Tauroursodeoxycholic acid inhibits apoptosis induced by Z alpha-1 antitrypsin via inhibition of Bad

Hepatology. 2007 Aug;46(2):496-503. doi: 10.1002/hep.21689.


Z alpha-1 antitrypsin (AAT) deficiency is a genetic disease associated with accumulation of misfolded AAT in the endoplasmic reticulum (ER) of hepatocytes. ZAAT-expressing cells display ER stress responses including nuclear factor kappaB activation and apoptosis. Using an in vitro model of ZAAT ER accumulation, we investigated the mechanism of ZAAT-mediated ER-induced apoptosis and evaluated methods to inhibit this process. Here we demonstrate that expression of ZAAT, but not normal MAAT, in HEK293 cells leads to cleavage and activation of caspase-4 and induces apoptosis that is characterized by activation of caspase-3 and caspase-7 and DNA fragmentation. Similar effects are also induced using the ER agonist thapsigargin. A caspase-4-specific short interfering RNA (siRNA) does not impair ZAAT-induced caspase-3/7 activation or cell death in these cells. However, inhibition studies performed using tauroursodeoxycholic acid (TUDCA) demonstrate its ability to inhibit caspase-4 and caspase-3/7 activation, mitochondrial cytochrome c release, and caspase-3 cleavage induced by ZAAT and to promote cell survival. The mechanism by which TUDCA (tauroursodeoxycholic acid) promotes cell survival in ZAAT-expressing cells involves phosphorylation and inactivation of the proapoptotic factor Bad. TUDCA is unable to rescue cells from apoptosis or phosphorylate Bad in the presence of LY294002, a selective P-I-3-kinase inhibitor.

Conclusion: These data show that caspase-4 is not essential for ZAAT-induced apoptosis in HEK293 cells and implicates P-I-3-kinase and Bad as potential therapeutic targets for the liver disease associated with ZAAT deficiency.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Caspase 3 / metabolism
  • Caspases, Initiator / physiology
  • Cells, Cultured
  • Cytochromes c / metabolism
  • Humans
  • Phosphatidylinositol 3-Kinases / physiology
  • Phosphorylation
  • Taurochenodeoxycholic Acid / pharmacology*
  • alpha 1-Antitrypsin / physiology*
  • bcl-Associated Death Protein / antagonists & inhibitors*
  • bcl-Associated Death Protein / metabolism


  • BAD protein, human
  • alpha 1-Antitrypsin
  • bcl-Associated Death Protein
  • Taurochenodeoxycholic Acid
  • ursodoxicoltaurine
  • Cytochromes c
  • CASP4 protein, human
  • Caspase 3
  • Caspases, Initiator