title: Osteoblast differentiation of NIH3T3 fibroblasts is associated with changes in the IGF-I/IGFBP expression pattern.
abstract: Insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) are essential regulators for osteoblast proliferation and differentiation. It has been reported that Dexamethasone (Dex), an active glucocorticoid (GC) analogue, synergizes the stimulatory effect of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) on osteoblast differentiation in the mouse fibroblastic cell line NIH3T3. I investigated whether this stimulatory effect is associated with changes in the expression pattern of the IGF/IGFBP system. Quantitative real-time PCR technology was used to quantify the gene expression levels of the IGF-system during osteoblast differentiation and in response to 1,25(OH)(2)D(3) or Dex alone under serum-containing and serum-free culture conditions. Interestingly, NIH3T3 was shown to express high mRNA levels of IGF-I, IGF-II and IGFBP-5, and low levels of both IGFBP-2 and-6. During osteoblast differentiation (days 6-12), IGF-I mRNA was repressed by more than 60%, while the transcript of IGFBP-5 was markedly up-regulated, by more than 50-fold. Similarly, treatment with Dex alone resulted in a dose-and time-dependent increase in the expression of IGFBP-5 and a decrease in IGF-I mRNA. Treatment with 1,25(OH)(2)D(3) alone increased the mRNA levels of IGF-I and IGFBP-6 by around 4-and 7-fold, respectively, in a dose-and time-dependent manner. In conclusion, my data demonstrated that osteoblast differentiation of NIH3T3 is associated with changes in the expression pattern of IGFs/IGFBPs, which are regulated by glucocorticoid in the presence of 1,25(OH)(2)D(3). Modulation of the IGF/IGFBP levels by glucocorticoid might suggest important roles for the IGF-system in mediating the osteoblast differentiation of the NIH3T3 cell line.
authors.affiliation: Department of Biochemistry, Faculty of Science, Helwan University, Cairo, Egypt. babdallah@health.sdu.dk
authors.forename: Basem M
authors.initials: BM
authors.lastname: Abdallah
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology*; D005786:Gene Expression Regulation / Q000502:physiology*; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D051379:Mice; D041681:NIH 3T3 Cells; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism
chemical_list: D018975:Insulin-Like Growth Factor Binding Protein 5; C519530:insulin-like growth factor-1, mouse; D007334:Insulin-Like Growth Factor I