The NF-κB RelA transcription factor is not required for CD8+ T-cell function in acute viral infection and cancer.

CD8+ T cells are critical mediators of pathogen clearance and anti-tumor immunity. Although signaling pathways leading to the activation of NF-κB transcription factors have crucial functions in the regulation of immune responses, the CD8+ T cell-autonomous roles of the different NF-κB subunits, are still unresolved. Here, we investigated the function of the ubiquitously expressed transcription factor RelA in CD8+ T-cell biology using a novel mouse model and gene-edited human cells. We found that CD8+ T cell-specific ablation of RelA markedly altered the transcriptome of ex vivo stimulated cells, but maintained the proliferative capacity of both mouse and human cells. In contrast, in vivo experiments showed that RelA deficiency did not affect the CD8+ T-cell response to acute viral infection or transplanted tumors. Our data suggest that in CD8+ T cells, RelA is dispensable for their protective activity in pathological contexts.

The alternative RelB NF-κB subunit is a novel critical player in diffuse large B-cell lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is the most frequent lymphoid malignancy affecting adults. The NF-κB transcription factor family is activated by 2 main pathways, the canonical and the alternative NF-κB activation pathway, with different functions. The alternative NF-κB pathway leads to activation of the transcriptionally active RelB NF-κB subunit. Alternative NF-κB activation status and its role in DLBCL pathogenesis remain undefined. Here, we reveal a frequent activation of RelB in a large cohort of DLBCL patients and cell lines, independently of their activated B-cell-like or germinal center B-cell-like subtype. RelB activity defines a new subset of patients with DLBCL and a peculiar gene expression profile and mutational pattern. Importantly, RelB activation does not correlate with the MCD genetic subtype, enriched for activated B-cell-like tumors carrying MYD88L265P and CD79B mutations that cooperatively activate canonical NF-κB, thus indicating that current genetic tools to evaluate NF-κB activity in DLBCL do not provide information on the alternative NF-κB activation. Furthermore, the newly defined RelB-positive subgroup of patients with DLBCL exhibits a dismal outcome after immunochemotherapy. Functional studies revealed that RelB confers DLBCL cell resistance to DNA damage-induced apoptosis in response to doxorubicin, a genotoxic agent used in the front-line treatment of DLBCL. We also show that RelB positivity is associated with high expression of cellular inhibitor of apoptosis protein 2 (cIAP2). Altogether, RelB activation can be used to refine the prognostic stratification of DLBCL and may contribute to subvert the therapeutic DNA damage response in a segment of patients with DLBCL.

NF-κB in the New Era of Cancer Therapy.

Although mortality rates have declined in recent years, the majority of cancers remain incurable and the medical challenge is evident. Recent progress in cancer genetics and genomics along with the identification of a novel generation of cancer hallmarks, that is, reprogramming of energy metabolism and evasion from immune surveillance, have led to the discovery of novel NF-κB-dependent cancer vulnerabilities. These discoveries have led to better patient stratification, and new drug combinations using cutting-edge therapies. This review aims to give an up-to-date view on the therapeutic potential of NF-κB transcription factors and the signaling pathways that control their activity in the new era of cancer therapy.

Model of the Interaction between the NF-κB Inhibitory Protein p100 and the E3 Ubiquitin Ligase ß-TrCP based on NMR and Docking Experiments.

NF-κB is a major transcription factor whose activation is triggered through two main activation pathways: the canonical pathway involving disruption of IκB-α/NF-κB complexes and the alternative pathway whose activation relies on the inducible proteolysis of the inhibitory protein p100. One central step controlling p100 processing consists in the interaction of the E3 ubiquitin ligase ß-TrCP with p100, thereby leading to its ubiquitinylation and subsequent either complete degradation or partial proteolysis by the proteasome. However, the interaction mechanism between p100 and ß-TrCP is still poorly defined. In this work, a diphosphorylated 21-mer p100 peptide model containing the phosphodegron motif was used to characterize the interaction with ß-TrCP by NMR. In parallel, docking simulations were performed in order to obtain a model of the 21P-p100/ß-TrCP complex. Saturation transfer difference (STD) experiments were performed in order to highlight the residues of p100 involved in the interaction with the ß-TrCP protein. These results highlighted the importance of pSer865 and pSer869 residues in the interaction with ß-TrCP and particularly the Tyr867 that fits inside the hydrophobe ß-TrCP cavity with the Arg474 guanidinium group. Four other arginines, Arg285, Arg410, Arg431, and Arg521, were found essential in the stabilization of p100 on the ß-TrCP surface. Importantly, the requirement for these five arginine residues of ß-TrCP for the interaction with p100 was further confirmed in vivo, thereby validating the docking model through a biological approach.