RECONSTITUTION OF THE FUNCTIONAL RECEPTORS FOR MURINE AND HUMAN INTERLEUKIN-5

The murine interleukin 5 receptor (mIL-5R) is composed of two distinct subunits, alpha and beta. The alpha subunit (mIL-5Ralpha) specifically binds IL-5 with low affinity. The beta subunit (mIL-5Rbeta) does not bind IL-5 by itself, but forms the high-affinity receptor with mIL-5Ralpha. mIL-5Rbeta has been revealed to be the mIL-3R-like protein, AIC2B which is shared with receptors for IL-3 and granulocyte/macrophage colony-stimulating factor. We demonstrated here the reconstitution of the functional receptors for murine and human IL-5 on the mouse IL-2-dependent cell line, CTLL-2. CTLL-2 was transfected with the cDNAs for mIL-5Ralpha and/or AIC2B. Only CTLL-2 transfectant expressing both mIL-5Ralpha and AIC2B expressed the high-affinity receptor and proliferated in response to murine IL-5. Then CTLL-2 was transfected with the cDNAs for hIL-5Ralpha and/or KH97 (beta(c)), the human homologue of AIC2B. Though beta(c) did not contribute much to binding affinity of hIL-5R, only CTLL-2 transfectant expressing both hIL-5Ralpha and beta(c) proliferated in response to human IL-5. These results showed that the beta subunit is indispensable in IL-5 signal transduction. We further investigated the function of IL-5-specific alpha subunit in transmitting IL-5 signals. Mutant mIL-5Ralpha, which lacks its whole cytoplasmic domain, was transfected into mouse IL-3-dependent cell line, FDC-P1 expressing AIC2B intrinsically. The resulting transfectant did not respond to IL-5, though the transfectant expressed the high-affinity IL-5R, indicating that the cytoplasmic portion of the alpha subunit also has some important role in IL-5-mediated signal transduction.