The immunobiology of Ro52 (TRIM21) in autoimmunity: a critical review

Ro52 is a common target of circulating autoantibodies in autoimmune disease. Data indicate that anti-Ro52 antibodies are associated with distinct clinical manifestations. It is therefore of major interest to understand how it becomes an antigenic target and what cells express this protein under what conditions and what cellular function it has. Ro52 contains a RING and a B-box motif, followed by a coiled-coil domain and a B30.2 (or PRYSPRY) region in the C-terminal end. This molecular structure places Ro52 within the family of tripartite motif proteins (TRIM), and it is also denoted TRIM21. Like several other TRIM proteins, Ro52 has E3 ligase activity and functions in the process of ubiquitination. Ro52 is expressed in the immune system as a predominantly cytoplasmic protein that can be upregulated and translocate to the nucleus in a proinflammatory environment. Reported substrates for Ro52-mediated ubiquitination include IRF3, IRF5, IRF7 and IRF8, and via these transcription factors Ro52 regulates type 1 interferon and cytokine production. Ro52 is upregulated at the site of autoimmune inflammation, such as cutaneous lupus lesions. This implies that Ro52 may have an important role in the pathogenesis of autoimmunity, and this paper will review the available data on the role of Ro52 in immune responses and autoimmune pathogenesis.