Toxoplasma gondii dense granule protein 15 induces apoptosis in choriocarcinoma JEG-3 cells through endoplasmic reticulum stress

Background: Toxoplasma gondii, a single-celled parasite commonly found in mammals, has been shown to induce trophoblast cell apoptosis and subsequently cause fetal damage and abortion. Although dense granule protein 15 (GRA15) has been identified as a key component in innate immunity to T. gondii infection and its pathogenesis, its role in host cell apoptosis remains unclarified. Methods: Type II GRA15 (GRA15(II)) cDNA was inserted into a plasmid encoding enhanced green fluorescent protein (pEGFP). Choriocarcinoma JEG-3 cells were transfected with either pEGFP or pEGFP-GRA15(II) and cultured for 24 h. Cell apoptosis and endoplasmic reticulum stress (ERS) responses were assessed. Inhibitors targeting inositol-requiring kinase 1 alpha (IRE1 alpha; 4 mu 8C, 100 nM) or c-Jun N-terminal kinase (JNK; SP6000125, 20 mu M) were added 12 h after plasmid transfection, followed by testing the effect of GRA15(II) on ERS. Results: When compared to pEGFP, pEGFP-GRA15(II) transfection facilitated cell apoptosis (P < 0.05), increased mRNA expression of caspase-3, caspase-4, 78-kDa glucose-regulated protein (GRP78), C/EBP homologous protein (CHOP) and X-box binding protein-1 (XBP1) (all P < 0.05), and promoted protein expression of cleaved caspase-3, cleaved poly(ADP-ribose) polymerase, Bax, CHOP, GRP78, phospho-JNK, and phospho-IRE1 alpha (all P < 0.05). The 4 mu 8C and SP6000125 decreased apoptosis and protein expression of XBP1s, CHOP, TNF receptor-associated factor 2 (TRAF2), phosphorylated apoptosis signal-regulating kinase 1 (ASK1), cleaved caspase-3, phospho-JNK, and Bax (all P < 0.05) in pEGFP-GRA15(II) transfected cells. Conclusions: Toxoplasma GRA15(II) induced ERS and subsequently caused apoptosis of choriocarcinoma JEG-3 cells.