Focal adhesion kinase mediates the interferon-γ-inducible GTPase-induced phosphatidylinositol 3-kinase/Akt survival pathway and further initiates a positive feedback loop of NF-κB activation

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Abstract
Interferon-γ-inducible GTPase (IGTP) expression is upregulated in coxsackievirus B3 (CVB3)-infected murine heart and inhibits CVB3-induced apoptosis through activation of the PI3 kinase/Akt pathway. However, the mechanism of this pathway activation is unknown. In this study, using doxcycycline-inducible Tet-On HeLa cells that overexpress IGTP, we have demonstrated that focal adhesion kinase (FAK) is phosphorylated in response to IGTP expression and that transfection of the Tet-On HeLa cells with a dominant negative FAK (FRNK) blocks Akt activation. Furthermore, induction of IGTP also promoted the NF-κB activation as evidenced by its enhanced nuclear translocation, binding to transcriptional promoters and increased transcriptional activity. However, FRNK transfection and phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 both blocked the IGTP-induced translocation and NF-κB activation. Furthermore, silencing NF-κB with siRNAs significantly inhibited the phosphorylation of FAK and Akt, but not their total expression levels, indicating that NF-κB activation is required for the IGTP-induced activation of FAK and PI3K/Akt. Finally, blocking this survival pathway by transfection of FRNK or silencing of NF-κB reduced CVB3 replication and enhanced cell death during CVB3 infection. Taken together, these results suggest that FAK is a mediator upstream of PI3K/Akt and NF-κB functions as a downstream effector and also positively regulates the activity of upstream kinases.

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