Tumours and tremors: how PTEN regulation underlies both

Mutations of the tumour suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) are seen in many human cancers. However, dysregulation of PTEN may be involved in other disease states such as Parkinson's disease. This minireview describes recent work examining PTEN regulation and its implications for the development of both cancer and neurodegenerative disease

Transcriptional Activation of Low-Density Lipoprotein Receptor Gene by DJ-1 and Effect of DJ-1 on Cholesterol Homeostasis

DJ-1 is a novel oncogene and also causative gene for familial Parkinson’s disease park7. DJ-1 has multiple functions that include transcriptional regulation, anti-oxidative reaction and chaperone and mitochondrial regulation. For transcriptional regulation, DJ-1 acts as a coactivator that binds to various transcription factors, resulting in stimulation or repression of the expression of their target genes. In this study, we found the low-density lipoprotein receptor (LDLR) gene is a transcriptional target gene for DJ-1. Reduced expression of LDLR mRNA and protein was observed in DJ-1-knockdown cells and DJ-1-knockout mice and this occurred at the transcription level. Reporter gene assays using various deletion and point mutations of the LDLR promoter showed that DJ-1 stimulated promoter activity by binding to the sterol regulatory element (SRE) with sterol regulatory element binding protein (SREBP) and that stimulating activity of DJ-1 toward LDLR promoter activity was enhanced by oxidation of DJ-1. Chromatin immunoprecipitation, gel-mobility shift and co-immunoprecipitation assays showed that DJ-1 made a complex with SREBP on the SRE. Furthermore, it was found that serum LDL cholesterol level was increased in DJ-1-knockout male, but not female, mice and that the increased serum LDL cholesterol level in DJ-1-knockout male mice was cancelled by administration with estrogen, suggesting that estrogen compensates the increased level of serum LDL cholesterol in DJ-1-knockout female mice. This is the first report that DJ-1 participates in metabolism of fatty acid synthesis through transcriptional regulation of the LDLR gene

A Plant DJ-1 Homolog Is Essential for Arabidopsis thaliana Chloroplast Development

Protein superfamilies can exhibit considerable diversification of function among their members in various organisms. The DJ-1 superfamily is composed of proteins that are principally involved in stress response and are widely distributed in all kingdoms of life. The model flowering plant Arabidopsis thaliana contains three close homologs of animal DJ-1, all of which are tandem duplications of the DJ-1 domain. Consequently, the plant DJ-1 homologs are likely pseudo-dimeric proteins composed of a single polypeptide chain. We report that one A. thaliana DJ-1 homolog (AtDJ1C) is the first DJ-1 homolog in any organism that is required for viability. Homozygous disruption of the AtDJ1C gene results in non-viable, albino seedlings that can be complemented by expression of wild-type or epitope-tagged AtDJ1C. The plastids from these dj1c plants lack thylakoid membranes and granal stacks, indicating that AtDJ1C is required for proper chloroplast development. AtDJ1C is expressed early in leaf development when chloroplasts mature, but is downregulated in older tissue, consistent with a proposed role in plastid development. In addition to its plant-specific function, AtDJ1C is an atypical member of the DJ-1 superfamily that lacks a conserved cysteine residue that is required for the functions of most other superfamily members. The essential role for AtDJ1C in chloroplast maturation expands the known functional diversity of the DJ-1 superfamily and provides the first evidence of a role for specialized DJ-1-like proteins in eukaryotic development

Molecular Basis for Vulnerability to Mitochondrial and Oxidative Stress in a Neuroendocrine CRI-G1 Cell Line

Many age-associated disorders (including diabetes, cancer, and neurodegenerative diseases) are linked to mitochondrial dysfunction, which leads to impaired cellular bioenergetics and increased oxidative stress. However, it is not known what genetic and molecular pathways underlie differential vulnerability to mitochondrial dysfunction observed among different cell types.Starting with an insulinoma cell line as a model for a neuronal/endocrine cell type, we isolated a novel subclonal line (named CRI-G1-RS) that was more susceptible to cell death induced by mitochondrial respiratory chain inhibitors than the parental CRI-G1 line (renamed CRI-G1-RR for clarity). Compared to parental RR cells, RS cells were also more vulnerable to direct oxidative stress, but equally vulnerable to mitochondrial uncoupling and less vulnerable to protein kinase inhibition-induced apoptosis. Thus, differential vulnerability to mitochondrial toxins between these two cell types likely reflects differences in their ability to handle metabolically generated reactive oxygen species rather than differences in ATP production/utilization or in downstream apoptotic machinery. Genome-wide gene expression analysis and follow-up biochemical studies revealed that, in this experimental system, increased vulnerability to mitochondrial and oxidative stress was associated with (1) inhibition of ARE/Nrf2/Keap1 antioxidant pathway; (2) decreased expression of antioxidant and phase I/II conjugation enzymes, most of which are Nrf2 transcriptional targets; (3) increased expression of molecular chaperones, many of which are also considered Nrf2 transcriptional targets; (4) increased expression of β cell-specific genes and transcription factors that specify/maintain β cell fate; and (5) reconstitution of glucose-stimulated insulin secretion.The molecular profile presented here will enable identification of individual genes or gene clusters that shape vulnerability to mitochondrial dysfunction and thus represent potential therapeutic targets for diabetes and neurodegenerative diseases. In addition, the newly identified CRI-G1-RS cell line represents a new experimental model for investigating how endogenous antioxidants affect glucose sensing and insulin release by pancreatic β cells

Genotype-Specific Differences between Mouse CNS Stem Cell Lines Expressing Frontotemporal Dementia Mutant or Wild Type Human Tau

Stem cell (SC) lines that capture the genetics of disease susceptibility provide new research tools. To assess the utility of mouse central nervous system (CNS) SC-containing neurosphere cultures for studying heritable neurodegenerative disease, we compared neurosphere cultures from transgenic mice that express human tau with the P301L familial frontotemporal dementia (FTD) mutation, rTg(tauP301L)4510, with those expressing comparable levels of wild type human tau, rTg(tauwt)21221. rTg(tauP301L)4510 mice express the human tauP301L variant in their forebrains and display cellular, histological, biochemical and behavioral abnormalities similar to those in human FTD, including age-dependent differences in tau phosphorylation that distinguish them from rTg(tauwt)21221 mice. We compared FTD-hallmark tau phosphorylation in neurospheres from rTg(tauP301L)4510 mice and from rTg(tauwt)21221 mice. The tau genotype-specific phosphorylation patterns in neurospheres mimicked those seen in mice, validating use of neurosphere cultures as models for studying tau phosphorylation. Genotype-specific tau phosphorylation was observed in 35 independent cell lines from individual fetuses; tau in rTg(tauP301L)4510 cultures was hypophosphorylated in comparison with rTg(tauwt)21221 as was seen in young adult mice. In addition, there were fewer human tau-expressing cells in rTg(tauP301L)4510 than in rTg(tauwt)21221 cultures. Following differentiation, neuronal filopodia-spine density was slightly greater in rTg(tauP301L)4510 than rTg(tauwt)21221 and control cultures. Together with the recapitulation of genotype-specific phosphorylation patterns, the observation that neurosphere lines maintained their cell line-specific-differences and retained SC characteristics over several passages supports the utility of SC cultures as surrogates for analysis of cellular disease mechanisms

A molecular analysis of desiccation tolerance mechanisms in the anhydrobiotic nematode Panagrolaimus superbus using expressed sequenced tags

<p>Abstract</p> <p>Background</p> <p>Some organisms can survive extreme desiccation by entering into a state of suspended animation known as anhydrobiosis. <it>Panagrolaimus superbus </it>is a free-living anhydrobiotic nematode that can survive rapid environmental desiccation. The mechanisms that <it>P. superbus </it>uses to combat the potentially lethal effects of cellular dehydration may include the constitutive and inducible expression of protective molecules, along with behavioural and/or morphological adaptations that slow the rate of cellular water loss. In addition, inducible repair and revival programmes may also be required for successful rehydration and recovery from anhydrobiosis.</p> <p>Results</p> <p>To identify constitutively expressed candidate anhydrobiotic genes we obtained 9,216 ESTs from an unstressed mixed stage population of <it>P. superbus</it>. We derived 4,009 unigenes from these ESTs. These unigene annotations and sequences can be accessed at <url>http://www.nematodes.org/nembase4/species_info.php?species=PSC</url>. We manually annotated a set of 187 constitutively expressed candidate anhydrobiotic genes from <it>P. superbus</it>. Notable among those is a putative lineage expansion of the <it>lea </it>(late embryogenesis abundant) gene family. The most abundantly expressed sequence was a member of the nematode specific <it>sxp/ral-2 </it>family that is highly expressed in parasitic nematodes and secreted onto the surface of the nematodes' cuticles. There were 2,059 novel unigenes (51.7% of the total), 149 of which are predicted to encode intrinsically disordered proteins lacking a fixed tertiary structure. One unigene may encode an exo-β-1,3-glucanase (GHF5 family), most similar to a sequence from <it>Phytophthora infestans</it>. GHF5 enzymes have been reported from several species of plant parasitic nematodes, with horizontal gene transfer (HGT) from bacteria proposed to explain their evolutionary origin. This <it>P. superbus </it>sequence represents another possible HGT event within the Nematoda. The expression of five of the 19 putative stress response genes tested was upregulated in response to desiccation. These were the antioxidants <it>glutathione peroxidase, dj-1 </it>and <it>1-Cys peroxiredoxin</it>, an <it>shsp </it>sequence and an <it>lea </it>gene.</p> <p>Conclusions</p> <p><it>P. superbus </it>appears to utilise a strategy of combined constitutive and inducible gene expression in preparation for entry into anhydrobiosis. The apparent lineage expansion of <it>lea </it>genes, together with their constitutive and inducible expression, suggests that LEA3 proteins are important components of the anhydrobiotic protection repertoire of <it>P. superbus</it>.</p

Interaction of DJ-1 with Daxx inhibits apoptosis signal-regulating kinase 1 activity and cell death

Investigations into the cellular and molecular biology of genes that cause inherited forms of Parkinson's disease, as well as the downstream pathways that they trigger, shed considerable light on our understanding the fundamental determinants of life and death in dopaminergic neurons. Homozygous deletion or missense mutation in DJ-1 results in autosomal recessively inherited Parkinson's disease, suggesting that wild-type DJ-1 has a favorable role in maintaining these neurons. Here, we show that DJ-1 protects against oxidative stress-induced cell death, but that its relatively modest ability to quench reactive oxygen species is insufficient to account for its more robust cytoprotective effect. To elucidate the mechanism of this cell-preserving function, we have screened out the death protein Daxx as a DJ-1-interacting partner. We demonstrate that wild-type DJ-1 sequesters Daxx in the nucleus, prevents it from gaining access to the cytoplasm, from binding to and activating its effector kinase apoptosis signal-regulating kinase 1, and therefore, from triggering the ensuing death pathway. All these steps are impaired by the disease-causing L166P mutant isoform of DJ-1. These findings suggest that the regulated sequestration of Daxx in the nucleus and keeping apoptosis signal-regulating kinase 1 activation in check is a critical mechanism by which DJ-1 exerts its cytoprotective function

Inactivation of Drosophila DJ-1 leads to impairments of oxidative stress response and phosphatidylinositol 3-kinase/Akt signaling

Parkinson's disease (PD) is the most common movement disorder characterized by dopaminergic dysfunction and degeneration. The cause of most PD cases is unknown, although postmortem studies have implicated the involvement of oxidative stress. The identification of familial PD-associated genes offers the opportunity to study mechanisms of PD pathogenesis in model organisms. Here, we show that DJ-1A, a Drosophila homologue of the familial PD-associated gene DJ-1, plays an essential role in oxidative stress response and neuronal maintenance. Inhibition of DJ-1A function through RNA interference (RNAi) results in cellular accumulation of reactive oxygen species, organismal hypersensitivity to oxidative stress, and dysfunction and degeneration of dopaminergic and photoreceptor neurons. To identify other genes that may interact with DJ-1A in regulating cell survival, we performed genetic interaction studies and identified components of the phosphatidylinositol 3-kinase (PI3K)/Akt-signaling pathway as specific modulators of DJ-1A RNAi-induced neurodegeneration. PI3K signaling suppresses DJ-1A RNAi phenotypes at least in part by reducing cellular reactive oxygen species levels. Consistent with the genetic interaction results, we also found reduced phosphorylation of Akt in DJ-1A RNAi animals, indicating an impairment of PI3K/Akt signaling by DJ-1A down-regulation. Together with recent findings in mammalian systems, these results implicate impairments of PI3K/Akt signaling and oxidative stress response in DJ-1-associated disease pathogenesis. We also observed impairment of PI3K/Akt signaling in the fly parkin model of PD, hinting at a common molecular event in the pathogenesis of PD. Manipulation of PI3K/Akt signaling may therefore offer therapeutic benefits for the treatment of PD