Proteomic dissection of FAK protein complexes in heart

Focal adhesions are anatomical structures in cardiac cells at the juxtaposition of the extracellular matrix and the sarcolemma and are involved in mechanotransduction, or the transmission of mechanical forces to enact intracellular responses. Focal adhesion kinase (FAK) is thought to mediate signaling between the membrane and intracellular organelles (e.g. nucleus), however, the proteins involved in FAK signaling at different subcellular locations remain unknown. Therefore, we examined specific subsets of FAK interacting proteins by optimized immunoprecipitation (IP). To identify robust interactions, we examined those that were retained when the IP procedure was conducted in 2% Triton X-100, followed by SDS-PAGE separation and identification by LC/MS/MS. This stringency of wash conditions retained interactions of FAK primarily with structural proteins including integrins, actin, myosin, vimentin and SERCA. We are repeating these analyses following isolation with less detergent (0.5% NP-40) to identify proteins more transiently interacting with FAK and therefore potentially involved in intracellular signaling. We are also using proteomics and confocal microscopy to evaluate the proteins involved in FAK signaling specifically at the nucleus. Together these studies will provide important insights into the signaling microenvironment of FAK in cardiac cells. Supported by AHA and NIH/NHLBI.