Soluble insulin-like growth factor II/mannose 6-phosphate receptor inhibits DNA synthesis in insulin-like growth factor II sensitive cells.
The soluble form of the insulin-like growth factor II (IGF-II)/mannose 6-P (IGF-II/M6P) receptor is released by cells in culture and circulates in the serum. It retains its ability to bind IGF-II and blocks IGF-II-stimulated DNA synthesis in isolated rat hepatocytes. Because these cells are not normally stimulated to divide by IGF-II in vivo, the effect of soluble IGF-II/M6P receptor on DNA synthesis has been further investigated in two cell lines sensitive to IGF-II; mouse 3T3(A31) fibroblasts, stimulated by low levels of IGF-II following priming by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) and Buffalo rat liver (BRL) cells, which secrete IGF-II and proliferate in the absence of exogenous growth factors. Soluble IGF-II/M6P receptor (0.2-2.0 microgram/ml) purified from a rat hepatoma cell line inhibited DNA synthesis (determined by dThd incorporation) in both cell lines. Basal DNA synthesis was very low in serum-free 3T3 cells, but high in serum-free BRL cells, possibly as a result of autocrine IGF-II production. The inhibitory effect was reversible in cells preincubated with soluble receptor prior to incubation with growth factors and could also be overcome by excess IGF-II. Soluble receptor was more potent in IGF-II-stimulated 3T3 cells and serum-free BRL cells than in BRL cells incubated with serum. Mean inhibition by four preparations of soluble receptor (1 microgram/ml) was 34.7% +/- 4.4% in BRL cells stimulated with fetal calf serum (FCS) (5%) compared to 54.8% +/- 4.2% in serum-free BRL cells (P = 0.05) and 60.6% +/- 6.5% (P = 0.02) in 3T3 cells stimulated by PDGF, EGF, and IGF-II. Soluble receptor had no effect on DNA synthesis in 3T3 cells stimulated with IGF-I. These results demonstrate that soluble receptor, at physiological concentrations, can block proliferation of cells by IGF-II and could therefore play a role in blocking tumor growth mediated by IGF-II.
Scott
C D
CD
Kolling Institute of Medical Research, Royal North Shore Hospital, St. Leonards, Australia. cscott@med.usyd.edu.au
Weiss
J
J
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D016895:Culture Media, Serum-Free; D004247:DNA / Q000096:biosynthesis* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004815:Epidermal Growth Factor / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051381:Rats; D017527:Receptor, IGF Type 2 / Q000037:antagonists & inhibitors / Q000502:physiology*; D012995:Solubility; D013936:Thymidine / Q000378:metabolism; D013997:Time Factors
D016895:Culture Media, Serum-Free; D010982:Platelet-Derived Growth Factor; D017527:Receptor, IGF Type 2; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D004247:DNA; D013936:Thymidine