Ribavirin-induced intracellular GTP depletion activates transcription elongation in coagulation factor VII gene expression

Biochem J. 2013 Jan 1;449(1):231-9. doi: 10.1042/BJ20121286.

Abstract

Coagulation FVII (Factor VII) is a vitamin K-dependent glycoprotein synthesized in hepatocytes. It was reported previously that FVII gene (F7) expression was up-regulated by ribavirin treatment in hepatitis C virus-infected haemophilia patients; however, its precise mechanism is still unknown. In the present study, we investigated the molecular mechanism of ribavirin-induced up-regulation of F7 expression in HepG2 (human hepatoma cell line). We found that intracellular GTP depletion by ribavirin as well as other IMPDH (inosine-5'-monophosphate dehydrogenase) inhibitors, such as mycophenolic acid and 6-mercaptopurine, up-regulated F7 expression. FVII mRNA transcription was mainly enhanced by accelerated transcription elongation, which was mediated by the P-TEFb (positive-transcription elongation factor b) complex, rather than by promoter activation. Ribavirin unregulated ELL (eleven-nineteen lysine-rich leukaemia) 3 mRNA expression before F7 up-regulation. We observed that ribavirin enhanced ELL3 recruitment to F7, whereas knockdown of ELL3 diminished ribavirin-induced FVII mRNA up-regulation. Ribavirin also enhanced recruitment of CDK9 (cyclin-dependent kinase 9) and AFF4 to F7. These data suggest that ribavirin-induced intracellular GTP depletion recruits a super elongation complex containing P-TEFb, AFF4 and ELL3, to F7, and modulates FVII mRNA transcription elongation. Collectively, we have elucidated a basal mechanism for ribavirin-induced FVII mRNA up-regulation by acceleration of transcription elongation, which may be crucial in understanding its pleiotropic functions in vivo.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antimetabolites / pharmacology*
  • Factor VII / biosynthesis
  • Factor VII / genetics*
  • Gene Expression Regulation* / drug effects
  • Guanosine Triphosphate / antagonists & inhibitors
  • Guanosine Triphosphate / deficiency*
  • Hep G2 Cells
  • Humans
  • Intracellular Fluid / metabolism*
  • Ribavirin / pharmacology*
  • Transcription Elongation, Genetic / drug effects
  • Transcription Elongation, Genetic / physiology*

Substances

  • Antimetabolites
  • Ribavirin
  • Guanosine Triphosphate
  • Factor VII