A phosphorylated prolactin is a kind of modified prolactin, which is produced through phosphorylation of native prolactin (PRL) by p21-activated kinase 2 (PAK2) in secretory granules in lactotrophs. Phosphorylated prolactin is involved in the regulation of the estrous cycle and in apoptosis in cancer cells, which seem to have important physiological and pathological roles, respectively. In previous research, it has been reported that estrogen induced the phosphorylation of prolactin in the mouse pituitary gland. However, the relationship between estrogen and PAK2 in the production of phosphorylated PRL has not been clarified yet. In order to examine whether PAK2 is involved in PRL phosphorylation by estrogen, we analyzed PAK2 protein levels in mice and phosphorylated prolactin levels in mouse pituitary cells by western blot analysis. The ratio of phosphorylated PAK2/total PAK2 was increased in estrogen implanted mice, but PAK2 protein and gene expression levels were decreased. In addition, the ratio of phosphorylated prolactin/non-phosphorylated prolactin was decreased in primary pituitary cells with introduced siPAK2. These findings suggest that estrogen could induce the phosphorylation of PRL through PAK2 activation. Therefore, this study contributes to better understanding of the mechanism of phosphorylated PRL production in physiological and pathological conditions associated with estrogen.

中文翻译：

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雌激素通过小鼠脑垂体中 p21 激活激酶 2 的激活诱导催乳素磷酸化

磷酸化催乳素是一种修饰的催乳素，它是由泌乳细胞分泌颗粒中的 p21 活化激酶 2 (PAK2) 磷酸化天然催乳素 (PRL) 产生的。磷酸化催乳素参与调节发情周期和癌细胞凋亡，这似乎分别具有重要的生理和病理作用。在之前的研究中，据报道雌激素诱导小鼠脑垂体中催乳素的磷酸化。然而，雌激素和PAK2在磷酸化PRL产生中的关系尚未阐明。为了检查 PAK2 是否参与雌激素引起的 PRL 磷酸化，我们通过蛋白质印迹分析分析了小鼠中的 PAK2 蛋白水平和小鼠垂体细胞中的磷酸化催乳素水平。雌激素植入小鼠中磷酸化PAK2/总PAK2的比率增加，但PAK2蛋白和基因表达水平降低。此外，在引入 siPAK2 的原代垂体细胞中，磷酸化催乳素/非磷酸化催乳素的比率降低。这些发现表明雌激素可以通过 PAK2 激活诱导 PRL 的磷酸化。因此，本研究有助于更好地了解与雌激素相关的生理和病理条件下磷酸化 PRL 产生的机制。这些发现表明雌激素可以通过 PAK2 激活诱导 PRL 的磷酸化。因此，本研究有助于更好地了解与雌激素相关的生理和病理条件下磷酸化 PRL 产生的机制。这些发现表明雌激素可以通过 PAK2 激活诱导 PRL 的磷酸化。因此，本研究有助于更好地了解与雌激素相关的生理和病理条件下磷酸化 PRL 产生的机制。