Sayers Edward John, Palmer Iwan, Hope Lucy, Hope Paul, Watson Peter, Jones Arwyn Tomos
School of Pharmacy and Pharmaceutical Sciences, Cardiff University, King Edward VII Avenue, Redwood Building, Cardiff CF10 3NB, Wales, UK.
Cardiff School of Biosciences, Cardiff University, Museum Avenue, The Sir Martin Evans Building, Cardiff CF10 3AX, Wales, UK.
Pharmaceutics. 2022 Apr 13;14(4):855. doi: 10.3390/pharmaceutics14040855.
The iron-binding protein lactoferrin and the cell-penetrating peptides derived from its sequence utilise endocytosis to enter different cell types. The full-length protein has been extensively investigated as a potential therapeutic against a range of pathogenic bacteria, fungi, and viruses, including SARS-CoV-2. As a respiratory antiviral agent, several activity mechanisms have been demonstrated for lactoferrin, at the extracellular and plasma membrane levels, but as a protein that enters cells it may also have intracellular antiviral activity. Characterisation of lactoferrin's binding, endocytic traffic to lysosomes, or recycling endosomes for exocytosis is lacking, especially in lung cell models. Here, we use confocal microscopy, flow cytometry, and degradation assays to evaluate binding, internalisation, endocytic trafficking, and the intracellular fate of bovine lactoferrin in human lung A549 cells. In comparative studies with endocytic probes transferrin and dextran, we show that lactoferrin binds to negative charges on the cell surface and actively enters cells via fluid-phase endocytosis, in a receptor-independent manner. Once inside the cell, we show that it is trafficked to lysosomes where it undergoes degradation within two hours. These findings provide opportunities for investigating both lactoferrin and derived cell-penetrating peptides activities of targeting intracellular pathogens.
铁结合蛋白乳铁蛋白及其序列衍生的细胞穿透肽利用内吞作用进入不同的细胞类型。全长蛋白作为一种针对多种病原菌、真菌和病毒(包括SARS-CoV-2)的潜在治疗药物已得到广泛研究。作为一种呼吸道抗病毒剂,乳铁蛋白在细胞外和质膜水平的几种活性机制已得到证实,但作为一种进入细胞的蛋白质,它可能也具有细胞内抗病毒活性。目前缺乏对乳铁蛋白的结合、向溶酶体的内吞运输或用于胞吐作用的再循环内体的表征,尤其是在肺细胞模型中。在此,我们使用共聚焦显微镜、流式细胞术和降解分析来评估牛乳铁蛋白在人肺A549细胞中的结合、内化、内吞运输以及细胞内命运。在与内吞探针转铁蛋白和右旋糖酐的对比研究中,我们表明乳铁蛋白与细胞表面的负电荷结合,并以受体非依赖的方式通过液相内吞作用主动进入细胞。一旦进入细胞,我们发现它被运输到溶酶体,在那里它会在两小时内被降解。这些发现为研究乳铁蛋白及其衍生的细胞穿透肽靶向细胞内病原体的活性提供了机会。
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