Fas-associated death-domain protein inhibits TNF-alpha mediated NF-kappaB 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-kappaB signaling, which is a proinflammatory pathway, has not been delineated. To investigate the role of FADD in CM NF-kappaB 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-alpha activated NF-kappaB in CMs as demonstrated by phosphorylation and degradation of inhibitory-kappaB (IkappaB)-alpha-enhanced nuclear p65 and NF-kappaB DNA-binding activity as well as increased mRNA for the NF-kappaB-dependent adhesion molecule VCAM-1 (19 +/- 4.1-fold) as measured by quantitative RT-PCR. Gene transfer of FADD inhibited TNF-alpha-induced IkappaB-alpha phosphorylation, decreased p65 nuclear translocation and NF-kappaB DNA-binding activity, and reduced VCAM-1 transcript levels by 53-65%. Interestingly, FADD-DED exhibited a similar but weaker inhibitory effect on NF-kappaB activation. The effects of FADD on NF-kappaB were cell-type specific. FADD expression also inhibited TNF-alpha-mediated NF-kappaB activation in human endothelial cells but not in rat pulmonary artery smooth muscle cells. In contrast, FADD expression actually activated NF-kappaB in human embryonic kidney (HEK)-293 cells. In CMs, FADD inhibited NF-kappaB activation as well as phosphorylation of IkappaB-alpha and IkappaB kinase (IKK)-beta in response to cytokine stimulation or expression of the upstream kinases NF-kappaB-inducing kinase and IKK-beta. These data demonstrate that FADD inhibits NF-kappaB activation in CMs, and this inhibition likely occurs at the level of phosphorylation and activation of IKK-beta.