LOCALIZATION OF THE EPITOPE OF A MONOCLONAL-ANTIBODY AGAINST HUMAN INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-1, FUNCTIONALLY INTERFERING WITH INSULIN-LIKE GROWTH-FACTOR BINDING

In order to identify regions in insulin-like growth factor binding pro tein-1 involved in the binding of IGFs, we tested three monoclonal ant ibodies, designated MAb A, B and C on their interference with IGF-bind ing. Monoclonal A interfered with the binding of IGF to IGFBP-1 as det ermined by immunoprecipitation whereas monoclonal B and C did not. Fur thermore MAb A was found to abolish IGFBP-1 inhibition of IGF stimulat ion in an in vitro proliferation assay. The epitopes of all three mono clonal antibodies were found to be located within the C-terminal part of IGFBP-1. The regions surrounding residue 188-196 and 222-227 are es pecially important for antibody recognition. These results indicate th at MAb A functionally interferes with the binding of IGF to IGFBP-1. F urthermore, we suggest that part of the epitope of MAb A is located at or sterically near the IGF binding domain of IGFBP-1.