Protoplasma

, Volume 167, Issue 3–4, pp 134–144

Identification of human milk α-lactalbumin as a cell growth inhibitor

  • M. P. Thompson
  • H. M. FarrellJr.
  • Sanjeeva Mohanam
  • Sue Liu
  • W. R. Kidwell
  • M. P. Bansal
  • R. G. Cook
  • D. Medina
  • Claire E. Kotts
  • Mozeena Bano
Article

DOI: 10.1007/BF01403376

Cite this article as:
Thompson, M.P., Farrell, H.M., Mohanam, S. et al. Protoplasma (1992) 167: 134. doi:10.1007/BF01403376

Summary

A growth inhibitory protein, mammary inhibitory activity (MIA), was purified to apparent homogeneity from human milk. At concentrations of 5 to 10 ng/ml, the factor inhibited the growth of mammary epithelial cells by 30–80% and also inhibited the growth of normal rat kidney cells. Whereas the cell division of normal human mammary epithelium in primary culture was inhibited by MIA, cell division by fibroblasts from the same tissues was unresponsive. Inhibition was dose and time dependent and readily reversed when MIA was removed. MIA also inhibited growth in culture for three cell lines. The growth inhibitory protein migrated as a 14 kDa protein under reducing conditions on polyacrylamide gels in the presence of sodium dodecyl sulfate. The apparent isoelectric point was pI 5.0. The amino acid composition of MIA resembled that of α-lactalbumin, and sequence analysis of the N-terminal region comprising residues 1–24 and an isolated peptide were identical with the N-terminal and residues 66–81 of human α-lactalbumin. In addition, MIA was active in the lactose synthase system. The results strongly suggest that MIA and α-lactalbumin are identical proteins. Consistent with these results, α-lactalbumin preparations from several mammalian species, including human, goat, cow and camel, were all found to be growth inhibitory for cultured mammary epithelial cells. The inhibitory activity associated with human α-lactalbumin was destroyed by digestion with pepsin or chymotrypsin, by carboxymethylation of cysteine, or by cleavage of methionine 90 following cyanogen bromide treatment. The results raise the possibility that during lactation α-lactalbumin, a product of mammary cell differentiation, could be a physiologically relevant feed-back inhibitor of mammary cell growth and perhaps of other cell types as well.

Keywords

Milk protein Mammary cells Cell growth Inhibition 

Abbreviations

MIA

mammary inhibitory activity

MDGI

mammary derived growth inhibitor

α-LA

alpha lactalbumin

H-α-LA

human α-lactalbumin

NRK

normal rat kidney

IMEM

improved minimal essential medium

DMEM

Dulbecco's modified Eagles medium

FCS

fetal calf serum

EGF

epidermal growth factor

TGF β

transforming growth factor β

CNBr

cyanogen bromide

SDS

sodium dodecyl sulfate

kDa

kilodaltons

ND-PAGE

non-denaturing polyacrylamide gel electrophoresis

TCA

trichloroacetic acid

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Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • M. P. Thompson
    • 8
  • H. M. FarrellJr.
    • 8
  • Sanjeeva Mohanam
    • 1
  • Sue Liu
    • 2
  • W. R. Kidwell
    • 3
  • M. P. Bansal
    • 4
  • R. G. Cook
    • 5
  • D. Medina
    • 4
  • Claire E. Kotts
    • 6
  • Mozeena Bano
    • 7
  1. 1.Cancer Biology Division, School of Biological SicencesMadurai Kamaraj UniversityMaduraiIndia
  2. 2.Surgery Branch, National Cancer InstituteNIHBethesda
  3. 3.Cellco Advanced Bioreactors, Inc.Kensington
  4. 4.Department of Cell BiologyBaylor College of MedicineHouston
  5. 5.Howard Hughes Medical Institute and Department of Microbiology and ImmunologyBaylor College of MedicineHouston
  6. 6.Department of Medicinal and Analytical ChemistryGenentech Inc.South San Francisco
  7. 7.Lombardi Cancer Research CenterGeorgetown UniversityWashington, D.C.
  8. 8.ARS, Eastern Regional Research CenterUSDAPhiladelphiaUSA

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