also has a role in repair of double-strand breaks. Non-homologous end joining(NHEJ) is a DNA repair pathway frequently used to repair DNA double-strand breaks. The first step in this pathway depends on the Ku70/Ku80 heterodimer that forms a highly stable ring structure encircling DNA ends. But the Ku heterodimer needs to be removed when NHEJ is completed, or it blocks transcription or replication. The Ku heterodimer is ubiquitylated in a DNA-damage and neddylation-dependent manner to promote the release of Ku and other NHEJ factors from the site of repair after the process is completed. In cancer chemotherapy As discussed by Jin and Roberston in their review, silencing of a DNA repair gene by hypermethylation of its promoter may be a very early step in progression to cancer. Gene silencing of a DNA repair gene at the transcription level is proposed to act similarly to a germ-line mutation in a DNA repair gene. Loss of DNA repair capability by either mechanism introduces genome instability and predisposes the cell and its descendants to progression to cancer. Epigenetically silenced DNA repair genes occur frequently in the 17 most common cancers (see e.g. Frequency of hypermethylation of DNA repair genes in cancer). As discussed above, activated-NEDD8 is needed in two DNA repair pathways: NER and NHEJ. If activation of NEDD8 is inhibited, cells with induced deficiency of NER or NHEJ may then die because of deficient DNA repair leading to accumulation of DNA damages. The effect of NEDD8 inhibition may be greater for cancer cells than for normal cells if the cancer cells are independently deficient in DNA repair due to prior epigenetic silencing of DNA repair genes active in alternative pathways (see synthetic lethality). Pevonedistat (MLN4924), a drug inhibiting activation of NEDD8, has shown a significant therapeutic effect in four Phase I clinical cancer trials in 2015-2016. These include pevonedistat trials against acute myeloid leukemia and myelodysplastic syndromes, relapsed/refractory multiple myeloma or lymphoma, metastatic melanoma, and advanced solid tumors. In preclinical studies PPARγ neddylation PPARγ has a crucial role in adipogenesis and lipid accumulation within adipocytes (fat cells). Activated NEDD8 stabilizes PPARγ, allowing increased adipogenesis. In experiments with mice, Pevonedistat, a drug inhibiting activation of NEDD8, prevented high-fat diet-induced obesity and glucose intolerance. NF-κB and NEDD8 The transcriptional activity of NF-κB is primarily regulated by physical interaction with inhibitory IκB proteins (IκBα and IκBβ), which prevents its nuclear translocation. Degradation of the IκBα