The oncogenic
beta-catenin/
T-cell factor (TCF) signal is a common trigger inducing expressions of various
cancer-related genes and is activated in various types of human
malignancy. The aim of this study was to create an effective
double-stranded DNA decoy that would interfere with endogenous TCF hyperactivity in
tumor cells. We first established the TCF-activated model using nontumor human embryonic kidney 293 (HEK293) cells by introducing a
beta-catenin cDNA. Based on a consensus TCF-binding sequence in the
cyclin D1 and c-myc promoters, several double-stranded
oligodeoxynucleotides were designed and tested for their ability to inhibit TCF activity in the HEK293 model. Among them, the 18-mer
oligodeoxynucleotide stably formed
double-stranded DNA and efficiently inhibited TCF activity.
FITC-labeled
oligodeoxynucleotide was efficiently incorporated into the nucleus at 6 hours and remained within cells for up to 72 to 96 hours. When compared with scrambled
oligodeoxynucleotide, we found that the 18-mer TCF decoy significantly inhibited TCF activity and promoter activities of the downstream target genes, such as
cyclin D1, c-myc, and
matrix metalloproteinase 7 in HCT116
colon cancer cells. Reverse transcription-PCR assays indicated that
mRNA expression of these genes decreased with treatment of the TCF decoy. Proliferation assay showed that the TCF decoy significantly inhibited growth of HCT116
tumor cells, but not of nontumor HEK293 cells. Our data provide evidence that the TCF decoy reduced both TCF activity and transcriptional activation of downstream target genes. Thus, this TCF decoy is potentially an efficient and nontoxic molecular targeting
therapy for controlling malignant properties of
cancer cells.