PHOSPHORYLATION OF INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-1 FROM DIFFERENT SOURCES

During purification, insulin-like growth factor binding protein-1 from amniotic fluid was separated into five different peaks by anion excha nge chromatography.1 These peaks represent differently phosphorylated forms of IGFBP-1. The major peak (peak 1) is non-phosphorylated. Peaks 3, 4, and 5 are more phosphorylated and, in native polyacrylamide gel electrophoresis (PAGE), they migrate faster than peaks 1 and 2. The m ore phosphorylated forms have higher IGF-I-binding affinity. Both deph osphorylated and phosphorylated peaks enhanced IGF-I stimulated DNA-sy nthesis in fetal skin fibroblast cell culture. They, however, inhibite d the binding of IGF-I to the same cells. The phosphorylation of IGFBP -1 was changed during pregnancy. In decidua and in amniotic fluid the degree of phosphorylation increased from early to late pregnancy, as i ndicated by faster mobility of IGFBP-1 in native PAGE and increased re lative amount of the more phosphorylated peaks in anion exchange chrom atography. Human ovarian follicular fluid, culture media from human gr anulosa cells and endometrial adenocarcinoma cells (HEC-1-B) consisted mostly of the non-phosphorylated form of IGFBP-1.