American journal of respiratory cell and molecular biology
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Am. J. Respir. Cell Mol. Biol. · Oct 1995
Insulin-like growth factor-I (IGF-I) regulates IGFBP-3 and IGFBP-4 by multiple mechanisms in A549 human adenocarcinoma cells.
The insulin-like growth factors (IGF-I and IGF-II) participate in the control of cell proliferation in normal and neoplastic lung cells. To examine the role of IGF binding proteins (IGFBPs) in modulating IGF actions in lung, we examined the production and regulation of IGFBPs from A549 cells, a human adenocarcinoma-derived lung cell line. Ligand blot and immunoblot analysis of conditioned media (CM) from A549 cells demonstrated IGFBP bands of relative molecular mass (M(r)) approximately 39-43,000 (IGFBP-3), 34,000 (IGFBP-2), 30,000 (IGFBP-1), and 24,000 (IGFBP-4). ⋯ These results suggest that ligand binding decreases IGFBP-3 clearance or increases IGFBP-3 accumulation in CM. IGF-I decreased IGFBP-4 abundance in A549 cell CM without decreasing IGFBP-4 mRNA transcripts and without increasing the amount of cell-associated IGFBP-4. To determine whether the decrease in IGFBP-4 was due to increased degradation, cell-free CM was incubated with and without IGF-I, and IGFBP-4 abundance measured by ligand and immunoblot analyses.(ABSTRACT TRUNCATED AT 400 WORDS)