FRI0012 Pronounced SYK phosphorylation and TRAF6 overexpression in B cells correlating with the activity of systemic lupus erythematosus
Authors: S. Iwata, K. Yamaoka, H. Niiro, K. Nakano, S.-P. Wang, K. Akashi, Y. Tanaka
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> B cells play a pivotal role in the pathological processes of SLE. We have reported that marked increase of activated memory B cells was observed in refractory SLE patients. Although the efficacy of B cell-targeted therapy such as rituximab has been undeartaken, clinical trials treating SLE with rituximab have failed and a novel strategy is prerequisite. Spleen tyrosine kinase (Syk) is a key molecule in B-cell receptor (BCR)-mediated signaling. We have recently reported that Syk-mediated BCR-signaling is prerequisite for optimal induction of TNF receptor-associated factor (TRAF)6, thereby allowing efficient propagation of CD40- and TLR9- signaling in human B cells in vitro. However, the underlying mechanism of Syk and TRAF6 in autoimmune diseases remains unclear. <h3>Objectives</h3> The aim of this study was to clarify the molecular mechanism of Syk and TRAF6 in B cell activation, differentiation and its relevance to SLE pathology. <h3>Methods</h3> PBMCs were isolated from healthy donors (n=27) and SLE patients (n=58). Phosphorylation and/or expression of Syk and TRAF6 in naïve (CD19<sup>+</sup>CD27<sup>-</sup>) and memory (CD19<sup>+</sup>CD27<sup>+</sup>) B cells were analysed by flow cytometry. A Syk specific inhibitor (BAY61-3606) was utilized for in vitro analysis and the disease activity of SLE was measured by SLEDAI. <h3>Results</h3> Syk was pronouncedly expressed and phosphorylated in peripheral B cells from SLE patients, compared to those from healthy donors, even without in vitro stimulation. The levels of Syk phosphorylation and ratio of phospho-Syk/Syk were significantly correlated with SLEDAI. Recently, we have reported that TRAF-6 is a common key molecule activated at downstream of BCR-mediated signaling in vitro. The TRAF6 expression level was also increased in SLE patients with a positive correlation with disease activity. It is noteworthy that TRAF6 expression strongly correlated with the ratio of phospho-Syk/Syk, suggesting that unabated Syk phosphorylation up-regulated TRAF6 expression in patients with active disease. The expression level of TRAF6 was higher in memory B cells compared to those in naïve B cells and the percentage of TRAF6-positive B cells significantly correlated with the abundance of memory B cells among total B cells in SLE patients. In vitro culture of SLE B cells with a Syk inhibitor reduced the level of phosphorylated Syk as well as TRAF6 expression. <h3>Conclusions</h3> Our current results suggest that Syk-mediated TRAF6 signal transduction is activated in SLE patients, in relation to the disease activity. In addition, we suggest that the Syk-mediated TRAF6 pathway leads to unabated activation and differentiation of pathogenic memory B cells in SLE. Therefore, we underscore the potential role of Syk in B-cell-mediated pathological processes in autoimmune disease such as SLE. Furthermore, inhibition of Syk has a potential to adequately control the disease activity of SLE by regulating pathogenic memory B cells. <h3>Disclosure of Interest</h3> S. Iwata: None Declared, K. Yamaoka: None Declared, H. Niiro: None Declared, K. Nakano: None Declared, S.-P. Wang: None Declared, K. Akashi: None Declared, Y. Tanaka Consultant for: Dr. Tanaka has received consulting fees, speaking fees, and/or honoraria from Mitsubishi-Tanabe Pharma, Chugai Pharma, Eisai Pharma, Pfizer, Abbott Immunology Pharma, Daiichi-Sankyo, Janssen Pharma, Astra-Zeneca, Takeda Industrial Pharma, Astellas Pharma, Asahi-kasei Pharma and GlaxoSmithKline and has received research grant support from Mitsubishi-Tanabe Pharma, Bristol-Myers Squibb, Takeda Industrial Pharma, MSD, Astellas Pharma, Eisai Pharma, Chugai Pharma, Pfizer and Daiichi-Sankyo.