Mitogenic activity and plasminogen activator in harvest fluid concentrates from mammary cells in culture

Harvest fluid concentrates (HFC's) from three human mammary tumor cell lines (T47D), HSO578T, and MDA-MB-157), one nontumorigenic human mammary cell line (HBL-100), and one mouse mammary tumor cell line (MCG-T14) stimulated thymidine incorporation in confluent quiescent BALB/c 3T3 cells in a dose-dependent manner. HFC's from all of the cell lines also exhibited plasminogen activator activity. Levels of mitogenic activity and plasminogen activator in the HFC preparations were not correlated with cell growth potential or with the amount of protein which was recovered in the HFC's. High levels of mitogenic activity and plasminogen activator in the HFC's from HBL-100 cells suggested that the production of these biological activities is not a unique feature of tumorigenic mammary cells. The HFC's from three human cell lines (T47D), HS0578T, MDA-MB-157) exhibited high levels of mitogenic activity but low levels of plasminogen activator. This suggested that plasminogen activator is not the source of the mitogenic activity in the HFC's from these cells. The HFC's from a human mammary carcinoma line, BT-20, contained very low levels of mitogenic activity and plasminogen activator. In addition, BT-20 HFC's inhibited the mitogenic activity of fetal bovine serum in a dose-dependent manner. It is proposed that BT-20 cells are the source of a macromolecular inhibitor of serum mitogens.