manipulation of host cell processes

bacterial CDT production

1. export across IM by Sec

2. secretion across OM - OMVs

3. CdtA/C bind receptor

4. endocytosis → ER transport

5. CtdB transport to nucleus

6. DSBs and G2/M arrest

CDT export across IM

assembly in periplasm
CdtA lipid anchor flips

OMVs

bacterial membrane and periplasm proteins contained within

CdtAC receptor binding

lectin subunit that binds host glycans

CdtBC retrograde transport

to ER
CdtA dissociates and leaves ER via ERAD pathway

CtdB transport to nucleus

NLS
causes DSBs in DNA leading to cell cycle arrest

Typhoid toxin

CDT-pertussis hybrid
A2B5
CtdB - cuts DNA
PltB - 15 glycan receptor binding pockets with different preferences that confer cell tropism

typhoid toxin secretory pathway

1. exported across IM via Sec

2. secretion across OM - OMVs

3. on SCV binds Neu5AC glycoprotein receptors

4. trafficked anterograde transport in exocytotic vesicles

5. PltB binds host cell surface - endocytosis to ER

6. CdtB dissociates - DSBs and cell cycle arrest

DSBs and cell cycle arrest

DSBs detected by ATM
signals CHK1/2 and p53 →p21
Cdc25 PPase inhibited
no activation of CDK-cyclin complex

colibactins mechanism of action

small cyclic peptides
alkylate DNA through electrophilic side chains that form interstrand adducts
DDR causes cell cycle arrest

colibactins secretory pathway

1. ClbM autotransport across IM

2. ClbP in periplasm cleaves protective side chains from precursor

3. diffuse into host cell

4. trafficked to nucleus

cytotoxic necrotising factors

single chain exotoxins
activate Rho GTPases
D1-3 is translocon
D4/5 is deamidase

CNFs secretory pathway

1. NTD and CTD bind receptors - endocytosis

2. endosome acidification causes toxin conformational change and release of D4-5

3. D4-5 deamidates RhoA

deamidation by CNFs

RhoA, Rac and Cdc42 deamidated at glutamate - locks in active state

outcome of CNFs

impairs cytokinesis, phagocytosis, ROS
actin reorganisation - stress fibres
membrane ruffling

CIFs

cycle inhibiting factors produced by EPEC and EHEC
T3SS injects Cif which deamidates NEDD8
NEDD8 can't activate CRL Ub ligase so CKIs not degraded
cell cycle arrest

H.pylori VacA

pore forming toxin
binds mitochondria causing calcium influx
ROS causes DSBs - pro apoptotic

H pylori CagA

injected by T4SS - antiapoptotic
phos by host kinases, binds SHP2 and activates - MAPK activation
inhibits BRCA1 localisation to nucleus by inhibiting PAR1b kinase
lncRNA reduces Rad51 transcription by acting as host miRNA decoy

H.pylori CagA independent DSBs

R loop formation due to transcription-replication conflicts in S phase leads to stalled forks that can collapse and give rise to DSBs

H.pylori GGT induces cell cycle arrest

catalyses transpeptidation and hydrolysis of a glutathione group leading to increased ROS production and G1/S arrest

viral subversion of cell signalling

entry and exit
modulating GF signalling
interference with immune response
manipulation of cell cycle

manipulation of host cell entry by viruses - coxsackie virus B

particle attaches to DAF
Abl activation - Rac activation - actin reorganisation - movement to tight junction and binding to CAR for entry
Fyn activation - phos of caveolin and entry

viral modulation of GFs or GFRs

homologues of GFs
homologues of GFRs
receptor transduction
second messenger transduction
TFs
regulation of host second messengers
modulation of transcription

viral homologues of GFs

poxvirus encodes EGFs
low affinity but high potency
induce tissue hyperplasia and cell motility - helps to spread

viral homologues of GFRs

KHSV K1 and EBV LMP2A have ITAM domain at C terminus similar to BCR
activates signalling to Syk pathway constitutively - cellular proliferation and survival

viral receptor transduction

avian erythroblastosis virus V-erbB gene encodes EGFR
no ligand binding domain and mutated kinase domain
always active and resistant to dephosphorylation

viral second messenger transduction

RSV vSrc

viral transcription factor

ASV v-Jun

Regulation of host second messengers

polyoma middle T binds Src and PP2A ensuring Src is always active

modulation of transcription - provirus formation

ALV activation of C-myc in B cell lymphomas
HTLV-1 CTCF links viral transcription through formation of large loops in cellular genes

modulation of transcription - co factors

HTLV tax hub protein has promiscuous binding domain

viral modulation of transcription - co factors 2

HTLV-1 HBZ protein binds bZip TFs

viral methods of interference with immune response

interfering with PRRs
interfering with IFN production
interfering with cytokine/chemokine signalling

viral interference with cytokine/chemokine signalling

modulation of cytokine transcription or translation
cytokine homologues
cytokine receptor homologues

viral modulation of cytokine transcription or translation

HCMV miRNAs inhibit NF-kB signalling

viral cytokine homologues

EBV v-IL-10 inhibits NK cells and APCs
GF for B cells

cytokine receptor homologues

poxvirus TNFRs
HCMV chemokine modulation - 4 viral chemokine receptors

viral manipulation of host cell cycle

Rb family
nuclear events
p53
senescence
apoptosis

normal Rb signalling

CDK4/6 phosphorylates Rb to release E2F and promote S phase entry
dephosphorylation occurs in G2
CKIs can inhibit phosphorylation to arrest cell cycle
P130 and 107 are Rb family that confer G0-1 entry in the same way

viral modulation of Rb

HPV E6 and E7
HTLV1 Tax
viral cyclin D

HPV E7

targets Rb regardless of phosphorylation state so E2F is free - S phase entry
displaces p130 and p107 in basal cells - G1 entry

binds FOXM1 - M entry
binds cyclin D/E - increase stability of phosphorylated Rb
inactivates CKIs

HPV E6

E7 induced Rb degradation leads to p53 increase
E6 recruits E6AP Ub ligase to target p53 for degradation

HTLV-1 Tax

induces transcription of IL2, cyclin D, CDK4/6
inhibits p16 and p53

mimics TCR signalling

viral cyclin D

KHSV vcD has higher stability and affinity
has different specificity to different CDKs

viral modulation of nuclear events - APC

HCV pUL2a degrades APC
HPV E2 and EBV degrade Cdc20 co factor
HSV-1 ICP0 inhibits cyclin B-cdk1 to prevent APC activation
all cause pseudo S phase entry

viral p53 modulation

E6 targets for degradation
E7 binds p21 to prevent activation by p53

viral modulation of senescence

HPV E6 activates hTERT
E7 lengthens telomeres via ALT pathway

viral modulation of apoptosis

KHSV LANA inhibits p53 and Rb and activates pro survival pathways

viral mechanisms of modulating transcription

integration
genome rearrangements
targeting TFs
exploiting ribosomal pausing

Integration - retroviruses

viral DNA binds integrase
LEDGF links integrase to host DNA at H3K3/6me3 sites via PWWP
AT hook binds DNA

integration - episomes

KHSV LANA tethers episomes to nucleus through chromosomes
LANA can stimulate proliferation

viral genome rearrangements

EBV EBNAs immortalise B cells by bringing super enhancers in close proximity to each other and distal genes
pro proliferative

viral targeting TFs

HSV VP16 - sequesters cellular TFs to viral promoters, binds DNA through Oct1
HBV Hbx - recruits TF2B and pol2

viral exploitation of ribosomal pausing - HIV

first 60nts of TAR form a hairpin where ribosome pauses - platform for tat
tat binds TAR RNA and recruits PTEF-b = productive transcription
Vpr induces conf change in TFIIB so tat can interact

viral exploitation of ribosomal pausing - influenza

cap snatching
PB2 binds 5' G0 cap
PA cleaves host mRNA
PB1 elongates

listeria histone modifications

LLO dephosphorylates H3S10
InlB promotes translocation of HDAC to nucleus where it deacetylates H3K18 to reduce ISG
BAHD1 HDAC complex recruited to ISG promoters - inhibitory

chlamydia histone methylation

Nue methylates H2B

B.anthracis lethal toxin

inactivation of MAPK means H3 isn't modified at IL-8 promoter so NF-kB can’t bind

Shigella OspF

phosphothreonine lyase, inactivates JNK and ERK
prevents H3S10 phosphorylation at NF-kB regulated promoters
no ISG transcription

parasitic modulation of transcription

induction of host epigenetic enzyme
secreted effectors driving genetic repression
secretion of non coding RNAs
induction of host miRNAs

parasitic induction of host epigenetic enzyme

therleria annulata upregulates SMYD3 which increases H3K4me3 on MMP promoter to increase expression

parasitic secreted effectors driving genetic repression

toxoplasma TEEGR

parasitic secretion of ncRNAs

cryptosporidium ncRNAs recruits histone methylation machinery to silence host immune genes

parasitic induction of host miRNAs

theileria upregulates miRNA that targets DET1 therefore stabilising c-Jun and creating a feedback loop to maintain cellular transformation

toxoplasma - ROP16

mimics JAKKs to activate STAT3/6 by phosphorylation leading to IL4 transcription
M2 polarisation and decreased IL12

toxoplasma - GRA16

binds HAUSP
may play role in G2/M arrest

toxoplasma TgIST

interacts with phosphorylated STAT1 to recruit repressor complex
disrupts ISGs

toxoplasma - TEEGR

recruits host transcription factors to induce EZH2 expression
EZH2 trimethylates H3K27 to repress NF-kB targets

toxoplasma - GRA24

molecular mimicry of scaffold protein
activates p38 MAPK

leishmania modulation of transcription

cleaves NF-kB and co regulators
increased negative regulators
epigenetic modulation

viral modulation of translation initiation

inhibitors and mitigators
manipulation of mTOR
EIF2 kinases

viral inhibition of translation initiation

picornaviruses 2A proteases cleaves 4E or 4G to prevent cap binding complex
caliciviurs VpG binds EIF3 in pre initiation complex to prevent initiation
BUNV and RVFV bind PABP to prevent association with pA

viral mitigators

IRES means no need for cap or pre initiation complex

viral manipulation of mTOR

normally mTOR inhibits autophagy and apoptosis so viruses want to activate
Stimulate PI3K
activate Akt
degrade TSC2 - Rheb is active - mTORC activated

viral manipulation of EIF2 kinases

PKR inhibited by EBV EBNAs that act as PKR decoys
PERK inactivated by VacV K3L
HR1 antagonised by HCMV TRS1

viral modulation of translation elongation

ribosomal frameshifting
KHSV LANA
viral miRNAs

ribosomal frameshifting

HIV - 20:1 ratio of gag to gag-pol
coronavirus - ratio between primase and RdRp
cardiovirus 2A - activates frameshifting and leads to more 2B* over 2B in late infection

KHSV LANA

LANA blocks SAT1 leading to increase in spermidine and therefore eIF5A hypusination which is essential for translation
eiF5A can now translate polyprolines - present in LANA

viral evasion of miRNA decay

protect RNA ends
recruit stabilising factors
inactivate decay machinery
promote decay to dominate translation

viral miRNAs in translation

HCV miR-122 increases translation

shigella SidL in translation

inhibits translation
binds directly to ribosome
tRNA mimicry
glycosylates ribosome to induce stalling
subsequent ribosomal collisions activate stress response