Partial purification and characterization of putative paracrine/autocrine bovine mammary epithelium growth factors

Abstract

Bovine prepartum milk-like secretion (BPMS) was found to be a rich source of mitogenic activity in an in vitro culture of bovine mammary epithelial cells, grown embedded in collagen and in mouse mammary gland-derived cell lines MME-CI and MME-L7. Partial purification of these mitogenic factors revealed that they are most likely novel heparin-binding growth factors (HBGFs) with molecular weights of 19 and 6 kDa. These factors exhibited strong synergism effect with insulin-like growth factor-I and basic fibroblast growth factor, some additive effect with epidermal growth factor but none with fetal calf serum. Mitogenic factors were also found in a conditioned medium obtained from primary cultures of bovine mammary epithelial cells. However, these factors did not bind to heparinagarose columns. Their partial purification by ion-exchange chromatography and gel-filtration revealed that these factors were small proteins of 6 kDa or less. While the origin of these BPMS-derived growth factors is not certain, the conditioned medium-derived activity is of paracrine or autocrine origin.