Hormonal Regulation of the Synthesis of Casein and α-Lactalbumin in a Primary Mammary Cell Culture System

Summary

The addition of 5 μg/ml of both insulin and prolactin, 3 μM cortisol and 5% fetal bovine serum stimulated casein synthesis during a 5 day culture of mammary epithelium from lactating mice using a floating collagen gel as a culture substratum. Omission of any of the three hormones or serum decreased casein synthesis substantially. The use of 10% serum or the attached gel culture system also decreased casein synthesis. Cells cultured with the combination of the three hormones and 5% serum contained a low level of casein mRNA on day 2, but it increased to much higher levels on day 4 and 5, amounting to over 30% of total mRNA on day 5. In contrast to casein synthesis, the maximal increase in α-lactalbumin synthesis required the presence of 0.03 μM cortisol. The combination of insulin, prolactin and 3 μM cortisol or insulin and prolactin elicited smaller increases. The translatable mRNA for α-lactalbumin in cells cultured with insulin, cortisol and prolactin for 5 days was detected, but not in cells with insulin and cortisol. Both a high and low concentration of cortisol in combination with insulin increased prolactin binding capacity of cultured cells to the same extent, whereas cells cultured with insulin alone contained much lower levels of prolactin binding. The difference in the capacity of prolactin binding between cells cultured with insulin alone and those cultured with insulin and cortisol correlated well with their ability to synthesize casein in response to prolactin.

Key-Words

Casein Synthesis - α-Lactalbumin Synthesis - Insulin - Prolactin - Cortisol - Fetal Bovine Serum - Mammary Cell Culture - Mice