Growth inhibition of BALB/c 3T3 cells by a high-molecular-weight mucin-like glycoprotein of human milk fat globule membrane.

PAS-O is a high-molecular-weight mucin-like glycoprotein of the human milk fat globule membrane, and originates from the lactating mammary epithelial cell membrane. The cell proliferation rate of BALB/c 3T3 cells was markedly reduced by addition of PAS-O to their culture medium, this inhibition being concentration-dependent (0-10 microgram/ml) and reversible. The inhibitory activity was removed by periodate or protease treatment of the glycoprotein. PAS-O may interact with 3T3 cells to mimic the effect of high cell density on growth. PAS-O, which has been recognized as a glycoprotein molecule carrying a differentiation antigen expressed on the mammary epithelial cell surface, may play a role in regulating the growth of the mammary cells.