GROWTH-REGULATORY MECHANISM OF 2 HUMAN ESOPHAGEAL-CANCER CELL-LINES IN PROTEIN-FREE CONDITIONS

We investigated the growth-regulatory mechanism of 2 esophageal squamo us-cancer cell lines, TE2-NS and TE3-OS cells, both of which can grow stably in protein-free conditions in vitro. Protein-free conditioned m edia from TE2-NS and TE3-OS cells stimulated the growth of these cells . Exogenous epidermal growth factor (EGF), transforming growth factor- alpha (TGF-alpha), insulin-like growth factor (IGF)-I and -II enhanced cell proliferation by 2.2- to 3.8-fold in protein-free conditions, as compared with an untreated control. Receptor-binding assays showed th at both TE2-NS and TE3-OS cells possessed a single class of high-affin ity binding sites for IGF-1 and 2 classes of binding sites for TGF-alp ha as confirmed on the cell membrane by immunochemistry. These results suggest that EGF, TGF-alpha and IGFs are candidates for the autocrine growth factor in cancer cells. The addition of inhibitory monoclonal antibodies against TGF-alpha and EGFR, but not those against either EG F or IGF-IR, significantly inhibited growth of the cells. Immunocytoch emical staining and ELISA of the conditioned media both confirmed the production of TGF-alpha protein, but not EGF protein, in these cell li nes. The data for a protein-free culture system strongly suggested tha t TGF-alpha but not EGF or IGF, is biologically important as an autocr ine growth factor in the growth of these cell lines in vitro. (C) 1993 Wiley-Liss, Inc.