Transforming growth factor-beta1 stimulates the production of insulin-like growth factor-I and insulin-like growth factor-binding protein-3 in human bone marrow stromal osteoblast progenitors.
While transforming growth factor-beta1 (TGF-beta1) regulates proliferation and differentiation of human osteoblast precursor cells, the mechanisms underlying these effects are not known. Several hormones and locally acting growth factors regulate osteoblast functions through changes in the insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs). Thus, we studied the effects of TGF-beta1 on IGFs and IGFBPs in human marrow stromal (hMS) osteoblast precursor cells. TGF-beta1 increased the steady-state mRNA level of IGF-I up to 8.5+/-0.6-fold (P<0.001) in a dose- (0.1-10 ng/ml), and time-dependent (12-72 h) manner. No significant effects on IGF-II gene expression were detectable. Employing RNase protection and nuclear run-on assays, these effects on IGF-I were found to take place at the transcriptional level and were not dependent on de novo protein synthesis. Using the transient transfection of various fragments of the IGF-I promoter 1, we found that TGF-beta responsive elements were present in a promoter fragment ranging from-65 bp to+55 bp relative to the major transcription start site in exon 1. In addition, TGF-beta1 treatment resulted in a dose- and time-dependent increase (2-fold) in the IGFBP-3 steady-state mRNA level as well as in protein production but did not affect IGFBP-2 or IGFBP-4 at mRNA or protein levels. Our results indicate that TGF-beta1 exerts significant effects on stimulatory components of the IGF-system and that may represent a mechanism mediating TGF-beta effects on the biological functions of osteoblasts.
Kveiborg
M
M
University Department of Endocrinology and Metabolism, Institute of Experimental Clinical Research, University of Aarhus, DK-8000 Aarhus C, Denmark.
Flyvbjerg
A
A
Eriksen
E F
EF
Kassem
M
M
D000328:Adult; D015152:Blotting, Northern; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000187:drug effects* / Q000378:metabolism; D018929:Cell Culture Techniques; D002455:Cell Division / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000096:biosynthesis*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017154:Stromal Cells / Q000187:drug effects / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1
D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D007334:Insulin-Like Growth Factor I; D000242:Cyclic AMP