Analysis of recombinant soluble mouse D-factor/LIF receptor.

The recombinant soluble mouse D-factor/LIF receptor (sD-factor-R) was expressed in COS-7 cells. Scatchard analysis of the bindings of mouse 125I-D-factor and human 125I-D-factor to the sD-factor-R indicated dissociation constants (Kd) of 12 and 0.267 nM, respectively, which were comparable to those of the binding protein in mouse serum. The apparent molecular masses of the sD-factor-R and human D-factor observed by gel filtration chromatography were 150 and 50 kDa, respectively. The size of the sD-factor-R.human D-factor complex was approximately 200 kDa, indicating that D-factor forms a 1:1 complex with the sD-factor-R. The sD-factor-R inhibited the induction of differentiation of mouse myeloid leukemic M1 cells by mouse D-factor by blocking the binding of this factor to the cells.