1. NF-κB

NF-κB

Target List in NF-κB(followed by the number of products) :

NF-κB Signaling Pathway:

Overview of NF-κB:

Rel/NF-κB proteins are dimeric, DNA sequence-specific transcription factors that coordinate inflammatory responses; innate and adaptive immunity; and cellular differentiation, proliferation, and survival in almost all multicellular organisms. In most cells NF-κB exists in the cytoplasm in an inactive complex bound to IkappaB. The NF-κB network consists of five family member protein monomers (p65/RelA, RelB, cRel, p50, and p52) that form homodimers or heterodimers that bind DNA differentially and are regulated by two pathways: the canonical, NF-κB essential modulator (NEMO)-dependent pathway and the noncanonical, NEMO-independent pathway.

The I Bs bind to NF-κB dimers and sterically block the function of their NLSs, thereby causing their cytoplasmic retention. Potent NF-κB activators, such as TNFα and IL-1, cause almost complete degradation of IκBs (especially I B ) by the 26S proteasome, and NF-κB is activated and enters the nucleus. Nfkb2/p100 is the primary signaling node at which canonical and noncanonical signals interact. NIK/IKK1 processes p100 into p52, enabling the activity of RelB, NIK degrades IκBδ, allowing for sustained RelA activity, and canonical pathway activity may boost noncanonical pathway activation of RelB:p52.

Activation of the NF-κB pathway is involved in the pathogenesis of chronic inflammatory diseases, such as asthma, rheumatoid arthritis, and inflammatory bowel disease. In addition, altered NF-κB regulation may be involved in other diseases such as atherosclerosis and Alzheimer’s disease and a variety of human cancers. Therefore, numerous drugs, natural products, and normal or recombinant proteins that inhibits NF-κB activation can used in the treatment of NF-κB-related diseases.

 

References:

[1] Karin M. Oncogene. 1999 Nov 22;18(49):6867-74.

[2] Yamamoto Y, et al. J Clin Invest. 2001 Jan;107(2):135-42.

[3] Mitchell S, et al. Wiley Interdiscip Rev Syst Biol Med. 2016 May;8(3):227-41.

nf-kappa-b-map.png

NF-κB transcription factors are critical regulators of immunity, stress responses, apoptosis and differentiation. In mammals, there are five members of the transcription factor NF-κB family: RELA (p65), RELB and c-REL, and the precursor proteins NF-κB1 (p105) and NF-κB2 (p100), which are processed into p50 and p52, respectively. NF-κB transcription factors bind as dimers to κB sites in promoters and enhancers of a variety of genes and induce or repress transcription. NF-κB activation occurs via two major signaling pathways: the canonical and the non-canonical NF-κB signaling pathways[1]

 

The canonical NF-κB pathway is triggered by signals from a large variety of immune receptors, such as TNFR, TLR, and IL-1R, which activate TAK1. TAK1 then activates IκB kinase (IKK) complex, composed of catalytic (IKKα and IKKβ) and regulatory (NEMO) subunits, via phosphorylation of IKKβ. Upon stimulation, the IKK complex, largely through IKKβ, phosphorylates members of the inhibitor of κB (IκB) family, such as IκBα and the IκB-like molecule p105, which sequester NF-κB members in the cytoplasm. IκBα associates with dimers of p50 and members of the REL family (RELA or c-REL), whereas p105 associates with p50 or REL (RELA or c-REL). Upon phosphorylation by IKK, IκBα and p105 are degradated in the proteasome, resulting in the nuclear translocation of canonical NF-κB family members, which bind to specific DNA elements, in the form of various dimeric complexes, including RELA-p50, c-REL-p50, and p50-p50. Atypical, IKK-independent pathways of NF-κB induction also provide mechanisms to integrate parallel signaling pathways to increase NF-κB activity, such as hypoxia, UV and genotoxic stress.

 

The non-canonical NF-κB pathway is induced by certain TNF superfamily members, such as CD40L, BAFF and lymphotoxin-β (LT-β), which stimulates the recruitment of TRAF2, TRAF3, cIAP1/2 to the receptor complex. Activated cIAP mediates K48 ubiquitylation and proteasomal degradation of TRAF3, resulting in stabilization and accumulation of the NFκB-inducing kinase (NIK). NIK phosphorylates and activates IKKα, which in turn phosphorylates p100, triggering p100 processing, and leading to the generation of p52 and the nuclear translocation of p52 and RELB[2][3].

 

Reference:

[1]. Oeckinghaus A, et al. The NF-kappaB family of transcription factors and its regulation.Cold Spring Harb Perspect Biol. 2009 Oct;1(4):a000034. 
[2]. Taniguchi K, et al. NF-κB, inflammation, immunity and cancer: coming of age. Nat Rev Immunol. 2018 May;18(5):309-324.
[3]. Perkins ND,et al. Integrating cell-signalling pathways with NF-kappaB and IKK function. Nat Rev Mol Cell Biol. 2007 Jan;8(1):49-62.