Received for publication January 28, 2005.
Revised March 25, 2005.
Accepted for publication March 25, 2005.

Protein Kinase C Regulates TNF-Induced Stannin Gene Expression

Abstract

Stannin (Snn) is a highly conserved vertebrate protein that has been closely linked to trimethyltin (TMT) toxicity. We have previously demonstrated that Snn is required for TMT-induced cell death. Others have shown that TMT exposure results in TNF production, and that TNF treatment induces Snn gene expression in human umbilical vein endothelial cells (HUVECs). In this study, we investigated a signaling mechanism by which Snn gene expression is regulated by TMT, and demonstrate that TNF stimulates Snn gene expression in a protein kinase C-dependent manner in HUVECs in response to TMT exposure. Supporting this, we show that TMT-induced toxicity is significantly blocked by pretreatment with an anti-TNF antibody in HUVECs. Using a quantitative real- time polymerase chain reaction assay, we also show that the level of Snn gene expression is significantly increased in HUVECs in response to either TMT or TNF treatment. This TNF-induced Snn gene expression is blocked when HUVECs were pretreated with bisindolylmaleimide I, an inhibitor of protein kinase C (PKC). In contrast, when HUVECs were treated with phorbol 12-myristate, 13-acetate, a PKC activator, we observed a significant increase in Snn gene expression. Using isotype-specific siRNA against PKC, we further show that knockdown of PKC, but not PKC- or - significantly blocked TNF- induced Snn gene expression. Together, these results indicate that TNF-induced, PKC- dependent Snn expression may be a critical factor in TMT- induced cytotoxicity.

Key words: PKC, Selective toxicity, Stannin, TNF, Trimethyltin, organotin