title: The proteasome is a molecular target of environmental toxic organotins.
abstract: BACKGROUND
  Because of the vital importance of the proteasome pathway, chemicals affecting proteasome activity could disrupt essential cellular processes. Although the toxicity of organotins to both invertebrates and vertebrates is well known, the essential cellular target of organotins has not been well identified. We hypothesize that the proteasome is a molecular target of environmental toxic organotins.
  
  
  OBJECTIVE
  Our goal was to test the above hypothesis by investigating whether organotins could inhibit the activity of purified and cellular proteasomes and, if so, the involved molecular mechanisms and downstream events.
  
  
  RESULTS
  We found that some toxic organotins [e.g., triphenyltin (TPT)] can potently and preferentially inhibit the chymotrypsin-like activity of purified 20S proteasomes and human breast cancer cellular 26S proteasomes. Direct binding of tin atoms to cellular proteasomes is responsible for the observed irreversible inhibition. Inhibition of cellular proteasomes by TPT in several human cell lines results in the accumulation of ubiquitinated proteins and natural proteasome target proteins, accompanied by induction of cell death.
  
  
  CONCLUSIONS
  The proteasome is one of the molecular targets of environmental toxic organotins in human cells, and proteasome inhibition by organotins contributes to their cellular toxicity.
authors.affiliation: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, People's Republic of China.
authors.forename: Guoqing
authors.initials: G
authors.lastname: Shi
authors.forename: Di
authors.initials: D
authors.lastname: Chen
authors.forename: Guangshu
authors.initials: G
authors.lastname: Zhai
authors.forename: Marina S
authors.initials: MS
authors.lastname: Chen
authors.forename: Qiuzhi Cindy
authors.initials: QC
authors.lastname: Cui
authors.forename: Qunfang
authors.initials: Q
authors.lastname: Zhou
authors.forename: Bin
authors.initials: B
authors.lastname: He
authors.forename: Q Ping
authors.initials: QP
authors.lastname: Dou
authors.forename: Guibin
authors.initials: G
authors.lastname: Jiang