Phosphorylation-Specific Antibodies For Focal Adhesion Kinase (FAK)Multicellular organisms comprise highly ordered arrangements of cells that require precise cell attachments for proper structure and function. Dynamic macromolecule assemblies called focal adhesions form at the cell:cell and cell:extracellular matrix (ECM) junctions, and it is their constant state of assembly and disassembly that mediates cell adhesion, proliferation, migration, and a host of other critical cell functions.
Focal adhesions allow diverse protein activities to concentrate at the cell membrane, providing both an anchorage for attachment to surrounding tissues and a conduit for transduction of signals between the cell and its environment. One hallmark of focal adhesions is the clustering of integrins—membrane receptors with an extracellular domain that binds collagen and other ECM proteins and an intracellular domain that associates with the cytoskeleton through adapter proteins. Integrin-mediated signaling requires the recruitment of many intracellular proteins to the focal adhesion, including focal adhesion kinase (FAK), a key regulator of adhesion and motility in normal and tumor cells.
FAK Signaling Through Phosphorylation
Invitrogen offers a comprehensive portfolio of antibodies for studying the different phosphorylated FAK species, as well as the proteins that interact with them (Table 1). FAK, a nonreceptor protein tyrosine kinase, is expressed in most tissues and cell types and is highly conserved across mammalian and other eukaryotic species . The phosphorylation of FAK’s tyrosine and serine residues in response to integrin engagement, mitogenic neuropeptides, lysophosphatidic acid, platelet-derived growth factor, activated Rho, and selected oncogenes leads to the formation of docking sites for a variety of signaling molecules that ultimately regulate cell morphology, locomotion, proliferation, differentiation, and apoptosis [1–3]. Uncovering the mechanisms of FAK phosphorylation and dephosphorylation, as well as the interactions of FAK with other signaling proteins, is vital to the understanding of these cell processes.
Figure 1. Immunocytochemistry with anti–FAK [pY397] ABfinity™ antibody. A549 (panels A and B) and HeLa (panels C and D) cells were labeled with anti–FAK [pY397] ABfinity™ recombinant rabbit monoclonal antibody at 40 ng/mL and 80 ng/mL, respectively, and then visualized with Alexa Fluor® 488 goat anti–rabbit antibody (panels A and C). In addition, cell nuclei were labeled with Hoechst 33342 stain and the cytoskeleton was labeled with F-actin–specific Alexa Fluor® 568 phalloidin (panels B and D). In the composite images, the focal adhesion complexes appear as green dots at the end of red actin filaments.
Detecting the Different Phosphorylated FAK Species
The FAK protein contains four distinct domains: the catalytic kinase core lies between the N-terminal FERM (band 4.1, ezrin, radixin, moesin) domain and the C-terminal FAT (focal adhesion targeting) domain, and an unstructured proline-rich area is found between the catalytic and FAT domains [1–4]. Table 1 shows these four major FAK domains along with several key tyrosine and serine phosphorylation sites and corresponding phosphorylation site–specific antibodies. In addition to polyclonal antibodies, we offer recombinant ABfinity™ antibodies that recognize specific phosphorylated FAK species (Figure 1). ABfinity™ antibodies are recombinant rabbit monoclonal antibodies that are produced on a large scale by expressing the immunogen-specific antibody gene in mammalian cells. This highly reproducible process results in unparalleled lot-to-lot consistency, specificity, and sensitivity. All of our FAK-specific antibodies are validated for use in major applications, including western blot, immunocytochemistry, immunohistochemistry, and flow cytometry.
Table 1. Functional domains of FAK and the corresponding phosphorylation site–specific FAK antibodies.
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New Directions for FAK Studies
The FAK signaling pathway influences many facets of normal cell function. Recent reports have shown that FAK colocalizes with the tight junction proteins occludin and ZO-1 , and that FAK contains nuclear localization signals consistent with a novel role in gene expression . Moreover, the overexpression of FAK in primary and metastatic tumors has made it an important target for anti-cancer therapies .
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- UniProtKB/Swiss-Prot. Q05397 (FAK1_HUMAN).
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