Background/Purpose: T cells from patients with systemic lupus erythematosus (SLE) produce insufficient amounts of the vital cytokine IL-2, and the molecular mechanisms leading to this defect are not fully known. IL-2 deficiency is critical in autoimmunity, because it is not only important for T cell responses but also for the maintenance and function of regulatory T cells (Tregs). We previously identified a novel role of the multifunctional protein serine arginine-rich splicing factor 1 (SRSF1) in the regulation of IL-2. We showed that SRSF1 is decreased in T cells from SLE patients, and associates with severe disease activity. Importantly, force expression of SRSF1 into SLE T cells rescues IL-2 production. We showed that SRSF1 enhances IL-2 production via transcriptional activation, however the molecular mechanisms underlying this regulation are not fully known. SLE T cells exhibit aberrant expression/function of the IL-2 regulating transcription factors NFκB, c-jun/c-fos (AP1) and NFAT. Here we asked whether SRSF1 controls IL-2 through the regulation of these factors.

Methods: T cells were isolated by negative selection from peripheral blood from healthy donors. SRSF1 was overexpressed in human T cells by transient transfection. T cell-restricted conditional Srsf1-cko mice were generated by crossing Srsf1-flox mice with d.Lck.Cre mice. Expression levels of NFAT, c-fos, and NFκB were assessed by quantitative RT-PCR and western blotting. To determine the recruitment of transcription factors to the IL-2 promoter, reporter-chromatin immunoprecipitation (R-ChIP) assays were performed in human T cells by transfection of an IL-2-promoter luciferase construct and SRSF1 overexpression. Cross-linked DNA-protein complexes were immunoprecipitated with appropriate antibodies, and purified DNA was amplified by quantitative PCR. T cells were stimulated with anti-CD3/CD28 or PMA and Ionomycin, and IL-2 production measured by intracellular cytokine staining and ELISA.

Results: Overexpression of SRSF1 enhanced IL-2 expression in human T cells. Further, SRSF1 overexpression led to increased mRNA and protein levels of NFAT and c-fos but not NFκB. In parallel, T cells from Srsf1-cko mice produced lower amounts of IL-2 and showed decreased expression levels of NFAT after stimulation with anti-CD3/CD28. To ask if SRSF1 affects the recruitment of NFAT and c-fos to the IL-2 promoter, R-ChIP assays were performed using SRSF1-transfected human T cells. An increased recruitment of NFAT and c-fos to the IL-2 promoter was observed in SRSF1-transfected compared to control-transfected cells. These results indicate that SRSF1 increases expression of NFAT and c-fos and their recruitment to the IL-2 promoter to increase transcriptional activity of IL-2.

Conclusion: SRSF1 increases the expression of NFAT and c-fos transcription factors to activate IL-2 production. These results suggest that decreased SRSF1 represents an important molecular defect which contributes to the IL-2 deficiency in SLE.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/serine-argininerich-splicing-factor-1-srsf1-increases-il-2-production-in-t-cells-by-increasing-the-expression-of-nfat-and-c-fos/