Influence of subunit combinations on signaling by receptors for oncostatin M, leukemia inhibitory factor, and interleukin-6.

Oncostatin M (OSM), leukemia inhibitory factor (LIF), and interleukin-6 (IL-6) induce expression of a similar set of acute phase plasma protein genes in hepatic cells. The redundant action of these cytokines has been ascribed to the involvement of the common signal-transducing receptor subunit, gp130, in combination with cytokine-specific, ligand-binding subunits. To define the specificity of the signal transduction by the LIF/OSM receptor (a heterodimer of gp130 and LIF receptor (LIFR)) and the OSM-specific receptor (a heterodimer of gp130 and OSM receptor (OSMR)), we reconstituted the receptor function by transfection into receptor-negative Hep3B hepatoma cells. Both receptors activate DNA binding activity of STAT1, -3, and -5B and induce gene transcription through IL-6-responsive elements. The signaling-competent cytoplasmic domain regions of OSMR and LIFR were defined by the analysis of progressive carboxyl-terminal deletion constructs. The 36 residue carboxyl-terminal region containing the distal box 3 sequence motif of OSMR is required for signal transduction by the OSM-specific receptor. In contrast, signaling by LIFR did not display the same requirement for receptor domains and was not strictly dependent on the box 3 elements. The signaling by endogenous LIF and OSM receptors differed from that by IL-6R by the prominent activation of STAT5 as shown in the mouse hepatoma cell line, Hepa-1. The data suggest that the signaling specificity of the receptors for the three cytokines is determined by the composition of the cytoplasmic domains associated in the signal-competent receptor complex and that the signaling is not identical among these cytokine receptors.