Direct effects of growth hormone on the differentiation of bovine mammary epithelial cells.

本研究旨在探讨生长激素(GH)对分离和培养的牛乳腺上皮细胞(BMEC)的直接作用及其机制。1.免疫组织化学染色和聚合酶链式反应显示BMEC表达GH受体蛋白和mRNA，并被乳源激素(胰岛素、催乳素和地塞米松)刺激。2.用抗α-51酪蛋白抗体用ELISA法测定BMEC的酪蛋白分泌。3.生长激素和催乳素在10-100 ng/ml浓度范围内均可引起BMEC STATS磷酸化水平的升高，分别在30-120分钟和30-60分钟出现。4.用Western配体和免疫印迹法检测细胞内信号转导蛋白MAP-K的磷酸化变化。GH和催乳素以100 ng/ml的剂量刺激BMEC中MAP激酶的磷酸化作用30min，而用抗MAP激酶抗体进行蛋白质印迹分析，结果表明，GH直接作用于牛乳腺上皮细胞，并刺激酪蛋白的合成和分泌。JAK-STAT和MAP激酶至少部分参与了GH的作用。

The purpose of this study was to assess the direct effect of growth hormone (GH) on mammary parenchyma using isolated and cultured bovine mammary epithelial cells (BMEC) and its mechanisms1.Immunohistochemical staining and polymerase chain reaction revealed that BMEC expressed GH receptor protein and mRNA and the mRNA expression was stimulated by lactogenic hormones (insulin, prolactin and dexamethasone).2.Casein secretion from BMEC was determined by ELISA using anti-alpha-51 casein antibody. Casein concentration in conditioned medium was increased by GH treatment for 4-7 days when BMEC was cultured on transwell inserts coated with type I collagen.3.GH as well as prolactin caused an increase in STATS phosphorylation in BMEC at a dose of 10-100 ng/ml. The increases were observed 30-120 min and 30-60 min after the addition of GH and prolactin, respectively.4.Changes in the phosphorylation of MAP kinase, an intracellular signal transducer, were determined by western ligand blot analysis using anti-phospho-MAP kinase antibody. GH and prolactin stimulated the phosphorylation of MAP kinase at a dose of 100 ng/ml for 30 min in BMEC, whereas the amount of MAP kinase protein, determined by western blot analysis using anti-total MAP kinase antibody, was not changed by these treatments.In conclusion, GH acts directly on bovine mammary epithelial cells and stimulate casein synthesis and secretion. JAK-STAT and MAP kinase are involved at least partly in the effect of GH.