Basic fibroblast growth factor regulates IGF-I binding proteins in the clonal osteoblastic cell line MC3T3-E1.
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.(ABSTRACT TRUNCATED AT 250 WORDS)
Hurley
M M
MM
Department of Medicine, University of Connecticut Health Center, Farmington, USA.
Abreu
C
C
Hakeda
Y
Y
D016475:3T3 Cells; D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D051379:Mice; D008970:Molecular Weight; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011863:Radioimmunoassay; D011994:Recombinant Proteins / Q000494:pharmacology; D013002:Somatomedins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics
D002352:Carrier Proteins; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013002:Somatomedins; D016222:Fibroblast Growth Factor 2; D007334:Insulin-Like Growth Factor I; D004247:DNA