Related Experiment Videos
E1B 19K inhibits Fas-mediated apoptosis through FADD-dependent sequestration of FLICE
1Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey 08854, USA.
Abstract:
E1B 19K, the adenovirus Bcl-2 homologue, is a potent inhibitor of apoptosis induced by various stimuli including Fas and tumor necrosis factor-alpha. Fas and TNFR-1 belong to a family of cytokine-activated receptors that share key components in their signaling pathways, Fas-associating protein with death domain (FADD) and FADD-like interleukin-1beta-converting enzyme (FLICE), to induce an apoptotic response. We demonstrate here that E1B 19K and Bcl-xL are able to inhibit apoptosis induced by FADD, but not FLICE. Surprisingly, apoptosis was abrogated by E1B 19K and Bcl-xL when FADD and FLICE were coexpressed. Immunofluorescence studies demonstrated that FADD expression produced large insoluble death effector filaments that may represent oligomerized FADD. E1B 19K expression disrupted FADD filament formation causing FADD and FLICE to relocalize to membrane and cytoskeletal structures where E1B 19K is normally localized. E1B 19K, however, does not detectably bind to FADD, nor does it inhibit FADD and FLICE from being recruited to the death-inducing signaling complex (DISC) when Fas is stimulated. Thus, E1B 19K may inhibit Fas-mediated cell death downstream of FADD recruitment of FLICE but upstream of FLICE activation by disrupting FADD oligomerization and sequestering an essential component of the DISC.
Insights
Adenovirus E1B 19K protein inhibits apoptosis by disrupting Fas-associating protein with death domain (FADD) filament formation. This mechanism prevents the assembly of the death-inducing signaling complex (DISC), blocking cell death signaling.
Area of Science:
- Molecular Biology
- Cell Biology
- Virology
Background:
- Adenovirus E1B 19K is a homologue of Bcl-2 and inhibits apoptosis.
- Fas and Tumor Necrosis Factor Receptor 1 (TNFR-1) initiate apoptosis through shared signaling proteins: Fas-associating protein with death domain (FADD) and FADD-like interleukin-1beta-converting enzyme (FLICE).
Purpose of the Study:
- To investigate the mechanism by which E1B 19K inhibits apoptosis mediated by FADD and FLICE.
- To determine if E1B 19K affects FADD and FLICE localization and function within the death-inducing signaling complex (DISC).
Main Methods:
- Co-expression of E1B 19K, Bcl-xL, FADD, and FLICE in cells.
- Immunofluorescence microscopy to visualize protein localization and filament formation.
- Analysis of apoptosis induction by various stimuli.
Main Results:
- E1B 19K and Bcl-xL inhibited FADD-induced apoptosis but not FLICE-induced apoptosis.
- Co-expression of E1B 19K and Bcl-xL with FADD and FLICE abrogated apoptosis.
- E1B 19K disrupted FADD filament formation and caused relocalization of FADD and FLICE.
- E1B 19K did not bind to FADD but inhibited apoptosis downstream of FLICE recruitment to the DISC.
Conclusions:
- E1B 19K inhibits Fas-mediated apoptosis by disrupting FADD oligomerization.
- This disruption prevents the formation of functional DISC, thereby blocking the apoptotic cascade.
- E1B 19K acts upstream of FLICE activation by interfering with FADD-mediated signaling complex assembly.