The specificity of the human IGF-2 receptor

The specificity of the type 2 insulinlike growth factor (IGF) receptor is evaluated in human placenta membranes and the human cell line K562. K562 cells have type 2 but not type 1 IGF receptors. Native IGF-2 isolated from human plasma and synthetic IGF-2 were equipotent in competing with labeled IGF-2 in both systems. Pure IGF-1 isolated from plasma, synthetic IGF-1 and recombinant IGF-1 could not crossreact with the type 2 IGF receptor in concentrations up to 1 microgram/ml in both systems. Studies on placenta membrane were done in the presence of 300 ug/ml insulin to block the type 1 IGF receptors. It is concluded that IGF-1, as well as insulin, cannot crossreact with the human type 2 IGF receptor.