Résumé
A major question in cancer research is: why do cancer cells continuously proliferate and invade adjacent tissue. Breast cancer cells are particularly suitable for studying this question since when they are differentiated, they contain estrogen receptors, and estrogen, specifically, triggers their growth. One approach to understanding the estrogen-induced growth stimulation in this model is to identify the estrogen-induced factors involved in the control of cell proliferation [1–6]. Here, we illustrate this approach in a study of growth regulation of MCF7 cells by estrogen, in which we found a secreted 52K protein with mitogenic activity. It was identified as a protease that is also possibly involved in the process of tumor cell metastasis.