Molecular Pathways: Targeting Death Receptors and Smac Mimetics

The adaptor protein TNF receptor-associated factor 3 (TRAF3) regulates signaling through B-lymphocyte receptors, including CD40, BAFF receptor, and Toll-like receptors, and also plays a critical role inhibiting B-cell homoeostatic survival. Consistent with these findings, loss-of-function human TRAF3 mutations are common in B-cell cancers, particularly multiple myeloma and B-cell lymphoma. B cells of B-cellspecific TRAF3−/− mice (B-Traf3) display remarkably enhanced survival compared with littermate control (WT) B cells. The mechanism for this abnormal homeostatic survival is poorly understood, a key knowledge gap in selecting optimal treatments for human B-cell cancers with TRAF3 deficiency. We show here for the first time to our knowledge that TRAF3 is a resident nuclear protein that associates with the transcriptional regulator cAMP response element binding protein (CREB) in both mouse and human B cells. The TRAF-C domain of TRAF3 was necessary and sufficient to localize TRAF3 to the nucleus via a functional nuclear localization signal. CREB protein was elevated in TRAF3 −/− B cells, without change in mRNA, but with a decrease in CREB ubiquitination. CREB-mediated transcriptional activity was increased in TRAF3-deficient B cells. Consistent with these findings, Mcl-1, an antiapoptotic target of CREBmediated transcription, was increased in the absence of TRAF3 and enhanced Mcl-1 was suppressed with CREB inhibition. TRAF3-deficient B cells were also preferentially sensitive to survival inhibition with pharmacologic CREB inhibitor. Our results identify a new mechanism by which nuclear TRAF3 regulates B-cell survival via inhibition of CREB stability, information highly relevant to the role of TRAF3 in B-cell malignancies.T RAF3 (TNF receptor-associated factor 3) is an important member of the TRAF adaptor family with distinct cell and context-specific roles (1). Our group previously generated CD19 Cre TRAF3 flox/flox mice (B-Traf3 −/− ) that lack TRAF3 specifically in B cells. This deletion results in remarkably enhanced B-cell survival in vitro and in vivo (2). Aged B-Traf3 −/− mice have substantially higher incidence of spontaneous B-cell lymphoma, further supporting the tumor-suppressive role of TRAF3 in B cells (3). Studies of human tumors identified loss-of-function TRAF3 mutations in nearly 20% of multiple myeloma (MM); TRAF3 is now recognized as one of the top 11 genes mutated in two-thirds of MM tumors (4). Additionally, ≥15% of diffuse large B-cell lymphomas are now known to harbor TRAF3 mutations (5, 6). Lesions in human TRAF3 genes are also seen in Hodgkin's lymphoma (7) and associated with particular chromosome 14 deletions in various B-cell lymphomas (8). Interestingly, Traf3 mutations are also common in canine B-cell lymphomas (5).TRAF3 is a negative regulator of the noncanonical NF-κB (NF-κB2) pathway, and enhanced survival in TRAF3-deficient B cells is associated with constitutive activation of NF-κB2 (2, 9). BAFF binds to BAFF receptor (BAFFR) to activate a complex signaling cascade that includes ...

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“…S3B). Smac mimetics (SMs) are small molecule inhibitors of IAP proteins (25), and CREB accumulated in B cells with SM treatment (Fig. S3C).…”

Section: Resultsmentioning

confidence: 99%

Nuclear TRAF3 is a negative regulator of CREB in B cells

Mambetsariev

Lin

Stunz

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Given the importance of NF-κB signaling in oncogenesis, strategies have been designed to interrupt this pathway at various points along the signaling cascade, and many of these have been described in detail in this Molecular Pathways series (47, 48). Opportunities for intervention exist from the start of signaling at the cell surface, as the signal is propagated through the cytoplasm, to the transcription factor binding DNA in the nucleus.…”

Section: Clinical-translational Advancesmentioning

confidence: 99%

Molecular Pathways: The Balance between Cancer and the Immune System Challenges the Therapeutic Specificity of Targeting Nuclear Factor-κB Signaling for Cancer Treatment

Zeligs

Neuman

Annunziata

2016

Clinical Cancer Research

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The Nuclear Factor-κB (NF-κB) signaling pathway is a complex network linking extracellular stimuli to cell survival and proliferation. Cytoplasmic signaling to activate NF-kB can occur as part of the DNA damage response or in response to a large variety of activators including viruses, inflammation, and cell death. NF-κB transcription factors play a fundamental role in tumorigenesis and are implicated in the origination and propagation of both hematologic and solid tumor types, including melanoma, breast, prostate, ovarian, pancreatic, colon, lung, and thyroid cancers. On the other hand, NF-kB signaling is key to immune function, and is likely necessary for anti-tumor immunity. This presents a dilemma when designing therapeutic approaches to target NF-kB. There is growing interest in identifying novel modulators to inhibit NF-κB activity since impeding different steps of the NF-κB pathway has potential to slow tumor growth, progression, and resistance to chemotherapy. Despite significant advances in our understanding of this pathway, our ability to effectively clinically block key targets for cancer therapy remains limited due to on-target effects in normal tissues. Tumor specificity is critical to developing therapeutic strategies targeting this anti-apoptotic signaling pathway in order to maintain anti-tumor immune surveillance when applying such therapy to patients.

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“…22, 29 In addition, SMAC mimetic-mediated cIAP depletion may sensitize cells to death by other insults, particularly by the death receptor pathway. 6, 7, 30 Our current data suggest that human cholangiocytes display limited sensitivity to SMAC mimetic-induced apoptosis, which occurs via the ripoptosome formation. Given the moderate apoptotic response, it appears unlikely that cholangiocyte cell death alone is the sole promoter of the PSC-like phenotype.…”

Section: Discussionmentioning

confidence: 65%

“…Cellular inhibitor of apoptosis protein 1 and 2 (cIAP-1 and cIAP-2) negatively regulate TRAIL signaling, 6, 7 suggesting that cIAP depletion in the biliary tracts may also promote sclerosing cholangitis syndromes in mice by potentiating TRAIL signaling. The major objective of this study was to examine this potential model of PSC and explore its pathogenesis.…”

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confidence: 99%

Biliary tract instillation of a SMAC mimetic induces TRAIL-dependent acute sclerosing cholangitis-like injury in mice

et al. 2017

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Primary sclerosing cholangitis (PSC) is a cholestatic liver disease of unknown etiopathogenesis characterized by fibrous cholangiopathy of large and small bile ducts. Systemic administration of a murine TNF-related apoptosis-inducing ligand (TRAIL) receptor agonist induces a sclerosing cholangitis injury in C57BL/6 mice, suggesting endogenous TRAIL may contribute to sclerosing cholangitis syndromes. Cellular inhibitor of apoptosis proteins (cIAP-1 and cIAP-2) are negative regulators of inflammation and TRAIL receptor signaling. We hypothesized that if endogenous TRAIL promotes sclerosing cholangitis, then cIAP depletion should also induce this biliary tract injury. Herein, we show that cIAP protein levels are reduced in the interlobular bile ducts of human PSC livers. Downregulation of cIAPs in normal human cholangiocytes in vitro by use of a SMAC mimetic (SM) induces moderate, ripoptosome-mediated apoptosis and RIP1-independent upregulation of proinflammatory cytokines and chemokines. Cytokine and chemokine expression was mediated by the non-canonical activation of NF-κB. To investigate whether downregulation of cIAPs is linked to generation of a PSC-like phenotype, an SM was directly instilled into the mouse biliary tree. Twelve hours after biliary instillation, TUNEL-positive cholangiocytes were identified; 5 days later, PSC-like changes were observed in the SM-treated mice, including a fibrous cholangiopathy of the interlobular bile ducts, portal inflammation, significant elevation of serum markers of cholestasis and cholangiographic evidence of intrahepatic biliary tract injury. In contrast, TRAIL and TRAIL-receptor deficient mice showed no sign of cholangiopathy following SM intrabiliary injection. We conclude that in vivo antagonism of cIAPs in mouse biliary epithelial cells is sufficient to trigger cholangiocytes apoptosis and a proinflammatory response resulting in a fibrous cholangiopathy resembling human sclerosing cholangitis. Therefore, downregulation of cIAPs in PSC cholangiocytes may contribute to the development of the disease. Our results also indicate that inhibition of TRAIL signaling pathways may be beneficial in the treatment of PSC.

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Molecular Pathways: Targeting Death Receptors and Smac Mimetics

Cited by 26 publications

References 58 publications

Nuclear TRAF3 is a negative regulator of CREB in B cells

Nuclear TRAF3 is a negative regulator of CREB in B cells

Molecular Pathways: The Balance between Cancer and the Immune System Challenges the Therapeutic Specificity of Targeting Nuclear Factor-κB Signaling for Cancer Treatment

Biliary tract instillation of a SMAC mimetic induces TRAIL-dependent acute sclerosing cholangitis-like injury in mice

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