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

Abstract

The purpose of the present studies was to determine the influence of the chemopreventive agents selenium, 4-(hydroxyphenyl)-retinamide (4-HPR) and beta-carotene, on functional differentiation (lactogenesis) of the mouse mammary gland cells. The hormone-induced expression of the milk-protein genes, beta-casein, epsilon-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 beta-carotene-treated glands remained similar to those observed in glands cultured in medium containing the hormones and hexane (the latter being the solvent for beta-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. beta-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.

Growth Control and Differentiation in Mammary Epithelial Cells

“…It has been reported that retinoids inhibit differentiation and proliferation in the mammary gland of experimental animal (168,169). Retinoic acid, but not retinyl acetate, can reverse the growth stimulation induced by ovarian hormones in lactating rat mammary gland in organ culture (19).…”

Identification of Retinoid Induced Growth Suppressing Genes

“…Vitamin A status is a possible factor contributing to the development of many human cancers, including those of the breast. Epidemiological studies, experiments with animal models and clinical trials have implicated vitamin A status as an important factor in the development of a variety of human cancers (1)(2)(3)(4)(5)(6). These studies establish a link between dietary retinoid intake and cancer risk, and further show that retinoids can prevent progression of some, but not all, human cancers.…”

Current Ideas on Selenium as a Chemopreventive Agent

“…Seleniuminduced inhibition of RNA and DNA poly merases [65], alterations in protein phos phorylation [45] and cellular glutathione [57,58] as well as hypomethylation of DNA [66] and induction of differentiation [67,68] have been reported recently. The signifi cance of these observations with respect to inhibition of cell growth has not been well defined with the exception of the effects on DNA polymerases.…”