Usp7 Is Associated With Greater Disease Activity In Systemic Lupus Erythematosus Via Stabilization Of The Ifn Alpha Receptor

An improved understanding of the mechanism of interferon (IFN)alpha activation in systemic lupus erythematosus (SLE) is likely to aid the identification of effective therapeutic targets. Increasing evidence has indicated that the activity of IFN alpha is mediated by the interplay of ubiquitylation/deubiquitylation enzyme regulators. The present study identified the deubiquitylation enzyme ubiquitin-specific-processing protease 7 (USP7) as a critical regulator of the human IFN alpha-2 receptor (IFNAR1) protein levels. A co-immunoprecipitation assay was used to demonstrate that USP7 was physically associated with IFNAR1 in vivo. A glutathione S-transferase pull down assay revealed that USP7 interacted with IFNAR1 directly in vitro. Furthermore, USP7 may disassemble IFNAR1 dependent poly-ubiquitin chains and stabilize IFNAR1 in vivo. The activation effects of USP7 on the IFN alpha pathway were confirmed by reverse transcription-quantitative polymerase chain reaction and western blot analysis. Knockdown of USP7 expression consistently reduced the expression levels of signal transducer and activator of transcription (STAT)-1, STAT-2 and selected IFN-inducible genes, including IFN-induced protein with tetratricopeptide repeats 3, MX dynamin like GTPase 1 and 2'-5'-oligoadenylate synthetase 1. The present study demonstrated that USP7 was significantly overexpressed in 210 SLE patients compared with healthy controls. Furthermore, the association between USP7 levels, IFN scores, SLE disease activity index scores and anti-double stranded DNA were analyzed and, as expected, positive correlations were demonstrated, indicating that USP7 may be associated with SLE disease activity through the stabilization of IFNAR1.