SPECIFIC BINDING OF LEUKEMIA INHIBITORY FACTOR TO MURINE MYOBLASTS INCULTURE

Leukemia inhibitory factor (LIF) is a member of the cytokine family of growth factors. it has been shown to exert a variety of actions on a diverse range of cell types, including neuronal, bone, and hemopoietic cells (Hilton, 1992, Trends Biochem. Sci., 77:72-76). In many of thes e cell types, studies have indicated the presence of specific receptor s for LIF (Godard et al., 1982, J. Biol. Chem., 267: 3214-3222; Hilton et al., 1988, Proc. Natl. Acad. Sci. USA, 85:5971-5975; Hilton and Ni cola, 1992, J. Biol. Chem., 267:10238-10247.). The mechanism by which these receptors act is believed to involve tyrosine phosphorylation an d the signal transducing receptor component gp130. We have previously shown that LIF is capable of inducing both human and murine myoblasts to proliferate in culture (Austin et al., 1992, J. Neurol. Sci., 112:1 85-191). We now report that LIF binds specifically to receptors on the surface of myoblasts, with an equilibrium dissociation constant of 40 0 pM and the number of receptors per cell varies with cell density. Bi nding competition studies showed that LIF binding to these receptor si tes was not competed for by a number of other growth factors which sti mulate myoblast proliferation including basic fibroblast growth factor (bFGF), transforming growth factor-alpha (TCF alpha), insulin-like gr owth factor 1 (IGF-1), and interleukin-6 (IL-6). There was a time and concentration-dependent down-regulation of receptor numbers following preincubation of myoblasts with LIF. The processing of these receptors subsequent to binding, involves as a first step, internalization and degradation by the myoblast. LIF appeared to stimulate myoblast prolif eration rather than cell survival. (C) 1995 Wiley-Liss, Inc.