Upregulation of the NADPH oxidase NOX4 by TGF-beta in hepatocytes is required for its pro-apoptotic activity

J Hepatol. 2008 Dec;49(6):965-76. doi: 10.1016/j.jhep.2008.07.021. Epub 2008 Sep 19.

Abstract

Background/aims: The transforming growth factor-beta (TGF-beta) induces apoptosis in hepatocytes through an oxidative stress process. Here, we have analyzed the role of different NADPH oxidase isoforms in the intracellular signalling induced by TGF-beta in hepatocytes, to later explore whether this mechanism is altered in liver tumor cells.

Methods: Primary cultures of rat and human hepatocytes, HepG2 and Hep3B cells were used in in vitro studies to analyze the TGF-beta response.

Results: TGF-beta-induced apoptosis in rat hepatocytes does not require Rac-dependent NADPH oxidases. TGF-beta upregulates the Rac-independent Nox4, which correlates with its pro-apoptotic activity. Regulation of Nox4 occurs at the transcriptional level and is counteracted by intracellular survival signals. siRNA targeted knock-down of Nox4 attenuates NADPH oxidase activity, caspase activation and cell death in rat hepatocytes. NOX4 upregulation by TGF-beta is also observed in human hepatocytes, coincident with apoptosis. In human hepatocellular carcinoma (HCC) cell lines, NOX4 upregulation by TGF-beta is only observed in cells that are sensitive to its cytotoxic effect, such as Hep3B cells. siRNA targeted knock-down of NOX4 in these cells impairs TGF-beta-induced apoptosis.

Conclusions: Upregulation of NOX4 by TGF-beta is required for its pro-apoptotic activity in hepatocytes. Impairment of this TGF-beta-induced response might confer apoptosis resistance in HCC cells.

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Apoptosis / physiology*
  • Carcinoma, Hepatocellular / pathology*
  • Cell Line, Tumor
  • Fetus / cytology
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Neoplastic
  • Genes, Reporter
  • Hepatocytes / cytology
  • Hepatocytes / drug effects
  • Hepatocytes / enzymology*
  • Humans
  • Liver Neoplasms / pathology*
  • NADPH Oxidase 4
  • NADPH Oxidases / genetics*
  • NADPH Oxidases / metabolism
  • RNA, Small Interfering
  • Rats
  • Rats, Wistar
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Transcription, Genetic / drug effects
  • Transcription, Genetic / physiology
  • Transforming Growth Factor beta / pharmacology*
  • Up-Regulation / drug effects
  • Up-Regulation / physiology

Substances

  • RNA, Small Interfering
  • Transforming Growth Factor beta
  • NADPH Oxidase 4
  • NADPH Oxidases
  • NOX4 protein, human
  • Nox4 protein, rat