338
Cell Junctions, Structure, Function, and Regulation
Tab. 5
Integrin binding proteins.
Integrin binding proteins
β
-tail
α
-tail
Other regions
Talin
β
1
,β
2
,β
3
Filamin
β
1
,β
2
,β
3
,β
7
α
-actinin
β
1
,β
2
Skelemin
β
1
,β
3
FAK
β
1
,β
2
,β
3
ICAP-1
a
β
1
Paxillin
a
β
1
,β
3
α
4
,α
9
Rack1
β
1
,β
2
,β
3
Cytohesin
a
β
2
β
-endonexin
a
β
2
ILK
β
1
,β
3
SHC
β
3
TAP-20
a
β
5
CD98
β
1
,β
3
Calreticulin
α
5
CIB
α
Iib
Nischarin
α
5
CD47(1AP) (tetraspanins)
α
v
β
3
,α
IIb
β
3
,α
2
β
1
CD9 (tetraspanins)
Multiple integrins
CD81 (tetraspanins)
α
3
β
1
,α
6
β
1
CD151 (tetraspanins)
α
3
β
1
,α
6
β
1
,α
6
β
4
,α
7
β
1
Caveolin
α
1
β
1
,α
5
β
1
,α
v
β
3
a
Paxillin has been shown to bind to both
α
-and
β
-tails.
processes requiring integrin-cytoskeletal
interactions. Talin also binds to FAK,
linking integrins to several signaling path-
ways (see Sect. 1.3.3). The cytoskeletal
proteins, flamin and
α
-actinin, provide
additional linkages between integrins and
the actin cytoskeleton. The actin bind-
ing protein
α
-actinin can bind to the
β
1
and
β
2
tails, whereas flamin binds to
the
β
1
,β
2
,and
β
7
tails. Filamin also links
integrins to signaling pathways that regu-
late the actin cytoskeleton, including RalA,
Rho ±amily GTPases, their activators, as
well as PAK. Thus, flamin–integrin in-
teractions may be important in directing
the actin assembly to sites o± integrin-
mediated adhesion. Skelemin has recently
b
e
ensh
ownt
ob
in
dt
oth
e
β
1
and
β
3
cytoplasmic tails, and current evidence
suggests that it may ±unction in regu-
lating integrin-mediated cell spreading.
Skelemin is a muscle-specifc protein that
binds to myosin; however, evidence is
accumulating suggesting that a skelemin-
related protein is expressed in nonmuscle
cells, suggesting that skelemin-
β
tail inter-
actions may regulate integrin ±unction in
severalcelltypes.
Integrin-
β
cytoplasmic domains have
also been shown to bind to signaling pro-
teins. The membrane-proximal regions o±
the
β
1
,β
2
,and
β
3
cytoplasmic domains
bind to FAK, and the same region o±
the
β
1
and
β
3
tails can also bind to pax-
illin. The ±unctional signifcance o± these
interactions is not yet known; however,
mutations in the FAK binding region in
the
β
-tail do not inhibit the activation
