Introduction of p130cas signaling complex formation upon integrin-mediated cell adhesion: a role for Src family kinases.
Integrin-mediated cell adhesion triggers intracellular signaling cascades, including tyrosine phosphorylation of intracellular proteins. Among these are the focal adhesion proteins p130cas (Cas) and focal adhesion kinase (FAK). Here we identify the kinase(s) mediating integrin-induced Cas phosphorylation and characterize protein-protein interactions mediated by phosphorylated Cas. We found that expression of a constitutively active FAK in fibroblasts results in a consecutive tyrosine phosphorylation of Cas. This effect required the autophosphorylation site of FAK, which is a binding site for Src family kinases. Integrin-mediated phosphorylation of Cas was not, however, compromised in fibroblasts lacking FAK. In contrast, adhesion-induced tyrosine phosphorylation of Cas was reduced in cells lacking Src, whereas enhanced phosphorylation of Cas was observed Csk- cells, in which Src kinases are activated. These results suggest that Src kinases are responsible for the integrin-mediated tyrosine phosphorylation of Cas. FAK seems not to be necessary for phosphorylation of Cas, but when autophosphorylated, FAK may recruit Src family kinases to phosphorylate Cas. Cas was found to form complexes with Src homology 2 (SH2) domain-containing signaling molecules, such as the SH2/SH3 adapter protein Crk, following integrin-induced tyrosine phosphorylation. Guanine nucleotide exchange factors C3G and Sos were found in the Cas-Crk complex upon integrin ligand binding. These observations suggest that Cas serves as a docking protein and may transduce signals to downstream signaling pathways following integrin-mediated cell adhesion.
Vuori
K
K
La Jolla Cancer Research Center, Burnham Institute, California 92037, USA.
Hirai
H
H
Aizawa
S
S
Ruoslahti
E
E
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001665:Binding Sites; D002448:Cell Adhesion / Q000502:physiology*; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D050719:Crk-Associated Substrate Protein; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D016023:Integrins / Q000502:physiology*; D051379:Mice; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology; D010750:Phosphoproteins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000502:physiology; D011506:Proteins; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050717:Retinoblastoma-Like Protein p130; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism; D018909:src Homology Domains; D019061:src-Family Kinases / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; C493842:Bcar1 protein, mouse; C493843:Bcar1 protein, rat; C082869:CRKL protein; D015815:Cell Adhesion Molecules; D050719:Crk-Associated Substrate Protein; D016023:Integrins; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D050717:Retinoblastoma-Like Protein p130; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496051:Ptk2 protein, mouse; C496052:Ptk2 protein, rat; D019061:src-Family Kinases