Response Gene to Complement-32 Expression Is Upregulated in Lupus T cells and Promotes IL-17A Expression

Abstract

RGC (Response Gene to Complement)-32 is a cell cycle regulator expressed in normal tissues, tumors and a variety of cell lines. RGC-32 is preferentially upregulated in murine Th17 cells and promotes their differentiation. Patients with Systemic Lupus Erythematosus (SLE) display increased serum levels, expanded frequency of IL-17 producing cells. Whether RGC-32 plays a role in human Th17 differentiation pathway and in Th17 abnormalities in lupus patients has not yet been investigated. RGC-32 mRNA expression was determined in CD4⁺ T cells stimulated under Th0, Th1, Th2, Th17 and Treg conditions and the effect of RGC-32 overexpression and silencing under Th17 conditions was determined by nucleofection. RGC-32 expression was evaluated by RT-PCR, flow cytometry and cDNA Array in PBMC from lupus patients vs controls. RGC-32 mRNA expression was upregulated by TCR stimulation and TGFβ, and was more robust under Th17 (3.2 ± fold) and Treg (2.6 ± 0.8 fold) vs. Th1 (1.3 ± 0.4 fold) and Th2 (1.8 ± 0.1 fold) conditions. Overexpression or silencing of RGC-32 in CD4⁺ T cells upregulated, respectively downregulated IL-17A transcript levels and protein secretion. RGC-32 mRNA and protein level was significantly increased in CD19⁺ B cells and CD3⁺ T from lupus patients compared to controls. These results suggest that RGC-32 promotes the differentiation of human Th17 cells. Furthermore, T cells from patients with SLE exhibit increased expression of RGC-32 compared to controls. These data support the idea that RGC-32 signaling may enhance disease expression in SLE by promoting abnormalities in the Th17 pathway and provide a compelling rationale for further investigating the therapeutic potential of blocking RGC-32 in SLE.