cDNA cloning and characterization of the human interleukin 13 receptor alpha chain

We have cloned cDNAs corresponding to the human interleukin 13 receptor alpha chain (IL-13R alpha). The protein has 76% homology to murine IL-13R alpha, with 95% amino acid identity in the cytoplasmic domain. Only weak IL-13 binding activity was found in cells transfected with only IL-13R alpha; however, the combination of both IL-13R alpha and IL-4R alpha resulted in substantial binding activity, with a K-d of approximately 400 pM, indicating that both chains are essential components of the IL-13 receptor. Whereas IL-13R alpha serves as an alternative accessory protein to the common cytokine receptor gamma chain (gamma(c)) for IL-4 signaling, it could not replace the function of gamma(c) in allowing enhanced IL-2 binding activity. Nevertheless, the overall size and length of the cytoplasmic domain of IL-13R alpha and gamma(c) are similar, and like gamma(c), IL-13R alpha is located on chromosome X.