BINDING INTERACTIONS OF LEUKEMIA INHIBITORY FACTOR AND CILIARY NEUROTROPHIC FACTOR WITH THE DIFFERENT SUBUNITS OF THEIR HIGH-AFFINITY RECEPTORS

Leukemia inhibitory factor(LIF) and ciliary neurotrophic factor (CNTF) share common components in their multimeric receptors. Both cytokine receptors contain gp130/interleukin-6-receptor transducer as well as g p190/low-affinity LIF receptor. For CNTF, addition of a third subunit, or a subunit, defines the high-affinity CNTF receptor. In the present study, we analyzed the binding interactions of LIF and CNTF in human cell lines and showed a mutual displacement for LIF and CNTF toward th e trimeric high-affinity CNTF receptor. Similar results were obtained in the JEG cell line, which only expressed the gp130/gp190 high-affini ty LIF receptor, by adding a soluble form of the alpha CNTF receptor t o the system to reconstitute the high-affinity-type CNTF receptor. The different receptor subunits were then expressed separately in transfe cted cells and their binding capacities analyzed. The results showed t hat the heterocomplex CNTF/alpha CNTF receptor bound to gp130 with an affinity of 3-5 x 10(-10) M, whereas LIF interacted mainly with gp190. In summary, the observed competition between LIF and CNTF does not re sult from the binding to a common site or receptor subunit, but rather to the interaction of the three receptor components to create a confo rmational site common to both LIF and CNTF.