Characterization of an insulin-related factor secreted by a teratoma cell line

The teratoma-derived insulin-independent cell line 1246-3A produces and secretes polypeptide mitogens in its culture serum-free medium. Mitogenic activities were separated by Sephadex G-50 chromatography into two fractions eluted, one in the void volume region, another one with an apparent Mr of 6 kDa. Only the 6 kDa mitogen presents properties similar to pancreatic insulin as estimated by radioimmunoassay, radio-receptor assay, and biochemical characterization. As a consequence, this factor is called insulin-related factor (IRF). Evidence presented in this paper indicate that ectopic IRF binds to insulin receptors on the producer cells, 1246-3A and acts in an autostimulatory manner.