Influence of some dietary chemopreventive agents on the expression of functional differentiation of the mouse mammary gland in vitro

The purpose of the present studies was to determine the influence of the chemopreventive agents selenium, 4‐(hydroxyphenyl)‐retinamide (4‐HPR) and β‐carotene, on functional differentiation (lactogenesis) of the mouse mammary gland cells. The hormone‐induced expression of the milk‐protein genes, β‐casein, ϵ‐casein and the whey acidic protein (WAP) was used as molecular marker of differentiation of the mammary cells in organ culture medium containing insulin, prolactin, aldosterone and hydrocortisone. Quantitative determination of the cellular concentration of the respective mRNA was ascertained by molecular hybridization of RNA to the specific cloned cDNA probes using both the solution and the filter hybridization methods. Selenium at 100 nm concentration caused a pronounced inhibition of accumulation of the respective mRNAs. The retinoid, 4‐HPR, also caused a dose‐dependent inhibition of expression of these mRNA sequences. In contrast, concentrations of the 3 mRNAs in β‐carotene‐treated glands remained similar to those observed in glands cultured in medium containing the hormones and hexane (the latter being the solvent for β‐carotene). The significant antagonistic action of selenium and 4‐HPR, however, was reversible after removal of the chemicals from the culture medium. Thus, among the 3 chemicals tested, selenium and retinoid can cause an adverse effect on functional differentiation (lactogenesis) of the mammary cells. This inhibitory effect, however, was reversible. β‐Carotene, on the other hand, caused no apparent antagonistic effect on expression of the milk‐protein genes in the isolated whole mammary organ in culture.