Selective inhibition of A-Raf and C-Raf mRNA expression by antisense oligodeoxynucleotides in rat vascular smooth muscle cells: role of A-Raf and C-Raf in serum-induced proliferation.

Raf kinases, cytoplasmic serine/threonine protein kinases, have been proposed as important participants in mitogen-induced signal transduction. However, the precise role that Raf kinase isozymes play in cellular responses such as proliferation has not been resolved. The present study investigates the ability of antisense phosphorothioate oligodeoxynucleotides (ODNs), targeted against rat C-Raf and A-Raf kinases, to reduce gene expression and proliferation of cultured rat A10 smooth muscle cells (SMCs). Exposure of A10 cells to ISIS 11061, an active C-Raf antisense ODN, resulted in a potent, dose-dependent inhibition (IC50 = 55 nM) of C-Raf mRNA and protein expression. This inhibition was completely dependent on ODN sequence because the incorporation of increasing numbers of mismatches (up to six) into the sequence resulted in sequential loss of potency. Similarly, a dose-dependent reduction (IC50 = 125 nM) in A-Raf gene expression was observed after treatment of cells with the active A-Raf ODN, ISIS 9069, whereas two scrambled controls were without effect. These results demonstrate that ISIS 11061 and ISIS 9069 reduced gene expression in a sequence-specific and isozyme-specific manner. Moreover, administration of ISIS 11061 and ISIS 9069 to rat SMCs resulted in a significant and potent diminution of serum-induced proliferation with corresponding IC50 values of 216 and 273 nM, respectively. Taken together, these results indicate that A-Raf and C-Raf kinases play an important role in regulating vascular SMC proliferation and that antisense-mediated inhibition of Raf kinase activity may serve as a therapeutic modality in the treatment of vascular proliferative disorders.