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


CONCLUSIONS
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.
Miller
Stanley D W
SD
Respiratory Research Division, Department of Medicine, Royal College of Surgeons in Ireland, Education and Research Centre, Beaumont Hospital, Dublin, Ireland.
Greene
Catherine M
CM
McLean
Caitriona
C
Lawless
Matthew W
MW
Taggart
Clifford C
CC
O'Neill
Shane J
SJ
McElvaney
Noel G
NG
D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D053471:Caspases, Initiator / Q000502:physiology; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D013655:Taurochenodeoxycholic Acid / Q000494:pharmacology*; D000515:alpha 1-Antitrypsin / Q000502:physiology*; D051025:bcl-Associated Death Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism
D053148:Caspase 3; D053471:Caspases, Initiator; D045304:Cytochromes c; D019869:Phosphatidylinositol 3-Kinases; D013655:Taurochenodeoxycholic Acid; D000515:alpha 1-Antitrypsin; D051025:bcl-Associated Death Protein; C494819:BAD protein, human; C031655:ursodoxicoltaurine; C093516:CASP4 protein, human