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Growth factor from human milk: purification and characterization
1Department of Biochemistry, Nippon Medical School, Tokyo, Japan.
Abstract:
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.
Insights
A novel protein from human milk, milk growth factor (MGF), stimulates the proliferation of human fetal lung fibroblast cells. This MGF is distinct from other known growth factors and activates cell growth in a dose-dependent manner.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Human milk contains various bioactive proteins that influence infant development.
- Cell proliferation is a fundamental biological process regulated by specific growth factors.
Purpose of the Study:
- To identify and characterize novel growth factors in human milk.
- To investigate the effect of a purified human milk protein on IMR-90 cell proliferation.
Main Methods:
- Protein purification from human milk (HPLC-P-1 fraction).
- SDS-PAGE and Western blotting to determine molecular size and confirm identity.
- Native PAGE to analyze protein isoforms.
- Amino acid composition and N-terminal sequencing.
- Radioimmunoassay (RIA) to detect other growth factors.
- Cell proliferation assays (cell number, 3H-thymidine incorporation, DNA amount) on IMR-90 cells.
- Neutralization assay using anti-human MGF antibody.
Main Results:
- A protein fraction (HPLC-P-1), named milk growth factor (MGF), was purified from human milk.
- Human MGF has a molecular size of 8 kDa and exists as two bands (MGF-S1, MGF-S2) on native PAGE.
- MGF's amino acid composition and N-terminal sequence are distinct from EGF, IGF-1, and TGF-beta.
- MGF dose-dependently increased IMR-90 cell number, 3H-thymidine incorporation, and DNA content.
- Anti-MGF antibody inhibited MGF's effect on 3H-thymidine incorporation.
Conclusions:
- Human milk contains a unique growth factor (MGF) that promotes IMR-90 cell proliferation.
- MGF's biological activity is mediated through specific interactions, as evidenced by antibody neutralization.
- MGF represents a novel mitogenic factor with potential roles in development or tissue repair.