| Summary: | 碩士 === 慈濟大學 === 神經科學研究所 === 95 === Serum- and glucocorticoid-inducible kinase (SGK), a Ser/Thr protein kinase, has been shown to play an important role in spatial memory formation in rats. The differentiation factor retinoic acid (RA) has also been found to participate in hippocampal long-term potentiation (LTP) and water maze learning through its binding to retinoic acid receptor alpha (RARα). RARα then binds to the retinoic acid response element (RARE) of specific genes, such as laminin B1, and regulates their gene expression. We have found that the transcriptional level of laminin B1 in hippocampal CA1 area was reduced in rats under spatial training. In the present study, we examined whether SGK would regulate laminin B1 gene expression through phosphorylation of RARα. Results from luciferase reporter activity have revealed that transfection of sgkWT decreased laminin B1 promoter activity. The luciferase reporter assay also showed that transfection of sgkWT diminished the reporter activity of RARE on laminin B1 promoter in PC12 cells. Results from in vitro kinase assay revealed that SGK phosphorylated RARα directly at Ser93 and Ser93 phosphorylation was required for RARα-mediated gene expression. However, transfection of sgkWT and its active forms with RAR mutants, including Ser93A, Ser154A and Ser366A, did not reverse the inhibitory effect of sgk on either endogenous laminin B1 promoter activity or laminin B1-RARE promoter in luciferase reporter assay. These results suggested that the residues of RARα studied above are not involved in laminin B1 regulation by SGK, indicating that there might be other residues of RARα participating in this mechanism. However, mutation on the laminin B1-RARE promoter did not reverse the inhibitory effect of SGK on laminin B1. Taken together, these results indicated that RARα is not involved in SGK regulation of laminin B1 expression.
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