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The Alzheimers disease was first described in 1906 and was identified as an "unusual disease of the cerebral cortex", which caused memory loss, disorientation, hallucinations.The most important hallmark in Alzheimers disease study was the establishment of amyloid hypothesis (Amyloid β).The Aβ aggregates on the CNS to form the senile plaque which disrupts the brain cells, clogs the points of cell-to-cell communications, and activates immune cells that trigger the inflammation and devour the disable cells and ultimately, kill cells.In our previous study, we demonstrated that Pur α protein can down-regulate the amyloid precursor protein (APP) gene expression.In order to better understand the mechanism, we checked the effects of Egr-1 on the transcriptional regulation of APP promoter.The experimental results demonstrated that Egr-1 was a positive regulator for APP promoter.Our data of luciferase assay showed that when Egr-1 binding sites were deleted, its function to up-regulate the APP promoter activity disappeared.The Purα also can suppress the function of Egr-1.Using the Purα-/-cells for transactivation test, the function of suppression was removed.The further data of gel shift, ChIPs assay as well as western blotting suggested that Purα suppress both the endogenous expression and the exogenous Egr-1 expression.The ChIPs assay and gel shift also showed that the Egr-1 and Purα can competitively bind to the same site in APP promoter.The immunohistological results also indicated the colocalization of these two proteins.From the above, we believe that there might be a displacement mechanism of Purα for Egr-1 in the transcriptional regulation and the interplay between Purα and Egr-1 can control APP expression.