Lactation of bovine mammary epithelial cells (BMEC) is a complex biological process that involves in various organelles. Studies have shown that lysosome and lysosomal membrane proteins (LMP) plays an important role in lactation of BMEC. But the LMP of BMEC remains poorly understood. To obtain a global view of the LMP of BMEC and the affect of lysosome on lactation, the LMP of BMEC was identified using sequential windowed acquisition of all theoretical mass spectra (LC-SWATH/MS). 1214 LMP were identified and 559 were reported to be localized on lysosomal membrane for the first time in BMEC. Gene ontology annotation of these identified proteins showed that both previously reported casein synthesis-related LMP, such as LAMTOR1, 2, 3, and rRagC, and newly identified casein and milk fat synthesis-related LMP, such as EIF4E and ACAA1, were found. KEGG pathway analysis of these identified proteins showed that some pathways involved in lactation, such as PI3K-Akt, mTOR, insulin, PPAR, and JAK-STAT pathway, were found. The lysosomal location of five proteins (PRKCA, EIF4E, ACAA1, HRAS, and THBS1) was analyzed by laser confocal microscopy, and all five were associated with the lysosomal membrane. These findings help to elucidate lysosome functions in the regulation of lactation. The results implicate lysosomes as important organelles in regulation of lactation of BMEC that have been previously undervalued.

中文翻译：

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牛乳腺上皮细胞溶酶体膜蛋白的蛋白质组学分析揭示了哺乳期溶酶体的潜在新功能


牛乳腺上皮细胞（BMEC）的泌乳是一个复杂的生物过程，涉及多种细胞器。研究表明，溶酶体和溶酶体膜蛋白（LMP）在BMEC的泌乳过程中发挥着重要作用。但 BMEC 的末次月经仍然知之甚少。为了全面了解 BMEC 的 LMP 以及溶酶体对泌乳的影响，使用所有理论质谱 (LC-SWATH/MS) 的顺序窗口采集来识别 BMEC 的 LMP。 BMEC 中鉴定出 1214 个 LMP，其中 559 个首次报道位于溶酶体膜上。这些鉴定的蛋白质的基因本体注释表明，发现了先前报道的酪蛋白合成相关的LMP，如LAMTOR1、2、3和rRagC，以及新鉴定的酪蛋白和乳脂合成相关的LMP，如EIF4E和ACAA1。对这些已鉴定蛋白质的KEGG通路分析表明，发现了一些与泌乳相关的通路，例如PI3K-Akt、mTOR、胰岛素、PPAR和JAK-STAT通路。通过激光共聚焦显微镜分析了五种蛋白质（PRKCA、EIF4E、ACAA1、HRAS 和 THBS1）的溶酶体位置，所有五种蛋白质都与溶酶体膜相关。这些发现有助于阐明溶酶体在泌乳调节中的功能。结果表明，溶酶体是调节 BMEC 泌乳的重要细胞器，而此前这一点被低估了。