NF-κB (nuclear factor-kappa B) is a highly regulated, homo- or hetero-dimeric transcription factor, present in almost all cell types. The NF-κB proteins are composed of five different subunits, RelA (p65), RelB, c-Rel (Rel), NF-κB1, and NF-κB2, all of which share a Rel homology domain (RHD) in their N-termini, and have a transactivation domain in their C-termini, except for NF-κB1 and NF-κB2. The NF-κB1 and NF-κB2 proteins are synthesized as longer precursors, p105, and p100, which undergo selective degradation of their C-terminal region containing ankyrin repeats to generate the active NF-κB subunits, p50 and p52, respectively. [i] Different dimer combinations act as transcriptional activators or repressors, respectively. The p50 and p52 NF-κB members play critical roles in modulating the specificity of NF-κB function by forming heterodimers with RelA, RelB, or c-Rel. The NF-κB RelA-p50 and RelB-p50 heterodimeric complexes are transcriptional activators. The NF-κB p50/p50 and p52/p52 homodimers are generally transcriptional repressors, but can function as transcriptional activators when bound to nuclear protein Bcl-3. 
NF-κB is a rapidly acting primary transcription factor, and is controlled by subcellular compartmentalization and post-translational modifications (PTMs) including phosphorylation, acetylation, methylation and ubiquitylation. NF-κB dimers are primarily sequestered as an inactive form in the cytoplasm by a protein complex called inhibitor of kappa B (IκB) among unstimulated cells. Activation of NF-κB occurs via the degradation of IκB, a process initiated by IκB kinase (IKK). A variety of stimuli such as cytokines and cellular stress can activate the IKK, resulting in ubiquitination and dissociation of the IκB from NF-κB. The activated NF-κB is then translocated into the nucleus to regulate gene expression. NF-κB regulates a broad range of genes involved in various biological processes including inflammation, immunity, differentiation, development, as well as genes regulating cell proliferation, apoptosis, cell adhesion and the cellular microenviroment. In addition, NF-κB activates its own repressor IκBα and IκBε, as well as the TNFAIP3 (A20) a negative regulator of IKK activation, forming a negative feedback loop. 
NF-κB has been found to be constitutively active in a number of diseases, including arthritis, chronic inflammation, asthma, neurodegenerative diseases, and heart disease, as well as in many types of human tumors. [ii] NF-κB has long been linked with cancer, primarily through aberrant constitutive NF-κB activation that suppresses apoptosis or promotes tumor growth, metastasis, and angiogenesis by inducing the expression of anti-apoptotic genes, proto-oncogenes, matrix metalloproteinase, cell adhesion genes, and genes associated with the growth of new blood vessels. Additionally, NF-κB promotes a metabolic switch in cancer cells from oxidative phosphorylation to glycolysis (the Warburg effect) by inducing the expression of glycolytic enzymes and inhibiting the expression of mitochondrial gene. Constitutive activation of NF-κB can result from continuous exposure to NF-κB activating stimuli, such as cytokine release by tumor-associated macrophages (TAMs), or from mutations in NF-κB subunits and genes involved in regulating NF-κB function. Inhibiting NF-κB activation can prevent tumor cell proliferation and induce cell death. Given the importance of NF-κB in initiating or enhancing cell survival, NF-κB is therefore considered as a promising target for anticancer therapies.