of insulin-like growth factor type I receptor by a triple-helix strategy
inhibits IGF-I transcription and tumorigenic potential of rat C6 glioblastoma
Rininsland F, Johnson TR, Chernicky CL, Schulze E, Burfeind P, Ilan J
Department of Pathology, Case Western Reserve University,
Cleveland, OH 44106, USA
Homopurine (AG) and homopyrimidine (CT) oligodeoxyribonucleotides predicted to
form triple-helical (triplex) structures have been shown to specifically
suppress gene expression when supplied to cultured cells.
Here we present evidence that homopurine RNA (effector) sequences designed to
form a triplex with a homopurine. homopyrimidine sequence 3' to the termination
codon of the insulin-like growth factor type I receptor (IGF-IR) structural gene
can efficiently suppress IGF-IR gene transcription.
Transfection vectors were constructed to drive transcription of either AG or CT
variant triplex-forming strands.
To increase the probability of obtaining stable transfectants with adequate
expression of effector sequences, these were designed to be transcribed together
with cDNA sequences conferring neomycin resistance as a fusion transcript.
Rat C6 glioblastoma cells transfected with the AG variant showed dramatic
reduction of IGF-IR transcripts compared with untransfected cells.
The AG transfectants also exhibited marked down-regulation of the IGF-I, and an
enhanced accumulation of serine protease inhibitor nexin-I mRNA.
Similar changes in gene expression were observed following transfection of C6
cells with constructs transcribing antisense RNA to IGF-IR transcripts, but were
not observed in C6 cells transfected with either the CT triplex variant or with
vector lacking triplex-forming sequences.
Moreover, C6 cells transfected with AG triplex variant displayed a dramatic
inhibition of tumor growth when injected into nude mice.
The results suggest that a triple-helix strategy can be used to inhibit
transcription elongation of the IGF-IR gene, and emphasize the efficacy of
triplex-mediated gene inhibition in an animal model.
PMID: 9159164 [PubMed - indexed for MEDLINE]