From the results of deletion analyses, the FERM domain of FAK has been proposed to inhibit enzymatic activity and repress FAK signaling. We have identified a sequence in the FERM domain that is important for FAK signaling in vivo. Point mutations in this sequence had little effect upon catalytic activity in vitro. However, the mutant exhibits reduced tyrosine phosphorylation and dramatically reduced Src family kinase binding. Further, the abilities of the mutant to transduce biochemical signals and to promote cell migration were severely impaired. The results implicate a FERM domain interaction in cell adhesion-dependent activation of FAK and downstream signaling. We also show that the purified FERM domain of FAK interacts with full-length FAK in vitro, and mutation of this sequence disrupts the interaction. These findings are discussed in the context of models of FAK regulation by its FERM domain.The focal adhesion kinase, FAK, plays a major role in transducing signals downstream of integrins (40,47). Upon integrinmediated adhesion, FAK becomes tyrosine phosphorylated and activated. Additional signaling molecules, e.g., Src and phosphatidylinositol 3-kinase, are recruited into complexes with FAK, leading to the transduction of biochemical signals that control important biological processes. Integrin signaling via FAK regulates cell migration, proliferation, and survival. FAK-dependent regulation of one or more of these processes is essential, since fak Ϫ/Ϫ mice exhibit embryonic lethality (27). Conversely, enhanced FAK signaling may lead to aberrant cell proliferation, survival, or migration, which may have pathological consequences in humans. For example, aberrant FAK signaling may contribute to cancer development and progression to metastatic disease (40).FAK contains three major domains, an N-terminal domain, a central catalytic domain, and a C-terminal domain (40, 47). The C-terminal domain can be further subdivided into the focal adhesion targeting (FAT) sequence, comprising the Cterminal 140 amino acids of the protein, and the region between the catalytic domain and the FAT sequence. Focal adhesion-associated FAT sequence binding partners have been identified, and insight into the molecular basis of FAT sequence function was recently obtained from crystal and nuclear magnetic resonance structure analyses (3,14,23,26,31). The sequence between the catalytic domain and the FAT sequence contains docking sites for SH3 domain-containing proteins and thus serves as a scaffold for the recruitment of signaling proteins. Several sites of tyrosine phosphorylation play important regulatory roles in FAK. Within the catalytic domain, two tyrosine residues in the activation loop, tyrosines 576 and 577, regulate catalytic activity. The major site of autophosphorylation, tyrosine 397, lies just N terminal to the catalytic domain and serves as a binding site for Src family kinases. While details regarding the function of the catalytic and C-terminal domains have been elucidated, fewer studies have examined the function of ...

Since its initial discovery as a substrate and binding partner for the Src oncogene, a role for the focal adhesion kinase (FAK) in cancer has been speculated. In this review the clinical evidence correlating FAK overexpression with cancer and the experimental evidence demonstrating that FAK can control some phenotypes associated with cancer will be discussed. In addition, the emerging theme of interactions between the FAK and growth factor signaling pathways will be described. The evidence presented in this review provides a compelling case for a role for FAK in the pathology of human cancer.

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that plays an important role in normal cellular processes such as adhesion, spreading, migration, proliferation and survival. In addition, FAK is overexpressed in a variety of cancer cells and tumours and may play a role in the development of human cancer. As a prelude to modelling the role of aberrant FAK signalling in the initiation of cancer, the goal of the present study was to engineer point mutations in FAK that would enhance enzymic activity. A number of substitutions that were reported as activating mutations in other tyrosine kinases were introduced into FAK. Glutamic acid substitutions for two lysine residues in the activation loop of FAK, based upon the K650E (Lys(650-->)Glu) mutant of fibroblast-growth-factor receptor 3, were made to create 'SuperFAK'. Two brain-specific exons were engineered into avian FAK to create FAK6.7. SuperFAK and, to a lesser extent, FAK6.7, exhibited increased catalytic activity in vitro compared with wild-type FAK. The expression of SuperFAK and FAK6.7 in fibroblasts led to hyperphosphorylation of FAK substrates. Although the catalytic activity of SuperFAK and FAK6.7 was largely independent of cell adhesion, tyrosine phosphorylation of downstream substrates was adhesion-dependent. Further, since SuperFAK exhibited the same ability as wild-type FAK to recruit Src family kinases, tyrosine phosphorylation of substrates was likely due to direct phosphorylation by FAK. In addition to enhanced biochemical signalling, SuperFAK also increased the motility of epithelial cells. SuperFAK and FAK6.7 may be valuable molecular tools to investigate the potential role of aberrant FAK signalling in human disease.

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