Stimulation of DNA synthesis in rat A10 vascular smooth muscle cells by threonine-59 insulin-like growth factor I.

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Abstract
The clonal smooth muscle cell line A10, derived from fetal rat aorta, binds 125I-insulin-like growth factor I at a Type 1 insulin-like growth factor receptor. Threonine-59 insulin-like growth factor I, multiplication stimulating activity, and insulin inhibit the binding with IC50 = 10 nM, 84 nM, and 500 nM, respectively. Insulin in high concentrations (greater than 5 microM) completely inhibits 125I-insulin-like growth factor I binding to A10 cells. Threonine-59 insulin-like growth factor I and insulin stimulate [3H]thymidine incorporation into DNA in A10 cells that had been growth arrested by incubation in serum-free media (DMEM/0.1% BSA) for 24-36 hours. The stimulation produced by the peptides is 50-60% of the stimulation produced by 10% fetal calf serum. Low levels of serum (0.1 and 0.5%) also stimulate DNA synthesis, and the effects of Threonine-59 insulin-like growth factor I and low serum are additive. The ED50 for the effects of Threonine-59 insulin-like growth factor I, multiplication stimulating activity, and insulin are 6.8 +/- 0.3 nM, 36 +/- 2.5 nM, and 360 +/- 242 nM, respectively. Incubation of A10 cells for 24 hours with Threonine-59 insulin-like growth factor I or serum increases the protein content per culture dish by 85 +/- 21 and 183 +/- 26%, respectively (mean +/- SEM). Thus, both protein levels and DNA synthesis are increased by incubation with peptides. However, Threonine-59 insulin-like growth factor I does not increase the number of cells in serum starved cultures, although 10% fetal calf serum does.(ABSTRACT TRUNCATED AT 250 WORDS)