IL-20 receptor beta (IL-20 R beta ), also known as IL-20 R2, is a type I transmembrane glycoprotein in the class II cytokine receptor family. These receptors are characterized by tandem fibronectin type III domains in their extracellular region and the lack of a WSXWS motif (1). Class II cytokine receptors form heterodimeric signaling receptor complexes that mediate class II cytokine signals. Subunits of the different receptor complexes are shared and serve multiple functions (1). Based on the structure of the human receptor, mouse IL-20 R beta should contain a 202 amino acid (aa) extracellular domain (ECD) with two fibronectin type III domains, a 16 aa transmembrane segment, and a 44 aa cytoplasmic domain (2). Within the ECD, mouse IL-20 R beta will share 81% aa sequence identity with human IL-20 R beta. It shares 18-29% aa sequence identity with the mouse class II cytokine receptors IFN-alpha R1, IFN-alpha R2, IFN-gamma R1, IFN-gamma R2, IL-10 R alpha, IL-10 R beta, IL-20 R alpha, IL-22BP, IL-22 R alpha, IL-28 R, and tissue factor. IL-20 R beta is generally expressed in psoriatic skin (keratinocytes and select endothelium), rheumatoid arthritis synovial membranes, and hepatocytes of LPS-treated mice, and it contributes to the local inflammatory reaction (3-6). IL-20 R beta heterodimerizes with IL-20 R alpha to form the receptor complex that mediates IL-19, IL-20, and IL-24 signals (3, 7-10). It also heterodimerizes with IL-22 R to form the functional receptor complex for IL-20 and IL-24 (7-9). Binding of these IL-10 family class II cytokines to their receptors induces activation of the JAK-STAT signal transduction pathway.
