NEDD4 ubiquitinates TRAF3 to promote CD40-mediated AKT activation.

CD40, a member of tumour necrosis factor receptor (TNFR) superfamily, has a pivotal role in B-cell-mediated immunity through various effector pathways including AKT kinase, but the signal transduction of CD40-meidated AKT activation is poorly understood. Here we report that the neural precursor cell expressed developmentally downregulated protein 4 (NEDD4), homologous to E6-AP Carboxyl Terminus family E3 ubiquitin ligase, is a novel component of the CD40 signalling complex. It has a key role in CD40-mediated AKT activation and is involved in modulating immunoglobulin class switch through regulating the expression of activation-induced cytidine deaminase. NEDD4 constitutively interacts with CD40 and mediates K63-linked ubiquitination of TNFR-associated factor3 (TRAF3). The ubiquitination of TRAF3 by NEDD4 is critical for CD40-mediated AKT activation. Thus, NEDD4 is a previously unknown component of the CD40 signalling complex necessary for AKT activation.

Dysregulation of the miR-324-5p-CUEDC2 axis leads to macrophage dysfunction and is associated with colon cancer.

CUEDC2, a CUE-domain-containing protein, modulates inflammation, but its involvement in tumorigenesis is still poorly understood. Here, we report that CUEDC2 is a key regulator of macrophage function and critical for protection against colitis-associated tumorigenesis. CUEDC2 expression is dramatically upregulated during macrophage differentiation, and CUEDC2 deficiency results in excessive production of proinflammatory cytokines. The level of CUEDC2 in macrophages is modulated by miR- 324-5p. We find that Cuedc2 KO mice are more susceptible to dextran-sodium-sulfate-induced colitis, and macrophage transplantation results suggest that the increased susceptibility results from the dysfunction of macrophages lacking CUEDC2. Furthermore, we find that Cuedc2 KO mice are more prone to colitis-associated cancer. Importantly, CUEDC2 expression is almost undetectable in macrophages in human colon cancer, and this decreased CUEDC2 expression is associated with high levels of interleukin-4 and miR-324-5p. Thus, CUEDC2 plays a crucial role in modulating macrophage function and is associated with both colitis and colon tumorigenesis.

ECHS1 interacts with STAT3 and negatively regulates STAT3 signaling.

Signal transducer and activator of transcription 3 (STAT3) is a critical transcriptional factor in a variety of cellular processes, and is frequently over-activated in a range of human tumors. However, the processes that regulate STAT3 activation need to be further clarified. With a yeast two-hybrid screening, we identified enoyl-CoA hydratase short chain 1 (ECHS1) as a novel STAT3 binding protein. We further confirmed the interaction between STAT3 and ECHS1 by GST-pull down and co-immnunoprecipitation. Importantly, we found that ECHS1 specifically represses STAT3 activity and negatively regulates the expression of several target genes of STAT3 through inhibiting STAT3 phosphorylation. Therefore, our findings will provide new insights into the mechanism of STAT3 signaling regulation.

RAD23A negatively regulates RIG-I/MDA5 signaling through promoting TRAF2 polyubiquitination and degradation.

RIG-I/MDA5 plays a pivotal role in innate immunity by detecting intracellular double-stranded RNA (dsRNA) and activating the transcription of type I interferons and proinflammatory factors, but the exactly regulating mechanism of RIG-I/MDA5 signaling remains elusive. In this study, UbL-UBA domain containing protein RAD23A was identified as a negative regulator of RIG-I/MDA5-mediated signaling activation through a small interfering RNA (siRNA)-based screening. Knockdown of RAD23A augmented the expression of RIG-I/MDA5-mediated expression of proinflammatory cytokines and IFN-ß whereas ectopic expression of RAD23A showed the converse effect. Moreover, we confirmed the interaction between RAD23A and tumor necrosis factor receptor-associated factor 2 (TRAF2), an essential mediator of RIG-I/MDA5 signaling, and found that RAD23A down-regulated TRAF2 protein level through ubiquitin-proteasome system. Therefore, this study identified RAD23A as a novel negative regulator of RIG-I/MDA5 mediated anti-virus response.

CUEDC2 (CUE domain-containing 2) and SOCS3 (suppressors of cytokine signaling 3) cooperate to negatively regulate Janus kinase 1/signal transducers and activators of transcription 3 signaling.

Janus kinase 1/signal transducers and activators of transcription 3 (JAK1/STAT3) pathway is one of the recognized oncogenic signaling pathways that frequently overactivated in a variety of human tumors. Despite rapid progress in elucidating the molecular mechanisms of activation of JAK/STAT pathway, the processes that regulate JAK/STAT deactivation need to be further clarified. Here we demonstrate that CUE domain-containing 2 (CUEDC2) inhibits cytokine-induced phosphorylation of JAK1 and STAT3 and the subsequent STAT3 transcriptional activity. Further analysis by a yeast two-hybrid assay showed that CUEDC2 could engage in a specific interaction with a key JAK/STAT inhibitor, SOCS3 (suppressors of cytokine signaling 3). The interaction between CUEDC2 and SOCS3 is required for the inhibitory effect of CUEDC2 on JAK1 and STAT3 activity. Additionally, we found CUEDC2 functions collaboratively with SOCS3 to inhibit JAK1/STAT3 signaling by increasing SOCS3 stability via enhancing its association with Elongin C. Therefore, our findings revealed a new biological activity for CUEDC2 as the regulator of JAK1/STAT3 signaling and paved the way to a better understanding of the mechanisms by which SOCS3 has been linked to suppression of the JAK/STAT pathway.