The human insulin-like growth factor (IGF) binding protein-3 inhibits the growth of fibroblasts with a targeted disruption of the IGF-I receptor gene.
The insulin-like growth factors (IGFs) are important mitogens that exert their proliferative effects on cells via the type I IGF receptors (IGF-R). The IGFs also associate with IGF binding proteins (IGFBPs). IGF-inhibitory, IGF-stimulatory, and IGF-independent effects of IGFBPs on cell growth have been reported. We have asked whether the IGFBP-3 has an effect on cell growth, which is independent of its ability to bind IGF-I and thus inhibit the activation of the IGF-I receptor. For this purpose, we have used a fibroblast cell line (R- cells) derived from mouse embryos homozygous for a targeted disruption of the IGF-R gene. When compared with wild type cells (W), which bind IGF-I with high affinity and specificity, R- cells transfected with a mammalian expression vector containing the human (h) IG-FBP-3 cDNA were selected (R-/BP3) and found to express hIGFBP-3 mRNA (detected by Northern blots) and to secrete hIGFBP-3 protein [detected by Western ligand blotting (WLB), immunoblotting, and immunoprecipitation as well as immunofluorescence confocal microscopy]. Growth of five different R- cells, and 10-fold slower compared with W cells, grown under identical conditions. Confluent R- cells. These experiments show that the overexpression of IGFBP-3 has an inhibitory effect on cell growth which does not involve IGF binding to, or signal transduction via, the type I IGF-R. We conclude that the cellular production of IGFBPs serves as a negative regulator of cell proliferation which involves a cellular signaling pathway separate from the IGF-IGF-R system.
Valentinis
B
B
Department of Pediatrics, University of Pennsylvania, Philadelphia 19104, USA.
Bhala
A
A
DeAngelis
T
T
Baserga
R
R
Cohen
P
P
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D017077:Culture Media, Conditioned; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000166:cytology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D051379:Mice; D018613:Microscopy, Confocal; D012333:RNA, Messenger / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000235:genetics*; D015398:Signal Transduction; D014162:Transfection
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1