Petersen H, Haldosén L A
Department of Medical Nutrition, Karolinska Institute, NOVUM, Hudddinge, S-141 86, Sweden.
Exp Cell Res. 1998 Sep 15;243(2):347-58. doi: 10.1006/excr.1998.4160.
HC11 mouse mammary epithelial cells are capable of differentiating in vitro. By growing cells in EGF-containing medium, and upon confluence withdrawing EGF, these cells become competent at responding to lactogenic hormone treatment and expressing milk proteins. We found that during proliferation and at confluence STAT5A and STAT5B proteins were expressed at equal levels or with STAT5B being predominant. In competent cells, expression levels of STAT5A and STAT5B increased markedly with STAT5A now being the predominant form, an expression pattern resembling the expression patterns of STAT5 proteins seen during mammary gland differentiation in vivo. This suggests that EGF has a suppressive effect on STAT5 expression, in particular, STAT5A, which we conclude to be mediated through ras/raf/MEK/MAPK pathway and to a lesser extent through a PI3-kinase-mediated pathway. Furthermore, we also found that EGF regulated a nuclear phosphatase capable of dephosphorylating tyrosine-phosphorylated STAT5. Our data show that HC11 cells have retained the expression patterns of STAT5 proteins seen in vivo. This makes HC11 cells useful for studying molecular mechanisms regulating expression of STAT factors and their participation in differentiation processes of mammary gland.
HC11小鼠乳腺上皮细胞能够在体外分化。通过在含表皮生长因子（EGF）的培养基中培养细胞，并在细胞汇合后去除EGF，这些细胞变得能够响应催乳激素处理并表达乳蛋白。我们发现，在增殖过程中和汇合时，信号转导及转录激活因子5A（STAT5A）和信号转导及转录激活因子5B（STAT5B）蛋白以相等水平表达，或STAT5B占主导。在具备分化能力的细胞中，STAT5A和STAT5B的表达水平显著增加，此时STAT5A成为主要形式，这种表达模式类似于在体内乳腺分化过程中观察到的STAT5蛋白的表达模式。这表明EGF对STAT5表达具有抑制作用，特别是对STAT5A，我们得出结论，这种抑制作用是通过ras/raf/丝裂原活化蛋白激酶/细胞外信号调节激酶（MEK）/丝裂原活化蛋白激酶（MAPK）途径介导的，在较小程度上是通过磷脂酰肌醇-3激酶（PI3-激酶）介导的途径。此外，我们还发现EGF调节一种能够使酪氨酸磷酸化的STAT5去磷酸化的核磷酸酶。我们的数据表明，HC11细胞保留了体内观察到的STAT5蛋白的表达模式。这使得HC11细胞可用于研究调节STAT因子表达的分子机制及其在乳腺分化过程中的参与情况。
