| Summary: | 碩士 === 國立清華大學 === 分子與細胞生物研究所 === 101 === Based on the results of our study, sFRP proteins have an association with Wnt3a through cysteine-rich domain (CRD) which is located at the N terminus; while the C terminus [netrin-related (NTR) domain] associates with β-catenin. The result derived from Luciferase reporter assay proves that overexpression full-length sFRP1 can apparently inhibit the level of TopFlash reporter activities to be almost as low as the basal level. In addition, the deletion mutants, the N and C terminus of sFRP1, also inhibit activities of TopFlash reporter. In the sFRP3-overexpressed stable clone, the transcriptional activity of TCF/β-catenin is enhanced, whereas the deletion mutants, the N and C terminus of sFRP3, highly inhibit activities of TopFlash reporter. Furthermore, our data showed that sFRP1 and sFRP3 antagonize Wnt3a-elicited LRP6 co-receptor activation, which also leads to the fall in its phosphorylation level. Interestingly, we observed that the deletion mutants of sFRPs would modulate Wnt3a-elicited LRP6 co-receptor activation. The N terminus of sFRP3 inhibits the phosphorylation level of LRP6 co-receptor, whereas overexpression the C terminus of sFRP1 enhances the phosphorylation level of LRP6 co-receptor. The activity of glycogen synthase kinase-3β (GSK-3β) which is in the downstream of LRP6 is also modulated by sFRP proteins. Moreover, it showed that overexpression sFRP1 could inhibit GSK-3β phosphorylation, whereas overexpression sFRP3 enhances the phosphorylation level of GSK-3β. Also, we observed that the full length, N, and C terminus of sFRP1 and the full length and C terminus of sFRP3 would stabilize β-catenin, which contributes to β-catenin accumulation in the cytosol and further entering into the cell nucleus. As the result showed in the sphere-forming assay, full-length sFRP1 would inhibit the formation of sphere. On the contrary, full-length sFRP3 facilitates the capability of sphere-forming. From what has been mentioned above, we can come to the conclusion that sFRP proteins are capable of modulating the Wnt signaling pathway. They control the activity of Wnt signaling pathway through different mechanisms. In this study, we provide several brand-new approaches to survey the biological effects of sFRPs. Furthermore, these findings characterize the roles of sFRP1 and sFRP3 involved in regulating Wnt activities and provide a new perspective regarding their biological effects and mode of action, distinguished by capable of modulating stemness and tumor-initiating abilities.
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