FAK dimerization controls its kinase-dependent functions at focal adhesions

Abstract

Focal adhesion kinase (FAK) controls adhesion-dependent cell motility, survival, and proliferation. FAK has kinase-dependent and kinase-independent functions, both of which play major roles in embryogenesis and tumor invasiveness. The precise mechanisms of FAK activation are not known. Using x-ray crystallography, small angle x-ray scattering, and biochemical and functional analyses, we show that the key step for activation of FAK's kinase-dependent functions-autophosphorylation of tyrosine-397-requires site-specific dimerization of FAK. The dimers form via the association of the N-terminal FERM domain of FAK and are stabilized by an interaction between FERM and the C-terminal FAT domain. FAT binds to a basic motif on FERM that regulates co-activation and nuclear localization. FAK dimerization requires local enrichment, which occurs specifically at focal adhesions. Paxillin plays a dual role, by recruiting FAK to focal adhesions and by reinforcing the FAT:FERM interaction. Our results provide a structural and mechanistic framework to explain how FAK combines multiple stimuli into a site-specific function. The dimer interfaces we describe are promising targets for blocking FAK activation.

Phosphatidylinositol 4,5-bisphosphate triggers activation of focal adhesion kinase by inducing clustering and conformational changes

“…A potential site is the conserved W266 and a neighboring pocket involving L327, which are involved in lattice contacts in almost all FAK crystals containing the FERM domain. Interestingly, a recent report suggests W266 to be involved in activating FAK dimer formation (42). Potentially, this dimer could be stabilized in PI(4,5)P 2 -induced clusters; however, it is likely that additional contacts are required to form the more extended clusters we observe.…”

Addressing the Functional Determinants of FAK during Ciliogenesis in Multiciliated Cells

“…Interestingly, even though the FAT domain is necessary and sufficient for FA localization, the FERM domain has been shown to be involved in regulating the dynamics of FAK at FAs and to be responsible for localization at the plasma membrane and at cell-cell junctions (21,22). Moreover, in addition to interactions with other proteins, the FERM domain has been shown to mediate the dimerization of FAK (through FERM-FERM and FERM-FAT interactions) specifically at FAs, raising the possibility that it may regulates FAK's localization and function at CAs through dimerization (28). However, given the qualitative differences in the localization of full-length FAK and the ⌬ FERM mutant, it is unlikely that the FERM domain's role is solely to mediate dimerization at CAs.…”

“…It was proposed that dimerization takes place specifically at FAs and that the dimers are stabilized through an additional interaction between the FERM and the FAT domain (FERM-FAT interaction). Interestingly, binding of paxillin on the FAT domain of FAK appears to further strengthen the FERM-FAT interaction and, therefore, the stabilization of the FAK dimmers (28).…”

“…These interactions retain FAK in a closed-inactive state through steric inhibition of the access to the activation site and the catalytic cleft by activating proteins (25,27). In addition, recent data by Brami-Cherrier et al (28) suggest that the FERM domain mediates intermolecular interactions leading to dimerization of the protein (FERM-FERM interaction), which is a critical step for its activation. It was proposed that dimerization takes place specifically at FAs and that the dimers are stabilized through an additional interaction between the FERM and the FAT domain (FERM-FAT interaction).…”

“…The aminoterminal domain of FAK (FERM domain) is known to mediate multiple interactions, including interactions with growth factor receptors, phosphoinositides, ezrin, and the Arp2/3 complex (2, 12, 13, 17, 18). Moreover, it mediates intramolecular, interactions important for the regulation and dynamics of FAK at FAs (21,25,28).…”