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Mol. Cell. Biol., Dec 1997, 6906-6914, Vol 17, No. 12
A Richardson, RK Malik, JD Hildebrand and JT Parsons
pp125FAK is a tyrosine kinase that appears to regulate the assembly of
focal adhesions and thereby promotes cell spreading on the extracellular
matrix. In some cells, the C terminus of pp125FAK is expressed as a
separate protein, pp41/43FRNK. We have previously shown that overexpression
of pp41/43FRNK inhibits tyrosine phosphorylation of pp125FAK and paxillin
and, in addition, delays cell spreading and focal adhesion assembly. Thus,
pp41/43FRNK functions as a negative inhibitor of adhesion signaling and
provides a tool to dissect the mechanism by which pp125FAK promotes cell
spreading. We report here that the inhibitory effects of pp41/43FRNK
expression can be rescued by the co- overexpression of wild-type pp125FAK
and partially rescued by catalytically inactive variants of pp125FAK.
However, coexpression of an autophosphorylation site mutant of pp125FAK,
which fails to bind the SH2 domain of pp60c-Src, or a mutant that fails to
bind paxillin did not promote cell spreading. In contrast, expression of
pp41/43FRNK and pp60c-Src reconstituted cell spreading and tyrosine
phosphorylation of paxillin but did so without inducing tyrosine
phosphorylation of pp125FAK. These data provide additional support for a
model whereby pp125FAK acts as a "switchable adaptor" that recruits
pp60c-Src to phosphorylate paxillin, promoting cell spreading. In addition,
these data point to tyrosine phosphorylation of paxillin as being a
critical step in focal adhesion assembly.
Copyright © 1997, American Society for Microbiology
Inhibition of cell spreading by expression of the C-terminal domain of focal adhesion kinase (FAK) is rescued by coexpression of Src or catalytically inactive FAK: a role for paxillin tyrosine phosphorylation
Department of Microbiology, Health Sciences Center, University of Virginia, Charlottesville 22908, USA.
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