A Complex Noncoordinate Regulation ofα-Lactalbumin and 25 Kβ-Casein by Corticosterone, Prolactin, and Insulin in Long Term Cultures of Normal Rat Mammary Cells*

Abstract

The concentrations of PRL, corticosterone, and insulin required by long term cultures of normal rat mammary cells to produce alpha-lactalbumin (alpha LA) and the 25,000 mol wt beta-casein were evaluated with a variety of hormone ratios and concentrations. For these studies a double antibody RIA for beta-casein capable of measuring 0.5 ng beta-casein/100 microliter growth media was developed and used along with our previously reported RIA for alpha LA. PRL was active at physiological levels (0.05-0.15 micrograms/ml) and quantitatively stimulated beta-casein more than alpha LA, whereas physiological levels of corticosterone (0.05-0.15 micrograms/ml) quantitatively stimulated alpha LA more than beta-casein. The concentration of corticosterone greatly altered the magnitude of the cells' response to insulin and PRL for alpha LA output by cells from either virginal or midpregnant rats. Insulin also enhanced production of these milk proteins, but very little effect was measured in the physiological range. alpha LA was increased more by insulin than by PRL, and beta-casein was enhanced more by insulin than by corticosterone. Cells from midpregnant rats required less insulin to stimulate beta-casein production than to stimulate alpha LA. Cells from virginal rats required a supraphysiological insulin level to stimulate both beta-casein and alpha LA under these conditions. These cells generally require 5-6 weeks to achieve a steady-state rate of milk protein output. The complexities of our observations help explain some of the conflicting reports in the literature concerning which hormone is of prime importance for quantitatively increasing the synthesis of a particular milk protein, particularly since high hormone levels are often employed and time in culture varies considerably among reports. We conclude that lower levels of all these hormones can and should be used in vitro. Our messenger RNA (mRNA) studies using cloned complementary DNA probes for two rat casein mRNAs show that cells grown for 2 months with hormones contain significant amounts of both alpha- and beta-casein mRNAs. Simultaneous quantification of beta-casein mRNA levels and rates of beta-casein protein production in these long term cell cultures indicated that a substantial portion of their beta-casein protein production is regulated by the amount of its mRNA. This could be controlled by mRNA synthesis and/or mRNA degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

The origins of lactation and the evolution of milk: a review with new hypotheses

“…In fact, a degree of hormonally controlled gland development and secretion may have predated substantial glandular hypertrophy, particularly if mammary glands are more closely related to sebaceous glands than to sweat glands. Prolactin is known to affect the growth and activity of sebaceous glands and mammary glands (Ebling, 1967;Nicoll & Bern, 1972), as well as a-lactalbumin and casein synthesis (Rosen, 1981;Ray et al, 1986). An investigation of the effects of prolactin on lysozyme synthesis may prove enlightening in this regard.…”

Serum human α-lactalbumin as a marker for breast cancer

“…RIAs of HMFG2 (Burchell et al, 1984), DF3 antigen (Hayes et al, 1985) and MAM6 antigen (Hilkens et al, 1984) have also shown high levels of the respective antigens in ovarian carcinoma. It may be that gynaecological tumours to produce and secrete milk proteins (Ray et al, 1986). However, the distinction between breast and gynaecological cancers is not a diagnostic problem.…”

Hydrocortisone and progesterone regulation of the proliferation, morphogenesis, and functional differentiation of normal rat mammary epithelial cells in three dimensional primary culture

“…Glucocorticoids have been shown to regulate various aspects of MEC branching morphogenesis and when provided in combination with insulin andlor prolactin induce the cytological and functional differentiation of MEC (Ray et al, 1986;Rosen et al, 1986;Hurley et al, 1989;Doppler et al, 1990;Puissant and Houdebine, 1991;Zettl et al, 1992). The specific role that steroids, polypeptides, ECM components, and mammary gland parenchymal as well as mesenchymal cells play in modulating the type, magnitude, andlor persistance of the epithelial cell-specific effects induced by glucocorticoids has not been clearly established.…”

“…Our findings indicate the hydrocortisone was required for the induction and maintenance of multilobular alveolar morphogenesis as well as the production and accumulation of casein and lipid. Additional studies will be required to determine whether the mechanism responsible for the reduction in the levels of accumulated casein involves the participation of MEC-derived proteins with caseinolytic activity or the downregulation of casein transcription and/or synthesis (Ray et al, 1986;Rosen et al, 1986;Dopper et al, 1990). Taken together, the morphological and biochemical changes suggest that a reversion in the functional capacity of the MEC does not have to involve the induction of apoptosis.…”