title: Characterization of DISC formation and TNFR1 translocation to mitochondria in TNF-α-treated hepatocytes.
abstract: Tumor necrosis factor receptor 1 (TNFR1) activation in hepatocytes can trigger apoptotic or inflammatory signaling. The factors that determine which signaling pathway dominates are not clear and are thought to relate to the efficiency of death-inducing signaling complex (DISC) formation. However, the steps involved in DISC formation in hepatocytes are poorly understood. In characterizing DISC formation within cultured hepatocytes, we demonstrated that TNF-α exposure leads to the rapid formation of a DISC involving TNF-α, the TNFR-associated death domain adaptor molecule (TRADD), the Fas-associated death domain adaptor molecule (FADD), caspase-8, TNFR-associated factor 2 (TRAF2), and receptor-interacting protein (RIP). The inclusion of the sensitizing agent actinomycin D both accelerated and amplified the appearance of the DISC. Notably, TNFR1 along with some DISC components also appeared within mitochondria within 30 minutes. Whereas TNFR1 consistently co-localized with the TRADD, FADD, the caspase-8, and TRAF2 in the cytosolic fraction, TNFR1 in the mitochondria was associated only with caspase-8 after TNF-α exposure. Similar observations were made in vivo using TNF-α with D-galactosamine. Actinomycin D alone also enhanced the appearance of DISC components in both cytosol and the mitochondria. Thus the DISC that includes TNFR1 forms in the cytosol of hepatocytes under both survival and pro-apoptotic conditions. The observations also suggest that TNF-α-mediated signaling includes the translocation of TNFR1 to mitochondria.
authors: Department of Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors: Hyun-Ae
authors: HA
authors: Eum
authors: Raghuveer
authors: R
authors: Vallabhaneni
authors: Yinna
authors: Y
authors: Wang
authors: Patricia A
authors: PA
authors: Loughran
authors: Donna Beer
authors: DB
authors: Stolz
authors: Timothy R
authors: TR
authors: Billiar
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053181:Caspase 8 / Q000378:metabolism; D002478:Cells, Cultured; D003609:Dactinomycin / Q000494:pharmacology; D053418:Death Domain Receptor Signaling Adaptor Proteins / Q000096:biosynthesis*; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism; D005690:Galactose / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000378:metabolism; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000378:metabolism*; D053199:TNF Receptor-Associated Death Domain Protein / Q000378:metabolism; D047992:TNF Receptor-Associated Factor 2 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D053418:Death Domain Receptor Signaling Adaptor Proteins; D053200:Fas-Associated Death Domain Protein; D047888:Receptors, Tumor Necrosis Factor, Type I; D053199:TNF Receptor-Associated Death Domain Protein; D047992:TNF Receptor-Associated Factor 2; D014409:Tumor Necrosis Factor-alpha; D003609:Dactinomycin; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D053181:Caspase 8; D005690:Galactose