The transcription factors Blimp-1 and IRF4 jointly control the differentiation and function of effector regulatory T cells

International audienc

IAPs CARRY AN EVOLUTIONARILY CONSERVED UBIQUITIN-BINDING DOMAIN THAT IS INDISPENSABLE FOR NF-KB REGULATION AND CELL SURVIVAL.

The covalent attachment of ubiquitin to target proteins influences various cellular processes, including DNA repair, NF-\u3baB signalling and cell survival1. The most common mode of regulation by ubiquitin-conjugation involves specialized ubiquitin-binding proteins that bind to ubiquitylated proteins and link them to downstream biochemical processes. Unravelling how the ubiquitin-message is recognized is essential because aberrant ubiquitin-mediated signalling contributes to tumour formation2. Recent evidence indicates that inhibitor of apoptosis (IAP) proteins are frequently overexpressed in cancer and their expression level is implicated in contributing to tumorigenesis, chemoresistance, disease progression and poor patient-survival3. Here, we have identified an evolutionarily conserved ubiquitin-associated (UBA) domain in IAPs, which enables them to bind to Lys 63-linked polyubiquitin. We found that the UBA domain is essential for the oncogenic potential of cIAP1, to maintain endothelial cell survival and to protect cells from TNF-\u3b1-induced apoptosis. Moreover, the UBA domain is required for XIAP and cIAP2\u2013MALT1 to activate NF-\u3baB. Our data suggest that the UBA domain of cIAP2\u2013MALT1 stimulates NF-\u3baB signalling by binding to polyubiquitylated NEMO. Significantly, 98% of all cIAP2\u2013 MALT1 fusion proteins retain the UBA domain, suggesting that ubiquitin-binding contributes to the oncogenic potential of cIAP2\u2013MALT1 in MALT lymphoma. Our data identify IAPs as ubiquitin-binding proteins that contribute to ubiquitinmediated cell survival, NF-\u3baB signalling and oncogenesis

CARP2 deficiency does not alter induction of NFkappaB by TNFα

TNFα can activate pathways leading to caspase-8-mediated apoptosis, as well as inflammatory pathways signaled by transcription factors. The adaptor protein RIP1 is a critical component for TNF receptor 1 (TNFR1)-mediated activation of NF-κB, because deletion of the gene encoding RIP1 in mice prevents induction of NF-κB by TNFα and causes severe runting with early postnatal lethality [1]. Recently, it has been proposed that caspase 8 and 10 associated RING protein-2 (CARP2, also named RIFIFYLIN/SAKURA) binds to the TNFR1 complex, leading to ubiquitylation and proteasome-mediated degradation of RIP1, thereby limiting the level of NF-κB activated by TNFα [2]. However, our experiments in mice lacking the Rififylin/Carp2 gene question this conclusion, because levels of RIP1 and induction of NF-κB by TNFα are normal in the absence of CARP2

The transcription factor IRF4 is essential for TCR affinity-mediated metabolic programming and clonal expansion of T cells

During immune responses, T cells are subject to clonal competition, which leads to the predominant expansion of high-affinity clones; however, there is little understanding of how this process is controlled. We found here that the transcription factor IRF4 was induced in a manner dependent on affinity for the T cell antigen receptor (TCR) and acted as a dose-dependent regulator of the metabolic function of activated T cells. IRF4 regulated the expression of key molecules required for the aerobic glycolysis of effector T cells and was essential for the clonal expansion and maintenance of effector function of antigen-specific CD8 + T cells. Thus, IRF4 is an indispensable molecular 'rheostat' that 'translates' TCR affinity into the appropriate transcriptional programs that link metabolic function with the clonal selection and effector differentiation of T cells

IAPs contain an evolutionarily conserved ubiquitin-binding domain that regulates NF-kappaB as well as cell survival and oncogenesis

The covalent attachment of ubiquitin to target proteins influences various cellular processes, including DNA repair, NF-kappaB signalling and cell survival. The most common mode of regulation by ubiquitin-conjugation involves specialized ubiquitin-binding proteins that bind to ubiquitylated proteins and link them to downstream biochemical processes. Unravelling how the ubiquitin-message is recognized is essential because aberrant ubiquitin-mediated signalling contributes to tumour formation. Recent evidence indicates that inhibitor of apoptosis (IAP) proteins are frequently overexpressed in cancer and their expression level is implicated in contributing to tumorigenesis, chemoresistance, disease progression and poor patient-survival. Here, we have identified an evolutionarily conserved ubiquitin-associated (UBA) domain in IAPs, which enables them to bind to Lys 63-linked polyubiquitin. We found that the UBA domain is essential for the oncogenic potential of cIAP1, to maintain endothelial cell survival and to protect cells from TNF-alpha-induced apoptosis. Moreover, the UBA domain is required for XIAP and cIAP2-MALT1 to activate NF-kappaB. Our data suggest that the UBA domain of cIAP2-MALT1 stimulates NF-kappaB signalling by binding to polyubiquitylated NEMO. Significantly, 98% of all cIAP2-MALT1 fusion proteins retain the UBA domain, suggesting that ubiquitin-binding contributes to the oncogenic potential of cIAP2-MALT1 in MALT lymphoma. Our data identify IAPs as ubiquitin-binding proteins that contribute to ubiquitin-mediated cell survival, NF-kappaB signalling and oncogenesis

Combination of IAP antagonist and IFNγ activates novel caspase-10- and RIPK1-dependent cell death pathways

Peptido-mimetic inhibitor of apoptosis protein (IAP) antagonists (Smac mimetics (SMs)) can kill tumour cells by depleting endogenous IAPs and thereby inducing tumour necrosis factor (TNF) production. We found that interferon-γ (IFNγ) synergises with SMs to kill cancer cells independently of TNF − and other cell death receptor signalling pathways. Surprisingly, CRISPR/Cas9 HT29 cells doubly deficient for caspase-8 and the necroptotic pathway mediators RIPK3 or MLKL were still sensitive to IFNγ/SM- induced killing. Triple CRISPR/Cas9-knockout HT29 cells lacking caspase-10 in addition to caspase-8 and RIPK3 or MLKL were resistant to IFNγ/SM killing. Caspase-8 and RIPK1 deficiency was, however, sufficient to protect cells from IFNγ/SM-induced cell death, implying a role for RIPK1 in the activation of caspase-10. These data show that RIPK1 and caspase-10 mediate cell death in HT29 cells when caspase-8-mediated apoptosis and necroptosis are blocked and help to clarify how SMs operate as chemotherapeutic agents