Selenium inhibition of survivin expression by preventing Sp1 binding to its promoter

Survivin, an antiapoptotic protein highly expressed in cancer, regulates multiple cellular network associated with cancer cell viability and drug resistance. Inhibition of survivin expression has been pursued as a valid cancer therapeutic target. In this study, we showed that selenium, an effective chemopreventive agent for many types of cancers, down-regulated survivin expression. Selenium inhibited survivin expression in both mRNA and protein levels in a dose- and time-dependent manner. Using a series of survivin promoter-luciferase constructs, a 37-bp DNA element in the survivin core promoter region that mediates the ability of selenium to inhibit survivin transcription was identified. Gel mobility shift assays and chromatin immunoprecipitation analyses revealed that selenium prevents the binding of Sp1 or Sp1-like proteins to the 37-bp cis-acting DNA element in the survivin promoter. Furthermore, inhibition of survivin expression by small interfering RNA enhanced selenium's inhibitory effects on cell growth, whereas overexpression of survivin in LNCaP human prostate cancer cells desensitized cancer cells to selenium effect, suggesting that the expression of survivin plays an important role in determining the response of cancer cells to selenium. Taken together, these results suggest that selenium down-regulated survivin expression by preventing the binding of Sp1 or Sp1-like proteins to the promoter of survivin, which contributes at least in part to the inhibitory effect of selenium on survivin gene transcription. In addition, down-regulation of survivin expression may account for one of the molecular mechanisms of the anticancer effects of selenium.