protein kinase C zeta type (PKCζ) serves the same purpose. Two residues in the TAD region are targeted by phosphorylation. After IL-1or TNFα stimulation, serine 529 is phosphorylated by casein kinase II (CKII), while serine 536 is phosphorylated by IκB kinases (IKKs). In response to DNA damage, ribosomal subunit kinase-1 (RSK1) also has the ability to phosphorylate RELA at serine 536 in a p53-dependent manner. A couple of other kinases are also able to phosphorylate RELA at different conditions, including glycogen-synthase kinase-3β (GSK3β), AKT/phosphatidylinositol 3-kinase (PI3K) and NF-κB activating kinase (NAK, i.e. TANK-binding kinase-1 (TBK1) and TRAF2-associated kinase (T2K)). The fact that RELA can be modified by a collection of kinases via phosphorylation at different sites/regions within the protein under different stimulations might suggest a synergistic effect of these modifications. Phosphorylation at these sites enhances NF-κB transcriptional response via tightened binding to transcription coactivators. For example, CBP and p300 binding to RELA are enhanced when serine 276 or 311 is phosphorylated. Status of several phosphorylation sites determines RELA stability mediated by the ubiquitin-mediated proteolysis. Cell-type-specific phosphorylation is also observed for RELA. Multiple-site phosphorylation is common in endothelial cells, and different cell types may contain different stimuli, leading to targeted phosphorylation of RELA by different kinases. For instance, IKK2 is found to be mainly responsible for phosphorylating serine 536 in monocytes and macrophages, or in CD40 receptor binding in hepatic stellate cells. IKK1 functions as the major kinase phosphorylating serine 536 under different stimuli, such as the ligand activation of the lymphotoxin-β receptor (LTβR). Acetylation In vivo studies revealed that RELA is also under acetylation modification in the nucleus, which is just as important as phosphorylation as a post-translational modification of proteins. Lysines 218, 221 and 310 are acetylation targets within RELA, and response to acetylation is site-specific. For instance, lysine 221 acetylation facilitates RELA dissociation from IκBα and enhances its DNA-binding affinity. Lysine 310 acetylation is indispensable for the full transcriptional activity of RELA, but does not affect its DNA-binding ability. Hypothesis about RELA acetylation suggests acetylation aids its subsequent recognition by transcriptional co-activators with bromodomains, which are specialized in recognizing acetylated lysine residues. Lysine 122 and 123 acetylation are found to be negatively correlated with RELA transcriptional activation. Unknown mechanisms mediate the acetylation of RELA possibly using p300/CBP and p300/CBP factor associated coactivators under TNFα or phorbol myristate acetate (PMF) stimulation both in vivo and in vitro. RELA is