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

OBJECTIVE: 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. STUDY DESIGN: 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. RESULTS: Binding studies with I-125-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 I-125-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 [H-3]thymidine into deoxyribonucleic acid of the cells. Insulin stimulated cell growth of all the cell lines. CONCLUSIONS: The results of this study indicate the potential role of hyperinsulinemia in the growth and development of endometrial cancer.