Toxoplasma gondii: Expression of GRA1 gene in endoplasmic reticulum promotes both growth and adherence and modulates intracellular calcium release in macrophages

In this study, effects of GRA1 organelle-targeted expression on macrophage functions were investigated. The recombinant plasmid pCMV/myc/ER-GRA1 was constructed and then was transfected into murine macrophage RAW264.7 by Lipofectamine, selected by resistance of G418. The selected mono-clone cell line was named ER-GRA1-RAW264.7. The expression of GRA1 was localized in ER of ER-GRA1-RAW264.7 cells by indirect immunofluorescence detection. GRA1 mRNA expression level in ER-GRA1-RAW264.7 cell was significantly enhanced with a concomitant increase in its growth and adherence activity. Fluorescence intensity of intracellular calcium in ER-GRA1-RAW264.7, ER-ctrl-RAW264.7 and RAW264.7 cells in the presence of 1 mmol/l arachidonic acid (AA) were assayed by confocal microscopy using calcium-sensitive dye, Fluo-3 AM. Cytoplasm [Ca2+]i peaked at about 18 s after AA treatment, and cytoplasm [Ca2+]i of RAW264.7 cell almost instantly stepped up after AA was added, and peaked in 3 s, with a minor cytoplasm [Ca2+]i vibration subsequently. These results demonstrated that the expression of GRA1 in ER of macrophages promotes both growth and adherence of macrophages and modulates the intracellular calcium release stimulated by AA.