Role of C6ORF120, an N-glycosylated protein, is implicated in apoptosis of CD4⁺ T lymphocytes.

Background: Although CD4(+) T cell apoptosis and CD8(+) T cell responses have been extensively studied during HIV infection, how apoptosis signals being initiated in CD4(+) T cells still need to be elucidated. The present study was designed to characterize the function-unknown gene, C6orf120, and elucidates its primary role in tunicamycin-induced CD4(+) T apoptosis.

Methods: The C6orf120 coding sequence was amplified from peripheral blood mononuclear cells (PBMCs) total RNA of AIDS patients. The DNA fragment was inserted into the pET-32a expression system, transformed into Escherichia coli, and preparation of C6ORF120 recombinant protein. The magnetic cell separation technology was used to prepare primary CD4(+) T cells and CD8(+) T cells. The primary T cells were cultured at 1 × 10(6) cells/ml, treated with 0, 0.1, 1, 10, 100, and 200 ng/ml of C6orf120 recombinant protein for 48 hours, then harvested for cell cycle and apoptosis analysis. Tunicamycin (0.5 µmol/L) was used to induce endoplasmic reticulum stress in Jurkat cells. The biomarker 78 KDa glucose-regulated protein (GRp78) and growth arrest and DNA damage (GADD) were used to evaluate endoplasmic reticulum stress of Jurkat cells.

Results: We prepared C6ORF120 recombinant protein and its polyclonal antibody. Immunohistochemical analysis showed that C6orf120 mainly expressed in hepatocytes and cells in germinal center of lymph node. At concentration of 0.1, 1, 10, 100, and 200 ng/ml, C6orf120 recombinant protein could induce apoptosis of Jurkat cells and primary CD4(+) T cells, and promoting G2 phase of its cell cycle. Western blotting analysis showed that C6ORF120 recombinant protein increased the expression of GRp78 and GADD in Jurkat cells in vitro.

Conclusion: Our results suggested that C6ORF120 could induce apoptosis of CD4(+) T cells, at least in part, mediated with endoplasmic reticulum stress.