Schizosaccharomyces pombe Ofd2 is a nuclear 2-oxoglutarate and iron dependent dioxygenase interacting with histones

DNA Methylation on N6-Adenine Regulates the Hyphal Development during Dimorphism in the Early-Diverging Fungus Mucor lusitanicus

The epigenetic modifications control the pathogenicity of human pathogenic fungi, which have been poorly studied in Mucorales, causative agents of mucormycosis. This order belongs to a group referred to as early-diverging fungi that are characterized by high levels of N6-methyldeoxy adenine (6mA) in their genome with dense 6mA clusters associated with actively expressed genes. AlkB enzymes can act as demethylases of 6mA in DNA, with the most remarkable eukaryotic examples being mammalian ALKBH1 and Caenorhabditis elegans NMAD-1. The Mucor lusitanicus (formerly M. circinelloides f. lusitanicus) genome contains one gene, dmt1, and two genes, dmt2 and dmt3, encoding proteins similar to C. elegans NMAD-1 and ALKBH1, respectively. The function of these three genes was analyzed by the generation of single and double deletion mutants for each gene. Multiple processes were studied in the mutants, but defects were only found in single and double deletion mutants for dmt1. In contrast to the wild-type strain, dmt1 mutants showed an increase in 6mA levels during the dimorphic transition, suggesting that 6mA is associated with dimorphism in M. lusitanicus. Furthermore, the spores of dmt1 mutants challenged with macrophages underwent a reduction in polar growth, suggesting that 6mA also has a role during the spore–macrophage interaction that could be important in the infection process.

Hallmarks of Basidiomycete Soft- and White-Rot in Wood-Decay -Omics Data of Two Armillaria Species

Wood-decaying Basidiomycetes are among the most efficient degraders of plant cell walls, making them key players in forest ecosystems, global carbon cycle, and in bio-based industries. Recent insights from -omics data revealed a high functional diversity of wood-decay strategies, especially among the traditional white-rot and brown-rot dichotomy. We examined the mechanistic bases of wood-decay in the conifer-specialists Armillaria ostoyae and Armillaria cepistipes using transcriptomic and proteomic approaches. Armillaria spp. (Fungi, Basidiomycota) include devastating pathogens of temperate forests and saprotrophs that decay wood. They have been discussed as white-rot species, though their response to wood deviates from typical white-rotters. While we observed an upregulation of a diverse suite of plant cell wall degrading enzymes, unlike white-rotters, they possess and express an atypical wood-decay repertoire in which pectinases and expansins are enriched, whereas lignin-decaying enzymes (LDEs) are generally downregulated. This combination of wood decay genes resembles the soft-rot of Ascomycota and appears widespread among Basidiomycota that produce a superficial white rot-like decay. These observations are consistent with ancestral soft-rot decay machinery conserved across asco- and Basidiomycota, a gain of efficient lignin-degrading ability in white-rot fungi and repeated, complete, or partial losses of LDE encoding gene repertoires in brown- and secondarily soft-rot fungi.

INCURVATA11 and CUPULIFORMIS2 Are Redundant Genes That Encode Epigenetic Machinery Components in Arabidopsis

All critical developmental and physiological events in a plant's life cycle depend on the proper activation and repression of specific gene sets, and this often involves epigenetic mechanisms. Some Arabidopsis thaliana mutants with disorders of the epigenetic machinery exhibit pleiotropic defects, including incurved leaves and early flowering, due to the ectopic and heterochronic derepression of developmental regulators. Here, we studied one such mutant class, the incurvata11 (icu11) loss-of-function mutants. We have identified ICU11 as the founding member of a small gene family that we have named CUPULIFORMIS (CP). This family is part of the 2-oxoglutarate/Fe(II)-dependent dioxygenase superfamily. ICU11 and its closest paralog, CP2, have unequally redundant functions: although cp2 mutants are phenotypically wild type, icu11 cp2 double mutants skip vegetative development and flower upon germination. This phenotype is reminiscent of loss-of-function mutants of the Polycomb-group genes EMBRYONIC FLOWER1 (EMF1) and EMF2 Double mutants harboring icu11 alleles and loss-of-function alleles of genes encoding components of the epigenetic machinery exhibit synergistic, severe phenotypes, and some are similar to those of emf mutants. Hundreds of genes are misexpressed in icu11 plants, including SEPALLATA3 (SEP3), and derepression of SEP3 causes the leaf phenotype of icu11 ICU11 and CP2 are nucleoplasmic proteins that act as epigenetic repressors through an unknown mechanism involving histone modification, but not DNA methylation.

OH, the Places You'll Go! Hydroxylation, Gene Expression, and Cancer

Hydroxylation is an emerging modification generally catalyzed by a family of ∼70 enzymes that are dependent on oxygen, Fe(II), ascorbate, and the Kreb's cycle intermediate 2-oxoglutarate (2OG). These "2OG oxygenases" sit at the intersection of nutrient availability and metabolism where they have the potential to regulate gene expression and growth in response to changes in co-factor abundance. Characterized 2OG oxygenases regulate fundamental cellular processes by catalyzing the hydroxylation or demethylation (via hydroxylation) of DNA, RNA, or protein. As such they have been implicated in various syndromes and diseases, but particularly cancer. In this review we discuss the emerging role of 2OG oxygenases in gene expression control, examine the regulation of these unique enzymes by nutrient availability and metabolic intermediates, and describe these properties in relation to the expanding role of these enzymes in cancer.

Non-homologous functions of the AlkB homologs

The DNA repair enzyme AlkB was identified in E. coli more than three decades ago. Since then, nine mammalian homologs, all members of the superfamily of alpha-ketoglutarate and Fe(II)-dependent dioxygenases, have been identified (designated ALKBH1-8 and FTO). While E. coli AlkB serves as a DNA repair enzyme, only two mammalian homologs have been confirmed to repair DNA in vivo. The other mammalian homologs have remarkably diverse substrate specificities and biological functions. Substrates recognized by the different AlkB homologs comprise erroneous methyl- and etheno adducts in DNA, unique wobble uridine modifications in certain tRNAs, methylated adenines in mRNA, and methylated lysines on proteins. The phenotypes of organisms lacking or overexpressing individual AlkB homologs include obesity, severe sensitivity to inflammation, infertility, growth retardation, and multiple malformations. Here we review the present knowledge of the mammalian AlkB homologs and their implications for human disease and development.

Isp7 is a novel regulator of amino acid uptake in the TOR signaling pathway

TOR proteins reside in two distinct complexes, TOR complexes 1 and 2 (TORC1 and TORC2), that are central for the regulation of cellular growth, proliferation, and survival. TOR is also the target for the immunosuppressive and anticancer drug rapamycin. In Schizosaccharomyces pombe, disruption of the TSC complex, mutations in which can lead to the tuberous sclerosis syndrome in humans, results in a rapamycin-sensitive phenotype under poor nitrogen conditions. We show here that the sensitivity to rapamycin is mediated via inhibition of TORC1 and suppressed by overexpression of isp7(+), a member of the family of 2-oxoglutarate-Fe(II)-dependent oxygenase genes. The transcript level of isp7(+) is negatively regulated by TORC1 but positively regulated by TORC2. Yet we find extensive similarity between the transcriptome of cells disrupted for isp7(+) and cells mutated in the catalytic subunit of TORC1. Moreover, Isp7 regulates amino acid permease expression in a fashion similar to that of TORC1 and opposite that of TORC2. Overexpression of isp7(+) induces TORC1-dependent phosphorylation of ribosomal protein Rps6 while inhibiting TORC2-dependent phosphorylation and activation of the AGC-like kinase Gad8. Taken together, our findings suggest a central role for Isp7 in amino acid homeostasis and the presence of isp7(+)-dependent regulatory loops that affect both TORC1 and TORC2.

ALKBH1 is a histone H2A dioxygenase involved in neural differentiation

AlkB homolog 1 (ALKBH1) is one of nine members of the family of mammalian AlkB homologs. Most Alkbh1(-/-) mice die during embryonic development, and survivors are characterized by defects in tissues originating from the ectodermal lineage. In this study, we show that deletion of Alkbh1 prolonged the expression of pluripotency markers in embryonic stem cells and delayed the induction of genes involved in early differentiation. In vitro differentiation to neural progenitor cells (NPCs) displayed an increased rate of apoptosis in the Alkbh1(-/-) NPCs when compared with wild-type cells. Whole-genome expression analysis and chromatin immunoprecipitation revealed that ALKBH1 regulates both directly and indirectly, a subset of genes required for neural development. Furthermore, our in vitro enzyme activity assays demonstrate that ALKBH1 is a histone dioxygenase that acts specifically on histone H2A. Mass spectrometric analysis demonstrated that histone H2A from Alkbh1(-/-) mice are improperly methylated. Our results suggest that ALKBH1 is involved in neural development by modifying the methylation status of histone H2A.

Human ALKBH4 interacts with proteins associated with transcription

The Fe(II)- and 2-oxoglutarate (2OG)-dependent dioxygenase AlkB from E. coli is a demethylase which repairs alkyl lesions in DNA, as well as RNA, through a direct reversal mechanism. Humans possess nine AlkB homologs (ALKBH1-8 and FTO). ALKBH2 and ALKBH3 display demethylase activities corresponding to that of AlkB, and both ALKBH8 and FTO are RNA modification enzymes. The biochemical functions of the rest of the homologs are still unknown. To increase our knowledge on the functions of ALKBH4 and ALKBH7 we have here performed yeast two-hybrid screens to identify interaction partners of the two proteins. While no high-confidence hits were detected in the case of ALKBH7, several proteins associated with chromatin and/or involved in transcription were found to interact with ALKBH4. For all interaction partners, the regions mediating binding to ALKBH4 comprised domains previously reported to be involved in interaction with DNA or chromatin. Furthermore, some of these partners showed nuclear co-localization with ALKBH4. However, the global gene expression pattern was only marginally altered upon ALKBH4 over-expression, and larger effects were observed in the case of ALKBH7. Although the molecular function of both proteins remains to be revealed, our findings suggest a role for ALKBH4 in regulation of gene expression or chromatin state.

The Schizosaccharomyces pombe AlkB homolog Abh1 exhibits AP lyase activity but no demethylase activity

2-Oxoglutarate (2OG) and iron (Fe(II)) dependent dioxygenases catalyze a wide range of biological oxidations, including hydroxylation and demethylation of proteins and nucleic acids. AlkB from Escherichia coli directly reverses certain methyl lesions in DNA, and defines a subfamily of 2OG/Fe(II) dioxygenases that has so far been shown to be involved in both nucleic acid repair and modification. The human genome encodes nine AlkB homologs and the function of most of these is still unknown. The fission yeast Schizosaccharomyces pombe has two AlkB homologs and here we have addressed the function of one of these, Abh1, which appears not to possess a classical AlkB-like repair activity. No enzymatic activity was found toward methylated DNA or etheno adducts, nor was the yeast abh1- mutant sensitive toward alkylating agents. Interestingly, heterologous expression of E. coli AlkB protected the fission yeast cells from alkylation induced cytotoxicity, suggesting that S. pombe lacks systems for efficient repair of lesions that are AlkB substrates. Further, we show that Abh1 possesses an unexpected DNA incision activity at apurinic/apyrimidinic (AP) sites. This AP lyase activity did not depend on 2OG and Fe(II) and was not repressed by dioxygenase inhibitors. Survival and complementation analyses failed to reveal any biological role for AP lyase cleavage by Abh1. It appears that in vitro AP lyase activity can be detected for a number of enzymes belonging to structurally and functionally unrelated families, but the in vivo significance of such activities may be questionable.

Novel AlkB dioxygenases--alternative models for in silico and in vivo studies

Background

ALKBH proteins, the homologs of Escherichia coli AlkB dioxygenase, constitute a direct, single-protein repair system, protecting cellular DNA and RNA against the cytotoxic and mutagenic activity of alkylating agents, chemicals significantly contributing to tumor formation and used in cancer therapy. In silico analysis and in vivo studies have shown the existence of AlkB homologs in almost all organisms. Nine AlkB homologs (ALKBH1–8 and FTO) have been identified in humans. High ALKBH levels have been found to encourage tumor development, questioning the use of alkylating agents in chemotherapy. The aim of this work was to assign biological significance to multiple AlkB homologs by characterizing their activity in the repair of nucleic acids in prokaryotes and their subcellular localization in eukaryotes.

Methodology and Findings

Bioinformatic analysis of protein sequence databases identified 1943 AlkB sequences with eight new AlkB subfamilies. Since Cyanobacteria and Arabidopsis thaliana contain multiple AlkB homologs, they were selected as model organisms for in vivo research. Using E. coli alkB⁻ mutant and plasmids expressing cyanobacterial AlkBs, we studied the repair of methyl methanesulfonate (MMS) and chloroacetaldehyde (CAA) induced lesions in ssDNA, ssRNA, and genomic DNA. On the basis of GFP fusions, we investigated the subcellular localization of ALKBHs in A. thaliana and established its mostly nucleo-cytoplasmic distribution. Some of the ALKBH proteins were found to change their localization upon MMS treatment.

Conclusions

Our in vivo studies showed highly specific activity of cyanobacterial AlkB proteins towards lesions and nucleic acid type. Subcellular localization and translocation of ALKBHs in A. thaliana indicates a possible role for these proteins in the repair of alkyl lesions. We hypothesize that the multiplicity of ALKBHs is due to their involvement in the metabolism of nucleo-protein complexes; we find their repair by ALKBH proteins to be economical and effective alternative to degradation and de novo synthesis.