Lecture 10: NFkb

Question 1

Five NFkB members

Answer 1

RelA (p65)
RelB
c-Rel
p50/p105 (NFkB1)
p52/p100 (NFkB2)

Question 2

N terminal Rel-homology domain (RHD)

Answer 2

mediates DNA binding and dimerization of NFkB

RelA, RelB, c-Rel contain unrelated c terminal transcriptional activation domains

Question 3

p105 and p100

Answer 3

ubiquitin-dependent proteolytic processing removes C-terminal domain and result in production of mature DNA-binding proteins (p50 and p52)

Question 4

Most common form of NFkB dimers

Answer 4

p50/p65 (NFkB1/RelA)

Rel B can only form heterodimers

Question 5

kB binding site symmetry

Answer 5

5’-GGGRNNYYCC-3’

each dimer subunit reacts with one half site

Question 6

Inhibitors of kappa B (IkBs)

Answer 6

IkB a

IkB b

other less studied forms are IkB gamma and BCL3

Question 7

Ank domains

Answer 7

IkB with Ank domains can interact with RHD sequences on Nf-kB and block the ability of NfkB dimers to bind DNA and nuclear translocation

most studied member is IkBa

Question 8

3 types of IkB kinase (IKK)

Answer 8

IKK-a
IKK-b
IKK-y (NEMO)

a and b together are catalytically active and y subunit serves as a regulatory function

Question 9

How does IKK activates NFkB activation cascade

Answer 9

phosphorylate IkB on Ser32 and Ser36

IkB recognize by B-TRCP and SCF (E3 ubiquitin ligase)

proteasomal degradation of IkB

p50/RelA translocate into nucleus

Question 10

NFkB can be activated by?

Answer 10

interleukin receptor (ILR) via TAK1

toll-like receptor (TLR) via TAK1

RTK and PI3K via AKT or tank binding kinase (TBK1)

Lymphocyte receptor via PKC

TNF receptor pathway activation TAK1 via RIPK1

PHOSPHORYLATES IKKy and activates its activity

Question 11

Non-canonical pathway of NFkB

Answer 11

NIK is activated by receptor ligation

phosphorylate IKKa and IKKb

proteasomal degradation of p100

RelB binds with p52 which has DNA binding activity

regulates distinct class of genes

Question 12

5 effects of NFkB transcription factors

Answer 12

1. negative control of apoptosis (BCL2, BCLXL, CIAP1,2, XIAP survivin)
2. cell proliferation (cyclin D, MYC)
3. cell adhesion and motility (ICAM, VCAM, fibronectin, metalloproteinases)
4. inflammation (IL-6)
5. angiogenesis (VEGF, COX2)

Question 13

Negative feedback for NFkB

Answer 13

1. induction of IkB proteins IkBa and IKB gamma
2. induction of A20 (encoded by TNFAIP3), a ubiquitin-editing enzyme, negatively regulates IKK activity (prevent activation)

Question 14

NFkB activation in leukemia and lymphogenesis

Answer 14

constitutively active in response to growth factors and cytokines or viral oncoproteins

NFkB activation can lead to production of CD40 ligand which positive feedback to increase signalling

activates cyclin D1 and D2 (promote G1 to S phase)

activates inhibitor of apoptosis (BCL-XL, cIAPS and A1/BFL1)

Question 15

2 pathways which contribute to induction of cyclin D1

Answer 15

1. activation of AP1 by growth factors (GF) through MAPK
2. activation of RANKL which binds to RANK and activated IKKa

promote G1 to S phase

Question 16

Role of NFkB in gastric and colorectal cancer

Answer 16

NFkB activation leads to production of inducible nitric oxide synthase (iNOS) and COX2

enhance production of ROS lead to DNA damage

enhance production of growth factors and cytokines can lead to further proliferation of transformed cells

Question 17

Antioxidant therapy

Answer 17

NFkB inhibitors to destroy ROS and RNS (reactive nitrogen species)

Question 18

Proteasome inhibitors

Answer 18

target 26S proteasome

Question 19

IkkB inhibitors

Answer 19

inhibit IKKB but can also have decrease affinity for IKKa

competitors for ATP binding which are required for IKKb activation

allosterically decrease IKK activity