Identification of a Sjögren's syndrome susceptibility locus at OAS1 that influences isoform switching, protein expression, and responsiveness to type I interferons

Abstract

Sjögren’s syndrome (SS) is a common, autoimmune exocrinopathy distinguished by keratoconjunctivitis sicca and xerostomia. Patients frequently develop serious complications including lymphoma, pulmonary dysfunction, neuropathy, vasculitis, and debilitating fatigue. Dysregulation of type I interferon (IFN) pathway is a prominent feature of SS and is correlated with increased autoantibody titers and disease severity. To identify genetic determinants of IFN pathway dysregulation in SS, we performed cis-expression quantitative trait locus (eQTL) analyses focusing on differentially expressed type I IFN-inducible transcripts identified through a transcriptome profiling study. Multiple cis-eQTLs were associated with transcript levels of 2'-5'-oligoadenylate synthetase 1 (OAS1) peaking at rs10774671 (PeQTL = 6.05 × 10−14). Association of rs10774671 with SS susceptibility was identified and confirmed through meta-analysis of two independent cohorts (Pmeta = 2.59 × 10−9; odds ratio = 0.75; 95% confidence interval = 0.66–0.86). The risk allele of rs10774671 shifts splicing of OAS1 from production of the p46 isoform to multiple alternative transcripts, including p42, p48, and p44. We found that the isoforms were differentially expressed within each genotype in controls and patients with and without autoantibodies. Furthermore, our results showed that the three alternatively spliced isoforms lacked translational response to type I IFN stimulation. The p48 and p44 isoforms also had impaired protein expression governed by the 3' end of the transcripts. The SS risk allele of rs10774671 has been shown by others to be associated with reduced OAS1 enzymatic activity and ability to clear viral infections, as well as reduced responsiveness to IFN treatment. Our results establish OAS1 as a risk locus for SS and support a potential role for defective viral clearance due to altered IFN response as a genetic pathophysiological basis of this complex autoimmune disease.

Recurrent loss-of-function mutations reveal costs to OAS1 antiviral activity in primates

“…While p42, p46, and p48 are robustly expressed, p44 and p52 protein levels are significantly decreased ( Figure 3B). Consistent with our results, a previous study failed to detect endogenous p44 and p52 isoforms in primary human cells 33 . To ensure the lack of RNase L activation is due to lowered expression, we directly tested enzymatic activity in vitro using equimolar amounts of full length purified protein ( Figure S3B).…”

“…In some cases, common genetic variants in key mediators of cellular immunity lead to partial or complete loss of protein function and can also be associated with disease. The human OAS1 variant associated with lower in vivo 2-5A levels is also associated with increased risk of infection with West Nile virus 44 and development of Sjörgens syndrome 33 , an autoimmune disease associated EBV and CMV infection. Despite these risks, the allele resulting in production of unstable OAS1 isoforms rose to near fixation in ancient African populations, proceeded by reintroduction of the ancestral high activity allele via introgression from Neandertals to non-African populations [45][46][47] .…”

Characteristics of Human OAS1 Isoform Proteins

“…In the present study, comparison of the expression efficiencies of different hOAS1 isoforms indicated that the p42 and p46 isoforms were expressed at much higher levels in HEK293 cells than the other isoforms tested, suggesting that these two isoforms may have a higher stability in a mammalian cell. A recent study also showed that p44 and p48 were expressed at lower levels compared to p42 and p46 after transfection of HEK 293 cells, even though the mRNA levels for all of the isoforms were similar [24]. Sequential truncation of the C-terminal ends of p44 and p48 resulted in increased expression levels, indicating that the C-terminal regions are responsible for the decreased stability of these two isoforms.…”

“…In another study, although the transcript levels for Xpress tagged p42, p44, p46 and p48 were equivalent in HEK 293T cells after 48 h of expression, p44 and p48 had impaired protein expression compared to p42 and p46. Also, only endogenous p42, p46 and p48 were detected at the protein level in non-transfected cells [24]. To analyze isoform-specific synthetase activity, HEK293 cells were transfected with an hOAS1 isoform cDNA (1 µg of plasmid DNA) and 24 h later, cells were either mock-or poly(I:C)-transfected for 6 h. Total intracellular RNA was then extracted and separated on a denaturing agarose gel to detect cellular rRNA cleavage by activated RNase L. Surprisingly, the most efficiently expressed isoforms (p42 and p46) both activated RNase L cleavage, as indicated by the additional bands detected below the 18S and 28S rRNA bands in the absence of poly(I:C) transfection ( Figure 3B).…”

Oral epithelial membrane‐associated mucins and transcriptional changes with Sjögren's syndrome

“…For example, evidence indicates reduced glycosylation and alterations in sialylation or sulfation of secreted salivary MUC5B and MUC7 in pSS patients (Alliende et al, 2008;Chaudhury, Proctor, Karlsson, Carpenter, & Flowers, 2016). Additionally, altered RNA splicing in pSS (Li et al, 2017) may produce MAM isoforms with reduced Ser/Thr-rich tandem repeats, decreasing potential glycosylation sites. It is well established that MAM expression, in vitro, can be altered in response to inflammatory cytokines (Dhanisha, Guruvayoorappan, Drishya, & Abeesh, 2018).…”