PRAME and LEF1 in Combined Deep Penetrating Nevus and Combined Blue Nevus: Utility and Pitfalls

ABSTRACT

Deep penetrating nevi (DPN), particularly those showing combined features, or combined deep penetrating nevi (CDPN), may show histopathological resemblance to blue nevus (BN) and melanoma. Preferentially Expressed Antigen in MElanoma (PRAME) is a marker that helps distinguish melanoma from benign melanocytic lesions. Lymphoid enhancer-binding factor 1 (LEF1) has been proposed to be used in conjunction with β-catenin for diagnosis of DPN. The immunohistochemical expression of PRAME and LEF1 was evaluated in 10 DPN (including 6 CDPN and 2 DPN-like proliferations with atypical features), 16 BN (including combined and cellular BN), and 2 melanomas with features of DPN or BN. PRAME was negative in most DPN (n = 10/10, n = 9/10, one case with discrepancy between readers) and all BN (n = 16/16), while the 2 melanomas included were positive (n = 2/2). All DPN were positive for LEF1 (n = 9/9) while only a subset of BN were positive (n = 6/16, P = 0.0028; n = 5/16, P = 0.001, per both readers). LEF1 seemed to be easier to interpret than β-catenin because of its nuclear pattern of expression. The expression of LEF1 in the regular nevus component of combined BN presents a potential pitfall in practice because it may lead to misinterpretation of LEF1 as positive in the BN component of the lesion. However, a subset (approximately one-third) of combined BN seemed to show true LEF1 expression. Taking into account pitfalls in interpretation, the combinatorial panel of PRAME and LEF1, in addition to conventional histopathological features, may be useful to distinguish CDPN from combined BN and other benign and malignant mimics.

Proteogenomic Profiling of High-Grade B-Cell Lymphoma With 11q Aberrations and Burkitt Lymphoma Reveals Lymphoid Enhancer Binding Factor 1 as a Novel Biomarker

High-grade B-cell lymphomas with 11q aberrations (HGBL-11q) represent a World Health Organization-defined group of lymphomas that harbor recurrent chromosome 11q aberrations involving proximal gains and telomeric losses. Although a limited number of HGBL-11q cases evaluated thus far appear to show a similar course and prognosis as Burkitt lymphoma (BL), many molecular differences have been appreciated, most notably the absence of MYC rearrangement. Despite biological differences between BL and HGBL-11q, histomorphologic and immunophenotypic distinction remains challenging. Here, we provide a comparative whole proteomic profile of BL- and HGBL-11q-derived cell lines, identifying numerous shared and differentially expressed proteins. Transcriptome profiling performed on paraffin-embedded tissue samples from primary BL and HGBL-11q lymphomas was additionally performed to provide further molecular characterization. Overlap of proteomic and transcriptomic data sets identified several potential novel biomarkers of HGBL-11q, including diminished lymphoid enhancer-binding factor 1 expression, which was validated by immunohistochemistry staining in a cohort of 23 cases. Altogether, these findings provide a comprehensive multimodal and comparative molecular profiling of BL and HGBL-11q and suggest the use of enhancer-binding factor 1 as an immunohistochemistry target to distinguish between these aggressive lymphomas.

Increased Expression of LEF1 and β-Catenin in Invasive Micropapillary Carcinoma of the Breast is Associated With Lymphovascular Invasion and Lymph Node Metastasis

Invasive micropapillary breast carcinoma (IMPC) is a rare breast cancer subtype characterized by small tumor cell clusters with loss of stromal attachment, an inside-out growth appearance, and lymphotropism. IMPC is associated with high incidence of lymphovascular invasion (LVI) and lymph node metastasis. Activated Wnt signaling has been implicated in the metastasis of other aggressive breast tumors, including triple-negative and basal-like carcinomas. In this study, we tested whether activated Wnt signaling could be detected in IMPC. Upon ligand binding, the central mediator of the Wnt pathway, β-catenin, accumulates in the cytosol and translocates to the nucleus where it forms a complex with lymphoid enhancer-binding factor 1 (LEF1) to regulate transcription. We performed immunostaining for β-catenin and LEF1 on a well-annotated cohort of 40 breast tumors and nodal metastases displaying micropapillary histopathology. Strong nuclear accumulation of β-catenin was not observed, however a dim cytosolic and/or nuclear accumulation of β-catenin was sometimes seen in IMPC and this expression pattern was significantly associated with nodal metastasis. β-catenin expression correlated with the upregulation of LEF1 in IMPC. LEF1 expression was detected in 26 of 40 (65%) cases and was specifically enriched at the invasive front of the tumor and in tumor clusters undergoing LVI. Detection of LEF1 expression in the primary tumor was associated with an increased rate of LVI, lymph node metastasis, and disease relapse. LEF1 and β-catenin expression levels were significantly higher in metastases compared with primary tumors. In summary, this study demonstrates an association between the upregulation of β-catenin/LEF1 and the metastasis of IMPC.

The WNT10B Network Is Associated with Survival and Metastases in Chemoresistant Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) commonly develops resistance to chemotherapy, yet markers predictive of chemoresistance in this disease are lacking. Here, we define WNT10B-dependent biomarkers for β-CATENIN/HMGA2/EZH2 signaling predictive of reduced relapse-free survival. Concordant expression of HMGA2 and EZH2 proteins is observed in MMTV-Wnt10b^LacZ transgenic mice during metastasis, and Hmga2 haploinsufficiency decreased EZH2 protein expression, repressing lung metastasis. A novel autoregulatory loop interdependent on HMGA2 and EZH2 expression is essential for β-CATENIN/TCF-4/LEF-1 transcription. Mechanistically, both HMGA2 and EZH2 displaced Groucho/TLE1 from TCF-4 and served as gatekeepers for K49 acetylation on β-CATENIN, which is essential for transcription. In addition, we discovered that HMGA2-EZH2 interacts with the PRC2 complex. Absence of HMGA2 or EZH2 expression or chemical inhibition of Wnt signaling in a chemoresistant patient-derived xenograft (PDX) model of TNBC abolished visceral metastasis, repressing AXIN2, MYC, EZH2, and HMGA2 expression in vivo. Combinatorial therapy of a WNT inhibitor with doxorubicin synergistically activated apoptosis in vitro, resensitized PDX-derived cells to doxorubicin, and repressed lung metastasis in vivo. We propose that targeting the WNT10B biomarker network will provide improved outcomes for TNBC. SIGNIFICANCE: These findings reveal targeting the WNT signaling pathway as a potential therapeutic strategy in triple-negative breast cancer.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/5/982/F1.large.jpg.

HMGB proteins and arthritis

The high-mobility group box (HMGB) family includes four members: HMGB1, 2, 3 and 4. HMGB proteins have two functions. In the nucleus, HMGB proteins bind to DNA in a DNA structure-dependent but nucleotide sequence-independent manner to function in chromatin remodeling. Extracellularly, HMGB proteins function as alarmins, which are endogenous molecules released upon tissue damage to activate the immune system. HMGB1 acts as a late mediator of inflammation and contributes to prolonged and sustained systemic inflammation in subjects with rheumatoid arthritis. By contrast, Hmgb2 ^-/- mice represent a relevant model of aging-related osteoarthritis (OA), which is associated with the suppression of HMGB2 expression in cartilage. Hmgb2 mutant mice not only develop early-onset OA but also exhibit a specific phenotype in the superficial zone (SZ) of articular cartilage. Given the similar expression and activation patterns of HMGB2 and β-catenin in articular cartilage, the loss of these pathways in the SZ of articular cartilage may lead to altered gene expression, cell death and OA-like pathogenesis. Moreover, HMGB2 regulates chondrocyte hypertrophy by mediating Runt-related transcription factor 2 expression and Wnt signaling. Therefore, one possible mechanism explaining the modulation of lymphoid enhancer binding factor 1 (LEF1)-dependent transactivation by HMGB2 is that a differential interaction between HMGB2 and nuclear factors affects the transcription of genes containing LEF1-responsive elements. The multiple functions of HMGB proteins reveal the complex roles of these proteins as innate and endogenous regulators of inflammation in joints and their cooperative roles in cartilage hypertrophy as well as in the maintenance of joint tissue homeostasis.

Ectopic activation of Wnt/β-catenin signaling in lens fiber cells results in cataract formation and aberrant fiber cell differentiation

The Wnt/β-catenin signaling pathway controls many processes during development, including cell proliferation, cell differentiation and tissue homeostasis, and its aberrant regulation has been linked to various pathologies. In this study we investigated the effect of ectopic activation of Wnt/β-catenin signaling during lens fiber cell differentiation. To activate Wnt/β-catenin signaling in lens fiber cells, the transgenic mouse referred to as αA-CLEF was generated, in which the transactivation domain of β-catenin was fused to the DNA-binding protein LEF1, and expression of the transgene was controlled by αA-crystallin promoter. Constitutive activation of Wnt/β-catenin signaling in lens fiber cells of αA-CLEF mice resulted in abnormal and delayed fiber cell differentiation. Moreover, adult αA-CLEF mice developed cataract, microphthalmia and manifested downregulated levels of γ-crystallins in lenses. We provide evidence of aberrant expression of cell cycle regulators in embryonic lenses of αA-CLEF transgenic mice resulting in the delay in cell cycle exit and in the shift of fiber cell differentiation to the central fiber cell compartment. Our results indicate that precise regulation of the Wnt/β-catenin signaling activity during later stages of lens development is essential for proper lens fiber cell differentiation and lens transparency.

Negative regulation of beta-catenin/Tcf signaling by naringenin in AGS gastric cancer cell

Functional activation of beta-catenin/Tcf signaling plays an important role in early events in carcinogenesis. We examined the effect of naringenin against beta-catenin/Tcf signaling in gastric cancer cells. Reporter gene assay showed that naringenin inhibited beta-catenin/Tcf signaling efficiently. In addition, the inhibition of beta-catenin/Tcf signaling by naringenin in HEK293 cells transiently transfected with constitutively mutant beta-catenin gene, whose product is not phosphorylated by GSK3beta, indicates that its inhibitory mechanism was related to beta-catenin itself or downstream components. To investigate the precise inhibitory mechanism, we performed immunofluorescence, Western blot, and EMSA. As a result, our data revealed that the beta-catenin distribution and the levels of nuclear beta-catenin and Tcf-4 proteins were unchanged after naringenin treatment. Moreover, the binding activities of Tcf complexes to consensus DNA were not affected by naringenin. Taken together, these data suggest that naringenin inhibits beta-catenin/Tcf signaling in gastric cancer with unknown mechanisms.

Recognition complex between the HMG domain of LEF-1 and its cognate DNA studied by molecular dynamics simulations with explicit solvation

Molecular dynamics simulations of the complex formed between the HMG box of the lymphoid enhancer-binding factor (LEF-1) and its cognate DNA duplex were carried out with explicit inclusion of water. The simulation started with an NMR-based model (pdb code 2LEF) and the dynamics was pursued for 10 nanoseconds without constraints. It revealed that water intervenes in many ionic/polar interactions, establishing in particular local equilibria between direct and water-mediated hydrogen bonds, and thus increasing the entropy of the complex. Quite unexpectedly, the simulation indicated that a binding pocket for a specific water molecule may be reversibly formed at the apex of the bend induced in the DNA helix by LEF-1 binding, where a methionine side chain intercalates between two destacked adenines. We observed that the specific water molecule can temporarily replace the intercalated S-CH(3) group, acting as a sort of "extension" of the side chain. The residence time of this water molecule was about 3.5 ns. Simulations of the cognate DNA alone showed that this sequence has no intrinsic tendency to bend; therefore, the bending occurs solely as a consequence of the recognition, following the "induced-fit" mechanism.

Transforming growth factor-beta signaling during epithelial-mesenchymal transformation: implications for embryogenesis and tumor metastasis

The molecular mechanisms of epithelial-mesenchymal transformation (EMT) have long been studied to gain a greater understanding of this distinct change in cellular morphology. Early studies of the developing embryo have designated the involvement of Wnt signaling in EMT, through an activated complex of the lymphoid-enhancing factor-1 (LEF-1) transcription factor and the cell adhesion molecule beta-catenin. However, more recent studies have implicated a significant role of the transforming growth factor-beta (TGF-beta) in causing EMT in both development and pathology. The ability of TGF-beta isoforms to signal through a variety of molecules such as Smads, phosphatidylinositol 3-kinase (PI3K), and mitogen-activated protein kinase (MAPK) creates an incredible complexity as to their role in this transition. Here we assess the biochemical signaling pathways of TGF-beta and their potential cross-interaction with traditional Wnt signaling molecules to bring about EMT during embryogenesis and tumor metastasis.

An internal ribosome entry site mediates translation of lymphoid enhancer factor-1

The lymphoid enhancer factor-1 LEF1 locus produces multiple mRNAs via alternative promoters. Full-length LEF-1 protein is produced via translation of an mRNA with a 1.2-kb, GC-rich 5'-untranslated region (UTR), whereas a truncated LEF-1 isoform is produced by an mRNA with a short, 60-nucleotide (nt) 5'-UTR. Full-length LEF-1 promotes cell growth via its interaction with the WNT signaling mediator beta-catenin. Truncated LEF-1 lacks the beta-catenin binding domain and opposes WNT signaling as a competitive inhibitor for WNT response elements. In this study we tested the hypothesis that the long, GC-rich 5'-UTR within the full-length LEF1 mRNA contains an internal ribosome entry site (IRES). Using a dicistronic vector in transient DNA transfections, we show that the LEF1 5'-UTR mediates cap-independent translation. Additional experiments involving a promoter-less dicistronic vector, Northern blot analysis, and transient transfections of dicistronic mRNAs into cultured mammalian cells compromised for cap-dependent translation demonstrate that the 5'-UTR of full-length LEF1 mRNA contains a bona fide IRES. Deletion analysis of the 5'-UTR shows that maximal IRES activity requires the majority of the 5'-UTR, consistent with the notion that cellular IRESs require multiple modules for efficient activity. This study demonstrates that full-length LEF1 mRNA has evolved to utilize a cap-independent mechanism for translation of full-length LEF-1, whereas the truncated isoform is produced via the canonical cap-dependent ribosome scanning mechanism.

Wnt-3a regulates chondrocyte differentiation via c-Jun/AP-1 pathway

Our previous study indicated that interleukin (IL)-1beta induces expression of several Wnt proteins in chondrocytes and causes chondrocyte dedifferentiation via the c-Jun/activator protein-1 (AP-1) pathway. This study examined whether Wnt-3a causes chondrocyte dedifferentiation via the c-Jun/AP-1 pathway. Wnt-3a inhibited chondrogenesis of mesenchymal cells by stabilizing cell-cell adhesion in a manner independent of beta-catenin transcriptional activity. Wnt-3a also induced dedifferentiation of articular chondrocytes by stimulating the transcriptional activity of beta-catenin-T cell-factor/lymphoid-enhancer-factor (Tcf/Lef) complex. In chondrocytes, Wnt-3a caused the expression of c-Jun and its phosphorylation by c-Jun N-terminal kinase (JNK), resulting in activation of AP-1. AP-1 activation suppressed the expression of Sox-9, a major transcription factor regulating type II collagen expression. Collectively, our results suggest that Wnt-3a inhibits chondrogenesis by stabilizing cell-cell adhesion and that it causes dedifferentiation of chondrocytes by activating of beta-catenin-Tcf/Lef transcriptional complex and the c-Jun/AP-1 pathway.

Identification of MYCBP as a beta-catenin/LEF-1 target using DNA microarray analysis

Abnormal activation of the beta-catenin signaling pathway can cause various types of cancer. Activation of Wnt pathway leads to stabilization of the beta-catenin protein, which results in its translocation to the nucleus and the formation of complexes with lymphoid enhancer factor-1 (LEF-1) and other T-cell factor (TCF) family of transcription factors to affect the transcription of target genes. However, the entrapment pattern of beta-catenin in the nucleus of normal epithelial cells differs from that in colon carcinoma cells. Normal epithelial cells may have different binding partners of beta-catenin and LEF-1 compared to tumor cells, which may result in differential expression of target genes. To investigate LEF-1-induced gene expression profiles, we used DNA microarrays to search the alterations of gene expression in normal epithelia versus cancer cells. Here, we reported 10 potential targets genes of beta-catenin/LEF-1. We showed that the expression of c-myc binding protein (MYCBP) in colon carcinoma cells was consistently upregulated by overexpressed LEF-1, which is confirmed by microarray data, RT-PCR and luciferase assay. We suggest that the MYCBP gene can be a direct target of beta-catenin/LEF-1 pathway through its LEF-1 binding site(s) in the MYCBP promoter, and that MYCBP up-regulation in colon carcinoma cell may play a co-activator role of c-MYC.

Coordinated expression of cyclin D1 and LEF-1/TCF transcription factor is restricted to a subset of hepatocellular carcinoma

BACKGROUND

While the Wnt pathway has been widely implicated in hepatocarcinogenesis, the role of cyclin D1 as a direct downstream target gene of beta-catenin-lymphoid enhancer factor-1 (LEF-1)/T-cell factor (TCF) signaling is controversely discussed.

METHODS

By immunohistochemical analyses we studied the subcellular localization of LEF-1/TCF and cyclin D1 in 162 hepatocellular carcinoma (HCC). Single- and double-label imaging by brightfield and confocal laser scanning microscopy was quantitated and correlated with beta-catenin, the Ki67(+) proliferation fraction (PF), tumor size, grade, the Okuda stage and patient survival.

RESULTS

The frequency of nuclear cyclin D1 expression was 28% and closely correlated with LEF-1/TCF (P<0.0001) and the Ki67(+) PF (P=0.03). Nuclear LEF-1/TCF expression was observed in 52% of all cases, but was also present in 42% of cyclin D1(-) cases. Nuclear beta-catenin was identified in 37% of all HCCs and correlated with LEF-1/TCF (P=0.04). The expression of cyclin D1, LEF-1/TCF or beta-catenin did not correlate with other clinico-pathological data.

CONCLUSIONS

A large proportion of HCCs does not appear to be linked to a deregulation of cyclin D1. However, the coordinated expression of cyclin D1 and LEF-1/TCF in some cases suggests the role of cyclin D1 as a Wnt target gene in a subset of HCCs.

β-Catenin can act as a nuclear import receptor for its partner transcription factor, lymphocyte enhancer factor-1 (lef-1)

Nuclear accumulation of beta-catenin plays an important role in the Wnt signaling pathway. In the nucleus, beta-catenin acts as a transcriptional co-activator for TCF/LEF family of transcription factors. It has been shown that lef-1 contains a typical basic type nuclear localization signal (NLS) and is transported into the nucleus by the conventional import pathway. In this study, we found that a mutant lef-1 lacking the classical NLS accumulated in the nucleus of living cells, when beta-catenin was co-expressed. In addition, in a cell-free import assay, lef-1 migrated into the nucleus in the presence of beta-catenin alone without any other soluble factors. In contrast, another mutant lef-1 lacking the beta-catenin binding domain failed to migrate into the nucleus, even in the presence of beta-catenin. These findings indicate that beta-catenin alone can mediate the nuclear import of lef-1 through the direct binding. Collectively, we propose that there are two distinct pathways for the nuclear import of lef-1: importin alpha/beta-mediated and beta-catenin-mediated one, which provides a novel paradigm for Wnt signaling pathway.

Antisense Tcf inhibits the neoplastic growth of liver cancer cells

PURPOSE

T cell transcription factors are nuclear effectors of the Wnt signaling transduction pathway and play crucial roles in embryonic and malignant development. Our previous study showed increased expression level of Tcf mRNA in liver cancer. In the present paper, antisense Tcf RNA was used to explore the possible therapeutic effect on liver cancer cells by interrupting the abnormal Wnt pathway.

METHODS

Antisense expression vectors containing the conserved sequence of Tcf cDNA were constructed and transfected into a human liver cancer cell line SMMC-7721. Tumorigenic potential was determined by cellular growth assay and tumor growth in nude mice.

RESULTS

The stable transfection of anti-sense Tcf in SMMC-7721 cells significantly reduced Tcf expression at both mRNA and protein levels compared with parental and mock-transfected cells. Antisense-mediated suppression of Tcf inhibited the in vitro proliferation and in vivo tumor formation ability. Furthermore, the apoptosis rate of antisense transfected cells was significantly higher than that of control, indicating that antisense RNA suppressed malignant growth by induction of apoptosis.

CONCLUSION

Our studies demonstrate the critical role of Wnt signaling pathway in the neoplastic growth of liver cancer cells and suggest that inhibition of Tcf activity with antisense Tcf RNA may be a potential new gene therapy method for liver cancer.

Selective inhibition of TGF-beta responsive genes by Smad-interacting peptide aptamers from FoxH1, Lef1 and CBP

Transforming growth factor beta (TGF-beta) stimulation results in the assembly of Smad-containing protein complexes that mediate activation or repression of TGF-beta responsive genes. To determine if disruption of specific Smad protein-protein interactions would selectively inhibit responses to TGF-beta or generally interfere with Smad-dependent signaling, we developed three Smad-binding peptide aptamers by introducing Smad interaction motifs from Smad-binding proteins CBP, FoxH1 and Lef1 into the scaffold protein E. coli thioredoxin A (Trx). All three classes of aptamers bound to Smads by GST pulldown assays and co-immunoprecipitation from mammalian cells. Expression of the aptamers in HepG2 cells did not generally inhibit Smad-dependent signaling as evaluated using seven TGF-beta responsive luciferase reporter genes. The Trx-xFoxH1b aptamer inhibited TGF-beta-induced expression from a reporter dependent on the Smad-FoxH1 interaction, A3-lux, by 50%. Trx-xFoxH1b also partially inhibited two reporters not dependent on a Smad-FoxH1 interaction, 3TP-lux and Twntop, and endogenous PAI-1 expression. Trx-Lef1 aptamer only inhibited expression of the Smad-Lef1 responsive reporter gene TwnTop. The Trx-CBP aptamer had no significant effect on reporter gene expression. The results suggest that Smad-binding peptide aptamers can be developed to selectively inhibit TGF-beta-induced gene expression.

Functional consequences of integrin-linked kinase activation in podocyte damage

BACKGROUND

The delicate foot process architecture of glomerular podocytes critically depends on integrin mediated cell-glomerular basement membrane (GBM) interaction. Integrin signaling via the integrin-linked kinase (ILK) is activated in podocyte damage and associated with considerable podocyte phenotype alterations. ILK has been shown to regulate cell fate via nuclear interaction of beta-catenin with lymphoid enhancer factor (LEF-1) transcription factors. The aim of this study was to elucidate the molecular mechanisms of ILK dependant phenotype regulation in podocytes.

METHODS

ILK function was evaluated in conditionally immortalized murine glomerular epithelial cells using overexpression of ILK and a small molecule ILK inhibitor in puromycin/adriamycin-induced podocyte damage in vitro and in vivo.

RESULTS

Kinase active, but not mutant ILK induced translocation of beta-catenin to the cell nucleus, de novo expression of LEF-1, and nuclear colocalization of beta-catenin and LEF-1. The role of ILK signaling in podocyte damage was evaluated using puromycin, an agent known to cause selective proteinuria and to increase ILK activity. The small molecular ILK inhibitor MC-5 blocked puromycin-induced nuclear translocation of beta-catenin, podocyte detachment, cell proliferation, and repression of the slit membrane molecules P-cadherin and CD2ap. In vivo activation of the beta-catenin pathway could be shown by nuclear colocalization of beta-catenin with WT-1 in adriamycin nephropathy.

CONCLUSION

ILK regulates podocyte cell matrix interaction, proliferation, and slit membrane gene expression in podocyte damage. As this pathway is amendable to pharmacologic intervention, further detailed studies of in vivo ILK function in glomerular disease appear justified.

Comprehensive survey of carapacial ridge-specific genes in turtle implies co-option of some regulatory genes in carapace evolution

The turtle shell is an evolutionary novelty in which the developmental pattern of the ribs is radically modified. In contrast to those of other amniotes, turtle ribs grow laterally into the dorsal dermis to form a carapace. The lateral margin of carapacial primordium is called the carapacial ridge (CR), and is thought to play an essential role in carapace patterning. To reveal the developmental mechanisms underlying this structure, we systematically screened for genes expressed specifically in the CR of the Chinese soft-shelled turtle, Pelodiscus sinensis, using microbead-based differential cDNA analysis and real-time reverse transcription-polymerase chain reaction. We identified orthologs of Sp5, cellular retinoic acid-binding protein-I (CRABP-I), adenomatous polyposis coli down-regulated 1 (APCDD1), and lymphoid enhancer-binding factor-1 (LEF-1). Although these genes are conserved throughout the major vertebrate lineages, comparison of their expression patterns with those in chicken and mouse indicated that these genes have acquired de novo expression in the CR in the turtle lineage. In association with the expression of LEF-1, the nuclear localization of beta-catenin protein was detected in the CR ectoderm, suggesting that the canonical Wnt signaling triggers carapace development. These findings indicate that the acquisition of the turtle shell did not involve the creation of novel genes, but was based on the co-option of pre-existing genes.

β-Catenin/T-cell factor-mediated transcription is modulated by cell density in human bronchial epithelial cells

The embryonic Wnt/beta-catenin ('canonical') pathway has been implicated in epithelial regeneration. To investigate the role of Wnt signal transduction in the airways, we characterised the expression of key pathway components in human bronchial epithelial cells (HBEC) and studied the influence of cell density on pathway activity, using sub-confluent cells in log-phase growth as a simple model of repairing epithelium. Primary HBEC and H292 bronchial epithelial cells were found to express TCF-4, TCF-3 and isoforms of LEF-1, transcription factors that are regulated by Wnt signalling. The cells also had the potential to respond to Wnt signalling through expression of several members of the Frizzled receptor family, including FZD-5 and -6. In confluent H292 cells, 20 mM lithium and 25% v/v Wnt-3a conditioned medium induced 4.5-fold (p = 0.008) and 1.4-fold (p = 0.006) increases in TOPflash activity, respectively. Under conditions of reduced cell density, TOPflash activity increased 1.8-fold (p = 0.002) in association with increased nuclear localisation of hypophosphorylated (active) beta-catenin and increased cell proliferation. This up-regulation in reporter activity occurred independently of EGF receptor activation and could not be recapitulated by use of low-calcium medium to disrupt cadherin-mediated cell-cell adhesion, but was associated with changes in FZD-6 expression. We conclude that reactivation of this embryonic pathway may play an important role in bronchial epithelial regeneration, and that modulation of Fzd-6 receptors may regulate Wnt signalling at confluence. Recognising that many chronic inflammatory disorders of the airways involve epithelial damage and repair, altered Wnt signalling might contribute to disease pathogenesis or progression.

Inhibition of the DNA binding by the TCF-1 binding RNA aptamer

The DNA binding architectural protein, TCF, and the transcriptional activator, beta-catenin, form a complex that regulates the expression of diverse target genes during early development and carcinogenesis. As an approach to modulating transcription by this complex, we selected an RNA aptamer that binds to the DNA binding domain of TCF-1. The aptamer interfered with the binding of TCF-1 to its specific DNA recognition sequences in vitro and also inhibited DNA binding of cellular TCF-1. We also developed the truncated version of the aptamer for efficient delivery to the cells. Structural analysis of the truncated aptamer revealed that a stem-loop with an internal loop was responsible for the binding to TCF-1. Similar approach may well be applicable to other proteins, especially DNA binding transcription factors, in order to modulate their DNA binding and transcriptional activity in the cells.

Beta-catenin and BMP-2 synergize to promote osteoblast differentiation and new bone formation

Mutations of critical components of the Wnt pathway profoundly affect skeletal development and maintenance, probably via modulation of beta-catenin signaling. We tested the hypothesis that beta-catenin is involved in mesenchymal lineage allocation to osteogenic cells using a beta-catenin mutant with constitutive transcriptional activity (DeltaN151). Although this stable beta-catenin had no effects by itself on osteogenic differentiation of multipotent embryonic cell lines, it synergized with bone morphogenetic protein-2 (BMP-2) resulting in dramatic stimulation of alkaline phosphatase activity, osteocalcin gene expression, and matrix mineralization. Likewise, DeltaN151 and BMP-2 synergistically stimulated new bone formation after subperiosteal injection in mouse calvaria in vivo. Conversely, DeltaN151 prevented adipogenic differentiation from pre-adipocytic or uncommitted mesenchymal cells in vitro. Intriguingly, the synergism with BMP-2 on gene transcription occurred without altering expression of Cbfa1/Runx2, suggesting actions independent or downstream of this osteoblast-specific transcription factor. Thus, beta-catenin directs osteogenic lineage allocation by enhancing mesenchymal cell responsiveness to osteogenic factors, such as BMP-2, in part via Tcf/Lef dependent mechanisms. In vivo, this synergism leads to increased new bone formation.

Activation of Wnt/beta-catenin/Tcf signaling in mouse skin carcinogenesis

Although Wnt/beta-catenin/Tcf signaling pathway has been shown to be an important factor in the development of many malignancies including colorectal, ovarian, prostate, and many other cancers, little is known about its role in non-melanoma skin cancers. Here, we report the first evidence that beta-catenin/Tcf signaling pathway is constitutively activated in non-melanocytic skin tumors induced by two stage chemical carcinogenesis protocol. Mouse skin tumors showed cytoplasmic and nuclear accumulation of beta-catenin, and upregulation of beta-catenin/Tcf target genes (c-myc and c-jun). We found high levels of skin-expressed Wnt proteins (Wnt 3, 4, and 10b) in different parts of the tumors, likely representing key upstream events in beta-catenin/Tcf activation during mouse skin carcinogenesis. Inhibition of beta-catenin/Tcf signaling by ectopic expression of dominant negative Tcf4 resulted in significant inhibition of growth in squamous cell carcinoma cells. A role of the constitutive activation of beta-catenin/Tcf signaling in skin carcinogenesis is discussed.

Cooperating pre-T-cell receptor and TCF-1-dependent signals ensure thymocyte survival

Intrathymic T-cell maturation critically depends on the selective expansion of thymocytes expressing a functionally rearranged T-cell receptor (TCR) beta chain. In addition, TCR-independent signals also contribute to normal T-cell development. It is unclear whether and how signals from the 2 types of pathways are integrated. Here, we show that T-cell factor-1 (TCF-1), a nuclear effector of the canonical wingless/int (wnt)/catenin signaling pathway, ensures the survival of proliferating, pre-TCR(+) thymocytes. The survival of pre-TCR(+) thymocytes requires the presence of the N-terminal catenin-binding domain in TCF-1. This domain can bind the transcriptional coactivator beta-catenin and may also bind gamma-catenin (plakoglobin). However, in the absence of gamma-catenin, T-cell development is normal, supporting a role for beta-catenin. Signaling competent beta-catenin is present prior to and thus arises independently from pre-TCR signaling and does not substantially increase on pre-TCR signaling. In contrast, pre-TCR signaling significantly induces TCF-1 expression. This coincides with the activation of a wnt/catenin/TCF reporter transgene in vivo. Collectively, these data suggest that efficient TCF-dependent transcription requires that pre-TCR signaling induces TCF-1 expression, whereas wnt signals may provide the coactivator such as beta-catenin. The 2 pathways thus have to cooperate to ensure thymocyte survival at the pre-TCR stage.

Wnt/beta-catenin signaling activates growth-control genes during overload-induced skeletal muscle hypertrophy

Beta-catenin is a transcriptional activator shown to regulate the embryonic, postnatal, and oncogenic growth of many tissues. In most research to date, beta-catenin activation has been the unique downstream function of the Wnt signaling pathway. However, in the heart, a Wnt-independent mechanism involving Akt-mediated phosphorylation of glycogen synthase kinase (GSK)-3beta was recently shown to activate beta-catenin and regulate cardiomyocyte growth. In this study, results have identified the activation of the Wnt/beta-catenin pathway during hypertrophy of mechanically overloaded skeletal muscle. Significant increases in beta-catenin were determined during skeletal muscle hypertrophy. In addition, the Wnt receptor, mFrizzled (mFzd)-1, the signaling mediator disheveled-1, and the transcriptional co-activator, lymphocyte enhancement factor (Lef)-1, are all increased during hypertrophy of the overloaded mouse plantaris muscle. Experiments also determined an increased association between GSK-3beta and the inhibitory frequently rearranged in advanced T cell-1 protein with no increase in GSK-3beta phosphorylation (Ser9). Finally, skeletal muscle overload resulted in increased nuclear beta-catenin/Lef-1 expression and induction of the transcriptional targets c-Myc, cyclin D1, and paired-like homeodomain transcription factor 2. Thus this study provides the first evidence that the Wnt signaling pathway induces beta-catenin/Lef-1 activation of growth-control genes during overload induced skeletal muscle hypertrophy.

Direct metabolic regulation of β-catenin activity by the p85α regulatory subunit of phosphoinositide 3-OH kinase

Class IA phosphoinositide 3-OH kinases (PI3K) are lipid kinases composed of catalytic and regulatory subunits. These lipid kinases can regulate the metabolic stability and signaling activity of beta-catenin, a central component of the E-cadherin/catenin cell-cell adhesion complex, and of the Wnt signaling pathway. This regulation occurs at the level of glycogen synthase kinase 3 (GSK3), a serine/threonine kinase that marks beta-catenin to enter a destruction pathway. In addition, the regulatory subunit p85alpha directly binds beta-catenin, but the role of this interaction in the context of the lipid kinase regulation of beta-catenin signaling is unknown. Here we report that expression of exogenous p85alpha in mouse keratinocytes increases the metabolic stability and has a strong synergistic effect on the transcriptional activity of beta-catenin. Both effects are associated to the formation of beta-catenin/p85alpha and inhibition of beta-catenin/APC complexes and are independent of GSK3 and PI3K activities. These findings suggest that p85alpha can act as a direct metabolic regulator of beta-catenin activity.

Expression of enamel proteins and LEF1 in adamantinomatous craniopharyngioma: evidence for its odontogenic epithelial differentiation

AIMS

Adamantinomatous craniopharyngioma (ACP) resembles histologically some odontogenic tumours, such as ameloblastoma and calcifying odontogenic cyst. However, there has been no evidence that ACP differentiates also functionally as odontogenic epithelium. The aim of this study was to gain evidence of odontogenic epithelial differentiation in ACP by means of immunohistochemistry. Among normal human tissues, enamel proteins are expressed exclusively in teeth, and lymphoid enhancer factor 1 (LEF1), in co-operation with beta-catenin, play an important role in tooth development. The expression of these proteins is therefore indicative of odontogenic epithelial differentiation.

METHODS AND RESULTS

The expression of enamel proteins and LEF1 was examined in 10 adamantinomatous and six papillary craniopharyngiomas. All the ACPs showed a variable degree of enamel protein expression, including amelogenin, enamelin and enamelysin, mainly in ghost cells. LEF1 was also heterogeneously expressed in ACPs; remarkably, its expression pattern was identical to that of nuclear beta-catenin accumulation. In contrast, none of the papillary craniopharyngiomas expressed enamel proteins or LEF1.

CONCLUSIONS

These results suggest that ACP consistently shows odontogenic epithelial differentiation. Since ACPs harbour beta-catenin mutation, the inappropriate activation of beta-catenin/LEF1 complex-dependent transcription may play a critical role in ACP tumorigenesis.

A T lymphocyte-specific transcription complex containing RUNX1 activates MHC class I expression

MHC class I expression is subject to both tissue-specific and hormonal regulatory mechanisms. Consequently, levels of expression vary widely among tissues, with the highest levels of class I occurring in the lymphoid compartment, in T cells and B cells. Although the high class I expression in B cells is known to involve the B cell enhanceosome, the molecular basis for high constitutive class I expression in T cells has not been explored. T cell-specific genes, such as TCR genes, are regulated by a T cell enhanceosome consisting of RUNX1, CBFbeta, LEF1, and Aly. In this report, we demonstrate that MHC class I gene expression is enhanced by the T cell enhanceosome and results from a direct interaction of the RUNX1-containing complex with the class I gene in vivo. T cell enhanceosome activation of class I transcription is synergistic with CIITA-mediated activation and targets response elements distinct from those targeted by CIITA. These findings provide a molecular basis for the high levels of MHC class I in T cells.

PITX2, beta-catenin and LEF-1 interact to synergistically regulate the LEF-1 promoter

PITX2, beta-catenin and lymphoid enhancer factor (LEF-1) are required for the inductive formation of several epithelial-derived organs, including teeth. Lef-1 is expressed in the dental epithelium after Pitx2, and both factors have overlapping expression patterns in the tooth bud and cap stages. Our analysis of Pitx2-/- mutant mice showed reduced Lef-1 expression in facial tissues by RT-PCR and quantitative RT-PCR. Consistent with these results we show that the human 2.5 kb LEF-1 promoter is activated by PITX2. Furthermore, the LEF-1 promoter is differentially activated by PITX2 isoforms, which are co-expressed in dental epithelium. The 2.5 kb LEF-1 promoter contains two regions that act to inhibit its transcription in concert with PITX2. The proximal region contains a Wnt-responsive element (WRE) that attenuates PITX2 activation. LEF-1 cannot autoregulate LEF-1 expression; however co-transfection of PITX2 and LEF-1 result in a synergistic activation of the 2.5 kb LEF-1 promoter. LEF-1 specifically interacts with the PITX2 C-terminal tail. Deletion of a distal 800 bp segment of the LEF-1 promoter resulted in enhanced PITX2 activation, and increased synergistic activation in the presence of LEF-1. Furthermore, beta-catenin in combination with PITX2 synergistically activates the LEF-1 promoter and this activation is independent of the Wnt-responsive element. beta-catenin directly interacts with PITX2 to synergistically regulate LEF-1 expression. We show a new mechanism where LEF-1 expression is regulated through PITX2, LEF-1 and beta-catenin direct physical interactions. LEF-1 and beta-catenin interactions with PITX2 provide new mechanisms for the regulation of PITX2 transcriptional activity.

Beta-catenin directly displaces Groucho/TLE repressors from Tcf/Lef in Wnt-mediated transcription activation

Wnt growth factors mediate cell fate determination during embryogenesis and in the renewal of tissues in the adult. Wnts act by stabilizing cellular levels of the transcriptional coactivator beta-catenin, which forms complexes with sequence-specific DNA-binding Tcf/Lef transcription factors. In the absence of nuclear beta-catenin, Tcf/Lefs act as transcriptional repressors by binding to Groucho/TLE proteins. The molecular basis of the switch from transcriptional repression to activation during Wnt signaling has not been clear, in particular whether factors other than beta-catenin are required to disrupt the interaction between Groucho/TLE and Tcf/Lef. Using highly purified proteins, we demonstrate that beta-catenin displaces Groucho/TLE from Tcf/Lef by binding to a previously unidentified second, low-affinity binding site on Lef-1 that includes sequences just N-terminal to the DNA-binding domain, and that overlaps the Groucho/TLE-binding site.

An RNA aptamer that binds to the beta-catenin interaction domain of TCF-1 protein

The architectural transcription factor TCF-1 interacts directly with beta-catenin and activates transcription of various target genes that are important for early development and carcinogenesis. We selected an RNA aptamer that specifically bound to the beta-catenin-interacting N-terminal motif of TCF-1. Structural analysis revealed that it formed a stem-loop structure that was responsible for binding TCF-1 and contained a pair of internal loops. The RNA aptamer interfered with the binding of TCF-1 to beta-catenin and also inhibited the formation of TCF-1/beta-catenin complexes. Disruption of TCF-1/beta-catenin complexes could alter the transcriptional activity of TCF-1. Taken together our observations show that a rationally designed RNA aptamer can disrupt protein-protein interactions required for the formation of an active transcription complex.

LEF1 is a critical epithelial survival factor during tooth morphogenesis

LEF1 is a cell-type-specific transcription factor and mediates Wnt signaling pathway by association with its co-activator beta-catenin. Wnt signaling is known to be critical for the specification of cranial neural crest (CNC) cells and may regulate the fate diversity of the CNC during craniofacial morphogenesis. Loss of Lef1 results in arrested tooth development at the late bud stage and LEF1 is required for a relay of a Wnt signaling to a cascade of FGF signaling activities to mediate the epithelial-mesenchymal interaction during tooth morphogenesis. It remains unclear, however, what is the cellular mechanism of LEF1 signaling in regulating tooth morphogenesis. To test the hypothesis that LEF1 signaling regulates the fate of the dental epithelial and the CNC-derived mesenchymal cells during tooth morphogenesis, we investigated and compared the cellular migration, proliferation, and apoptotic activity within the tooth germ between the wild-type and Lef1 null mutant mice. Using the Wnt1-Cre/R26R transgenic system for indelibly marking the progenies of CNC cells, we show that there is no CNC migration defect in the Lef1 null mutant mice, indicating that the arrest in tooth development is not the result of shortage of the CNC contribution into the first branchial arch in the Lef1 mutant. Furthermore, there is no alteration in cell proliferation or condensation of the CNC-derived dental mesenchyme in the Lef1 null mutant, suggesting that LEF1 may not affect the cell cycle progression of the multipotential CNC cells during tooth morphogenesis. Importantly, apoptotic activity is significantly increased within the dental epithelium in the Lef1 null mutant mice. As the result of this increased cell death, the bud stage tooth germ fails to advance to the cap stage in the absence of Lef1. Inhibition of apoptotic activity by FGF4 rescues the tooth development in the Lef1 null mutant. Our studies suggest that LEF1 is a critical survival factor for the dental epithelial cells during tooth morphogenesis.

Alterations of lymphoid enhancer factor-1 isoform expression in solid tumors and acute leukemias

Two major transcripts of lymphoid enhancer factor-1 (LEF-1) have been described. The long isoform with b-catenin binding domain functions as a transcriptional enhancer factor. The short isoform derives from an intronic promoter and exhibits dominant negative activity. Recently, alterations of LEF-1 isoforms distribution have been described in colon cancer. In the current study we employed a quantitative real-time reverse transcription PCR method (TaqMan) to analyze expression of LEF-1 isoforms in a large cohort of human tumor (n = 304) and tumor-free control samples (n = 56). The highest expression level of LEF-1 was found in carcinoma samples whereas brain cancer samples expressed little. Expression of LEF-1 was different in distinct cancer types. For example, the mRNA level of LEF-1 was lower in testicular tumor samples compared with tumor-free control samples. Besides epithelial cancers, significant LEF-1 expression was also found in hematopoietic cells. In hematological malignancies, overall LEF-1 level was higher in lymphocytic leukemias compared with myeloid leukemias and normal hematopoiesis. However, acute myeloid leukemia and acute lymphocytic leukemia showed a significantly increased fraction of the oncogenic LEF-1 compared with chronic lymphocytic leukemia and chronic myeloid leukemia. Taken together, these data suggest that LEF-1 is abundantly expressed in human tumors and the ratio of the oncogenic and the dominant negative short isoform altered not only in carcinomas but also in leukemia.

A second protein kinase CK1-mediated step negatively regulates Wnt signalling by disrupting the lymphocyte enhancer factor-1/β-catenin complex

Deregulated activation of the canonical Wnt signalling pathway leads to stabilization of beta-catenin and is critically involved in carcinogenesis by an inappropriate induction of lymphocyte enhancer factor (LEF-1)/beta-catenin-dependent transcription of Wnt target genes. Phosphorylation of the pathway components beta-catenin, Dishevelled, Axin and APC (adenomatous polyposis coli) by glycogen synthase kinase-3beta, CK1 and CK2 is of central importance in the regulation of the beta-catenin destruction complex. Here, we identify CK1 and CK2 as major kinases that directly bind to and phosphorylate LEF-1 inducing distinct, kinase-specific changes in the LEF-1/DNA complex. Moreover, CK1-dependent phosphorylation in contrast to CK2 disrupts the association of beta-catenin and LEF-1 but does not impair DNA binding of LEF-1. Sequential phosphorylation assays revealed that for efficient disruption of the LEF-1/beta-catenin complex, beta-catenin also has to be phosphorylated. Consistent with these observations, CK1-dependent phosphorylation inhibits, whereas CK2 activates LEF-1/beta-catenin transcriptional activity in reporter gene assays. These data are in line with a negative regulatory function of CK1 in the Wnt signalling pathway, where CK1 in addition to the beta-catenin destruction complex at a second level acts as a negative regulator of the LEF-1/beta-catenin transcription complex, thereby protecting cells from development of cancer.

Transdifferentiation of corneal epithelium into epidermis occurs by means of a multistep process triggered by dermal developmental signals

Differentiated cells of the corneal epithelium are converted to hair, along with their associated stem cells, then interfollicular epidermis, by means of a multistep process triggered by dermal developmental signals. The committed basal cells of the adult corneal epithelium dedifferentiate under the control of signals from an associated embryonic hair-forming dermis, likely Wnts, and revert to a limbal basal cell phenotype. This initial process involves the down-regulation of Pax6 and the loss of expression of corneal-specific keratins and the induction of basal keratinocyte markers. These dedifferentiated cells are able to reinduce dermal condensations, which in turn induce the formation of hair follicles from cells that have lost Pax6 expression, by means of a Noggin-dependent mechanism. An epidermis is subsequently formed by cells derived from the newly segregated hair stem cells.

Suppression of immune system genes by methylprednisolone in exacerbations of multiple sclerosis. Preliminary results

Acute relapses of multiple sclerosis (MS) are treated with intravenous methylprednisolone (IVMP), which speeds recovery from exacerbation. It is known that IVMP suppresses the immunological activation which occurs during an acute attack of MS. However, the specific target genes affected by this therapy remain obscure. A cDNA microarray for 448 genes was used to identify the target genes in IVMP therapy. Total RNA was isolated from peripheral blood mononuclear cells derived from six MS patients immediately before and after completion of therapy. IVMP significantly reduced mRNA levels for T-cell-specific transcription factor 7 (p=0.02), T-cell-specific protein-tyrosine kinase (p=0.02), T-cell surface glycoprotein CD5 (p=0.05) and interferon-stimulated gene factor 3 gamma subunit (p=0.04). Significantly increased expression was found for eosinophil-derived neurotoxin (p=0.05). The suppression of expression of genes associated with T-cell differentiation and antigen-specific T-cell activation detected in this study may contribute to the beneficial effect of MP in relapses of MS.

Morphological and transcriptional responses of untransformed intestinal epithelial cells to an oncogenic β-catenin protein

Aberrant transactivation of a certain set of target genes by the beta-catenin and T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription factor complexes has been implicated in the process of intestinal epithelial cells entering early colorectal carcinogenesis. A rat intestinal epithelial cell line IEC6 became elongated, extended protrusions at cell periphery, and increased stress fibers and focal contacts upon the induction of beta-catenin protein stabilized by deletion of the N-terminal glycogen synthase kinase-3beta (GSKbeta) phosphorylation sites (beta-catenin DeltaN89). We used the GeneChiptrade mark oligonucleotide microarray system to examine approximately 24 000 genes and identified 13 genes whose expression was altered during the course of this morphological transformation. Those genes included known negative regulators of the Wnt signaling pathway, Sfrp4 and Axin2; extracellular matrix and related molecule, Hxb and Crtl1; cell adhesion and cytoskeletal proteins, Podxl, Igaf4, and Itab6; and molecules involved in the insulin and insulin-like growth factor (IGF) signaling pathways, Enpp1, Igfbp2, and Sgk. We report the finding that insulin-like growth factor-binding protein-2 (IGFBP2) is a direct target gene of the beta-catenin and TCF/LEF complexes. The IGFBP2 protein interacts with integrins. Disruption of the multigene network system regulating cell adhesion and cytoskeleton may be crucial in the initiation of colorectal carcinogenesis.

Airway glandular development and stem cells

Submucosal glands in the lung play important roles in several hypersecretory lung disease processes, including chronic bronchitis, asthma, and cystic fibrosis. In this context, submucosal glands undergo abnormal growth and differentiation through processes that are poorly understood. To better understand the pathophysiological mechanisms that lead to submucosal gland hypertrophy and hyperplasia in the adult human lung, efforts have been made to dissect the molecular signals and cell types responsible for normal submucosal gland development in the airway. Such studies have revealed a close relationship between progenitor?stem cell phenotypes in the surface airway epithelia and submucosal glands, and thus it has been suggested that submucosal glands serve as a protective niche for surface airway epithelial stem cells. Furthermore, the pluripotent progenitor cells that exist in the surface airway epithelium, which have the capacity to differentiate into ciliated, secretory, intermediate, and basal cells, also have a developmental capacity for submucosal glands. This putative adult stem cell compartment of the airway epithelium has been the focus of research attempting to identify molecular markers for signaling pathways that control stem cell phenotypes and their capacity for proliferation and differentiation following airway injury.

Interaction between Smad7 and beta-catenin: importance for transforming growth factor beta-induced apoptosis

Members of the transforming growth factor beta (TGF-beta) and Wnt/wingless superfamilies regulate cell fate during development and tissue maintenance. Here we report that Smad7 interacts with beta-catenin and lymphoid enhancer binding factor 1/T-cell-specific factor (LEF1/TCF), transcriptional regulators in Wnt signaling, in a TGF-beta-dependent manner. Smad7 was found to be required for TGF-beta1-induced accumulation of beta-catenin and LEF1 in human prostate cancer (PC-3U) cells as well as in human keratinocytes (HaCaT cells). Moreover, when the endogenous Smad7 was repressed by specific small interfering RNA, TGF-beta-induced increase of activated p38, Akt phosphorylated on Ser473, glycogen synthase kinase 3beta phosphorylated on Ser9 was prevented, as well as the TGF-beta-induced association between beta-catenin and LEF1. Notably, the observed physical association of Smad7 and beta-catenin was found to be important for TGF-beta-induced apoptosis, since suppression of beta-catenin expression by small interfering RNA decreased the apoptotic response to TGF-beta.

Role of a BCL9-related beta-catenin-binding protein, B9L, in tumorigenesis induced by aberrant activation of Wnt signaling

Wnt signaling plays a crucial role in a number of developmental processes and in tumorigenesis. beta-Catenin is stabilized by Wnt signaling and associates with the TCF/LEF family of transcription factors, thereby activating transcription of Wnt target genes. Constitutive activation of beta-catenin-TCF-mediated transcription resulting from mutations in adenomatous polyposis coli (APC), beta-catenin, or Axin is believed to be a critical step in tumorigenesis among divergent types of cancers. Here we show that the transactivation potential of the beta-catenin-TCF complex is enhanced by its interaction with a BCL9-like protein, B9L, in addition to BCL9. We found that B9L is required for enhanced beta-catenin-TCF-mediated transcription in colorectal tumor cells and for beta-catenin-induced transformation of RK3E cells. Furthermore, expression of B9L was aberrantly elevated in about 43% of colorectal tumors, relative to the corresponding noncancerous tissues. These results suggest that B9L plays an important role in tumorigenesis induced by aberrant activation of Wnt signaling.

Regulation of the versican promoter by the beta-catenin-T-cell factor complex in vascular smooth muscle cells

The proteoglycan versican is pro-atherogenic and central to vascular injury and repair events. We identified the signaling pathways and promoter elements involved in regulation of versican expression in vascular smooth muscle cells. Phosphatidylinositol 3-kinase inhibitor, LY294002, significantly decreased versican-luciferase (Luc) promoter activity and endogenous mRNA levels. We further examined the roles of protein kinase B and glycogen synthase kinase (GSK)-3beta, downstream effectors of phosphatidylinositol 3-kinase, in the regulation of versican transcription. Co-transfection of dominant negative and constitutively active protein kinase B constructs with a versican-Luc construct decreased and increased promoter activity, respectively. Inhibition of GSK-3beta activity by LiCl augmented accumulation of beta-catenin and caused induction of versican-Luc activity as well as versican mRNA levels. Beta-catenin has no DNA binding domain, therefore it cannot directly induce transcription of the versican promoter. Software analysis of the versican promoter revealed two potential binding sites for T-cell factors (TCFs), proteins that confer transcriptional activation of beta-catenin. Electrophoretic mobility shift and supershift assays revealed specific binding of human TCF-4 and beta-catenin to oligonucleotides corresponding to a potential TCF binding site in the versican promoter. In addition to binding assays, we directly assessed the dependence of versican promoter activity on TCF binding sites. Site-directed mutagenesis of the TCF site located -492 bp relative to the transcription start site markedly diminished versican-Luc activity. Co-transfection of TCF-4 with versican-Luc did not increase promoter activity, but addition of beta-catenin and TCF-4 significantly stimulated basal versican promoter activity. Our findings suggest that versican transcription is predominantly mediated by the GSK-3beta pathway via the beta-catenin-TCF transcription factor complex in smooth muscle cells, wherein such regulation contributes to the normal or aberrant formation of provisional matrix in vascular injury and repair events.

Activation of the {beta}-catenin/T-cell-specific transcription factor/lymphoid enhancer factor-1 pathway by plasminogen activators in ECV304 carcinoma cells

Besides its involvement in clot lysis, the plasminogen activator (PA) system elicits various cellular responses involved in cell migration, adhesion, and proliferation and plays a key role in the progression of cancers. beta-Catenin interacts with E-cadherins and functions as transcriptional coactivator of the Wnt-signaling pathway, which is implicated in tumor formation when aberrantly activated. We report that tissue-type plasminogen activator (tPA) elicited tyrosine phosphorylation and cytosolic accumulation of an active (non-serine-threonin phosphorylated, nonubiquitinated) form of beta-catenin in ECV304 carcinoma cells. tPA-dependent beta-catenin activation is mediated through epidermal growth factor receptor (EGFR) transactivation (via Src), suggested by the inhibitory effects of AG1478 and PP2 (specific inhibitors of EGFR and Src, respectively) and by the lack of beta-catenin activation in EGFR-negative B82 fibroblasts. EGFR phosphorylation and beta-catenin activation were inhibited by plasminogen activator inhibitor 1 and pertussis toxin, two inhibitors of the urokinase-type plasminogen activator (uPA)/uPA receptor system. beta-Catenin activation was correlated with the phosphorylation of glycogen synthase kinase-3beta through a phosphatidylinositol 3-kinase/Akt-dependent mechanism. Gel shift experiments revealed the activation of beta-catenin/T-cell-specific transcription factor (Tcf)/lymphoid enhancer factor-1 (Lef) transcriptional complex, evidenced by an increased binding of nuclear extracts to oligonucleotides containing the cyclin D1 Lef/Tcf site. beta-Catenin silencing through small interfering RNA and antisense oligonucleotides inhibited both the tPA-mediated cyclin D1 expression and cell proliferation. A similar activation of the beta-catenin pathway was triggered by amino-terminal fragment, the NH(2)-terminal catalytically inactive fragment of tPA, thus suggesting that this effect was independent of the proteolytic activity of plasminogen activators. In conclusion, the beta-catenin/Lef/Tcf pathway is activated by tPA and is involved in cell cycle progression and proliferation.

Aberrant expression and function of TCF4 in the proliferation of hepatocellular carcinoma cell line BEL-7402

Wnt signaling pathway is essential for development and tumorigenesis, however, this signaling pathway in the progress of hepatocellular carcinoma (HCC) remains unclear. In this paper, we studied the function of human T-cell transcription factor-4 (TCF4), a key factor of Wnt signaling pathway, on the proliferation of HCC cell line. We showed that the expression of TCF4 mRNA in HCC cell line BEL-7402 was higher than that in immortalized normal liver cell line L02. Blockage of Wnt pathway by Delta-NTCF4, a dominant negative TCF4, could suppress BEL-7402 cells growth and decrease the expression of cyclin D1 and c-myc, two of target genes of Wnt pathway. On the other hand, stimulating Wnt pathway by introducing a degradation-resistant -catenin S37A could increase BEL-7402 cells proliferation. But all the treatments had no effect on L02 cells. Our data indicated that TCF4 might be another key factor in Wnt pathway involved in HCC cells proliferation and TCF4 could be an effective therapeutic target for suppressing the growth of hepatocellular cancers.

Ternary complex factor-serum response factor complex-regulated gene activity is required for cellular proliferation and inhibition of apoptotic cell death

Members of the ternary complex factor (TCF) subfamily of the ETS-domain transcription factors are activated through phosphorylation by mitogen-activated protein kinases (MAPKs) in response to a variety of mitogenic and stress stimuli. The TCFs bind and activate serum response elements (SREs) in the promoters of target genes in a ternary complex with a second transcription factor, serum response factor (SRF). The association of TCFs with SREs within immediate-early gene promoters is suggestive of a role for the ternary TCF-SRF complex in promoting cell cycle entry and proliferation in response to mitogenic signaling. Here we have investigated the downstream gene regulatory and phenotypic effects of inhibiting the activity of genes regulated by TCFs by expressing a dominantly acting repressive form of the TCF, Elk-1. Inhibition of ternary complex activity leads to the downregulation of several immediate-early genes. Furthermore, blocking TCF-mediated gene expression leads to growth arrest and triggers apoptosis. By using mutant Elk-1 alleles, we demonstrated that these effects are via an SRF-dependent mechanism. The antiapoptotic gene Mcl-1 is identified as a key target for the TCF-SRF complex in this system. Thus, our data confirm a role for TCF-SRF-regulated gene activity in regulating proliferation and provide further evidence to indicate a role in protecting cells from apoptotic cell death.

Expression pattern of zebrafishtcf7 suggests unexplored domains of Wnt/?-catenin activity

Tcf/Lef transcription factors play an important role in mediating canonical Wnt signaling. When bound by beta-catenin, Tcf/Lef proteins either activate or de-repress gene transcription. In zebrafish, four members have been identified: Lef1, Tcf3, Tcf3b, and Tcf4. Here, we report the cloning and expression of the tcf7 gene. Forms of Tcf7 expressed in the embryo contain two highly conserved regions: an N-terminal beta-catenin binding domain and a C-terminal HMG domain. Tcf7 lacks a putative Groucho corepressor binding site, suggesting that, like Lef1, it functions as a transcriptional activator. We isolated three C-terminal splice variants of tcf7 corresponding to human B, C, and D isoforms. tcf7 expression overlaps with lef1 expression maternally, in the tail bud, fin buds, and paraxial mesoderm, and we expect that the two genes function redundantly in those areas. tcf7 is also expressed in nonoverlapping areas such as the prechordal mesoderm, dorsal retina, and median fin fold, suggesting unique functions.

TGF-? induces novel Lef-1 splice variants through a Smad-independent signaling pathway

The lymphoid enhancer-binding factor (Lef-1) transcription factor is best known for the ability to transduce Wnt signals during development and to mediate excessive Wnt signaling in certain types of cancer. We recently identified and characterized a novel Wnt-like effect of transforming growth factor-beta (TGF-beta) on beta-catenin, the binding partner of Lef-1. Therefore, we sought to determine the effect of TGF-beta on expression of the Lef/T-cell-specific transcription factor (TCF) components of the Wnt pathway. We found that TGF-beta markedly induced Lef-1 mRNA expression in cell lines originating from fetal lung (Mv1Lu) and newborn skin (Balb/MK), tissues that normally express Lef-1 during development. Lef-1 induction was temporally related to but independent of TGF-beta-induced G1 cell cycle arrest. Furthermore, the induction of Lef-1 was independent of both new protein synthesis and Smad-mediated signaling. Using TGF-beta-treated Mv1Lu cells, we identified multiple splice forms of Lef-1, including novel variants that lack both exons 2 and 3. We conclude that the induction of Lef-1 has permissive effects on the well-characterized TGF-beta signal that inhibits c-myc expression and induces a G1 arrest.

Role of the intracellular domains of LRP5 and LRP6 in activating the Wnt canonical pathway

LDL-receptor related proteins 5 and 6 (LRP5/6) are co-receptors of Frizzled receptors that mediate Wnt-induced activation of the transcription factor family TCF/LEF-1. Even though LRP5 and LRP6 are highly homologous, LRP6, but not LRP5, is expressed primarily in the nervous system and deletion of the LRP6 gene results in significant brain abnormalities, while deletion of LRP5 results in primarily decreased bone density. Additionally, the exact function of LRP5 and LRP6 have not been clearly defined, although it is clear that they both play key roles in the Wnt canonical pathway. In this study the role of the intracellular domains of LRP5/6 in mediating Wnt signaling was examined. In the absence of exogenous Wnt 3a, full-length (FL) LRP6, but not LRP5, increased TCF/LEF-1 transcriptional activity, however both significantly potentiated Wnt 3a-induced TCF/LEF-1 activation. In contrast to the findings with the FL constructs, the intracellular domains (membrane-anchored and cytosolic) of both LRP5 and LRP6 significantly increased TCF/LEF-1 activation in the absence of Wnt 3a, and potentiated the Wnt 3a-induced decrease in beta-catenin phosphorylation, increase in free beta-catenin levels and the increase in TCF/LEF-1 activity. These findings demonstrate that: (1) LRP5 and LRP6 differentially modulate TCF/LEF-1 activation in the absence of Wnt 3a and (2) the intracellular C-terminal domains of LRP5/6 potentiate Wnt 3a-induced TCF/LEF-1 activation whether or not they are membrane-anchored. These findings provide significant new insights into the roles of LRP5/6 in modulating canonical Wnt signaling.

Laser capture microdissection (LCM) for analysis of gene expression in specific tissues during embryonic epithelial-mesenchymal transformation

The analysis of gene expression in developing organs is a valuable tool for the assessment of genetic fingerprints during the various stages of tissue differentiation and epithelial-mesenchymal transformation (EMT). However, the variety of differentiating cells and the close association of epithelial and mesenchymal cells makes it difficult to extract protein and mRNA from specific cells and tissue and, thus, to assign expressed genes to specific cell populations. We report here the analysis of LEF1 mRNA in epithelial and mesenchymal cells isolated by LCM from different stages of EMT during development of the mouse palate and describe our techniques in detail. By applying a laser capture microdissection (LCM) technique and real-time polymerase chain reaction, we were able to determine mRNA levels that accurately reflect changes in gene expression in specific cells. The sensitivity of the technique is remarkable. Indeed, the mRNAs can be detected for many proteins too low in abundance to stain with antibodies. These techniques will enable embryologists to collect homogeneous groups of cells from heterogeneous populations in developing organs, which otherwise would not be available for gene analysis.

LEF1-mediated regulation of Delta-like1 links Wnt and Notch signaling in somitogenesis

Wnt signaling, which is mediated by LEF1/TCF transcription factors, has been placed upstream of the Notch pathway in vertebrate somitogenesis. Here, we examine the molecular basis for this presumed hierarchy and show that a targeted mutation of Lef1, which abrogates LEF1 function and impairs the activity of coexpressed TCF factors, affects the patterning of somites and the expression of components of the Notch pathway. LEF1 was found to bind multiple sites in the Dll1 promoter in vitro and in vivo. Moreover, mutations of LEF1-binding sites in the Dll1 promoter impair expression of a Dll1-LacZ transgene in the presomitic mesoderm. Finally, the induced expression of LEF1-beta-catenin activates the expression of endogenous Dll1 in fibroblastic cells. Thus, Wnt signaling can affect the Notch pathway by a LEF1-mediated regulation of Dll1.

WNT signaling, in synergy with T/TBX6, controls Notch signaling by regulating Dll1 expression in the presomitic mesoderm of mouse embryos

Notch signaling in the presomitic mesoderm (psm) is critical for somite formation and patterning. Here, we show that WNT signals regulate transcription of the Notch ligand Dll1 in the tailbud and psm. LEF/TCF factors cooperate with TBX6 to activate transcription from the Dll1 promoter in vitro. Mutating either T or LEF/TCF sites in the Dll1 promoter abolishes reporter gene expression in vitro as well as in the tail bud and psm of transgenic embryos. Our results indicate that WNT activity, in synergy with TBX6, regulates Dll1 transcription and thereby controls Notch activity, somite formation, and patterning.

Global Inhibition of Lef1/Tcf-dependent Wnt Signaling at Its Nuclear End Point Abrogates Development in Transgenic Xenopus Embryos

Analysis of canonical Wnt signaling during vertebrate development by means of knock-out or transgenic approaches is often hampered by functional redundancy as well as pathway bifurcations downstream of the manipulated components. We report the design of an optimized chimera capable of blocking transcriptional activation of Lef1/Tcf-beta-catenin target genes, thus enabling intervention with the canonical Wnt pathway at its nuclear end point. This construct was made hormone-inducible, both functionally and transcriptionally, and was transgenically integrated in Xenopus embryos. Down-regulation of target genes was clearly observed upon treatment of these embryos with dexamethasone. In addition, exposure of variously aged transgenic embryos to dexamethasone caused complex phenotypes with many new but also several recognizable features stemming from inhibition of canonical Wnt signaling. At least in some tissues, a significant reduction in cell proliferation and an increase in programmed cell death appeared to underlie these phenotypes. Our inducible transgenic system can serve a broad range of experimental settings designed to unveil new functional aspects of Lef1/Tcf-beta-catenin signaling during vertebrate embryogenesis.