These complex modifications may not occur in bacterial systems in such a way as to yield proteins of desired potency. As a result, proteins produced in bacteria may have to be chemically manipulated before recombinant proteins can be used for therapeutic or industrial purposes. Using this technique, mammary epithelial cells have been engineered to secrete proteins of therapeutic interest such as human protein C and tissue plasminogen activator, important mediators of hemostasis and coagulation, and human 1 -antitrypsin, which is involved in emphysema. Using the mammary gland to produce proteins may have important implications in environmental health and neonatal toxicology research. Transgenic mammary epithelial cells could provide gene knock-out models to investigate modulation of expression in response to environmental chemicals.
Many environmental agents appear to influence the physiology of the lactating mammary gland.
For instance, tumor promoters such as phorbol esters have deleterious effects on synthesis and secretion of milk components, in particular the caseins and the whey protein -lactalbumin. These changes lead to dissociation of protein complexes necessary for maintaining cell-cell contacts and induce disruption of cell morphology. As a result, normal cells may take on characteristics of tumor cells. Other compounds such as the potent dioxin TCDD may compromise lipid synthesis and the secretory activity of the mammary gland. Potential Pitfalls Because farm species are an integral component of the natural ecologic system and human microenvironment, the manipulation of the genetic makeup of the mammary gland may be a concern.