| Abstract: | The actions of insulin, hydrocortisone, prolactin and growth hormone on the synthesis of macromolecules in MCF-7 cells was determined in a serum-free defined medium. The inclusion of the polyamine spermidine in the medium was shown to enhance the insulin stimulation of the rate of 3H]uridine incorporation into RNA in a manner similar to that demonstrated for hydrocortisone. Spermidine, in addition to insulin and hydrocortisone, was also essential for prolactin to manifest a stimulation of the rate of 3H]uridine incorporation; this effect of spermidine was optimal with spermidine concentrations between 1 and 5 mM. Prolactin also stimulated the rate of 3H]leucine incorporation into total cellular protein and into an isoelectrically precipitable (pH 4.6) phosphoprotein fraction. The actions of prolactin on total protein and phosphoprotein synthesis were only expressed if spermidine, in addition to insulin and hydrocortisone, was contained in the culture medium. All of the prolactin responses were observed employing physiological concentrations of prolactin. Specificity of the prolactin responses was established by demonstrating that porcine growth hormone had no effects on RNA or phosphoprotein synthesis in the MCF-7 cells. |
