EFFECT OF MAMMARY-DERIVED GROWTH INHIBITOR ON PROLIFERATION OF MAC-T BOVINE MAMMARY EPITHELIAL-CELLS

An established bovine mammary epithelial cell line (MAC-T) was used as a model to examine the effect of mammary-derived growth inhibitor on mammary epithelial cell proliferation. Prior to each proliferation ass ay, cells were synchronized in G(1)/G(0) by culturing for 24 h without serum. Flow cytometry revealed that 90% of cells were in G(1)/G(0), 4 % in G(2)/M, and 6% in the S-phase after serum deprivation. Approximat ely 2 x 10(3) cells per well were seeded onto 24-well plates. Cells we re incubated for 5 to 6 d with various amounts of mammary-derived grow th inhibitor (0 to 100 ng/ml). Mammary-derived growth inhibitor and me dium were changed daily. Mammary-derived growth inhibitor decreased ma mmary epithelial cell proliferation at .1 ng/ml. Synchronization of ce lls in G(1)/G(0) was necessary for inhibition of cell proliferation. C ells not arrested by serum deprivation were not responsive to mammary derived-growth inhibitor. Inhibition of cell proliferation was transie nt and observed up to 96 h in culture. Mammary-derived growth inhibito r appears to act in vitro by inhibiting the resumption of stationary c ell proliferation following starvation.