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Objective: To investigate the role of Sp1 as transcription factor required for transactivation of LRP16 gene by estrogen. Methods: Specific antibodies of Erα and Sp1 were used to precipitate the target DNA/protein complexes of MCF-7 cells at different time points after estrogen treatment (Chromatin immunoprecipitation assay), the promoter region of LRP16 gene was amplified by semi-nested polymerase chain reaction (snPCR). Small interfering RNA (siRNA) against Sp1 was transiently cotransfected with LRP16-Luc (containing the region from -213bp to -126bp of LRP16 gene promoter) in MCF-7 cells. The luciferase activities were measured by dual-luciferase assay. Results: The results of chromatin immunoprecipitation assay showed that Sp1 protein directly bound to the -213bp to -126bp region of LRP16 gene, and Erα could enhance the affinity of Sp1 to DNA. Sp1-siRNA specifically decreased the transactivation of LRP16-Luc by 17β-estradiol to 70-80%. Conclusion: The estrogen-induced transactivation of the human LRP16 gene was mediated by Sp1 protein. Moreover, the interactions of ER(/Sp1 functional complex with LRP16 promoter DNA were required for enhanced LRP16 gene transactivation.