Transcript When NF-kB is inhibited

Role of NF-B in the
Regulation of Immunity
and Apoptosis
Kavitha Bharatham
Abstract
•
•
•
•
•
•
•
Introduction
Structural Description
Role as regulator of Immune responses
Role as regulator of apoptosis
Regulation Mechanism
As target for Therapy
Conclusions
Introduction
Nuclear Factor kappa B (NF- B)
• Multifunctional transcription factor
• Play central role in the cellular response to a variety of stress
signal by regulating genes
• Exists as homo or hetero-dimers found inactive in the
cytoplasm
• Upon stimulation, active NF-B rapidly translocates to the
nucleus where it binds B-sites and activates target genes
Role of NF- B/Rel family
• Involved in proinflammatory response: a first line of defense
against infectious diseases and cellular stress
– Signal  Activated NF- B  immune defence activated
– Immune response, inflammatory response, accute phase
response
• NF-B also a major anti-apoptopic factor
– aberrant activation of NF- B causes
Inflammatory diseases, Rheumatoid arthritis,
Asthma, Atherosclerosis, Alzheimer
– helps keeping cancer cells alive
• NF-B also promoting growth
– Activated NF- B  cyclin D expression enhanced  growth
Factors that induce NF-kB
Reactive Oxygen
Species (ROS)
Leukemia 16:1053-1068, 2002
Genes Regulated by NF-kB
Nat.Rev.Cancer 2:301-310, 2002
Disorders associated with aberrant
NF-B activation
•
•
•
•
•
•
•
•
Rheumatoid arthritis
Atherosclerosis
Vascular dysfunction
Multiple sclerosis
Neurodegenerative disorders
Inflammatory bowel disease
H. pylori-associated gastritis
Systemic inflammatory
response syndrome
• And the list is growing…
• Autoimmune thyroid
disease
• Cystic fibrosis
• Diabetes
• Aging
• Macular degeneration
• HIV/AIDS
• Cancer
• Septic shock
Structural Description
The NF- B/Rel family
NF-B belongs to the Rel family, which contains five
mammalian Rel/NF- B proteins:
1.
2.
3.
1.
2.
Potent transactivators synthesized in their mature form
RelA (p65)
c-Rel
RelB
Synthesized as precursors that are post translationally processed with no
transactivation properties
NF- B1 (p105 undergoes proteolytic maturation to p50)
NF- B2 (p100 undergoes proteolytic maturation to p52)
RelB forms dimer only with p50/p52
Most Common form: p50/p65 (NF-B1/RelA)
NF- B proteins structure
- TAD
NH2
Rel homology domain
GGG C-terminal IkB-like domains
p105
p50
Ankyrin Repeats
p100
+TAD
p52
RelA(p65)
cRel
RelB
TransActivation
domains (TAD)
Structural Details
• Rel Homology Domain (RHD): 300aa conserved domain of
Rel family which contains NLS (Nuclear localisation sequence)
with several functions
– DNA-binding (N-terminal half)
– Dimerization (C-terminal half)
– IB-interaction (C-terminal half)
• IB (Inhibitor of Nf- B) blocks NLS and abolish
translocation to nucleus
–
–
–
–
IB family includes IB-, IB-, IB- and IB-, Bcl-3, etc.,
They posess ankyrin-repeats which are necessary for RHD-interaction
impedes DNA-binding
Upon Signal undergoes dissociation and degradation
Dimerization
p50
Dimer formation is necessary
for DNA-binding
Each subunit interacts with one
half site
B-sites are symmetric:
5´-GGGRNNYYCC-3
Structure: NFkB (p50-p65) + DNA
Side view
b
–--5´-GGGRNNYYCC-3´-–- 3´-CCCYNNRRGG-5´--
Role as Regulator of
Immune responses
Role in inflammation
Inflammation is a
process by which
the body attempts to
dilute, destroy, or
isolate a noxious
(harmful) agent and
repair damage
TNF-alpha
Transcription
TNF
Il-1
Up regulation of adhesion molecules (ICAM-1, VCAM-1)
Cytokines that further enhance the immune response
activators of inflammatory pathways (arachidonic acid met
abolites, superoxides and nitric oxide)
Role of IKK in Activating NF-B
Pro-inflamatory cytokines,
Pathogen associated molecular patterns (PAMPs), TNF Receptor (TNFR),
Toll-like Receptor (TLR), Interleukin-1 receptor (IL-1R)
Two types of inactive
complexes in the cytoplasm
Trimers = RHD-Homo-or
heterodimers bound to an IBrepressor
Heterodimers = Rel-protein +
unprocessed RHD-precursor
(p105, p110)
Transcription
NLS is exposed and
translocated to
Nucleus
B site
Two main signaling pathways
Innate
Adaptive
NUCLEUS
mRNA
Target genes
Transcription
Innate vs Adaptive
NF-kB activation pathway
Canonical/Classical/Innate
NF-B activation pathway
Applies to RelA-p50 and c-Rel-p50
Retained in cytoplasm by IB
NonCanonical/NonClassical/Adaptive
NF-B activation pathway
Affects NF-B2, which preferentially
dimerizes with RELB
Triggered by microbial and viral
infections and exposure to proinfl
ammatory cytokines
Triggered by members of the tumornecrosis factor (TNF) cytokine family
Depends mainly on the IKK sub
unit of the IKK complex.
Depends selectively on activation of the
IKK subunit + another kinase NIK.
Induce the phosphorylation-depen
dent proteolytic removal of the I
B
Induce the phosphorylation-dependent
proteolytic removal of the IB-like
C-terminal domain of NF-B2
Role as Regulator of
Apoptosis
Apoptosis is Programmed Cell Death
Apoptosis is needed to destroy cells
that represent a threat to the integrity
of the organism
Inducers:
• Damage-related inducers
– heat shock, viral infection, bacterial toxins,
oncogenes (myc, rel, E1A), tumor
suppressors (p53), cytolytic T cells,
oxidants
• Therapy-associated agents
– Chemotherapeutic drugs (e.g., cispatin,
nitrogen mustard)
– Antracyclines (doxorubicin), gamma
radiation, UV radiation
• Toxins
– Ethanol, -amyloid peptide
Diseases Associated with Deregulated
Apoptosis
Increased Apoptosis
AIDS
Neurodegernative disorders
Alzeheimer’s disease,
Parkinson’s disease,
Amyotrophic lateral sclerosis
Retinitis pigmentosa
Myelodysplastic syndromes
Aplastic anaemia
Ischaemic Injury
Myocardial infarction,
Stroke,
Reperfusion injury
Toxin-Induced liver disease
Alcohol
Inhibition of Apoptosis
Cancer
Follicular lymphomas
carinomas with p53 mutations
hormone dependent tumours:
breast cancer, prostate cancer,
ovarian cancer
Autoimmune Disorders
Systemic lupus erythematosus
Immune-mediated glomerulonephritus
Viral Infections
Herpesvirus, poxvirus, adenovirus
NF-B is an anti-apoptotic factor
Via NF-B
TNF blocks its own cell death potential
Chemotherapy activates NF-B
within tumor cells
NF-B inhibitors
augment chemotherapy
Mechanism behind Anti-apoptotic
activity
RIP: Receptor interacting protein
FADD: Fas associated Death domain
IAP: Inhibitor of Apoptosis
TRAF: TNFR associated protein
Bid: Bcl-2 interacting domain
JNK: Jun N-terminal kinase
Cell Death
Balance between life and death
When NF-B is not
inhibited
ANTI-APOPTOTIC
PROTEINS
When NF-B is
inhibited
PRO-APOPTOTIC
PROTEINS
Regulation Mechanism
Negative feedback: Attenuation of
NF-B response
• Negative loop: IB is under direct control of NF-B
IB
RelA
ib
IB
p50
kB site
• RIP and TRAF1 are cleaved
Caspase 8
RIP
TRAF1
Cleaved
Therapeutic inhibition of NFB
Conclusions
• The NF-B is an important pathway in regulating the stress
response in the body
• It plays a key role in oncogenesis
• Work continues on manipulating the pathway for use in
therapy
• Complete elucidation of the mechanisms involved in
regulation of NF-B activation is required to generate
inhibitors
• Therapeutic inhibitors that selectively block NF-B activation
in cancer cells without effecting normal functions are required
References
•
•
•
•
•
Seminars in Cancer Biology 13 (2003) 107–114
TRENDS in Immunology Vol.25 No.6 June 2004
Clinical Chemistry 45:1 7–17 (1999)
The Journal of Clinical Investigation January 2001 Volume 107 Number 2
Human Molecular Genetics, 2002, Vol. 11, No. 20