title: Noxa mediates hepatic stellate cell apoptosis by proteasome inhibition.
abstract: OBJECTIVE
  Induction of hepatic stellate cell (HSC) apoptosis is a viable therapeutic strategy to reduce liver fibrogenesis. Although BH3-only proteins of the Bcl-2 family trigger pro-apoptotic pathways, the BH3-only proteins mediating HSC apoptosis have not been well defined. Our aim, using proteasome inhibition as a model to induce HSC apoptosis, was to examine the BH3-only proteins contributing to cell death of this key liver cell subtype.
  
  
  METHODS
  Apoptosis was induced by treating LX-2 cells, an immortalized human hepatic stellate cell line, and primary rat stellate cells with the proteasome inhibitor MG-132.
  
  
  RESULTS
  Treatment with proteasome inhibitors increased expression of Noxa both at the mRNA (16-fold) and protein (22-fold) levels indicating that both transcriptional and post-translational mechanisms contributed to the increase in cellular Noxa levels. Knockdown of Noxa by siRNA significantly attenuated cell death, mechanistically implicating Noxa as a key apoptotic mediator of proteasome inhibitor-induced cell death. Given the pivotal role for the anti-apoptotic Bcl-2 protein A1 in activated HSC survival, we determined if Noxa bound to this survival protein. Noxa was shown to physically bind the anti-apoptotic Bcl-2 protein A1 by co-immunoprecipitation.
  
  
  CONCLUSIONS
  Noxa contributes to proteasome inhibitor-induced apoptosis of stellate cells likely by binding A1. Strategies to therapeutically increase Noxa expression may be useful for inducing HSC apoptosis.
authors.affiliation: Divisions of Gastroenterology and Hepatology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA.
authors.forename: Ivette M
authors.initials: IM
authors.lastname: Sosa Seda
authors.forename: Justin L
authors.initials: JL
authors.lastname: Mott
authors.forename: Yuko
authors.initials: Y
authors.lastname: Akazawa
authors.forename: Fernando J
authors.initials: FJ
authors.lastname: Barreyro
authors.forename: Steven F
authors.initials: SF
authors.lastname: Bronk
authors.forename: Scott H
authors.initials: SH
authors.lastname: Kaufmann
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Gores