Overexpression of the growth arrest and DNA damage-induced 45alpha gene contributes to autoimmunity by promoting DNA demethylation in lupus T cells

Abstract

Objective: Demethylation of CD11a and CD70 regulatory regions in CD4+ T cells contributes to the development of autoreactivity and overstimulation of autoantibodies. Because growth arrest and DNA damage-induced 45alpha (GADD45alpha) reduces epigenetic silencing of genes by removing methylation marks, this study examined whether the gadd45A gene could contribute to autoimmunity by promoting DNA demethylation in T cells from patients with systemic lupus erythematosus (SLE).

Methods: Levels of GADD45alpha, CD11a, and CD70 messenger RNA (mRNA) and protein were detected by real-time reverse transcription-polymerase chain reaction and Western blotting or flow cytometry. Global DNA methylation was evaluated using Methylamp global DNA methylation quantification kits. Detection of CD4+ T cell proliferation and autologous B cell IgG antibodies was performed using commercially available kits. CD11a and CD70 promoter methylation was determined with bisulfite sequencing.

Results: Elevated gadd45A mRNA expression and global DNA hypomethylation were observed in CD4+ T cells from SLE patients. The levels of gadd45A mRNA were inversely proportional to the levels of DNA methylation. Positive correlations were found between gadd45A and CD11a/CD70 mRNA levels. Expression of gadd45A mRNA was increased in CD4+ T cells following ultraviolet B irradiation, and this was accompanied by increased levels of CD11a and CD70 mRNA. Moreover, increased expression of gadd45A, CD11a, and CD70 mRNA was accompanied by increased autoreactivity and excessive B cell stimulation in gadd45A-transfected CD4+ T cells. CD11a promoter methylation was also significantly reduced in transfected cells. Transfection of gadd45A small interfering RNA inhibited the autoreactivity of SLE CD4+ T cells and led to significant increases in the methylation levels of the CD11a and CD70 promoter regions.

Conclusion: These findings indicate that gadd45A may contribute to lupus-like autoimmunity by promoting DNA demethylation in SLE CD4+ T cells.