EF-hand, extracellular calcium-binding (EC) motif, found in follistatin-related protein 1 (FRP-1)
FRP-1, also termed follistatin-like protein 1 (fstl-1), TGF-beta-stimulated clone 36 (TSC-36/Flik), or TGF-beta inducible protein, is a secreted glycoprotein that is overexpressed in certain inflammatory diseases and has been implicated in many autoimmune diseases. FRP-1 functions as an important proinflammatory factor in the pathogenesis of osteoarthritis (OA) by activating the canonical NF-kappaB-mediated inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta) and interleukin-6 (IL-6), and enhancing fibroblast like synoviocytes proliferation. It also acts as a critical mediator of collagen-induced arthritis (CIA), juvenile rheumatoid arthritis (JRA), as well as Lyme arthritis observed after Borrelia burgdorferi infection. Meanwhile, it enhances nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome-mediated IL-1beta secretion from monocytes and macrophages. Moreover, FRP-1 shows critical functions in the nervous system. It differentially regulates transforming growth factor beta (TGF-beta) and bone morphogenetic protein (BMP) signaling, leading to epithelial injury and fibroblast activation. Furthermore, FRP-1 functions as a cardiokine with cardioprotective properties. It may play a potential role in ischemic stroke through decreasing neuronal apoptosis and improving neurological deficits via disco-interacting protein 2 homolog A (DIP2A)/Akt pathway after middle cerebral artery occlusion (MCAO). Plasma FRP-1 is elevated in Kawasaki disease (KD) and thus may play a possible role in the formation of coronary artery aneurysm (CAA). FRP-1 contains a follistatin-like (FS) domain, an extracellular calcium-binding (EC) domain including a pair of EF hands, and a von Willebrand factor type C (VWC) domain. The EC domain does not undergo characteristic structural changes upon calcium addition or depletion and therefore is not a functional calcium binding domain.
Jiyao W et al.(2023). "The conserved domain database in 2023.",