Regulation of vascular smooth muscle cell insulin-like growth factor I receptors by phosphorothioate oligonucleotides. Effects on cell growth and evidence that sense targeting at the ATG site increases receptor expression.

We have recently shown that insulin-like growth factor I (IGF I) is a mediator of angiotensin II-induced mitogenesis in vascular smooth muscle cells (Delafontaine, P., and Lou H. (1993) J. Biol. Chem. 268, 16866-16870). To study the role of the IGF I receptor in vascular smooth muscle cell growth, phosphorothioate oligonucleotides were used to modulate IGF I receptors. An antisense oligonucleotide targeting the ATG site inhibited basal and serum-induced DNA synthesis in vascular smooth muscle cells. Mismatch oligonucleotide had no effect, while surprisingly sense oligonucleotide increased IGF I receptor number and basal and serum-induced DNA synthesis. A 51% reduction in IGF I receptor number following exposure to 5 microM antisense oligonucleotide markedly inhibited angiotensin II-induced mitogenesis. A 70% increase in IGF I receptor number following exposure to 5 microM sense oligonucleotide resulted in a 4-fold increase in basal [3H]thymidine incorporation, and angiotensin II (1-1000 nM) had no additive stimulatory effect. An antisense oligonucleotide targeting a sequence starting at +109 base pairs (relative to ATG) also reduced IGF I receptor number, however, the corresponding sense oligonucleotide was without effect. These findings demonstrate that alterations in vascular smooth muscle cell IGF I receptor density play a critical role in the proliferative response of vascular smooth muscle cells to serum and to angiotensin II. In addition, the surprising observation that an ATG-directed sense oligonucleotide up-regulates IGF I receptors identifies a novel effect of oligonucleotides on gene expression.