Human leukemic T and B lymphoblasts produce insulin-like growth factor binding proteins 2 and 4

The production of insulin-like growth factors and insulin-like growth factor binding proteins by twelve human leukemic lymphoblast cell lines was evaluated by radioimmunoassay, affinity cross-linking, ligand blot, and immunoprecipitation of conditioned media. In all cell lines, detectable IGF-I and IGF-II levels were less than 0.1 micrograms/l and less than 0.3 micrograms/l, respectively. IGF binding proteins were identified in 6/12 of the lymphoblast cell lines studied. A pair of IGF binding proteins at 31 and 33 kD, immunoprecipitated with an antibody recognizing IGF binding protein 2 but not by an IGF binding protein 3 antibody, was produced by both T and B cells. A 24 kD IGF binding protein, presumably IGF binding protein 4, since it was not recognized by the antibodies for IGF binding proteins 1, 2, and 3, was produced by B cell precursor cells and faintly by one T cell line. These IGF binding proteins were not altered by deglycosylation. Neither IGF binding protein 1 nor IGF binding protein 3 was identified in any of the conditioned media. We speculate that local production of IGF binding proteins 2 and 4 regulates access of the IGFs to lymphoblasts and to hematopoietic precursors in general.