Osteogenic protein-1 and insulin-like growth factor I synergistically stimulate rat osteoblastic cell differentiation and proliferation.
Previous studies have shown that osteogenic protein-1 (OP-1; also known as BMP-7) alters the steady state levels of messenger RNA (mRNA) encoding insulin-like growth factor I (IGF-I), IGF-II, and IGF-binding proteins (IGFBPs) in primary cultures of fetal rat calvaria (FRC) cells. In the present study, the effects of exogenous IGF-I on bone cell differentiation and mineralized bone nodule formation induced by OP-1 were examined. Exogenous IGF-I synergistically and dose dependently enhanced OP-1 action in stimulating [3H]thymidine incorporation, alkaline phosphatase activity, PTH-dependent cAMP level, and bone nodule formation. Maximal synergism between OP-1 and IGF-I was observed when both factors were added simultaneously. Synergism was not observed when FRC cells were pretreated with IGF-I for 24 h, followed by OP-1 treatment. These findings suggest that IGF-I acted on OP-1-sensitized FRC cells. To examine the mechanism(s) by which this sensitization may occur, levels of mRNA encoding OP-1 receptor, IGF-I receptor, and IGFBPs were measured. The mRNA levels of both type I and II OP-1 receptors were elevated by OP-1, but were not changed further by combined OP-1 and IGF-I treatment. IGF-I receptor gene expression was not changed by OP-1, IGF-I, or a combination of both factors. OP-1 alone or together with IGF-I increased the steady state IGFBP-3 mRNA level and reduced the steady state mRNA levels of IGFBP-4, -5, and -6. IGF-I alone did not change the steady state mRNA levels of IGFBP-3, -4, and -6, but elevated that of IGFBP-5. Des(1-3)-IGF-I, which has a lower affinity for IGFBPs, was more effective than the full-length IGF-I in enhancing the OP-1-induced alkaline phosphatase activity. Exogenous IGFBP-5 inhibited the OP-1-induced alkaline phosphatase activity and reduced the synergistic stimulatory effect of IGF-I and OP-1. These findings strongly suggest that the OP-1-induced down-regulation of IGFBPs, especially that of IGFBP-5, is an important mechanism by which OP-1 and IGF-I synergize to stimulate FRC cell differentiation.
Yeh
L C
LC
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760, USA.
Adamo
M L
ML
Olson
M S
MS
Lee
J C
JC
D000469:Alkaline Phosphatase / Q000032:analysis / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000032:analysis / Q000378:metabolism; D018076:DNA, Complementary / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005786:Gene Expression Regulation; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D012886:Skull / Q000166:cytology / Q000196:embryology; D013936:Thymidine / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology
C525821:Bmp7 protein, rat; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D018076:DNA, Complementary; D018974:Insulin-Like Growth Factor Binding Protein 4; D018975:Insulin-Like Growth Factor Binding Protein 5; D018976:Insulin-Like Growth Factor Binding Protein 6; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I; D000242:Cyclic AMP; D017526:Receptor, IGF Type 1; D000469:Alkaline Phosphatase; D013936:Thymidine