The Molecular Basis of Filamin Binding to Integrins and Competition with Talin

Abstract

The ability of adhesion receptors to transmit biochemical signals and mechanical force across cell membranes depends on interactions with the actin cytoskeleton. Filamins are large, actin-crosslinking proteins that connect multiple transmembrane and signaling proteins to the cytoskeleton. Here, we describe the high-resolution structure of an interface between filamin A and an integrin adhesion receptor. When bound, the integrin beta cytoplasmic tail forms an extended beta strand that interacts with beta strands C and D of the filamin immunoglobulin-like domain (IgFLN) 21. This interface is common to many integrins, and we suggest it is a prototype for other IgFLN domain interactions. Notably, the structurally defined filamin binding site overlaps with that of the integrin-regulator talin, and these proteins compete for binding to integrin tails, allowing integrin-filamin interactions to impact talin-dependent integrin activation. Phosphothreonine-mimicking mutations inhibit filamin, but not talin, binding, indicating that kinases may modulate this competition and provide additional means to control integrin functions.

β2 integrin phosphorylation on Thr758 acts as a molecular switch to regulate 14-3-3 and filamin binding

“…13 The region in the ␤2 cytoplasmic tail that binds 14-3-3 proteins has been reported to interact with filamin in other integrins, 14 and for the strong filamin-binder ␤7 integrin, phosphorylation mimicking substitutions of 3 threonine residues (TTT) reduces filamin affinity. 3 Filamin has been reported to associate with ␤2 integrins in vivo 15,16 and it binds a ␤2 integrin peptide containing the TTT sequence in vitro. 7 The filamin-integrin cytoplasmic tail interaction negatively regulates talin binding and talin-dependent integrin activation 3 ; it also regulates cell migration.…”

“…Modulation of integrin activity occurs through tightly regulated interactions between cytoplasmic molecules and integrin intracellular tails. Factors binding to integrin cytoplasmic domains regulating integrin adhesiveness include the cytoskeletal proteins talin 1,2 and filamin, 3 and the 14-3-3 proteins, which are molecular adaptors that bind to phosphorylated serine or threonine (pSer/ pThr) containing polypeptide sequences. 4 The ␤2 integrins are expressed exclusively on leukocytes and bind ICAM molecules on other leukocytes and endothelial cells after cell activation.…”

Filamin structure, function and mechanics: are altered filamin-mediated force responses associated with human disease?

“…The structures of FLNA repeat 21 and β7-integrin peptide (Kiema et al 2006), and repeat 17 in complex with the GPIbα peptide , have defined the molecular interactions between FLNA repeat domains and these membrane receptors. The structure of FLNA repeats 19-21 strikingly revealed that the repeats do not necessarily fold linearly as distinct domains (Lad et al 2007).…”

“…Domain 21 is positioned between repeats 19 and 20 (Fig. 2), with repeat 20 partially unfolded contributing its N-terminal β-strand (strand A) to the β-integrin binding site on repeat 21 (Kiema et al 2006). A mechanism proposed for mechanosensing, supported by molecular dynamics calculations, involves a force (Kesner et al 2009;Pentikainen and Ylanne 2009) and/or phosphorylation-induced (Chen et al 2009) conformational change displacing this domain-swapped β-strand uncovering this cryptic β-integrin binding site recruiting FLN to adhesion sites (Lad et al 2007).…”

Filamin A mediates interactions between cytoskeletal proteins that control cell adhesion

“…In addition to actin filaments, filamin A binds >70 other proteins [9,10], many of which are key determinants of cell adhesion, spreading and migration such as the b1 integrin [11]. The importance of filamin A in cell adhesion is underlined by observations that filamin-deficient melanoma cells (M2) exhibit half the adhesion strength of filamin-expressing cells (A7), which has been measured in two different assays [12,13].…”