The role of helioxanthin in inhibiting human hepatitis B viral replication and gene expression by interfering with the host transcriptional machinery of viral promoters.

A non-nucleosidic compound, Helioxanthin (HE-145), was found to suppress HBV gene expression and replication in HCC cells. To understand the molecular mode of action of HE-145 on HBV gene expression, the effects of HE-145 on four viral promoter activities using luciferase as a reporter were examined. It was found that HE-145 selectively suppresses surface antigen promoter II (SPII) and core promoter (CP) but has no effect on surface antigen promoter I (SPI) or promoter for X gene (Xp). The suppressive effects of HE-145 on either SPII or CP activity is liver-specific, since no suppressive activity of HE-145 was observed when CP or SPII promoter activity was assayed in non-liver cells such as HeLa or 293T. To examine the mode of action of HE-145, EMSA analysis revealed that HE-145 decreased the DNA-binding activity of nuclear extract of HepA2 cells to specific cis element of HBV promoter for core antigen, including peroxisome proliferator-activated receptors (PPARs), PPARs binding site (PPRE), alpha-fetoprotein transcription factor (FTF), and Sp1. Ectopic expression of PPAR gamma or HNF4 alpha partially reversed the HE-145-mediated suppression of HBV RNA. Therefore, HE-145 may represent a novel class of anti-HBV agents which selectively modulate transcriptional machinery of human liver cells to suppress HBV gene expression and replication.