EXPRESSION AND SYNTHESIS OF INSULIN-LIKE GROWTH FACTOR-BINDING PROTEINS IN HUMAN GLIOMA CELL-LINES

We previously demonstrated the presence of insulinlike growth factors (IGFs) and IGF-receptors in human glioma cell lines derived from prima ry glioblastomas. The biological action of IGFs is modulated by specif ic IGF-binding proteins (IGFBP)-1 to -7. By means of polymerase chain reaction (PCR), we detected mRNA transcripts for IGFBP-1 in 42%, IGFBP -2 in 65%, IGFBP-3 in 97%, IGFBP-4 in 3%, IGFBP-5 in 74%, IGFBP-6 in 9 4% and IGFBP-7 in 87% of the glioma cell lines. The specificity of the PCR reaction was verified by direct sequencing of the PCR product. In addition, the content of the most prevalent IGFBP-3 was measured in c onditioned medium from glioma cells by specific radioimmunoassay with levels ranging from <1 to 620 ng/ml. Moreover, the presence of membran e-bound IGFBPs (44, 50 and 60 kDa) as well as IGF-II receptors was dem onstrated by using I-125-labelled IGF-II as a ligand. In conclusion, I GFBPs may modulate the IGF-mediated effects in these cell lines.