Casper Is a FADD- and Caspase-Related Inducer of Apoptosis

AbstractCaspases are cysteine proteases that play a central role in apoptosis. Caspase-8 may be the first enzyme of the proteolytic cascade activated by the Fas ligand and tumor necrosis factor (TNF). Caspase-8 is recruited to Fas and TNF receptor-1 (TNF-R1) through interaction of its prodomain with the death effector domain (DED) of the receptor-associating FADD. Here we describe a novel 55 kDa protein, Casper, that has sequence similarity to caspase-8 throughout its length. However, Casper is not a caspase since it lacks several conserved amino acids found in all caspases. Casper interacts with FADD, caspase-8, caspase-3, TRAF1, and TRAF2 through distinct domains. When overexpressed in mammalian cells, Casper potently induces apoptosis. A C-terminal deletion mutant of Casper inhibits TNF- and Fas-induced cell death, suggesting that Casper is involved in these apoptotic pathways

Embryonic Lethality, Liver Degeneration, and Impaired NF-κB Activation in IKK-β-Deficient Mice

AbstractIκB kinase-α and -β (IKK-α and IKK-β), the catalytic subunits of the IKK complex, phosphorylate IκB proteins on specific serine residues, thus targeting IκB for degradation and activating the transcription factor NF-κB. To elucidate the in vivo function of IKK-β, we generated IKK-β-deficient mice. The homozygous mouse embryo dies at ∼14.5 days of gestation due to liver degeneration and apoptosis. IKK-β-deficient embryonic fibroblasts have both reduced basal NF-κB activity and impaired cytokine-induced NF-κB activation. Similarly, basal and cytokine-inducible kinase activities of the IKK complex are greatly reduced in IKK-β-deficient cells. These results indicate that IKK-β is crucial for liver development and regulation of NF-κB activity and that IKK-α can only partially compensate for the loss of IKK-β

The IκB Function of NF-κB2 p100 Controls Stimulated Osteoclastogenesis

The prototranscription factor p100 represents an intersection of the NF-κB and IκB families, potentially serving as both the precursor for the active NF-κB subunit p52 and as an IκB capable of retaining NF-κB in the cytoplasm. NF-κB–inducing kinase (NIK) controls processing of p100 to generate p52, and thus NIK-deficient mice can be used to examine the biological effects of a failure in such processing. We demonstrate that treatment of wild-type osteoclast precursors with the osteoclastogenic cytokine receptor activator of NF-κB ligand (RANKL) increases both expression of p100 and its conversion to p52, resulting in unchanged net levels of p100. In the absence of NIK, p100 expression is increased by RANKL, but its conversion to p52 is blocked, leading to cytosolic accumulation of p100, which, acting as an IκB protein, binds NF-κB complexes and prevents their nuclear translocation. High levels of unprocessed p100 in osteoclast precursors from NIK−/− mice or a nonprocessable form of the protein in wild-type cells impair RANKL-mediated osteoclastogenesis. Conversely, p100-deficient osteoclast precursors show enhanced sensitivity to RANKL. These data demonstrate a novel, biologically relevant means of regulating NF-κB signaling, with upstream control and kinetics distinct from the classical IκBα pathway

RANTES Secretion by Gene-Modified Tumor Cells Results in Loss of Tumorigenicity In Vivo: Role of Immune Cell Subpopulations

Overview summary Members of the chemokine superfamily mediate potent and selective chemoattraction of a variety of immune cell subsets, which is concentration dependent. This important and novel biologic activity raises the possibility of using chemokines as adjuvants in cancer vaccine strategies. We describe here the in vitro chemotactic capacity of RANTES for murine CD8+ tumor-infiltrating lymphocytes (TIL). Moreover, murine fibrosarcoma cells transfected with the cDNA encoding RANTES and secreting high levels of this chemokine become nontumorigenic in immunocompetent mice. The antitumor effect of RANTES is dependent on inherent tumor immunogenicity and is mediated through the participation of host-derived T cells and macrophages. Thus, the general chemoattractant properties exhibited by RANTES in vitro appear to be relevant in an in vivo model. These data warrant further investigation of other distinct members of the chemokine superfamily for their potential use, either alone or in combination, in gene therapy approaches that employ tumor cells as immunogens.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63285/1/hum.1996.7.13-1545.pd

NF-κB Antiapoptosis: Induction of TRAF1 and TRAF2 and c-IAP1 and c-IAP2 to Suppress Caspase-8 Activation

Tumor necrosis factor α (TNF-α) binding to the TNF receptor (TNFR) potentially initiates apoptosis and activates the transcription factor nuclear factor kappa B (NF-κB), which suppresses apoptosis by an unknown mechanism. The activation of NF-κB was found to block the activation of caspase-8. TRAF1 (TNFR-associated factor 1), TRAF2, and the inhibitor-of-apoptosis (IAP) proteins c-IAP1 and c-IAP2 were identified as gene targets of NF-κB transcriptional activity. In cells in which NF-κB was inactive, all of these proteins were required to fully suppress TNF-induced apoptosis, whereas c-IAP1 and c-IAP2 were sufficient to suppress etoposide-induced apoptosis. Thus, NF-κB activates a group of gene products that function cooperatively at the earliest checkpoint to suppress TNF-α–mediated apoptosis and that function more distally to suppress genotoxic agent–mediated apoptosis

The TNF receptor 1-associated protein TRADD signals cell death and NF-κB activation

AbstractMany diverse activities of tumor necrosis factor (TNF) are signaled through TNF receptor 1(TNFR1). We have identified a novel 34 kDa protein, designated TRADD, that specifically interacts with an intracellular domain of TNFR1 known to be essential for mediating programmed cell death. Overexpression of TRADD leads to two major TNF-induced responses, apoptosis and activation of NF-κB. The C-terminal 118 amino acids of TRADD are sufficient to trigger both of these activities and likewise sufficient for interaction with the death domain of TNFR1. TRADD-mediated cell death can be suppressed by the crmA gene, which encodes a specific inhibitor of the interleukin-1 β-converting enzyme. However, NF-κB activation by TRADD is not inhibited by crmA expression, demonstrating that the signaling pathways for TNF-induced cell death and NF-κB activation are distinct

Dissection of TNF Receptor 1 Effector Functions: JNK Activation Is Not Linked to Apoptosis While NF-κB Activation Prevents Cell Death

AbstractThrough its type 1 receptor (TNFR1), the cytokine TNF elicits an unusually wide range of biological responses, including inflammation, tumor necrosis, cell proliferation, differentiation, and apoptosis. We investigated how TNFR1 activates different effector functions; the protein kinase JNK, transcription factor NF-κB, and apoptosis. We found that the three responses are mediated through separate pathways. Recruitment of the signal transducer FADD to the TNFR1 complex mediates apoptosis but not NF-κB or JNK activation. Two other signal transducers, RIP and TRAF2, mediate both JNK and NF-κB activation. These two responses, however, diverge downstream to TRAF2. Most importantly, JNK activation is not involved in induction of apoptosis, while activation of NF-κB protects against TNF-induced apoptosis