Myotonic dystrophy-related Cdc42-binding kinase alpha (MRCKα) is an integral component of signaling pathways controlling vital cellular processes, including cytoskeletal reorganization, cell proliferation and cell survival. In this study, we investigated the physiological role of MRCKα in milk protein and fat production in dairy cows, which requires a dynamic and strict organization of the cytoskeletal network in bovine mammary epithelial cells (BMEC). Within a selection of 9 Holstein cows, we found that both mRNA and protein expression of MRCKα in the mammary gland were upregulated during lactation and correlated positively (r > 0.89) with the mRNA and protein levels of β-casein. Similar positive correlations (r > 0.79) were found in a primary culture of BMEC stimulated with prolactin for 24 h. In these cells, silencing of MRCKα decreased basal β-casein, sterol-regulatory element binding protein (SREBP)-1 and cyclin D1 protein level, phosphorylation of mTOR, triglyceride secretion, cell number and viability—while overexpression of MRCKα displayed the reversed effect. Notably, silencing of MRCKα completely prevented the stimulatory action of prolactin on the same parameters. These data demonstrate that MRCKα is a critical mediator of prolactin-induced lactogenesis via stimulation of the mTOR/SREBP1/cyclin D1 signaling pathway.

强直性营养不良相关的 Cdc42 结合激酶 α (MRCKα) 是控制重要细胞过程的信号通路的一个组成部分，包括细胞骨架重组、细胞增殖和细胞存活。在本研究中，我们研究了 MRCKα 在奶牛乳蛋白和脂肪生产中的生理作用，这需要牛乳腺上皮细胞 (BMEC) 中的细胞骨架网络动态而严格的组织。在选择的 9 头荷斯坦奶牛中，我们发现乳腺中 MRCKα 的 mRNA 和蛋白质表达在泌乳期间均上调，并且与 β-酪蛋白的 mRNA 和蛋白质水平呈正相关（ r > 0.89）。相似的正相关 ( r > 0.79）在用催乳素刺激 24 小时的 BMEC 原代培养物中发现。在这些细胞中，MRCKα 的沉默降低了基础 β-酪蛋白、甾醇调节元件结合蛋白 (SREBP)-1 和细胞周期蛋白 D1 蛋白水平、mTOR 的磷酸化、甘油三酯分泌、细胞数量和活力——而 MRCKα 的过表达显示了相反的效果. 值得注意的是，MRCKα的沉默完全阻止了催乳素对相同参数的刺激作用。这些数据表明，MRCKα 是通过刺激 mTOR/SREBP1/cyclin D1 信号通路促进催乳素诱导泌乳的关键介质。