Presence of mRNAs encoding the soluble D-factor/LIF receptor in human choriocarcinoma cells and production of the soluble receptor.

Four different kinds of cDNAs encoding the receptor for the differentiation stimulating factor (D-factor)/leukemia inhibitory factor (LIF) were isolated from a human liver cDNA library. Three kinds of the cDNAs had different intronic sequences, which introduced a termination codon before the transmembrane domain. However, the site of insertion in human cDNAs is different from those in mouse cDNAs. Recombinant proteins produced by COS-7 cells after transfection of these cDNAs bound D-factor/LIF. mRNAs corresponding to these cDNAs are expressed by the human liver, placenta, and choriocarcinoma cell line NJG. In conditioned medium of choriocarcinoma cells, a native soluble receptor for the D-factor/LIF with a dissociation constant of 7.8 nM and a MW of 160 kDa was found.