INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEIN PRODUCTION AND REGULATION IN FETAL-RAT LUNG-CELLS

Insulin-like growth factor binding proteins (IGFBPs) are expressed in lung from early in gestation and may modulate IGF-stimulated fetal lun g cell proliferation and/or differentiation. To begin to define IGFBP production and regulation in lung cells during development, we prepare d primary cultures of 19 day gestation fetal rat lung fibroblasts and epithelial cells and identified IGFBPs secreted into medium. Ligand bl ot analysis of conditioned media (CM) from both cell types demonstrate d IGFBP bands of approximately 39,000-45,000, 32,000, 24,000, and 22,0 00 M(r). These migration characteristics allowed the identification of the 39,000-45,000 M(r) bands as IGFBP-3 and the 24,000 M(r) band as I GFBP-4, while Western-immunoblot analyses localized IGFBP-2 to the 32, 000 M(r) band and IGFBP-5 to the 22,000 M(r) band. Polymerase chain re action amplification of cDNAs generated by reverse transcription of fi broblast and epithelial cell RNA using specific oligodeoxynucleotide p rimers for IGFBPs 1 through 6, demonstrated the presence of amplified products for IGFBP-2, -3, -4, -5, and -6. In both cell types, IGFBP-2 and -3 production was sustained during 48 h of incubation in serum-fre e medium, whereas IGFBP-4 abundance increased only during the first 6 to 12 h of incubation. CM from fibroblasts and epithelial cells plated at low densities contained a high abundance of IGFBP-2 per mug cellul ar DNA compared with cells at higher densities. In contrast, IGFBP-3 a nd -4 abundance normalized to cell DNA did not change with differing c ell densities. In fibroblasts, IGF-I and dibutyryl cyclic adenosine mo nophosphate (dcAMP) each increased the abundance of the 32,000 M(r) IG FBP(s), while retinoic acid and dcAMP each increased IGFBP-4, and dexa methasone decreased IGFBP-3. Epithelial cells incubated with IGF-I inc reased the abundance of IGFBP-3, dcAMP and retinoic acid each increase d IGFBP-4, and dexamethasone decreased IGFBP-3 and -4. These results d emonstrate that multiple IGFBPs are produced by both epithelial and me senchymal cells from fetal lung. Specific IGFBPs are regulated differe ntly by serum withdrawal and cell density, as well as by agents that i nfluence lung cell growth and differentiation. These findings suggest that changes in IGFBP production may influence IGF actions during feta l lung growth and development.