Involvement of cell-cell interactions in the rapid stimulation of Cas tyrosine phosphorylation and Src kinase activity by transforming growth factor-beta 1.
Transforming growth factor-beta (TGF-beta) regulates a wide range of physiological and pathological cellular processes, including cell migration, mesenchymal transition, extracellular matrix synthesis, and cell death. Cas (Crk-associated substrate, 130 kDa), an adaptor protein localized at focal adhesions and stress fibers, is also known to have important functions in cell migration and the induction of immediate-early gene expression. Here, we report that a rapid and transient tyrosine phosphorylation of Cas is induced by TGF-beta 1 and that E-cadherin-mediated cell-cell interaction and the Src kinase pathway are involved in this early TGF-beta signaling. The addition of TGF-beta 1 to epithelial cells rapidly induced tyrosine phosphorylation of Cas and promoted the formation of complexes between focal adhesion molecules. Cas phosphorylation required the integrity of the actin cytoskeleton but was not dependent on cell adhesion, implying that Cas-dependent signaling may be distinct from integrin signaling. TGF-beta 1 also stimulated Src kinase activity, and specific inhibitors of Src completely blocked the induction of Cas phosphorylation by TGF-beta 1. The Cas phosphorylation and Src kinase activation seen in our results were induced in an epithelial phenotype-specific manner. Stable transfection of E-cadherin to L929 cells and L cells as well as E-cadherin blocking assay revealed that E-cadherin-mediated cell-cell interactions were essential for both Cas phosphorylation and Src kinase activation. Taken together, our data suggest that rapid Cas phosphorylation and Src kinase activation may play a novel role in TGF-beta signal transduction.
Kim
Jong-Tak
JT
Laboratory of Visual Science, College of Medicine, The Catholic University of Korea, and Catholic Research Institutes of Medical Science, Seoul 137 040, Korea.
Joo
Choun-Ki
CK
D016475:3T3 Cells; D000818:Animals; D015820:Cadherins / Q000235:genetics / Q000502:physiology; D002450:Cell Communication / Q000502:physiology*; D002460:Cell Line; D029563:Cellular Apoptosis Susceptibility Protein / Q000378:metabolism*; D016895:Culture Media, Serum-Free; D003598:Cytoskeletal Proteins / Q000494:pharmacology; D004789:Enzyme Activation; D004847:Epithelial Cells; D005347:Fibroblasts; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D066298:In Vitro Techniques; D015603:Keratinocytes / Q000502:physiology; D007739:L Cells; D051379:Mice; D051419:Paxillin; D010750:Phosphoproteins / Q000494:pharmacology; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D019061:src-Family Kinases / Q000378:metabolism*
D015820:Cadherins; D029563:Cellular Apoptosis Susceptibility Protein; D016895:Culture Media, Serum-Free; D003598:Cytoskeletal Proteins; C496061:PXN protein, human; D051419:Paxillin; D010750:Phosphoproteins; C496062:Pxn protein, mouse; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496051:Ptk2 protein, mouse; D019061:src-Family Kinases