Receptor Subunit-specific Action of Oncostatin M in Hepatic Cells and Its Modulation by Leukemia Inhibitory Factor*

Abstract

The related cytokines, interleukin-6 (IL-6), oncostatin M (OSM), and leukemia inhibitory factor (LIF) direct the formation of specific heteromeric receptor complexes to achieve signaling. Each complex includes the common signal-transducing subunit gp130. OSM and LIF also recruit the signaling competent, but structurally distinct OSMRβ and LIFRα subunits, respectively. To test the hypothesis that the particularly prominent cell regulation by OSM is due to signals contributed by OSMRβ, we introduced stable expression of human or mouse OSMRβ in rat hepatoma cells which have endogenous receptors for IL-6 and LIF, but not OSM. Both mouse and human OSM engaged gp130 with their respective OSMRβ subunits, but only human OSM also acted through LIFR. Signaling by OSMRβ-containing receptors was characterized by highest activation of STAT5 and ERK, recruitment of the insulin receptor substrate and Jun-N-terminal kinase pathways, and induction of a characteristic pattern of acute phase proteins. Since LIF together with LIFRα appear to form a more stable complex with gp130 than OSM with gp130 and OSMRβ, co-activation of LIFR and OSMR resulted in a predominant LIF-like response. These results suggest that signaling by IL-6 cytokines is not identical, and that a hierarchical order of cytokine receptor action exists in which LIFR ranks as dominant member.