Rong Guo

The Caenorhabditis elegans hif-1 gene encodes a bHLH-PAS protein that is required for adaptation to hypoxia

Hypoxia-inducible factor, a heterodimeric transcription complex, regulates cellular and systemic responses to low oxygen levels (hypoxia) during normal mammalian development or tumor progression. Here, we present evidence that a similar complex mediates response to hypoxia in Caenorhabditis elegans. This complex consists of HIF-1 and AHA-1, which are encoded by C. elegans homologs of the hypoxia-inducible factor (HIF) α and β subunits, respectively. hif-1 mutants exhibit no severe defects under standard laboratory conditions, but they are unable to adapt to hypoxia. Although wild-type animals can survive and reproduce in 1% oxygen, the majority of hif-1-defective animals die in these conditions. We show that the expression of an HIF-1:green fluorescent protein fusion protein is induced by hypoxia and is subsequently reduced upon reoxygenation. Both hif-1 and aha-1 are expressed in most cell types, and the gene products can be coimmunoprecipitated. We conclude that the mechanisms of hypoxia signaling are likely conserved among metazoans. Additionally, we find that nuclear localization of AHA-1 is disrupted in an hif-1 mutant. This finding suggests that heterodimerization may be a prerequisite for efficient nuclear translocation of AHA-1.

Generation of transgenic maize with enhanced provitamin A content.

Vitamin A deficiency (VAD) affects over 250 million people worldwide and is one of the most prevalent nutritional deficiencies in developing countries, resulting in significant socio-economic losses. Provitamin A carotenoids such as β-carotene, are derived from plant foods and are a major source of vitamin A for the majority of the worlds population. Several years of intense research has resulted in the production of ‘Golden Rice 2’ which contains sufficiently high levels of provitamin A carotenoids to combat VAD. In this report, the focus is on the generation of transgenic maize with enhanced provitamin A content in their kernels. Overexpression of the bacterial genes crtB (for phytoene synthase) and crtI (for the four desaturation steps of the carotenoid pathway catalysed by phytoene desaturase and ζ-carotene desaturase in plants), under the control of a ‘super γ-zein promoter’ for endosperm-specific expression, resulted in an increase of total carotenoids of up to 34-fold with a preferential accumulation of β-carotene in the maize endosperm. The levels attained approach those estimated to have a significant impact on the nutritional status of target populations in developing countries. The high β-carotene trait was found to be reproducible over at least four generations. Gene expression analyses suggest that increased accumulation of β-carotene is due to an up-regulation of the endogenous lycopene β-cylase. These experiments set the stage for the design of transgenic approaches to generate provitamin A-rich maize that will help alleviate VAD.

Spatial Analysis of Arabidopsis thaliana Gene Expression in Response to Turnip mosaic virus Infection

Virus-infected leaf tissues comprise a heterogeneous mixture of cells at different stages of infection. The spatial and temporal relationships between sites of virus accumulation and the accompanying host responses, such as altered host gene expression, are not well defined. To address this issue, we utilized Turnip mosaic virus (TuMV) tagged with the green fluorescent protein to guide the dissection of infection foci into four distinct zones. The abundance of Arabidopsis thaliana mRNA transcripts in each of the four zones then was assayed using the Arabidopsis ATH1 GeneChip oligonucleotide microarray (Affymetrix). mRNA transcripts with significantly altered expression profiles were determined across gradients of virus accumulation spanning groups of cells in and around foci at different stages of infection. The extent to which TuMV-responsive genes were up- or downregulated primarily correlated with the amount of virus accumulation regardless of gene function. The spatial analysis also allowed new suites of coordinately regulated genes to be identified that are associated with chloroplast functions (decreased), sulfate assimilation (decreased), cell wall extensibility (decreased), and protein synthesis and turnover (induced). The functions of these downregulated genes are consistent with viral symptoms, such as chlorosis and stunted growth, providing new insight into mechanisms of pathogenesis.

Nonconvulsive seizures are common in critically ill children

Background: Retrospective studies have reported the occurrence of nonconvulsive seizures in critically ill children. We aimed to prospectively determine the incidence and risk factors of nonconvulsive seizures in critically ill children using predetermined EEG monitoring indications and EEG interpretation terminology. Methods: Critically ill children (non-neonates) with acute encephalopathy underwent continuous EEG monitoring if they met institutional clinical practice criteria. Study enrollment and data collection were prospective. Logistic regression analysis was utilized to identify risk factors for seizure occurrence. Results: One hundred children were evaluated. Electrographic seizures occurred in 46 and electrographic status epilepticus occurred in 19. Seizures were exclusively nonconvulsive in 32. The only clinical risk factor for seizure occurrence was younger age (p = 0.03). Of patients with seizures, only 52% had seizures detected in the first hour of monitoring, while 87% were detected within 24 hours. Conclusions: Seizures were common in critically ill children with acute encephalopathy. Most were nonconvulsive. Clinical features had little predictive value for seizure occurrence. Further study is needed to confirm these data in independent high-risk populations, to clarify which children are at highest risk for seizures so limited monitoring resources can be allocated optimally, and to determine whether seizure detection and management improves outcome.

ODC1 Is a Critical Determinant of MYCN Oncogenesis and a Therapeutic Target in Neuroblastoma

Neuroblastoma is a frequently lethal childhood tumor in which MYC gene deregulation, commonly as MYCN amplification, portends poor outcome. Identifying the requisite biopathways downstream of MYC may provide therapeutic opportunities. We used transcriptome analyses to show that MYCN-amplified neuroblastomas have coordinately deregulated myriad polyamine enzymes (including ODC1, SRM, SMS, AMD1, OAZ2, and SMOX) to enhance polyamine biosynthesis. High-risk tumors without MYCN amplification also overexpress ODC1, the rate-limiting enzyme in polyamine biosynthesis, when compared with lower-risk tumors, suggesting that this pathway may be pivotal. Indeed, elevated ODC1 (independent of MYCN amplification) was associated with reduced survival in a large independent neuroblastoma cohort. As polyamines are essential for cell survival and linked to cancer progression, we studied polyamine antagonism to test for metabolic dependence on this pathway in neuroblastoma. The Odc inhibitor alpha-difluoromethylornithine (DFMO) inhibited neuroblast proliferation in vitro and suppressed oncogenesis in vivo. DFMO treatment of neuroblastoma-prone genetically engineered mice (TH-MYCN) extended tumor latency and survival in homozygous mice and prevented oncogenesis in hemizygous mice. In the latter, transient Odc ablation permanently prevented tumor onset consistent with a time-limited window for embryonal tumor initiation. Importantly, we show that DFMO augments antitumor efficacy of conventional cytotoxics in vivo. This work implicates polyamine biosynthesis as an arbiter of MYCN oncogenesis and shows initial efficacy for polyamine depletion strategies in neuroblastoma, a strategy that may have utility for this and other MYC-driven embryonal tumors.

Hepatic pathology may develop before the Fontan operation in children with functional single ventricle: An autopsy study

OBJECTIVE Liver fibrosis has emerged as an important long-term complication of the Fontan operation. We aimed to describe liver histology at autopsy in patients who had undergone the Fontan operation and to determine whether patient variables are associated with the degree of fibrosis. METHODS A review was performed of all patients with a history of the Fontan operation who died and underwent autopsy at our institution from 1980 to 2009. Autopsy liver slides were evaluated independently by 2 pathologists. RESULTS Twenty-two patients were studied. The median interval between Fontan and death was 20 days (range, 1 day-17.5 years). Portal fibrosis was observed in 20 (91%) patients and sinusoidal fibrosis was observed in 17 (77%) patients. Using simple linear regression, time from the Fontan operation was significantly associated with the degree of portal fibrosis on Ishak (P = .03) and modified Scheuer fibrosis (P = .02) scales. Significant portal fibrosis was observed in 8 (57%) of the 14 patients who died 30 days or less after the Fontan operation. In these 14 patients, severity of portal fibrosis was associated with length of hospitalization after pre-Fontan cardiac operations (P = .03) and pre-Fontan mean right atrial pressure (P = .04). CONCLUSIONS At autopsy, hepatic fibrosis was commonly observed in patients who had undergone the Fontan operation. Portal fibrosis has been previously unrecognized in this population. Significant portal fibrosis occurred in most who died soon after the Fontan procedure and was associated with pre-Fontan morbidity. Hepatic disease in the single-ventricle population is multifactorial and may begin before the Fontan operation.

Impact of a household environmental intervention delivered by lay health workers on asthma symptom control in urban, disadvantaged children with asthma.

OBJECTIVES We examined whether a home-based educational and environmental intervention delivered by lay health educators would improve asthma symptom control in inner-city children with asthma. METHODS Children 2 to 16 years of age with diagnosed asthma and at least 1 asthma-related hospitalization or 2 emergency visits in the prior year were randomly assigned into 2 groups (immediate and delayed intervention) in a crossover study. Each group participated in the active phase (intervention) and the inactive phase. Outcomes included asthma symptoms, albuterol use, emergency department visits, hospitalizations, and trigger reduction. RESULTS A total of 264 primarily Black (94%) children were enrolled. The mean number of emergency visits decreased by 30% and inpatient visits decreased by 53% (P < .001) after the intervention. Reductions were seen in pests, presence of carpets in bedrooms, and dust. Nighttime wheezing was significantly reduced after the intervention in both groups (P < .001). CONCLUSIONS Lay health educators effectively reduced asthma triggers and increased caregiver asthma knowledge, which resulted in reduced emergency department visits, hospitalizations, and asthma symptoms. The relationships formed between the caregivers and the lay health educators appeared to positively impact asthma outcomes in this disadvantaged population.

Interobserver reproducibility of electroencephalogram interpretation in critically ill children.

Correct outcome prediction after cardiac arrest in children may improve clinical decision making and family counseling. Investigators have used EEG to predict outcome with varying success, but a limiting issue is the potential lack of reproducibility of EEG interpretation. Therefore, the authors aimed to evaluate interobserver agreement using standardized terminology in the interpretation of EEG tracings obtained from critically ill children after cardiac arrest. Three pediatric neurophysiologists scored 74 EEG samples using standardized categories, terminology, and interpretation rules. Interobserver agreement was evaluated using kappa and intraclass correlation coefficients. Agreement was substantial for the categories of continuity, burst suppression, sleep architecture, and overall rating. Agreement was moderate for seizure occurrence and interictal epileptiform discharge type. Agreement was fair for interictal epileptiform discharge presence, beta activity, predominant frequency, and fastest frequency. Agreement was slight for maximum voltage and focal slowing presence. The variability of interrater agreement suggests that some EEG features are superior to others for use in a predictive algorithm. Using only reproducible EEG features is needed to ensure the most accurate and consistent predictions. Because even seizure identification had only moderate agreement, studies of nonconvulsive seizures in critically ill patients must be conducted and interpreted cautiously.

Antibody targeting of anaplastic lymphoma kinase induces cytotoxicity of human neuroblastoma

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase aberrantly expressed in neuroblastoma, a devastating pediatric cancer of the sympathetic nervous system. Germline and somatically acquired ALK aberrations induce increased autophosphorylation, constitutive ALK activation and increased downstream signaling. Thus, ALK is a tractable therapeutic target in neuroblastoma, likely to be susceptible to both small-molecule tyrosine kinase inhibitors and therapeutic antibodies—as has been shown for other receptor tyrosine kinases in malignancies such as breast and lung cancer. Small-molecule inhibitors of ALK are currently being studied in the clinic, but common ALK mutations in neuroblastoma appear to show de novo insensitivity, arguing that complementary therapeutic approaches must be developed. We therefore hypothesized that antibody targeting of ALK may be a relevant strategy for the majority of neuroblastoma patients likely to have ALK-positive tumors. We show here that an antagonistic ALK antibody inhibits cell growth and induces in vitro antibody-dependent cellular cytotoxicity of human neuroblastoma-derived cell lines. Cytotoxicity was induced in cell lines harboring either wild type or mutated forms of ALK. Treatment of neuroblastoma cells with the dual Met/ALK inhibitor crizotinib sensitized cells to antibody-induced growth inhibition by promoting cell surface accumulation of ALK and thus increasing the accessibility of antigen for antibody binding. These data support the concept of ALK-targeted immunotherapy as a highly promising therapeutic strategy for neuroblastomas with mutated or wild-type ALK.

Mitochondrial Bcl-2 family dynamics define therapy response and resistance in neuroblastoma

Neuroblastoma is a childhood tumor in which transient therapeutic responses are typically followed by recurrence with lethal chemoresistant disease. In this study, we characterized the apoptotic responses in diverse neuroblastomas using an unbiased mitochondrial functional assay. We defined the apoptotic set point of neuroblastomas using responses to distinct BH3 death domains providing a BH3 response profile and directly confirmed survival dependencies. We found that viable neuroblastoma cells and primary tumors are primed for death with tonic sequestration of Bim, a direct activator of apoptosis, by either Bcl-2 or Mcl-1, providing a survival dependency that predicts the activity of Bcl-2 antagonists. The Bcl-2/Bcl-xL/Bcl-w inhibitor ABT-737 showed single-agent activity against only Bim:Bcl-2 primed tumor xenografts. Durable complete regressions were achieved in combination with noncurative chemotherapy even for highest risk molecular subtypes with MYCN amplification and activating ALK mutations. Furthermore, the use of unique isogenic cell lines from patients at diagnosis and at the time of relapse showed that therapy resistance was not mediated by upregulation of Bcl-2 homologues or loss of Bim priming, but by repressed Bak/Bax activation. Together, our findings provide a classification system that identifies tumors with clinical responses to Bcl-2 antagonists, defines Mcl-1 as the principal mediator of Bcl-2 antagonist resistance at diagnosis, and isolates the therapy resistant phenotype to the mitochondria.