Insulin-like growth factor-binding protein-5 inhibits growth and induces differentiation of mouse osteosarcoma cells.
The precise role of insulin-like growth factor-binding protein-5 (IGFBP-5) in regulating the growth of tumor cells, especially of bone-derived malignant cells, is not well understood. We have investigated the biological activity of IGFBP-5 by transfecting OS/50-K8 mouse osteosarcoma cells with an expression vector containing the osteocalcin promoter and the complete mouse IGFBP-5 cDNA (OC-IGFBP-5). Overexpression of IGFBP-5 mRNA and secretion of increased amounts of bioactive protein in conditioned media were demonstrated in different clones. For the analysis of cell proliferation, three clones exhibiting high levels of IGFBP-5 expression were selected and compared to a mock clone and to nontransfected parental cells. IGFBP-5-secreting clones displayed reduced proliferation under both anchorage-dependent and -independent conditions (P < 0.05). The increase in proliferation observed in IGFBP-5-secreting clones after addition of exogenous IGF was significantly lower than that observed in mock-transfected or parental cells. A similar result was obtained with long[R3]IGF-I which has a low affinity for all IGFBPs, suggesting that the inhibitory effect of IGFBP-5 is only partially IGF-dependent. OC-IGFBP-5-transfected clones expressed significantly higher amounts of osteocalcin mRNA (P < 0.05) and secreted more osteocalcin protein than a mock clone or parental OS-50/K8 cells. Thus, part of the growth-inhibiting effect of IGFBP-5 may be due to an induction of differentiation in these cells.
Schneider
M R
MR
Institute of Molecular Animal Breeding, Gene Center of the Ludwig-Maximilian University, Feodor-Lynen-Strasse 25, D-81377 Munich, Germany. schnder@lmb.uni-muenchen.de
Zhou
R
R
Hoeflich
A
A
Krebs
O
O
Schmidt
J
J
Mohan
S
S
Wolf
E
E
Lahm
H
H
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D015675:Osteocalcin / Q000378:metabolism; D012516:Osteosarcoma / Q000378:metabolism / Q000473:pathology*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured
D018975:Insulin-Like Growth Factor Binding Protein 5; D012333:RNA, Messenger; D015675:Osteocalcin