Functional annotation of the 2q35 breast cancer risk locus implicates a structural variant in influencing activity of a long-range enhancer element.

A combination of genetic and functional approaches has identified three independent breast cancer risk loci at 2q35. A recent fine-scale mapping analysis to refine these associations resulted in 1 (signal 1), 5 (signal 2), and 42 (signal 3) credible causal variants at these loci. We used publicly available in silico DNase I and ChIP-seq data with in vitro reporter gene and CRISPR assays to annotate signals 2 and 3. We identified putative regulatory elements that enhanced cell-type-specific transcription from the IGFBP5 promoter at both signals (30- to 40-fold increased expression by the putative regulatory element at signal 2, 2- to 3-fold by the putative regulatory element at signal 3). We further identified one of the five credible causal variants at signal 2, a 1.4 kb deletion (esv3594306), as the likely causal variant; the deletion allele of this variant was associated with an average additional increase in IGFBP5 expression of 1.3-fold (MCF-7) and 2.2-fold (T-47D). We propose a model in which the deletion allele of esv3594306 juxtaposes two transcription factor binding regions (annotated by estrogen receptor alpha ChIP-seq peaks) to generate a single extended regulatory element. This regulatory element increases cell-type-specific expression of the tumor suppressor gene IGFBP5 and, thereby, reduces risk of estrogen receptor-positive breast cancer (odds ratio = 0.77, 95% CI 0.74-0.81, p = 3.1 × 10-31).

Functional annotation of breast cancer risk loci: current progress and future directions.

Genome-wide association studies coupled with large-scale replication and fine-scale mapping studies have identified more than 150 genomic regions that are associated with breast cancer risk. Here, we review efforts to translate these findings into a greater understanding of disease mechanism. Our review comes in the context of a recently published fine-scale mapping analysis of these regions, which reported 352 independent signals and a total of 13,367 credible causal variants. The vast majority of credible causal variants map to noncoding DNA, implicating regulation of gene expression as the mechanism by which functional variants influence risk. Accordingly, we review methods for defining candidate-regulatory sequences, methods for identifying putative target genes and methods for linking candidate-regulatory sequences to putative target genes. We provide a summary of available data resources and identify gaps in these resources. We conclude that while much work has been done, there is still much to do. There are, however, grounds for optimism; combining statistical data from fine-scale mapping with functional data that are more representative of the normal "at risk" breast, generated using new technologies, should lead to a greater understanding of the mechanisms that influence an individual woman's risk of breast cancer.

Activity of Selumetinib in Neurofibromatosis Type 1-Related Plexiform Neurofibromas.

BACKGROUND: Effective medical therapies are lacking for the treatment of neurofibromatosis type 1-related plexiform neurofibromas, which are characterized by elevated RAS-mitogen-activated protein kinase (MAPK) signaling. METHODS: We conducted a phase 1 trial of selumetinib (AZD6244 or ARRY-142886), an oral selective inhibitor of MAPK kinase (MEK) 1 and 2, in children who had neurofibromatosis type 1 and inoperable plexiform neurofibromas to determine the maximum tolerated dose and to evaluate plasma pharmacokinetics. Selumetinib was administered twice daily at a dose of 20 to 30 mg per square meter of body-surface area on a continuous dosing schedule (in 28-day cycles). We also tested selumetinib using a mouse model of neurofibromatosis type 1-related neurofibroma. Response to treatment (i.e., an increase or decrease from baseline in the volume of plexiform neurofibromas) was monitored by using volumetric magnetic resonance imaging analysis to measure the change in size of the plexiform neurofibroma. RESULTS: A total of 24 children (median age, 10.9 years; range, 3.0 to 18.5) with a median tumor volume of 1205 ml (range, 29 to 8744) received selumetinib. Patients were able to receive selumetinib on a long-term basis; the median number of cycles was 30 (range, 6 to 56). The maximum tolerated dose was 25 mg per square meter (approximately 60% of the recommended adult dose). The most common toxic effects associated with selumetinib included acneiform rash, gastrointestinal effects, and asymptomatic creatine kinase elevation. The results of pharmacokinetic evaluations of selumetinib among the children in this trial were similar to those published for adults. Treatment with selumetinib resulted in confirmed partial responses (tumor volume decreases from baseline of ≥20%) in 17 of the 24 children (71%) and decreases from baseline in neurofibroma volume in 12 of 18 mice (67%). Disease progression (tumor volume increase from baseline of ≥20%) has not been observed to date. Anecdotal evidence of decreases in tumor-related pain, disfigurement, and functional impairment was observed. CONCLUSIONS: Our early-phase data suggested that children with neurofibromatosis type 1 and inoperable plexiform neurofibromas benefited from long-term dose-adjusted treatment with selumetinib without having excess toxic effects. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT01362803 .).

An evaluation of National Health Service England's Care Maker Programme: A mixed-methods analysis.

AIMS AND OBJECTIVES: To investigate the impact and sustainability of the Care Maker programme across England from the perspective of those involved in its delivery. BACKGROUND: The Care Maker programme was launched in England in 2013. It aims to support the "Compassion in Practice" strategy, with particular emphasis on the 6Cs of care, compassion, competence, communication, courage and commitment. Care Makers were recruited in an ambassadorial role. The intention was to inspire individuals throughout the National Health Service in England to bridge national policy with those delivering care. DESIGN: A mixed methods design was chosen, but this article focuses on two of the four distinct empirical data collection phases undertaken as part of this evaluation: a questionnaire with Care Makers; and two case studies of separate National Health Service trust sites. METHOD: Data were collected for this evaluation in 2015. An online questionnaire was distributed to the total population of Care Makers across the National Health Service in England. It included a combination of open and closed questions. The case studies involved semistructured telephone interviews with a range of professionals engaged with the Care Maker programme across the trust sites. RESULTS: Care Makers reported that participation in the programme had offered opportunities in terms of improving the quality-of-care provision in the workplace as well as contributing towards their own professional development. CONCLUSION: The Care Maker programme has supported and helped underpin the nursing, midwifery and care strategy "Compassion in Practice". RELEVANCE TO CLINICAL PRACTICE: This model of using volunteers to embed strategy and policy could potentially be used in other areas of clinical practice and indeed in other countries.

Acceptance and commitment therapy in youth with neurofibromatosis type 1 (NF1) and chronic pain and their parents: A pilot study of feasibility and preliminary efficacy.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder affecting about 1 in 3,500 individuals. Chronic pain is commonly reported among individuals with NF1 and plexiform neurofibroma tumors (PNs). Acceptance and Commitment Therapy (ACT), an empirically supported method for addressing chronic pain, helps individuals re-focus on valued relationships and activities. This pilot study investigated the feasibility and preliminary efficacy of a brief ACT workshop in the NF1 population. Eligible participants included adolescents and young adults (AYA; 12-21 years) with NF1 and chronic pain that interfered with daily functioning and their parents. Patients and parents completed baseline measures of pain interference, pain intensity, functional disability, pain acceptance, depression, and anxiety. Then, AYA and parents participated separately in a 2-day small-group ACT workshop. A telephone booster session occurred 1 month post-intervention. Three-month post-treatment measures were completed by mail. Ten adolescents (4 males; M age = 16.9 years) and seven parents provided baseline and 3-month data. Mean satisfaction with the study was moderate to high (3.9 for patients and 4.6 for parents on a 1-5 scales). Patients and parents reported significant declines in patients' pain interference at 3 months post-treatment. Patient-reported pain intensity significantly declined from baseline to 3 months. Parents reported marginally greater acceptance of their child's pain. No changes emerged in functional ability or mood. Preliminary findings suggest that a brief ACT group intervention is feasible and may help AYA with NF1 and PNs cope with their chronic pain, although larger randomized studies are needed to confirm treatment efficacy. © 2016 Wiley Periodicals, Inc.

Pain interference in youth with neurofibromatosis type 1 and plexiform neurofibromas and relation to disease severity, social-emotional functioning, and quality of life.

The physical manifestations of neurofibromatosis type 1 (NF1) can cause chronic pain. This study investigated the impact of pain in youth with NF1 and plexiform neurofibromas (PNs) and its relationship to disease factors, social-emotional functioning, and quality of life (QOL) within a biopsychosocial framework. Caregivers of 59 children and adolescents with NF1 and PNs (6-18 years), and 41 of these youth (10-18 years), completed questionnaires assessing social-emotional functioning and QOL, including an item on pain interference. Measures of disease severity included total PN volume by percent body weight and number of disease complications. Both caregiver (73%) and self-report (59%) ratings indicated that pain interferes with the child's daily functioning despite 33% taking pain medication. Based on caregivers' behavior ratings, more symptoms of anxiety and larger tumor volumes predicted greater pain interference, while greater pain interference, worse depressive symptoms, and more disease complications predicted poorer QOL. As rated by adolescents, more symptoms of anxiety predicted greater pain interference, while greater pain interference and social stress predicted poorer QOL. Further, social-emotional problems mediate the relationship between pain interference and QOL. Thus, pain interferes with daily functioning in the majority of youth with NF1 and PNs even when using pain medication. The impact of pain interference, disease severity, and particularly social-emotional problems on QOL highlights the interaction between physical and psychological states in NF1. Future research and treatment of pain in this population should utilize a biopsychosocial approach and involve multidisciplinary therapies including psychological interventions that target social-emotional functioning.

Attitudes about internet support groups among adolescents and young adults with neurofibromatosis type 1 and their parents.

Youth with neurofibromatosis type 1 (NF1) have multiple, complex symptoms associated with physical, social-emotional, and cognitive difficulties. In addition, caring for a child with NF1 can be extremely challenging for parents. Since research with other chronic illness populations suggests that social support, including internet support groups (ISGs), can be beneficial, this survey study aimed to determine the attitudes and preferences of adolescents and young adults with NF1 and parents of a child with NF1 regarding ISGs. Thirty patients and 30 caregivers completed a 24-item survey about ISGs. Many patients and parents are not aware of any ISGs for NF1, but are interested in using one in the future for a variety of reasons, including to get answers to their questions about NF1, to find out about research studies, and to discuss problems and concerns about NF1. Specific concerns of interest include physical, social-emotional, and cognitive aspects of NF1. ISGs have potential as a social support intervention within the NF1 community. ISGs for the NF1 population should include patients with NF1 (or parents of children with NF1) as well as a health professional, and both chat rooms and discussion boards likely would be well-received.

SLAM-ITseq identifies that Nrf2 induces liver regeneration through the pentose phosphate pathway.

The liver exhibits a remarkable capacity to regenerate following injury. Despite this unique attribute, toxic injury is a leading cause of liver failure. The temporal processes by which the liver senses injury and initiates regeneration remain unclear. Here, we developed a transgenic zebrafish model wherein hepatocyte-specific expression of uracil phosphoribosyltransferase (UPRT) enabled the implementation of SLAM-ITseq to investigate the nascent transcriptome during initiation of liver injury and regeneration. Using this approach, we identified a rapid metabolic transition from the fed to the fasted state that was followed by induction of the nuclear erythroid 2-related factor (Nrf2) antioxidant program. We find that activation of Nrf2 in hepatocytes is required to induce the pentose phosphate pathway (PPP) and improve survival following liver injury. Mechanistically, we demonstrate that inhibition of the PPP disrupts nucleotide biosynthesis to prevent liver regeneration. Together, these studies provide fundamental insights into the mechanism by which early metabolic adaptation to injury facilitates tissue regeneration.

Comparative cofactor screens show the influence of transactivation domains and core promoters on the mechanisms of transcription.

Eukaryotic transcription factors (TFs) activate gene expression by recruiting cofactors to promoters. However, the relationships between TFs, promoters and their associated cofactors remain poorly understood. Here we combine GAL4-transactivation assays with comparative CRISPR-Cas9 screens to identify the cofactors used by nine different TFs and core promoters in human cells. Using this dataset, we associate TFs with cofactors, classify cofactors as ubiquitous or specific and discover transcriptional co-dependencies. Through a reductionistic, comparative approach, we demonstrate that TFs do not display discrete mechanisms of activation. Instead, each TF depends on a unique combination of cofactors, which influences distinct steps in transcription. By contrast, the influence of core promoters appears relatively discrete. Different promoter classes are constrained by either initiation or pause-release, which influences their dynamic range and compatibility with cofactors. Overall, our comparative cofactor screens characterize the interplay between TFs, cofactors and core promoters, identifying general principles by which they influence transcription.

18-fluorodeoxyglucose-positron emission tomography (FDG-PET) evaluation of nodular lesions in patients with Neurofibromatosis type 1 and plexiform neurofibromas (PN) or malignant peripheral nerve sheath tumors (MPNST).

BACKGROUND: Individuals with Neurofibromatosis type 1 (NF1) are at risk for developing malignant peripheral nerve sheath tumors (MPNST), which frequently arise in preexisting plexiform neurofibromas (PN). Magnetic resonance imaging (MRI) with volumetric analysis and 18-fluorodeoxyglucose-positron emission tomography (FDG-PET) were utilized to monitor symptomatic nodular lesions. PROCEDURE: Patients with NF1 and PN on a NCI natural history trial were monitored for total body tumor volume (TTV) using volumetric MRI. FDG-PET was performed in individuals with a nodular well-demarcated lesion ≥3 cm if they were growing, painful, or there was a prior history of MPNST (target lesions). Asymptomatic nodular lesions were evaluated as non-target lesions. RESULTS: Fifteen patients (8m, 7f) median age of 18.3 years (range, 10-45 years) had a single target and non-target (n = 46) nodular lesions identified on MRI. Target lesions arose within (n = 8) or outside (n = 3) a PN, and all but 1 had increased FDG uptake. FDG uptake was increased in non-target lesions but to a lesser degree. FDG uptake in the surrounding PN was low, similar to background activity. Pathologic evaluation performed in 11 patients demonstrated neurofibroma (n = 6), atypical neurofibroma (n = 2) and malignancy (n = 3). CONCLUSIONS: Nodular target lesions identified on MRI in individuals with NF1 and PN demonstrate increased FDG uptake similar to MPNST, but may be benign on biopsy. Nodular target lesions may be at greater risk for malignant transformation, but their biologic and clinical behavior has not been well studied. Careful longitudinal evaluation will be required to better understand the malignant potential of these lesions.

Age-associated microenvironmental changes highlight the role of PDGF-C in ER+ breast cancer metastatic relapse.

Patients with estrogen receptor (ER)-positive breast cancer are at risk of metastatic relapse for decades after primary tumor resection and treatment, a consequence of dormant disseminated tumor cells (DTCs) reawakening at secondary sites. Here we use syngeneic ER+ mouse models in which DTCs display a dormant phenotype in young mice but accelerated metastatic outgrowth in an aged or fibrotic microenvironment. In young mice, low-level Pdgfc expression by ER+ DTCs is required for their maintenance in secondary sites but is insufficient to support development of macrometastases. By contrast, the platelet-derived growth factor (PDGF)-Chi environment of aging or fibrotic lungs promotes DTC proliferation and upregulates tumor cell Pdgfc expression stimulating further stromal activation, events that can be blocked by pharmacological inhibition of PDGFRα or with a PDGF-C-blocking antibody. These results highlight the role of the changing microenvironment in regulating DTC outgrowth and the opportunity to target PDGF-C signaling to limit metastatic relapse in ER+ breast cancer.

Inhibition of METTL3 Results in a Cell-Intrinsic Interferon Response That Enhances Antitumor Immunity.

Therapies that enhance antitumor immunity have altered the natural history of many cancers. Consequently, leveraging nonoverlapping mechanisms to increase immunogenicity of cancer cells remains a priority. Using a novel enzymatic inhibitor of the RNA methyl-transferase METTL3, we demonstrate a global decrease in N6-methyladenosine (m6A) results in double-stranded RNA (dsRNA) formation and a profound cell-intrinsic interferon response. Through unbiased CRISPR screens, we establish dsRNA-sensing and interferon signaling are primary mediators that potentiate T-cell killing of cancer cells following METTL3 inhibition. We show in a range of immunocompetent mouse models that although METTL3 inhibition is equally efficacious to anti-PD-1 therapy, the combination has far greater preclinical activity. Using SPLINTR barcoding, we demonstrate that anti-PD-1 therapy and METTL3 inhibition target distinct malignant clones, and the combination of these therapies overcomes clones insensitive to the single agents. These data provide the mole-cular and preclinical rationale for employing METTL3 inhibitors to promote antitumor immunity in the clinic. SIGNIFICANCE: This work demonstrates that METTL3 inhibition stimulates a cell-intrinsic interferon response through dsRNA formation. This immunomodulatory mechanism is distinct from current immunotherapeutic agents and provides the molecular rationale for combination with anti-PD-1 immune-checkpoint blockade to augment antitumor immunity. This article is featured in Selected Articles from This Issue, p. 2109.

Targeting Menin disrupts the KMT2A/B and polycomb balance to paradoxically activate bivalent genes.

Precise control of activating H3K4me3 and repressive H3K27me3 histone modifications at bivalent promoters is essential for normal development and frequently corrupted in cancer. By coupling a cell surface readout of bivalent MHC class I gene expression with whole-genome CRISPR-Cas9 screens, we identify specific roles for MTF2-PRC2.1, PCGF1-PRC1.1 and Menin-KMT2A/B complexes in maintaining bivalency. Genetic loss or pharmacological inhibition of Menin unexpectedly phenocopies the effects of polycomb disruption, resulting in derepression of bivalent genes in both cancer cells and pluripotent stem cells. While Menin and KMT2A/B contribute to H3K4me3 at active genes, a separate Menin-independent function of KMT2A/B maintains H3K4me3 and opposes polycomb-mediated repression at bivalent genes. Release of KMT2A from active genes following Menin targeting alters the balance of polycomb and KMT2A at bivalent genes, facilitating gene activation. This functional partitioning of Menin-KMT2A/B complex components reveals therapeutic opportunities that can be leveraged through inhibition of Menin.

Social-emotional functioning of children and adolescents with neurofibromatosis type 1 and plexiform neurofibromas: relationships with cognitive, disease, and environmental variables.

OBJECTIVE: This descriptive cross-sectional study aimed to determine how cognitive, disease, and environmental variables relate to social-emotional functioning in youth with NF1 and plexiform neurofibromas. METHODS: Psychological assessments were administered to 53 children (mean age 12.4 years); parents and teachers completed the behavior assessment system for children-second edition (BASC-2). Disease severity was quantified by nurse-practitioner ratings and tumor burden, and parents completed a life events checklist to indicate environmental stressors. RESULTS: Notable proportions of children scored in the at-risk/clinically significant ranges on several parent and teacher BASC-2 subscales including somatization, attention problems, depression, and withdrawal. Combinations of cognitive, disease, and environmental variables predicted scores on parent BASC-2 internalizing problems, behavior symptoms index, and Adaptive Skills composites. CONCLUSIONS: Cognitive, disease, and environmental variables relate to social-emotional outcomes in children with NF1. These youth may benefit from interventions targeting social skills, cognitive functioning, and adaptive ways of coping with NF1-related pain.

Assessment of the Molecular Heterogeneity of E-Cadherin Expression in Invasive Lobular Breast Cancer.

Mutations and loss of E-cadherin protein expression define the vast majority of invasive lobular carcinomas. In a subset of these cases, the heterogeneous expression of E-cadherin is observed either as wild-type (strong membranous) expression or aberrant expression (cytoplasmic expression). However, it is unclear as to whether the two components would be driven by distinct genetic or epigenetic alterations. Here, we used whole genome DNA sequencing and methylation array profiling of two separately dissected components of nine invasive lobular carcinomas with heterogeneous E-cadherin expression. E-cadherin negative and aberrant/positive components of E-cadherin heterogeneous tumours showed a similar mutational, copy number and promoter methylation repertoire, suggesting they arise from a common ancestor, as opposed to the collision of two independent tumours. We found that the majority of E-cadherin heterogeneous tumours harboured CDH1 mutations in both the E-cadherin negative and aberrant/positive components together with somatic mutations in additional driver genes known to be enriched in both pure invasive carcinomas of no special type and invasive lobular breast cancers, whereas these were less commonly observed in CDH1 wild-type tumours. CDH1 mutant tumours also exhibited a higher mutation burden as well as increased presence of APOBEC-dependent mutational signatures 2 and 13 compared to CDH1 wild-type tumours. Together, our results suggest that regardless of E-cadherin protein expression, tumours showing heterogeneous expression of E-cadherin should be considered as part of the spectrum of invasive lobular breast cancers.

Inhibition of the CtBP complex and FBXO11 enhances MHC class II expression and anti-cancer immune responses.

There is increasing recognition of the prognostic significance of tumor cell major histocompatibility complex (MHC) class II expression in anti-cancer immunity. Relapse of acute myeloid leukemia (AML) following allogeneic stem cell transplantation (alloSCT) has recently been linked to MHC class II silencing in leukemic blasts; however, the regulation of MHC class II expression remains incompletely understood. Utilizing unbiased CRISPR-Cas9 screens, we identify that the C-terminal binding protein (CtBP) complex transcriptionally represses MHC class II pathway genes, while the E3 ubiquitin ligase complex component FBXO11 mediates degradation of CIITA, the principal transcription factor regulating MHC class II expression. Targeting these repressive mechanisms selectively induces MHC class II upregulation across a range of AML cell lines. Functionally, MHC class II+ leukemic blasts stimulate antigen-dependent CD4+ T cell activation and potent anti-tumor immune responses, providing fundamental insights into the graft-versus-leukemia effect. These findings establish the rationale for therapeutic strategies aimed at restoring tumor-specific MHC class II expression to salvage AML relapse post-alloSCT and also potentially to enhance immunotherapy outcomes in non-myeloid malignancies.

Red Blood Cell Contribution to Hemostasis.

Red Blood Cells (RBCs) have been increasingly recognized to play important roles in hemostasis and the mechanisms by which they do so continue to be elucidated. First and foremost, RBC biomechanics are the principal determinant of viscosity and flow dynamics of blood, which strongly influence all features of hemostasis. Of note, morphologic pathology, such as that found in sickle cell disease, leads to increased risk of thrombotic disease. RBC surface interactions govern signaling between platelets and RBCs and also aid in the conversion of prothrombin to thrombin. Additionally, RBCs generate microparticles which have been shown to reduce clotting time. Finally, blood clot structure and maturation are dependent on the inclusion of RBCs in forming thrombi. Here, we review the above mechanisms of RBC contribution to hemostasis.

Identifying high-confidence capture Hi-C interactions using CHiCANE.

The ability to identify regulatory interactions that mediate gene expression changes through distal elements, such as risk loci, is transforming our understanding of how genomes are spatially organized and regulated. Capture Hi-C (CHi-C) is a powerful tool to delineate such regulatory interactions. However, primary analysis and downstream interpretation of CHi-C profiles remains challenging and relies on disparate tools with ad-hoc input/output formats and specific assumptions for statistical modeling. Here we present a data processing and interaction calling toolkit (CHiCANE), specialized for the analysis and meaningful interpretation of CHi-C assays. In this protocol, we demonstrate applications of CHiCANE to region capture Hi-C (rCHi-C) and promoter capture Hi-C (pCHi-C) libraries, followed by quality assessment of interaction peaks, as well as downstream analysis specific to rCHi-C and pCHi-C to aid functional interpretation. For a typical rCHi-C/pCHi-C dataset this protocol takes up to 3 d for users with a moderate understanding of R programming and statistical concepts, although this is dependent on dataset size and compute power available. CHiCANE is freely available at https://cran.r-project.org/web/packages/chicane .

Phase I trial of pirfenidone in children with neurofibromatosis 1 and plexiform neurofibromas.

We aimed to define the dose of pirfenidone in children and adolescents with neurofibromatosis 1 and plexiform neurofibromas that is pharmacokinetically comparable to the active adult dose. Pirfenidone was administered orally on a continuous dosing schedule. The starting dose level was 250 mg/m2/dose. The second dose level (500 mg/m2/dose) corresponded to the adult dose that previously showed activity in sclerosing conditions. A dose was considered pharmacokinetically comparable if the drug exposure in children was <1 standard deviation below the drug exposure in adults treated with 800 mg three times a day. Pharmacokinetic sampling was performed for 24 hours after the first dose. Response to treatment was evaluated using automated volumetric magnetic resonance imaging analysis; quality of life was evaluated using the Impact of Pediatric Illness Scale. Sixteen patients were entered and evaluated for toxicity. Dose-limiting toxicities were observed in 2 of 12 patients receiving 500 mg/m2 three times a day. The plasma pharmacokinetics of pirfenidone were highly variable, but not age dependent. The second dose level was the pharmacokinetically comparable dose and is being used in an ongoing phase II trial of pirfenidone for children with neurofibromatosis 1 and progressive plexiform neurofibroma.

Detoxification of polycyclic aromatic hydrocarbons (PAHs) in Arabidopsis thaliana involves a putative flavonol synthase.

Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants with cytotoxic, teratogenic and carcinogenic properties. Bioremediation studies with bacteria have led to the identification of dioxygenases (DOXs) in the first step to degrade these recalcitrant compounds. In this study, we characterized the role of the Arabidopsis thaliana AT5G05600, a putative DOX of the flavonol synthase family, in the transformation of PAHs. Phenotypic analysis of loss-of-function mutant lines showed that these plant lines were less sensitive to the toxic effects of phenanthrene, suggesting possible roles of this gene in PAH degradation in vivo. Interestingly, these mutant lines showed less accumulation of H2O2 after PAH exposure. Transgenic lines over-expressing At5g05600 showed a hypersensitive response and more oxidative stress after phenanthrene treatments. Moreover, fluorescence spectra results of biochemical assays with the recombinant His-tagged protein AT5G05600 detected chemical modifications of phenanthrene. Taken together, these results support the hypothesis that AT5G05600 is involved in the catabolism of PAHs and the accumulation of toxic intermediates during PAH biotransformation in plants. This research represents the first step in the design of transgenic plants with the potential to degrade PAHs, leading to the development of vigorous plant varieties that can reduce the levels of these pollutants in the environment.