A STAT3-decoy oligonucleotide induces cell death in a human colorectal carcinoma cell line by blocking nuclear transfer of STAT3 and STAT3-bound NF-κB

INSERM, Unité 978, Bobigny, France.
BMC Cell Biology (Impact Factor: 2.34). 04/2011; 12(1):14. DOI: 10.1186/1471-2121-12-14
Source: PubMed


The transcription factor STAT3 (signal transducer and activator of transcription 3) is frequently activated in tumor cells. Activated STAT3 forms homodimers, or heterodimers with other TFs such as NF-κB, which becomes activated. Cytoplasmic STAT3 dimers are activated by tyrosine phosphorylation; they interact with importins via a nuclear localization signal (NLS) one of which is located within the DNA-binding domain formed by the dimer. In the nucleus, STAT3 regulates target gene expression by binding a consensus sequence within the promoter. STAT3-specific decoy oligonucleotides (STAT3-decoy ODN) that contain this consensus sequence inhibit the transcriptional activity of STAT3, leading to cell death; however, their mechanism of action is unclear.
The mechanism of action of a STAT3-decoy ODN was analyzed in the colon carcinoma cell line SW 480. These cells' dependence on activated STAT3 was verified by showing that cell death is induced by STAT3-specific siRNAs or Stattic. STAT3-decoy ODN was shown to bind activated STAT3 within the cytoplasm, and to prevent its translocation to the nucleus, as well as that of STAT3-associated NF-κB, but it did not prevent the nuclear transfer of STAT3 with mutations in its DNA-binding domain. The complex formed by STAT3 and the STAT3-decoy ODN did not associate with importin, while STAT3 alone was found to co-immunoprecipitate with importin. Leptomycin B and vanadate both trap STAT3 in the nucleus. They were found here to oppose the cytoplasmic trapping of STAT3 by the STAT3-decoy ODN. Control decoys consisting of either a mutated STAT3-decoy ODN or a NF-κB-specific decoy ODN had no effect on STAT3 nuclear translocation. Finally, blockage of STAT3 nuclear transfer correlated with the induction of SW 480 cell death.
The inhibition of STAT3 by a STAT3-decoy ODN, leading to cell death, involves the entrapment of activated STAT3 dimers in the cytoplasm. A mechanism is suggested whereby this entrapment is due to STAT3-decoy ODN's inhibition of active STAT3/importin interaction. These observations point to the high potential of STAT3-decoy ODN as a reagent and to STAT3 nucleo-cytoplasmic shuttling in tumor cells as a potential target for effective anti-cancer compounds.

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    • "Our approach is based on the rationale that the introduction in the cells of short DNA fragments harboring the binding site of a transcription factor should compete with the binding of the transcription factor to its natural target in the promoter, with the effect of inhibiting transcription. When a decoy strategy was applied against NF-kB and STAT3, the oligonucleotides strongly inhibited the binding of NF-kB or STAT3 to the corresponding cis-elements (28–31). "
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    • "As previously shown [22,23], the consensus-carrying hpdODN A can efficiently induce the death of cells of the SW480 line (Figure 4A and 4B); but it also inhibits STAT1, thus blocking the STAT1-dependent IFNγ-induced mortality of these cells (Figure 4A, B and 4C) as previously shown [22,23]. hpdODN B was designed by replacing three base pairs in hpdODN A. T replaced dC in position 1003, dC replaced dG in 1011, and dG replaced dC in position 1017 (Figure 3). "
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