| Research Abstract |
I performed the experiments using primary cultuted cells and SV-40A255-immortalized cells of murine mammary gland to clarify the mechanism and roles of the expression of milk fat globule-characteristic carbohydrate chains during the periods of pregnancy and lactation. The primary cultured cells were maintained in the basal medium containing cortisol and epidermal growth factor, and were found to be initiated the secretion of milk by addition of prolactin in the basal medium. Synthesis of GD1alpha ganglioside was simultaneously obserbed as an event associated with the secretion of milk under stimulation with prolactin, and was found to be trigered by activations of GM1balpha2-6 sialyltransferase and ceramide lactoside beta1-4N-acetylgalactosaminyltransferase. Also, cholesterol sulfotransferase was highly activated in the cells with secretion of milk, but it was found to be induced by stimulation with epidermal growth factor alone, indicating that the induction of cholesterol sulfotransf
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erase is associated with the growth of mammary epithelial cells. In the case of immortalized cells, the induction of cholesterol sulfotrasferase was observed under stimulation of epidermal growth factor, but production of milk fat grobule, as well as synthesis of GD1alpha, was not observed under the same condition as that for primary cultured cells. The enzuymes thus regulated during the process of milk secretion were found to be controled at the translational level. Then, I invertigated the possible roles of cholesterol sulfate and GD1alpha ganglioside. From the observation that cholesterol sulfate was distributed in the epithelial cells of gastrointestinal tract under the duodenum, where was exposed to the pancreatic digestive enzymes, it was expected to protect the cells from the action of digestive enzymes. As was expected, cholesterol sulfate was found to possess the inhibitory activity toward several proteases, DNase and glycosidases, and one of the major function of cholesterol sulfate in the epithelial cells of mammary gland was found to protect the cells from tissue injury with several enzymes screted during the production of milk. On the other hand, GD1alpha gangloside as the major negatively charged lipids in the fat globule membrane was clarified to be the receptor molecules for toxins from Cl.botulinum type A and type E,and Cl.tetani, indicating that it fuction to protect neonates from the bacterial infections. Less
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