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Basic fibroblast growth factor regulates IGF‐I binding proteins in the clonal osteoblastic cell line MC3T3‐E1
Author(s) -
Hurley Marja M.,
Abreu Christine,
Hakeda Yoshiyuki
Publication year - 1995
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1002/jbmr.5650100208
Subject(s) - basic fibroblast growth factor , insulin like growth factor binding protein , growth factor , medicine , endocrinology , cell culture , messenger rna , paracrine signalling , biology , aphidicolin , dna synthesis , fibroblast growth factor , insulin like growth factor 2 , fibroblast , insulin like growth factor , binding protein , cell growth , microbiology and biotechnology , receptor , dna , biochemistry , gene , genetics
In previous studies, we reported that basic fibroblast growth factor (bFGF) regulates insulin‐like growth factor messenger RNAs and protein levels in the osteoblastic MC3T3‐E1 cells. In the present study, we examined the expression of insulin‐like growth factor binding proteins (IGFBPs) in MC3T3‐E1 cells and determined whether bFGF altered IGFBP mRNAs and protein levels. Since previous studies suggested that IGFBPs can inhibit DNA synthesis stimulated by IGF‐I, we wondered whether the mitogenic effect of bFGF was altered by exogenous IGFBP‐3. Confluent MC3T3‐E1 cells were serum‐deprived for 24 h and then treated with bFGF for 6–24 h. In control cultures, MC3T3‐E1 cells expressed the mRNAs for IGF‐I, IGF‐II, and IGFBP‐2, 4, 5, and 6 but not IGFBP‐1 or 3. A 24 h treatment with bFGF at 10 −8 M decreased IGF‐I mRNA by 97%, IGF‐II mRNA by 73%, IGFBP‐2 by 64%, IGFBP‐4 by 73%, IGFBP‐5 by 95%, and IGFBP‐6 by 65%. The inhibitory effect of bFGF on IGF‐I and IGFBP mRNA levels was not altered by aphidicolin, an inhibitor of cell replication. bFGF 10 nM decreased IGF‐I levels determined by radioimmunoassay after acidification by 45% and 72% at 24 and 48 h, respectively. Western ligand blot for IGF binding proteins revealed that MC3T3‐E1 cells expressed IGFBPs of 24, 30, and 34 kD. Treatment with bFGF 10 −8 M decreased the levels of the 24 and 30 kD band at 24 h but increased the 34 kD band. Western immunoblot revealed that the 24 kD protein was IGFBP‐4 and the 34 kD band was IGFBP‐2. bFGF at 10 −9 ‐10 −8 M increased thymidine incorporation into DNA (TdR) in a dose‐dependent manner. When exogenous IGFBP‐3 was added to the cultures there was a significant reduction in DNA synthesis while the mitogenic effect of bFGF was not blocked. In summary, bFGF not only regulates IGF‐I mRNA and protein levels but it also regulates the IGF‐II mRNA and mRNA and protein levels of the IGFBPs expressed in MC3T3‐E1 cells. However, the mitogenic effect of bFGF may be independent of endogenous IGF‐I. These results may be important in understanding the role of bFGF in bone cell function.