Growth factor from human milk: purification and characterization.

A protein (HPLC-P-1) purified from human milk induced the proliferation of IMR-90 cells (human fetal lung fibroblast cells, diploid) and was named milk growth factor (MGF). The human MGF (HPLC-P-1 fraction) showed a molecular size of 8 kDa on SDS-polyacrylamide gel electrophoresis (PAGE). The band on SDS-PAGE was also detected by Western blotting with anti-human MGF. However, this MGF showed two bands (MGF-S1 and MGF-S2) on 9.8% polyacrylamide native PAGE. The amino acid compositions of MGF-S1 and MGF-S2 were almost the same, but completely different from those of EGF, IGF-1 and TGF beta. The amino acid sequence of NH2-terminal of MGF was T.K.F.E.L.Y.Q.L.L.K.D.I. Neither EGF nor IGF-1 was detectable in the human MGF fraction by RIA. The effects of human MGF on IMR 90 cells (increases in cell number, incorporation of 3H-thymidine and DNA amount) were dose dependent. The activating effect on incorporation of 3H-thymidine (methyl-3H) was suppressed by anti-human MGF antibody in a dose-dependent manner. All these results indicate that MGF purified from human milk activates the growth of IMR-90 cells.