EXPRESSION CLONING OF A CDNA-ENCODING THE MURINE INTERLEUKIN-4 RECEPTOR BASED ON LIGAND-BINDING

Interleukin 4 (IL-4) is a potent mediator of growth and differentiation for various lymphoid and myeloid cells. To isolate a cDNA encoding the murine IL-4 receptor, we have developed an expression cloning method that uses biotinylated ligand as a probe and that may be generally applicable to cloning of receptor genes. COS-7 cells transiently transfected with the cloned full-length cDNA bind murine IL-4 specifically with a K(d) = 165 pM. Crosslinking of 125I-labeled IL-4 to COS-7 cells transfected with the cDNA reveals binding to proteins of 120-140 kDa. IL-4-responsive cells also express IL-4-binding proteins of 120-140 kDa but show additional bands at 60-70 kDa; the relationship of the smaller proteins to the larger ones is unclear. The nucleotide sequence indicates that the full-length cDNA encodes 810 amino acids including the signal sequence. While no censensus for protein kinases is present in the cytoplasmic domain, a sequence comparison with the erythropoietin receptor, the IL-6 receptor, and the β chain of the IL-2 receptor reveals a significant homology in the extracellular domain, indicating that the IL-4 receptor is a member of the cytokine receptor family.