Partial purification and characterization of mammary stimulating factor, a protein which promotes proliferation of mammary epithelium

Abstract

The partial purification and characterization of mammary stimulating factor (MSF), a mitogenic peptide isolated from serum which initiates growth in mouse mammary epithelium, are described. By using ion-exchange chromatography, gel filtration and isoelectric focusing, MSF was purified 250-fold from porcine serum. It is a heat-stable protein of MW 10,100-10,400 with an isoelectric point of 5.5-6.0. MSF initiates DNA synthesis in vitro in mammary epithelium to a greater extent than in mouse mammary tumor cells (CZF), 3T3 cells, or chick embryo cells. Comparison of the biological, physical, and immunological properties of MSF with other established growth-promoting peptides suggests that MSF is a unique serum factor.