An allosteric pan-TEAD inhibitor blocks oncogenic YAP/TAZ signaling and overcomes KRAS G12C inhibitor resistance.

The Hippo pathway is a key growth control pathway that is conserved across species. The downstream effectors of the Hippo pathway, YAP (Yes-associated protein) and TAZ (transcriptional coactivator with PDZ-binding motif), are frequently activated in cancers to drive proliferation and survival. Based on the premise that sustained interactions between YAP/TAZ and TEADs (transcriptional enhanced associate domain) are central to their transcriptional activities, we discovered a potent small-molecule inhibitor (SMI), GNE-7883, that allosterically blocks the interactions between YAP/TAZ and all human TEAD paralogs through binding to the TEAD lipid pocket. GNE-7883 effectively reduces chromatin accessibility specifically at TEAD motifs, suppresses cell proliferation in a variety of cell line models and achieves strong antitumor efficacy in vivo. Furthermore, we uncovered that GNE-7883 effectively overcomes both intrinsic and acquired resistance to KRAS (Kirsten rat sarcoma viral oncogene homolog) G12C inhibitors in diverse preclinical models through the inhibition of YAP/TAZ activation. Taken together, this work demonstrates the activities of TEAD SMIs in YAP/TAZ-dependent cancers and highlights their potential broad applications in precision oncology and therapy resistance.

AK2 is an AMP-sensing negative regulator of BRAF in tumorigenesis.

The RAS-BRAF signaling is a major pathway of cell proliferation and their mutations are frequently found in human cancers. Adenylate kinase 2 (AK2), which modulates balance of adenine nucleotide pool, has been implicated in cell death and cell proliferation independently of its enzyme activity. Recently, the role of AK2 in tumorigenesis was in part elucidated in some cancer types including lung adenocarcinoma and breast cancer, but the underlying mechanism is not clear. Here, we show that AK2 is a BRAF-suppressor. In in vitro assays and cell model, AK2 interacted with BRAF and inhibited BRAF activity and downstream ERK phosphorylation. Energy-deprived conditions in cell model and the addition of AMP to cell lysates strengthened the AK2-BRAF interaction, suggesting that AK2 is involved in the regulation of BRAF activity in response to cell metabolic state. AMP facilitated the AK2-BRAF complex formation through binding to AK2. In a panel of HCC cell lines, AK2 expression was inversely correlated with ERK/MAPK activation, and AK2-knockdown or -knockout increased BRAF activity and promoted cell proliferation. Tumors from HCC patients showed low-AK2 protein expression and increased ERK activation compared to non-tumor tissues and the downregulation of AK2 was also verified by two microarray datasets (TCGA-LIHC and GSE14520). Moreover, AK2/BRAF interaction was abrogated by RAS activation in in vitro assay and cell model and in a mouse model of HRASG12V-driven HCC, and AK2 ablation promoted tumor growth and BRAF activity. AK2 also bound to BRAF inhibitor-insensitive BRAF mutants and attenuated their activities. These findings indicate that AK2 monitoring cellular AMP levels is indeed a negative regulator of BRAF, linking the metabolic status to tumor growth.

Machine-Learning and Chemicogenomics Approach Defines and Predicts Cross-Talk of Hippo and MAPK Pathways.

Hippo pathway dysregulation occurs in multiple cancers through genetic and nongenetic alterations, resulting in translocation of YAP to the nucleus and activation of the TEAD family of transcription factors. Unlike other oncogenic pathways such as RAS, defining tumors that are Hippo pathway-dependent is far more complex due to the lack of hotspot genetic alterations. Here, we developed a machine-learning framework to identify a robust, cancer type-agnostic gene expression signature to quantitate Hippo pathway activity and cross-talk as well as predict YAP/TEAD dependency across cancers. Further, through chemical genetic interaction screens and multiomics analyses, we discover a direct interaction between MAPK signaling and TEAD stability such that knockdown of YAP combined with MEK inhibition results in robust inhibition of tumor cell growth in Hippo dysregulated tumors. This multifaceted approach underscores how computational models combined with experimental studies can inform precision medicine approaches including predictive diagnostics and combination strategies. SIGNIFICANCE: An integrated chemicogenomics strategy was developed to identify a lineage-independent signature for the Hippo pathway in cancers. Evaluating transcriptional profiles using a machine-learning method led to identification of a relationship between YAP/TAZ dependency and MAPK pathway activity. The results help to nominate potential combination therapies with Hippo pathway inhibition.This article is highlighted in the In This Issue feature, p. 521.

The Tumor Suppressor BAP1 Regulates the Hippo Pathway in Pancreatic Ductal Adenocarcinoma.

The deubiquitinating enzyme BAP1 is mutated in a hereditary cancer syndrome with a high risk for mesothelioma and melanocytic tumors. Here, we show that pancreatic intraepithelial neoplasia driven by oncogenic mutant KrasG12D progressed to pancreatic adenocarcinoma in the absence of BAP1. The Hippo pathway was deregulated in BAP1-deficient pancreatic tumors, with the tumor suppressor LATS exhibiting enhanced ubiquitin-dependent proteasomal degradation. Therefore, BAP1 may limit tumor progression by stabilizing LATS and thereby promoting activity of the Hippo tumor suppressor pathway. SIGNIFICANCE: BAP1 is mutated in a broad spectrum of tumors. Pancreatic Bap1 deficiency causes acinar atrophy but combines with oncogenic Ras to produce pancreatic tumors. BAP1-deficient tumors exhibit deregulation of the Hippo pathway.See related commentary by Brekken, p. 1624.

DR4-Ser424 O-GlcNAcylation Promotes Sensitization of TRAIL-Tolerant Persisters and TRAIL-Resistant Cancer Cells to Death.

TNF-related apoptosis-inducing ligand (TRAIL) resistance, including nongenetically acquired tolerance in cancer persister cells, is a major obstacle to translating TRAIL therapy into patients with cancer. However, the underlying mechanisms remain to be elucidated. Here, we show that DR4/TRAIL-R1 is O-GlcNAcylated at Ser424 in its death domain to mediate both apoptosis and necrosis upon TRAIL ligation. We found that DR4-Ser424 mutations, identified from our cell-based functional screen using a cancer patient-derived cDNA expression library and from The Cancer Genome Atlas, caused TRAIL resistance in various human cancer cell lines. Using O-GlcNAc transferase knockdown cells, DR4-preferred versus DR5-preferred cancer cells, and a DR5-neutralizing antibody, we evaluated the essential role of DR4-specific O-GlcNAc modification in TRAIL cytotoxicity. In contrast to DR4, DR5 was not O-GlcNAcylated by TRAIL treatment, discriminating DR4 from DR5-mediated signaling. Apart from genetic changes in DR4-Ser424, we further classified various cancer cell lines originated from stomach, colon, lung, and glioblastoma according to their sensitivity to and receptor preference upon TRAIL death signaling and generated TRAIL-tolerant persister-derived DLD-1PER cells. Among these, we discovered that DR4 was not modified by O-GlcNAc in most of the TRAIL-resistant cancer cells and DLD-1PER cells. Interestingly, promoting DR4 O-GlcNAcylation intentionally using 2-deoxy-d-glucose or a high concentration of glucose sensitized those resistant cancer cells to TRAIL. The O-GlcNAcylation-defective DR4 failed to form DISC/necrosome and could not translocate to aggregated platforms for receptor clustering. Our findings demonstrate that DR4 O-GlcNAcylation is crucial for TRAIL death signaling, providing new opportunities for TRAIL therapy overcoming TRAIL resistance in cancers. SIGNIFICANCE: This study reports that a novel posttranslational modification by O-GlcNAcylation of one of the two human TRAIL receptors with a death domain, TRAIL-R1 (DR4), plays a crucial role in enabling both apoptotic and necroptotic cell death induction by TRAIL.

Muscle-splitting approach to thoracoacromial vein for superdrainage in deep inferior epigastric artery perforator flap breast reconstruction.

BACKGROUND: Thoracoacromial vein (TAv) is seldomly considered as a secondary outflow recipient option when venous congestion of deep inferior epigastric artery perforator (DIEP) flap is encountered. The purpose of this study was to present a computed tomography (CT)-based anatomy and a method of approaching TAv in performing superdrainage using superficial inferior epigastric vein (SIEV) in DIEP flap breast reconstruction. METHODS: For CT-based anatomical study, 42 thoracoacromial vessels (TAV) of 21 patients who underwent DIEP flap breast reconstruction were analyzed. From November 2016 to May 2018, pectoralis major (PM) muscle splitting approach to TAv in the first intercostal space was applied to 7 patients who required superdrainage via SIEV. RESULTS: TAVs at mid-first intercostal space (ICS) were located 83.5 ± 9.8 mm lateral to the sternal border (H), 41.5 ± 12.9 mm below the clavicle (V), and 11.7 ± 3.2 mm deep to the outer surface of PM muscle (D). Mean oblique distances from TAV to internal mammary vessels in the 2nd and 3rd ICS were 75.7 ± 9.7 mm and 98.2 ± 10.9 mm, respectively. Seven DIEP flaps presenting intraoperative venous congestion were successfully salvaged intraoperatively with superdrainge procedure. TAvs were harvested without cutting the PM muscle in any patient. Their mean size at anastomosis was 1.61 ± 3.2 mm (range, 0.9-2.5 mm). All flaps survived without perfusion-related complications including fat necrosis. CONCLUSIONS: Harvest of TAv by muscle-splitting approach is an alternative option when additional venous anastomosis using SIEV is mandated for managing venous congestion of DIEP flap.

The tumor suppressor BAP1 cooperates with BRAFV600E to promote tumor formation in cutaneous melanoma.

The deubiquitinating enzyme BAP1 is mutated in a hereditary cancer syndrome with a high risk of mesothelioma and melanocytic tumors. Here, we show that Bap1 deletion in melanocytes cooperates with the constitutively active, oncogenic form of BRAF (BRAFV600E ) and UV to cause melanoma in mice, albeit at very low frequency. In addition, Bap1-null melanoma cells derived from mouse tumors are more aggressive and colonize and grow at distant sites more than their wild-type counterparts. Molecularly, Bap1-null melanoma cell lines have increased DNA damage measured by γH2aX and hyperubiquitination of histone H2a. Therapeutically, these Bap1-null tumors are completely responsive to BRAF- and MEK-targeted therapies. Therefore, BAP1 functions as a tumor suppressor and limits tumor progression in melanoma.

The Hippo pathway effector TAZ induces TEAD-dependent liver inflammation and tumors.

The Hippo signaling pathway regulates organ size and plays critical roles in maintaining tissue growth, homeostasis, and regeneration. Dysregulated in a wide spectrum of cancers, in mammals, this pathway is regulated by two key effectors, YAP and TAZ, that may functionally overlap. We found that TAZ promoted liver inflammation and tumor development. The expression of TAZ, but not YAP, in human liver tumors positively correlated with the expression of proinflammatory cytokines. Hyperactivated TAZ induced substantial myeloid cell infiltration into the liver and the secretion of proinflammatory cytokines through a TEAD-dependent mechanism. Furthermore, tumors with hyperactivated YAP and TAZ had distinct transcriptional signatures, which included the increased expression of inflammatory cytokines in TAZ-driven tumors. Our study elucidated a previously uncharacterized link between TAZ activity and inflammatory responses that influence tumor development in the liver.

Ras-MEK Signaling Mediates a Critical Chk1-Dependent DNA Damage Response in Cancer Cells.

Cancer cell line profiling to identify previously unrecognized kinase dependencies revealed a novel nonmutational dependency on the DNA damage response checkpoint kinase Chk1. Although Chk1 is a promising therapeutic target in p53-deficient cancers, we found that Ras-MEK signaling engages Chk1 in a subset of osteosarcoma, ovarian, and breast cancer cells to enable their survival upon DNA damage, irrespective of p53 mutation status. Mechanistically, Ras-MEK signaling drives Chk1 expression and promotes cancer cell growth that produces genotoxic stress that requires Chk1 to mediate a response to the consequent DNA damage. Reciprocally, Chk1 engages a negative feedback loop to prevent hyperactivation of Ras-MEK signaling, thereby limiting DNA damage. Furthermore, exogenous DNA damage promotes Chk1 dependency, and pharmacologic Chk1 inhibition combined with genotoxic chemotherapy potentiates a DNA damage response and tumor cell killing. These findings reveal a mechanism-based diagnostic strategy to identify cancer patients that may benefit from Chk1-targeted therapy. Mol Cancer Ther; 16(4); 694-704. ©2017 AACR.

SUMO-Modified FADD Recruits Cytosolic Drp1 and Caspase-10 to Mitochondria for Regulated Necrosis.

Fas-associated protein with death domain (FADD) plays a key role in extrinsic apoptosis. Here, we show that FADD is SUMOylated as an essential step during intrinsic necrosis. FADD was modified at multiple lysine residues (K120/125/149) by small ubiquitin-related modifier 2 (SUMO2) during necrosis caused by calcium ionophore A23187 and by ischemic damage. SUMOylated FADD bound to dynamin-related protein 1 (Drp1) in cells both in vitro and in ischemic tissue damage cores, thus promoting Drp1 recruitment by mitochondrial fission factor (Mff) to accomplish mitochondrial fragmentation. Mitochondrial-fragmentation-associated necrosis was blocked by FADD or Drp1 deficiency and SUMO-defective FADD expression. Interestingly, caspase-10, but not caspase-8, formed a ternary protein complex with SUMO-FADD/Drp1 on the mitochondria upon exposure to A23187 and potentiated Drp1 oligomerization for necrosis. Moreover, the caspase-10 L285F and A414V mutants, found in autoimmune lymphoproliferative syndrome and non-Hodgkin lymphoma, respectively, regulated this necrosis. Our study reveals an essential role of SUMOylated FADD in Drp1- and caspase-10-dependent necrosis, providing insights into the mechanism of regulated necrosis by calcium overload and ischemic injury.

CSP0510 Lotion as a Novel Moisturizer Containing Citric Acid and Trisodium Phosphate Relieves Objective and Subjective Symptoms of Atopic Dermatitis.

BACKGROUND: Moisturizers with anti-inflammatory or anti-itch activity should be developed for the safe and effective management of atopic dermatitis (AD). OBJECTIVE: This study evaluated the efficacy of a newly developed moisturizer, CSP0510 lotion (Twolines Inc., Korea), containing citric acid (CA) and trisodium phosphate (TSP) as active ingredients, in mild to moderate AD. METHODS AND RESULTS: CSP0510 lotion applied twice daily for 4 weeks to eczematous lesions improved objective and subjective (itch) symptoms of AD. The physician's global assessment (PGA) score for objective symptoms decreased from 2.5±0.6 before application to 1.3±0.5 after application in the CSP0510-treated group (n=42, p<0.001). Also, the PGA score decreased from 2.3±0.6 to 1.9±0.5 by vehicle-treated (without CA and TSP) control group (p=0.001), but there was no statistical difference between CSP0510-treated and vehicle-treated groups (p=0.089). The visual analogue scale score for itch decreased from 4.8±1.3 to 2.0±0.9 in the CSP0510-treated group (p<0.001), and from 4.6±1.1 to 3.5±0.9 in the control group (p=0.075), showing a statistical significance between two groups (p=0.002). Our results in humans were further supported by in vitro and animal experiments. In HaCaT cells treated with compound 48/80 (7.5 µg/ml), CA:TSP (1:1, vol:vol) synergistically suppressed the compound 48/80-induced upregulation of thymic stromal lymphopoietin, nerve grow factor, and calcitonin gene-related peptide. Application of CSP0510 to the dorsal skin of hairless mice for 3 weeks suppressed the oxazolone-induced allergic skin inflammation. CONCLUSION: In conclusion, CSP0510 lotion has anti-itch and anti-inflammatory activity in the skin, which improves both objective and subjective symptoms of AD.

Introduction of the Reliable Estimation of Atopic Dermatitis in ChildHood: Novel, Diagnostic Criteria for Childhood Atopic Dermatitis.

PURPOSE: Questionnaire-based diagnostic criteria for atopic dermatitis (AD) have been proposed to detect the major group of AD with flexural dermatitis. We aimed to develop novel, questionnaire-based diagnostic criteria for childhood AD, which can detect more comprehensive AD including non-flexural type. METHODS: The draft version of questionnaire to detect childhood AD was prepared to be used for preliminary hospital- (n=1,756) and community-based (n=1,320) surveys. From analysis, the Reliable Estimation of Atopic dermatitis of ChildHood (REACH) was derived and verified in derivation (n=1,129) and validation (n=1,191) sets by community-based surveys. RESULTS: The REACH consists of 11 questions including 2 major and 9 minor criteria. AD is diagnosed as the major group of 'eczema on the antecubital or popliteal fossa' to fulfill the 2 major criteria (2M), and the minor group of 'eczema on the non-antecubital or popliteal fossa' to fulfill the 1 major plus 4 or more minor criteria (1M+4m). In the validation set, the overall 1-year AD prevalence by the REACH was estimated as 12.3% (95% CI, 10.5%-14.2%), and the REACH showed a sensitivity of 75.2%, a specificity of 96.1%, and an error rate of 6.4%. The REACH demonstrated better diagnostic performance than the ISAAC in terms of the number of misclassification (10.0%). CONCLUSIONS: We propose the REACH as new full, questionnaire-based diagnostic criteria for childhood AD in epidemiological surveys. Further studies are warranted to validate the REACH in different populations or countries in the context of large-scale, epidemiological surveys.

Drug resistance via feedback activation of Stat3 in oncogene-addicted cancer cells.

Pathway-targeted cancer drugs can produce dramatic responses that are invariably limited by the emergence of drug-resistant cells. We found that many drug-treated "oncogene-addicted" cancer cells engage a positive feedback loop leading to Stat3 activation, consequently promoting cell survival and limiting overall drug response. This was observed in cancer cells driven by diverse activated kinases, including EGFR, HER2, ALK, and MET, as well as mutant KRAS. Specifically, MEK inhibition led to autocrine activation of Stat3 via the FGF receptor and JAK kinases, and pharmacological inhibition of MEK together with JAK and FGFR enhanced tumor regression. These findings suggest that inhibition of a Stat3 feedback loop may augment the response to a broad spectrum of drugs that target pathways of oncogene addiction.

The DUSP26 phosphatase activator adenylate kinase 2 regulates FADD phosphorylation and cell growth.

Adenylate kinase 2 (AK2), which balances adenine nucleotide pool, is a multi-functional protein. Here we show that AK2 negatively regulates tumour cell growth. AK2 forms a complex with dual-specificity phosphatase 26 (DUSP26) phosphatase and stimulates DUSP26 activity independently of its AK activity. AK2/DUSP26 phosphatase protein complex dephosphorylates fas-associated protein with death domain (FADD) and regulates cell growth. AK2 deficiency enhances cell proliferation and induces tumour formation in a xenograft assay. This anti-growth function of AK2 is associated with its DUSP26-stimulating activity. Downregulation of AK2 is frequently found in tumour cells and human cancer tissues showing high levels of phospho-FADD(Ser194). Moreover, reconstitution of AK2 in AK2-deficient tumour cells retards both cell proliferation and tumourigenesis. Consistent with this, AK2(+/-) mouse embryo fibroblasts exhibit enhanced cell proliferation with a significant alteration in phospho-FADD(Ser191). These results suggest that AK2 is an associated activator of DUSP26 and suppresses cell proliferation by FADD dephosphorylation, postulating AK2 as a negative regulator of tumour growth.

Noncovalent wild-type-sparing inhibitors of EGFR T790M.

UNLABELLED: Approximately half of EGFR-mutant non-small cell lung cancer (NSCLC) patients treated with small-molecule EGFR kinase inhibitors develop drug resistance associated with the EGF receptor (EGFR) T790M "gatekeeper" substitution, prompting efforts to develop covalent EGFR inhibitors, which can effectively suppress EGFR T790M in preclinical models. However, these inhibitors have yet to prove clinically efficacious, and their toxicity in skin, reflecting activity against wild-type EGFR, may limit dosing required to effectively suppress EGFR T790M in vivo. While profiling sensitivity to various kinase inhibitors across a large cancer cell line panel, we identified indolocarbazole compounds, including a clinically well-tolerated FLT3 inhibitor, as potent and reversible inhibitors of EGFR T790M that spare wild-type EGFR. These findings show the use of broad cancer cell profiling of kinase inhibitor efficacy to identify unanticipated novel applications, and they identify indolocarbazole compounds as potentially effective EGFR inhibitors in the context of T790M-mediated drug resistance in NSCLC. SIGNIFICANCE: EGFR-mutant lung cancer patients who respond to currently used EGFR kinase inhibitors invariably develop drug resistance, which is associated with the EGFR T790M resistance mutation in about half these cases. We unexpectedly identified a class of reversible potent inhibitors of EGFR T790M that do not inhibit wild-type EGFR, revealing a promising therapeutic strategy to overcome T790M-associated drug-resistant lung cancers.

Intracellular cleavage of osteopontin by caspase-8 modulates hypoxia/reoxygenation cell death through p53.

Osteopontin (OPN) is highly expressed in cancer patients and plays important roles in many stages of tumor progression, such as anti-apoptosis, proliferation, and metastasis. From functional screening of human cDNA library, we isolated OPN as a caspase-8 substrate that regulates cell death during hypoxia/reoxygenation (Hyp/RO). In vitro cleavage assays demonstrate that OPN is cleaved at Asp-135 and Asp-157 by caspase-8. Cellular cleavage of OPN is observed in apoptotic cells exposed to Hyp/RO among various apoptotic stimuli and its cleavage is blocked by zVAD or IETD caspase inhibitor. Further, over-expression of OPN, the form with secretion signal, inhibits Hyp/RO-induced cell death. Caspase cleavage-defective OPN mutant (OPN D135A/D157A) is more efficient to suppress Hyp/RO-induced cell death than wild-type OPN. OPN D135A/D157A sustains AKT activity to increase cell viability through inhibition of caspase-9 during Hyp/RO. In addition, OPN is highly induced in some tumor cells during Hyp/RO, such as HeLa and Huh-7 cells, which is associated with their resistance to Hyp/RO by sustaining AKT activity. Notably, OPN C-terminal cleavage fragment produced by caspase-8 is detected in the nucleus. Plasmid-encoded expression of OPN C-terminal cleavage fragment increases p53 protein level and induces apoptosis of wild-type mouse embryonic fibroblast cells, but not p53(-/-) mouse embryonic fibroblast cells. These observations suggest that the protective function of OPN during Hyp/RO is inactivated via the proteolytic cleavage by caspase-8 and its cleavage product subsequently induces cell death via p53, postulating caspase-8 as a negative regulator of tumorigenic activity of OPN.

Compensatory activation of ERK1/2 in Atg5-deficient mouse embryo fibroblasts suppresses oxidative stress-induced cell death.

Despite of the increasing evidence that oxidative stress may induce non-apoptotic cell death or autophagic cell death, the mechanism of this process is unclear. Here, we report a role and a down-stream molecular event of Atg5 during oxidative stress-induced cell death. Compared to wild type (WT) cells, Atg5-deficient mouse embryo fibroblasts (Atg5-/- MEFs) and Atg5 knockdown HT22 neuronal cells were more resistant to cell death induced by H2O2. On the contrary, Atg5-/- MEFs were as sensitive to tumor necrosis factor (TNF)-alpha and cycloheximide as WT cells, and were more sensitive to cell death triggered by amino acid-deprivation than WT MEFs. Treatment with H2O2 induced the recruitment of a GFP-LC3 fusion protein and conversion of LC3 I to LC3 II, correlated with the extent of autophagosome formation in WT cells, but much less in Atg5-deficient cells. Among stress kinases, ERK1/2 was markedly activated in Atg5-/- MEFs and Atg5 knockdown HT22 and SH-SY5Y neuronal cells. The inhibition of ERK1/2 by MEK1 inhibitor (PD98059) or dominant negative ERK2 enhanced the susceptibility of Atg5-/- MEFs to H2O2-induced cell death. Further, reconstitution of Atg5 sensitized Atg5-/- MEFs to H2O2 and suppressed the activation of ERK1/2. These results suggest that the inhibitory effect of Atg5 deficiency on cell death is attributable by the compensatory activation of ERK1/2 in Atg5-/- MEFs during oxidative stress-induced cell death.

AK2 activates a novel apoptotic pathway through formation of a complex with FADD and caspase-10.

Mitochondrial proteins function as essential regulators in apoptosis. Here, we show that mitochondrial adenylate kinase 2 (AK2) mediates mitochondrial apoptosis through the formation of an AK2-FADD-caspase-10 (AFAC10) complex. Downregulation of AK2 attenuates etoposide- or staurosporine-induced apoptosis in human cells, but not that induced by tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) or Fas ligand (FasL). During intrinsic apoptosis, AK2 translocates to the cytoplasm, whereas this event is diminished in Apaf-1 knockdown cells and prevented by Bcl-2 or Bcl-X(L). Addition of purified AK2 protein to cell extracts first induces activation of caspase-10 via FADD and subsequently caspase-3 activation, but does not affect caspase-8. AFAC10 complexes are detected in cells undergoing intrinsic cell death and AK2 promotes the association of caspase-10 with FADD. In contrast, AFAC10 complexes are not detected in several etoposide-resistant human tumour cell lines. Taken together, these results suggest that, acting in concert with FADD and caspase-10, AK2 mediates a novel intrinsic apoptotic pathway that may be involved in tumorigenesis.

Essential roles of Atg5 and FADD in autophagic cell death: dissection of autophagic cell death into vacuole formation and cell death.

Autophagic cell death is characterized by the accumulation of vacuoles in physiological and pathological conditions. However, its molecular event is unknown. Here, we show that Atg5, which is known to function in autophagy, contributes to autophagic cell death by interacting with Fas-associated protein with death domain (FADD). Down-regulation of Atg5 expression in HeLa cells suppresses cell death and vacuole formation induced by IFN-gamma. Inversely, ectopic expression of Atg5 using adenoviral delivery induces autophagic cell death. Deletion mapping analysis indicates that procell death activity resides in the middle and C-terminal region of Atg5. Cells harboring the accumulated vacuoles triggered by IFN-gamma or Atg5 expression become dead, and vacuole formation precedes cell death. 3-Methyladenine or expression of Atg5(K130R) mutant blocks both cell death and vacuole formation triggered by IFN-gamma, whereas benzyloxycarbonyl-VAD-fluoromethyl ketone (Z-VAD-fmk) inhibits only cell death but not vacuole formation. Atg5 interacts with FADD via death domain in vitro and in vivo, and the Atg5-mediated cell death, but not vacuole formation, is blocked in FADD-deficient cells. These results suggest that Atg5 plays a crucial role in IFN-gamma-induced autophagic cell death by interacting with FADD.