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Partial Purification of Transforming Growth Factors from Human Milk

Laboratory of Pathophysiology [J. A. Z., M. B., W. R. K.] and Laboratory of Tumor Immunology and Biology [D. S. S.], National Cancer Institute, Bethesda, Maryland 20205, and Department of Clinical Chemistry, Fredericksborg County Hospital, DK 3400, Hillerod, Denmark [E. N.]

Crude, delipidated milk and the acid:ethanol extracts of primary human breast tumors contain several activities that biologically resemble transforming growth factors (TGFs) in that they promote the anchorage-independent growth of normal rat kidney and Mm5mt/c₁ mouse mammary tumor cells in soft agar. Three major TGF species with isoelectric points (pl) of about 4.0, 6.0–6.5, and 7.0 have been detected in both tumors and milk. The pl 4.0 species from milk has been purified about 10,000-fold by isoelectric focusing and high-performance liquid chromatography. This species, designated milk-derived growth factor II (MDGF_II), coelutes from gel filtration columns with an authentic human epidermal growth factor standard when using a low ionic strength eluting buffer. However, on the same column, MDGF_II is completely resolved from human epidermal growth factor with high ionic strength eluting buffers. Nevertheless, MDGF_II purified by the latter technique still competes with ¹²⁵I-epidermal growth factor for receptor binding to A431 cell membranes. Additionally the TGF activity of MDGF_II present in the pl 4.0 fraction of milk is markedly inhibited by anti-epidermal growth factor receptor antibody preparations. Consequently MDGF_II appears to be an -TGF. MDGF_II is a pepsin-sensitive, disulfide reducing agentsensitive, heat-stable protein that may be physiologically important for the mammary gland or the neonate.

¹ To whom requests for reprints should be addressed.

Received 7/ 3/84. Revised 11/19/84. Revised 8/20/85. Accepted 10/23/85.

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