Differential regulation of focal adhesion kinase and mitogen-activated protein kinase tyrosine phosphorylation during insulin-like growth factor-I-mediated cytoskeletal reorganization.
In SH-SY5Y human neuroblastoma cells, insulin-like growth factor (IGF)-I mediates membrane ruffling and growth cone extension. We have previously shown that IGF-I activates the tyrosine phosphorylation of focal adhesion kinase (FAK) and extracellular signal-regulated protein kinase (ERK) 2. In the current study, we examined which signaling pathway underlies IGF-I-mediated FAK phosphorylation and cytoskeletal changes and determined if an intact cytoskeleton was required for IGF-I signaling. Treatment of SH-SY5Y cells with cytochalasin D disrupted the actin cytoskeleton and prevented any morphological changes induced by IGF-I. Inhibitors of phosphatidylinositol 3-kinase (PI 3-K) blocked IGF-I-mediated changes in the actin cytoskeleton as measured by membrane ruffling. In contrast, PD98059, a selective inhibitor of ERK kinase, had no effect on IGF-I-induced membrane ruffling. In parallel with effects on the actin cytoskeleton, cytochalasin D and PI 3-K inhibitors blocked IGF-I-induced FAK tyrosine phosphorylation, whereas PD98059 had no effect. It is interesting that cytochalasin D did not block IGF-I-induced ERK2 tyrosine phosphorylation. Therefore, it is likely that FAK and ERK2 tyrosine phosphorylations are regulated by separate pathways during IGF-I signaling. Our study suggests that integrity as well as dynamic motility of the actin cytoskeleton mediated by PI 3-K is required for IGF-I-induced FAK tyrosine phosphorylation, but not for ERK2 activation.
Kim
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Department of Neurology, University of Michigan, Ann Arbor 48109-0588, USA.
Feldman
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D000730:Androstadienes / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002867:Chromones / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1; D009025:Morpholines / Q000494:pharmacology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism*; D000077191:Wortmannin
D000730:Androstadienes; D015815:Cell Adhesion Molecules; D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009025:Morpholines; D015638:Cytochalasin D; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000077191:Wortmannin