Risk Allele rs117026326-Mediated Alternative Splicing of GTF2I Promotes B Cell Proliferation in Primary Sjögren's Syndrome.

Objectives: Primary Sjögren's syndrome (pSS) is associated with a risk allele T of rs117026326 located at a potential splicing enhancer within the intronic region of general transcription factor II-I (GTF2I). This study aimed to explore the rs117026326-regulated alternative splicing of GTF2I and its role in B cell overactivation in pSS. Methods: GTF2I isoform expressions and rs117026326 genotypes of pSS peripheral blood mononuclear cells (PBMCs) were examined using quantitative PCR and Sanger sequencing, respectively. GTF2IΔ was overexpressed in B cells, T cells, and macrophages using plasmid transfection. Proliferation of B cells and T cells was determined using Cell Counting Kit-8 (CCK8) assay. CD4⁺ T cell differentiation was inspected using flow cytometry. Proinflammatory cytokine production of macrophages was investigated using quantitative PCR. c-FOS expression in GTF2IΔ-transfected B cells was tested by quantitative PCR, and proliferation of GTF2IΔ-transfected B cells treated with c-FOS siRNA or c-FOS inhibitor was interrogated using CCK8 assay. Results: pSS patients with risk allele of rs117026326 expressed higher levels of GTF2IΔ and GTF2Iζ isoforms. GTF2IΔ expression was correlated with serum immunoglobulin G (IgG). GTF2IΔ promoted B cell proliferation and upregulated c-FOS expression. Knocking down or inhibition of c-FOS reversed B cell proliferation driven by GTF2IΔ. Conclusion: pSS risk allele of rs117026326 modulates alternative splicing of GTF2I and upregulates GTF2IΔ isoform, which promotes B cell proliferation through enhancing binding and transcription of c-FOS.