Journal of General Virology (2006), 87, 3161–3167
Short
Communication
DOI 10.1099/vir.0.82001-0
Adenovirus RID complex enhances degradation of
internalized tumour necrosis factor receptor 1
without affecting its rate of endocytosis
Y. Rebecca Chin14 and Marshall S. Horwitz1,23
Correspondence
Y. Rebecca Chin
[email protected]
Received 3 March 2006
Accepted 7 July 2006
Department of Microbiology and Immunology1 and Division of Infectious Diseases, Department
of Pediatrics2, Albert Einstein College of Medicine, Forchheimer Building, Room 411,
1300 Morris Park Avenue, Bronx, NY 10461, USA
The receptor internalization and degradation (RID) complex of adenovirus plays an important role in
modulating the immune response by downregulating the surface levels of tumour necrosis factor
receptor 1 (TNFR1), thereby inhibiting NF-kB activation. Total cellular content of TNFR1 is also
reduced in the presence of RID, which can be inhibited by treatment with lysosomotropic agents. In
this report, surface biotinylation experiments revealed that, although RID and TNFR1 were able to
form a complex on the cell surface, the rate of TNFR1 endocytosis was not affected by RID.
However, the degradation of internalized TNFR1 was enhanced significantly in the presence of RID.
Therefore, these data suggest that RID downregulates TNFR1 levels by altering the fate of
internalized TNFR1 that becomes associated with RID at the plasma membrane, probably by
promoting its sorting into endosomal/lysosomal degradation compartments.
The successful replication and survival of viruses in the host
requires evasion of the immune system. Many of the
immunomodulatory genes of adenovirus (Ad) are encoded
in early region 3 (E3) (Fessler et al., 2004b; Horwitz, 2004).
The E3 receptor internalization and degradation (RID)
complex, composed of two RIDa and one RIDb subunits,
downregulates a specific set of plasma-membrane receptors,
including FAS (Shisler et al., 1997; Elsing & Burgert, 1998;
Tollefson et al., 1998), tumour necrosis factor (TNF)-related
apoptosis-inducing ligand receptor 1 (TRAIL-R1) (Benedict
et al., 2001; Tollefson et al., 2001) and epidermal growth
factor receptor (EGFR) (Carlin et al., 1989; Tollefson et al.,
1991). Together with another E3 protein, E3/6.7K, RID also
reduces the surface expression of TRAIL-R2 (Lichtenstein
et al., 2004). Whilst both of the RID subunits are critical for
the downregulation of FAS and TRAIL receptors, it appears
that the RIDa subunit is sufficient to downregulate EGFR
under certain experimental conditions (Hoffman et al.,
1990). Recently, we demonstrated that RID also downregulates TNFR1, thereby inhibiting TNF-induced NF-kB
activation, which mediates the transcription of a large
number of genes involved in inflammation and immune
responses such as chemokine expression (Fessler et al.,
2004a; Delgado-Lopez & Horwitz, 2006).
3Deceased. This paper is dedicated to his memory.
4Present address: Department of Pathology, Beth Israel Deaconess
Medical Center, Harvard Medical School, 330 Brookline Avenue,
Research North 216, Boston, MA 02215, USA.
0008-2001 G 2006 SGM
In vivo experiments have shown that RID is an essential
component of the Ad E3 cassette, which facilitates transplantation of allogeneic pancreatic cells (Efrat et al., 1995)
and decreases autoimmune type 1 diabetes incidence (von
Herrath et al., 1997; Efrat et al., 2001; Pierce et al., 2003). To
potentially use RID as a therapeutic immunomodulator, it is
important to elucidate the molecular mechanism of RIDmediated downregulation of receptors. We recently showed
that the tyrosine sorting motifs of RIDb and clathrin play
important roles in the downregulation of TNFR1, and that
RID-mediated TNFR1 degradation occurs via an endosomal/
lysosomal pathway (Chin & Horwitz, 2005). In this report,
we further examined the effect of RID on TNFR1 trafficking.
Specifically, we tested the ability of RID to interact with
TNFR1 on the cell surface and investigated whether RID
enhances TNFR1 endocyotosis, or rather promotes the
degradation of internalized TNFR1.
We have shown previously that mutation in the tyrosine
sorting motif of RIDb [122tyrosine (Y) mutated to phenylalanine (F); RIDb(YF)] not only abolishes the downregulation of surface TNFR1, but paradoxically increases
surface TNFR1 expression, suggesting that RID and TNFR1
may form a complex on the cell surface (Chin & Horwitz,
2005). To investigate this directly, cell-surface biotinylation
was performed followed by co-immunoprecipitation and
NeutrAvidin pull-down (Fig. 1a). HeLa cells were infected
with a total m.o.i. of 5000 particles per cell (1 p.f.u. is
equivalent to 20 virus particles) of Ad vectors (Chin &
Horwitz, 2005) for 14 h. Cells were washed twice with ice-cold
PBS and incubated with 300 mg EZ-link Sulfo-NHS-biotin
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Y. R. Chin and M. S. Horwitz
Fig. 1. Co-immunoprecipitation of RID with TNFR1 at the cell surface and intracellularly. (a) Experimental scheme for the
detection of protein–protein interactions at the cell surface. HeLa cells were infected with a total m.o.i. of 5000 particles per
cell of the indicated Ad vectors as shown in (b). WT indicates infection with Ad encoding WT RIDa plus Ad encoding WT
RIDb, whereas b(YF) indicates infection with Ad encoding WT RIDa plus Ad encoding mutant RIDb. Ad encoding WT RIDa,
WT RIDb and mutant RIDb were constructed in our laboratory by using the yeast FLP recombinase-based AdMax system
(Microbix Biosystems Inc.). These Ad vectors are E1/E3-deleted and the open reading frame (ORF) of the RID subunit was
inserted in the E1 region driven by the cytomegalovirus (CMV) promoter. Ad/null, a kind gift of Dr William S. M. Wold (St Louis
University, St Louis, MO, USA), is the corresponding negative control with no ORF in the E1 region of Ad. Fourteen hours
post-infection, cells were surface-biotinylated and whole-cell lysates were prepared. RID-interacting proteins were recovered
by anti-RIDb immunoprecipitation. Following elution from the antibody, biotinylated proteins were precipitated with immobilized
NeutrAvidin. Proteins precipitated by NeutrAvidin beads (cell-surface proteins), as well as proteins that could not be
precipitated by NeutrAvidin (intracellular proteins), were analysed by Western blotting with rabbit anti-RIDb antiserum, mouse
anti-TNFR1 antibody and anti-transferrin receptor antibody. (b) Results are representative of three independent experiments
performed as described in (a). The multiple bands of RIDb were fully consistent with different post-translational modifications
of RIDb (Tollefson et al., 1990), including phosphorylation and O-glycosylation (Krajcsi & Wold, 1992; Krajcsi et al., 1992).
Interestingly, the higher- and lower-molecular-mass species of RIDb were found on the cell surface and intracellularly,
respectively. To our knowledge, these are the first observations to suggest that certain post-translational modifications allow
the trafficking of RIDb to the cell surface. Nevertheless, our results showed that both high- and low-molecular-mass RIDb
were able to interact with TNFR1. NIgG, Non-immune rabbit IgG; WB, Western blotting; co-IP, co-immunoprecipitation.
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Journal of General Virology 87
Degradation of internalized TNFR1 by RID
ml21 (Pierce) in PBS for 30 min at 4 uC. The biotinylation
reaction was quenched by rinsing cells three times with
Tris-buffered saline. Whole-cell lysates were prepared and
co-immunoprecipitation was performed by using a Seize
primary mammalian immunoprecipitation kit (Pierce),
where affinity-purified rabbit anti-RIDb antibody (Genemed
Synthesis Inc.; Chin & Horwitz, 2005) or non-immune
rabbit IgG (Santa Cruz Biotechnology) was cross-linked to
immobilized protein G before immunoprecipitation. The
immunoprecipitated complex was eluted in an acidic
elution buffer and the eluant was neutralized by adding
2?5 ml 1 M Tris (pH 9?5) per 50 ml of sample. The immunoprecipitated complex was then dissociated in 1 % SDS by
heating at 95 uC for 7 min and then diluted 20-fold with lysis
buffer [1 % Triton X-100, 150 mM NaCl, 1 mM EDTA,
2 mM Na2P2O7, 30 mM NaF, 20 mM Tris/HCl (pH 7?5)
and 16 complete proteinase inhibitor cocktail (Roche
Molecular Biochemicals)]. Biotinylated proteins were then
precipitated with 30 ml immobilized NeutrAvidin (Pierce)
for 2 h at 4 uC. The beads were washed four times with lysis
buffer and once with PBS. Proteins precipitated by
NeutrAvidin beads were analysed by Western blotting
[cell-surface proteins, left panel of Fig. 1(b)] with rabbit
anti-RIDb antiserum (Genemed Synthesis Inc.), mouse
anti-TNFR1 antibody (Santa Cruz Biotechnology) and
mouse anti-transferrin receptor antibody (Zymed). The
non-biotinylated proteins remaining in the supernatant
after NeutrAvidin precipitation were also collected, concentrated with 10 % trichloroacetic acid and analysed by
Western blot [intracellular proteins, middle panel of
Fig. 1(b)]. Equal amounts of whole-cell lysates from
different samples were also immunoblotted [right panel of
Fig. 1(b)] to determine expression levels of RID, TNFR1 and
transferrin receptor.
Biotinylated TNFR1 was co-immunoprecipitated with
biotinylated RIDb from cells infected with Ad/RIDa and
Ad/RIDb [left panel of Fig. 1(b)], suggesting that RID and
TNFR1 are able to interact on the cell surface, either directly
or through an intermediate bridging molecule. On the other
hand, transferrin receptor, which was shown previously not
to be downregulated by RID (Carlin et al., 1989; Tollefson
et al., 1998), did not co-immunoprecipitate with RIDb,
thus providing a specificity control for the Western blot.
RIDb(YF), which itself has a higher level of surface expression, co-immunoprecipitated more plasma-membrane
TNFR1 than did wild-type (WT) RIDb [left panel of
Fig. 1(b)]. These results agree with previous observations
that the tyrosine sorting motif of RIDb plays an important
role in determining surface levels of RID (Hilgendorf et al.,
2003) and TNFR1 (Chin & Horwitz, 2005). Interestingly,
although there was less RIDb(YF) mutant present intracellularly than WT RIDb, similar amounts of intracellular
TNFR1 were co-immunoprecipitated [middle panel of
Fig. 1(b)]. It is possible that TNFR1, or the molecule that
mediates the interaction between TNFR1 and RID, has a
higher affinity for the RIDb(YF) mutant than the WT RIDb.
Taken together, although we cannot completely rule out the
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possibility that part of the surface TNFR1 signal may be
derived from internal labelling, the increased signal detected
for RIDb(YF) supports the view that labelling indeed
occurred at the cell surface. Therefore, these data suggest
that RID is able to associate with TNFR1 on the cell surface.
It is also noteworthy that, although TNFR1 appears to
interact with RID on the cell surface, the interaction is much
more pronounced in the intracellular fraction.
We next investigated whether RID downregulates surface
TNFR1 by enhancing its endocytosis rate, or rather by
promoting degradation of internalized TNFR1. In order to
find the most appropriate time to carry out the assays, we
first performed a kinetic study of RID-mediated TNFR1
downregulation. 293 cells (56105) were infected with 1000
particles Ad/null per cell for 13 h or 1000 particles Ad/RID
per cell for various durations (0–13 h). Downregulation of
surface TNFR1 by RID was then assayed by flow cytometry
as described previously (Chin & Horwitz, 2005). As shown
in Fig. 2(a), the maximal TNFR1 downregulation activity by
RID was between 5 and 7 h post-infection (the steepest
slope of the curve). Therefore, the endocytosis assay was
performed at 5?5 h post-infection, when RID had a
significant activity towards downregulation of surface
TNFR1, yet sufficient amounts of surface TNFR1 were
still present to enable accurate quantification.
Cleavable biotin was used in the surface biotinylation
assay to measure TNFR1 endocytosis. 293 cells were infected
with 1000 particles Ad/null or Ad/RID per cell for 5?5 h. To
label cell-surface proteins, cells were washed three times
with ice-cold PBS with 0?1 mM CaCl2 and 1 mM MgCl2
(PBS-CM), followed by incubation with 480 mg cleavable
EZ-link Sulfo-NHS-SS-biotin ml21 (Pierce) for 30 min at
4 uC. Unreacted biotin was quenched by rinsing once with
50 mM glycine in PBS-CM and twice with PBS-CM.
Recombinant human TNF (100 ng ml21; R&D Systems)
was added to the indicated samples. Cells were then
incubated at 4 uC to block internalization or at 37 uC for 4
or 6 min to allow endocytosis to occur. Cells were rinsed
twice with ice-cold PBS-CM/10 % fetal bovine serum
(FBS). The remaining surface biotin was cleaved by incubating with glutathione cleavage buffer (50 mM reduced
glutathione in 75 mM NaCl, 75 mM NaOH, 10 % FBS)
twice for 20 min at 4 uC, whereas the internalized biotinylated proteins were protected from the cleavage. Cells
were washed with Dulbecco’s modified Eagle’s medium
(DMEM; Cellgro) and then incubated with PBS-CM with
1 % FBS and 1 mg iodoacetamide ml21 for 15 min at 4 uC.
Cells were lysed and biotinylated proteins were precipitated
with NeutrAvidin. Samples were subjected to Western
blotting and protein levels were quantified by using Scion
Image software.
Fig. 2(b) shows that the kinetics of TNFR1 endocytosis
were very similar in Ad/null- and Ad/RID-infected cells,
with approximately 10 and 20 % of surface TNFR1 internalized in 4 and 6 min, respectively (Fig. 2c). TNFR1
endocytosis was also examined up to 15 min incubation at
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Y. R. Chin and M. S. Horwitz
Fig. 2. TNFR1 endocytosis rate was not affected by RID. (a) Kinetics of TNFR1 downregulation by RID. 293 cells were
infected with 1000 particles Ad/null per cell for 13 h or 1000 particles Ad/RID per cell for the indicated times. Ad/RID is an
E1/E3-deleted Ad vector, which was a kind gift of Dr William S. M. Wold (St Louis University, St Louis, MO, USA). It contains
the RIDa and RIDb ORFs from the Ad2/Ad5 chimera rec700 and was inserted in the E1 region driven by the CMV promoter.
Surface levels of TNFR1 were analysed by flow cytometry and plotted as percentages of geometric mean fluorescence
intensities (gMFI) obtained from Ad/null-infected cells (Ad/null gMFI=100 %, isotype-control gMFI=0 %). (b) 293 cells were
infected with 1000 particles Ad/RID or Ad/null per cell or mock-infected. At 5?5 h post-infection, cells were biotinylated on
ice. Biotinylated proteins were internalized by transferring the cells to 37 6C for 4 and 6 min in the presence or absence of
TNF. Endocytosed proteins were protected from glutathione reduction, precipitated with immobilized NeutrAvidin and
analysed by Western blot. Although the intracellular protein b-tubulin was expressed (as shown in the whole-cell lysates
panel), no b-tubulin was precipitated with the NeutrAvidin beads. This indicates that only cell-surface proteins were
biotinylated. (c) Three Western blots of TNFR1, as per the one shown in (b), were quantified by using Scion Image and the
results were plotted as percentages of biotinylated TNFR1 without glutathione reduction ±SEM. *P<0?05 compared with
Ad/null-infected cells (Student’s t-test, n=3).
37 uC, with no difference observed between Ad/null- and
Ad/RID-infected cells (data not shown). RID was detectable
on the cell surface as well as being endocytosed (Fig. 2b),
suggesting that the lack of an effect in TNFR1 internalization
rate was not due to the lack of RID expression. To control
for potential leakage of biotin across the plasma membrane,
the amount of biotinylated b-tubulin was quantified on the
same blot. The abundant intracellular protein b-tubulin was
not biotinylated (Fig. 2b), suggesting that only cell-surface
proteins were biotinylated and cell integrity was maintained during biotinylation. For comparison, cells were also
stimulated with TNF, which has been shown to induce
TNFR1 internalization (Higuchi & Aggarwal, 1994; Porteu
& Hieblot, 1994). As expected, TNFR1 endocytosis was
increased significantly in the presence of TNF (Fig. 2b).
These results are in accord with the notion that TNFR1
internalizes continuously (Yoshie et al., 1986). Importantly,
the data showed that RID did not downregulate TNFR1 by
increasing its endocyotsis rate. Therefore, we hypothesized
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that RID downregulates surface TNFR1 by altering the fate
of internalized TNFR1.
We have shown previously that RID decreases the total
levels of TNFR1, which can be reversed by inhibitors of
endosomal acidification (Chin & Horwitz, 2005). However,
these studies assessed total cellular TNFR1 levels. In order to
focus specifically on the fate of internalized TNFR1 and
determine whether its degradation was enhanced in the
presence of RID, a modified surface biotinylation assay was
used. 293 cells were infected with 1000 particles Ad/null or
Ad/RID per cell. At 4 h post-infection, when RID had no
effect on the cell-surface level of TNFR1 (Fig. 2a), cells were
rinsed twice with ice-cold PBS. Surface proteins were
biotinylated with 300 mg EZ-link Sulfo-NHS-biotin ml21
(Pierce) as described in the legend to Fig. 1. Cells were then
lysed immediately to determine the initial amount of surface
TNFR1 or incubated in DMEM supplemented with 2 % FBS
for various times (2, 3 or 4 h) at 37 uC to allow trafficking
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Journal of General Virology 87
Degradation of internalized TNFR1 by RID
Fig. 3. Degradation of internalized TNFR1 was enhanced by RID. (a) 293 cells were infected with 1000 particles Ad/null or
Ad/RID per cell. At 4 h post-infection, cell-surface biotinylation was performed. Cells were then incubated at 37 6C for the
indicated times. Proteins were extracted and subjected to NeutrAvidin precipitation followed by Western blot analysis. Results
are representative of three independent experiments. (b) Levels of TNFR1 were quantified by using Scion Image and data
were plotted as the percentage of total biotinylated TNFR1 remaining ±SEM at each incubation time. *P<0?05 (Student’s
t-test, n=3). The lines represent the best-fit second-order polynomial curves used for calculating the half-life of surface
TNFR1. The equations and r2 values are as follows: Ad/null: y=2?6371x2”34?93x+100?34, r2=0?9977; Ad/RID:
y=7?3468x2”53?902x+98?659, r2=1.
and degradation of biotinylated TNFR1. NeutrAvidin precipitation was then performed to recover biotinylated
TNFR1 remaining on and inside the cells. Detection of
biotinylated TNFR1 and transferrin receptor on the Western
blot was done as described above.
As shown in Fig. 3(a), there were similar amounts of
biotinylated TNFR1 in Ad/null- and Ad/RID-infected cells
at 4 h post-infection. After incubating cells at 37 uC for
2–4 h, there was less biotinylated TNFR1 recovered from the
Ad/RID-infected cells than from the Ad/null-infected cells
at all time points examined, indicating that internalized
TNFR1 was degraded more rapidly in the presence of RID.
By fitting a second-order polynomial curve to the data, the
half-life of degradation of surface TNFR1 in Ad/nullinfected cells was approximately 99 min, whereas in the
presence of RID, the half-life of TNFR1 was shortened to
63 min (Fig. 3b). For comparison, the amount of transferrin receptor was also quantified on the same blot (Fig. 3a).
Biotinylated transferrin receptors exhibited little or no
degradation at all time points examined, agreeing with
previous observations that, once being internalized, transferrin receptors were recycled back to the plasma membrane
instead of being degraded in lysosomes (Mayor et al., 1993).
The constant levels of biotinylated transferrin receptor also
control for the possible non-specific effects of viral infection
on cell viability and function. In addition, the lack of effect
on transferrin receptor by RID suggests that the effect of
RID on TNFR1 degradation was specific. As a control,
biotinylation of the intracellular protein b-tubulin was not
observed (data not shown), confirming that no biotin leaked
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across the plasma membrane during the biotinylation
procedure. These results indicated that RID enhanced the
degradation of internalized TNFR1.
As TNF is a proinflammatory cytokine that modulates viral
pathogenesis (reviewed by Herbein & O’Brien, 2000), a
number of viral proteins target the TNF receptor and components of its associated signalling pathways. In this study,
we have demonstrated that RID downregulates the surface
levels of TNFR1 without accelerating its rate of endocytosis.
To our knowledge, this is the first report showing that a
viral protein promotes the degradation of endocytosed
TNFR1. The mechanisms by which RID enhances TNFR1
degradation remain to be elucidated. It is possible that, by
associating with TNFR1 on the cell surface, RID stimulates
mono-ubiquitination of TNFR1 or causes the exposure of
a cryptic degradation or sorting signal on TNFR1, thereby
rerouting the recycling TNFR1 to the endosomal/lysosomal
pathway. Interestingly, RID also downregulates EGFR by
enhancing its degradation, without affecting its endocytosis
rate (Hoffman & Carlin, 1994); this agrees with the finding
that RIDa associates with EGFR in early endosomes (Crooks
et al., 2000). For TNFR1, we showed here that RID could
associate with TNFR1 on the cell surface. In addition,
downregulation of TNFR1 by RID is decreased in the
presence of small interfering RNAs against the m2 subunit of
AP-2, a complex that plays an important role in clathrinmediated endocytosis (Chin & Horwitz, 2005). However,
RID has no effect on the TNFR1 endocytosis rate. These
data suggested that, instead of accelerating the internalization of TNFR1, RID and clathrin play an important role in
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Y. R. Chin and M. S. Horwitz
mediating delivery of TNFR1 to intracellular sites that
accelerate its degradation, probably late endosomes or
lysosomes, as lysosomotropic agents prevent degradation of
TNFR1 by RID (Chin & Horwitz, 2005).
epidermal growth factor receptor trafficking by interacting directly
with receptors in early endosomes. Mol Biol Cell 11, 3559–3572.
Experiments in this study did not address whether RID was
degraded together with TNFR1 in the lysosomes. However,
previous observations showed limited co-localization of
RIDb and FAS in lysosomes (Hilgendorf et al., 2003). In
addition, whereas EGFR was degraded in lysosomes, RIDa
was retained on the limiting membrane of multivesicular
bodies (Crooks et al., 2000). Thus, it is possible that RID
escapes to the recycling pathway for another round of
internalization. Indeed, it would be advantageous for the
virus to use the same protein repeatedly for enhancing the
efficiency of receptor downregulation.
Efrat, S., Fejer, G., Brownlee, M. & Horwitz, M. S. (1995). Prolonged
Although experiments of the current study were performed
with CMV promoter-driven RID, previous flow-cytometry
experiments from our laboratory have shown that infection
of 293 cells with WT adenovirus led to a modest (~17 %)
downregulation of TNFR1 (data not shown), suggesting that
TNFR1 downregulation by RID is not restricted to an
artificial system. We believe that our current mechanistic
studies with the potentially overexpressed CMV promoterdriven RID are relevant for natural adenovirus infection, as
expression levels and effects of RID in vivo are likely to be
dependent on the cell type, as well as many other
parameters. Nonetheless, the potential of expressing and
utilizing E3 proteins, including RID, out of the context of
adenovirus to facilitate allogeneic cell transplantation and
decrease the incidence of type I autoimmune diabetes
prompts further studies aimed at dissecting precise
mechanisms of RID-mediated TNFR1 degradation.
Acknowledgements
Delgado-Lopez, F. & Horwitz, M. S. (2006). Adenovirus RIDab
complex inhibits lipopolysaccharide signaling without altering TLR4
cell surface expression. J Virol 80, 6378–6386.
survival of pancreatic islet allografts mediated by adenovirus immunoregulatory transgenes. Proc Natl Acad Sci U S A 92, 6947–6951.
Efrat, S., Serreze, D., Svetlanov, A., Post, C. M., Johnson, E. A.,
Herold, K. & Horwitz, M. S. (2001). Adenovirus early region 3 (E3)
immunomodulatory genes decrease the incidence of autoimmune
diabetes in NOD mice. Diabetes 50, 980–984.
Elsing, A. & Burgert, H.-G. (1998). The adenovirus E3/10.4K–14.5K
proteins down-modulate the apoptosis receptor Fas/Apo-1 by
inducing its internalization. Proc Natl Acad Sci U S A 95, 10072–
10077.
Fessler, S. P., Chin, Y. R. & Horwitz, M. S. (2004a). Inhibition of
tumor necrosis factor (TNF) signal transduction by the adenovirus
group C RID complex involves downregulation of surface levels of
TNF receptor 1. J Virol 78, 13113–13121.
Fessler, S. P., Delgado-Lopez, F. & Horwitz, M. S. (2004b).
Mechanisms of E3 modulation of immune and inflammatory
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Herbein, G. & O’Brien, W. A. (2000). Tumor necrosis factor (TNF)-a
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Higuchi, M. & Aggarwal, B. B. (1994). TNF induces internalization of
the p60 receptor and shedding of the p80 receptor. J Immunol 152,
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Hilgendorf, A., Lindberg, J., Ruzsics, Z., Höning, S., Elsing, A.,
Löfqvist, M., Engelmann, H. & Burgert, H.-G. (2003). Two distinct
transport motifs in the adenovirus E3/10.4-14.5 proteins act in
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Hoffman, B. L., Ullrich, A., Wold, W. S. M. & Carlin, C. R. (1990).
This research was supported by NIH grants 1PO1DK52956 and
1RO1DK-06744. We thank Steve Porcelli, Ana Maria Cuervo and Todd
Evans for critical reading of the manuscript. This research was
conducted by Y. R. C. in partial fulfilment of the requirements for the
degree of Doctor of Philosophy at Albert Einstein College of Medicine,
Yeshiva University, NY, USA.
Retrovirus-mediated transfer of an adenovirus gene encoding an
integral membrane protein is sufficient to down regulate the receptor
for epidermal growth factor. Mol Cell Biol 10, 5521–5524.
Horwitz, M. S. (2004). Function of adenovirus E3 proteins and their
interactions with immunoregulatory cell proteins. J Gene Med 6,
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Krajcsi, P. & Wold, W. S. M. (1992). The adenovirus E3-14.5K protein
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