Effects of IGF-I and -II, IGF binding protein-3 (IGFBP-3), and transforming growth factor-beta (TGF-beta) on growth and apoptosis of human osteosarcoma Saos-2/B-10 cells: lack of IGF-independent IGFBP-3 effects.
OBJECTIVE
Insulin-like growth factor binding protein-3 (IGFBP-3) inhibits cell growth. Previous reports have suggested the existence of plasma membrane IGFBP-3 receptors that could mediate direct, IGF-independent effects. Thus far, however, the only well-defined putative IGFBP-3 receptor is the type V transforming growth factor-beta (TGF-beta) receptor, a membrane glycoprotein that mediates TGF-beta-induced growth inhibition in selected cells. The aim of the study was to test whether IGFBP-3 and TGF-beta exert short-term effects in an osteosarcoma cell line that produces no IGF but contains type 1 IGF receptors.


METHODS
DNA synthesis and apoptosis in Saos-2/B-10 cells were measured in response to IGF-I, IGF-II, IGFBP-3 and TGF-beta2, and to type 1 IGF receptor ligands with poor affinity for IGFBP-3 ([QAYL]-IGF-I and insulin).


RESULTS
IGF-I and IGF-II stimulated thymidine incorporation into DNA and suppressed apoptosis in a dose-dependent manner with maximal effects at 1 and 3 nM respectively. TGF-beta2 slightly increased thymidine incorporation into DNA but had no effect on apoptosis. IGFBP-3 had no effect by itself. Whereas it blocked the above effects of 1 nmol/l IGF-I, it did not block those of 1 nmol/l [QAYL]-IGF-I or 100 nmol/l insulin.


CONCLUSIONS
IGFBP-3 does not affect DNA synthesis or apoptosis in an IGF-independent manner in IGF-responsive osteosarcoma cells. It therefore appears to act essentially by sequestration of IGF.
Schmid
C
C
Division of Endocrinology and Diabetes, Department of Medicine, University Hospital, 8091 Zurich, Switzerland. ndozaj@usz.unizh.ch
Ghirlanda-Keller
C
C
Zapf
J
J
D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D053938:DNA Fragmentation / Q000187:drug effects; D004273:DNA, Neoplasm / Q000096:biosynthesis; D004797:Enzyme-Linked Immunosorbent Assay; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000096:biosynthesis / Q000302:isolation & purification / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000494:pharmacology*; D012516:Osteosarcoma / Q000378:metabolism / Q000473:pathology*; D017526:Receptor, IGF Type 1 / Q000502:physiology; D011972:Receptor, Insulin / Q000502:physiology; D015398:Signal Transduction; D013002:Somatomedins / Q000096:biosynthesis; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
D004273:DNA, Neoplasm; D006131:Growth Inhibitors; D018972:Insulin-Like Growth Factor Binding Protein 3; D013002:Somatomedins; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin