Biochemistry
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Although prominent FRAT/GBP exhibits a limited degree of homology to Axin, the binding sites on GSK3 for FRAT/GBP and Axin may overlap to prevent the effect of FRAT/GBP in stabilizing beta-catenin in the Wnt pathway. Using a yeast two-hybrid screen, we identified a novel protein, GSK3beta interaction protein (GSKIP), which binds to GSK3beta. We have defined a 25-amino acid region in the C-terminus of GSKIP that is highly similar to the GSK3beta interaction domain (GID) of Axin. ⋯ Furthermore, our data indicate that overexpression of GSKIP induces beta-catenin accumulation in the cytoplasm and nucleus as visualized by immunofluorescence. A functional assay also demonstrates that GSKIP-transfected cells have a significant effect on the transactivity of Tcf-4. Collectively, we define GSKIP as a naturally occurring protein that is homologous with the GSK3beta interaction domain of Axin and is able to negatively regulate GSK3beta of the Wnt signaling pathway.
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In vivo bioluminescence imaging has become a cornerstone technology for preclinical molecular imaging. This imaging method is based on light-emitting enzymes, luciferases, which require specific substrates for light production. When linked to a specific biological process in an animal model of human biology or disease, the enzyme-substrate interactions become biological indicators that can be studied noninvasively in living animals. ⋯ The three substrates exhibited different kinetic properties and different intracellular accumulation profiles due to differences in their molecular structure, which in turn influenced their biodistribution in animals. Glycine-d-aminoluciferin had a longer in vivo circulation time than the other two substrates. The ability to assay luciferase in vitro and in vivo using these substrates, which exhibit different pharmacokinetic and pharmacodynamic properties, will provide flexibility and improve current imaging capabilities.