NEMO differentially regulates TCR and TNF-I- induced NF-IoB pathways and has an inhibitory role in TCR-induced NF-IoB activation

• Published in: Cellular signalling 2012-08, Vol.24 (8), p.1556-1564
• Main Authors: Wang, Kai, Diao, Liang-Hui, Gong, Yu, Liu, Xin, Li, Yingqiu
• Format: Article
• Language: English
• Subjects: Activation; Cellular; Degradation; Genes; Kinases; Pathways; Ribonucleic acids; Signalling
• ISSN: 0898-6568
• DOI: 10.1016/j.cellsig.2012.03.022

NF-IoB essential modulator (NEMO), the regulatory subunit of the IIoB kinase (IKK) complex, is an essential adaptor both for inflammation stimuli and TCR-induced NF-IoB activation. However, the exact mechanism of its function has not been fully understood. Here, we report that knockdown of NEMO by RNA interference in Jurkat E6.1 cells enhanced TCR-induced NF-IoB report gene activity and IL-2 production by promotion of IIoBI- degradation and p65 nuclear translocation, whereas inhibited TNF-I- and LPS-induced IIoBI- degradation without influencing the phosphorylation of MAPKs. In human primary T and Jurkat E6.1 cells, both CD3/CD28 and PMA/Ionomycin induced NF-IoB activation showed a para-curve correlation with the dosage of small interfering RNA targeting NEMO (siNEMO): the NF-IoB report gene activity was increased along with ascending doses of transfected siNEMO and reached the highest activity when knockdown about 70% of NEMO, then turned to decline and gradually be blocked once almost thoroughly knockdown of NEMO. Meanwhile, TNF-I- induced NF-IoB was always inhibited no matter how much NEMO was knockdown. Subcellular fractionation results suggested that upon CD3/CD28 costimulation, NEMO and IKKI2 may not cotranslocate to cytoskeleton fraction as a conventional NEMO/IKK complex with a static stoichiometric ratio, instead the ratio of NEMO: IKKI2 continuously shift from high to low. Depletion of NEMO accelerated TCR-induced cytoskeleton translocation of IKKI2. Altogether, this study suggests that NEMO may function as a rheostat exerting a negative action on TCR-induced NF-IoB activation and differentially regulates TNF-I- and TCR-induced NF-IoB pathways.