Hirano Seishiro, Kanno Sanae
NanoTox, RCER, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
Legal Medicine, St. Marianna University School of Medicine, 2-16-1 Sugao, Miyamae-ku, Kawasaki, Kanagawa 216-8511, Japan.
PLoS One. 2015 Nov 6;10(11):e0142062. doi: 10.1371/journal.pone.0142062. eCollection 2015.
The Macrophage Receptor with COllagenous structure (MARCO) protein is a plasma membrane receptor for un-opsonized or environmental particles on phagocytic cells. Here, we show that MARCO was internalized either by ruffling of plasma membrane followed by macropinocytosis or by endocytosis followed by fusion with autophagosome in CHO-K1 cells stably transfected with GFP-MARCO. The macropinocytic process generated large vesicles when the plasma membrane subsided. The endocytosis/autophagosome (amphisome) generated small fluorescent puncta which were visible in the presence of glutamine, chloroquine, bafilomycin, ammonia, and other amines. The small puncta, but not the large vesicles, co-localized with LC3B and lysosomes. The LC3-II/LC3-I ratio increased in the presence of glutamine, ammonia, and chloroquine in various cells. The small puncta trafficked between the peri-nuclear region and the distal ends of cells back and forth at rates of up to 2-3 μm/sec; tubulin, but not actin, regulated the trafficking of the small puncta. Besides phagocytosis MARCO, an adhesive plasma membrane receptor, may play a role in incorporation of various extracellular materials into the cell via both macropinocytic and endocytic pathways.
具有胶原结构的巨噬细胞受体（MARCO）蛋白是吞噬细胞上未被调理素包被的或环境颗粒的质膜受体。在此，我们发现，在稳定转染了绿色荧光蛋白（GFP）-MARCO的中国仓鼠卵巢细胞（CHO-K1）中，MARCO可通过质膜褶皱继之以巨胞饮作用而内化，或通过内吞作用继之以与自噬体融合而内化。当质膜消退时，巨胞饮过程产生大的囊泡。内吞作用/自噬体（两性体）产生小的荧光斑点，在谷氨酰胺、氯喹、巴弗洛霉素、氨和其他胺存在的情况下可见。这些小斑点而非大囊泡与微管相关蛋白1轻链3β（LC3B）和溶酶体共定位。在各种细胞中，谷氨酰胺、氨和氯喹存在时，LC3-II/LC3-I比率升高。这些小斑点以高达2-3μm/秒的速度在细胞核周围区域和细胞远端之间来回运输；微管蛋白而非肌动蛋白调节这些小斑点的运输。除了吞噬作用外，MARCO作为一种黏附性质膜受体，可能在通过巨胞饮和内吞途径将各种细胞外物质纳入细胞的过程中发挥作用。
