Hormone responsive human breast cancer in long-term tissue culture: effect of insulin.

Abstract

The mechanisms of steroid and peptide hormone action in human breast cancer are poorly understood. We have previously characterized a cell line of human breast cancer in long-term tissue culture that possesses various steroid hormone receptors and responses, providing a model for the study of steroid hormone action. The present studies describe a human breast cancer in vitro that responds to physiologic concentrations of insulin with an increased rate of macromolecular synthesis and growth. Thymidine and uridine incorporation in cells in serum-free medium are stimulated by 10-11 M insulin and are maximal with 10-8 M. Leucine incorporation is stimulated by 5 X 10-11 M insulin and is maximal with 10-9 M. Significant stimulation of uridine and leucine incorporation is evident by 3 hr and maximal by 10 hr. A 10-hr lag period exists for insulin stimulation of thymidine incorporation, which is maximal from 14 to 24 hr. The effect of 10-8 M insulin on macromolecular synthesis is accompanied by a 69% increase above controls in the number of cells after 24 hr. The effect on macromolecular synthesis is observed in glucose-free medium. Insulin's effect on protein synthesis is not blocked by inhibition of RNA synthesis with actinomycin D. Glucocorticoids partially inhibit the action of insulin in these cells. This system provides a model for studying insulin action, and suggests that some human breast cancer may show growth regulation by insulin. We have recently characterized a model system for the study of steroid hormone action using human breast cancer cells maintained in long-term tissue culture (1, 2). One cell line in particular, MCF-7, possesses specific high affinity receptors for estradiol, progesterone, androgens, and glucocorticoids (1-4). In addition, these cells respond to estrogen and androgen with an increased rate of DNA, RNA, and protein synthesis, while inhibition of macromolecular synthesis is observed with glucocorticoids and the antiestrogen, Tamoxifen (ICI 46474) (1-3).The effect of peptide hormones on these cells is unknown. However, insulin is known to influence mammary gland growth and development in human (5) and rodent glands in organ culture (6), and other studies suggest that insulin regulates proliferation of rat mammary carcinomata induced by the carcinogen dimethylbenz[a]anthracene (7,8).In the present study we demonstrate that the MCF-7 cell line is responsive to physiologic concentrations of insulin and propose that this cell line provides a provocative model for the study of insulin action and mechanisms of growth regulation in breast cancer. Cells and Tissue Culture Techniques. The MCF-7 cell line, a cloned breast cancer line derived from a malignant pleural effusion (9), was generously provided by Dr. Marvin Rich, Michigan Cancer Foundation. The human and mammary nature of this line has been substantiated by chromosomal analysis, morphological features, and a-lactalbumin synthesis (10). The cells (at approximately the 100th passage) were maintained in monolayer cultures in Impro...

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