Functional receptors for epidermal growth factor on human osteosarcoma cells

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Abstract
Previous studies have shown that epidermal growth factor (EGF) stimulates bone resorption in organ culture via a prostaglandin‐mediated pathway, and that there are specific receptors for EGF on mouse bone (Tashjian and Levine, ′78; Shupnik et al., ′80). The present study demonstrates that a clonal line of human osteosarcoma cells, G‐292 (Clone A141B1) has specific, high‐affinity receptors for EGF and responds to treatment with EGF by increased prostaglandin production. Binding of 125I‐EGF to G‐292 cells exhibited a prolonged plateau phase (6 hours); thereafter, binding slowly declined (t1/2 = 6 hours) to 30–40% of the maximal level. This decrease in cell‐associated 125I‐EGF was prevented by leupeptin (50 μg/ml). EGF binding was of high affinity (Kd = 1.9 × 10−9 M) and was to a single class of non‐interacting binding sites. Pretreatment of cells for 48 hours with EGF caused a maximum threefold increase in PGE2 production, with a half‐maximal response at 9.8 × 10−10 M EGF. Increased PGE2 production was detectable within 2 hours and the constant presence of EGF was needed to maintain the response. Although EGF is mitogenic in several other systems, it did not increase DNA synthesis in the osteosarcoma cells. EGF treatment also did not increase medium or intracellular cyclic AMP in these cells, although parathyroid hormone and exogenous PGE2 (200 ng/ml) increased cyclic AMP three‐ to tenfold over control levels. Pretreatment with EGF decreased the level of subsequent 125I‐EGF binding; receptor number decreased to 30–40% of control after 48 hours of treatment, and the half‐maximal effect occurred with pretreatment concentrations of 1.6 × 10−9 M EGF. In all respects tested, the binding and biological actions of EGF on the human osteosarcoma cells were the same as those in whole mouse bone. G‐292 cells thus provide a convenient model system to study EGF action on osseous tissue.