Background/Purpose: RGC (Response Gene to Complement)-32 is a cell cycle regulator widely expressed in normal tissues including brain, kidney, spleen, thymus, multiple tumors and in a variety of cell lines. RGC-32 is localized in the cytoplasm and translocates to the nucleus upon upregulation by complement activation, growth factors and cytokines. RGC-32 is induced by TGFβ in fibroblasts, astrocytes and human renal proximal tubular cells and mediates TGFβ dependent profibrotic pathways. Depending on the cell type, physiological or pathological conditions, RGC-32 can either stimulate or suppress cell growth. We have shown that RGC-32 is preferentially upregulated in murine Th17 cells and promotes their differentiation in vitro and in vivo. Patients with Systemic Lupus Erythematosus (SLE) display increased serum levels, expanded frequency of IL-17 producing cells in blood and organs such as the kidney. Whether RGC-32 is expressed in human CD4⁺ T cells and whether it plays a role in the Th17 pathway abnormalities in lupus patients has not yet been investigated.

Methods: RGC-32 mRNA expression was first assessed with the Autoimmune Disease Profiling cDNA Array (BD Bioscience) spotted with cDNA from CD3⁺, CD19⁺ and CD14⁺ cells from 10 lupus patients and 10 controls. PBMC were obtained from 20 patients with lupus and 18 controls. RGC-32 expression was determined by RT-PCR and flow cytometry in CD4⁺ T cells and CD19⁺ B cells. RGC-32 expression in naïve CD4⁺ T cells from normal controls stimulated under Th1, Th2, Th17 and Treg conditions was determined by RT-PCR. RGC-32 overexpression and silencing was performed by nucleofection and the effect on IL-17A mRNA levels in CD4⁺ T cells under Th17 conditions was determined by RT-PCR.

Results: RGC-32 mRNA expression was significantly increased in CD19⁺ B cells, CD14⁺ monocytes and CD3⁺ T from lupus patients compared to controls. By intracellular staining, CD4⁺ and CD19⁺ cells SLE lupus patients display higher intracellular RGC-32 expression ex vivo (1.5± 0.5 fold and 1.9 ± 0.7 fold, respectively) as compared to controls. By RT-PCR, RGC-32 mRNA expression was significantly higher in CD4⁺ T cells from patients vs. controls. In vitro, RGC-32 mRNA expression increased upon TCR stimulation and was further increased by TGFβ in CD4⁺ T cells from healthy controls. Other cytokines such as IFNα, IL-1β, TNFα did not upregulate RGC-32 mRNA either alone or in combination with TCR stimulation. RGC-32 mRNA upregulation was more robust under Th17 (3.2 ± fold) and Treg (2.6 ± 0.8 fold) as compared to Th1 (1.3 ± 0.4 fold) and Th2 (1.8 ± 0.1 fold) conditions. Overexpression of RGC-32 in CD4⁺ T cells upregulated IL-17A mRNA expression while RGC-32 silencing significantly downregulated IL-17A transcript levels under Th17 polarizing conditions.

Conclusion: These results suggest that T cells from patients with SLE exhibit increased expression of RGC-32 compared to normal controls. In vitro, RGC-32 promotes the differentiation of human Th17 cells. 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.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/response-gene-to-complement-32-expression-is-upregulated-in-lupus-t-cells-and-promotes-il-17a-expression/