NF-kappa-B essential modulator (NEMO) also known asinhibitor of nuclear factor kappa-B kinase subunit gamma (IKK-γ) is aprotein that in humans is encoded by theIKBKGgene. NEMO is a subunit of theIκB kinase complex that activatesNF-κB.[5] The human gene for IKBKG is located on the chromosome bandXq28.[6] Multiple transcript variants encoding different isoforms have been found for this gene.
NEMO (IKK-γ) is the regulatory subunit of the inhibitor ofIκB kinase (IKK) complex, which activatesNF-κB resulting in activation of genes involved in inflammation, immunity, cell survival, and other pathways.
Incontinentia Pigmenti (IP) is an X-linked dominant disease caused by a mutation in the IKBKG gene. Since IKBKG helps activate NF-κB, which protects cells againstTNF-alpha inducedapoptosis, a lack of IKBKG (and hence a lack of active NF-κB) makes cells more prone to apoptosis.
Moreover, NEMO has been shown to play a role in preeclampsia and may offer insights into the genetic etiology of this condition. An increased level of NEMO gene expression was found in the blood of pregnant women with preeclampsia and their children.[9] However, a decrease of the mRNA levels of total NEMO and the transcripts 1A, 1B, and 1C in placentas derived from preeclamptic women may be the main reason for intensified apoptosis.[9] Sanger sequencing has indicated two distinct variations in the 3’ UTR region of the NEMO gene in preeclamptic women (IKBKG:c.*368C>A and IKBKG:c.*402C>T).[10] The occurrence of a maternal TT genotype and either a TT genotype in the daughter or T allele in the son increases the risk of preeclampsia by 2.59 fold. The configuration of those maternal and fetal genotypes (TT mother/TT daughter or TT mother/T son) is also associated with the level of NEMO gene expression.[10]
NEMO deficiency syndrome is a rare genetic condition relating to a fault in IKBKG. It mostly affects males and has a highly variable set of symptoms and prognoses.[11]
A drug called NEMO Binding Domain (NBD) has been designed to inhibit activation ofNF-κB.[12] NBD is a peptide that acts by binding to regulatory subunit NEMO (IKK-γ) thereby preventing it from binding subunits IKK-α and IKK-β and activating the IKK complex. In the absence of regulatory subunit IKK-γ the IKK complex is inactive, preventing the downstreamsignal transduction cascade leading to NF-κB activation. Binding of IKK-γ to IKK-α and IKK-β subunits activates the IKK complex leading tophosphorylation ofIκB kinase,IκBα, and release of NF-κB dimersp105 andRELA to translocate to the nucleus and activate transcription of NF-κB responsivegenes. In the presence of the NBD peptide, the IKK complex remains inactive and IκBα sequesters NF-κB dimers in the cytoplasm inhibiting transcription of NF-κB responsive genes. While NF-κB inhibitory drugs have previously been attractive to disease such aschronic inflammation anddiabetes, specificcancers have been shown to have constitutive NF-κB activity.[13] AdvancedB-cell lymphoma (ABC), a subtype ofDiffuse large B-cell lymphoma (DLBCL) has been shown to have fundamental andupregulated NF-κB activity.[13] ABC lymphoma also has the lowest survival rate compared to DLBCL subtypes,Germinal CenterB-cell-like and Undefined Type 3 lymphoma, highlighting the great clinical need to define targets for cancer therapy.[13] Notably, the NBD peptide targets the inflammation induced NF-κB activation pathway sparing the protective functions of basal NF-κB activity allowing for greater therapeutic value and fewer undesired side effects.
The NBDpeptide was designed by identifying the amino acid binding sequence on IKK-α and IKK-β to which NEMO binds.[12] A small region on thecarboxyl terminus of IKK-α (L738-L743) and IKK-β (L737-L742) is essential for a stable interaction with NEMO and for the assembly of the active IKK complex. Henceforth this region is called the NEMO binding domain (NBD). The NBD peptide consists of the region from T735 to E745 of the IKK-β subunit fused with a sequence derived from theAntennapediahomeodomain that mediates membranetranslocation. Furthermore,wild type NBD peptide has been shown to dose-dependently inhibit interaction of IKKB with NEMO compared tomutant controls.[12] Additionally, NF-κB activation was suppressed inHeLa cells after incubation with NBD wild type peptides.[12] Moreover, to better understand the potential efficacy of the NBD peptide in suppressing inflammation, NBD peptide was tested on collagen inducedrheumatoid arthritis mouse models. Notably, aberrant NF-κB activity is strongly associated with many aspects of thepathology of rheumatoid arthritis. Mice injected with wild-type NBD peptide showed only slightly visual signs of paw and joint swelling whereas mice injected with PBS or mutant NBD control peptides developed severe joint inflammation.[14] Additionally, analysis of the number ofosteoclasts present in the joints of rheumatoid arthritic showed to be more prevalent in mice treated with PBS or the mutant NBD peptide compared to the NBD wild type peptide.[14] Markedly, throughout the mouse model studies neither toxicity or lethality nor damage to kidneys or livers, was observed.
Despite the potential for NBD peptide as a viable NF- κB inhibitory drug, disadvantages arise because of its peptide form. Peptides as drugs lack membrane permeability, are poorly orally viable, and generally have lower metabolic stability thansmall molecule drugs.[15] Therefore, the NBD peptide is unable to be an orally available compound and must be administered eitherintravenously or viaintraperitoneal injection.
^Jin DY, Jeang KT (1999). "Isolation of full-length cDNA and chromosomal localization of human NF-kappaB modulator NEMO to Xq28".Journal of Biomedical Science.6 (2):115–20.doi:10.1159/000025378.PMID10087442.S2CID202651606.
^abcdMay MJ, D'Acquisto F, Madge LA, Glöckner J, Pober JS, Ghosh S (September 2000). "Selective inhibition of NF-kappaB activation by a peptide that blocks the interaction of NEMO with the IkappaB kinase complex".Science.289 (5484):1550–4.Bibcode:2000Sci...289.1550M.doi:10.1126/science.289.5484.1550.PMID10968790.
^Craik DJ, Fairlie DP, Liras S, Price D (January 2013). "The future of peptide-based drugs".Chemical Biology & Drug Design.81 (1):136–47.doi:10.1111/cbdd.12055.PMID23253135.S2CID9546063.
^abShifera AS, Horwitz MS (March 2008). "Mutations in the zinc finger domain of IKK gamma block the activation of NF-kappa B and the induction of IL-2 in stimulated T lymphocytes".Molecular Immunology.45 (6):1633–45.doi:10.1016/j.molimm.2007.09.036.PMID18207244.
Jin DY, Jeang KT (1999). "Isolation of full-length cDNA and chromosomal localization of human NF-kappaB modulator NEMO to Xq28".Journal of Biomedical Science.6 (2):115–20.doi:10.1159/000025378.PMID10087442.S2CID202651606.
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May MJ, D'Acquisto F, Madge LA, Glöckner J, Pober JS, Ghosh S (September 2000). "Selective inhibition of NF-kappaB activation by a peptide that blocks the interaction of NEMO with the IkappaB kinase complex".Science.289 (5484):1550–4.Bibcode:2000Sci...289.1550M.doi:10.1126/science.289.5484.1550.PMID10968790.
Jain A, Ma CA, Liu S, Brown M, Cohen J, Strober W (March 2001). "Specific missense mutations in NEMO result in hyper-IgM syndrome with hypohydrotic ectodermal dysplasia".Nature Immunology.2 (3):223–8.doi:10.1038/85277.PMID11224521.S2CID9425501.
Döffinger R, Smahi A, Bessia C, Geissmann F, Feinberg J, Durandy A, Bodemer C, Kenwrick S, Dupuis-Girod S, Blanche S, Wood P, Rabia SH, Headon DJ, Overbeek PA, Le Deist F, Holland SM, Belani K, Kumararatne DS, Fischer A, Shapiro R, Conley ME, Reimund E, Kalhoff H, Abinun M, Munnich A, Israël A, Courtois G, Casanova JL (March 2001). "X-linked anhidrotic ectodermal dysplasia with immunodeficiency is caused by impaired NF-kappaB signaling".Nature Genetics.27 (3):277–85.doi:10.1038/85837.PMID11242109.S2CID24898789.
Galgóczy P, Rosenthal A, Platzer M (June 2001). "Human-mouse comparative sequence analysis of the NEMO gene reveals an alternative promoter within the neighboring G6PD gene".Gene.271 (1):93–8.doi:10.1016/S0378-1119(01)00492-9.PMID11410370.
