Transcript Viral avoidance and exploitation of the ubiquitin system

Viral avoidance and exploitation
of the ubiquitin system
Felix Randow and Paul J. Lehner
NATURE CELL BIOLOGY May 2009
overview
Introduction
Ubiquitin
Ubiquitylation (Enzymes, Steps)
Ubiquitin chain types
Main part
examples of viral avoidance/ exploitation
of the ubiquitin system
Ubiquitin
Lys 63
Lys 48
•
C terminal tail
•
7 Lysine residues
•
Highly conserved regulatory protein
•
Ubiquitously expressed in
eukaryotes
•
Can be covalently attached to a
protein via an isopeptide bond
•
has a role in regulating many
pathways:
protein degradation,
protein trafficking,
transcription,
cell cycle control,
cell signaling
Ubiquitiylation (Enzymes)
Requires the action of 3 enzymes:
•
E1: ubiquitin activating enzymes (2)
•
E2: ubiquitin conjugating enzymes (40)
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E3: ubiquitin ligases (400):
•
•
RING (really interesting new gene)
RING complexes
•
HECT (homologous to E6AP carboxy terminus)
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U-box (UFD2 homology)
DUBs: deubiquitylating enzymes (90)
cullin-
Ubiquitylation (Steps)
E1
forms aubiquitin
thiol
with the
C-terminal
Proteolytic
removal
of
covalently
attached
Attachment
to theester
substrate
protein
through
Activated
is transferred
onto
a Gly
of
Ubiquitin
in bond
an ATP
dependent
ubiquitin
isconjugating
catalyzed
byenzyme
deubiquitylating
an
isopeptide
through
one
ofreaction
the
ubiquitin
(E2)
by
(activation
for nucleophilic
attack)
enzymes
ubiquitin
ligases
(E3)
transesterification
Ubiquitin chain types
•
Incoming ubiquitin can react
with the N-terminal Meth or
one of the seven Lys of the
acceptor ubiquitin
•
E2s determine linkage
specificity in conjunction
with associated proteins
•
Lys 48 and Lys 63 chains
mark proteins for
proteasomal degradation
•
Met-1 chains contribute to
NF-κB signalling
Ubiquitin as a target for viruses
Ubiquitin encoded in viral genomes
Baculoviruses:
•
encode their own ubiquitin gene :
•
most distantly related, (58/76 residues from
animal ubiquitin)
•
additional Lys residue
•
virions incorporate their own and cellular
ubiquitin into their membranes in a phospholipid
modified form
Ubiquitin encoded in viral genomes
Bovine viral diarrhoea viruses:
•
Ubiquitin and Ubiquitin-like genes (UBL)
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Cytopathic strains have a partial duplication of their
genome with in-frame insertions of UBLs upstream
of the viral NS3 gene
•
The polyprotein requires proteolytic processing
=>the insertion of the UBL leads to release of NS3
(missing in noncytopathic strains)
E3 ligases encoded in viral
genomes
•
Viruses can encode their own E3 ligase or use
adaptor proteins to recruit cellular E3 ligases
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Most viral E3 belong to the RING family , some
don‘t have a RING nor a HECT motif (Replication
Transactivation Activator of HHV8)
•
Other viral genes encoding E3 ligase activity : viral
RING-CH family and the ICP0 family
E3 ligases encoded in viral
genomes
Herpes simplex virus type 1:
•
Encodes ICP0 :
•
RING domain with E3 ligase acivity
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Transactivates viral and cellular genes
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for reactivation from latency and suppression of innate
immunity
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Induces ubiquitilation and proteasome dependent
degradation of Promyelocytic leukemia protein (PML) =>
destruction of PML nuclear bodies
The RING-CH family of viral
ligases
•
E3 ligases with a RING containing a C4HC3 CysHis configuration
•
Promote viral evasion
•
Function: ubiquitilation and downregulation of
receptors (clathrin dependent sorting to an
endosomal compartment/ proteasome-mediated
degradation using the ERAD pathway
The RING-CH family of viral
ligases
Human and murine γ-herspesviruses
•
Encode the canonical viral RING-CH ligase K3
•
Associates and ubiquitilates MHC class I in a post
ER compartment=> internalization, ESCRT
(Endosomal sorting complex required for
transport) depentent sorting and lysosomal
degradation
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Endolysosomal sorting requires Lys 63-linked
polyubiquitin chains
The RING-CH family of viral
ligases
Karposi‘s sarcoma associated
herpesvirus:
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Encodes K3 RING-CH ligase
•
K3 binds and
polyubiquitylates MHC class
I ->Clathrin-mediated
internalization ->
endolysosomal degradation
Non-canonical viral E3 ligases
•
Karposi‘s sarcoma associated herpesvirus:
•
Encodes a replication and transcription activator
(RTA) with intrinsic E3 ligase activity
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Triggers the transition from latency to lytic cycle
replication
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Can be suppressed by cellular factors (IRF7)
•
Blocks IRF7 mediated interferon production by
promoting its ubiquitylation and degradation
Viral adaptors recruiting cellular E3
ligases
•
Human papillomavirus 16 and 18:
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Encode the E6 oncoprotein
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Redirects host cell E3 ligases to ubiquitylate host
proteins => degradation
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E6 induces degradation of p53 by recruiting a
cellular E3 ligase (E6AP)
Viral use of cullin-RING E3 ligases
Human immunodeficiency virus:
•
Cell Host & Microbe 5,
June 18 2009
Viral infectivity factor (Vif):
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Induces polyubiquitylation and
proteasomal degradation of
apolipoprotein B editing compelx
(APOBEC)
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Vif acts as an adaptor to recruit
APOBECG to the CUl5 elongin
B/C-Rbx SCF ligase
•
Depletes the pool of cytosolic
APOBEC3G
Viral use of cullin-RING E3 ligases
Apolipoprotein B editing complex (APOBEK):
•
•
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Deamination of the non-coding strand of the viral genome
from deoxyC to deoxyU => G to A hypermutaion in the
coding strand
restricts the propagation of the virus
If Vif fails to neutralize all APOBEC3F/G activity, Vpr
forms a complex with Cul1 and Cul4 to target cellular uracil
DNA glycosylase for ubiquitylation and proteasomal
degradation
Viral use of cullin-RING E3 ligases
Several paramyxoviruses:
•
Limit the activity of Interferons by targeting STATs
for ubiquitilation and degradation
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V proteins bind directly to STATs and recruit them
to DNA Damage Binding Protein 1 (DDB1) a
substrate adaptor of the Cul4A E3 ligase
Viral genes target cellular substrates for
destruction through the ERAD pathway
stringent quality control in the ER:
proteins failing to assemble =>
translocation back to the cytosol for proteasomemediated degradation
Subversion of this pathway:
viruses target host proteins in the secretory pathway
for rapid degradation
Viral genes target cellular substrates for
destruction through the ERAD pathway
Human cytomegalovirus:
•
Encodes the proteins US2 and US11:
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Catalyse the translocation of MHC
class I from the ER back to the
cytosol
•
Derlin 1 and SEL1L are required
for US11-mediated dislocation
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Signal peptide peptidase is required
for US2- mediated translocation
Viral genes target cellular substrates for
destruction through the ERAD pathway
Human immunodeficiency virus:
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Vpu acts as viral adaptor:
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Induces the proteosomal
degradation of the HIV cell
surface receptor CD4:
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Binds to cytoplasmic tail of CD4
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Recruits ß-transducin repeatcontaining protein , the substrate
adaptor for the cullin RINGßTrCP ligase
Viruses encode DUBs
•
Herpes simplex virus 1:
•
Encodes UL36 a ubiquitin specific Cys protease
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Physiological substrate and role in viral life cycle
unclear
•
Viruses with inactive UL36 show slight
replication impairment and less pathogenicity
Do viruses avoid self-ubiquitylation
by encoding Lys-free proteins?
•
Most substrates are ubiquitylated on an aceptor Lys residue =>
Lys-free proteins could be advantageous to viruses
•
HSV1 (68%GC content/genome) harbours 8 Lys-free proteins
Do viruses avoid self-ubiquitylation
by encoding Lys-free proteins?
•
Epstein-Barr-Virus:
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Lys free protein BHRF1 (Bcl2 family member)
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Controls apoptosis by regulating cytochrome C
release from mitochondria
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Removal of Lys residues from Bcl2 inhibits
degradation and apoptosis
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Possibly escapes ubiquitylation under proapoptotic conditions
A role for ubiquitin in viral egress
Oncogene 2004
23, 1972–1984
•
Cellular machinery for budding virions
equals the formation of multivescular
bodies
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Viral L-domain motifs interact with
components of the ESCRT pathway
and recruit NEDD4 E3 ligases for
membrane fission
•
Essential role of ubiquitin in the release
of enveloped viruses from the plasma
membrane
Conclusions
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Identification of viral ineraction with the ubiquitin
system provides insights into viral pathogenesis and
into basic cellular prosesses (Endoplasmatic
Reticulum Associated protein Degradation, receptor
internalization)
•
More information about non Lys-48 /Lys-63 chains
and their manipulation by viruses is needed
Thank you for your attention!
For further reading:
Isaacson, MK and Hiddle, LP (2009)
Ubiquitination, Ubiquitin-like Modifiers, and Deubiquitination in Viral
Infection
Cell Host & Microbe 5, June 18