Abstract-Focal adhesion kinase (FAK) is a nonreceptor protein tyrosine kinase involved in adhesion-dependent signal transduction. FAK is highly expressed in cultured neonatal rat ventricular myocytes (NRVMs) and undergoes tyrosine autophosphorylation in response to cell adhesion, stretch, and growth factor stimulation. We previously showed that inhibition of FAK phosphorylation by adenovirally mediated overexpression of FRNK (the autonomously expressed C-terminal domain of FAK) prevented endothelin-1 (ET)-induced NRVM hypertrophy. One question raised by these studies was whether FRNK localized to focal adhesions and displaced FAK from sites required for downstream signaling. Therefore, we constructed a replication-defective adenovirus encoding a GFP-FRNK fusion protein (Adv-GFP-FRNK) and examined its effects on NRVM cytoarchitecture and signaling. Uninfected NRVMs contained small amounts of endogenous FRNK. NRVMs infected with Adv-GFP-FRNK expressed much larger amounts of a 66-/68-kDa protein that localized to costameres and focal adhesions. GFP-FRNK overexpression suppressed basal and ET-induced FAK phosphorylation and also inhibited ET-induced phosphorylation of PYK2, the other member of the FAK family of nonreceptor protein tyrosine kinases. In contrast, GFP-FRNK overexpression did not prevent ET-induced ERK, JNK, or p70S6K phosphorylation. Furthermore, GFP-FRNK resulted in the loss of detectable FAK and paxillin in focal adhesions, which was accompanied by reduced levels of total paxillin and, ultimately, cell detachment and apoptosis. We conclude that FRNK functions as a dominant-negative inhibitor of adhesion-dependent signaling by displacing FAK from focal adhesions and interfering with the anchorage of NRVMs that is necessary for cell survival, a process known as anoikis. Costamere-like structures containing integrins are found in cultured neonatal and adult cardiac myocytes. 2 Cultured cardiomyocytes also form focal adhesions (similar to focal adhesions assembled by adherent nonmuscle cells in culture) containing  1 -integrins and vinculin. Their organization is highly regulated by peptide growth factors and externally applied or intrinsically generated mechanical load. [3][4][5][6] In addition to their structural role, focal adhesions and costameres are major sites for the localization of cell signaling molecules that are activated during cardiomyocyte hypertrophy. 7-9 Furthermore, disruption of normal cardiomyocyte anchorage during the transition from hypertrophy to early failure leads to apoptosis in an experimental model of ascending aortic coarctation. 10 Focal adhesion kinase (FAK) is a nonreceptor protein tyrosine kinase that is localized to focal adhesions and costameres in cardiomyocytes. FAK undergoes autophosphorylation at a specific tyrosine residue (Y397) in response to cell adhesion, integrin clustering, and growth factor stimulation. 11 In addition, a homologous protein, known as FRNK (FAK-related non-kinase), is also a product of the FAK gene but is autonomously expressed under the cont...
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