serine 154 residue of TCF4. Small interfering RNA targeting TNIK inhibited the proliferation of colorectal cancer cells and the growth of tumors produced by injecting colorectal cancer cells s.c. into immunodeficient mice. The growth inhibition was abolished by restoring the catalytic domain of TNIK, thus confirming that its enzyme activity is essential for the maintenance of colorectal cancer growth. Several ATP-competing kinase inhibitors have been applied to cancer treatment and have shown significant activity. Our findings suggest TNIK as a feasible target for pharmacologic intervention to ablate aberrant Wnt signaling in colorectal cancer.

E-cadherin negatively regulates neoplastic growth in non-small cell lung cancer: role of Rho GTPases

Non-small cell lung cancers (NSCLC) that express the cell surface adhesion protein E-cadherin may carry a better prognosis than E-cadherin-negative tumors. Here, we found substantial inhibition of anchorage-independent growth in soft agar and cell migration in each of four NSCLC lines stably transfected with E-cadherin. The inhibitory effects were independent of the EGFR and beta-catenin/Wnt-signaling pathways. However, E-cadherin expression was associated with an adhesion-dependent reduction in the activity of Rho family proteins, RhoA in two lines and Cdc42 in the other two. The reduction of RhoA activity was dependent on DLC-1 Rho-GAP and p190 Rho-GAP and associated with an increase in a membrane-associated p190 Rho-GAP/p120 Ras-GAP complex. In parental cells with high levels of RhoA-GTP, siRNA-mediated knock-down of RhoA reduced cell migration and agar growth in a manner analogous to E-cadherin. In parental cells with high levels of Cdc42-GTP, transfection of a Cdc42 dominant-negative mutant reduced cell growth and migration similarly to cells expressing E-cadherin. Thus, E-cadherin can negatively regulate cell proliferation and migration in NSCLC by reducing the level of the predominant active form of Rho family protein, RhoA or Cdc42. These proteins can be considered downstream effectors of E-cadherin and might represent therapeutic targets in some NSCLC.

High lymphoid enhancer-binding factor-1 expression is associated with disease progression and poor prognosis in chronic lymphocytic leukemia

We determined lymphoid enhancer-binding factor-1 (LEF1) mRNA expression in 112 chronic lymphocytic leukemia (CLL) samples and assessed correlations with the prognostic markers ZAP70 and CD38, Binet stages, the percentage of lymphocytes in the peripheral blood, and fibromodulin (FMOD) transcripts. The mean LEF1 relative expression ratios (RER) were 53.72 and 37.10 in ZAP70-positive and ZAP70-negative patients, respectively (P=0.004). However, we did not observe a significant difference in LEF1 expression between CD38-positive and CD38-negative patients. Moreover, patients requiring treatment showed a mean LEF1 RER of 85.61 whereas patients in recently diagnosed Binet A stage had a mean of only 22.01 (P<0.001). We also found significant correlations of LEF1 with the percentage of lymphocytes and FMOD expression. Our results suggest that high LEF1 expression is associated with poor prognosis and disease progression. Thus, LEF1 might be involved in the process of disease progression and possibly can serve as a molecular parameter for risk assessment and/or monitoring of CLL.

Genomic characterization of Wilms' tumor suppressor 1 targets in nephron progenitor cells during kidney development

The Wilms' tumor suppressor 1 (WT1) gene encodes a DNA- and RNA-binding protein that plays an essential role in nephron progenitor differentiation during renal development. To identify WT1 target genes that might regulate nephron progenitor differentiation in vivo, we performed chromatin immunoprecipitation (ChIP) coupled to mouse promoter microarray (ChIP-chip) using chromatin prepared from embryonic mouse kidney tissue. We identified 1663 genes bound by WT1, 86% of which contain a previously identified, conserved, high-affinity WT1 binding site. To investigate functional interactions between WT1 and candidate target genes in nephron progenitors, we used a novel, modified WT1 morpholino loss-of-function model in embryonic mouse kidney explants to knock down WT1 expression in nephron progenitors ex vivo. Low doses of WT1 morpholino resulted in reduced WT1 target gene expression specifically in nephron progenitors, whereas high doses of WT1 morpholino arrested kidney explant development and were associated with increased nephron progenitor cell apoptosis, reminiscent of the phenotype observed in Wt1(-/-) embryos. Collectively, our results provide a comprehensive description of endogenous WT1 target genes in nephron progenitor cells in vivo, as well as insights into the transcriptional signaling networks controlled by WT1 that might direct nephron progenitor fate during renal development.

Knockdown of Li-cadherin increases metastatic behaviors of LoVo cells

PURPOSE

The aim of this study was to investigate the role of Li-cadherin in invasion and metastasis in LoVo cells.

METHODS

We applied RNA interference mediated downregulation of Li-cadherin expression in LoVo cells. Li-cadherin expression in LoVo cells was examined by semiquantitative polymerase chain reaction, immunofluorescence, western blot, and immunoprecipitation, respectively. Effect of suppression of Li-cadherin expression on cell migration, invasion, and adhesion was detected by wound healing assay, migration assay, invasion assay, and adhesion assay. Expression and activity of MMP-2 and MMP-9 were analyzed by gelatin zymography.

RESULTS

Cell migration, invasion, and adhesion were increased concomitantly with the reduction in Li-cadherin protein expression. Furthermore, downregulation of Li-cadherin expression induced secretion of proMMP-9, active MMP-9 and active MMP-2.

CONCLUSIONS

This study suggests that silencing Li-cadherin has positive actions in the processes of LoVo cells invasion and metastasis, and the interactions among MMP-2, MMP-9, and Li-cadherin participate in the multiple steps of invasion and metastasis in LoVo colorectal cancer cells.

Co-localization of the amyloid precursor protein and Notch intracellular domains in nuclear transcription factories

The beta-amyloid precursor protein (APP) plays a major role in Alzheimer's disease. The APP intracellular domain (AICD), together with Fe65 and Tip60, localizes to spherical nuclear AFT complexes, which may represent sites of transcription. Despite a lack of co-localization with several described nuclear compartments, we have identified a close apposition between AFT complexes and splicing speckles, Cajal bodies and PML bodies. Live imaging revealed that AFT complexes were highly mobile within nuclei and following pharmacological inhibition of transcription fused into larger assemblies. We have previously shown that AICD regulates the expression of its own precursor APP. In support of our earlier findings, transfection of APP promoter plasmids as substrates resulted in cytosolic AFT complex formation at labeled APP promoter plasmids. In addition, identification of chromosomal APP or KAI1 gene loci by fluorescence in situ hybridization showed their close association with nuclear AFT complexes. The transcriptional activator Notch intracellular domain (NICD) localized to the same nuclear spots as occupied by AFT complexes suggesting that these nuclear compartments correspond to transcription factories. Fe65 and Tip60 also co-localized with APP in the neurites of primary neurons. Pre-assembled AFT complexes may serve to assist fast nuclear signaling upon endoproteolytic APP cleavage.

Von Hippel Lindau syndrome

Von Hippel-Lindau syndrome (VHLS) is an autosomal dominant familial cancer syndrome arising from germ-line inactivation of the VHL gene on the short arm of chromosome 3. VHLS manifests in a myriad of hyper-vascular tumors of both benign and malignant nature. Incidence of VHLS is roughly 1 in 36,000 live births and has over 90% penetrance by the age of 65. Improved understanding of the natural history and biology of VHLS has led to the introduction of screening protocols, early interventions and improved treatments, all of which resulted in a substantially improved prognosis for this disease. Further details regardingvariegated molecular pathways and mechanisms ofVHLS are emerging with the subsequent advent of novel treatment protocols that are currently in clinical trials.

Alternative splicing of Tcf7l2 transcripts generates protein variants with differential promoter-binding and transcriptional activation properties at Wnt/beta-catenin targets

Alternative splicing can produce multiple protein products with variable domain composition from a single gene. The mouse Tcf7l2 gene is subject to alternative splicing. It encodes TCF4, a member of the T-cell factor (TCF) family of DNA-binding proteins and a nuclear interaction partner of β-catenin which performs essential functions in Wnt growth factor signalling. Multiple TCF4 isoforms, potentially exhibiting cell-type-specific distribution and differing in gene regulatory properties, could strongly influence tissue-specific Wnt responses. Therefore, we have examined mouse Tcf7l2 splice variants in neonatal tissues, embryonic stem cells and neural progenitors. By polymerase chain reaction amplification, cloning and sequencing, we identify a large number of alternatively spliced transcripts and report a highly flexible combinatorial repertoire of alternative exons. Many, but not all of the variants exhibit a broad tissue distribution. Moreover, two functionally equivalent versions of the C-clamp, thought to represent an auxiliary DNA-binding domain, were identified. Depending upon promoter context and precise domain composition, TCF4 isoforms exhibit strikingly different transactivation potentials at natural Wnt/β-catenin target promoters. However, differences in C-clamp-mediated DNA binding can only partially explain functional differences among TCF4 variants. Still, the cell-type-specific complement of TCF4 isoforms is likely to be a major determinant for the context-dependent transcriptional output of Wnt/β-catenin signalling.

VentX, a novel lymphoid-enhancing factor/T-cell factor-associated transcription repressor, is a putative tumor suppressor

Lymphoid-enhancing factor/T-cell factors (LEF1/TCF) are a high-mobility group of transcriptional factors that play essential roles in cell fate determination during early embryogenesis and ontogenesis. Aberrant activations of LEF1/TCF-mediated transcription have been implicated in a variety of malignancies. Our recent studies on vertebrate embryogenesis identified Xom, a homeobox protein of the bone morphogenetic protein 4 pathway, as a novel LEF/TCF-associated transcriptional modulator. Here, we report that VentX, a human Xom homologue, is a LEF/TCF-associated inhibitor of canonical Wnt/beta-catenin signaling and a negative regulator of cell proliferation. VentX is predominantly expressed in hematopoietic cells, and its expression is significantly downregulated in chronic lymphocytic leukemia. Altered expression of VentX is associated with corresponding changes of LEF/TCF target oncogenes such as cyclin D1, suggesting a potential role of VentX in the clinical behavior of hematopoietic malignancies.

KLF4 interacts with beta-catenin/TCF4 and blocks p300/CBP recruitment by beta-catenin

Wnt signaling is crucial in the organization and maintenance of the human intestinal epithelium, and somatic mutations that result in deregulated Wnt signaling are an early event in the development of colorectal cancer. The Wnt ligand ultimately results in the stabilization of cytoplasmic beta-catenin, which is then free to enter the nucleus and activate transcription through its interaction with the transcription factor TCF4. Our laboratory recently found that KLF4, a transcription factor highly expressed in the adult intestine and critical for intestinal differentiation, interacts with beta-catenin and inhibits Wnt signaling. In this study, we characterize the molecular mechanisms of KLF4-mediated inhibition of Wnt/beta-catenin signaling. We find that the KLF4 directly interacts with the C-terminal transactivation domain of beta-catenin and inhibits p300/CBP recruitment by beta-catenin. KLF4 inhibits p300/CBP-mediated beta-catenin acetylation as well as histone acetylation on Wnt target genes. In addition, we observe that KLF4 directly interacts with TCF4 independently of beta-catenin and that KLF4 and TCF4 are expressed in similar patterns within the large intestine, with greatest staining near the epithelial surface. These results provide a deeper understanding of the regulation of beta-catenin in the intestine and will have important implications in cancer and stem cell research.

Osteopontin induces beta-catenin signaling through activation of Akt in prostate cancer cells

Secretion of osteopontin (OPN) by cancer cells is a known mediator of tumorigenesis and cancer progression in both experimental and clinical studies. Our work demonstrates that OPN can activate Akt, an important step in cancer progression. Both ILK and PI3K are integral proteins in the OPN/Akt pathway, as inhibition of either kinase leads to a loss of OPN-mediated Akt activation. Subsequent to OPN-induced Akt activation, we observe inactivation of GSK-3beta, a regulator of beta-catenin. Osteopontin stimulation leads to an overall increase in beta-catenin protein levels with a resultant transfer of beta-catenin to the nucleus. Through the nuclear import of beta-catenin, OPN increases both the transcription and protein levels of MMP-7 and CD44, which are known TCF/LEF transcription targets. This work describes an important aspect of cancer progression induced by OPN.

Runx2 and bone morphogenic protein 2 regulate the expression of an alternative Lef1 transcript during osteoblast maturation

Lymphoid Enhancer Binding Factor (Lef) 1 is a transcriptional effector of the Wnt/Lrp5/beta-catenin signaling cascade, which regulates osteoblast differentiation, bone density, and skeletal strength. In this study, we describe the expression and function of an alternative Lef1 isoform in osseous cells. Lef1DeltaN is a naturally occurring isoform driven by a promoter (p2) within the intron between exons 3 and 4 of Lef1. Lef1DeltaN is induced during late osteoblast differentiation. This is converse to the expression pattern of the full-length Lef1 protein, which as we previously showed, decreases during differentiation. Agonists of osteoblast maturation differentially affected Lef1DeltaN expression. BMP2 stimulated Lef1DeltaN expression, whereas Wnt3a blocked basal and BMP2-induced expression of Lef1DeltaN transcripts during osteoblast differentiation. We determined that the Lef1DeltaN p2 promoter is active in osteoblasts and Runx2 regulates its activity. Stable overexpression of Lef1DeltaN in differentiating osteoblasts induced the expression of osteoblast differentiation genes, osteocalcin and type 1 collagen. Taken together, our results suggest Lef1DeltaN is a crucial regulator of terminal differentiation in osseous cells.

Guanylyl cyclase C in colorectal cancer: susceptibility gene and potential therapeutic target

Colorectal cancer is one of the leading causes of tumor-related morbidity and mortality worldwide. While mechanisms underlying this disease have been elucidated over the past two decades, these molecular insights have failed to translate into efficacious therapy. The oncogenomic view of cancer suggests that terminal transformation reflects the sequential corruption of signal transduction circuits regulating key homeostatic mechanisms, whose multiplicity underlies the therapeutic resistance of most tumors to interventions targeting individual pathways. Conversely, the paucity of mechanistic insights into proximal pathophysiological processes that initiate and amplify oncogenic circuits preceding accumulation of mutations and transformation impedes development of effective prevention and therapy. In that context, guanylyl cyclase C (GCC), the intestinal receptor for the paracrine hormones guanylin and uroguanylin, whose early loss characterizes colorectal transformation, has emerged as a component of lineage-specific homeostatic programs organizing spatiotemporal patterning along the crypt-surface axis. Dysregulation of GCC signaling, reflecting hormone loss, promotes tumorigenesis through reprogramming of replicative and bioenergetic circuits and genomic instability. Compensatory upregulation of GCC in response to hormone loss provides a unique translational opportunity for prevention and treatment of colorectal tumors by hormone-replacement therapy.