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Identification of a Type II Insulin-Like Growth Factor Receptor in Fish Embryos¹

Departament de Fisiologia, Facultat de Biologia, D. III Universitat de Barcelona, 08028 Barcelona, Spain

Address all correspondence and requests for reprints to: Joaquim Gutiérrez, Departament de Fisiologia, Facultat de Biologia, D. III Universitat de Barcelona, Avenida Diagonal 645, 08028 Barcelona, Spain. E-mail: joaquim{at}porthos.bio.ub.es

To determine whether fish have an insulin-like growth factor II/mannose 6-phosphate (IGF-II/M6-P) receptor similar to that of mammals, we have performed binding, cross-linking, and immunoprecipitation experiments with wheat-germ-agglutinin- and mannose 6-phosphate (M6-P)-affinity-purified receptor preparations from fish embryos. In both receptor preparations, IGF-II binding was specific, because labeled IGF-II could only be completely displaced by cold IGF-II but not by IGF-I or insulin. Labeled IGF-II bound to a protein with a molecular mass of approximately 250 kDa, which could be immunoprecipitated with an antibody against the rat IGF-II receptor. IGF-II stimulated tyrosine kinase activity in wheat germ agglutinin preparations and was more potent than insulin or IGF-I, but neither peptide stimulated tyrosine kinase activity in M6-P preparations. Two fish cell lines (CHSE-214 and EPC) were used to confirm the IGF-II binding data obtained in the receptor preparations, revealing the presence of highly specific IGF-II binding and the absence of insulin binding. Furthermore, a decrease of the IGF-I receptors on the cell surface did not alter IGF-II binding in EPC cells. In conclusion, we have detected the presence of IGF-II/M6-P receptors in fish embryos that are similar in structure and specificity for their ligand to those found in mammals.

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