| Summary: | 碩士 === 高雄醫學大學 === 生物化學研究所碩士班 === 95 === Glycogen synthase kinase 3β(GSK3β) is an essential protein kinase that regulates numerous functions within the cell. It is regulated by both phosphorylation and protein–protein interactions. Emerging evidence has shown that GSK3β plays a pivotal role in regulating the specification of axons and dendrites. The outgrowth of neurites from a neuronal cell and the differentiation into an axon and several dendrites depends on microtubule associated proteins such as tau protein. Tau is one of the critically important substrates of GSK3β. Phosphorylation of tau by GSK3β, decreases the ability of tau to bind and stabilize microtubules. In our previous study, we found a novel GSK3β interaction protein (GSKIP) that is homologous with the GSK3β interaction domain of Axin and is able to negatively regulate GSK3β. To examine the involvements of GSKIP in neuronal differentiation, a human neuroblastoma SH-SY5Y cell line that treatment with retinoic acid (RA) differentiates to neuron-like cells was used in this study. Using an indirect immuofluorescence assay, we found that transient expression of GSKIP in SH-SY5Y cell inhibited neurites outgrowth, which was the similar result as in the presence of a direct inhibitor of GSK3β (lithium or SB415286), suggesting that GSKIP maybe involved in neuronal differentiation via negatively regulating GSK3β. Moreover, we demonstrated that GSKIP could inhibit the site-specific phosphorylation of tau by GSK3β, but it has no effects on specific site that phosphorylated by CDK5. Furthermore, GSKIP could increase the amount of β-catenin and cyclin D1, and it also raised the proliferation rate of overexpressing GSKIP cells by MTT assay. Altogether, these data provide the first evidence and strongly indicate that overexpression of GSKIP is able to inhibit neurites outgrowth in differentiated SH-SY5Y cell via negatively affecting the phosphorylation of tau by GSK3β and promote cell proliferation.
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