Characterization of receptors for human colony-stimulating factor (GM-CSF and IL-3)

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GM-CSF and EL-3 can act on a broad range of hematopoietic cells and support their growth and differentiation. Although their biological role is striking, little is known about the molecular mechanism of their intracellular signaling pathway. In this study, we have demonstrated that high affinity-binding site of GM-CSF is partially blocked by the addition of IL-3.We have also shown that low affinity receptor for GM-CSF is expressed not only in hematopoietic cells but also in a human choriocarcinoma line. Furthen-nore, addition of GM-CSF to this cell line could induce the production of gonadotropin. Therefore, 1E is likely that low affinity receptor for GM-CSF itself can transduce some signals.Recently, soluble type of receptors has been identified for many lymphokines. These soluble receptors are presumed to have significant biological role, such as competitive inhibitor of membrane receptor. We. could reveal that there is a soluble type of GMCSF receptor. A soluble protein of 62 kDa in the supernatant of a human choriocarcinoma cell line was shown to bind to ^<125>I-labeled GM-CSF. This binding was specifically blocked by the excess addition of non-labeled GM-CSF. We could not recognize this type of receptor in the supernatant of hematopoietic cells.The structure and the biological role of this soluble GM-CSF receptor is currently under investigation.