The CARMA1-Bcl10 Signaling Complex Selectively Regulates JNK2 Kinase in the T Cell Receptor-Signaling Pathway

SummaryMembers of the c-Jun NH2-terminal kinase (JNK) family play crucial roles in cell activation, differentiation, and apoptosis. Although many studies have indicated that JNK1 and JNK2 have functional differences and redundancy, the upstream signaling pathway that selectively activates JNK1 or JNK2 remains unknown. In this study, we have revealed a selective mechanism of JNK activation, in which JNK2, but not JNK1, was regulated by CARMA1, a scaffold molecule, after stimulation of the T cell receptor (TCR). This CARMA1-dependent regulation of JNK2 worked through the scaffold molecule Bcl10, which was inducibly associated with JNK2 and served as a JNK-interacting protein (JIP)-like scaffold to assemble the kinases JNK2, MKK7, and TAK1. Finally, we showed that CARMA1- and Bcl10-mediated JNK2 activation had a critical role in regulating the amount of c-Jun protein. Together, our studies provide genetic evidence that JNK1 and JNK2 are differentially regulated in the TCR-signaling pathway and play different functions

USP18 inhibits NF-κB and NFAT activation during Th17 differentiation by deubiquitinating the TAK1–TAB1 complex

Reversible ubiquitin modification of cell signaling molecules has emerged as a critical mechanism by which cells respond to extracellular stimuli. Although ubiquitination of TGF-β–activated kinase 1 (TAK1) is critical for NF-κB activation in T cells, the regulation of its deubiquitination is unclear. We show that USP18, which was previously reported to be important in regulating type I interferon signaling in innate immunity, regulates T cell activation and T helper 17 (Th17) cell differentiation by deubiquitinating the TAK1–TAB1 complex. USP18-deficient T cells are defective in Th17 differentiation and Usp18(−/−) mice are resistant to experimental autoimmune encephalomyelitis (EAE). In response to T cell receptor engagement, USP18-deficient T cells exhibit hyperactivation of NF-κB and NFAT and produce increased levels of IL-2 compared with the wild-type controls. Importantly, USP18 is associated with and deubiquitinates the TAK1–TAB1 complex, thereby restricting expression of IL-2. Our findings thus demonstrate a previously uncharacterized negative regulation of TAK1 activity during Th17 differentiation, suggesting that USP18 may be targeted to treat autoimmune diseases

CARMA1-mediated NF-κB and JNK activation in lymphocytes

Activation of transcription factor nuclear factor-κB (NF-κB) and Jun N-terminal kinase (JNK) play the pivotal roles in regulation of lymphocyte activation and proliferation. Deregulation of these signaling pathways leads to inappropriate immune response and contributes to the development of leukemia/lymphoma. The scaffold protein CARMA1 [caspase-recruitment domain (CARD) membrane-associated guanylate kinase (MAGUK) protein 1] has a central role in regulation of NF-κB and the JNK2/c-Jun complex in both B and T lymphocytes. During last several years, the tremendous work has been done to reveal the mechanism by which CARMA1 and its signaling partners, Bcl10 (B cell CLL-lymphoma 10) and MALT1 (mucosa-associated lymphoid tissue 1), are activated and mediate NF-κB and JNK activation. In this review, we summarize our findings in revealing the roles of CARMA1 in the NF-κB and JNK signaling pathways in the context of recent advances in this field

ATF3, a new player in DLBCL cell survival

In this issue of Blood, Juilland and colleagues reveal the expression pattern and the role of different members of the activating transcription factor (ATF) family in survival of diffuse large B-cell lymphoma (DLBCL) cells

Restoration of NF-κB Activation by Tumor Necrosis Factor Alpha Receptor Complex-Targeted MEKK3 in Receptor-Interacting Protein-Deficient Cells

Receptor-interacting protein (RIP) plays a critical role in tumor necrosis factor alpha (TNF-α)-induced NF-κB activation. However, the mechanism by which RIP mediates TNF-α-induced signal transduction is not fully understood. In this study, we reconstituted RIP-deficient Jurkat T cells with a fusion protein composed of full-length MEKK3 and the death domain of RIP (MEKK3-DD). In these cells, MEKK3-DD substitutes for RIP and directly associates with TRADD in TNF receptor complexes following TNF-α stimulation. We found that TNF-α-induced NF-κB activation was fully restored by MEKK3-DD in these cells. In contrast, expression of a fusion protein composed of NEMO, a component of the IκB kinase complex, and the death domain of RIP (NEMO-DD) cannot restore TNF-α-induced NF-κB activation in RIP-deficient cells. These results indicate that the role of RIP is to specifically recruit MEKK3 to the TNF-α receptor complex, whereas the forced recruitment of NEMO to the TNF-α receptor complex is insufficient for TNF-α-induced NF-κB activation. Although MEKK2 has a high degree of homology with MEKK3, MEKK2-DD, unlike MEKK3-DD, also fails to restore TNF-α-induced NF-κB activation in RIP-deficient cells, indicating that RIP-dependent recruitment of MEKK3 plays a specific role in TNF-α signaling

Dampening NF-κB Signaling by “Self-Eating”

Activation of NF-κB transcription factor is crucial for survival, proliferation, and differentiation of T cells. In this issue of Immunity, Paul et al. (2012) demonstrate that autophagy is a pathway by which TCR-activated NF-κB is turned over

Ubiquitination of RIP Is Required for Tumor Necrosis Factor α-induced NF-κB Activation

Stimulation of cells with tumor necrosis factor (TNFα) triggers a recruitment of various signaling molecules, such as RIP, to the TNFαreceptor 1 complex, leading to activation of NF-κB. Previous studies indicate that RIP plays an essential role for TNFα-induced NF-κB activation, but the molecular mechanism by which RIP mediates TNFαsignals to activate NF-κB is not fully defined. Earlier studies suggest that RIP undergoes a ligand-dependent ubiquitination. However, it remains to be determined whether the ubiquitination of RIP is required for TNFα-induced NF-κB activation. In this study, we have identified Lys377 of RIP as the functional ubiquitination site, because mutating this residue to arginine completely abolished RIP-mediated NF-κB activation. The K377R mutation of RIP cannot undergo ligand-dependent ubiquitination and fails to recruit its downstream signaling components into the TNFαreceptor 1 complex. Together, our studies provide the first genetic evidence that the ubiquitination of RIP is required for TNFα-induced NF-κB activation

Regulation of Linear Ubiquitin Chain Assembly Complex by Caspase-Mediated Cleavage of RNF31

Cell death and survival signaling pathways have opposed but fundamental functions for various cellular processes and maintain cell homeostasis through cross talk. Here we report a novel mechanism of interaction between these two pathways through the cleavage of RNF31 by caspases. RNF31, a component of the linear ubiquitin chain assembly complex (LUBAC), regulates cell survival by inducing linear ubiquitination of NF-κB signaling components. We found that RNF31 is cleaved under apoptosis conditions through various stimulations. The effector caspases caspase 3 and caspase 6 are responsible for this event, and aspartates 348, 387, and 390 were identified as target sites for this cleavage. Cleavage of RNF31 suppressed its ability to activate NF-κB signaling; thus, mutation of cleavage sites inhibited the induction of apoptosis by treatment with tumor necrosis factor alpha (TNF-α). Our findings elucidate a novel regulatory loop between cell death and the survival signal and may provide guidance for the development of therapeutic strategies for cancers through the sensitization of tumor cells to death-inducing drugs

MALT1 is required for EGFR induced NF-κB activation and contributes to EGFR-driven lung cancer progression

The transcription factor NF-κB has been implicated in playing a crucial role in the tumorigenesis of many types of human cancers. Although Epidermal Growth Factor Receptor (EGFR) can directly activate NF-κB, the mechanism by which EGFR induces NF-κB activation and the role of NF-κB in EGFR-associated tumor progression is still not fully defined. Herein, we found that Mucosa-Associated Lymphoid Tissue 1 (MALT1) is involved in EGFR-induced NF-κB activation in cancer cells, and MALT1 deficiency impaired EGFR-induced NF-κB activation. MALT1 mainly functions as a scaffold protein by recruiting E3 ligase TRAF6 to IKK complex to activate NF-κB in response to EGF stimulation. Functionally, MALT1 inhibition shows significant defects in EGFR-associated tumor malignancy, including cell migration, metastasis and anchorage independent growth. To further access a physiological role of MALT1-dependent NF-κB activation in EGFR-driven tumor progression, we generated triple transgenic mouse model (tetO-EGFR L858R ; CCSP-rtTA; Malt1 −/− ), in which mutant EGFR-driven lung cancer was developed in the absence of MALT1 expression. MALT1-deficient mice show significantly less lung tumor burden when compared to its heterozygous controls, suggesting that MALT1 is required for the progression of EGFR-induced lung cancer. Mechanistically, MALT1 deficiency abolished both NF-κB and STAT3 activation in vivo , which is a result of a defect of IL-6 production. In comparison, MALT1 deficiency does not affect tumor progression in a mouse model (LSL-K-ras G12D ; CCSP-Cre; Malt1 −/− ) in which lung cancer is induced by expressing a K-ras mutant. Thus, our study has provided the cellular and genetic evidence that suggests MALT1-dependent NF-κB activation is important in EGFR-associated solid tumor progression

TAK1 Is Recruited to the Tumor Necrosis Factor-α (TNF-α) Receptor 1 Complex in a Receptor-interacting Protein (RIP)-dependent Manner and Cooperates with MEKK3 Leading to NF-κB Activation

Receptor-interacting protein (RIP) plays a critical role in tumor necrosis factor-α (TNF-α)-induced IκB kinase (IKK) activation and subsequent activation of transcription factor NF-κB. However, the molecular mechanism by which RIP mediates TNF-α-induced NF-κB activation is not completely defined. In this study, we have found that TAK1 is recruited to the TNF-α receptor complex in a RIP-dependent manner following the stimulation of TNF-α receptor 1 (TNF-R1). Moreover, a forced recruitment of TAK1 to TNF-R1 in the absence of RIP is sufficient to mediate TNF-α-induced NF-κB activation, indicating that the major function of RIP is to recruit its downstream kinases to the TNF-R1 complex. Interestingly, we also find that TAK1 and MEKK3 form a functional complex, in which TAK1 regulates autophosphorylation of MEKK3. The TAK1-mediated regulation of MEKK3 phosphorylation is dependent on the kinase activity of TAK1. Although TAK1-MEKK3 interaction is not affected by overexpressed TAB1, TAB1 is required for TAK1 activation and subsequent MEKK3 phosphorylation. Together, we conclude that TAK1 is recruited to the TNF-R1 complex via RIP and likely cooperates with MEKK3 to activate NF-κB in TNF-α signaling