NAPP2, a peroxisomal membrane protein, is also a transcriptional corepressor

A mutable albino allele in rice reveals that formation of thylakoid membranes requires the SNOW-WHITE LEAF1 gene

Active DNA transposons are important tools for gene functional analysis. The endogenous non-autonomous transposon, nDart1-0, in rice (Oryza sativa L.) is expected to generate various transposon-insertion mutants because nDart1-0 elements tend to insert into genic regions under natural growth conditions. We have developed a specific method (nDart1-0-iPCR) for efficient detection of nDart1-0 insertions and successfully identified the SNOW-WHITE LEAF1 (SWL1) gene in a variegated albino (swl1-v) mutant obtained from the nDart1-promoted rice tagging line. The variegated albino phenotype was caused by insertion and excision of nDart1-0 in the 5'-untranslated region of the SWL1 gene predicted to encode an unknown protein with the N-terminal chloroplast transit peptide. SWL1 expression was detected in various rice tissues at different developmental stages. However, immunoblot analysis indicated that SWL1 protein accumulation was strictly regulated in a tissue-specific manner. In the swl1 mutant, formations of grana and stroma thylakoids and prolamellar bodies were inhibited. This study revealed that SWL1 is essential for the beginning of thylakoid membrane organization during chloroplast development. Furthermore, we provide a developmental perspective on the nDart1-promoted tagging line to characterize unidentified gene functions in rice.

MPN patients harbor recurrent truncating mutations in transcription factor NF-E2

The molecular etiology of myeloproliferative neoplasms (MPNs) remains incompletely understood, despite recent advances incurred through the discovery of several different mutations in MPN patients. We have recently described overexpression of the transcription factor NF-E2 in MPN patients and shown that elevated NF-E2 levels in vivo cause an MPN phenotype and predispose to leukemic transformation in transgenic mice. We report the presence of acquired insertion and deletion mutations in the NF-E2 gene in MPN patients. These result in truncated NF-E2 proteins that enhance wild-type (WT) NF-E2 function and cause erythrocytosis and thrombocytosis in a murine model. NF-E2 mutant cells acquire a proliferative advantage, witnessed by clonal dominance over WT NF-E2 cells in MPN patients. Our data underscore the role of increased NF-E2 activity in the pathophysiology of MPNs.

Integration of peroxisomes into an endomembrane system that governs cellular aging

The peroxisome is an organelle that has long been known for its essential roles in oxidation of fatty acids, maintenance of reactive oxygen species (ROS) homeostasis and anaplerotic replenishment of tricarboxylic acid (TCA) cycle intermediates destined for mitochondria. Growing evidence supports the view that these peroxisome-confined metabolic processes play an essential role in defining the replicative and chronological age of a eukaryotic cell. Much progress has recently been made in defining molecular mechanisms that link cellular aging to fatty acid oxidation, ROS turnover, and anaplerotic metabolism in peroxisomes. Emergent studies have revealed that these organelles not only house longevity-defining metabolic reactions but can also regulate cellular aging via their dynamic communication with other cellular compartments. Peroxisomes communicate with other organelles by establishing extensive physical contact with lipid bodies, maintaining an endoplasmic reticulum (ER) to peroxisome connectivity system, exchanging certain metabolites, and being involved in the bidirectional flow of some of their protein and lipid constituents. The scope of this review is to summarize the evidence that peroxisomes are dynamically integrated into an endomembrane system that governs cellular aging. We discuss recent progress in understanding how communications between peroxisomes and other cellular compartments within this system influence the development of a pro- or anti-aging cellular pattern. We also propose a model for the integration of peroxisomes into the endomembrane system governing cellular aging and critically evaluate several molecular mechanisms underlying such integration.

High resolution analysis of follicular lymphoma genomes reveals somatic recurrent sites of copy-neutral loss of heterozygosity and copy number alterations that target single genes

A multiplatform approach, including conventional cytogenetic techniques, BAC array comparative genomic hybridization, and Affymetrix 500K SNP arrays, was applied to the study of the tumor genomes of 25 follicular lymphoma biopsy samples with paired normal DNA samples to characterize balanced translocations, copy number imbalances, and copy-neutral loss of heterozygosity (cnLOH). In addition to the t(14;18), eight unique balanced translocations were found. Commonly reported FL-associated copy number regions were revealed including losses of 1p32-36, 6q, and 10q, and gains of 1q, 6p, 7, 12, 18, and X. The most frequent regions affected by copy-neutral loss of heterozygosity were 1p36.33 (28%), 6p21.3 (20%), 12q21.2-q24.33 (16%), and 16p13.3 (24%). We also identified by SNP analysis, 45 aberrant regions that each affected one gene, including CDKN2A, CDKN2B, FHIT, KIT, PEX14, and PTPRD, which were associated with canonical pathways involved in tumor development. This study illustrates the power of using complementary high-resolution platforms on paired tumor/normal specimens and computational analysis to provide potential insights into the significance of single-gene somatic aberrations in FL tumorigenesis.

Identification of a novel PEX14 mutation in Zellweger syndrome

Here we report a patient with Zellweger syndrome, who presented at the age of 3 months with icterus, dystrophy, axial hypotonia, and hepatomegaly. Abnormal findings of metabolic screening tests included hyperbilirubinaemia, hypoketotic dicarboxylic aciduria, increased C(26:0) and decreased C(22:0) plasma levels, and strongly reduced plasmalogen concentrations. In fibroblasts, both peroxisomal α- and β-oxidation were impaired. Liver histology revealed bile duct paucity, cholestasis, arterial hyperplasia, very small branches of the vena portae, and parenchymatic destruction. Immunocytochemical analysis of cultured fibroblasts demonstrated that the cells contain peroxisomal remnants lacking apparent matrix protein content and PEX14, a central membrane component of the peroxisomal matrix protein import machinery. Transfection of fibroblasts with a plasmid coding for wild-type PEX14 restored peroxisomal matrix protein import. Mutational analysis of this gene revealed a genomic deletion leading to the deletion of exon 3 from the coding DNA (c.85-?_170+?del) and a concomitant change of the reading frame (p.[Ile29_Lys56del;Gly57GlyfsX2]).

Neuroblastoma tumors with favorable and unfavorable outcomes: Significant differences in mRNA expression of genes mapped at 1p36.2

The distal part of 1p is frequently deleted in aggressive neuroblastoma, and the region is believed to harbor one or more tumor suppressor genes relevant to tumor development. To analyze differences among neuroblastoma tumors, an expression profile was established for the genes mapped within a previously described shortest region of overlap of deletions at 1p36.2. The gene expression levels were quantified by TaqMan real-time (RT)-PCR for 30 transcripts using 55 primary neuroblastoma tumors. Here we report on a significant decrease in gene expression of the genes RERE, PIK3CD, LZIC, PGD, and PEX14 and an increase of SLC2A5 when comparing tumors of favorable biology to Stage 4 neuroblastomas. When comparing 1p-deleted tumors of all stages to tumors with an intact 1p, a significant difference at gene-by-gene level in TNFRSF9, RERE, PIK3CD, CLSTN1, CTNNBIP1, and CASZ1 was detected. A complete loss of expression could not be seen for any single gene analyzed. Several of the genes with diminished expression in unfavorable or 1p-deleted tumors have functions that could contribute to tumor development. It is also possible that a combination of lowly expressed genes at 1p, rather than one single classical tumor suppressor gene, causes the unfavorable outcome associated with 1p-deletion in neuroblastoma.

Induction of fetal hemoglobin in the treatment of sickle cell disease

Reactivation of fetal hemoglobin (HbF) expression is an important therapeutic option in patients with hemoglobin disorders. In sickle cell disease (SCD), an increase in HbF inhibits the polymerization of sickle hemoglobin and the resulting pathophysiology. Hydroxyurea, an inducer of HbF, has already been approved for the treatment of patients with moderate and/or severe SCD. Recent clinical trials with other pharmacological inducers of HbF, such as butyrate and decitabine, have shown considerable promise. In this chapter, we highlight the important clinical trials with pharmacological inducers of HbF, discuss their mechanisms of action and speculate about the future of this therapeutic approach in the treatment of patients with SCD.

The peroxisome: orchestrating important developmental decisions from inside the cell

The peroxisome has long been known for its role in lipid metabolism and hydrogen peroxide detoxification. However, growing evidence supports the view that this organelle can also function both as an intracellular signaling compartment and as an organizing platform that orchestrates certain developmental decisions from inside the cell. This review highlights various strategies that peroxisomes employ to regulate the processes of development, differentiation, and morphogenesis and critically evaluates several molecular mechanisms by which peroxisomes promote these processes.

A WW domain-binding motif within the activation domain of the hematopoietic transcription factor NF-E2 is essential for establishment of a tissue-specific histone modification pattern

Histone H3 methylated at lysine 4 (H3-meK4) co-localizes with hyperacetylated histones H3 and H4 in transcriptionally active chromatin, but mechanisms that establish H3-meK4 are poorly understood. Previously, we showed that the hematopoietic-specific activator NF-E2, which is required for beta-globin transcription in erythroleukemia cells, induces histone H3 hyperacetylation and H3-meK4 at the adult beta-globin genes (betamajor and betaminor). Chromatin immunoprecipitation analysis indicated that NF-E2 occupies hypersensitive site two (HS2) of the beta-globin locus control region. The mechanism of NF-E2-mediated chromatin modification was investigated by complementation analysis in NF-E2-null CB3 erythroleukemia cells. The activation domain of the hematopoietic-specific subunit of NF-E2 (p45/NF-E2) contains two WW domain-binding motifs (PXY-1 and PXY-2). PXY-1 is required for activation of beta-globin transcription. Here, we determined which step in NF-E2-dependent transactivation is PXY-1-dependent. A p45/NF-E2 mutant lacking 42 amino acids of the activation domain, including both PXY motifs, and a mutant lacking only PXY-1 were impaired in inducing histone H3 hyperacetylation, H3-meK4, and RNA polymerase II recruitment. The PXY motifs were not required for transactivation in the context of a GAL4 DNA-binding domain fusion to p45/NF-E2 in transient transfection assays. As the PXY-1 mutant occupied HS2 normally, the chromatin modification defect occurred post-DNA binding. PXY-1 was not required for recruitment of the histone acetyltransferases cAMP-responsive element-binding protein-binding protein (CBP) and p300 to HS2. These results indicate that PXY-1 confers chromatin-specific transcriptional activation via interaction with a co-regulator distinct from CBP/p300 or by regulating CBP/p300 function.