Decreased Expression of Serine/Arginine‐Rich Splicing Factor 1 in T Cells From Patients With Active Systemic Lupus Erythematosus Accounts for Reduced Expression of RasGRP1 and DNA Methyltransferase 1

摘要

Objective T cells from systemic lupus erythematosus (SLE) patients have reduced protein levels of RasGRP1, a guanine nucleotide exchange factor for Ras, and increased transcript of alternatively spliced (AS) forms lacking exon 11. Serine/arginine‐rich splicing factor 1 (SRSF1) binds pre–messenger RNA (pre‐mRNA) to regulate AS forms of several genes, including CD3ζ in SLE T cells. This study was undertaken to assess whether SRSF1 controls the expression of RasGRP1 in T cells from patients with SLE. Methods We studied T cells from 45 SLE patients and 18 healthy subjects. Expression levels of SRSF1, wild‐type (WT) RasGRP1, and DNA methyltransferase 1?(DNMT1) were assessed by quantitative polymerase chain reaction. Direct binding of SRSF1 to exon 11 of RasGRP1 mRNA was evaluated with an oligonucleotide–protein pulldown assay. Healthy T cells and SLE T cells were treated with SRSF1‐specific small interfering RNA or SRSF1 expression vector, respectively, and then evaluated for mRNA/protein expression. Results SRSF1 expression levels were significantly lower in T cells from SLE patients compared to those from healthy subjects, and correlated inversely with disease activity and positively with levels of RasGRP1‐WT and DNMT1. SRSF1 bound directly to exon 11 of RasGRP1 mRNA. Silencing of SRSF1 in human T cells led to increased ratios of RasGRP1‐AS to RasGRP1‐WT and decreased levels of RasGRP1 protein, whereas overexpression of SRSF1 in SLE T cells caused recovery of RasGRP1, which in turn induced DNMT1/interleukin‐2 expression. Conclusion SRSF1 controls the alternative splicing of RasGRP1 and subsequent protein expression. Our findings extend evidence that alternative splicing plays a central role in the aberrant T cell function in patients with SLE by controlling the expression of multiple genes.