A Functional Intronic Variant In The GTF2I Gene Confers Risk For Primary Sj(?)gren's Syndrome

Primary Sj(?)gren's syndrome(pSS)is a chronic and systemic autoimmune disease characterized by T and B lymphocytes infiltration,which can lead to dry mouths(xerostomia)and dry eyes(xerophthalmia)as a result of the destruction of the exocrine glands,and multi-organ disorders,such as kidneys,lungs and vessels.The pathogenesis of the pSS is still unclear,while the genetic tendency has been implicated as an important factor.A genome-wide association study published in 2013 demonstrated that,among all the susceptible genes associated with pSS,GTF2IRD1-GTF2 I loci is specific to Chinese Han population,and the rs117026326 in the intron of GTF2 I gene had the most significant association with pSS by meas of fine mapping.The objective of this study: to evaluate the association between the SNP of GTF2IRD1-GTF2 I gene and the susceptibility of pSS in the Chinese Han population and to explore the role of GTF2 I gene in the pathogenesis of pSS and potential mechnisms of pSS susceptibility.Methods are as follows: Genotyping of SNP rs117026326(GTF2I),rs112502846(GTF2IRD1-GTF2I),and rs113066392(GTF2IRD 1-GTF2)was performed in 603 pSS cases and 1204 matched healthy controls who all belong to northern Chinese Han population by Taqman SNP genotyping assay and Sanger Seqencing.Four more SNPs(in LD with rs112502846)with their genotyping results were imputed.The association of these seven SNPs with the susceptibility of pSS,as well as the antibodies,were analyzed.The expression levels of GTF2 I,GTF2I isoforms and its downstream gene c-fos in PBMC from patients and healthy controls were evaluated using real-time PCR,and their association with SNP rs117026326 were detected.The regulatory roles of different GTF2 I isoforms in the expression of c-fos gene were investigated by the overexpression of different isoforms in HEK-293 T cell line.The results are as follows,all the seven SNPs in the GTF2IRD1-GTF2 I loci were in LD,and associated with pathogenesis of pSS in north Chinese Han population(P < 5×10-5).The seven SNPs belonged to the only one independent association signal at GTF2IRD1-GTF2 I loci analyzed by the Conditional logistic regression analysis(Online Methods),and had significant association with both antibody positive and antibody negative pSS.The expression level of GTF2 I gene in PBMC of the patients was higher than that in healthy controls(P < 0.001),but not in association with rs117026326 genotype in both populations(P > 0.05);while that of its isoforms,GTF2I? and GTF2I?,as well as its downstream gene c-fos is significantly associated with rs117026326 genotype.In patients,the expression level of c-fos gene in those with C/C allele was lower than those with T/T risk allele(P < 0.05).GTF2I? could significantly increase the m RNA expression of c-fos gene than GTF2I? in HEK-293 T cells overexpressing these two isoforms(P < 0.05).According to the results above,we can draw the following conclusions: GTF2IRD1-GTF2 I loci is the susceptible gene of pSS in north Chinese Han population.SNP rs117026326 was associated with the m RNAexpression levels of GTF2I?/GTF2I?,which may indicate its possible role in the pre-m RNA splicing of the GTF2 I gene.SNP rs117026326 T risk allele could increase the m RNA expression level of GTF2I? gene,activate the downstream c-fos gene,further stimulate intracellular chronic inflammatory response,and result in the pathogenesis of pSS ultimately.