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