Iavnilovitch Elena, Groner Bernd, Barash Itamar
Institute of Animal Science, ARO, The Volcani Center, Bet-Dagan, Israel.
Mol Cancer Res. 2002 Nov;1(1):32-47.
Signal transducer and activator of transcription 5 (Stat5) transduces extracellular cytokine and growth factor signals to the nucleus of mammary epithelial cells and thereby regulates gene transcription during pregnancy, lactation, and weaning. Gene constructs were prepared which subject the wild-type Stat5 or a constitutively active variant of Stat5 to the control of the beta-lactoglobulin (BLG) regulatory sequences and direct it to the mammary epithelium. The integrity and functionality of these constructs were confirmed through introduction into cultured mammary epithelial cells and hormone induction experiments. Expression levels and states of activity of Stat5 in mammary gland tissue were manipulated by introducing Stat5 variants as transgenes into the pronuclei of transgenic mice. The consequences of enhanced Stat5 expression and activation on the development of alveoli, their differentiated functions, and on postlactational involution were investigated. As expected, the transgenic mouse lines expressed the wild-type Stat5 construct (BLG/STAT5) and the constitutively active Stat5 variant (BLG/STAT5ca) exclusively in mammary epithelial cells during pregnancy and lactation. BLG/STAT5 mice exhibited larger alveoli at mid-pregnancy and a delayed onset of involution. Condensed alveoli, a high degree of cellular proliferation, and delayed involution were associated with STAT5ca expression. Elevated levels of beta-casein gene expression were found in BLG/STAT5 and STAT5ca transgenic mice during late pregnancy and lactation, indicating a limiting role for Stat5 under normal physiological conditions. This was accompanied by higher levels of beta-casein secretion into the milk and enhanced growth of pups. Transgenic animals expressing the BLG/STAT5ca transgene were predisposed to tumor formation in the mammary gland. This study extends the functional observations made in cultured mammary epithelial cells and in gene knockout mice. It identifies Stat5 as a multifunctional regulator of mammary cell proliferation, milk protein gene expression, and postlactational apoptosis.
信号转导及转录激活因子5（Stat5）将细胞外细胞因子和生长因子信号转导至乳腺上皮细胞的细胞核，从而在怀孕、哺乳和断奶期间调节基因转录。制备了基因构建体，使野生型Stat5或Stat5的组成型活性变体受β-乳球蛋白（BLG）调控序列的控制，并将其导向乳腺上皮。通过将这些构建体导入培养的乳腺上皮细胞并进行激素诱导实验，证实了其完整性和功能。通过将Stat5变体作为转基因导入转基因小鼠的原核，来操纵乳腺组织中Stat5的表达水平和活性状态。研究了Stat5表达和激活增强对肺泡发育、其分化功能以及哺乳后退化的影响。正如预期的那样，转基因小鼠品系在怀孕和哺乳期间仅在乳腺上皮细胞中表达野生型Stat5构建体（BLG/STAT5）和组成型活性Stat5变体（BLG/STAT5ca）。BLG/STAT5小鼠在怀孕中期肺泡较大，退化开始延迟。浓缩的肺泡、高度的细胞增殖和延迟的退化与STAT5ca表达相关。在怀孕后期和哺乳期间，BLG/STAT5和STAT5ca转基因小鼠中β-酪蛋白基因表达水平升高，表明在正常生理条件下Stat5起限制作用。这伴随着乳汁中β-酪蛋白分泌水平的提高和幼崽生长的增强。表达BLG/STAT5ca转基因的转基因动物易患乳腺肿瘤。这项研究扩展了在培养的乳腺上皮细胞和基因敲除小鼠中所做的功能观察。它确定Stat5是乳腺细胞增殖、乳蛋白基因表达和哺乳后细胞凋亡的多功能调节因子。
