['Hepatitis B virus (HBV) is a small DNA virus that requires cellular transcription factors for the expression of its genes. To understand the molecular mechanisms that regulate HBV gene expression, we conducted a yeast one-hybrid screen to identify novel cellular transcription factors that may control HBV gene expression. Here, we demonstrate that Krüppel-like factor 15 (KLF15), a liver-enriched transcription factor, can robustly activate HBV surface and core promoters. Mutations in the putative KLF15 binding site in the HBV core promoter abolished the ability of KLF15 to activate the core promoter in luciferase assays. Furthermore, the overexpression of KLF15 stimulated the expression of HBV surface antigen (HBsAg) and the core protein and enhanced viral replication. Conversely, small interfering RNA knockdown of the endogenous KLF15 in Huh7 cells resulted in a reduction in HBV surface- and core-promoter activities. In electrophoretic mobility shift and chromatin immunoprecipitation assays, KLF15 binds to DNA probes derived from the core promoter and the surface promoter. Introduction of an expression vector for KLF15 short hairpin RNA, together with the HBV genome into the mouse liver using hydrodynamic injection, resulted in a significant reduction in viral gene expression and DNA replication. Additionally, mutations in the KLF15 response element in the HBV core promoter significantly reduced viral DNA levels in the mouse serum.'] Does krüppel-like factor 15 activate hepatitis B virus gene expression and replication?