Deletion of the gene for the African swine fever virus BCL-2 family member A179L increases virus uptake and apoptosis but decreases virus spread in macrophages and reduces virulence in pigs

IMPORTANCE

African swine fever virus (ASFV) causes a lethal disease of pigs with high economic impact in affected countries in Africa, Europe, and Asia. The virus encodes proteins that inhibit host antiviral defenses, including the type I interferon response. Host cells also activate cell death through a process called apoptosis to limit virus replication. We showed that the ASFV A179L protein, a BCL-2 family apoptosis inhibitor, is important in reducing apoptosis in infected cells since deletion of this gene increased cell death and reduced virus replication in cells infected with the A179L gene-deleted virus. Pigs immunized with the BeninΔA179L virus showed no clinical signs and a weak immune response but were not protected from infection with the deadly parental virus. The results show an important role for the A179L protein in virus replication in macrophages and virulence in pigs and suggest manipulation of apoptosis as a possible route to control infection.

KLF11 deficiency enhances chemokine generation and fibrosis in murine unilateral ureteral obstruction

Progression of virtually all forms of chronic kidney disease (CKD) is associated with activation of pro-inflammatory and pro-fibrotic signaling pathways. Despite extensive research, progress in identifying therapeutic targets to arrest or slow progression of CKD has been limited by incomplete understanding of basic mechanisms underlying renal inflammation and fibrosis in CKD. Recent studies have identified Kruppel-like transcription factors that have been shown to play critical roles in renal development, homeostasis, and response to injury. Although KLF11 deficiency has been shown to increase collagen production in vitro and tissue fibrosis in other organs, no previous study has linked KLF11 to the development of CKD. We sought to test the hypothesis that KLF11 deficiency promotes CKD through upregulation of pro-inflammatory and pro-fibrogenic signaling pathways in murine unilateral ureteral obstruction (UUO), a well-established model of renal fibrosis. We found that KLF11-deficiency exacerbates renal injury in the UUO model through activation of the TGF-β/SMAD signaling pathway and through activation of several pro-inflammatory chemokine signaling pathways. Based on these considerations, we conclude that agents increase KLF11 expression may provide novel therapeutic targets to slow the progression of CKD.

Grim-19 deficiency promotes decidual macrophage autophagy in recurrent spontaneous abortion

Dysregulation of decidual macrophages leads to the occurrence of recurrent spontaneous abortion (RSA). However, the role of macrophages in RSA occurrence remains unclear. In this study, we found that the expression of Grim-19 was decreased, and the expression of autophagy related proteins Beclin1, LC3B II/I and BNIP3 was markedly upregulated in decidual macrophages of RSA patients compared with the normal pregnancy group. Furthermore, we demonstrated that downregulation of GRIM-19 increased the expression of autophagy related proteins Beclin1, LC3B II/I, BNIP3 and the proinflammatory cytokines IL1B, IL6 and TNFa in uterine mononuclear cells of GRIM-19^+/- mice. The proportion of CD45+CD11b+F4/80+LC3B+ cells in GRIM-19^+/- mouse uteri was significantly higher than that in WT mouse uteri. In addition, we confirmed that inhibition of Grim-19 by siRNA enhanced the expression of autophagy related proteins in RAW264.7 cells and THP-1 cells. More importantly, downregulation of Grim-19 in RAW264.7 cells promoted the release of proinflammatory cytokines and promoted phagocytic activity, which could be reversed by autophagy blockade. For THP-1-derived macrophages, the results of RNA-seq suggested that Grim-19 mainly modulates immune and inflammatory-related pathways, leading to cytokine production, and thus contributing to inflammation. Therefore, our data reveal that Grim-19 deficiency influences macrophage function, characterized by enhanced proinflammatory cytokines and phagocytic activity, and this might be regulated by autophagy. This may represent a novel mechanism for the occurrence of RSA.

DDX17 is an essential mediator of sterile NLRC4 inflammasome activation by retrotransposon RNAs

Detection of microbial products by multiprotein complexes known as inflammasomes is pivotal to host defense against pathogens. Nucleotide-binding domain leucine-rich repeat (NLR) CARD domain containing 4 (NLRC4) forms an inflammasome in response to bacterial products; this requires their detection by NLR family apoptosis inhibitory proteins (NAIPs), with which NLRC4 physically associates. However, the mechanisms underlying sterile NLRC4 inflammasome activation, which is implicated in chronic noninfectious diseases, remain unknown. Here, we report that endogenous short interspersed nuclear element (SINE) RNAs, which promote atrophic macular degeneration (AMD) and systemic lupus erythematosus (SLE), induce NLRC4 inflammasome activation independent of NAIPs. We identify DDX17, a DExD/H box RNA helicase, as the sensor of SINE RNAs that licenses assembly of an inflammasome comprising NLRC4, NLR pyrin domain–containing protein 3, and apoptosis-associated speck-like protein–containing CARD and induces caspase-1 activation and cytokine release. Inhibiting DDX17-mediated NLRC4 inflammasome activation decreased interleukin-18 release in peripheral blood mononuclear cells of patients with SLE and prevented retinal degeneration in an animal model of AMD. Our findings uncover a previously unrecognized noncanonical NLRC4 inflammasome activated by endogenous retrotransposons and provide potential therapeutic targets for SINE RNA–driven diseases.

BAG3 epigenetically regulates GALNT10 expression via WDR5 and facilitates the stem cell-like properties of platin-resistant ovarian cancer cells

Ovarian cancer is the most lethal gynecologic malignant cancer, frequently due to its late diagnosis and high recurrence. Cancer stem cells (CSCs) from different malignancies including ovarian cancer have been linked to chemotherapy resistance and poor prognosis. Therefore, identifying the molecular mechanisms mediating therapy resistance is urgent to finding novel targets for therapy-resistant tumors. Aberrant O-glycosylation ascribed to subtle alteration of GALNT family members during malignant transformation facilitate metastasis in various cancers. The current study demonstrated that BAG3 was upregulated in platin-resistant ovarian cancer tissues and cells, and high BAG3 predicted dismal disease-free survival of patients with ovarian cancer. In addition, the current study showed that BAG3 facilitated CSC-like properties of ovarian cancer cells via regulation of GALTN10. In a term of mechanism, BAG3 epigenetically regulated GALNT10 transactivation via histone H3 lysine 4 (H3K4) presenter WDR5. We demonstrated that WDR5 increased H3K4 trimethylation (H3K4me3) modification at the promoter regions of GALNT10, facilitating recruitment of transcription factor ZBTB2 to the GALNT10 promoter. Collectively, our study uncovers an epigenetic upregulation of GALNT10 by BAG3 via WDR5 to facilitate CSCs of platin-resistant ovarian cancers, providing additional information for further identification of attractive targets with therapeutic significance in platin-resistant ovarian cancer.

TNFAIP8 Regulates Intestinal Epithelial Cell Differentiation and May Alter Terminal Differentiation of Secretory Progenitors

The intestine is a highly proliferative dynamic environment that relies on constant self-renewal of the intestinal epithelium to maintain homeostasis. Tumor necrosis factor-alpha-induced protein 8 (TNFAIP8 or TIPE0) is a regulator of PI3K-mediated signaling. By binding to PIP2 and PIP3, TIPE family members locally activate PI3K activity while globally inhibiting PI3K activity through sequestration of membranous PIP2. Single-cell RNA sequencing survey of Tipe0-/- small intestine was used to investigate the role of TIPE0 in intestinal differentiation. Tipe0-/- intestinal cells were shown to shift towards an undifferentiated state, with the notable exception of goblet cells. Additionally, three possible novel regulators of terminal cell fate decisions in the secretory lineage were identified: Nupr1, Kdm4a, and Gatad1. We propose that these novel regulators drive changes involved in goblet cell (Nupr1) or tuft cell (Kdm4a and Gatad1) fate commitment and that TIPE0 may play a role in orchestrating terminal differentiation.

Caveolae-mediated Tie2 signaling contributes to CCM pathogenesis in a brain endothelial cell-specific Pdcd10-deficient mouse model

Cerebral cavernous malformations (CCMs) are vascular abnormalities that primarily occur in adulthood and cause cerebral hemorrhage, stroke, and seizures. CCMs are thought to be initiated by endothelial cell (EC) loss of any one of the three Ccm genes: CCM1 (KRIT1), CCM2 (OSM), or CCM3 (PDCD10). Here we report that mice with a brain EC-specific deletion of Pdcd10 (Pdcd10BECKO) survive up to 6-12 months and develop bona fide CCM lesions in all regions of brain, allowing us to visualize the vascular dynamics of CCM lesions using transcranial two-photon microscopy. This approach reveals that CCMs initiate from protrusion at the level of capillary and post-capillary venules with gradual dissociation of pericytes. Microvascular beds in lesions are hyper-permeable, and these disorganized structures present endomucin-positive ECs and α-smooth muscle actin-positive pericytes. Caveolae in the endothelium of Pdcd10BECKO lesions are drastically increased, enhancing Tie2 signaling in Ccm3-deficient ECs. Moreover, genetic deletion of caveolin-1 or pharmacological blockade of Tie2 signaling effectively normalizes microvascular structure and barrier function with attenuated EC-pericyte disassociation and CCM lesion formation in Pdcd10BECKO mice. Our study establishes a chronic CCM model and uncovers a mechanism by which CCM3 mutation-induced caveolae-Tie2 signaling contributes to CCM pathogenesis.

Ifit2 deficiency restricts microglial activation and leukocyte migration following murine coronavirus (m-CoV) CNS infection

The interferon-induced tetratricopeptide repeat protein (Ifit2) protects mice from lethal neurotropic viruses. Neurotropic coronavirus MHV-RSA59 infection of Ifit2^-/- mice caused pronounced morbidity and mortality accompanied by rampant virus replication and spread throughout the brain. In spite of the higher virus load, induction of many cytokines and chemokines in the brains of infected Ifit2^-/- mice were similar to that in wild-type mice. In contrast, infected Ifit2^-/- mice revealed significantly impaired microglial activation as well as reduced recruitment of NK1.1 T cells and CD4 T cells to the brain, possibly contributing to the lack of viral clearance. These two deficiencies were associated with a lower level of microglial expression of CX3CR1, the receptor of the CX3CL1 (Fractalkine) chemokine, which plays a critical role in both microglial activation and leukocyte recruitment. The above results uncovered a new potential role of an interferon-induced protein in immune protection.

Interferons (IFNs) are known to protect from virus dissemination and pathogenesis. Several IFN stimulated genes (ISG) regulate neuropathogenesis but the mechanisms underlying the antiviral effects are not clearly understood. IFN induced tetratricopeptide repeats (Ifit) are a class of ISGs. Among the Ifits, Ifit2 is known to play a beneficial role in restricting neurotropic viral replication. To provide better cellular insights into the protective mechanisms of Ifit2 functions, using a neurotropic coronavirus infection in Ifit2 depleted mice we report that in the absence of Ifit2, viral replication is dramatically increased and mice develop severe clinical signs and symptoms of neurological deficit. Despite the enormous viral load, Ifit2 deficient mice are impaired in microglial activation and recruitment of peripheral leukocytes into the CNS. This impaired leuocyte infiltration in Ifit2 deficient mice was also associated with reduced expression of a novel chemokine receptor CX3CR1,which is important for viral induced microglial activation and maintaining tissue homeostasis.

Genetic compensation prevents myopathy and heart failure in an in vivo model of Bag3 deficiency

Mutations in the molecular co-chaperone Bcl2-associated athanogene 3 (BAG3) are found to cause dilated cardiomyopathy (DCM), resulting in systolic dysfunction and heart failure, as well as myofibrillar myopathy (MFM), which is characterized by protein aggregation and myofibrillar disintegration in skeletal muscle cells. Here, we generated a CRISPR/Cas9-induced Bag3 knockout zebrafish line and found the complete preservation of heart and skeletal muscle structure and function during embryonic development, in contrast to morpholino-mediated knockdown of Bag3. Intriguingly, genetic compensation, a process of transcriptional adaptation which acts independent of protein feedback loops, was found to prevent heart and skeletal muscle damage in our Bag3 knockout model. Proteomic profiling and quantitative real-time PCR analyses identified Bag2, another member of the Bag protein family, significantly upregulated on a transcript and protein level in bag3^-/- mutants. This implied that the decay of bag3 mutant mRNA in homozygous bag3^-/- embryos caused the transcriptional upregulation of bag2 expression. We further demonstrated that morpholino-mediated knockdown of Bag2 in bag3^-/- embryos evoked severe functional and structural heart and skeletal muscle defects, which are similar to Bag3 morphants. However, Bag2 knockdown in bag3^+/+ or bag3^+/- embryos did not result in (cardio-)myopathy. Finally, we found that inhibition of the nonsense-mediated mRNA decay (NMD) machinery by knockdown of upf1, an essential NMD factor, caused severe heart and skeletal muscle defects in bag3^-/- mutants due to the blockade of transcriptional adaptation of bag2 expression. Our findings provide evidence that genetic compensation might vitally influence the penetrance of disease-causing bag3 mutations in vivo.

One form of genetic compensation is described as transcriptional adaptation of gene expression triggered by deleterious gene mutations. Although the precise molecular mechanism that induces genetic compensation needs to be defined, it represents a powerful biological phenomenon that warrants genetic robustness. We find that antisense-mediated knockdown of Bag3 in zebrafish embryos causes heart failure and myopathy. By contrast, CRISPR/Cas9-induced depletion of Bag3 does not result in the abrogation of heart and skeletal muscle function in zebrafish embryos. We find here that transcriptional activation of the Bag family member bag2 is capable of restoring heart and skeletal muscle function in bag3 mutant embryos, whereas this compensatory mechanism is not present in the bag3 morphants. Furthermore, we show that nonsense-mediated decay of bag3 mRNA is the molecular trigger for the compensatory upregulation of bag2. Our study provides evidence that genetic compensation via transcriptional adaptation is a vital modulator of disease peculiarity and penetrance in bag3 mutant zebrafish and that this biological phenomenon might also be active in certain human BAG3 mutation carriers.

Frontline Science: Anthrax lethal toxin-induced, NLRP1-mediated IL-1β release is a neutrophil and PAD4-dependent event

Anthrax lethal toxin (LT) is a protease that activates the NLRP1b inflammasome sensor in certain rodent strains. Unlike better-studied sensors, relatively little is known about the priming requirements for NLRP1b. In this study, we investigate the rapid and striking priming-independent LT-induced release of IL-1β in mice within hours of toxin challenge. We find IL-1β release to be a NLRP1b- and caspase-1-dependent, NLRP3 and caspase-11-independent event that requires both neutrophils and peptidyl arginine deiminiase-4 (PAD4) activity. The simultaneous LT-induced IL-18 response is neutrophil-independent. Bone marrow reconstitution experiments in mice show toxin-induced IL-1β originates from hematopoietic cells. LT treatment of neutrophils in vitro did not induce IL-1β, neutrophil extracellular traps (NETs), or pyroptosis. Although platelets interact closely with neutrophils and are also a potential source of IL-1β, they were unable to bind or endocytose LT and did not secrete IL-1β in response to the toxin. LT-treated mice had higher levels of cell-free DNA and HMGB1 in circulation than PBS-treated controls, and treatment of mice with recombinant DNase reduced the neutrophil- and NLRP1-dependent IL-1β release. DNA sensor AIM2 deficiency, however, did not impact IL-1β release. These data, in combination with the findings on PAD4, suggest a possible role for in vivo NETs or cell-free DNA in cytokine induction in response to LT challenge. Our findings suggest a complex interaction of events and/or mediators in LT-treated mice with the neutrophil as a central player in induction of a profound and rapid inflammatory response to toxin.

Deficiency of GABARAP but not its Paralogs Causes Enhanced EGF-induced EGFR Degradation

The γ-aminobutyric acid type A receptor-associated protein (GABARAP) and its close paralogs GABARAPL1 and GABARAPL2 constitute a subfamily of the autophagy-related 8 (Atg8) protein family. Being associated with a variety of dynamic membranous structures of autophagic and non-autophagic origin, Atg8 proteins functionalize membranes by either serving as docking sites for other proteins or by acting as membrane tethers or adhesion factors. In this study, we describe that deficiency for GABARAP alone, but not for its close paralogs, is sufficient for accelerated EGF receptor (EGFR) degradation in response to EGF, which is accompanied by the downregulation of EGFR-mediated MAPK signaling, altered target gene expression, EGF uptake, and EGF vesicle composition over time. We further show that GABARAP and EGFR converge in the same distinct compartments at endogenous GABARAP expression levels in response to EGF stimulation. Furthermore, GABARAP associates with EGFR in living cells and binds to synthetic peptides that are derived from the EGFR cytoplasmic tail in vitro. Thus, our data strongly indicate a unique and novel role for GABARAP during EGFR trafficking.

The TIPE Molecular Pilot That Directs Lymphocyte Migration in Health and Inflammation

Lymphocytes are some of the most motile cells of vertebrates, constantly navigating through various organ systems. Their specific positioning in the body is delicately controlled by site-specific directional cues such as chemokines. While it has long been suspected that an intrinsic molecular pilot, akin to a ship's pilot, guides lymphocyte navigation, the nature of this pilot is unknown. Here we show that the TIPE (TNF-α-induced protein 8-like) family of proteins pilot lymphocytes by steering them toward chemokines. TIPE proteins are carriers of lipid second messengers. They mediate chemokine-induced local generation of phosphoinositide second messengers, but inhibit global activation of the small GTPase Rac. TIPE-deficient T lymphocytes are completely pilot-less: they are unable to migrate toward chemokines despite their normal ability to move randomly. As a consequence, TIPE-deficient mice have a marked defect in positioning their T lymphocytes to various tissues, both at the steady-state and during inflammation. Thus, TIPE proteins pilot lymphocytes during migration and may be targeted for the treatment of lymphocyte-related disorders.

ASPP1 deficiency promotes epithelial-mesenchymal transition, invasion and metastasis in colorectal cancer

The apoptosis-stimulating protein of p53 (ASPP) family of proteins can regulate apoptosis by interacting with the p53 family and have been identified to play an important role in cancer progression. Previously, we have demonstrated that ASPP2 downregulation can promote invasion and migration by controlling β-catenin-dependent regulation of ZEB1, however, the role of ASPP1 in colorectal cancer (CRC) remains unclear. We analyzed data from The Cancer Genome Atlas (TCGA) and coupled this to in vitro experiments in CRC cell lines as well as to experimental pulmonary metastasis in vivo. Tissue microarrays of CRC patients with information of clinical-pathological parameters were also used to investigate the expression and function of ASPP1 in CRC. Here, we report that loss of ASPP1 is capable of enhancing migration and invasion in CRC, both in vivo and in vitro. We demonstrate that depletion of ASPP1 could activate expression of Snail2 via the NF-κB pathway and in turn, induce EMT; and this process is further exacerbated in RAS-mutated CRC. ASPP1 could be a prognostic factor in CRC, and the use of NF-κB inhibitors may provide new strategies for therapy against metastasis in ASPP1-depleted CRC patients.

Genome-wide association study of adipocyte lipolysis in the GENetics of adipocyte lipolysis (GENiAL) cohort

OBJECTIVES

Lipolysis, hydrolysis of triglycerides to fatty acids in adipocytes, is tightly regulated, poorly understood, and, if perturbed, can lead to metabolic diseases including obesity and type 2 diabetes. The goal of this study was to identify the genetic regulators of lipolysis and elucidate their molecular mechanisms.

METHODS

Adipocytes from abdominal subcutaneous adipose tissue biopsies were isolated and were incubated without (spontaneous lipolysis) or with a catecholamine (stimulated lipolysis) to analyze lipolysis. DNA was extracted and genome-wide genotyping and imputation conducted. After quality control, 939 samples with genetic and lipolysis data were available. Genome-wide association studies of spontaneous and stimulated lipolysis were conducted. Subsequent in vitro gene expression analyses were used to identify candidate genes and explore their regulation of adipose tissue biology.

RESULTS

One locus on chromosome 19 demonstrated genome-wide significance with spontaneous lipolysis. 60 loci showed suggestive associations with spontaneous or stimulated lipolysis, of which many influenced both traits. In the chromosome 19 locus, only HIF3A was expressed in the adipocytes and displayed genotype-dependent gene expression. HIF3A knockdown in vitro increased lipolysis and the expression of key lipolysis-regulating genes.

CONCLUSIONS

In conclusion, we identified a genetic regulator of spontaneous lipolysis and provided evidence of HIF3A as a novel key regulator of lipolysis in subcutaneous adipocytes as the mechanism through which the locus influences adipose tissue biology.

APOPT1/COA8 assists COX assembly and is oppositely regulated by UPS and ROS

Loss-of-function mutations in APOPT1, a gene exclusively found in higher eukaryotes, cause a characteristic type of cavitating leukoencephalopathy associated with mitochondrial cytochrome c oxidase (COX) deficiency. Although the genetic association of APOPT1 pathogenic variants with isolated COX defects is now clear, the biochemical link between APOPT1 function and COX has remained elusive. We investigated the molecular role of APOPT1 using different approaches. First, we generated an Apopt1 knockout mouse model which shows impaired motor skills, e.g., decreased motor coordination and endurance, associated with reduced COX activity and levels in multiple tissues. In addition, by achieving stable expression of wild-type APOPT1 in control and patient-derived cultured cells we ruled out a role of this protein in apoptosis and established instead that this protein is necessary for proper COX assembly and function. On the other hand, APOPT1 steady-state levels were shown to be controlled by the ubiquitination-proteasome system (UPS). Conversely, in conditions of increased oxidative stress, APOPT1 is stabilized, increasing its mature intramitochondrial form and thereby protecting COX from oxidatively induced degradation.

NLRP3 signaling drives macrophage-induced adaptive immune suppression in pancreatic carcinoma

The tumor microenvironment (TME) in pancreatic ductal adenocarcinoma (PDA) is characterized by immune tolerance, which enables disease to progress unabated by adaptive immunity. However, the drivers of this tolerogenic program are incompletely defined. In this study, we found that NLRP3 promotes expansion of immune-suppressive macrophages in PDA. NLRP3 signaling in macrophages drives the differentiation of CD4+ T cells into tumor-promoting T helper type 2 cell (Th2 cell), Th17 cell, and regulatory T cell populations while suppressing Th1 cell polarization and cytotoxic CD8+ T cell activation. The suppressive effects of NLRP3 signaling were IL-10 dependent. Pharmacological inhibition or deletion of NLRP3, ASC (apoptosis-associated speck-like protein containing a CARD complex), or caspase-1 protected against PDA and was associated with immunogenic reprogramming of innate and adaptive immunity within the TME. Similarly, transfer of PDA-entrained macrophages or T cells from NLRP3-/- hosts was protective. These data suggest that targeting NLRP3 holds the promise for the immunotherapy of PDA.

ASPP2 deficiency causes features of 1q41q42 microdeletion syndrome

Chromosomal abnormalities are implicated in a substantial number of human developmental syndromes, but for many such disorders little is known about the causative genes. The recently described 1q41q42 microdeletion syndrome is characterized by characteristic dysmorphic features, intellectual disability and brain morphological abnormalities, but the precise genetic basis for these abnormalities remains unknown. Here, our detailed analysis of the genetic abnormalities of 1q41q42 microdeletion cases identified TP53BP2, which encodes apoptosis-stimulating protein of p53 2 (ASPP2), as a candidate gene for brain abnormalities. Consistent with this, Trp53bp2-deficient mice show dilation of lateral ventricles resembling the phenotype of 1q41q42 microdeletion patients. Trp53bp2 deficiency causes 100% neonatal lethality in the C57BL/6 background associated with a high incidence of neural tube defects and a range of developmental abnormalities such as congenital heart defects, coloboma, microphthalmia, urogenital and craniofacial abnormalities. Interestingly, abnormalities show a high degree of overlap with 1q41q42 microdeletion-associated abnormalities. These findings identify TP53BP2 as a strong candidate causative gene for central nervous system (CNS) defects in 1q41q42 microdeletion syndrome, and open new avenues for investigation of the mechanisms underlying CNS abnormalities.

Silencing microRNA-143 protects the integrity of the blood-brain barrier: implications for methamphetamine abuse

MicroRNA-143 (miR-143) plays a critical role in various cellular processes; however, the role of miR-143 in the maintenance of blood-brain barrier (BBB) integrity remains poorly defined. Silencing miR-143 in a genetic animal model or via an anti-miR-143 lentivirus prevented the BBB damage induced by methamphetamine. miR-143, which targets p53 unregulated modulator of apoptosis (PUMA), increased the permeability of human brain endothelial cells and concomitantly decreased the expression of tight junction proteins (TJPs). Silencing miR-143 increased the expression of TJPs and protected the BBB integrity against the effects of methamphetamine treatment. PUMA overexpression increased the TJP expression through a mechanism that involved the NF-κB and p53 transcription factor pathways. Mechanistically, methamphetamine mediated up-regulation of miR-143 via sigma-1 receptor with sequential activation of the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3' kinase (PI3K)/Akt and STAT3 pathways. These results indicated that silencing miR-143 could provide a novel therapeutic strategy for BBB damage-related vascular dysfunction.

Pdcd4 Is Involved in the Formation of Stress Granule in Response to Oxidized Low-Density Lipoprotein or High-Fat Diet

Stress granules (SGs) in response to various stresses have been reported in many diseases. We previously reported the implication of programmed cell death 4 (Pdcd4) in obesity-induced stress responses, but the possible link between Pdcd4 and SGs remains lacking. In this study we showed that oxidized low-density lipoprotein (ox-LDL) or high-fat diet (HFD) induced SG formation in mouse macrophages and liver tissues, and Pdcd4 deficiency in mice remarkably reduced its formation. In response to ox-LDL, either endogenous or ectopic Pdcd4 displayed granule-like expression and co-localized with SG markers including T-cell-restricted intracellular antigen-1, fragile X mental retardation-related protein 1, and eukaryotic initiation factor 4A. Ectopic expression of truncated Pdcd4 that depleted specific RNA-binding motif significantly disrupted the SG formation, suggesting the direct involvement of Pdcd4 in ox-LDL-induced SGs through its RNA-binding activity. Additionally, Pdcd4 deficiency drove AKT activation and suppression of eIF2α phosphorylation, thereby contributing to the resistance to ox-LDL or HFD-induced SG formation. Collectively, our data suggest that Pdcd4 as a crucial regulator in SGs induced by ox-LDL or HFD maybe a potential target for mitigating SG-associated stress responses in obesity and related diseases.

The Cell Death Inhibitor ARC Is Induced in a Tissue-Specific Manner by Deletion of the Tumor Suppressor Gene Men1, but Not Required for Tumor Development and Growth

Multiple endocrine neoplasia type 1 (MEN1) is a genetic disorder characterized by tissue-specific tumors in the endocrine pancreas, parathyroid, and pituitary glands. Although tumor development in these tissues is dependent upon genetic inactivation of the tumor suppressor Men1, loss of both alleles of this gene is not sufficient to induce these cancers. Men1 encodes menin, a nuclear protein that influences transcription. A previous ChIP on chip analysis suggested that menin binds promoter sequences of nol3, encoding ARC, which is a cell death inhibitor that has been implicated in cancer pathogenesis. We hypothesized that ARC functions as a co-factor with Men1 loss to induce the tissue-restricted distribution of tumors seen in MEN1. Using mouse models that recapitulate this syndrome, we found that biallelic deletion of Men1 results in selective induction of ARC expression in tissues that develop tumors. Specifically, loss of Men1 in all cells of the pancreas resulted in marked increases in ARC mRNA and protein in the endocrine, but not exocrine, pancreas. Similarly, ARC expression increased in the parathyroid with inactivation of Men1 in that tissue. To test if ARC contributes to MEN1 tumor development in the endocrine pancreas, we generated mice that lacked none, one, or both copies of ARC in the context of Men1 deletion. Studies in a cohort of 126 mice demonstrated that, although mice lacking Men1 developed insulinomas as expected, elimination of ARC in this context did not significantly alter tumor load. Cellular rates of proliferation and death in these tumors were also not perturbed in the absence of ARC. These results indicate that ARC is upregulated by loss Men1 in the tissue-restricted distribution of MEN1 tumors, but that ARC is not required for tumor development in this syndrome.

Pharmacologically blocking p53-dependent apoptosis protects intestinal stem cells and mice from radiation

Exposure to high levels of ionizing radiation (IR) leads to debilitating and dose-limiting gastrointestinal (GI) toxicity. Using three-dimensional mouse crypt culture, we demonstrated that p53 target PUMA mediates radiation-induced apoptosis via a cell-intrinsic mechanism, and identified the GSK-3 inhibitor CHIR99021 as a potent radioprotector. CHIR99021 treatment improved Lgr5+ cell survival and crypt regeneration after radiation in culture and mice. CHIR99021 treatment specifically blocked apoptosis and PUMA induction and K120 acetylation of p53 mediated by acetyl-transferase Tip60, while it had no effect on p53 stabilization, phosphorylation or p21 induction. CHIR99021 also protected human intestinal cultures from radiation by PUMA but not p21 suppression. These results demonstrate that p53 posttranslational modifications play a key role in the pathological and apoptotic response of the intestinal stem cells to radiation and can be targeted pharmacologically.

Prion pathogenesis in the absence of NLRP3/ASC inflammasomes

The accumulation of the scrapie prion protein PrP^Sc, a misfolded conformer of the cellular prion protein PrP^C, is a crucial feature of prion diseases. In the central nervous system, this process is accompanied by conspicuous microglia activation. The NLRP3 inflammasome is a multi-molecular complex which can sense heterogeneous pathogen-associated molecular patterns and culminates in the activation of caspase 1 and release of IL 1β. The NLRP3 inflammasome was reported to be essential for IL 1β release after in vitro exposure to the amyloidogenic peptide PrP^106-126 and to recombinant PrP fibrils. We therefore studied the role of the NLRP3 inflammasome in a mouse model of prion infection. Upon intracerebral inoculation with scrapie prions (strain RML), mice lacking NLRP3 (Nlrp3^-/-) or the inflammasome adaptor protein ASC (Pycard^-/-) succumbed to scrapie with attack rates and incubation times similar to wild-type mice, and developed the classic histologic and biochemical features of prion diseases. Genetic ablation of NLRP3 or ASC did not significantly impact on brain levels of IL 1β at the terminal stage of disease. Our results exclude a significant role for NLRP3 and ASC in prion pathogenesis and invalidate their claimed potential as therapeutic target against prion diseases.

Lipid Trafficking Defects Increase Beclin-1 and Activate Autophagy in Niemann-Pick Type C Disease

Niemann-Pick type C disease (NPC) is a sphingolipid storage disorder characterized by progressive neurodegeneration that typically shows juvenile onset. Mutations in the Npc1 gene cause approximately 95% of NPC cases. NPC1 is a multipass transmembrane protein involved in lipid and cholesterol trafficking. Loss of function mutations in Npc1 lead to the accumulation of sphingolipids and cholesterol in late endosomes and lysosomes. In our study, we demonstrated that NPC1 deficiency results in increased basal autophagy in human fibroblasts and in mice. We further demonstrated that NPC1 deficiency activate basal autophagy through increased expression of Beclin-1, a highly conserved member of the class III PI3K complex that is critical for the formation of autophagosomes. In contrast, enhanced basal autophagy was not associated with activation of the Akt-mTORp70 S6K signaling pathway. Increased Beclin-1 levels and elevated autophagy were also observed in other sphingolipid storage diseases characterized by disrupted cholesterol and sphingolipid trafficking. We propose a model in which the disordered cholesterol trafficking that occurs in many sphingolipid storages diseases results in upregulation of Beclin-1 and enhanced levels of autophagy.

Blockade of macrophage autophagy ameliorates activated lymphocytes-derived DNA induced murine lupus possibly via inhibition of proinflammatory cytokine production

OBJECTIVES

Systemic lupus erythematosus (SLE) is a typical inflammatory autoimmune disease for its unknown pathogenesis and potential fatality. It has been reported that autophagy has a crosstalk with autoimmunity, but its impact on the pathogenesis of SLE remains unclear. Here, we investigated the role of autophagy in inflammatory response of macrophages under SLE conditions.

METHODS

First, we detected the expression of autophagy-related genes (Atg5, Atg12 and Beclin 1) in the macrophages derived from activated lymphocytes-derived DNA (ALD-DNA) induced murine lupus as well as in the PBMC from SLE patients. And then through adoptive transfer of Beclin 1 knockdown macrophages, we further investigated the potential effect of macrophage autophagy on the SLE-associated inflammatory response and disease severity by evaluating serum anti-dsDNA antibodies and proteinuria levels, immune complex deposition as well as renal pathological changes.

RESULTS

We found that autophagy related genes were significantly upregulated in the splenic and renal macrophages of lupus mice and in the PBMC of SLE patients. Adoptive transfer of Beclin 1 knockdown macrophages could significantly decrease the anti-dsDNA antibodies and proteinuria levels, robustly reduce renal immune complex deposition and remit glomerulonephritis, indicating the amelioration of murine lupus. This protective effect was associated with the obviously decreased production of proinflammatory cytokines IL-6 and TNF-α.

CONCLUSIONS

Our results suggested that aberrant activated autophagy in macrophages contributed to the pathogenesis of murine lupus possibly via promoting the production of proinflammatory cytokines TNF-α and IL-6, and inhibition of autophagy might represent a novel regulation strategy for excessive activation of proinflammatory macrophages and a new therapeutic regime for SLE.

Suppression of autophagy enhances preferential toxicity of paclitaxel to folliculin-deficient renal cancer cells

BACKGROUND

Paclitaxel, a widely used chemotherapeutic drug, can induce apoptosis in variety of cancer cells. A previous study has shown preferential toxicity of paclitaxel to FLCN-deficient kidney cancer cell line, UOK257. In this report, we investigate the cellular and molecular mechanism of paclitaxel-induced autophagy and apoptosis in renal cancer cells with and without FLCN expression.

METHODS

Two pairs of cell lines were used: FLCN siRNA-silenced ACHN cell line (ACHN-5968) and scrambled ACHN cell line (ACHN-sc); FLCN-null UOK257 cell line and UOK257-2 cell line restored with ectopic expression of FLCN. Autophagy was examined by western blot, GFP-LC3, transmission electron microscopy, and MDC assay. Cell viability and apoptosis were detected using MTT assay, DAPI stain and TUNEL assay. After inhibition of autophagy with 3-Methyladenine (3-MA) or Beclin 1 siRNA, cell viability and apoptosis were measured by MTT assay and TUNEL assay.

RESULTS

After paclitaxel treatment, a dose-dependent decrease in cell viability and increase in apoptosis were observed in FLCN-deficient UOK257 and ACHN-5968 cells compared to their FLCN-expressing counterparts, suggesting that renal cancer cells without FLCN were more sensitive to paclitaxel. Enhanced autophagy was found to be associated with paclitaxel treatment in FLCN-deficient RCC cells. The MAPK pathway was also identified as a key pathway for the activation of autophagy in these kidney cancer cells. Inhibition of phosphorylated ERK with ERK inhibitor U0126 showed a significant decrease in autophagy. Furthermore, after inhibition of autophagy with 3-Methyladenine (3-MA) or Beclin 1 siRNA, apoptosis induced by paclitaxel was significantly increased in FLCN-deficient UOK257 and ACHN-5968 cells.

CONCLUSIONS

Preferential toxicity of paclitaxel to FLCN-deficient kidney cancer cells is associated with enhanced autophagy. Suppression of autophagy further enhances paclitaxel-induced apoptosis in FLCN-deficient renal cancer cells. Our results suggest that paclitaxel combined with an autophagy inhibitor might be a potentially more effective chemotherapeutic approach for FLCN-deficient renal cancer.

Serine/threonine kinase 17A is a novel candidate for therapeutic targeting in glioblastoma

STK17A is a relatively uncharacterized member of the death-associated protein family of serine/threonine kinases which have previously been associated with cell death and apoptosis. Our prior work established that STK17A is a novel p53 target gene that is induced by a variety of DNA damaging agents in a p53-dependent manner. In this study we have uncovered an additional, unanticipated role for STK17A as a candidate promoter of cell proliferation and survival in glioblastoma (GBM). Unexpectedly, it was found that STK17A is highly overexpressed in a grade-dependent manner in gliomas compared to normal brain and other cancer cell types with the highest level of expression in GBM. Knockdown of STK17A in GBM cells results in a dramatic alteration in cell shape that is associated with decreased proliferation, clonogenicity, migration, invasion and anchorage independent colony formation. STK17A knockdown also sensitizes GBM cells to genotoxic stress. STK17A overexpression is associated with a significant survival disadvantage among patients with glioma which is independent of age, molecular phenotype, IDH1 mutation, PTEN loss, and alterations in the p53 pathway and partially independent of grade. In summary, we demonstrate that STK17A provides a proliferative and survival advantage to GBM cells and is a potential target to be exploited therapeutically in patients with glioma.

Histone deacetylase 6-mediated selective autophagy regulates COPD-associated cilia dysfunction

Chronic obstructive pulmonary disease (COPD) involves aberrant airway inflammatory responses to cigarette smoke (CS) that are associated with epithelial cell dysfunction, cilia shortening, and mucociliary clearance disruption. Exposure to CS reduced cilia length and induced autophagy in vivo and in differentiated mouse tracheal epithelial cells (MTECs). Autophagy-impaired (Becn1+/- or Map1lc3B-/-) mice and MTECs resisted CS-induced cilia shortening. Furthermore, CS increased the autophagic turnover of ciliary proteins, indicating that autophagy may regulate cilia homeostasis. We identified cytosolic deacetylase HDAC6 as a critical regulator of autophagy-mediated cilia shortening during CS exposure. Mice bearing an X chromosome deletion of Hdac6 (Hdac6-/Y) and MTECs from these mice had reduced autophagy and were protected from CS-induced cilia shortening. Autophagy-impaired Becn1-/-, Map1lc3B-/-, and Hdac6-/Y mice or mice injected with an HDAC6 inhibitor were protected from CS-induced mucociliary clearance (MCC) disruption. MCC was preserved in mice given the chemical chaperone 4-phenylbutyric acid, but was disrupted in mice lacking the transcription factor NRF2, suggesting that oxidative stress and altered proteostasis contribute to the disruption of MCC. Analysis of human COPD specimens revealed epigenetic deregulation of HDAC6 by hypomethylation and increased protein expression in the airways. We conclude that an autophagy-dependent pathway regulates cilia length during CS exposure and has potential as a therapeutic target for COPD.

Insulin receptor substrate signaling suppresses neonatal autophagy in the heart

The induction of autophagy in the mammalian heart during the perinatal period is an essential adaptation required to survive early neonatal starvation; however, the mechanisms that mediate autophagy suppression once feeding is established are not known. Insulin signaling in the heart is transduced via insulin and IGF-1 receptors (IGF-1Rs). We disrupted insulin and IGF-1R signaling by generating mice with combined cardiomyocyte-specific deletion of Irs1 and Irs2. Here we show that loss of IRS signaling prevented the physiological suppression of autophagy that normally parallels the postnatal increase in circulating insulin. This resulted in unrestrained autophagy in cardiomyocytes, which contributed to myocyte loss, heart failure, and premature death. This process was ameliorated either by activation of mTOR with aa supplementation or by genetic suppression of autophagic activation. Loss of IRS1 and IRS2 signaling also increased apoptosis and precipitated mitochondrial dysfunction, which were not reduced when autophagic flux was normalized. Together, these data indicate that in addition to prosurvival signaling, insulin action in early life mediates the physiological postnatal suppression of autophagy, thereby linking nutrient sensing to postnatal cardiac development.

Bryostatin 5 induces apoptosis in acute monocytic leukemia cells by activating PUMA and caspases

Acute leukemia is a malignant clonal hematopoietic stem cell disease. In the current study, we examined the effects of bryostatin 5 on acute monocytic leukemia cells in vitro and in vivo. We also explored the mechanisms and pathways underlying the increase in apoptosis induced by bryostatin 5. Bryostatin 5 inhibited the growth of primary acute monocytic leukemia cells and U937 cells in a dose- and time-dependent manners. Bryostatin 5 also induced an increase in apoptosis and a decrease in the mitochondrial membrane potential (MMP) in U937 cells. Transmission electron microscopy (TEM) revealed that bryostatin 5-treated cells displayed typical apoptotic characteristics (chromatin condensation, karyopyknosis and formation of crescents and apoptotic bodies). In addition, bryostatin 5 increased the expression of P53 upregulated modulator of apoptosis (PUMA) and slightly increased P53 expression. Bryostatin 5 also significantly decreased Bcl-XL expression and significantly increased the expression levels of Bak, Bax, cleaved caspase 9 and cleaved caspase 3. The pro-apoptotic activity of bryostatin 5 in U937 cells was inhibited by PUMA siRNA and z-LEHD-fmk (a specific caspase 9 inhibitor). In addition, the PUMA siRNA significantly affected the expression of cleaved caspase 9, whereas z-LEHD-fmk had little effect on the expression of PUMA. The results suggest that PUMA is located upstream of caspase 9 in this apoptotic signaling pathway. These novel findings provide mechanistic insight into the induction of apoptosis by bryostatin 5 and might facilitate the development of clinical strategies to enhance the therapeutic efficacy of treatments for acute monocytic leukemia.

Analysis of expression, cellular localization, and function of three inhibitors of apoptosis (IAPs) from Litopenaeus vannamei during WSSV infection and in regulation of antimicrobial peptide genes (AMPs)

Inhibitors of apoptosis (IAPs) play important roles in apoptosis and NF-κB activation. In this study, we cloned and characterized three IAPs (LvIAP1-3) from the Pacific white shrimp, Litopenaeusvannamei. LvIAP1-3 proteins shared signature domains and exhibited significant similarities with other IAP family proteins. The tissue distributions of LvIAP1-3 were studied. The expression of LvIAP1-3 was induced in the muscle after white spot syndrome virus (WSSV) infection. LvIAP1 expression in the gill, hemocytes, hepatopancreas, and intestine was responsive to WSSV and Vibrioalginolyticus infections. LvIAP2 expression in the gill, hemocytes, and hepatopancreas was also responsive to WSSV infection. The expression of LvIAP3 in the gill, hemocytes, and intestine was reduced after V. alginolyticus infection. When overexpressed in Drosophila S2 cells, GFP labeled-LvIAP2 was distributed in the cytoplasm and appeared as speck-like aggregates in the nucleus. Both LvIAP1 and LvIAP3 were widely distributed throughout the cytoplasm and nucleus. The expression of LvIAP1, LvIAP2, and LvIAP3 was significantly knocked down by dsRNA-mediated gene silencing. In the gill of LvIAP1- or LvIAP3-silenced shrimp, the expression of WSSV VP28 was significantly higher than that of the dsGFP control group, suggesting that LvIAP1 and LvIAP3 may play protective roles in host defense against WSSV infection. Intriguingly, the LvIAP2-silenced shrimp all died within 48 hours after dsLvIAP2 injection. In the hemocytes of LvIAP2-silenced shrimps, the expression of antimicrobial peptide genes (AMPs), including Penaeidins, lysozyme, crustins, Vibriopenaeicidae-induced cysteine and proline-rich peptides (VICPs), was significantly downregulated, while the expression of anti-lipopolysaccharide factors (ALFs) was upregulated. Moreover, LvIAP2 activated the promoters of the NF-κB pathway-controlled AMPs, such as shrimp Penaeidins and Drosophila drosomycin and attacin A, in Drosophila S2 cells. Taken together, these results reveal that LvIAP1 and LvIAP3 might participate in the host defense against WSSV infection, and LvIAP2 might be involved in the regulation of shrimp AMPs.

The identification of a novel gene, MAPO2, that is involved in the induction of apoptosis triggered by O⁶-methylguanine

O⁶-Methylguanine, one of alkylated DNA bases, is especially mutagenic. Cells containing this lesion are eliminated by induction of apoptosis, associated with the function of mismatch repair (MMR) proteins. A retrovirus-mediated gene-trap mutagenesis was used to isolate new genes related to the induction of apoptosis, triggered by the treatment with an alkylating agent, N-methyl-N-nitrosourea (MNU). This report describes the identification of a novel gene, MAPO2 (O⁶-methylguanine-induced apoptosis 2), which is originally annotated as C1orf201. The MAPO2 gene is conserved among a wide variety of multicellular organisms and encodes a protein containing characteristic PxPxxY repeats. To elucidate the function of the gene product in the apoptosis pathway, a human cell line derived from HeLa MR cells, in which the MAPO2 gene was stably knocked down by expressing specific miRNA, was constructed. The knockdown cells grew at the same rate as HeLa MR, thus indicating that MAPO2 played no role in the cellular growth. After exposure to MNU, HeLa MR cells and the knockdown cells underwent cell cycle arrest at G₂/M phase, however, the production of the sub-G₁ population in the knockdown cells was significantly suppressed in comparison to that in HeLa MR cells. Moreover, the activation of BAK and caspase-3, and depolarization of mitochondrial membrane, hallmarks for the induction of apoptosis, were also suppressed in the knockdown cells. These results suggest that the MAPO2 gene product might positively contribute to the induction of apoptosis triggered by O⁶-methylguanine.

The microtubule poison vinorelbine kills cells independently of mitotic arrest and targets cells lacking the APC tumour suppressor more effectively

Colorectal cancers commonly carry truncation mutations in the adenomatous polyposis coli (APC) gene. The APC protein contributes to the stabilization of microtubules. Consistently, microtubules in cells lacking APC depolymerize more readily in response to microtubule-destabilizing drugs. This raises the possibility that such agents are suitable for treatment of APC-deficient cancers. However, APC-deficient cells have a compromised spindle assembly checkpoint, which renders them less sensitive to killing by microtubule poisons whose toxicity relies on the induction of prolonged mitotic arrest. Here, we describe the novel discovery that the clinically used microtubule-depolymerizing drug vinorelbine (Navelbine) kills APC-deficient cells in culture and in intestinal tissue more effectively than it kills wild-type cells. This is due to the ability of vinorelbine to kill cells in interphase independently of mitotic arrest. Consistent with a role for p53 in cell death in interphase, depletion of p53 renders cells less sensitive to vinorelbine, but only in the presence of wild-type APC. The pro-apoptotic protein BIM (also known as BCL2L11) is recruited to mitochondria in response to vinorelbine, where it can inhibit the anti-apoptotic protein BCL2, suggesting that BIM mediates vinorelbine-induced cell death. This recruitment of BIM is enhanced in cells lacking APC. Consistently, BIM depletion dampens the selective effect of vinorelbine on these cells. Our findings reveal that vinorelbine is a potential therapeutic agent for colorectal cancer, but they also illustrate the importance of the APC tumour suppressor status when predicting therapeutic efficacy.

Bacille Calmette Guérin (BCG) can induce Kawasaki disease-like features in programmed death-1 (PD-1) gene knockout mice

OBJECTIVES

Various genetic variants of inhibitory immune signals have been suspected as feasible causes of Kawasaki disease (KD). We investigated the associative role of programmed death-1 (PD-1) gene in the pathogenesis of KD by injecting bacilli Calmette Guérin (BCG) to PD-1 gene knockout (PD-1KO) mice.

METHODS

In order to induce KD-like clinical manifestations in young PD-1KO mice, intradermal injection of the bacilli Calmette Guérin (BCG) was performed twice on the abdominal skin with a 4-week interval. For defining the role of BCG, heat shock protein (HSP) 65 was challenged. In addition, Staphylococcus aureus was adopted as a microorganism that does not contain HSP65 structure. One month after the second injection, heart, liver, and kidneys were removed and examined.

RESULTS

PD-1KO mice showed KD-like features including prolonged fever for more than 5 days, erythematous swelling on soles, tail skin desquamation, and gallbladder (GB) hydrops. Inflammatory cell aggregation and intimal proliferation in at least more than one coronary artery was found in all PD-1KO mice whereas scanty coronary lesion was found in wild type (WT) mice. When the PD-1KO mice were injected twice with HSP65, coronary arterial lesions similar to those seen after BCG injection were observed. Inflammatory reactions in other organs including hepatic arteries, renal arteries, and biliary arteries were also observed in PD-1KO mice.

CONCLUSIONS

Our data suggest that PD-1 gene may be one of the genetic predispositions of KD and antigens containing HSP65 structure could be a triggering factor of KD by our animal model of KD.

LAG-3, TGF-β, and cell-intrinsic PD-1 inhibitory pathways contribute to CD8 but not CD4 T-cell tolerance induced by allogeneic BMT with anti-CD40L

Administration of a single dose of anti-CD40L mAb at the time of allogeneic BM transplantation tolerizes peripheral alloreactive T cells and permits establishment of mixed hematopoietic chimerism in mice. Once engrafted, mixed chimeras are systemically tolerant to donor Ags through a central deletion mechanism and will accept any donor organ indefinitely. We previously found that the PD-1/PD-L1 pathway is required for CD8 T-cell tolerance in this model. However, the cell population that must express PD-1 and the role of other inhibitory molecules were unknown. Here, we report that LAG-3 is required for long-term peripheral CD8 but not CD4 T-cell tolerance and that this requirement is CD8 cell-extrinsic. In contrast, adoptive transfer studies revealed a CD8 T cell-intrinsic requirement for CTLA4/B7.1/B7.2 and for PD-1 for CD8 T-cell tolerance induction. We also observed that both PD-L1 and PD-L2 are independently required on donor cells to achieve T-cell tolerance. Finally, we uncovered a requirement for TGF-β signaling into T cells to achieve peripheral CD8 but not CD4 T-cell tolerance in this in vivo system.

BID, BIM, and PUMA are essential for activation of the BAX- and BAK-dependent cell death program

Although the proteins BAX and BAK are required for initiation of apoptosis at the mitochondria, how BAX and BAK are activated remains unsettled. We provide in vivo evidence demonstrating an essential role of the proteins BID, BIM, and PUMA in activating BAX and BAK. Bid, Bim, and Puma triple-knockout mice showed the same developmental defects that are associated with deficiency of Bax and Bak, including persistent interdigital webs and imperforate vaginas. Genetic deletion of Bid, Bim, and Puma prevented the homo-oligomerization of BAX and BAK, and thereby cytochrome c-mediated activation of caspases in response to diverse death signals in neurons and T lymphocytes, despite the presence of other BH3-only molecules. Thus, many forms of apoptosis require direct activation of BAX and BAK at the mitochondria by a member of the BID, BIM, or PUMA family of proteins.

Sepsis-induced apoptosis leads to active suppression of delayed-type hypersensitivity by CD8+ regulatory T cells through a TRAIL-dependent mechanism

Patients who survive severe sepsis often display severely compromised immune function. One hallmark of such immune suppression in septic patients is an impaired delayed-type hypersensitivity (DTH) response, manifested by a loss of skin testing to recall Ags. Because sepsis induces significant apoptosis in lymphoid and myeloid cells, and apoptotic cells are themselves tolerogenic, we tested the hypothesis that suppression of DTH is mediated by tolerogenic properties of the apoptotic cells generated during sepsis. Mice subjected to cecal ligation and puncture demonstrated a loss of DTH for the 7 d following cecal ligation and puncture; however, the immune response returned to normal by day 10. Blocking sepsis-induced apoptosis via Bcl-2 overexpression or Bim deficiency prevented the loss of DTH. Importantly, injection of apoptotic cells into Bim-/- mice prevented an effective DTH response, thereby suggesting a causal link between apoptotic cells and immune suppression. Surprisingly, when TRAIL null mice were examined, we found that these animals had significant apoptosis but retained their DTH responses. Further studies revealed that apoptotic cells generated during sepsis induced a CD8+ regulatory T cell that suppressed DTH by TRAIL production. These results establish a link between apoptotic cells and immune suppression during sepsis and suggest TRAIL may be a viable therapeutic target for boosting the adaptive immune response following sepsis.

p53-Dependent p21-mediated growth arrest pre-empts and protects HCT116 cells from PUMA-mediated apoptosis induced by EGCG

The tumor suppressor protein p53 plays a key role in regulation of negative cellular growth in response to EGCG. To further explore the role of p53 signaling and elucidate the molecular mechanism, we employed colon cancer HCT116 cell line and its derivatives in which a specific transcriptional target of p53 is knocked down by homologous recombination. Cells expressing p53 and p21 accumulate in G1 upon treatment with EGCG. In contrast, same cells lacking p21 traverse through the cell cycle and eventually undergo apoptosis as revealed by TUNEL staining. Treatment with EGCG leads to induction of p53, p21 and PUMA in p21 wild-type, and p53 and PUMA in p21(-/-) cells. Ablation of p53 by RNAi protects p21(-/-) cells, thus indicating a p53-dependent apoptosis by EGCG. Furthermore, analysis of cells lacking PUMA or Bax with or without p21 but with p53 reveals that all the cells expressing p53 and p21 survived after EGCG treatment. More interestingly, cells lacking both PUMA and p21 survived ECGC treatment whereas those lacking p21 and Bax did not. Taken together, our results present a novel concept wherein p21-dependent growth arrest pre-empts and protects cells from otherwise, in its absence, apoptosis which is mediated by activation of pro-apoptotic protein PUMA. Furthermore, we find that p53-dependent activation of PUMA in response to EGCG directly leads to apoptosis with out requiring Bax as is the case in response to agents that induce DNA damage. p21, thus can be used as a molecular switch for therapeutic intervention of colon cancer.

Pdx1 and other factors that regulate pancreatic beta-cell survival

A progressive reduction in beta-cell mass occurs in the evolution of diabetes. Thus understanding the mechanisms responsible for this reduction in beta-cell mass is important for understanding the pathogenesis of diabetes and in developing novel approaches to prevention and treatment. Pancreatic duodenal homeobox 1 (Pdx1) is a transcription factor that plays a central role in pancreatic beta-cell function and survival. Complete deficiency of Pdx1 is associated with pancreatic agenesis, and partial deficiency leads to severe beta-cell dysfunction, and increases beta-cell death and diabetes both in rodent and human. Chronic hyperglycaemia and dyslipidaemia, which are major features of type 2 diabetes, cause beta-cell dysfunction via reduced Pdx1 expression. Inhibition of insulin/insulin-like growth factor (Igf) signalling followed by reduced Pdx1 expression is a common pathway induced by the majority of the mechanisms in apoptotic beta-cells. Although the report so far paid little attention to non-apoptotic beta-cell death (autophagy and necrosis), we expect these are also involved in the pathogenesis of diabetes. The potential role of Pdx1 in non-apoptotic beta-cell death should also be considered in future studies in diabetes, and in attempts to develop novel agents that target this process for prevention and treatment of the disorder.

PD-1 regulates self-reactive CD8+ T cell responses to antigen in lymph nodes and tissues

PD-1, an inhibitory receptor expressed on activated lymphocytes, regulates tolerance and autoimmunity. We tested the role of PD-1:PD-1 ligand (PD-L) interactions in cross-presentation and the generation and control of CD8(+) responses against self-Ag. Ag-naive PD-1(-/-) OVA-specific OT-I CD8(+) T cells exhibited exacerbated responses to cross-presented Ag in mice expressing soluble OVA under the control of the rat insulin promoter (RIP-ova(high)). Following adoptive transfer into RIP-ova(high) recipients, PD-1(-/-) OT-I T cells expanded in the pancreatic lymph node. In contrast to wild-type OT-I cells, PD-1(-/-) OT-I T cells secreted IFN-gamma and migrated into the pancreas, ultimately causing diabetes. Loss of PD-1 affected CD8(+) cells intrinsically, and did not significantly alter the responses of wild-type OT-I T cells adoptively transferred into the same RIP-ova(high) recipient mouse. PD-1:PD-L interactions also limited CD8(+) effector cells, and PD-L1 expression on parenchymal tissues protected against effector OT-I T cell attack. Finally, we found that the loss of PD-1 on effector OT-I cells lowers the threshold for Ag recognition in peripheral tissues. These findings indicate two checkpoints where PD-1 attenuates self-reactive T cell responses: presentation of self-Ag to naive self-reactive T cells by dendritic cells in the draining lymph node and reactivation of pathogenic self-reactive T cells in the target organ.

Bim regulates BCR-induced entry of B cells into the cell cycle

BH3-only Bcl-2 homologs are key regulators of the intrinsic apoptotic pathway. In particular, Bim, is critical for mediating apoptosis of hematopoietic cells including B cells. While studies using Bcl-2 Tg mice have defined an important role for Bcl-2 in cell cycle control, the role of BH3-only proteins is less clear. Using Bim KO mice, we show that Bim is required for B cells to enter the cell cycle normally. Bim KO B cells had reduced cell division compared to WT B cells in response to BCR, TLR3 or TLR4 signaling, whereas Bim deficiency did not affect TLR9-induced B cell division. Cell cycle progression in BCR- and LPS-stimulated Bim KO B cells was blocked at the G0-G1 stage. BCR-induced p130 degradation and pRb hyperphosphorylation on Ser807/811, which are critical for G1 entry, were reduced in Bim KO compared to WT B cells. Likewise, BCR-induced p27(Kip1) degradation was decreased in Bim KO compared to WT B cells. These defects in BCR-induced cell cycle entry correlated with a proximal defect in BCR-mediated intracellular calcium release in Bim KO B cells. Our results suggest that the balance of pro- and anti-apoptotic Bcl-2 family proteins is critical for controlling both cell cycle progression and apoptosis in B cells.

Bim expression indicates the pathway to retinal cell death in development and degeneration

Programmed cell death (PCD) during development of the mouse retina involves activation of the mitochondrial pathway. Previous work has shown that the multidomain Bcl-2 family proteins Bax and Bak are fundamentally involved in this process. To induce mitochondrial membrane permeabilization, Bax and Bak require that prosurvival members of the family be inactivated by binding of "BH3-only" members. We showed previously that the BH3-only protein BimEL is highly expressed during postnatal retinal development but decreases dramatically thereafter. The purpose of this study was to investigate a possible role for Bim, in retinal development and degeneration, upstream of Bax and Bak. Bim-/- mice analyzed for defective retinal development exhibit an increase in retinal thickness and a delay in PCD, thereby confirming a role for Bim. We also demonstrate that in response to certain death stimuli, bim+/+ retinal explants upregulate BimEL leading to caspase activation and cell death, whereas bim-/- explants are resistant to apoptosis. Finally, we analyzed Bim expression in the retinal degeneration (rd) mouse, an in vivo model of retinal degeneration. Bim isoforms, which decrease during development, are not reexpressed during retinal degeneration and ultimately photoreceptor cells die by a caspase-independent mechanism. Thus, we conclude that in cases in which BimEL is reexpressed during pathological cell death, developmental cell death pathways are reactivated. However, the absence of BimEL expression correlates with caspase-independent death in the rd model.

Bim and Bcl-2 mutually affect the expression of the other in T cells

The life and death of T cells is controlled to a large extent by the relative amounts of Bcl-2-related proteins they contain. The antiapoptotic protein Bcl-2 and the proapoptotic protein Bim are particularly important in this process with the amount of Bcl-2 per cell dropping by about one-half when T cells prepare to die. In this study we show that Bcl-2 and Bim each control the expression of the other. Absence of Bim leads to a drop in the amount of intracellular Bcl-2 protein, while having no effect on the amounts of mRNA for Bcl-2. Conversely, high amounts of Bcl-2 per cell allow high amounts of Bim, although in this case the effect involves increases in Bim mRNA. These mutual effects occur even if Bcl-2 is induced acutely. Thus these two proteins control the expression of the other, at either the protein or mRNA level.

Cideb regulates diet-induced obesity, liver steatosis, and insulin sensitivity by controlling lipogenesis and fatty acid oxidation

OBJECTIVE

Our previous study suggests that Cidea, a member of Cide family proteins that share sequence homology with the DNA fragmentation factor and are expressed at high levels in brown adipose tissue, plays an important role in the development of obesity. Cideb, another member of Cide family protein, is highly expressed in the liver. We would like to understand the physiological role of Cideb in the regulation of energy expenditure and lipid metabolism.

RESEARCH DESIGN AND METHODS

We generated Cideb-null mice by homolog recombination and then fed both wild-type and Cideb-null mice with high-fat diet (58% fat). We then characterized the animals' adiposity index, food intake, whole-body metabolic rate, liver morphology, rate of fatty acid synthesis and oxidation, insulin sensitivity, and gene expression profile.

RESULTS

Cideb-null mice had lower levels of plasma triglycerides and free fatty acids and were resistant to high-fat diet-induced obesity and live steatosis. In addition, Cideb mutant mice displayed significantly increased insulin sensitivity and enhanced rate of whole-body metabolism and hepatic fatty acid oxidation. More importantly, Cideb-null mice showed decreased lipogenesis and reduced expression levels of acetyl-CoA carboxylase, fatty acid synthase, and stearol-CoA desaturase. We further demonstrated that expression levels of sterol response element binding protein 1c was significantly decreased in Cideb-deficient mice.

CONCLUSIONS

Our data demonstrate that Cideb is a novel important regulator in lipid metabolism in the liver. Cideb may represent a new therapeutic target for the treatment of obesity, diabetes, and liver steatosis.

Programmed cell death 1 (PD-1) and its ligand PD-L1 are required for allograft tolerance

Programmed cell death-1 (PD-1, CD279) and its widely expressed, inducible ligand, PD-L1 (CD274), together dampen T cell activation, but whether they are essential for allograft tolerance is unknown. We show, using gene-deficient mice and blocking mAbs in wild-type mice, that costimulation blockade is ineffectual in PD-1(-/-) or PD-L1(-/-) allograft recipients, or in wild-type allograft recipients treated with anti-PD-1 or anti-PD-L1 mAb. Alloreactive PD-1(-/-) CD4 and CD8 T cells had enhanced proliferation and cytokine production compared to wild-type controls, and anergy could not be induced in PD-1-deficient CD4 T cells. We conclude that without inhibitory signals from PD-1 ligation, alloantigen-induced T cell proliferation and expansion cannot be regulated by costimulation blockade, and peripheral tolerance induction cannot occur.

A natural hypomorphic variant of the apoptosis regulator Gimap4/IAN1

The Gimap/IAN family of GTPases has been implicated in the regulation of cell survival, particularly in lymphomyeloid cells. Prosurvival and prodeath properties have been described for different family members. We generated novel serological reagents to study the expression in rats of the prodeath family member Gimap4 (IAN1), which is sharply up-regulated at or soon after the stage of T cell-positive selection in the thymus. During these investigations we were surprised to discover a severe deficiency of Gimap4 expression in the inbred Brown Norway (BN) rat. Genetic analysis linked this trait to the Gimap gene cluster on rat chromosome 4, the probable cause being an AT dinucleotide insertion in the BN Gimap4 allele (AT(+)). This allele encodes a truncated form of Gimap4 that is missing 21 carboxyl-terminal residues relative to wild type. The low protein expression associated with this allele appears to have a posttranscriptional cause, because mRNA expression was apparently normal. Spontaneous and induced apoptosis of BN and wild-type T cells was analyzed in vitro and compared with the recently described mouse Gimap4 knockout. This revealed a "delayed" apoptosis phenotype similar to but less marked than that of the knockout. The Gimap4 AT(+) allele found in BN was shown to be rare in inbred rat strains. Nevertheless, when wild rat DNA samples were studied the AT(+) allele was found at a high overall frequency ( approximately 30%). This suggests an adaptive significance for this hypomorphic allele.

Inositol 1,3,4,5-tetrakisphosphate controls proapoptotic Bim gene expression and survival in B cells

The contribution of the B isoform of inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] 3-kinase (or Itpkb) and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P(4)], its reaction product, to B cell function and development remains unknown. Here, we show that mice deficient in Itpkb have defects in B cell survival leading to specific and intrinsic developmental alterations in the B cell lineage and antigen unresponsiveness in vivo. The decreased B cell survival is associated with a decreased phosphorylation of Erk1/2 and increased Bim gene expression. B cell survival, development, and antigen responsiveness are normalized in parallel to reduced expression of Bim in Itpkb(-/-) Bim(+/-) mice. Analysis of the signaling pathway downstream of Itpkb revealed that Ins(1,3,4,5)P(4) regulates subcellular distribution of Rasa3, a Ras GTPase-activating protein acting as an Ins(1,3,4,5)P(4) receptor. Together, our results indicate that Itpkb and Ins(1,3,4,5)P(4) mediate a survival signal in B cells via a Rasa3-Erk signaling pathway controlling proapoptotic Bim gene expression.

Kruppel-like factor 5 modulates p53-independent apoptosis through Pim1 survival kinase in cancer cells

Although Kruppel-like factor 5 (KLF5) is a transcription factor that has been implicated in pathways critical to carcinogenesis, controversy persists as to whether it functions as a tumor suppressor or as an oncogene. Here, we describe a novel role for KLF5 in a p53-independent apoptotic pathway. Using RNA-interference technology, we show that cells deficient in KLF5 have increased sensitivity to DNA damage, regardless of p53 status. Both p53 and p53-dependent factors are unaffected by KLF5 depletion. Instead, the apoptotic phenotype consequent to damage is associated with reduced bad phosphorylation, and downregulation of Pim1. Consistently, transfection of wild-type Pim1 is sufficient to rescue this phenotype. Previous data have shown a number of putative Sp1-binding consensus sequences on the Pim1 promoter. Remarkably, chromatin immunoprecipitation studies show that KLF5 binds to the Pim1 promoter, and that binding increases soon after damage. These results identify a novel, p53-independent apoptotic pathway through which KLF5 functions in response to DNA damage. Therapeutic deregulation of this pathway could be used to modulate chemosensitivity.

Bim/Bcl-2 balance is critical for maintaining naive and memory T cell homeostasis

We examined the role of the antiapoptotic molecule Bcl-2 in combating the proapoptotic molecule Bim in control of naive and memory T cell homeostasis using Bcl-2^−/− mice that were additionally deficient in one or both alleles of Bim. Naive T cells were significantly decreased in Bim^+/−Bcl-2^−/− mice, but were largely restored in Bim^−/−Bcl-2^−/− mice. Similarly, a synthetic Bcl-2 inhibitor killed wild-type, but not Bim^−/−, T cells. Further, T cells from Bim^+/−Bcl-2^−/− mice died rapidly ex vivo and were refractory to cytokine-driven survival in vitro. In vivo, naive CD8⁺ T cells required Bcl-2 to combat Bim to maintain peripheral survival, whereas naive CD4⁺ T cells did not. In contrast, Bim^+/−Bcl-2^−/− mice generated relatively normal numbers of memory T cells after lymphocytic choriomeningitis virus infection. Accumulation of memory T cells in Bim^+/−Bcl-2^−/− mice was likely caused by their increased proliferative renewal because of the lymphopenic environment of the mice. Collectively, these data demonstrate a critical role for a balance between Bim and Bcl-2 in controlling homeostasis of naive and memory T cells.