Toll-like receptor 3 stimulation promotes Ro52/TRIM21 synthesis and nuclear redistribution in salivary gland epithelial cells, partially via type I interferon pathway

Abstract

SummaryUp-regulated expression of Ro52/tripartite motif-containing protein 21 (TRIM21), Ro60/TROVE domain family, member 2 (TROVE2) and lupus LA protein/Sjögren's syndrome antigen B (La/SSB) autoantigens has been described in the salivary gland epithelial cells (SGEC) of patients with Sjögren's syndrome (SS). SGECs, the key regulators of autoimmune SS responses, express high levels of surface functional Toll-like receptor (TLR)-3, whereas Ro52/TRIM21 negatively regulates TLR-3-mediated inflammation. Herein, we investigated the effect of TLR-3-signalling on the expression of Ro52/TRIM21, as well as Ro60/TROVE2 and La/SSB autoantigens, by SGECs. The effect of TLR-3 or TLR-4 stimulation on autoantigen expression was evaluated by polyI:C or lipopolysaccharide (LPS) treatment, respectively, of SGEC lines (10 from SS patients, 12 from non-SS controls) or HeLa cells, followed by analysis of mRNA and protein expression. PolyI:C, but not LPS, resulted in a two-step induction of Ro52/TRIM21 mRNA expression by SGECs, a 12-fold increment at 6 h followed by a 2·5-fold increment at 24-48 h, whereas it induced a late two-fold up-regulation of Ro60/TROVE2 and La/SSB mRNAs at 48 h. Although protein expression levels were not affected significantly, the late up-regulation of Ro52/TRIM21 mRNA was accompanied by protein redistribution, from nucleolar-like pattern to multiple coarse dots spanning throughout the nucleus. These late phenomena were mediated significantly by interferon (IFN)-β production, as attested by cognate secretion and specific inhibition experiments and associated with IFN regulatory factor (IRF)3 degradation. TLR-3-signalling had similar effects on SGECs obtained from SS patients and controls, whereas it did not affect the expression of these autoantigens in HeLa cells. TLR-3 signalling regulates the expression of autoantigens by SGECs, implicating innate immunity pathways in their over-expression in inflamed tissues and possibly in their exposure to the immune system.

Interaction between innate immunity and Ro52-induced antibody causes Sjögren's syndrome-like disorder in mice

“…28 In addition, expression and location of Ro52 in different cellular compartments have been modulated by activation of innate immunity through toll-like receptor 3 (TLR3), interferon-alpha (IFN-α) and nitric oxide. [29][30][31] In NZM2758 mice, we observed that alum treatment caused significant upregulation of circulating KC, IL-1α, MIG, MIP2 and PDGF-β (see online supplementary figure S5). At present it is unclear as to how these cytokines influence antibody-mediated SG dysfunction.…”

Cutting Edge: Commensal Microbiota Has Disparate Effects on Manifestations of Polyglandular Autoimmune Inflammation

“…GF animals are free of viruses except endogenous retroviruses, which have been shown to stimulate MyD88 pathway through toll-like receptor (TLR)-7 (34). In SPF mice other viruses may contribute to sialitis even in MyD88-independent manner: stimulation of MyD88-independent TLR3, which is highly expressed on the surface of salivary gland epithelial cells from Sjögren patients (35), by viral dsRNA is considered a likely contributor to Sjögren’s syndrome (36). …”

Innate immunity in Sjögren's syndrome

“…Further studies using human salivary epithelium support a role for TLR3 ligation in glandular apoptosis [84, 96]. Importantly, activation of TLR3 expressed by SGECs induces secretion of BAFF and promotes the synthesis of Ro52, an autoantigen included in the diagnostic criteria for SS [97–99]. Data from mouse models and SS patients show that both local and systemic BAFF expression is integral to SS pathogenesis.…”