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Mol. Cell. Biol., 06 1996, 2606-2613, Vol 16, No. 6
K Vuori, H Hirai, S Aizawa and E Ruoslahti
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.
Copyright © 1996, American Society for Microbiology
Introduction of p130cas signaling complex formation upon integrin- mediated cell adhesion: a role for Src family kinases
La Jolla Cancer Research Center, Burnham Institute, California 92037, USA.
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