Target dependence of antisense oligodeoxynucleotide inhibition of c-Ha-ras p21 expression and focus formation in T24-transformed NIH3T3 cells.

The relationship of antisense oligodeoxynucleotide inhibition to the predicted secondary structure of human c-Ha-ras oncogene mRNA was examined. Three antisense pentadecade-oxynucleotides complementary to the 5' cap region, a predicted loop in the 5' untranslated region, and the initiation codon region of c-Ha-ras mRNA were synthesized. T24-transformed NIH3T3 cells were treated for 24 hr with each anti-ras oligomer or control sequence. The levels of c-Ha-ras p21 antigen were then analyzed by radioimmunoprecipitation. Inhibition of p21 expression was sequence-specific and dose-dependent. The efficacy of the cap sequence in reducing p21 expression was greater than that of the initiation codon target, which in turn was more effective than the target upstream of the initiation codon. Antisense inhibition of p21 expression correlated with inhibition of focus formation.