The E3 ubiquitin ligase RNF121 is a positive regulator of NF-κB activation.
BACKGROUND
The nuclear factor κB (NF-κB) family members regulate several biological processes as cell proliferation and differentiation, inflammation, immunity and tumor progression. Ubiquitination plays a key role in NF-κB activation and the ubiquitylated transmitters of the NF-κB signaling cascade accumulate in close proximity to endomembranes.


RESULTS
We performed an unbiased siRNA library screen targeting the 46 E3 ubiquitin ligases bearing transmembrane domains to uncover new modulators of NF-κB activation, using tumor necrosis factor-α (TNF-α) receptor (TNFR) stimulation as a model. We report here the identification of a new Golgi Apparatus-resident protein, RNF121, as an enhancer of NF-κB promoter activity through the catalytic function of its RING domain. From a molecular standpoint, while knocking down RNF121 did not alter RIP1 ubiquitination and IKK activation, the proteasomal degradation of IκBα was impaired suggesting that this E3 ubiquitin ligase regulates this process. However, RNF121 did not directly ubiquitinate IκBα While they were found in the same complex. Finally, we discovered that RNF121 acts as a broad regulator of NF-κB signaling since its silencing also dampens NF-κB activation following stimulation of Toll-Like Receptors (TLRs), Nod-Like Receptors (NLRs), RIG-I-Like Receptors (RLRs) or after DNA damages.


CONCLUSIONS
These results unveil an unexpected role of Golgi Apparatus and reveal RNF121 as a new player involved in the signaling leading to NF-κB activation.
INSERM, UMR_S 1014, Hôpital Paul Brousse, Villejuif, 94800, France. naima.zemirli@inserm.fr.|Université Paris-Sud P11, Orsay, 91400, France. naima.zemirli@inserm.fr.|Equipe Labellisée Ligue contre le Cancer, Villejuif, 94800, France. naima.zemirli@inserm.fr.
Naima
N
Zemirli
INSERM, UMR_S 1014, Hôpital Paul Brousse, Villejuif, 94800, France. marie.pourcelot@inserm.fr.|Université Paris-Sud P11, Orsay, 91400, France. marie.pourcelot@inserm.fr.|Equipe Labellisée Ligue contre le Cancer, Villejuif, 94800, France. marie.pourcelot@inserm.fr.
Marie
M
Pourcelot
INSERM, UMR_S 1014, Hôpital Paul Brousse, Villejuif, 94800, France. ness.dogan@gmail.com.|Université Paris-Sud P11, Orsay, 91400, France. ness.dogan@gmail.com.|Equipe Labellisée Ligue contre le Cancer, Villejuif, 94800, France. ness.dogan@gmail.com.
Neslihan
N
Dogan
INSERM, UMR_S 1014, Hôpital Paul Brousse, Villejuif, 94800, France. aime.vazquez@inserm.fr.|Université Paris-Sud P11, Orsay, 91400, France. aime.vazquez@inserm.fr.|Equipe Labellisée Ligue contre le Cancer, Villejuif, 94800, France. aime.vazquez@inserm.fr.
Aimé
A
Vazquez
INSERM, UMR_S 1014, Hôpital Paul Brousse, Villejuif, 94800, France. damien.arnoult@inserm.fr.|Université Paris-Sud P11, Orsay, 91400, France. damien.arnoult@inserm.fr.|Equipe Labellisée Ligue contre le Cancer, Villejuif, 94800, France. damien.arnoult@inserm.fr.
Damien
D
Arnoult
D006056:Golgi Apparatus / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics
D008565:Membrane Proteins; D016328:NF-kappa B; D034741:RNA, Small Interfering; C000598237:ring finger protein 121, human