Heparin-binding growth factors (HBGF) are a recently characterized family of polypeptides that regulate growth and differention of mesenchymal, neuroectodermal and some epithelial cells. HBGF have intrinsic affinity for abundant heparin-like sites on or around cells which act as a reservoir of active factor and specific polypeptide receptor sites on plasma membranes which presumably mediate the biological effects. A specific human hepatoma cell line (HepG2) appears to be an overproducer of polypeptide receptor sites and exhibits two-affinity classes of HBGF binding sites which consist of a single polypeptide of apparent molecular weight of 130 kD. Occupation of abundant low-affinity sites mediate inhibitory effects on HepG2 cell growth and positive effects on secretory function while less abundant high-affinity sites stimulate cell growth. An abundant 130 kD glycoprotein (gp130) has been purified to apparent homogeneity from HepG2 cell membranes and is a candidate for the HBGF receptor. This project will isolate and determine structure of gp130 by cloning gp130 cDNA from a HepG2 lambda gt11 expression library. Conditions for assay of ligand- binding and phosphorylation activity of solubilized HBGF receptor will be established. Antibodies against and immunoassay for gp130 and the HBGF receptor will be established. Properties of gp130 and the HBGF receptor will be compared to determine whether they are the same or related proteins. DNA coding for gp130 will be expressed by DNA-directed transfection of heterologous host cells and host cells tested for human HBGF receptor activities. If gp130 is rot the HBGF receptor, then alternative strategies for affinity purification of authentic receptor glycoprotein and/or rescue of the HBGF receptor gene from heterologous host cells transfected with HepG2 genomic DNA will be carried out. Antireceptor antibodies and cDNA will be used to characterize expression and function of the two-affinity classes of HBGF receptor in growth and secretory function of human hepatoma and normal liver cells. Long-term goals are to elucidate the structural determinants of the dual affinity and dual function of the HBGF receptor.
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