Cell and Molecular Biology Program, University of Vermont College of Medicine, Burlington, Vermont, USA.
Infect Immun. 2012 Jun;80(6):2008-18. doi: 10.1128/IAI.06287-11. Epub 2012 Apr 2.
Phagocytosis of host cells is characteristic of tissue invasion by the intestinal ameba Entamoeba histolytica, which causes amebic dysentery and liver abscesses. Entamoeba histolytica induces host cell apoptosis and uses ligands, including C1q, on apoptotic cells to engulf them. Two mass spectrometry analyses identified calreticulin in amebic phagosome preparations, and, in addition to its function as an endoplasmic reticulum chaperone, calreticulin is believed to be the macrophage receptor for C1q. The purpose of this study was to determine if calreticulin functions as an E. histolytica C1q receptor during phagocytosis of host cells. Calreticulin was localized to the surface of E. histolytica during interaction with both Jurkat lymphocytes and erythrocytes and was present in over 75% of phagocytic cups during amebic erythrophagocytosis. Presence of calreticulin on the cell surface was further demonstrated using a method that selectively biotinylated cell surface proteins and by flow cytometry using trophozoites overexpressing epitope-tagged calreticulin. Regulated overexpression of calreticulin increased E. histolytica's ability to phagocytose apoptotic lymphocytes and calcium ionophore-treated erythrocytes but had no effect on amebic adherence to or destruction of cell monolayers or surface expression of the GalNAc lectin and serine-rich E. histolytica protein (SREHP) receptors. Finally, E. histolytica calreticulin bound specifically to apoptotic lymphocytes and to human C1q. Collectively, these data implicate cell surface calreticulin as a receptor for C1q during E. histolytica phagocytosis of host cells.
宿主细胞的吞噬作用是肠道阿米巴原虫溶组织内阿米巴侵袭组织的特征，它会导致阿米巴痢疾和肝脓肿。溶组织内阿米巴诱导宿主细胞凋亡，并利用凋亡细胞上的配体，包括 C1q，吞噬它们。两项质谱分析鉴定出在阿米巴吞噬体制剂中存在钙网蛋白，除了作为内质网伴侣的功能外，钙网蛋白被认为是巨噬细胞 C1q 的受体。本研究旨在确定钙网蛋白在吞噬宿主细胞过程中是否作为溶组织内阿米巴的 C1q 受体发挥作用。钙网蛋白在与 Jurkat 淋巴细胞和红细胞相互作用时定位于溶组织内阿米巴的表面，并且在阿米巴红细胞吞噬过程中超过 75%的吞噬杯中存在。通过选择性生物素化细胞表面蛋白的方法和使用过表达表位标记的钙网蛋白的滋养体的流式细胞术进一步证明了钙网蛋白存在于细胞表面。钙网蛋白的调控过表达增加了溶组织内阿米巴吞噬凋亡淋巴细胞和钙离子载体处理的红细胞的能力，但对阿米巴对细胞单层的黏附和破坏或半乳糖胺凝集素和富含丝氨酸的溶组织内阿米巴蛋白（SREHP）受体的表面表达没有影响。最后，溶组织内阿米巴钙网蛋白特异性结合凋亡淋巴细胞和人 C1q。总的来说，这些数据表明细胞表面钙网蛋白是溶组织内阿米巴吞噬宿主细胞过程中 C1q 的受体。
