Absolute requirement of glucocorticoid for expression of the casein gene in the presence of prolactin.

Abstract

Second thoracic mammary glands of immature BALB/c female mice were stimulated to pregnancy-like lobuloalveolar (LA) development after 6 days of incubation in a corticosteroid-free step I culture medium containing insulin, prolactin, estradiol, progesterone, and growth hormone. A low basal level (0.0009%) of casein mRNA (mRN4.,) sequences was detectable in the LA glands by a specific cDNA probe. Subsequent incubation of the LA glands for 3 days in medium containing insulin and prolactin or insulin and cortisol failed to elicit mRNAesn above the basal level, indicating that neither prolactin nor cortisol alone can support casein gene expression.However, an increase in mRNA. levels was observed when the 3-day incubation with insulin and cortisol or insulin and prolactin was followed by 3 days of culture in presence of insulin, prolactin, and cortisol. When a 3-day incubation with insulin and prolactin was followed by 3 days in insulin and cortisol medium, mRNAes. levels in the gland remained similar to the basal level. However, a 20-fold increase in the mRNAesn levels ensued when the LA glands were sequentially incubated for 3 days in insulin and cortisol and then for another 3 days in insulin and prolactin medium. After a preincubation in insulin and cortisol medium, the LA glands retained residual cortisol during subsequent incubation in insulin and prolactin medium, and the mRNAes. levels in these glands were related to the level of residual cortisol present. When mRNAesn and the residual cortisol level reached a minimum, addition of fresh cortisol to the medium caused a 20-fold increase in the mRNAesn levels. This indicates that cortisol is a limiting factor in insulin and prolactin medium and its presence is absolutely required for casein gene expression.The requirement that prolactin and cortisol be present for lactogenesis was delineated over 2 decades ago (1, 2). Since then, numerous studies have shown that, during lactation, a marked increase of mammary cell RNA and protein, including casein, is dependent upon stimulation by prolactin and cortisol (3, 4). We have shown that cortisol is required for the maintenance of casein-synthesizing polysomes, poly(A)+RNA synthesis, and casein mRNA (mRNAsn) accumulation in the lactating mammary gland of the mouse (5-7). Moreover, a regulatory action of the glucocorticoid on transcription of the casein gene in the mammary gland in vivo has been demonstrated (7). However, complexities in the animal limit elucidation of the discrete role of polypeptide and steroid hormones which regulate specific expression of the casein gene in breast cells.Fragments of mammary tissue from pregnant mice were demonstrated to be capable of synthesizing casein in a culture medium containing the lactogenic hormones plus insulin (8). This provided an in vitro model for studying molecular responses of the mammary cells to prolactin and glucocorticoid action in a chemically defined medium containing insulin, which is needed for viability of the mammary parenchyma in vitro (9). Subsequen...

The selection, expression, and organization of a set of head-specific genes in Drosophila

“…al., 1978;Chan et al, 1978;Ganguly et al, 1979Ganguly et al, , 1980Derman, 1981;Hager and Palmiter, 1981). Individual genes other than those controlled by steroid hormones have been shown to be under transcriptional control, including eleven tissue-specific sequences from mammalian liver , adenovirus transcripts from infected cells (Darnell, 1979;Wilson et al, 1979a;1979b), and certain gene sequences expressed differentially during development of both plants and animals (Daneholt, 1975;Williams et al, 1979;Maekawa and Suzuki, 1980;Goldberg et al, 1981).…”

Differential Interactions of Specific Nuclear Factor I Isoforms with the Glucocorticoid Receptor and STAT5 in the Cooperative Regulation of WAP Gene Transcription

“…Several transcription factors, various peptide and steroid hormones, cytokines, and cell-cell and cell-substratum interactions have been shown to influence milk protein gene expression (5,11,18,24,31,32,54,56). The rat whey acidic protein (WAP) gene, the major whey protein expressed in rodents, has been employed in our laboratory as a model system to study the transcriptional regulation of milk protein genes.…”

Both cell substratum regulation and hormonal regulation of milk protein gene expression are exerted primarily at the posttranscriptional level.

“…The expression of the milk protein genes in mammary epithelial cells (MEC) is regulated by a variety of factors, including peptide and steroid hormones and cell-cell and cell-substratum interactions (6,19,26,32,34,53). Much of the work directed at defining the hormonal requirements for milk protein mRNA and protein accumulation has been done with mammary gland explant cultures.…”