Cloning of the human IL-13R alpha 1 chain and reconstitution with the IL-4R alpha of a functional IL-4/IL-13 receptor complex

The human homologue of the recently cloned murine IL-13 binding protein (IL-13R alpha 1) was cloned from a cDNA library derived from the carcinoma cell line CAKI-1, The cloned cDNA encodes a 427 amino acid protein with tao consensus patterns characteristic of the hematopoietic cytokine receptor family and a short cytoplasmic tail, The human protein is 74% identical to the murine IL-13R alpha 1, and 27% identical to the human IL-13R alpha 2. CHO cells expressing recombinant hIL-13R alpha 1 specifically bind IL-13 (K-d approximate to 4 nM) but not IL-4. Coexpression of the cloned cDNA with that of IL-4R alpha resulted in a receptor complex that displayed high affinity for IL-13 (K-d approximate to 30 pM), and that allowed cross-competition of IL-13 and IL-4. Electrophoretic mobility shift assay showed that IL-13 and IL-4 were able to activate Stat6 in cells expressing both IL-4R alpha and IL-13R alpha 1, while no activation was observed in cells expressing either one or the other alone.