Gc. Tu et al., INHIBITION OF GENE-EXPRESSION BY TRIPLE-HELIX FORMATION IN HEPATOMA-CELLS, The Journal of biological chemistry, 270(47), 1995, pp. 28402-28407
The aim of this study was to selectively inhibit human mitochondrial a
ldehyde dehydrogenase (ALDH(2)) gene expression by triple helix assemb
ly. Eight 21-mer oligodeoxyribonucleotides were designed to bind to tw
o purine-rich sequences in the 5'-flanking region of the human ALDH(2)
gene. Gel mobility shift assays showed that tripler formation is sequ
ence-specific for the target duplex and the third strand oligonucleoti
de, In the presence of Mg2+, but absence of K+, tripler-forming oligon
ucleotides bind to their target sites with apparent dissociation const
ants (K-d) in the 10(-7) to 10(-9) M range. Potassium cation virtually
suppressed the tripler formation of G-C-rich duplex DNA with natural
oligonucleotides, but did not prevent tripler formation with phosphoro
thioate-modified oligonucleotides. Phosphoro-thioate-modified oligonuc
leotides were delivered into human hepatoma Hep G2 cells by cationic l
iposomes. The reduction in ALDH(2) mRNA levels in the cells was determ
ined by the competitive reverse transcription-polymerase chain reactio
n. One of the phosphorothioate-modified oligonucleotides designed to f
orm an antiparallel tripler with a target in the 5'-flanking region of
human ALDH(2) gene (-105 to -125 from the translation initiation codo
n ATG) reduced by 80-90% the ALDH(2) mRNA levels without affecting alb
umin mRNA levels. Data suggest that triple-helix formation may provide
a means to selectively inhibit hepatic ALDH(2) gene expression for th
erapeutic use.