Disruption of cell-substrate adhesion activates the protein tyrosine kinase pp60(c-src).
Treatment of confluent chicken embryo fibroblasts (CEFs) with trypsin results in a dose- and time-dependent increase in c-Src protein tyrosine kinase (PTK) activity. A similar, but less marked, increase in c-Src PTK activity occurs upon incubation of CEFs in calcium-free phosphate-buffered saline, which also causes a decrease in cell-substrate adhesion. The increase in c-Src PTK activity following disruption of cell-substrate adhesion correlates with a decrease in the phosphorylation of c-Src at the regulatory site, Tyr527. The phosphotyrosine phosphatase inhibitor phenylarsine oxide blocks the increase in c-Src PTK activity seen following treatment with trypsin and the morphological changes associated with the disruption of cell-substrate adhesion. In contrast, disruption of cell-substrate adhesion causes a decrease in FAK PTK activity that rapidly returns to control levels when the cells are plated on fibronection-coated dishes. Treatment of cells with cytochalasin D, which disrupts actin filaments but not cell-substrate adhesion, causes only a slight increase in c-Src PTK activity. Thus, these studies demonstrate a ligand-independent mechanism for the activation of c-Src that is consistent with its role in both cell adhesion and cell motility. Furthermore, these data suggest that similar to adhesion, loss of adhesion is not a passive process but can activate specific signaling pathways that may have significant effects on cellular function.
Maher
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Department of Cell Biology, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, California, 92037, USA. pmaher@scripps.edu
D000818:Animals; D001152:Arsenicals / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002642:Chick Embryo; D015638:Cytochalasin D / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D005353:Fibronectins / Q000378:metabolism; D051416:Focal Adhesion Protein-Tyrosine Kinases; D010766:Phosphorylation; D011107:Polylysine / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D014357:Trypsin; D014443:Tyrosine / Q000378:metabolism
D001152:Arsenicals; D004791:Enzyme Inhibitors; D005353:Fibronectins; C029341:oxophenylarsine; D015638:Cytochalasin D; D011107:Polylysine; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D051416:Focal Adhesion Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src); D017027:Protein Tyrosine Phosphatases; D014357:Trypsin