T oll‐like receptor 3 stimulation promotes Ro 52/ TRIM 21 synthesis and nuclear redistribution in salivary gland epithelial cells, partially via type I interferon pathway

Summary Up‐regulated expression of Ro 52/tripartite motif‐containing protein 21 ( TRIM 21), Ro60/TROVE domain family, member 2 ( TROVE 2) 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 S jögren's syndrome ( SS ). SGEC s, the key regulators of autoimmune SS responses, express high levels of surface functional Toll‐like receptor ( TLR)‐ 3, whereas Ro 52/ TRIM 21 negatively regulates TLR‐ 3‐mediated inflammation. Herein, we investigated the effect of TLR‐ 3‐signalling on the expression of Ro 52/ TRIM 21, as well as Ro 60/ TROVE 2 and La / SSB autoantigens, by SGEC s. The effect of TLR‐ 3 or TLR‐ 4 stimulation on autoantigen expression was evaluated by poly I : 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. Poly I : C , but not LPS , resulted in a two‐step induction of Ro 52/ TRIM 21 mRNA expression by SGEC s, 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 Ro 60/ TROVE 2 and La / SSB mRNA s at 48 h. Although protein expression levels were not affected significantly, the late up‐regulation of Ro 52/ TRIM 21 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 SGEC s 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 SGEC s, implicating innate immunity pathways in their over‐expression in inflamed tissues and possibly in their exposure to the immune system.