Fas-associated death-domain protein inhibits TNF-α mediated NF-κB activation in cardiomyocytes

Fas-associated death-domain protein (FADD) is an adaptor molecule that links death receptors to caspase-8 in many cell types including cardiomyocytes (CMs). Although FADD has previously been reported to play an important role in CM apoptosis, the effect of FADD on CM NF-κB signaling, which is a proinflammatory pathway, has not been delineated. To investigate the role of FADD in CM NF-κB activation, we utilized adenoviral gene transfer of wild-type FADD and a truncation mutant that lacks the death-effector domain (FADD-DED) in rat CMs in vitro. TNF-α activated NF-κB in CMs as demonstrated by phosphorylation and degradation of inhibitory-κB (IκB)-α-enhanced nuclear p65 and NF-κB DNA-binding activity as well as increased mRNA for the NF-κB-dependent adhesion molecule VCAM-1 (19 ± 4.1-fold) as measured by quantitative RT-PCR. Gene transfer of FADD inhibited TNF-a-induced IκB-α phosphorylation, decreased p65 nuclear translocation and NF-κB DNA-binding activity, and reduced VCAM-1 transcript levels by 53-65%. Interestingly, FADD-DED exhibited a similar but weaker inhibitory effect on NF-κB activation. The effects of FADD on NF-κB were cell-type specific. FADD expression also inhibited TNF-α-mediated NF-κB activation in human endothelial cells but not in rat pulmonary artery smooth muscle cells. In contrast, FADD expression actually activated NF-κB in human embryonic kidney (HEK)-293 cells. In CMs, FADD inhibited NF-κB activation as well as phosphorylation of IκB-α and IκB kinase (IKK)-β in response to cytokine stimulation or expression of the upstream kinases NF-κB-inducing kinase and IKK-β. These data demonstrate that FADD inhibits NF-κB activation in CMs, and this inhibition likely occurs at the level of phosphorylation and activation of IKK-β.