OSM is a pleiotropic cytokine that initiates its biological activities by binding to specific cell surface receptors. The biological activity of human OSM is mediated either by the LIF/OSM receptor complex composed of gp130 and LIF R alpha or by a human OSM specific receptor composed of gp130 and OSM R alpha. The gp130, a signal transducing component ( beta subunit) of the IL-6, LIF and CNTF receptor complexes, was identified as a low-affinity OSM receptor that does not transduce OSM signals. The low affinity LIF receptor (LIF R, a gp130-related protein) has been identified to be a component of a high-affinity OSM receptor that will transduce OSM signals. Besides its growth inhibitory activities on human A375 melanoma and mouse M1 myeloid leukemic cells, as well as on other solid tumor cells, OSM also has growth stimulatory activities on normal fibroblasts, AIDS-Kaposi’s sarcoma cells, and a human erythroleukemia cell line, TF-1. Other OSM-mediated activities reported to date include: stimulation of plasminogen activator activity in cultured bovine aortic endothelial cells; regulation of IL-6 expression in human endothelial cells; and stimulation of LDL uptake and up-regulation of cell surface LDL receptors in HepG2 cells.
