Specific binding and growth-promoting activity of insulin in endometrial cancer cells in culture.

Insulin is known to be mitogenic to a variety of cells in culture. The purpose of this study was to investigate the possible role of insulin in the growth and development of endometrial cancers. Specific binding and growth effects of insulin were studied in 5 different human endometrial cancer cell lines derived from cancers with different degrees of differentiation: HEC-1-A and HEC-1-B (from a moderately well-differentiated adenocarcinoma), RL95-2 (from a moderately well-differentiated adenosquamous carcinoma), KLE (from poorly differentiated carcinoma), and AN3 CA (from a metastatic undifferentiated endometrial carcinoma). The receptors were further characterized by competitive binding and chemical cross-linking studies. Binding studies with 125I-insulin revealed the presence of high-affinity binding sites for insulin on all the 5 cell lines. Binding of insulin was found to be highly specific. Competitive binding studies with 125I-insulin revealed that insulin was most effective in displacing the labeled hormone, whereas insulin-like growth factor-I and insulin-like growth factor-II competed for binding only at very high concentrations. Scatchard analysis of the binding data revealed that the association constant for the high-affinity binding sites ranged from 0.72 to 1.91 x 10(9) L/mol. Estrogen-receptor-negative cell lines HEC-1-A and HEC-1-B had the highest number of insulin receptors, whereas the estrogen-receptor-positive cell line RL95-2 had the least number of receptors. The effect of insulin on cell proliferation was studied by monitoring cell number and incorporating [3H]thymidine into deoxyribonucleic acid of the cells. Insulin stimulated cell growth of all the cell lines. The results of this study indicate the potential role of hyperinsulinemia in the growth and development of endometrial cancer.