Wnt signalling: a theme with nuclear variations

Docosahexaenoic Acid-Enriched Phosphatidylcholine Exerted Superior Effects to Triglyceride in Ameliorating Obesity-Induced Osteoporosis through Up-Regulating the Wnt/β-Catenin Pathway

A growing number of studies reported that obesity is one of the major inducements for osteoporosis by promoting excessive adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Marine-derived DHA-enriched phosphatidylcholine (DHA-PC) exhibited activities to improve ovariectomized-induced osteoporosis and kidney damage. However, the potential effect of DHA-PC and efficacy differences between DHA-PC and traditional DHA (DHA-triglyceride, DHA-TG) on BMSCs differentiation in obesity-induced osteoporosis were not clear. In the present study, obesity-induced osteoporotic mice were supplemented with DHA-TG and DHA-PC for 120 days. Results showed that supplementing with DHA-PC improved the bone mineral density and biomechanical properties, increased the new bone formation rate by 55.2%, and reduced the amount of bone marrow fat to a greater extent than DHA-TG. Further in vitro results showed that DHA-PC significantly promoted the osteogenic differentiation and inhibited the adipogenic differentiation of BMSCs. Mechanistically, DHA-PC supplement up-regulated Wnt/β-catenin pathway in BMSCs and up-regulated the expression of osteogenic transcription factors, thereby promoting osteogenic differentiation. In summary, DHA-PC exerted a superior effect to DHA-TG in improving obesity-induced osteoporosis. The results provided new evidence for the application of different molecular forms of DHA in treatment of osteoporosis.

Hymenialdisine: A Marine Natural Product That Acts on Both Osteoblasts and Osteoclasts and Prevents Estrogen-Dependent Bone Loss in Mice

Excessive osteoclast (OC) activity together with relatively weak osteoblast (OB) function are strongly connected to osteolytic diseases, including osteoporosis, tumor-induced osteolysis, and inflammatory bone erosion. Very few natural products or compounds have been shown to exert therapeutic effects on both OCs and OBs, limiting the potential development of natural compounds for clinical application. Hymenialdisine (HMD) is a marine sponge-derived natural inhibitor of protein kinases with previously reported anti-osteoarthritis and anti-cancer properties. However, the roles of HMD in OCs, OBs, and osteoporosis have not yet been well established. Here, we found that HMD not only suppressed osteoclastogenesis but also promoted OB differentiation. HMD exerted dose-dependent inhibitory effects on RANKL-induced OC formation, bone resorption, and OC-specific gene expression. These strong inhibitory effects were achieved by blocking the NF-κB and MAPK signaling pathways, and NFATc1 expression. In addition, HMD potentially stimulated OB differentiation by activating alkaline phosphatase (ALP) and enhancing OB matrix mineralization. We found that HMD can activate the glycogen synthase kinase 3β (GSK-3β)/β-catenin/T-cell factor (TCF)/lymphoid enhancer factor (LEF) signaling pathway to upregulate Runx-2 expression, the main transcription factor in this pathway. Increased expression of Runx-2 was also correlated with expression of the OB-specific genes Col1a1 and osteocalcin (Ocn). Furthermore, we also evaluated the therapeutic potential of HMD in a female C57BL/6j mouse model of ovariectomy (OVX)-induced systematic bone loss. HMD showed a remarkable ability to prevent decreases in bone volume (BV/TV) and trabecular thickness (Tb.Th). In summary, HMD exerts notable effects in inhibiting OC-related osteolysis and enhancing OB-induced ossification, suggesting the potential application of HMD in osteoporosis treatment. © 2020 American Society for Bone and Mineral Research.

The genetic factors associated with Wnt signaling pathway in colorectal cancer

Colorectal cancer (CRC) is a common cancer with poor prognosis and high mortality. There is growing information about the factors involved in the pathogenesis of CRC. However, the knowledge of the predisposing factors is limited. The development of CRC is strongly associated with the Wingless/Integrated (Wnt) signaling pathway. This pathway comprises several major target proteins, including LRP5/6, GSK3β, adenomatous polyposis coli (APC), axis inhibition protein (Axin), and β-catenin. Genetic variations in these components of the Wnt signaling pathway may lead to the activation of β-catenin, potentially increasing the proliferation of colorectal cells. Because of the potentially important role of the Wnt signaling pathway in CRC, we aimed to review the involvement of different mutations in the main downstream proteins of this pathway, including LRP5/6, APC, GSK3β, Axin, and β-catenin. Determination of the genetic risk factors involved in the progression of CRC may lead to novel approaches for the early diagnosis of CRC and the identification of potential therapeutic targets in the treatment of CRC.

Increased Expression of Adherens Junction Components in Mouse Liver following Bile Duct Ligation

Adherens junctions, consisting of cadherins and catenins, are a group of cell-to-cell junctions that mediate mechanistic linkage between neighboring cells. By doing so, adherens junctions ensure direct intercellular contact and play an indispensable role in maintaining tissue architecture. Considering these critical functions, it is not surprising that adherens junctions are frequently involved in disease. In the present study, the effects of bile duct ligation—a surgical procedure to experimentally induce cholestatic and fibrotic liver pathology—on hepatic adherens junctions were investigated in mice. In essence, it was found that liver mRNA and protein levels of E-cadherin, β-catenin and γ-catenin drastically increase following bile duct ligation. These results could suggest a cytoprotective role for hepatic adherens junctions following bile duct ligation.

The Construction and Analysis of ceRNA Network and Patterns of Immune Infiltration in Mesothelioma With Bone Metastasis

Background: Mesothelioma is a rare and aggressive tumor. Bone metastasis often occurs in the later stages of this disease along with poor quality of life. Thus, it is important to explore the tumorigenesis and bone metastasis mechanism of invasive mesothelioma. For this purpose, we established two nomograms based on tumor-infiltrating immune cells and ceRNA networks to describe the molecular immunity and the clinical prediction of mesothelioma patients with bone metastasis.

Method: The expression profiles of mRNAs, lncRNAs, and miRNAs of 87 primary mesotheliomas were obtained from the TCGA database; there were four patients with bone metastasis and 83 patients without. We constructed a ceRNAs network based on the differentially expressed RNAs between mesothelioma and bone metastasis. CIBERSORT was used to distinguish 22 immune cell types from the tumor transcriptomes. Kaplan–Meier survival analysis and the Cox proportional hazards model were used to evaluate the prognostic value of each factor. Prognosis-associated immune cells and ceRNAs were applied to establish prediction nomograms. The receiver operating characteristic curves (ROC) and calibration curves were utilized to assess the discrimination and accuracy of the nomogram.

Results: Differential analysis revealed that 20 lncRNAs, 15 miRNAs, and 230 mRNAs were significantly different in mesothelioma samples vs. bone metastasis samples. We constructed the ceRNA network to include 10 protein-coding mRNAs, 8 lncRNAs, and 10 miRNAs. Nine of 28 ceRNAs were found to be significant in the Kaplan–Meier analysis. Out of the 22 cell types, the fraction of dendritic cells resting (P = 0.018) was significantly different between the bone metastasis group and the non-bone metastasis group. The ROC and the calibration curves, based on ceRNA networks and tumor-infiltrating immune cells, respectively, suggested acceptable accuracy (AUC of 3-year survival: 0.827, AUC of 5-year survival: 0.840; AUC of 3-year survival: 0.730; AUC of 5-year survival: 0.753). Notably, based on the co-expression patterns between ceRNAs and Immune cells, we found that the hsa-miR-582-5p, CASP9, dendritic cells resting, ANIX2, T cells CD8, and T cells CD4 memory resting might be associated with the mesothelioma bone metastasis.

Conclusion: Based on ceRNA networks and patterns of immune infiltration, our study provided a valid bioinformatics basis in order to explore the molecular mechanism and predict the possibility of mesothelioma bone metastasis.

The association between three AXIN2 variants and cancer risk

Plenty of epidemiological studies have assessed the effects of AXIN2 polymorphisms on the risk of developing cancer, but the available results were somewhat inconclusive. Odds ratios (ORs) with 95% confidence intervals (CIs) were utilized to investigate the relationship between three AXIN2 variants (rs2240308 C/T, rs1133683 C/T, and rs4791171 A/G) and overall cancer susceptibility. In silico tools were undertaken to investigate the correlation of AXIN2 expression with cancer risk and survival time. Furthermore, we explored the serum expression of AXIN2 by enzyme-linked immunosorbent assay. A total of 4167 cancer patients and 3515 control subjects were evaluated. The overall results demonstrated that there was no major association of these polymorphisms on cancer risk. However, stratified analysis by cancer type showed evidence that rs2240308 C/T polymorphism had a lower risk in lung cancer (OR, 0.76; 95% CI, 0.63-0.92; P_{heterogeneity}  = 0.865) and prostate cancer (OR, 0.54; 95% CI, 0.35-0.84; P_{heterogeneity}  = 0.088) by heterozygote comparison. Similar results were indicated in Asian descendants and population-based studies. In silico analysis showed evidence that AXIN2 expressions in lung cancer and prostate cancer were lower than that in normal counterpart. High expression of AXIN2 may have longer overall survival time than low expression group for lung cancer participants. In addition, individuals who were CC/TC carriers had a higher serum expression level than TT carriers. In conclusion, this pooled analysis suggested that AXIN2 rs2240308 C/T variant may decrease both lung and prostate cancer susceptibility, particularly in Asian descendants and population-based studies. Future large scale and well-designed research are required to validate these effects in more detail.

Genetics of Combined Pituitary Hormone Deficiency: Roadmap into the Genome Era

The genetic basis for combined pituitary hormone deficiency (CPHD) is complex, involving 30 genes in a variety of syndromic and nonsyndromic presentations. Molecular diagnosis of this disorder is valuable for predicting disease progression, avoiding unnecessary surgery, and family planning. We expect that the application of high throughput sequencing will uncover additional contributing genes and eventually become a valuable tool for molecular diagnosis. For example, in the last 3 years, six new genes have been implicated in CPHD using whole-exome sequencing. In this review, we present a historical perspective on gene discovery for CPHD and predict approaches that may facilitate future gene identification projects conducted by clinicians and basic scientists. Guidelines for systematic reporting of genetic variants and assigning causality are emerging. We apply these guidelines retrospectively to reports of the genetic basis of CPHD and summarize modes of inheritance and penetrance for each of the known genes. In recent years, there have been great improvements in databases of genetic information for diverse populations. Some issues remain that make molecular diagnosis challenging in some cases. These include the inherent genetic complexity of this disorder, technical challenges like uneven coverage, differing results from variant calling and interpretation pipelines, the number of tolerated genetic alterations, and imperfect methods for predicting pathogenicity. We discuss approaches for future research in the genetics of CPHD.

Genetic Redundancies Enhance Information Transfer in Noisy Regulatory Circuits

Cellular decision making is based on regulatory circuits that associate signal thresholds to specific physiological actions. This transmission of information is subjected to molecular noise what can decrease its fidelity. Here, we show instead how such intrinsic noise enhances information transfer in the presence of multiple circuit copies. The result is due to the contribution of noise to the generation of autonomous responses by each copy, which are altogether associated with a common decision. Moreover, factors that correlate the responses of the redundant units (extrinsic noise or regulatory cross-talk) contribute to reduce fidelity, while those that further uncouple them (heterogeneity within the copies) can lead to stronger information gain. Overall, our study emphasizes how the interplay of signal thresholding, redundancy, and noise influences the accuracy of cellular decision making. Understanding this interplay provides a basis to explain collective cell signaling mechanisms, and to engineer robust decisions with noisy genetic circuits.

There is increasing evidence that the presence of molecular noise greatly influences function in biological systems. This could imply, for instance, that genetic circuits adopt particular architectures in order to reduce noise. On the other hand, noise can be beneficial. Here, we show that this could be the case for the functioning of analog to digital genetic devices, which are commonly found in cellular decision making situations. We use the framework of information theory to illustrate first how noise can enhance information transfer in these devices. In those regimes in which noise is detrimental, we discuss how genetic redundancies allow information to be maximized, and how this effect depends on the specifics of the devices, and the interdependence among them. These results provide overall an additional rationale for genetic redundancies in genomic systems.

Transcription factor 7-like 1 is involved in hypothalamo-pituitary axis development in mice and humans

Aberrant embryonic development of the hypothalamus and/or pituitary gland in humans results in congenital hypopituitarism (CH). Transcription factor 7-like 1 (TCF7L1), an important regulator of the WNT/β-catenin signaling pathway, is expressed in the developing forebrain and pituitary gland, but its role during hypothalamo-pituitary (HP) axis formation or involvement in human CH remains elusive. Using a conditional genetic approach in the mouse, we first demonstrate that TCF7L1 is required in the prospective hypothalamus to maintain normal expression of the hypothalamic signals involved in the induction and subsequent expansion of Rathke's pouch progenitors. Next, we reveal that the function of TCF7L1 during HP axis development depends exclusively on the repressing activity of TCF7L1 and does not require its interaction with β-catenin. Finally, we report the identification of two independent missense variants in human TCF7L1, p.R92P and p.R400Q, in a cohort of patients with forebrain and/or pituitary defects. We demonstrate that these variants exhibit reduced repressing activity in vitro and in vivo relative to wild-type TCF7L1. Together, our data provide support for a conserved molecular function of TCF7L1 as a transcriptional repressor during HP axis development in mammals and identify variants in this transcription factor that are likely to contribute to the etiology of CH.

Silencing of p53 RNA through transarterial delivery ameliorates renal tubular injury and downregulates GSK-3β expression after ischemia-reperfusion injury

p53, a pivotal protein in the apoptotic pathway, has been identified as a mediator of transcriptional responses to ischemia-reperfusion (IR) injury. The characteristics and functional significance of the p53 response in vivo are largely unknown in IR-induced kidney injury. Therapeutic opportunities of delivering small interfering RNA (siRNA) via venous injection have gained recognition; however, systemic adverse effects of siRNA therapy should be considered. To prevent IR-induced kidney injury, we tested the efficacy of transarterial administration of siRNA targeting p53 (p53 siRNA). Female C57BL/6 mice underwent unilateral renal artery ischemia for 30 min, followed by reperfusion. siRNA experiments utilized short hairpin (sh) RNA plasmid-based approaches. Transfection of shRNA was performed using cationic polymer transfection reagent. Injection of synthetic p53 shRNA into the left renal artery just after ischemia improved tubular injury, apoptosis, and the swelling of mitochondria in cells of the thick ascending limb of Henle (mTALH) at the outer medullary regions. Staining of upregulated p53 was colocalized with the inducible expression of glycogen synthase kinase-3β (GSK-3β) at mTALH after IR injury. p53 shRNA inhibited GSK-3β expression and restored β-catenin expression at mTALH. For IR-induced kidney injury, transarterial delivery of p53 siRNA is an effective pharmacological intervention. Targeting siRNA to p53 leads to an attenuation of apoptosis and mitochondrial damage through the downregulation of GSK-3β expression and upregulation of β-catenin. Local delivery of vectors such as p53 siRNA through a transaortic catheter is clinically useful in reducing the adverse effect of siRNA-related therapy.

Wnt signaling in kidney development and disease

The Wnt gene family, which encodes secreted growth and differentiation factors, has been implicated in kidney organogenesis. The Wnts control both ureteric bud development and signaling, but they also serve as inductive factors to regulate nephrogenesis in the mesenchcymal cells. Several of the Wnt genes are expressed in the developing kidney, and gene knock-out studies have revealed specific developmental functions for these. Consistent with this, changes in Wnt ligands and pathway components are associated with many kidney diseases, including kidney cancers, renal fibrosis, cystic kidney diseases, acute renal failure, diabetic nephropathy and ischaemic injury. It is these associations of the Wnt signaling system with kidney development and kidney diseases that form to topic of this review.

Iron chelators for the treatment of cancer

The study of iron chelators as anti-tumor agents is still in its infancy. Iron is important for cellular proliferation and this is demonstrated by observations that iron-depletion results in cell cycle arrest and also apoptosis. In addition, many iron chelators are known to inhibit ribonucleotide reductase, the iron-containing enzyme that is the rate-limiting step for DNA synthesis. Desferrioxamine is a well known chelator used for the treatment of iron-overload disease, but it has also been shown to possess anti-cancer activity. Another class of chelators, namely the thiosemicarbazones, have been shown to possess anti-cancer activity since the 1950's, although their mechanism(s) of action have only recently been more comprehensively elucidated. In fact, the redox activity of thiosemicarbazone iron complexes is thought to be important in mediating their potent cytotoxicity. Moreover, unlike typical iron chelators which simply act to deplete tumors of iron, several thiosemicarbazones (i.e., Bp44mT and Dp44mT) do not induce this effect, their anti-cancer efficacy being due to other mechanisms e.g., redox activity. Other reports have also shown that some thiosemicarbazones inhibit topoisomerase IIα, demonstrating that this class of agents have multiple molecular targets and act by various mechanisms. The most well characterized thiosemicarbazone iron chelator in terms of its assessment in humans is 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP). Observations from these clinical trials highlight the less than optimal activity of this ligand and several side effects related to its use, including myelo-suppression, hypoxia and methemoglobinemia. The mechanisms responsible for these latter effects must be elucidated and the design of the ligand altered to minimize these problems and increase efficacy. This review discusses the development of chelators as unique agents for cancer treatment.

Non-channel functions of connexins in cell growth and cell death

Cellular communication mediated by gap junction channels and hemichannels, both composed of connexin proteins, constitutes two acknowledged regulatory platforms in the accomplishment of tissue homeostasis. In recent years, an abundance of reports has been published indicating functions for connexin proteins in the control of the cellular life cycle that occur independently of their channel activities. This has yet been most exemplified in the context of cell growth and cell death, and is therefore as such addressed in the current paper. Specific attention is hereby paid to the molecular mechanisms that underpin the cellular non-channel roles of connexin proteins, namely the alteration of the expression of tissue homeostasis determinants and the physical interaction with cell growth and cell death regulators. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Signaling networks in RUNX2-dependent bone development

RUNX2 is an essential transcription factor for osteoblast differentiation and chondrocyte maturation. SP7, another transcription factor, is required for osteoblast differentiation. Major signaling pathways, including FGF, Wnt, and IHH, also play important roles in skeletal development. RUNX2 regulates Sp7 expression at an early stage of osteoblast differentiation. FGF2 upregulates Runx2 expression and activates RUNX2, and gain-of-function mutations of FGFRs cause craniosynostosis and limb defect with upregulation of Runx2 expression. Wnt signaling upregulates Runx2 expression and activates RUNX2, and RUNX2 induces Tcf7 expression. IHH is required for Runx2 expression in osteoprogenitor cells during endochondral bone development, and RUNX2 directly regulates Ihh expression in chondrocytes. Thus, RUNX2 regulates osteoblast differentiation and chondrocyte maturation through the network with SP7 and with FGF, Wnt, and IHH signaling pathways during skeletal development.

Connexins: sensors and regulators of cell cycling

It is nowadays well established that gap junctions are critical gatekeepers of cell proliferation, by controlling the intercellular exchange of essential growth regulators. In recent years, however, it has become clear that the picture is not as simple as originally anticipated, as structural precursors of gap junctions can affect cell cycling by performing actions not related to gap junctional intercellular communication. Indeed, connexin hemichannels also foresee a pathway for cell growth communication, albeit between the intracellular compartment and the extracellular environment, while connexin proteins as such can directly or indirectly influence the production of cell cycle regulators independently of their channel activities. Furthermore, a novel set of connexin-like proteins, the pannexins, have lately joined in as regulators of the cell proliferation process, which they can affect as either single units or as channel entities. In the current paper, these multifaceted aspects of connexin-related signalling in cell cycling are reviewed.

Wnt3-frizzled 1 chimera as a model to study canonical Wnt signaling

Wnt proteins initiate signaling by binding to seven transmembrane spanning receptors of the frizzled (Fz) family together with the members of the low-density lipoprotein receptor-related protein (LRP) 5 and 6. A chimera of human Wnt3 and Fz1 receptor was developed that efficiently activated the TCF-luciferase reporter. Deletion of the cytoplasmic tail and point mutations in the PDZ binding region in the chimera resulted in the loss of Wnt signaling, suggesting a critical role for the Fz cytoplasmic region in Wnt signaling. The Fz CRD is also critical for Wnt signaling, as a deletion of 29 amino acids in the 2nd cysteine loop resulted in the total loss of TCF-luciferase activation. DKK-1 protein blocks upregulation of the TCF-luciferase reporter by the Wnt3-Fz1 chimera, suggesting involvement of LRP in Wnt3-Fz1 signaling. Expression of a Wnt3-Fz1 chimera in C3H10T1/2 cells resulted in the upregulation of alkaline phosphatase activity and inhibition of adipocyte formation, demonstrating that the Wnt3-Fz1 chimera is a potent activator of differentiation of C3H10T1/2 cells into osteoblasts and an inhibitor of their differentiation into the adipocyte lineage. In summary, the Wnt-Fz chimera approach has the potential to better our understanding of the mechanism of Wnt action and its role, particularly in stem cell differentiation. In addition, this methodology can be utilized to identify inhibitors of either Wnt, Fz or interactors of the canonical pathway, which may have potential therapeutic value in the treatment of cancers and other diseases.

High expression of Pitx-2 in the ICAT-deficient metanephros leads to developmental arrest

ICAT (Inhibitor of β-catenin and T cell factor) inhibits the interaction between β-catenin and TCF/LEF transcription factor and serves as a negative regulator of Wnt signaling. In a subset of ICAT knockout mice, significant delay in the ureteric bud branching and renal agenesis are observed. In order to examine the process of this developmental defect, molecular changes were analyzed in fetal ICAT–/– kidneys with a focus on Wnt-signaling associated factors. The protein level of active β-catenin was elevated in ICAT–/– kidneys. DNA microarray and immunohistochemical analyses revealed that the expression of a Wnt target gene Pitx-2 was enhanced in ICAT–/– kidneys. There was no genotypic difference in the expression level of another Wnt target gene, c-Ret. These results suggest that the enhancement of Pitx-2 expression induced by activated Wnt signaling leads to delays in ureteric bud branching and subsequent renal agenesis. In the ICAT–/– kidneys which developed to E18.5 without any apparent defect, renal glomeruli, convoluted tubules and collecting ducts were decreased in density and showed abnormal structure. ICAT may be required for various developmental stages during renal development.

Melanoma biomarkers: current status and utility in diagnosis, prognosis, and response to therapy

Melanoma is the most devastating form of skin cancer and represents a leading cause of cancer death, particularly in young adults. As even relatively small melanomas can readily metastasize, accurate staging of progression is critical. Diagnosis is typically made on the basis of histopathologic criteria; with tumor thickness (Breslow), invasion level (Clark), ulceration, and the extent of lymph node involvement being important prognostic indicators. However, histologic criteria alone cannot diagnose all melanomas and there are often problems in distinguishing subsets of benign nevi from melanoma. There also exists a group of patients with thin primary melanomas for whom surgery should be curative but who ultimately go on to develop metastases. Therefore, there is an urgent need to develop molecular biomarkers that identify melanoma patients with high-risk primary lesions to facilitate greater surveillance and possible adjuvant therapy. The advent of large-scale genomic profiling of melanoma is revealing considerable heterogeneity, suggesting that melanomas could be subgrouped according to their patterns of oncogenic mutation and gene expression. It is hoped that this subgrouping will allow for the personalization of melanoma therapy using novel molecularly targeted agents. Much effort is now geared toward defining the genetic markers that may predict response to targeted therapy agents as well as identifying pharmacodynamic markers of therapy response. In this review, we discuss the utility of melanoma biomarkers for diagnosis and prognosis and suggest how novel molecular signatures can help guide both melanoma diagnosis and therapy selection.

Beta-catenin promotes survival of renal epithelial cells by inhibiting Bax

Ischemia activates Bax, a proapoptotic BCL2 protein, as well as the prosurvival beta-catenin/Wnt signaling pathway. To test the hypothesis that beta-catenin/Wnt signaling regulates Bax-mediated apoptosis after induction of metabolic stress, which occurs during renal ischemia, we infected immortalized and primary proximal tubular epithelial cells with adenovirus to express either constitutively active or dominant negative beta-catenin constructs. Constitutively active beta-catenin significantly decreased apoptosis and improved cell survival after metabolic stress. Furthermore, active beta-catenin decreased Bax activation, oligomerization, and translocation to mitochondria, and reduced both organelle membrane injury and apoptosis. Dominant negative beta-catenin had the opposite effects. Because Akt regulates Bax, we examined the effects of the beta-catenin mutants on Akt expression and activation. Constitutively active beta-catenin increased Akt-1 expression and activation before and after stress, and treatment with a phosphatidylinositol-3 kinase inhibitor antagonized the protective effects of beta-catenin on Akt activation, Bax inhibition, and cell survival. In addition, beta-catenin significantly increased the rate of phosphorylation at Bax serine(184), an Akt-specific target. Taken together, these results suggest that beta-catenin/Wnt signaling promotes survival of renal epithelial cells after metabolic stress, in part by inhibiting Bax in a phosphatidylinositol-3 kinase/Akt-dependent manner.

Assessment of circulating Dickkopf-1 with a new two-site immunoassay in healthy subjects and women with breast cancer and bone metastases

The aim of our study was to investigate the sex- and age-related changes of serum Dickkopf-1 (Dkk-1), a soluble inhibitor of the Wnt signaling pathway, in healthy individuals and in patients with breast cancer (BC) and bone metastases (BM) using a new ELISA. Association of serum Dkk-1 with markers of bone turnover was also investigated. Serum Dkk-1 measurements were performed using a commercial sandwich ELISA in 150 healthy men, 175 healthy pre- and postmenopausal women (20-65 years), 22 women with BC and BM (mean age 63 years), and 16 women with BC and metastases at sites other than bone (mean age 53 years). Intra- and interassay coefficients of variation were below 7% and 12%, respectively. The detection limit was determined to be 0.018 microg/L. In healthy women and men, Dkk-1 did not change with age. Serum Dkk-1 modestly correlated with serum bone alkaline phosphatase (r = 0.19, P = 0.013) and serum C-terminal cross-linking telopeptide of type I collagen (r = 0.19, P = 0.014) in women but not in men. Dkk-1 levels were higher in women with BC and BM (5.57 +/- 5.50 microg/L) than in healthy age-matched controls (3.47 +/- 1.47 microg/L, P < 0.0001) and women with metastases at sites other than bone (3.57 +/- 1.66 microg/L, P = 0.0003). In conclusion, serum Dkk-1 is stable with age in healthy women and men and increases in patients with BC and BM. Measurements of circulating Dkk-1 with this new ELISA may be useful for the clinical investigation of patients with malignant bone diseases.

Identification of phylogenetically conserved enhancer elements implicated in pancreas development in the WISP1 and CTGF orthologs

WISP1 and CTGF are members of the CCN family of growth factors encoding extracellular matrix proteins participating in several developmental and tumorigenic processes. Both are induced by the WNT signaling pathway, and microarray data suggest that expression of WISP1 and CTGF is repressed by Neurogenin3 (Ngn3 (NEUROG3)), a transcription factor directing specification of the endocrine pancreas. Single-cell reverse transcription polymerase chain reaction analysis suggested that this was a cell autonomous effect. To identify possible common regulatory networks involved in WISP1 and CTGF gene expression, their genomic regions were searched for common transcription factor motifs using a combination of in silico approaches and documented knowledge concerning pancreas development. This analysis revealed the presence of a conserved enhancer in both CTGF and WISP1 regulatory regions in 10 species covering a wide evolutionary distance. This enhancer contains binding sites for Ngn1/3 (NEUROG1/3) and transcription factors that are critically involved in pancreas development. Furthermore, it contained binding sites for three additional transcription factor families, which may indicate novel players are involved in this process.

Differential Wnt pathway gene expression and E-cadherin truncation in sporadic colorectal cancers with and without microsatellite instability

PURPOSE

Alterations in the Wnt pathway play a major role in colorectal cancer with high (MSI-H) or low microsatellite instability (MSS/MSI-L). However, the differential impact of the Wnt pathway components on these tumors is poorly understood. MMP-3 (stromelysin-1) promoter is a target of the mutator phenotype in sporadic colorectal cancer. Among MMP-3 targets, we investigated E-cadherin integrity status in both groups of tumors. Because beta-catenin is the main effector of the Wnt pathway, we have also investigated the differential cellular status of beta-catenin.

EXPERIMENTAL DESIGN

Expression profiles of 114 genes related to the Wnt pathway were analyzed by oligo microarrays in 48 tumors classified by their MSI status. In addition, we analyzed 48 sporadic colorectal cancers for E-cadherin integrity status. We performed investigation of beta-catenin and cyclin D1 by immunohistochemistry using tissue arrays containing 96 tumors.

RESULTS

Our data show that a group of genes that negatively regulate Wnt signaling are downregulated in MSS/MSI-L as compared with MSI-H colorectal tumors. E-cadherin truncation was significantly higher in MSS/MSI-L as compared with MSI-H tumors. Moreover, MSI-H tumors showed low or null beta-catenin nuclear presence, whereas the group of tumors classified as MSS or MSI-L displayed a high content of the nuclear beta-catenin location.

CONCLUSIONS

Our results suggest that the differential expression of genes that negatively regulate the Wnt pathway, as well as the status of E-cadherin and beta-catenin in MSI-H or MSS/MSI-L colorectal tumors, shed some light on the different clinical behavior showed by the two groups.

Pygopus and the Wnt signaling pathway: a diverse set of connections

Identification of Pygopus in Drosophila as a dedicated component of the Wg (fly homolog of mammalian Wnt) signaling cascade initiated many inquiries into the mechanism of its function. Surprisingly, the nearly exclusive role for Pygopus in Wg signal transduction in flies is not seen in mice, where Pygopus appears to have both Wnt-related and Wnt-independent functions. This review addresses the initial findings of Pygopus as a Wg/Wnt co-activator in light of recent data from both fly and mammalian studies. We compare and contrast the developmental phenotypes of pygopus mutants to those characterized for known Wg/Wnt transducers and explore the data regarding a role for mammalian Pygopus 2 in tumorigenesis. We further analyze the roles of the two conserved domains of Pygopus proteins in transcription, and propose a model for the molecular mechanism of Pygopus function in both Wg/Wnt signaling and Wnt-independent transcriptional regulation.

Wnt signaling control of bone cell apoptosis

Wnts are a large family of growth factors that mediate essential biological processes like embryogenesis, morphogenesis and organogenesis. These proteins also play a role in oncogenesis, and they regulate apoptosis in many tissues. Wnts bind to a membrane receptor complex comprised of a frizzled (FZD) G-protein-coupled receptor and a low-density lipoprotein (LDL) receptor-related protein (LRP). The formation of this ligand-receptor complex initiates a number of signaling cascades that include the canonical/beta-catenin pathway as well as several noncanonical pathways. In recent years, canonical Wnt signaling has been reported to play a significant role in the control of bone formation. Clinical studies have found that mutations in LRP-5 are associated with reduced bone mineral density (BMD) and fractures. Investigations of knockout and transgenic mouse models of Wnt pathway components have shown that canonical Wnt signaling modulates most aspects of osteoblast physiology including proliferation, differentiation, function and apoptosis. Transgenic mice expressing a gain of function mutant of LRP-5 in bone, or mice lacking the Wnt antagonist secreted frizzled-related protein-1, exhibit elevated BMD and suppressed osteoblast apoptosis. In addition, preclinical studies with pharmacologic compounds such as those that inhibit glycogen synthase kinase-3beta support the importance of the canonical Wnt pathway in modulation of bone formation and osteoblast apoptosis.

EGFR regulates RhoA-GTP dependent cell motility in E-cadherin mutant cells

Gastric cancer associated E-cadherin germline missense mutations lead to significant functional consequences, in both the structural and signalling properties of the protein. In this study, we have characterized the effect of four E-cadherin germline missense mutations (T340A, A634V, P799R and V832M) in the interaction with the epidermal growth factor receptor (EGFR). We challenged the hypothesis that E-cadherin mutations perturb its ability to bind to EGFR, leading to constitutional activation of the EGFR, triggering activation of downstream effectors. We verified that missense mutations localized in the extracellular domain of the protein (T340A and A634V) exhibited reduced stability of the EGFR/E-cadherin heterodimers in contrast to germline mutations localized at the cytoplasmatic domain of the protein (P799R and V832M). We observed that cells expressing E-cadherin extracellular mutants displayed increased levels of phosphorylated EGFR upon ligand stimulation, when compared with cells expressing wild-type E-cadherin or intracellular mutants. We showed that upon treatment of E-cadherin extracellular mutant cells with the EGFR inhibitor, the increase of RhoA activation is abrogated and accompanied by decreased migratory behaviour, supporting the idea that Rho-like proteins are EGFR downstream effectors. Our results bring new insights into the understanding of the distinct in vitro behaviours observed for E-cadherin missense mutations localized in different domains of the protein. Furthermore, we demonstrate that E-cadherin-dependent EGFR activation contributes to enhanced cell motility, in a mechanism involving RhoA activation.

The Wnt-dependent signaling pathways as target in oncology drug discovery

Our current understanding of the Wnt-dependent signaling pathways is mainly based on studies performed in a number of model organisms including, Xenopus, Drosophila melanogaster, Caenorhabditis elegans and mammals. These studies clearly indicate that the Wnt-dependent signaling pathways are conserved through evolution and control many events during embryonic development. Wnt pathways have been shown to regulate cell proliferation, morphology, motility as well as cell fate. The increasing interest of the scientific community, over the last decade, in the Wnt-dependent signaling pathways is supported by the documented importance of these pathways in a broad range of physiological conditions and disease states. For instance, it has been shown that inappropriate regulation and activation of these pathways is associated with several pathological disorders including cancer, retinopathy, tetra-amelia and bone and cartilage disease such as arthritis. In addition, several components of the Wnt-dependent signaling pathways appear to play important roles in diseases such as Alzheimer’s disease, schizophrenia, bipolar disorder and in the emerging field of stem cell research. In this review, we wish to present a focused overview of the function of the Wnt-dependent signaling pathways and their role in oncogenesis and cancer development. We also want to provide information on a selection of potential drug targets within these pathways for oncology drug discovery, and summarize current data on approaches, including the development of small-molecule inhibitors, that have shown relevant effects on the Wnt-dependent signaling pathways.

Insights into unbinding mechanisms upon two mutations investigated by molecular dynamics study of GSK3β-axin complex: Role of packing hydrophobic residues

Glycogen synthase kinase 3beta (GSK 3beta) is a key component of several cellular processes including Wnt and insulin signalling pathways. The interaction of GSK3beta with scaffolding peptide axin is thought to be responsible for the effective phosphorylation of beta-catenin, the core effector of Wnt signaling, which has been linked with the occurrence of colon cancer and melanoma. It has been demonstrated that the binding of axin to GSK3beta is abolished by the single-point mutation of Val267 to Gly (V267G) in GSK3beta or Leu392 to Pro (L392P) in axin. Molecular dynamics (MD) simulations were performed on wild type (WT), V267G mutant and L392P one to elucidate the two unbinding mechanisms that occur through different pathways. Besides, rough energy and residue-based energy decomposition were calculated by MM_GBSA (molecular mechanical Generalized_Born surface area) approach to illuminate the instability of the two mutants. The MD simulations of the two mutants and WT reveal that the structure of GSK3beta remains unchanged, while axin moves away from the interfacial hydrophobic pockets in both two mutants. Axin exhibits positional shift in V267G mutant, whereas, losing the hydrogen bonds that are indispensable for stabilizing the helix structure of wild type axin, the helix of axin is distorted in L392P mutant. To conclude, both two mutants destroy the hydrophobic interaction that is essential to the stability of GSK3beta-axin complex.

Bone anabolic effects of parathyroid hormone are blunted by deletion of the Wnt antagonist secreted frizzled-related protein-1

Secreted frizzled-related protein (sFRP)-1 is a Wnt antagonist that when deleted in mice leads to increased trabecular bone formation in adult animals after 13 weeks of age. Treatment of mice with parathyroid hormone (PTH) also increases trabecular bone formation, and some of the anabolic actions of this hormone may result from altered expression of Wnt pathway components. To test this hypothesis, we treated +/+ and -/- female sFRP-1 mice with PTH 1-34 for 30 days and measured distal femur trabecular bone parameters by peripheral quantitative computed tomography (pQCT) and high-resolution micro-computed tomography. During the course of the 32-week study, volumetric bone mineral density (vBMD) declined 41% in vehicle-treated +/+ mice, but increased 24% in vehicle-treated -/- animals. At 8 weeks of age when vBMD was not altered by deletion of sFRP-1, treatment of +/+ and -/- mice with PTH increased vBMD by 147 and 163%, respectively. In contrast, at 24 weeks of age when vBMD was 75% higher in -/- mice than in +/+ controls, treatment with PTH increased vBMD 164% in +/+ animals, but only 58% in -/- mice. Furthermore, at 36 weeks of age when vBMD was 117% higher in -/- mice than in +/+ controls, treatment with PTH increased vBMD 74% in +/+ animals, while no increase was observed in -/- mice. At each of these time points, PTH treatment increased vBMD to a similar level in +/+ and -/- mice, and this level declined with age. In addition, at 36 weeks of age, the vBMD level reached by PTH treatment of +/+ mice was the same as that achieved solely by deletion of sFRP-1. These results indicate that loss of sFRP-1 and PTH treatment increase vBMD to a similar extent. Moreover, as the effects of sFRP-1 deletion on vBMD increase, the ability of PTH to enhance vBMD declines suggesting that there are overlapping mechanisms of action.

Hepatocellular expression of glutamine synthetase: an indicator of morphogen actions as master regulators of zonation in adult liver

Glutamine synthetase (GS) has long been known to be expressed exclusively in pericentral hepatocytes most proximal to the central veins of liver lobuli. This enzyme as well as its peculiar distribution complementary to the periportal compartment for ureogenesis plays an important role in nitrogen metabolism, particularly in homeostasis of blood levels of ammonium ions and glutamine. Despite this fact and intensive studies in vivo and in vitro, many aspects of the regulation of its activity on the protein and on the genetic level remained enigmatic. Recent experimental advances using transgenic mice and new analytic tools have revealed the fundamental role of morphogens such as wingless-type MMTV integration site family member signals (Wnt), beta-catenin, and adenomatous polyposis coli in the regulation of this particular enzyme. In addition, novel information concerning the structure of transcription factor binding sites within regulatory regions of the GS gene and their interactions with signalling pathways could be collected. In this review we focus on all aspects of the regulation of GS in the liver and demonstrate how the new findings have changed our view of the determinants of liver zonation. What appeared as a simple response of hepatocytes to blood-derived factors and local cellular interactions must now be perceived as a fundamental mechanism of adult tissue patterning by morphogens that were considered mainly as regulators of developmental processes. Though GS may be the most obvious indicator of morphogen action among many other targets, elucidation of the complex regulation of the expression of the GS gene could pave the road for a better understanding of the mechanisms involved in patterning of liver parenchyma. Based on current knowledge we propose a new concept of how morphogens, hormones and other factors may act in concert, in order to restrict gene expression to small subpopulations of one differentiated cell type, the hepatocyte, in different anatomical locations. Although many details of this regulatory network are still missing, and an era of exciting new discoveries is still about to come, it can already be envisioned that similar mechanisms may well be active in other organs contributing to the fine-tuning of organ-specific functions.

The Krüppel-like zinc finger protein Glis2 functions as a negative modulator of the Wnt/beta-catenin signaling pathway

To gain insight into the mechanism by which Gli-similar 2 (Glis2) regulates transcription, we performed yeast-two hybrid cDNA library screening using Glis2 as bait. This screening identified beta-catenin as a potential Glis2-interacting protein. Mammalian two-hybrid, co-immunoprecipitation, and GST-pulldown analyses supported the interaction between Glis2 and beta-catenin. Pulldown analyses with several Glis2 deletion mutants indicated that the 1st zinc finger motif of Glis2 is critical for its interaction with beta-catenin, while the armadillo repeats of beta-catenin are important in its interaction with Glis2. Reporter analyses showed that Glis2 represses T-cell factor (TCF)-mediated transcriptional activation. In addition, Glis2 represses the expression of the TCF target gene cyclin D1. Our results indicate that Glis2 interacts with beta-catenin and suggest that Glis2 functions as a negative modulator of beta-catenin/TCF-mediated transcription.

The Wnt Signaling Receptor Lrp5 Is Required for Mammary Ductal Stem Cell Activity and Wnt1-induced Tumorigenesis

Canonical Wnt signaling has emerged as a critical regulatory pathway for stem cells. The association between ectopic activation of Wnt signaling and many different types of human cancer suggests that Wnt ligands can initiate tumor formation through altered regulation of stem cell populations. Here we have shown that mice deficient for the Wnt co-receptor Lrp5 are resistant to Wnt1-induced mammary tumors, which have been shown to be derived from the mammary stem/progenitor cell population. These mice exhibit a profound delay in tumorigenesis that is associated with reduced Wnt1-induced accumulation of mammary progenitor cells. In addition to the tumor resistance phenotype, loss of Lrp5 delays normal mammary development. The ductal trees of 5-week-old Lrp5-/- females have fewer terminal end buds, which are structures critical for juvenile ductal extension presumed to be rich in stem/progenitor cells. Consequently, the mature ductal tree is hypomorphic and does not completely fill the fat pad. Furthermore, Lrp5-/- ductal cells from mature females exhibit little to no stem cell activity in limiting dilution transplants. Finally, we have shown that Lrp5-/- embryos exhibit substantially impaired canonical Wnt signaling in the primitive stem cell compartment of the mammary placodes. These findings suggest that Lrp5-mediated canonical signaling is required for mammary ductal stem cell activity and for tumor development in response to oncogenic Wnt effectors.

Involvement of cell junctions in hepatocyte culture functionality

In liver, like in other multicellular systems, the establishment of cellular contacts is a prerequisite for normal functioning. In particular, well-defined cell junctions between hepatocytes, including adherens junctions, desmosomes, tight junctions, and gap junctions, are known to play key roles in the performance of liver-specific functionality. In a first part of this review article, we summarize the current knowledge concerning cell junctions and their roles in hepatic (patho)physiology. In a second part, we discuss their relevance in liver-based in vitro modeling, thereby highlighting the use of primary hepatocyte cultures as suitable in vitro models for preclinical pharmaco-toxicological testing. We further describe the actual strategies to regain and maintain cell junctions in these in vitro systems over the long-term.

Quantitative trait loci for locomotor behavior in Drosophila melanogaster

Locomotion is an integral component of most animal behaviors and many human diseases and disorders are associated with locomotor deficits, but little is known about the genetic basis of natural variation in locomotor behavior. Locomotion is a complex trait, with variation attributable to the joint segregation of multiple interacting quantitative trait loci (QTL), with effects that are sensitive to the environment. We assessed variation in a component of locomotor behavior (locomotor reactivity) in a population of 98 recombinant inbred lines of Drosophila melanogaster and mapped four QTL affecting locomotor reactivity by linkage to polymorphic roo transposable element insertion sites. We used complementation tests of deficiencies to fine map these QTL to 12 chromosomal regions and complementation tests of mutations to identify 13 positional candidate genes affecting locomotor reactivity, including Dopa decarboxylase (Ddc), which catalyzes the final step in the synthesis of serotonin and dopamine. Linkage disequilibrium mapping in a population of 164 second chromosome substitution lines derived from a single natural population showed that polymorphisms at Ddc were associated with naturally occurring genetic variation in locomotor behavior. These data implicate variation in the synthesis of bioamines as a factor contributing to natural variation in locomotor reactivity.

Wnt signaling and osteoblastogenesis

Wnts are a large family of growth factors that mediate fundamental biological processes like embryogenesis, organogenesis and tumorigenesis. These proteins bind to a membrane receptor complex comprised of a frizzled (FZD) G-protein-coupled receptor (GPCRs) and a low-density lipoprotein (LDL) receptor-related protein (LRP). The formation of this ligand-receptor complex initiates a number of intracellular signaling cascades that includes the canonical/beta-catenin pathway, as well as several GPCR-mediated noncanonical pathways. In recent years, canonical Wnt signaling has been shown to play a substantial role in the control of bone formation. Clinical investigations have found that mutations in LRP-5 are associated with bone mineral density and fractures. For example, loss-of-function mutations in LRP-5 cause osteoporosis pseudoglioma syndrome, while gain-of-function mutations lead to high bone mass phenotypes. Studies of knockout and transgenic mouse models for Wnt pathway components like Wnt-10b, LRP-5/6, secreted frizzled-related protein-1, dickkopf-2, Axin-2 and beta-catenin have demonstrated that canonical signaling modulates most aspects of osteoblast physiology including proliferation, differentiation, bone matrix formation/mineralization and apoptosis as well as coupling to osteoclastogenesis and bone resorption. Future studies in this rapidly growing area of research should focus on elucidating Wnt/FZD specificity in the control of bone cell function, the role of noncanonical pathways in skeletal remodeling, and direct effects of Wnts on cells of the osteoclast lineage.

The inflammatory mediator leukotriene D4 induces beta-catenin signaling and its association with antiapoptotic Bcl-2 in intestinal epithelial cells

Increased levels of the inflammatory mediator leukotriene D4 (LTD4) are present at sites of inflammatory bowel disease, and such areas also exhibit an increased risk for subsequent cancer development. It is known that LTD4 affects the expression of many proteins that influence survival and proliferation of intestinal epithelial cells. We demonstrate here that after LTD4 exposure, beta-catenin translocates to the nucleus where it signals activation of the TCF/LEF family of transcription factors. These events are mediated via a phosphatidylinositol 3-kinase-dependent phosphorylation of the inhibitory Ser-9 residue of glycogen synthase kinase 3beta. We also show that in the presence of LTD4, free beta-catenin translocates to the mitochondria where it associates with the cell survival protein Bcl-2. We hypothesize that LTD4 may enhance cell survival via activation of beta-catenin signaling, in particular, by promoting the association of beta-catenin with Bcl-2 in the mitochondria. Similar to Wnt-1 signaling, LTD4 signals an increased level of free beta-catenin and elevated TCF/LEF promotor activity. This work in intestinal epithelial cells further lends credence to the idea that inflammatory signaling pathways are intrinsically linked with potential oncogenic signals involved in cell survival and apoptosis.

Transcriptional regulation of mesendoderm formation in Xenopus

Mesoderm and endoderm formation in Xenopus involves the coordinated efforts of maternally and zygotically expressed transcription factors together with growth factor signalling, including members of the TGFbeta and wnt families. In this review we discuss our current state of knowledge of these pathways, and describe in more detail some of the transcription factor-DNA interactions that are involved in mesendoderm formation.

Dynamic EGFR-Ras signalling in Drosophila leg development

In Drosophila, as in many other animals, EGFR-Ras signalling has multiple developmental roles from oogenesis to differentiation. In leg development, in particular, it has been described to be responsible for the establishment of distal leg fates in a graded manner. Here, we investigate the patterns of expression of activators of EGFR-Ras signalling, as well as some of the effectors, in order to better understand the patterning of the distal leg, and to investigate further roles of this signalling pathway. These patterns, together with genetic data obtained by different mutant conditions for EGFR-Ras members and transgene expression, suggest two rounds of signalling in leg development. Early, the EGFR ligand Vein is the main player in distal leg patterning, possibly supported later by another ligand activated by Rhomboid. Later, in a second wave of signalling when all the proximal-distal leg fates have been specified, domains of EGFR/Ras activation appear inside each leg segment to regulate Notch-mediated joint development, and also some organs such as tendons and sensory organs. This second wave relies on a ligand activated by Rhomboid.

Beta-catenin signaling marks the prospective site of primitive streak formation in the mouse embryo

Beta-catenin signaling has been shown to be involved in triggering axis formation in several organisms, including Xenopus and zebrafish. Genetic analysis has demonstrated that the Wnt/beta-catenin signaling pathway is also involved in axis formation in the mouse, since a targeted deletion of beta-catenin results in embryos that have a block in anterior-posterior axis formation, fail to initiate gastrulation, and do not form mesoderm. However, because beta-catenin is ubiquitously expressed, the precise time and cell types in which this signaling pathway is active during early embryonic development remain unknown. Thus, to better understand the role of the Wnt/beta-catenin signaling pathway in axis formation and mesoderm specification, we have examined both the distribution and signaling activity of beta-catenin during early embryonic development in the mouse. We show that the N-terminally nonphosphorylated form of beta-catenin as well as beta-catenin signaling is first detectable in the extraembryonic visceral endoderm in day 5.5 embryos. Before the initiation of gastrulation at day 6.0, beta-catenin signaling is asymmetrically distributed within the epiblast and is localized to a small group of cells adjacent to the embryonic--extraembryonic junction. At day 6.5 and onward, beta-catenin signaling was detected in the primitive streak and mature node. Thus, beta-catenin signaling precedes primitive streak formation and is present in epiblast cells that will go on to form the primitive streak. These results support a critical role for the Wnt/beta-catenin pathway in specifying cells to form the primitive streak and node in the mammalian embryo as well as identify a novel domain of Wnt/beta-catenin signaling activity during early embryogenesis.

Functional significance of type 1 insulin-like growth factor-mediated nuclear translocation of the insulin receptor substrate-1 and beta-catenin

Previous work has shown that the transcriptional regulator beta-catenin can translocate to the nuclei when cells are stimulated with the type 1 insulin-like growth factor (IGF-1). We show by immunocoprecipitation and by confocal microscopy that beta-catenin binds to and co-localizes with the insulin receptor substrate-1 (IRS-1), a docking protein for both the insulin and the IGF-1 receptors. IRS-1 is required for IGF-1-mediated nuclear translocation of beta-catenin, resulting in the activation of the beta-catenin target genes. IGF-1-mediated nuclear translocation of beta-catenin is facilitated by the nuclear translocation of IRS-1. Both IRS-1 and beta-catenin are recruited to the cyclin D1 promoter, an established target for beta-catenin, but only IRS-1 is recruited to the ribosomal DNA (rDNA) promoter. UBF proteins (known to interact with both IRS-1 and beta-catenin) are also detectable in the cyclin D1 and rDNA promoters. These results indicate that IRS-1 (activated by the IGF-1 receptor) is one of several proteins that regulate the subcellular localization and activity of beta-catenin. The ability of IRS-1 to localize to both RNA polymerase II (with beta-catenin) and RNA polymerase I-regulated promoters suggest an explanation for the effect of IRS-1 on both cell growth in size and cell proliferation. This possibility is supported by the demonstration that enforced nuclear localization of IRS-1 causes nuclear translocation of beta-catenin and transformation of normal mouse embryo fibroblasts (colony formation in soft agar).

Decoding cis-regulatory systems in ascidians

Ascidians, or sea squirts, are lower chordates, and share basic gene repertoires and many characteristics, both developmental and physiological, with vertebrates. Therefore, decoding cis-regulatory systems in ascidians will contribute toward elucidating the genetic regulatory systems underlying the developmental and physiological processes of vertebrates. cis-Regulatory DNAs can also be used for tissue-specific genetic manipulation, a powerful tool for studying ascidian development and physiology. Because the ascidian genome is compact compared with vertebrate genomes, both intergenic regions and introns are relatively small in ascidians. Short upstream intergenic regions contain a complete set of cis-regulatory elements for spatially regulated expression of a majority of ascidian genes. These features of the ascidian genome are a great advantage in identifying cis-regulatory sequences and in analyzing their functions. Function of cis-regulatory DNAs has been analyzed for a number of tissue-specific and developmentally regulated genes of ascidians by introducing promoter-reporter fusion constructs into ascidian embryos. The availability of the whole genome sequences of the two Ciona species, Ciona intestinalis and Ciona savignyi, facilitates comparative genomics approaches to identify cis-regulatory DNAs. Recent studies demonstrate that computational methods can help identify cis-regulatory elements in the ascidian genome. This review presents a comprehensive list of ascidian genes whose cis-regulatory regions have been subjected to functional analysis, and highlights the recent advances in bioinformatics and comparative genomics approaches to cis-regulatory systems in ascidians.

LvGroucho and nuclear beta-catenin functionally compete for Tcf binding to influence activation of the endomesoderm gene regulatory network in the sea urchin embryo

In the sea urchin embryo, specification of the endomesoderm is accomplished by the activity of a network of regulatory genes in the vegetal hemisphere, called the endomesoderm gene regulatory network (GRN). The activation of this network is mediated primarily through the activity of the Wnt pathway, though details of pathway activation remain unclear. To gain further insight into control of endomesoderm GRN activation, we have identified a sea urchin homologue of the co-repressor Groucho (LvGroucho) that has been shown to antagonize beta-catenin/Tcf activation complexes during Wnt signaling in other systems. Groucho functions by recruiting the histone deacetylase Rpd3 to the DNA template via interaction with site-specific transcription factors, resulting in localized chromatin condensation and transcriptional silencing. Our results show that the LvGroucho protein localizes to all nuclei throughout embryonic development. Interaction assays demonstrate that LvGroucho interacts with Tcf via both the Q and the WD domains of the protein. LvGroucho interacts with Tcf to antagonize the expression of key endomesoderm regulatory genes. Assays demonstrate that LvGroucho and n beta-catenin functionally compete for binding to Tcf as a major mechanism by which the Tcf-control switch is regulated. Functional analysis of the N-terminal AES197 domain of LvGroucho shows that it is sufficient to recapitulate the function of full-length LvGroucho. This finding strongly supports the conclusion that the effects of LvGro overexpression are due primarily to its interactions with Tcf and not other Groucho interacting partners, since Tcf is the only protein present in the sea urchin known to interact with AES197. Because the Q domain is unable to bind Rpd3, it was expected to behave as a dominant negative LvGroucho. Unexpectedly, overexpression of the Q domain gave functional results similar to LvGroucho and the AES197 domain. This is the first evidence for an inherent repressive function for the Q domain alone. Together, our results indicate that LvGroucho functionally competes with beta-catenin for Tcf binding, and this competitive mechanism regulates one of the earliest steps in the initiation of the sea urchin endomesoderm GRN.

Calcium Sensing Receptor in Human Colon Carcinoma: Interaction with Ca2+ and 1,25-Dihydroxyvitamin D3

Recent studies show that the human parathyroid calcium sensing receptor (CaSR) is expressed in human colon epithelium and functions to regulate epithelial proliferation and differentiation. In this study, we show that the cells of the colon crypt acquire CaSR expression as they differentiate and migrate towards the apex of the crypt. CaSR expression was weak in colon carcinomas with a more-differentiated histologic pattern, whereas CaSR expression was undetectable in less-differentiated tumors. We found that Ca2+ and/or 1,25(OH)2D3 stimulated CaSR promoter activity and CaSR protein expression in the human colon carcinoma CBS cells, which possessed a functional CaSR. Both agents concomitantly induced a series of changes in the CBS cells that influence proliferation and differentiation, but cellular responses to the two agents were not identical. Ca2+ strongly induced E-cadherin expression and inhibited the expression of the nuclear transcription factor, TCF4. 1,25(OH)2D3 was weaker in its effect on E-cadherin and was not able to inhibit TCF4 expression. 1,25(OH)2D3 was as strong or stronger than Ca2+ in its induction of the cyclin-dependent kinase inhibitors, P21 and p27. It is concluded that CaSR may function in the colon to regulate epithelial differentiation and that loss of CaSR expression may be associated with abnormal differentiation and/or malignant progression. Extracellular Ca2+ and 1,25(OH)2D3 are potential candidates involved in regulating CaSR expression in the colon and the chemopreventive actions of Ca2+ and 1,25(OH)2D3 in colon cancer may be mediated, in part, through the CaSR.

Receptor and secreted targets of Wnt-1/beta-catenin signalling in mouse mammary epithelial cells

BACKGROUND

Deregulation of the Wnt/ beta-catenin signal transduction pathway has been implicated in the pathogenesis of tumours in the mammary gland, colon and other tissues. Mutations in components of this pathway result in beta-catenin stabilization and accumulation, and the aberrant modulation of beta-catenin/TCF target genes. Such alterations in the cellular transcriptional profile are believed to underlie the pathogenesis of these cancers. We have sought to identify novel target genes of this pathway in mouse mammary epithelial cells.

METHODS

Gene expression microarray analysis of mouse mammary epithelial cells inducibly expressing a constitutively active mutant of beta-catenin was used to identify target genes of this pathway.

RESULTS

The differential expression in response to DeltaNbeta-catenin for five putative target genes, Autotaxin, Extracellular Matrix Protein 1 (Ecm1), CD14, Hypoxia-inducible gene 2 (Hig2) and Receptor Activity Modifying Protein 3 (RAMP3), was independently validated by northern blotting. Each of these genes encodes either a receptor or a secreted protein, modulation of which may underlie the interactions between Wnt/beta-catenin tumour cells and between the tumour and its microenvironment. One of these genes, Hig2, previously shown to be induced by both hypoxia and glucose deprivation in human cervical carcinoma cells, was strongly repressed upon DeltaNbeta-catenin induction. The predicted N-terminus of Hig2 contains a putative signal peptide suggesting it might be secreted. Consistent with this, a Hig2-EGFP fusion protein was able to enter the secretory pathway and was detected in conditioned medium. Mutation of critical residues in the putative signal sequence abolished its secretion. The expression of human HIG2 was examined in a panel of human tumours and was found to be significantly downregulated in kidney tumours compared to normal adjacent tissue.

CONCLUSIONS

HIG2 represents a novel non-cell autonomous target of the Wnt pathway which is potentially involved in human cancer.

The role of altered cell-cell communication in melanoma progression

Under normal homeostasis, melanocyte growth and behaviour is tightly controlled by the surrounding keratinocytes. Keratinocytes regulate melanocyte behaviour through a complex system of paracrine growth factors and cell-cell adhesion molecules. Pathological changes, leading to development of malignant melanoma, upset this delicate homeostatic balance and can lead to altered expression of cell-cell adhesion and cell-cell communication molecules. In particular, there is a switch from the E-cadherin-mediated keratinocyte-melanocyte partnership to the N-cadherin-mediated melanoma-melanoma and melanoma-fibroblast interaction. Other changes include the alteration in the gap junctions formed between the melanocyte and keratinocyte. Changes in the connexin expression, in particular the loss of connexin 43, may result in a reduction or a loss of gap junctional activity, which is thought to contribute towards tumour progression. In the current review we describe the alterations in cell-cell adhesion and communication associated with melanoma development and progression, and discuss how a greater understanding of these processes may aid the future therapy of this disease.

Decreased BMD and limb deformities in mice carrying mutations in both Lrp5 and Lrp6

Humans and mice lacking Lrp5 have low BMD. To evaluate whether Lrp5 and Lrp6 interact genetically to control bone or skeletal development, we created mice carrying mutations in both Lrp5 and the related gene Lrp6. We found that compound mutants had dose-dependent deficits in BMD and limb formation, suggesting functional redundancy between these two genes in bone and limb development.

INTRODUCTION

Lrp5 and Lrp6 are closely related members of the low density lipoprotein receptor family and are co-receptors for Wnt ligands. While Lrp5 mutations are associated with low BMD in humans and mice, the role of Lrp6 in bone formation has not been analyzed.

MATERIALS AND METHODS

To address whether Lrp5 and Lrp6 play complimentary roles in bone and skeletal development, we created mice with mutations in both genes. We inspected limbs of mice from the different genotypic classes of compound mutants to identify abnormalities. DXA and muCT were used to evaluate the effect of mutations in Lrp5 and Lrp6 on BMD and microarchitecture.

RESULTS

Mice heterozygous for mutations in Lrp6 and either heterozygous or homozygous for a mutation in Lrp5 (Lrp6(+/-);Lrp5(+/-) or Lrp6(+/-);Lrp5(-/-)) display limb defects with incomplete penetrance and variable expression. DXA analysis showed that BMD decreased as mice progressively were more deficient in Lrp5 and Lrp6. Lrp6(+/-);Lrp5(-/-) mice were more severely affected than Lrp6(+/+);Lrp5(-/-) mice, whereas Lrp6(+/-);Lrp5(+/-) mice had statistically higher BMD than Lrp6(+/+);Lrp5(-/-) mice and lower BMD compared with wildtype mice and mice heterozygous for either mutation alone.

CONCLUSIONS

Lrp6 and Lrp5 genetically interact in limb development in mice. Furthermore, heterozygosity for an inactivating mutation in Lrp6 further reduces BMD in both male and female mice lacking Lrp5.