Mammary-derived growth inhibitor protein and messenger ribonucleic acid concentrations in different physiological states of the gland

Challenges in enriching milk fat with polyunsaturated fatty acids

Milk fatty acid composition is determined by several factors including diet. The milk fatty acid profile of dairy cows is low in polyunsaturated fatty acids, especially those of the n-3 series. Efforts to change and influence fatty acid profile with longer chain polyunsaturated fatty acids have proven challenging. Several barriers prevent easy transfer of dietary polyunsaturated fatty acids to milk fat including rumen biohydrogenation and fatty acid esterification. The potential for cellular uptake and differences in fatty acid incorporation into milk fat might also have an effect, though this has received less research effort. Given physiological impediments to enriching milk fat with polyunsaturated fatty acids, manipulating the genome of the cow might provide a greater increase than diet alone, but this too may be challenged by the physiology of the cow.

Isolation and sequence characterization of mammary derived growth inhibitor gene of riverine buffalo (Bubalus bubalis)

In this study, attempts have been made to identify and characterize water buffalo (Bubalus bubalis) mammary derived growth inhibitor (MDGI) gene, isolated from a mammary gland cDNA library of lactating buffalo. The complete MDGI cDNA was of 698 nucleotides, consisting 61 nucleotides in 5' UTR, coding region of 402 nucleotides, and 235 nucleotides representing the 3' UTR. Comparison of nucleotide and deduced amino acid sequence data with that of MDGI/fatty acid binding protein (FABP) of other species shows three buffalo specific nucleotide changes while seven nucleotide changes were common to cattle and buffalo. Buffalo and cattle MDGI had 100% amino acid sequence similarity, which also shared three amino acid changes: 34 (Ala-Gly), 109 (Leu-Met), and 132 (Glu-Gln) as compared to other species. Comparison with FABPs reported from other cattle tissues revealed highest amino acid sequence similarity with FABP-heart (100%) and least with FABP-liver (20.5%). Phylogenetic analysis revealed cattle MDGI to be closest to buffalo, while mouse MDGI was distantly placed, whereas different tissue derived FABPs of cattle showed FABP-heart closest and FABP-epidermis most distantly placed from buffalo MDGI. This report also differs from the earlier findings that MDGI is intermediate of FABP-heart and adipose.

Hormonal and extracellular matrix regulation of plasminogen activator in a bovine mammary epithelial cell line

The effects of lactogenic hormones on urokinase plasminogen activator (u-PA) produced by bovine mammary epithelial cells (MAC-T) were examined. High levels of u-PA activity were detected in growth arrested cells cultured on plastic. This suggests that high levels of PA activity alone are not sufficient to induce proliferation of bovine mammary epithelial cells. Cells were cultured on various extracellular matrices: plastic, fibronectin, collagen, matrigel, and laminin. Basal levels of u-PA activity in media from MAC-T cells cultured on matrigel were 1.6-, 2-, 2- and 3.5-fold higher than that of cells cultured on plastic, fibronectin, collagen, and laminin, respectively. Insulin increased (P<0.01) mammary epithelial u-PA activity on a per cell basis, an effect observed irrespectively of the type of extracellular matrix onto which cells were cultured. Not unexpectedly, insulin-like growth factor (IGF)-I, Des(1-3) IGF-I and IGF-II increased mammary epithelial u-PA activity on a per cell basis and u-PA mRNA levels, thus, mimicking the effect of insulin. Dexamethasone suppressed (P<0.01) u-PA activity but was unable to suppress the insulin-induced increase in u-PA activity of cells cultured on various extracellular matrices. These data indicate that u-PA activity is modulated by both lactogenic hormones and the type of extracellular matrix.

In vitro inhibition of mammary cell growth by lactoferrin: a comparative study

The effect of lactoferrin (Lf) on mammary epithelial cell growth in culture was tested in a comparative study of bovine and human Lf. Bovine Lf was inhibitory to growth of a bovine mammary epithelial cell line, both in the presence and absence of fetal bovine serum in the medium. The growth inhibition activity of bovine Lf was not affected by iron-saturation status of the protein. In contrast with bovine Lf, human Lf had minimal inhibitory activity on bovine cell growth in the presence of serum, and cell growth was stimulated by human Lf in the absence of serum. In the latter case, human Lf may have acted as an iron-transport protein for the cells. Bovine Lf and human Lf had no effect on growth of MCF-7 human breast tumor cells and only minimal inhibitory activity toward the MDA-MB 231 human breast tumor cell line. The effect of bovine Lf on bovine mammary epithelial cells could be prevented by immunoneutralization of the Lf. These results indicate that Lf can be inhibitory to growth of mammary epithelial cells in culture, but this response to specific for the species origin of the Lf and of the mammary cell.

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 assay, cells were synchronized in G1/G0 by culturing for 24 h without serum. Flow cytometry revealed that 90% of cells were in G1/G0, 4% in G2/M, and 6% in the S-phase after serum deprivation. Approximately 2 x 10(3) cells per well were seeded onto 24-well plates. Cells were incubated for 5 to 6 d with various amounts of mammary-derived growth inhibitor (0 to 100 ng/ml). Mammary-derived growth inhibitor and medium were changed daily. Mammary-derived growth inhibitor decreased mammary epithelial cell proliferation at .1 ng/ml. Synchronization of cells in G1/G0 was necessary for inhibition of cell proliferation. Cells not arrested by serum deprivation were not responsive to mammary derived-growth inhibitor. Inhibition of cell proliferation was transient and observed up to 96 h in culture. Mammary-derived growth inhibitor appears to act in vitro by inhibiting the resumption of stationary cell proliferation following starvation.