Bolander F F, Nicholas K R, Van Wyk J J, Topper Y J
Proc Natl Acad Sci U S A. 1981 Sep;78(9):5682-4. doi: 10.1073/pnas.78.9.5682.
In the presence of cortisol and prolactin, insulin at concentrations as low as 1 ng/ml significantly stimulates casein synthesis in mammary explants from midpregnant mice; maximal synthesis occurs at 10 ng/ml. However, in the absence of insulin, no detectable immunoprecipitable casein is produced. Insulin also supports enhanced accumulation of casein mRNA in the presence of cortisol and prolactin; neither epidermal growth factor nor somatomedin C has this effect. These inductive actions of insulin are not secondary to a general maintenance effect on the mammary epithelial cell; insulin, epidermal growth factor, and somatomedin C can support the accumulation of RNA in rough endoplasmic reticulum equally well. In addition, these effects do not reflect a specific insulin requirement for prolactin sensitivity; epidermal growth factor can support prolactin-induced total RNA synthesis as well as insulin can. The results demonstrate that, although insulin, epidermal growth factor, and somatomedin C can all function as cell maintenance agents, only insulin, together with cortisol and prolactin, can induce casein mRNA accumulation.
在存在皮质醇和催乳素的情况下，低至1纳克/毫升浓度的胰岛素就能显著刺激妊娠中期小鼠乳腺外植体中酪蛋白的合成；最大合成量出现在10纳克/毫升时。然而，在没有胰岛素的情况下，检测不到可免疫沉淀的酪蛋白产生。胰岛素在存在皮质醇和催乳素时还能促进酪蛋白mRNA的积累增加；表皮生长因子和生长调节素C都没有这种作用。胰岛素的这些诱导作用并非继发于对乳腺上皮细胞的一般维持作用；胰岛素、表皮生长因子和生长调节素C都能同样良好地支持粗面内质网中RNA的积累。此外，这些作用并不反映对催乳素敏感性有特定的胰岛素需求；表皮生长因子能像胰岛素一样支持催乳素诱导的总RNA合成。结果表明，虽然胰岛素、表皮生长因子和生长调节素C都能作为细胞维持因子发挥作用，但只有胰岛素与皮质醇和催乳素一起才能诱导酪蛋白mRNA的积累。
