CHARACTERIZATION OF THE MOUSE INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEIN-4 GENE REGULATORY REGION AND EXPRESSION STUDIES

Insulin-like growth factor binding protein 4 (IGFBP-4) is known as a p otent inhibitor of IGFs action in various cell types. In this study, t he mouse IGPBP-4 gene 5' flanking region, the IGFBP-4 mRNA expression, and the IGFBP-4s intracellular transport were investigated. The regul atory region exhibits all elements typical for an eukaryotic TATA elem ent containing promoter and was found to also contain functional eleme nts to direct transcriptional activation of a luc reporter gene constr uct that gradually decreased by 5' unidirectional deletions. Responsiv eness of the IGFBP-4 promoter activity was tested with thyroid hormone and found only within extended constructs but not when a potential TR alpha 1-binding site had been deleted. By using exon specific probes, we observed a varying expression pattern of IGFBP-4 transcripts in th ree rodent cell lines. Surprisingly, mouse fibroblastic NIH/3T3 cells displayed exclusively about a 2.0-kb transcript apparently lacking the IGFBP-4 mRNA 5' region. Studies on the intracellular transport by est ablishment of an IGFBP4/green fluorescent protein (GFP) fusion protein clearly demonstrate that IGFBP-4 is transported continuously along th e intracellular secretory pathway and is excluded from other intracell ular compartments. The description of the genomic IGFBP-4 region in th e mouse now opens new perspectives for further clarification of the ro le of IGFBP-4 in growth and development.