Recombinant Canine TNF RI/TNFRSF1A Protein

TNF receptor 1 (TNF RI; also called TNF R-p55/p60, TNFRSF1A and CD120a) is a type I transmembrane protein that belongs to the TNF receptor superfamily (1, 2). TNF RI is widely expressed and is present on the cell surface as a trimer of 55 kDa subunits. It serves as a receptor for both TNF-alpha and TNF-beta /lymphotoxin. Each subunit contains four TNF-alpha trimer-binding cysteine-rich domains (CRD) in its extracellular domain (ECD) (1 - 6). TNF-alpha binding to TNF R1 induces the sequestration of TNF RI in lipid rafts, where it activates NF kappaB and is cleaved by ADAM-17/TACE (7, 8). Release of the 28 - 34 kDa TNF RI ECD occurs constitutively, and in response to products of pathogens such as LPS, CpG DNA or S. aureus protein A (1, 7 - 12). Full-length TNF RI may also be released in exosome-like vesicles (12). This release helps to resolve inflammatory reactions as it down-regulates cell surface TNF RI and provides soluble TNF RI to bind TNF-alpha (6, 13, 14). Exclusion from lipid rafts causes endocytosis of TNF RI complexes and induces apoptosis (7, 15). Although there is a second receptor for TNF-alpha (TNF R2), TNF RI is thought to mediate most of the cellular effects of TNF-alpha (3). TNF R1 is essential for proper development of lymph node germinal centers and Peyer’s patches, and for combating intracellular pathogens such as Listeria monocytogenes (1 - 3). Canine TNF RI is a 452 amino acid (aa) protein (16). Based on human, its ECD will contain a PLAD domain that mediates constitutive trimer formation (6). The PLAD domain will be followed by four CRDs, a transmembrane domain, and a cytoplasmic sequence that contains a neutral sphingomyelinase activation domain and a death domain. The ECD of canine TNF RI shows approximately 87%, 75%, 80%, 66% and 67% aa identity with feline, porcine, human, rat and mouse TNF RI, respectively.