EXPRESSION OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-4 (IGFBP-4) BY RAT NEURAL CELLS - COMPARISON TO OTHER IGFBPS

We recently isolated and characterized the 24 kDa and N-glycosylated 2 8 kDa insulin-like growth factor binding protein-4 (rIGFBP4) from the B104s rat neuronal cell line (Endocrinology, 129 (1991) 1009-1115). To examine the prevalence of IGFBP4 secretion by cells of neural origin, we assessed the expression of IGFBP-4 in different neural cell types using ligand blotting, immunoblotting and blot hybridization with rele vant cDNAs. A specific IGFBP-4 antibody raised against a synthetic 20 amino acid peptide was used for immunologic recognition. In all the ne ural cells tested (B104s, C6 astrocytoma, primary neonatal astrocytes and primary fetal neurons), IGFBP-4 was definitively identified by imm unoblotting. Blot hybridization using a rat cDNA probe revealed expres sion of IGFBP-4 mRNA transcripts by all these cells. Using a combinati on of the same techniques, expression of IGFBP-1, -2, and -3 were also examined. The B104s cells secreted primarily IGFBP-4; C6 cells secret ed predominantly IGFBP-3 and small amount of IGFBP-4; both primary neo natal astrocytes and fetal neurons secreted IGFBP-2 as the major IGFBP accompanied by a small quantity of IGFBP-4. IGFBP-1 was not identifie d in any of the cell media. When probed with the respective IGFBP cDNA s, the mRNA abundance generally reflected the media IGFBP content. The expression of IGFBP-4 mRNA in vivo was examined as well and compared to that of IGFBP-1 and IGFBP-2. Transcripts for both IGFBP-2 and IGFBP 4 were found in all gross anatomical divisions of the rat brain from e mbryonic day 15 until adulthood, whereas IGFBP-1 was not detected at a ny time. IGFBP-4 mRNA tended to be more abundant at the youngest ages whereas IGFBP-2 increased during development. These data indicate that IGFBP-4 is produce by a variety of neural cell types and suggest that it may play a role in brain development.