Molecular mechanism of upregulation of survivin transcription by the AT-rich DNA-binding ligand, Hoechst33342: evidence for survivin involvement in drug resistance

We have previously shown that hedamycin, a GC-rich DNA-binding antitumor agent, downregulates survivin transcription (Wu et al. (2005) Molecular mechanism of inhibition of survivin transcription by the GC-rich sequence selective DNA-binding antitumor agent, hedamycin: evidence of survivin downregulation associated with drug sensitivity. J. Biol. Chem., 280, 9745-9751). Here, we report that treatment of cancer cells with Hoechst33342, an AT-rich DNA-binding ligand, upregulated survivin protein, mRNA and promoter activity. Functional analysis of survivin promoter-luciferase constructs followed by in vivo footprinting experiments identified a 28-bp AT-rich DNA element (-908 to -881, designated as H369W) that mediates a major effect of Hoechst33342 on the upregulation of survivin promoter activity. Electrophoresis mobility shift assay (EMSA) experiments showed that Hoechst33342 binds to H369W and abrogates H369W-protein interactions. Intriguingly, there is a highly conserved DNA-binding motif for growth factor independence 1 (Gfi-1), a transcriptional repressor protein, in the H369W DNA element. Accordingly, EMSA experiments demonstrated that either the cold canonical Gfi-1-binding DNA oligonucleotide or the cold H369W specifically competes with H369W-protein complexes. Consistently, anti-Gfi-1 antibody is able to supershift the H369W-protein complex on the EMSA gel. Lastly, our data reveal that upregulation of survivin by Hoechst33342 is involved in cancer drug resistance. We propose that hindrance of H369W-Gfi-1 interactions in the survivin promoter, initiated by Hoechst33342, contributes to upregulation of survivin transcription, and as a consequence, hampers Hoechst33342's cytotoxicity.