The inhibitor of apoptosis (IAP) family of proteins enhances cell survival through mechanisms that remain uncertain. In this report, we show that cIAP1 and cIAP2 promote cancer cell survival by functioning as E3 ubiquitin ligases that maintain constitutive ubiquitination of the RIP1 adaptor protein. We demonstrate that AEG40730, a compound modeled on BIR-binding tetrapeptides, binds to cIAP1 and cIAP2, facilitates their autoubiquitination and proteosomal degradation, and causes a dramatic reduction in RIP1 ubiquitination. We show that cIAP1 and cIAP2 directly ubiquitinate RIP1 and induce constitutive RIP1 ubiquitination in cancer cells and demonstrate that constitutively ubiquitinated RIP1 associates with the prosurvival kinase TAK1. When deubiquitinated by AEG40730 treatment, RIP1 binds caspase-8 and induces apoptosis. These findings provide insights into the function of the IAPs and provide new therapeutic opportunities in the treatment of cancer.

Stable expression of short-hairpin RNAs (shRNAs) directed against the X-linked inhibitor of apoptosis (XIAP) resulted in the generation of three MDA-MB-231 cell lines (XIAP shRNA cells) with reductions in XIAP mRNA and protein levels 485% relative to MDA-MB-231 cells stably transfected with the U6 RNA polymerase III promoter alone (U6 cells). This RNA interference (RNAi) approach dramatically sensitized these cells to killing by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Importantly, loss of XIAP also sensitized the cells to killing by taxanes but had no additional effects on killing by carboplatin and doxorubicin. The increased sensitivity of the XIAP shRNA cells to killing by TRAIL and taxanes correlated with enhanced caspase cleavage and activation, including caspase-8, and robust processing of poly(ADP-ribose) polymerase and BID compared to U6 cells. Additionally, increasing XIAP levels by adenovirus-mediated expression protected both XIAP shRNA and U6 cells from TRAIL killing in a dose-dependent manner. The effects observed by stable RNAi with respect to TRAIL sensitization were also achieved following downregulation of XIAP in Panc-1 cells treated with a second-generation, mixed-backbone antisense oligonucleotide, AEG 35156/GEM640. These data indicate that reducing XIAP protein expression by either RNAi or antisense approaches increases cancer cell susceptibility to functionally diverse chemotherapeutic agents and supports the notion that downregulation of XIAP in vivo may synergize with disease-relevant chemotherapeutic regimes, including TRAIL and taxanes, to increase the effectiveness of antineoplastic agents.

The objective of this study was to generate an immortal cell line representative of specialized human brain microvascular endothelia forming the blood-brain barrier (BBB) in vivo. Human capillary and microvascular endothelial cells (HCEC) were transfected with the plasmid pSV3-neo coding for the SV40 large T antigen and the neomycin gene. The neomycin-resistant transfected cells overcame proliferative senescence, and after a 6-8 wk period of crisis produced immortalization-competent cell colonies. Single-cell clones of near-diploid genotype were isolated from these colonies, propagated, and characterized. Immortalized HCEC (SV-HCEC) exhibited accelerated proliferation rates, but remained serum and anchorage dependent and retained the characteristic cobblestone morphology at confluence. SV-HCEC displayed a stable nuclear expression of SV40 large T antigen, lacked the invasiveness of transformed cells, and maintained major phenotypic properties of early passage control cells including expression of factor VIII-related antigen, uptake of acetylated low-density lipoprotein, binding of fluorescently labeled lectins, expression of transferrin receptor and transferrin receptor-mediated endocytosis, and high activities of the BBB-specific enzymes alkaline phosphatase and gamma-glutamyl transpeptidase. The diffusion of radiolabeled sucrose across SV-HCEC monolayers was fivefold lower than that observed with human lung microvascular endothelial cells. Furthermore, media conditioned by fetal human astrocytes increased the transendothelial electrical resistance of SV-HCEC monolayers by 2.5-fold. Therefore, this newly established human cell line expressing the specialized phenotype of BBB endothelium may serve as a readily available in vitro model for studying the properties of the human BBB.

Purpose: Cancer cells can use X-linked inhibitor of apoptosis (XIAP) to evade apoptotic cues, including chemotherapy. The antitumor potential of AEG35156, a novel second-generation antisense oligonucleotide directed toward XIAP, was assessed in human cancer models when given as a single agent and in combination with clinically relevant chemotherapeutics. Experimental Design: AEG35156 was characterized for its ability to cause dose-dependent reductions of XIAP mRNA and protein in vitro and in vivo, to sensitize cancer cell lines to death stimuli, and to exhibit antitumor activity in multiple human cancer xenograft models as a single agent or in combination with chemotherapy. Results: AEG35156 reduced XIAP mRNA levels with an EC 50 of 8 to 32 nmol/L and decreased XIAP protein levels by >80%. Loss of XIAP protein correlated with increased sensitization to tumor necrosis factor^related apoptosis-inducing ligand (TRAIL)^mediated apoptosis in Panc-1 pancreatic carcinoma cells. AEG35156 exhibited potent antitumor activity relative to control oligonucleotides in three human cancer xenograft models (prostate, colon, and lung) and was capable of inducing complete tumor regression when combined with taxanes. Antitumor effects of AEG35156 correlated with suppression of tumor XIAP levels. Conclusions: AEG35156 reduces XIAP levels and sensitizes tumors to chemotherapy. AEG35156 is presently under clinical assessment in multiple phase I trials in cancer patients as a single agent and in combination with docetaxel in solid tumors or cytarabine/idarubicin in leukemia.Chemotherapy is the mainstay of clinical treatment for many solid tumors. However, the development of chemoresistance is a common feature, resulting in a decrease or loss of therapeutic effectiveness. One of the major mechanisms responsible for chemoresistance is the loss of apoptotic sensitivity in cancer cells. Possible causes include alterations in the initiation or execution of the apoptotic machinery, which results from increased activity of antiapoptotic proteins. Novel anticancer therapies that specifically target antiapoptotic mechanisms or that act to lower the apoptotic threshold of cancer cells are in preclinical development or under clinical evaluation (1). An appealing therapeutic candidate target is the X-linked inhibitor of apoptosis (XIAP), a potent antiapoptotic protein whose overexpression and dysfunction is associated with resistance to chemotherapy and radiotherapy (2 -5).Although apoptotic pathways in cells are complex, most seem to converge on a single family of proteases, the caspases that dismantle the cell in an orderly, noninflammatory fashion. The human IAP family, characterized by the presence of one to three baculovirus IAP repeat motifs at the NH 2 terminus of the polypeptide chain (reviewed in refs. 3, 6), are the only known cellular inhibitors of caspases. Specifically, they inhibit two key effector caspases, caspase-3 and caspase-7, and the key initiator caspase, caspase-9, which is responsible for the intrinsic mitochondria...

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Excitatory synaptic transmission in the central nervous system is mediated primarily by the release of glutamate from presynaptic terminals onto postsynaptic channels gated by N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors. The myriad intracellular responses arising from the activation of the NMDA and AMPA receptors have previously been attributed to the flow of Ca2+ and/or Na+ through these ion channels. Here we report that the binding of the agonist AMPA to its receptor can generate intracellular signals that are independent of Ca2+ and Na+ in rat cortical neurons. In the absence of intracellular Ca2+ and Na+, AMPA, but not NMDA, brought about changes in a guanine-nucleotide-binding protein (Galpha[il]) that inhibited pertussis toxin-mediated ADP-ribosylation of the protein in an in vitro assay. This effect was observed in intact neurons treated with AMPA as well as in isolated membranes exposed to AMPA, and was also found in MIN6 cells, which express functional AMPA receptors but have no metabotropic glutamate receptors. AMPA also inhibited forskolin-stimulated activity of adenylate cyclase in neurons, demonstrating that Gi proteins were activated. Moreover, both Gbetagamma blockage and co-precipitation experiments demonstrated that the modulation of the Gi protein arose from the association of Galpha(il) with the glutamate receptor-1 (GluR1) subunit. These results suggest that, as well as acting as an ion channel, the AMPA receptor can exhibit metabotropic activity.

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