Inhibition of TRAIL-induced apoptosis and forced internalization of TRAIL receptor 1 by adenovirus proteins

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induc es apoptosis through two receptors, TRAIL-R1 (also known as death receptor 4) and TRAIL-R2 (also known as death receptor 5), that are members of the T NF receptor superfamily of death domain-containing receptors. We show that human adenovirus type 5 encodes three proteins, named RID (previously named E3-10.4K/14.5K), E3-14.7K, and E1B-19K, that independently inhibit TRAIL-i nduced apoptosis of infected human cells. This conclusion was derived from studies using wild-type adenovirus, adenovirus replication-competent mutant s that lack one or more of the RID, E3-14.7K, and E1B-19K genes, and adenov irus E1-minus replication-defective vectors that express all E3 genes, RID plus E3-14.7K only, RID only, or E3-14.7K only. RID inhibits TRAIL-induced apoptosis when cells are sensitized to TRAIL either by adenovirus infection or treatment with cycloheximide. RID induces the internalization of TRAIL- R1 from the cell surface, as shown by flow cytometry and indirect immunoflu orescence for TRAIL-R1. TRAIL-R1 was internalized in distinct vesicles whic h are very likely to be endosomes and lysosomes. TRAIL-R1 is degraded, as i ndicated by the disappearance of the TRAIL-R1 immunofluorescence signal. De gradation was inhibited by bafilomycin A1, a drug that prevents acidificati on of vesicles and the sorting of receptors from late endosomes to lysosome s, implying that degradation occurs in lysosomes. RID was also shown previo usly to internalize and degrade another death domain receptor, Fas, and to prevent apoptosis through Fas and the TNF receptor. RID was shown previousl y to force the internalization and degradation of the epidermal growth fact or receptor. E1B-19K was shown previously to block apoptosis through Fas, a nd both E1B-19K and E3-14.7K were found to prevent apoptosis through the TN F receptor. These findings suggest that the receptors for TRAIL, Fas ligand , and TNF play a role in limiting virus infections. The ability of adenovir us to inhibit killing through these receptors may prolong acute and persist ent infections.