1,25-Dihydroxycholecalciferol Receptor Regulation in Hormonally Induced Differentiation of Mouse Mammary Gland in Culture*

Abstract

Mammary explants from pregnant mouse cultured in the presence of insulin, cortisol, and PRL express their differentiated function by producing milk proteins such as casein. Sucrose density gradient analysis of high salt extract of cultured explants showed the presence of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3 specific binding activity sedimenting at 3.3 S. Specific 1,25-(OH)2D3 binding activity in mammary explants varied as a function of the hormonal milieu in culture. The highest activity was found in explants cultured in the presence of insulin, cortisol, and PRL, whereas only a marginal activity was present in explants cultured with insulin. The comparison of 1,25-(OH)2D3 binding activity in explants cultured with insulin and with the three hormone combination by Scatchard plot analysis indicated that the synergistic actions of insulin, cortisol, and PRL increased the number of 1,25-(OH)2D3 specific binding proteins as much as 6-fold; however, the affinity constant of the binding protein was relatively constant in the two systems. Time course studies showed that the increase in 1,25-(OH)2D3 binding activity was detectable as early as 12 h after the addition of cortisol and PRL to insulin-primed explants. The increase was inhibited by the presence of actinomycin D and cycloheximide, suggesting that the hormonal stimulation of 1,25-(OH)2D3 binding activity involves both transcriptional and translational process. These results indicate that insulin, cortisol, and PRL stimulate the specific 1,25-(OH)2D3 binding activity during the induction of mammary functional differentiation when milk protein synthesis takes place.

Mechanisms implicated in the growth regulatory effects of vitamin D in breast cancer.

“…Studies in experimental animals have demonstrated that the VDR is dynamically regulated during pregnancy and lactation, but little is known about its specific functions. The VDR is expressed at low levels in mammary gland in virgin rats and is upregulated in response to the differentiation inducing hormones cortisol, prolactin and insulin (Mezzetti et al 1987). Highest levels of VDR in mammary gland are seen during lactation, being maximal at 3 days post partum when the concentration of calcium in milk is highest (Colston et al 1988).…”

Vitamin D Actions in Mammary Gland and Breast Cancer

“…The dynamic regulation of VDR in mammary gland during the reproductive cycle suggests that hormones and/or growth factors which impact on glandular development may modulate VDR expression under physiologic conditions. Indeed, lactogenic hormones upregulate VDR in normal mammary gland and nontransformed mammary cells in vitro [87,125]; however, the specific factors responsible for VDR regulation in the normal mammary gland have yet to be defined.…”

Growth Control and Differentiation in Mammary Epithelial Cells

“…The addition of vitamin D3 significantly increases casein production in mouse mammary explants cultured in the presence of insulin, cortisol, and prolactin (175). Moreover, Bhattacharjee et al found that mammary gland explants from rachitic rats and mice show a decreased production of milk proteins when cultured in the presence of insulin, prolactin, and glucocorticoid (176).…”

“…The action of vitamin D3 is specifically directed to the epithelial cells, that have been shown to concentrate the hormone in their nuclei (177). In addition, mouse mammary epithelial cells have been shown to possess specific vitamin D receptors, the level of which is enhanced by insulin, prolactin, and glucocorticoid (178). These data strongly suggest that vitamin D3 at physiological concentrations may be involved in the control of lactogenesis.…”