STIMULATION OF DNA-SYNTHESIS AND C-FOS EXPRESSION IN CORNEAL ENDOTHELIUM BY INSULIN OR INSULIN-LIKE GROWTH FACTOR-I

Purpose. To study the growth regulation of bovine corneal endothelium, the effects of insulin and insulin-like growth factor-I on the expression of the c-fos proto-oncogene as well as on DNA synthesis were analyzed. Bovine corneal endothelial cells were also analyzed for the presence of insulin and insulin-like growth factor-I receptors. Methods. Indirect immunofluorescence was used to assess the effect of stimulation by insulin and insulin-like growth factor-I on c-fos protein expression and DNA synthesis quiescent bovine corneal endothelium. Receptor number was determined by I-125-insulin or I-125-IGF-I binding studies. Results. Fetal bovine serum strongly stimulated c-fos protein expression and DNA synthesis. Insulin-like growth factor-I was less effective while insulin was effective only at high concentrations. Scatchard analysis of I-125-insulin-like growth factor-I and I-125-insulin binding to bovine corneal endothelium revealed 180,000 IGF-I receptors and 7,000 insulin receptors. Conclusions. The number of insulin-like growth factor-I receptors far exceeds the number of insulin receptors in bovine corneal endothelium, suggesting that the effects of insulin on c-fos gene expression and mitogenesis were likely to be mediated through the insulin-like growth factor-I receptor.