Adhesion Molecule Phosphorylation in Cancer Chemotherapy - Adhesion Molecules - page 347

577

925

397 576

Fig. 4 Interaction between FAK and Src. h e protein domains of FAK include the amino-(NH)
terminal FERM (band four point one, ezrin, radixin, and moesin homology domain), followed
by the kinase domain (KD) and the focal adhesion targeting (FAT) domain at the carboxyl-
(COOH) terminus. h e FAT domain includes two poly-proline (-PXXP-) motifs that mediate
interaction with Src Homology 3(SH3) domain-containing proteins. Following integrin receptor
stimulation, FAK undergoes auto-phosphorylation of Y 530 . h is creates a binding site for the
Src Homology 2 (SH2) domain of Src (and other proteins). Docking of Src to FAK pY 397 then
promotes Src-mediated phosphorylation of the FAK tyrosine residues Y 576 , Y 577 and Y 925 creating
new docking sites. h e schematics (not to scale) are based on information in Brunton and Frame
(2008) and references therein.

Paxillin

In contrast to Src and FAK, paxillin contains no intrinsic kinase activity (reviewed
in Deakin et al. 2008). Instead, paxillin is a multi-domain scaf old that organizes
complexes of signalling proteins at adhesion sites. Paxillin interaction with partner
proteins such as either the anti-apoptotic protein Bcl-2 or the actin-binding
protein vinculun can stimulate anti-apoptosis signalling and thus paxillin may
promote cancer cell resistance to apoptosis (Deakin et al. 2008). Recent in vitro
data suggests that paxillin phosphorylation by Src may be required for adhesion
turnover that is essential for mesenchymal cell motility (Bach et al. 2009).
Paxilllin binds to the focal adhesion targeting (FAT) domain in the FAK
c-terminus. Together, FAK and Src stimulate the phosphorylation of two main
paxillin tyrosine residues Y 31 and Y 118 (Deakin et al. 2008) (Fig. 5A) . h is creates
binding sites for SH2 domain-containing proteins including the adaptor protein
Crk—a critical step in the regulation of cell motility. Available phospho-antibodies
for paxillin pY 31 and pY 118 are highly successful for immunoblotting (e.g., Chang
et al. 2008, Bach et al. 2009) and immunol uorescence (e.g., Bach et al. 2009).