21-169 Sigma-AldrichFOPflash (mutant TCF binding sites)

We demonstrate for the first time that the pro-inflammatory cytokine interleukin (IL)-18 stimulates rapid and significant proliferation of SMC derived from human saphenous vein (VSMC), but not coronary artery. IL-18 also stimulates VSMC growth. Further investigations revealed that IL-18-induced VSMC proliferation was Wnt inducible secreted protein-1 (WISP1) dependent. In addition to inducing its own expression via phosphatidylinositol 3-kinase/Akt-dependent IKK/NF-?B activation, IL-18 stimulated glycogen synthase kinase 3? phosphorylation and degradation, ?-catenin nuclear translocation and stabilization, T-cell factor-lymphoid enhancer binding factor (TCF-LEF) activation, and WISP1 induction. Moreover, WISP1 induced its own expression, and that of survivin and multiple matrix metalloproteinases via ?-catenin/TCF-LEF interaction. WISP1 also activated AP-1, but not NF-?B, and induced matrix metalloproteinase (MMP)9 transcription in part via AP-1. Interestingly, WISP1 failed to regulate tissue inhibitors of matrix metalloproteinases (TIMP) expression. These novel findings indicate that IL-18 induces a series of signaling events that result in WISP1-mediated VSMC proliferation, survival and MMP induction that are key components of vein graft stenosis and this may be amplified by IL-18 and WISP1 autoregulation and cross-regulation.

beta-Catenin is a transcriptional activator that regulates embryonic development as part of the Wnt pathway and also plays a role in tumorigenesis. The mechanisms leading to Wnt-induced stabilization of beta-catenin, which results in its translocation to the nucleus and activation of transcription, have been an area of intense interest. However, it is not clear whether stimuli other than Wnts can lead to important stabilization of beta-catenin and, if so, what factors mediate that stabilization and what biologic processes might be regulated. Herein we report that beta-catenin is stabilized in cardiomyocytes after these cells have been exposed to hypertrophic stimuli in culture or in vivo. The mechanism by which beta-catenin is stabilized is distinctly different from that used by Wnt signaling. Although, as with Wnt signaling, inhibition of glycogen synthase kinase-3 remains central to hypertrophic stimulus-induced stabilization of beta-catenin, the mechanism by which this occurs involves the recruitment of activated PKB to the beta-catenin-degradation complex. PKB stabilizes the complex and phosphorylates glycogen synthase kinase-3 within the complex, inhibiting its activity directed at beta-catenin. Finally, we demonstrate via adenoviral gene transfer that beta-catenin is both sufficient to induce growth in cardiomyocytes in culture and in vivo and necessary for hypertrophic stimulus-induced growth. Thus, in these terminally differentiated cells, beta-catenin is stabilized by hypertrophic stimuli acting via heterotrimeric G protein-coupled receptors. The stabilization occurs via a unique Wnt-independent mechanism and results in cellular growth.

The Wnt signalling pathway regulates many developmental processes through a complex of beta-catenin and the T-cell factor/lymphoid enhancer factor (TCF/LEF) family of high-mobility-group transcription factors. Wnt stabilizes cytosolic beta-catenin, which then binds to TCF and activates gene transcription. This signalling cascade is conserved in vertebrates, Drosophila and Caenorhabditis elegans. In C. elegans, the proteins MOM-4 and LIT-1 regulate Wnt signalling to polarize responding cells during embryogenesis. MOM-4 and LIT-1 are homologous to TAK1 (a kinase activated by transforming growth factor-beta) mitogen-activated protein-kinase-kinase kinase (MAP3K) and MAP kinase (MAPK)-related NEMO-like kinase (NLK), respectively, in mammalian cells. These results raise the possibility that TAK1 and NLK are also involved in Wnt signalling in mammalian cells. Here we show that TAK1 activation stimulates NLK activity and downregulates transcriptional activation mediated by beta-catenin and TCF. Injection of NLK suppresses the induction of axis duplication by microinjected beta-catenin in Xenopus embryos. NLK phosphorylates TCF/LEF factors and inhibits the interaction of the beta-catenin-TCF complex with DNA. Thus, the TAK1-NLK-MAPK-like pathway negatively regulates the Wnt signalling pathway.

Tcf transcription factors interact with beta-catenin and Armadillo to mediate Wnt/Wingless signaling. We now report the characterization of genes encoding two murine members of the Tcf family, mTcf-3 and mTcf-4. mTcf-3 mRNA is ubiquitously present in embryonic day 6.5 (E6.5) mouse embryos but gradually disappears over the next 3 to 4 days. mTcf-4 expression occurs first at E10.5 and is restricted to di- and mesencephalon and the intestinal epithelium during embryogenesis. The mTcf-3 and mTcf-4 proteins bind a canonical Tcf DNA motif and can complex with the transcriptional coactivator beta-catenin. Overexpression of Wnt-1 in a mammary epithelial cell line leads to the formation of a nuclear complex between beta-catenin and Tcf proteins and to Tcf reporter gene transcription. These data demonstrate a direct link between Wnt stimulation and beta-catenin/Tcf transcriptional activation and imply a role for mTcf-3 and -4 in early Wnt-driven developmental decisions in the mouse embryo.

Tcf/Lef transcription factors mediate signalling from Wingless/Wnt proteins by recruiting Armadillo/beta-catenin as a transcriptional co-activator. However, studies of Drosophila, Xenopus and Caenorhabditis elegans have indicated that Tcf factors may also be transcriptional repressors. Here we show that Tcf factors physically interact with members of the Groucho family of transcriptional repressors. In transient transfection assays, the Xenopus Groucho homologue XGrg-4 inhibited activation of transcription of synthetic Tcf reporter genes. In contrast, the naturally truncated Groucho-family member XGrg-5 enhanced transcriptional activation. Injection of XGrg-4 into Xenopus embryos repressed transcription of Siamois and Xnr-3, endogenous targets of beta-catenin-Tcf. Dorsal injection of XGrg-4 had a ventralizing effect on Xenopus embryos. Secondary-axis formation induced by a dominant-positive Armadillo-Tcf fusion protein was inhibited by XGrg-4 and enhanced by XGrg-5. These data indicate that expression of Tcf target genes is regulated by a balance between Armadillo and Groucho.