Moreover, although other C2 domains in conventional PKCs and SYT1 can function as Ca2+-binding sensors to facilitate the translocation of C2 domain-containing proteins to the plasma membrane35,57, PLCη2 and its C2 domain do not promote membrane translocation in response to increased cytosolic Ca2+ in RA FLSs. Here, SYT1 is linked to rheumatoid arthritis.