title: Fluid shear stress synergizes with insulin-like growth factor-I (IGF-I) on osteoblast proliferation through integrin-dependent activation of IGF-I mitogenic signaling pathway.
abstract: This study tested the hypothesis that shear stress interacts with the insulin-like growth factor-I (IGF-I) pathway to stimulate osteoblast proliferation. Human TE85 osteosarcoma cells were subjected to a steady shear stress of 20 dynes/cm(2) for 30 min followed by 24-h incubation with IGF-I (0-50 ng/ml). IGF-I increased proliferation dose-dependently (1.5-2.5-fold). Shear stress alone increased proliferation by 70%. The combination of shear stress and IGF-I stimulated proliferation (3.5- to 5.5-fold) much greater than the additive effects of each treatment alone, indicating a synergistic interaction. IGF-I dose-dependently increased the phosphorylation level of Erk1/2 by 1.2-5.3-fold and that of IGF-I receptor (IGF-IR) by 2-4-fold. Shear stress alone increased Erk1/2 and IGF-IR phosphorylation by 2-fold each. The combination treatment also resulted in synergistic enhancements in both Erk1/2 and IGF-IR phosphorylation (up to 12- and 8-fold, respectively). Shear stress altered IGF-IR binding only slightly, suggesting that the synergy occurred primarily at the post-ligand binding level. Recent studies have implicated a role for integrin in the regulation of IGF-IR phosphorylation and IGF-I signaling. To test whether the synergy involves integrin-dependent mechanisms, the effect of echistatin (a disintegrin) on proliferation in response to shear stress +/- IGF-I was measured. Echistatin reduced basal proliferation by approximately 60% and the shear stress-induced mitogenic response by approximately 20%. It completely abolished the mitogenic effect of IGF-I and that of the combination treatment. Shear stress also significantly reduced the amounts of co-immunoprecipitated SHP-2 and -1 with IGF-IR, suggesting that the synergy between shear stress and IGF-I in osteoblast proliferation involves integrin-dependent recruitment of SHP-2 and -1 away from IGF-IR.
authors.affiliation: Musculoskeletal Disease Center, Jerry L. Pettis Memorial Veterans Affairs Medical Center, Loma Linda, California 92357, USA.
authors.forename: Sonia
authors.initials: S
authors.lastname: Kapur
authors.forename: Subburaman
authors.initials: S
authors.lastname: Mohan
authors.forename: David J
authors.initials: DJ
authors.lastname: Baylink
authors.forename: K-H William
authors.initials: KH
authors.lastname: Lau
mesh_terms: D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D016023:Integrins / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008934:Mitogens / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D010766:Phosphorylation; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013314:Stress, Mechanical
chemical_list: D016023:Integrins; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008934:Mitogens; D010455:Peptides; D016222:Fibroblast Growth Factor 2; C057986:echistatin; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; C516724:PTPN11 protein, human; C509249:PTPN6 protein, human; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases