BANK1 interacts with TRAF6 and MyD88 in innate immune signaling in B cells

Abstract

Evidence supports a possible role of BANK1 in innate immune signaling in B cells. In the present study, we investigated the interaction of BANK1 with two key mediators in interferon and inflammatory cytokine production, TRAF6 and MyD88. We revealed by coimmunoprecipitation (CoIP) analyses the binding of BANK1 with TRAF6 and MyD88, which were mediated by the BANK1 Toll/ interleukin-1 receptor (TIR) domain. In addition, the natural BANK1-40C variant showed increased binding to MyD88. Next, we demonstrated in mouse splenic B cells that BANK1 colocalized with Toll-like receptor (TLR) 7 and TLR9 and that after stimulation with TLR7 and TLR9 agonists, the number of double-positive BANK1-TLR7, -TLR9, -TRAF6, and -MyD88 cells increased. Furthermore, we identified five TRAF6-binding motifs (BMs) in BANK1 and confirmed by point mutations and decoy peptide experiments that the C-terminal domain of BANK1-full-length (-FL) and the N-terminal domain of BANK1-Delta2 (-D2) are necessary for this binding. Functionally, we determined that the absence of the TIR domain in BANK1-D2 is important for its lysine (K)63linked polyubiquitination and its ability to produce interleukin (IL)-8. Overall, our study describes a specific function of BANK1 in MyD88-TRAF6 innate immune signaling in B cells, clarifies functional differences between the two BANK1 isoforms and explains for the first time a functional link between autoimmune phenotypes including SLE and the naturally occurring BANK1-40C variant.

Immunogenetics in systemic lupus erythematosus: Transitioning from genetic associations to cellular effects

“…BANK1 participates in the MyD88‐TRAF6‐signalling complex that is important for TLR signalling and type I IFN production 81,82 . A low‐frequency coding BANK1 variant (MAF < 2%) with impaired repression of TRAF6‐mediated IRF5 nuclear localization and type I IFN production was recently identified 76 .…”

Connection of BANK1, Tolerance, Regulatory B cells, and Apoptosis: Perspectives of a Reductionist Investigation

“…Inhibition of BANK1 expression by siRNA is associated with a decrease of apoptosis, suggesting that BANK1 display a pro-apoptotic function ( 39 ), in accordance, with higher level of apoptosis in B cells from tolerant patients. Finally, BANK1 interacts directly with MyD88 and TRAF6, two major actors of TLR signaling ( 54 ) and controls TLR7-mediated type I IFN production and STAT1 activation ( 55 ), fitting with the decrease of TLR signaling observed in cells from tolerant patients ( 56 ). We found literature associations of FcγRIIb, STAT1, TNFAIP3 and BCR signaling ( 57 – 60 ) and we have previously shown an increased level of FcγRIIb in blood from tolerant recipients ( 56 ).…”

“…Among these diseases, systemic lupus erythematosus (SLE) is the most studied. Thus, functional variants of BANK1 are associated with SLE ( 52 , 54 , 61 – 63 ), rheumatoid arthritis ( 64 ), diffuse cutaneous systemic sclerosis ( 65 , 66 ), multifocal motor neuropathy ( 67 ), type I diabetes ( 68 ), autoimmune thyroid disease ( 69 ), B cell lymphoma ( 70 ), LDL cholesterol ( 71 ), psoriasis ( 72 ), primary Sjogren’s syndrome ( 73 ), polymyositis/dermatomyositis ( 74 ), and systemic sclerosis ( 75 ), pointing an important functional role for BANK1 in immune system, without, however explaining its role.…”

Negative Regulation of TLR Signaling by BCAP Requires Dimerization of Its DBB Domain

“…BANK1 DBB domain dimerization also provides a mechanism of regulating the relative activity of BANK1 isoforms with and without the TIR domain. It was recently shown that the strength of TIR domain interactions between BANK1 and MyD88 is linked to several autoimmune phenotypes, including SLE (37). DBB domain dimerization likely regulates this TIR domain activity through the formation of BANK1 heterodimers composed of the full-length protein and isoform lacking the TIR domain (BANK1-D2).…”