Journal of Cell Science
Akt1 promotes focal adhesion disassembly and cell
motility through phosphorylation of FAK in growth
Maiko Higuchi*,`, Rina Kihara, Tomohiko Okazaki, Ichiro Aoki, Shiro Suetsugu and Yukiko Gotoh
Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
*Author for correspondence (Maiko.Higuchi@mpi-bn.mpg.de)
`Present address: Department III - Developmental Genetics, Max Planck Institute for Heart and Lung Research, Ludwigstrasse 43, 71231, Bad Nauheim, Germany
Accepted 5 December 2012
Journal of Cell Science 126, 745–755
? 2013. Published by The Company of Biologists Ltd
The crosstalk between spatial adhesion signals and temporal soluble signals is key in regulating cellular responses such as cell migration.
Here we show that soluble growth factors enhance integrin signaling through Akt phosphorylation of FAK at Ser695 and Thr700. PDGF
treatment or overexpression of active Akt1 in fibroblasts increased autophosphorylation of FAK at Tyr397, an essential event for
integrin turnover and cell migration. Phosphorylation-defective mutants of FAK (S695A and T700A) underwent autophosphorylation at
Tyr397 and promoted cell migration in response to the integrin ligand fibronectin, but importantly, not in response to PDGF. This study
has unveiled a novel function of Akt as an ‘ignition kinase’ of FAK in growth factor signaling and may shed light on the mechanism by
which growth factors regulate integrin signaling.
Key words: Akt, FAK, Growth factor, Integrin, Migration
Cell migration is essential for many biological processes
including embryonic development, wound healing, and immune
responses, and aberrant motility can also facilitate disease
progression in cancer. Cell migration is mediated by signals
from adhesion systems in combination with soluble signals such
as growth factors (GFs). Although integrins and growth factor
receptors (GFRs) can be activated independently by their own
ligands, integrin-mediated adhesion to the extracellular matrix
(ECM) can induce GFR activation and vice versa (Trusolino
et al., 1998; Woodard et al., 1998; Zheng and Clemmons, 1998;
Adelsman et al., 1999; DeMali et al., 1999). Evidence from
several model systems has demonstrated that integrins can
physically associate with GFRs, thereby regulating the capacity
of integrins and GFRs to propagate downstream signaling
(Miyamoto et al., 1996; Schneller et al., 1997; Goel et al.,
2004). However, an indirect crosstalk that does not require an
association between these receptors has also been proposed (Sieg
et al., 2000; Aplin and Juliano, 2001; Baron et al., 2003). This
type of crosstalk between integrins and GFRs may take place at
the level of reorganization of cytoskeleton or lipid raft, or more
downstream signaling molecules such as focal adhesion kinase
FAK is a central regulator of integrin-mediated signaling. FAK
is present in focal adhesions and is essential for focal adhesion
turnover (e.g. disassembly) and cell migration (Ilic ´ et al., 1995;
Gilmore and Romer, 1996; Owen et al., 1999; Sieg et al., 1999;
Webb et al., 2004). Clustering of integrins activates FAK, which
results in autophosphorylation of Tyr397, formation of a complex
with Src, and increased phosphorylation of the targets of the
FAK–Src complex, such as paxillin and p130Cas (Schaller et al.,
1994; Calalb et al., 1995; Schaller and Parsons, 1995; Tachibana
et al., 1997). In addition to being a component of focal adhesions,
FAK can physically associate with GFRs including c-Met,
epidermal growth factor receptor (EGFR) and platelet-derived
growth factor receptor (PDGFR) (Sieg et al., 2000; Chen and
Chen, 2006). Although previous reports proposed that GFR
binding to FAK leads to activation of FAK by changing its
conformation (Sieg et al., 2000; Chen and Chen, 2006), this is
unlikely to be the case since a FAK mutant unable to bind to c-
Met still could promote hepatocyte growth factor (HGF)-induced
cell migration (Chen and Chen, 2006). Therefore the precise
mechanism by which GFRs activate FAK has remained unclear.
Akt, a downstream target of GFRs, is a key regulator of
biological processes including cell migration (Higuchi et al.,
2001; Kim et al., 2001). The Akt family of serine-threonine
kinases consists of three members: Akt1, Akt2 and Akt3.
Although all the Akt family members share a similar domain
structure, accumulating evidence suggests that they each have
unique roles in various biological processes (Chen et al., 2001;
Cho et al., 2001b; Cho et al., 2001a; Garofalo et al., 2003;
Tschopp et al., 2005). In terms of cell motility, the specific role
of each individual Akt family member seems to depend, in large
part, on the cell type studied. In fibroblasts, which we use in this
study, Akt1 specifically is responsible for promoting cell motility
(Zhou et al., 2006; Higuchi et al., 2008). Although several Akt
substrates; such as ACAP1, Girdin and Skp2; have been
implicated in the regulation of cell migration (Enomoto et al.,
2005; Li et al., 2005; Lin et al., 2009), it remains to be
determined whether phosphorylation of these proteins is indeed
required for Akt-mediated cell motility in various cellular
Journal of Cell Science
Fig. 1. See next page for legend.
Journal of Cell Science 126 (3)746
Journal of Cell Science
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Akt1 is an ignition kinase of FAK755