Construction of a highly-active, liver-specific transcriptional regulatory element through combination of the albumin promoter and α-fetoprotein enhancer

In an attempt to construct a highly active, liver-specific transcriptional regulatory element, the mouse albumin promoter (ALBp) and α-fetoprotein enhancer (AFPe) were obtained. To verify its hepatic specificity and activity, the AFPe–ALBp-containing fragment was cloned into the plasmids, pVAX-S and pGL3-Luc with original promoter removed. Plasmid pVAX-AFPe-ALBp-S was then transfected into hepatic and non-hepatic cells in vitro, and delivered into mouse by intravenous injection and intramuscular injection, respectively. In addition, pGL3-AFPe-ALBp-Luc was transfected into hepatic and non-hepatic cell lines; pVAX1, pVAX1/S, and pGL3-ALBp-Luc were used as controls. The expression of hepatitis B surface antigen (HBsAg) was observed, and luciferase activity in cells was measured. For plasmid pVAX-AFPe-ALBp-S, the expression of HBsAg was observed in hepatic cell lines, but not in a non-hepatic cell line. Using pVAX-S, the expression of HBsAg was observed in both hepatic and non-hepatic cell lines. In cells expressing pGL3-AFPe-ALBp-Luc, the level of luciferase activity was significantly higher in hepatic cell lines, compared with the non-hepatic cell lines. In addition, the level of luciferase activity in cells expressing pGL3-AFPe-ALBp-Luc was significantly higher than that of pGL3-ALBp-Luc in hepatic cell lines, suggesting that AFPe could enhance target gene expression under the control of ALBp. The expression of HBsAg was detected in mouse liver, but not muscle when using pVAX-AFPe-ALBp-S. In contrast, the expression of HBsAg was detected in both mouse liver and muscle upon transfection with pVAX-S. In conclusion, the AFPe-ALBp element could be used as a tool to induce liver-specific expression of a target gene.