The core promoter dictates the expression of the HBV e antigen, core
protein, and DNA polymerase. The X promoter controls the transcription of the X RNA. After its synthesis, the core protein packages the core RNA, which is larger than the genome size and is also known as the pregenomic RNA (pgRNA), to form the core particle. The pgRNA then serves as the template to direct the synthesis of the partially double-stranded viral DNA genome, using the viral DNA polymerase that is also packaged. The core RNA plays a pivotal role in the HBV life cycle and its increased expression has been shown to enhance viral replication.3, 4 The identification of host factors that interact with the HBV DNA genome has made significant contributions to our understanding of mechanisms that regulate HBV gene
expression. Indeed, both liver-enriched and ubiquitous transcription factors, such as hepatocyte Tanespimycin ic50 nuclear factor 1 (HNF1), HNF3, HNF4, CCAAT enhancer-binding protein (C/EBP), chicken ovalbumin upstream promoter transcription factor (COUP-TF), nuclear transcription factor Y (NF-Y), and specificity protein 1 (Sp1), have been shown to regulate the expression NU7441 supplier of the S and C genes.5-13 The liver specificity of the preS1 promoter, the major surface promoter, and the core promoter is attributed to the need of liver-enriched transcription factors for their activities.10, 14-18 In this study, we used a yeast one-hybrid screen to identify additional transcription factors that could activate the major surface promoter. Using cDNA libraries prepared from the human hepatoma cell line, Huh7, and mouse liver, we identified several MCE members of the Krüppel-like factor (KLF) family as potential activators of the surface promoter (T. Tan and T.S.B. Yen, unpublished
data). KLF family members are characterized by their three carboxy-terminal C2H2 zinc fingers and share a high degree of homology with Sp1-like proteins. At least 21 Sp1/KLF proteins have been identified in the human genome. They have highly conserved DNA-binding domains, but show significant variations in the transactivation domain in their amino terminus.19, 20 Krüppel-like factor 15 (KLF15) has been shown to regulate the expression of a number of genes involved in many aspects of physiological homeostasis, including glucose uptake and adipogenesis.21-25 Moreover, KLF15 is highly expressed in the human liver.25 These observations led us to hypothesize that KLF15 might be a potential activator for HBV gene expression. Indeed, our results indicate that KLF15 can activate the expression of the HBV S and C genes both in vitro and in vivo. Our results thus uncovered previously unrecognized functions of KLF15 in HBV gene expression.