Mechanisms of Cdc48/VCP-mediated cell death — from yeast apoptosis to human disease

Protein oxidation in Huntington disease

Huntington disease (HD) is an inherited neurodegenerative disorder caused by expansion of CAG repeats in the huntingtin gene, affecting initially the striatum and progressively the cortex. Oxidative stress, and consequent protein oxidation, has been described as important to disease progression. This review focuses on recent advances in the field, with a particular emphasis on the identified target proteins and the role that their oxidation has or might have in the pathophysiology of HD. Oxidation and the resulting inactivation and/or degradation of important proteins can explain the impairment of several metabolic pathways in HD. Oxidation of enzymes involved in ATP synthesis can account for the energy deficiency observed. Impairment of protein folding and degradation can be due to oxidation of several heat shock proteins and Valosin-containing protein. Oxidation of two enzymes involved in the vitamin B6 metabolism could result in decreased availability of pyridoxal phosphate, which is a necessary cofactor in transaminations, the kynurenine pathway and the synthesis of glutathione, GABA, dopamine and serotonin, all of which have a key role in HD pathology. In addition, protein oxidation often contributes to oxidative stress, aggravating the molecular damage inside the cell.

Proteomic analysis of a drosophila IBMPFD model reveals potential pathogenic mechanisms

IBMPFD, Inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia, is a hereditary degenerative disorder due to single missense mutations in VCP (Valosin-Containing Protein). The mechanisms of how mutations of VCP lead to IBMPFD remain mysterious. Here we utilize two-dimensional difference gel electrophoresis (2D-DIGE) combined with mass spectrometry to study the IBMPFD disorder at the protein level. With this set-up, we are able to employ comparative proteomics to analyze IBMPFD disease using Drosophila melanogaster as our disease model organism. Head proteome of transgenic D. melanogaster expressing wild type VCP is compared, respectively, with the head proteome of transgenic mutant type VCPs that correspond to human IBMPFD disease alleles (TER94(A229E), TER94(R188Q), and TER94(R152H)). Of all the proteins identified, a significant fraction of proteins altered in TER94(A229E) and TER94(R188Q) mutants belong to the same functional categories, i.e. apoptosis and metabolism. Among these, Drosophila transferrin is observed to be significantly up-regulated in mutant flies expressing TER94(A229E). A knock-down experiment suggests that fly transferrin might be a potential modifier in IBMPFD disease. The molecular analysis of IBMPFD disease may benefit from the proteomics approach which combines the advantages of high throughput analysis and the focus on protein levels.

Global gene profiling of VCP-associated inclusion body myopathy

Inclusion body myopathy associated with Paget's disease of bone and frontotemporal dementia (IBMPFD) is an autosomal dominant disorder caused by mutations in the Valosin-containing protein (VCP) gene on chromosome 9p12-13. Patients demonstrate limb girdle muscle weakness, which eventually progresses to involve respiratory muscles, and death from respiratory and cardiac failure. This is the first investigation to analyze key molecular mediators and signaling cascades in skeletal muscle causing myopathy by global gene microarray in hopes of understanding the dysregulated genes and molecular mechanisms underlying IBMPFD and the hope of finding novel therapeutic targets. We determined expression profiles using Human Genome Array microarray technology in Vastus lateralis muscles from patients and their first-degree relatives. We analyzed gene annotations by Database for Annotation, Visualization and Integration Discovery and identified differentially dysregulated genes with roles in several novel biological pathways, including regulation of actin cytoskeleton, ErbB signaling, cancer, in addition to regulation of autophagy, and lysosomal signaling, known disrupted pathways in VCP disease. In this report, we present data from the first global microarray analyzing IBMPFD patient muscles and elucidating dysregulated pathways to further understand the pathogenesis of the disease and discover potential therapeutics.

Target deletion of the AAA ATPase PpCDC48II in Physcomitrella patens results in freezing sensitivity after cold acclimation

CDC48 is a highly conserved protein in eukaryotes and belongs to the AAA (ATPase associated with a variety of cellular activities) superfamily. It can interact with many different co-factors and form protein complexes that play important roles in various cellular processes. According to the Physcomitrella patens database, one member of the ATPases, the cell cycle gene PpCDC48II, was cloned. PpCDC48II contains two typical ATPase modules and is highly homologous to AtCDC48A. PpCDC48II was up-regulated in mRNA levels after incubation at 0°C for 36 and 72 h. To further elucidate protein function, we disrupted the PpCDC48II gene by transforming P. patens with the corresponding linear genomic sequences. When treated to the same freezing stress, it was found that PpCDC48II knockout plants were less resistant to freezing treatment than wild type after acclimation. This suggested that PpCDC48II was an essential gene for low-temperature-induced freezing tolerance in P. patens cells.

Critical role of VCP/p97 in the pathogenesis and progression of non-small cell lung carcinoma

Background

Valosin-containing protein (VCP)/p97 is an AAA ATPase molecular chaperone that regulates vital cellular functions and protein-processing. A recent study indicated that VCP expression levels are correlated with prognosis and progression of non-small cell lung carcinoma (NSCLC). We not only verified these findings but also identified the specific role of VCP in NSCLC pathogenesis and progression.

Methodology/Principal Findings

Our results show that VCP is significantly overexpressed in non-small cell lung carcinoma (NSCLC) as compared to normal tissues and cell lines (p<0.001). Moreover, we observed the corresponding accumulation of ubiquitinated-proteins in NSCLC cell lines and tissues as compared to the normal controls. VCP inhibition by si/shRNA or small-molecule (Eeyarestatin I, EerI) significantly (p<0.05, p<0.00007) suppressed H1299 proliferation and migration but induced (p<0.00001) apoptosis. Cell cycle analysis by flow cytometry verified this data and shows that VCP inhibition significantly (p<0.001, p<0.003) induced cell cycle arrest in the G0/G1 phases. We also found that VCP directly regulates p53 and NFκB protein levels as a potential mechanism to control tumor cell proliferation and progression. Finally, we evaluated the therapeutic potential of VCP inhibition and observed significantly reduced NSCLC tumor growth in both in vitro and xenograft murine (athymic-nude) models after EerI treatment (p<0.05).

Conclusions/Significance

Thus, targeting VCP in NSCLC may provide a novel strategy to restore p53 and NFκB levels and ameliorate the growth and tumorigenicity, leading to improved clinical outcomes.

Characterization of the Asian myopathy patients with VCP mutations

BACKGROUND AND PURPOSE

Mutations in the valosin-containing protein (VCP) gene are known to cause inclusion body myopathy with Paget's disease of bone and frontotemporal dementia (IBMPFD) and familial amyotrophic lateral sclerosis (ALS). Despite an increasing number of clinical reports, only one Asian family with IBMPFD has been described.

METHODS

To characterize patients with VCP mutations, we screened a total of 152 unrelated Asian families who were suspected to have rimmed vacuolar myopathy.

RESULTS

We identified VCP mutations in seven patients from six unrelated Asian families. Five different missense mutations were found, including a novel p.Ala439Pro substitution. All patients had adult-onset progressive muscle wasting with variable involvement of axial, proximal, and distal muscles. Two of seven patients were suggested to have mild brain involvement including cerebellar ataxia, and only one showed radiological findings indicating a change in bone. Findings from skeletal muscle indicated mixed neurogenic and myogenic changes, fibers with rimmed vacuoles, and the presence of cytoplasmic and nuclear inclusions. These inclusions were immunopositive for VCP, ubiquitin, transactivation response DNA-binding protein 43, and also histone deacetylase 6 (HDAC6), of which function is regulated by VCP. Evidence of early nuclear and mitochondrial damage was also characteristic.

CONCLUSIONS

  Valosin-containing protein mutations are not rare in Asian patients, and gene analysis should be considered for patients with adult-onset rimmed vacuolar myopathy with neurogenic changes. A wide variety of central and peripheral nervous system symptoms coupled with rare bone abnormalities may complicate diagnosis.

Identification of phosphorylated serine-15 and -82 residues of HSPB1 in 5-fluorouracil-resistant colorectal cancer cells by proteomics

To identify the proteins involved in 5-fluorouracil (5-FU) resistance, a comparison of the total and phosphorylated proteins between the human colorectal cancer (CRC) cell line DLD-1 and its 5-FU-resistant subclone DLD-1/5-FU was performed. Using 2-DE and MALDI-TOF/TOF-based proteomics, 17 up-regulated and 19 down-regulated protein spots were identified in the 5-FU-resistant DLD-1/5-FU cells compared with the parent cell lines. In DLD-1/5-FU cells, 7 anti-apoptotic proteins (HSPB1, proteasome subunit α-5, transitional endoplasmic reticulum ATPase, 14-3-3 β, 14-3-3 γ, 14-3-3 σ, and phosphoglycerate kinase 1) were up-regulated and 4 proapoptotic proteins (cofilin-1, pyruvate kinase M2, glyceraldehyde-3-phosphate dehydrogenase, and nucleophosmin) were down-regulated. The results show that the acquired drug resistance of DLD-1/5-FU cells is caused by the prevention of drug-induced apoptosis, in particular through the enhanced constitutive expression of HSPB1 and its phosphorylated form. Short interfering RNA knockdown of endogenous HSPB1 in DLD-1/5-FU cells restored the sensitivity to 5-FU. Furthermore, MALDI-TOF/TOF and 2-DE Western blot analysis identified the phosphorylated residues of HSPB1 as Ser-15 and Ser-82 in the main (diphosphorylated) form and Ser-15, Ser-78, and Ser-82 in the minor (triphosphorylated) form. The current findings indicate that phosphorylated HSPB1 may play an important role in 5-FU resistance.

The general definition of the p97/valosin-containing protein (VCP)-interacting motif (VIM) delineates a new family of p97 cofactors

Cellular functions of the essential, ubiquitin-selective AAA ATPase p97/valosin-containing protein (VCP) are controlled by regulatory cofactors determining substrate specificity and fate. Most cofactors bind p97 through a ubiquitin regulatory X (UBX) or UBX-like domain or linear sequence motifs, including the hitherto ill defined p97/VCP-interacting motif (VIM). Here, we present the new, minimal consensus sequence RX(5)AAX(2)R as a general definition of the VIM that unites a novel family of known and putative p97 cofactors, among them UBXD1 and ZNF744/ANKZF1. We demonstrate that this minimal VIM consensus sequence is necessary and sufficient for p97 binding. Using NMR chemical shift mapping, we identified several residues of the p97 N-terminal domain (N domain) that are critical for VIM binding. Importantly, we show that cellular stress resistance conferred by the yeast VIM-containing cofactor Vms1 depends on the physical interaction between its VIM and the critical N domain residues of the yeast p97 homolog, Cdc48. Thus, the VIM-N domain interaction characterized in this study is required for the physiological function of Vms1 and most likely other members of the newly defined VIM family of cofactors.

Choice of biological source material supersedes oxidative stress in its influence on DJ-1 in vivo interactions with Hsp90

DJ-1 is a small but relatively abundant protein of unknown function that may undergo stress-dependent cellular translocation and has been implicated in both neurodegenerative diseases and cancer. As such, DJ-1 may be an excellent study object to elucidate the relative influence of the cellular context on its interactome and for exploring whether acute exposure to oxidative stressors alters its molecular environment. Using quantitative mass spectrometry, we conducted comparative DJ-1 interactome analyses from in vivo cross-linked brains or livers and from hydrogen peroxide-treated or naïve embryonic stem cells. The analysis identified a subset of glycolytic enzymes, heat shock proteins 70 and 90, and peroxiredoxins as interactors of DJ-1. Consistent with a role of DJ-1 in Hsp90 chaperone biology, we document destabilization of Hsp90 clients in DJ-1 knockout cells. We further demonstrate the existence of a C106 sulfinic acid modification within DJ-1 and thereby establish that this previously inferred modification also exists in vivo. Our data suggest that caution has to be exerted in interpreting interactome data obtained from a single biological source material and identify a role of DJ-1 as an oxidative stress sensor and partner of a molecular machinery notorious for its involvement in cell fate decisions.

Recent advances in p97/VCP/Cdc48 cellular functions

p97/VCP/Cdc48 is one of the best-characterized type II AAA (ATPases associated with diverse cellular activities) ATPases. p97 is suggested to be a ubiquitin-selective chaperone and its key function is to disassemble protein complexes. p97 is involved in a wide variety of cellular activities. Recently, novel functions, namely autophagy and mitochondrial quality control, for p97 have been uncovered. p97 was identified as a causative factor for inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD) and more recently as a causative factor for amyotrophic lateral sclerosis (ALS). In this review, we will summarize and discuss recent progress and topics in p97 functions and the relationship to its associated diseases.

Cdc48: a power machine in protein degradation

Cdc48 is an essential, highly prominent ATP driven machine in eukaryotic cells. Physiological function of Cdc48 has been found in a multitude of cellular processes, for instance cell cycle progression, homotypic membrane fusion, chromatin remodeling, transcriptional and metabolic regulation, and many others. The molecular function of Cdc48 is arguably best understood in endoplasmic reticulum-associated protein degradation by the ubiquitin proteasome system. In this review, we summarize the general characteristics of Cdc48/p97 and the most recent results on the molecular function of Cdc48 in some of the above processes, which were found to finally end in proteolysis-connected pathways, either involving the proteasome or autophagocytosis-mediated lysosomal degradation.

Neurotoxic 43-kDa TAR DNA-binding protein (TDP-43) triggers mitochondrion-dependent programmed cell death in yeast

Pathological neuronal inclusions of the 43-kDa TAR DNA-binding protein (TDP-43) are implicated in dementia and motor neuron disorders; however, the molecular mechanisms of the underlying cell loss remain poorly understood. Here we used a yeast model to elucidate cell death mechanisms upon expression of human TDP-43. TDP-43-expressing cells displayed markedly increased markers of oxidative stress, apoptosis, and necrosis. Cytotoxicity was dose- and age-dependent and was potentiated upon expression of disease-associated variants. TDP-43 was localized in perimitochondrial aggregate-like foci, which correlated with cytotoxicity. Although the deleterious effects of TDP-43 were significantly decreased in cells lacking functional mitochondria, cell death depended neither on the mitochondrial cell death proteins apoptosis-inducing factor, endonuclease G, and cytochrome c nor on the activity of cell death proteases like the yeast caspase 1. In contrast, impairment of the respiratory chain attenuated the lethality upon TDP-43 expression with a stringent correlation between cytotoxicity and the degree of respiratory capacity or mitochondrial DNA stability. Consistently, an increase in the respiratory capacity of yeast resulted in enhanced TDP-43-triggered cytotoxicity, oxidative stress, and cell death markers. These data demonstrate that mitochondria and oxidative stress are important to TDP-43-triggered cell death in yeast and may suggest a similar role in human TDP-43 pathologies.

Critical role of proteostasis-imbalance in pathogenesis of COPD and severe emphysema

The environmental, genetic, and/or age-related changes in proteostasis induce inflammation, oxidative stress, and apoptosis. We quantified the correlation of protein expression of critical proteostasis mediators to severity of chronic lung disease using lung tissue samples from control and chronic obstructive pulmonary disease (COPD) subjects (GOLD stage 0-IV) and cigarette smoke (CS)-induced murine model. The human bronchial epithelial cells, HEK-293, and Beas2B cells were used for in vitro experiments to verify the mechanisms. Our data verifies the correlation of higher expression of valosin-containing protein (VCP) retrograde translocation complex (VCP-Rma1-gp78) with severity of emphysema in COPD lung tissues and over-expression of inflammatory, ER stress and apoptotic mediators like NFκB, GADD-153/CHOP, and p-eIF2α. Moreover, subjects with severe emphysema had a higher accumulation of ubiquitinated proteins and deubiquitinating enzyme, UCHL-1, indicating towards the aggregation of misfolded or damaged proteins. The modulation of both protein degradation and synthesis rates by CS-extract substantiates the pathogenetic role of proteostasis-imbalance in emphysema and COPD. We identified that VCP also mediates proteasomal degradation of HDAC2 and Nrf2, as a potential mechanism for increased oxidative stress and corticosteroid resistance in COPD subjects with emphysema. Next, we confirmed that higher VCP expression associates with increased inflammation and apoptosis using in vitro and murine models. Our data clearly shows aberrant proteostasis in COPD subjects with severe emphysema. In addition, we evaluate therapeutic efficacy of salubrinal (ER stress inhibitor) to correct the proteostasis-imbalance based on its ability to control VCP expression and ubiquitin accumulation. Overall, our data demonstrate for the first time the critical role of proteostasis-imbalance in pathogenesis of severe emphysema.

The complexities of p97 function in health and disease

p97 is a homohexameric, toroidal machine that harnesses the energy of ATP binding and hydrolysis to effect structural reorganization of a diverse and primarily uncharacterized set of substrate proteins. This action has been linked to endoplasmic reticulum associated degradation (ERAD), homotypic membrane fusion, transcription factor control, cell cycle progression, DNA repair, and post-mitotic spindle disassembly. Exactly how these diverse processes use p97 is not fully understood, but it is clear that binding sites, primarily on the N- and C-domains of p97, facilitate this diversity by coordinating a growing collection of cofactors. These cofactors act at the levels of mechanism, sub-cellular localization, and substrate modification. Another unifying theme is the use of ubiquitylation. Both p97 and many of the associated cofactors have demonstrable ubiquitin-binding competence. The present review will discuss some of the current mechanistic studies and controversies and how these relate to cofactors as well as discussing potential therapeutic targeting of p97.

Copper stress proteomics highlights local adaptation of two strains of the model brown alga Ectocarpus siliculosus

Ectocarpus siliculosus is a cosmopolitan brown alga with capacity to thrive in copper enriched environments. Analysis of copper toxicity was conducted in two strains of E. siliculosus isolated from (i) an uncontaminated coast in southern Peru (Es32) and (ii) a copper polluted rocky beach in northern Chile (Es524). Es32 was more sensitive than Es524, with toxicity detected at 50 microg/L Cu, whereas Es524 displayed negative effects only when exposed to 250 microg/L Cu. Differential soluble proteome profiling for each strain exposed to sub-lethal copper levels allowed to identify the induction of proteins related to processes such as energy production, glutathione metabolism as well as accumulation of HSPs. In addition, the inter-strain comparison of stress-related proteomes led to identify features related to copper tolerance in Es524, such as striking expression of a PSII Mn-stabilizing protein and a Fucoxanthine chlorophyll a-c binding protein. Es524 also expressed specific stress-related enzymes such as RNA helicases from the DEAD box families and a vanadium-dependent bromoperoxidase. These observations were supported by RT-qPCR for some of the identified genes and an enzyme activity assay for vanadium-dependent bromoperoxidase. Therefore, the occurrence of two different phenotypes within two distinct E. siliculosus strains studied at the physiological and proteomic levels strongly suggest that persistent copper stress may represent a selective force leading to the development of strains genetically adapted to copper contaminated sites.

Quantitative proteome profiling of respiratory virus-infected lung epithelial cells

Respiratory virus infections are among the primary causes of morbidity and mortality in humans. Influenza virus, respiratory syncytial virus (RSV), parainfluenza (PIV) and human metapneumovirus (hMPV) are major causes of respiratory illness in humans. Especially young children and the elderly are susceptible to infections with these viruses. In this study we aim to gain detailed insight into the molecular pathogenesis of respiratory virus infections by studying the protein expression profiles of infected lung epithelial cells. A549 cells were exposed to a set of respiratory viruses [RSV, hMPV, PIV and Measles virus (MV)] using both live and UV-inactivated virus preparations. Cells were harvested at different time points after infection and processed for proteomics analysis by 2-dimensional difference gel electrophoresis. Samples derived from infected cells were compared to mock-infected cells to identify proteins that are differentially expressed due to infection. We show that RSV, hMPV, PIV3, and MV induced similar core host responses and that mainly proteins involved in defense against ER stress and apoptosis were affected which points towards an induction of apoptosis upon infection. By 2-D DIGE analyses we have gathered information on the induction of apoptosis by respiratory viruses in A549 cells.

Valosin-containing protein (VCP) in novel feedback machinery between abnormal protein accumulation and transcriptional suppression

Abnormal protein accumulation is often observed in human neurodegenerative disorders such as polyglutamine diseases and Parkinson disease. Genetic and biochemical analyses indicate that valosin-containing protein (VCP) is a crucial molecule in the pathogenesis of human neurodegenerative disorders. We report here that VCP was specifically modified in neuronal cells with abnormal protein accumulation; this modification caused the translocation of VCP into the nucleus. Modification-mimic forms of VCP induced transcriptional suppression with deacetylation of core histones, leading to cell atrophy and the decrease of de novo protein synthesis. Preventing VCP nuclear translocation in polyglutamine-expressing neuronal cells and Drosophila eyes mitigated neurite retraction and eye degenerations, respectively, concomitant with the recovery of core histone acetylation. This represents a novel feedback mechanism that regulates abnormal protein levels in the cytoplasm during physiological processes, as well as in pathological conditions such as abnormal protein accumulation in neurodegenerations.

Quantitative nuclear proteomics identifies mTOR regulation of DNA damage response

Cellular nutritional and energy status regulates a wide range of nuclear processes important for cell growth, survival, and metabolic homeostasis. Mammalian target of rapamycin (mTOR) plays a key role in the cellular responses to nutrients. However, the nuclear processes governed by mTOR have not been clearly defined. Using isobaric peptide tagging coupled with linear ion trap mass spectrometry, we performed quantitative proteomics analysis to identify nuclear processes in human cells under control of mTOR. Within 3 h of inhibiting mTOR with rapamycin in HeLa cells, we observed down-regulation of nuclear abundance of many proteins involved in translation and RNA modification. Unexpectedly, mTOR inhibition also down-regulated several proteins functioning in chromosomal integrity and up-regulated those involved in DNA damage responses (DDRs) such as 53BP1. Consistent with these proteomic changes and DDR activation, mTOR inhibition enhanced interaction between 53BP1 and p53 and increased phosphorylation of ataxia telangiectasia mutated (ATM) kinase substrates. ATM substrate phosphorylation was also induced by inhibiting protein synthesis and suppressed by inhibiting proteasomal activity, suggesting that mTOR inhibition reduces steady-state (abundance) levels of proteins that function in cellular pathways of DDR activation. Finally, rapamycin-induced changes led to increased survival after radiation exposure in HeLa cells. These findings reveal a novel functional link between mTOR and DDR pathways in the nucleus potentially operating as a survival mechanism against unfavorable growth conditions.

Nervous yeast: modeling neurotoxic cell death

Neurodegeneration is characterized by the disease-specific loss of neuronal activity, culminating in the irreversible destruction of neurons. Neuronal cell death can proceed via distinct subroutines such as apoptosis and necrosis, but the underlying molecular mechanisms remain poorly understood. Saccharomyces cerevisiae is an established model for programmed cell death, characterized by distinct cell death pathways conserved from yeast to mammals. Recently, yeast models for several major classes of neurodegeneration, namely alpha-synucleinopathies, polyglutamine disorders, beta-amyloid diseases, tauopathies, and TDP-43 proteinopathies, have been established. Heterologous expression of the human proteins implicated in these disorders has unraveled important insights in their detrimental function, pointing to ways in which yeast might advance the mechanistic dissection of cell death pathways relevant for human neurodegeneration.

Valosin containing protein associated inclusion body myopathy: abnormal vacuolization, autophagy and cell fusion in myoblasts

Inclusion body myopathy associated with Paget's disease and frontotemporal dementia (IBMPFD) is caused by mutations in the valosin containing protein (VCP) gene. The disease is associated with progressive proximal muscle weakness, inclusions and vacuoles in muscle fibers, malfunction in the bone remodeling process resulting in Paget's disease, and premature frontotemporal dementia. VCP is involved in several cellular processes related to the endoplasmic reticulum associated degradation of proteins. To understand the pathological mechanisms underlying the myopathy in IBMPFD, we have studied the cellular consequences of VCP mutations in human primary myoblasts. Our results revealed that patients' myoblasts accumulate large vacuoles. Lysosomal membrane proteins Lamp1 and Lamp2 show increased molecular weights in patients' myoblasts due to differential N-glycosylation. Additionally, mutant myoblasts show increased autophagy when cultured in the absence of nutrients, as well as defective cell fusion and increased apoptosis. Our results elucidate that VCP mutations result in disturbances in several cellular processes, which will help us in the understanding of the pathological mechanisms resulting in muscle weakness and other features of VCP associated disease.

FAS-associated factor 1 (FAF1): diverse functions and implications for oncogenesis

FAS-associated factor 1, FAF1, is an evolutionarily conserved protein that has several protein interaction domains. Although FAF1 was initially identified as a member of the FAS death-inducing signaling complex, subsequent work has revealed that FAF1 functions in diverse biological processes. FAF1 has been shown to play an important role in normal development and neuronal cell survival, whereas FAF1 downregulation may contribute to multiple aspects of tumorigenesis. In particular, there is compelling evidence implicating FAF1 as a tumor suppressor involved in the regulation of apoptosis and NFkappaB activity, as well as in ubiquitination and proteasomal degradation. Here, we highlight FAF1's role in NFkappaB signaling and postulate that this pathway has critical connotations for the pathogenesis and treatment of human cancers.

New approaches to the treatment of frontotemporal lobar degeneration

PURPOSE OF REVIEW

Treatment approaches for frontotemporal lobar degeneration (FTLD) are rapidly evolving with improved understanding of the disease. This brief review highlights recent advances.

RECENT FINDINGS

Early-onset dementia has a devastating impact on families and rids its victims of their most productive and rewarding years. Over the past 10 years, FTLD has emerged as the commonest cause of dementia under the age of 60 years, outstripping even Alzheimer's disease in prevalence. Remarkable progress has occurred in our understanding of FTLD both as a set of distinctive clinical syndromes and as a set of disorders with unique genetic and pathological profiles. Although there are no Food and Drug Administration-approved medications for FTLD, new evidence of specific genetic and neurochemical defects is beginning to provide a strong rationale for pharmacological treatment.

SUMMARY

Behavioral changes, which are common in behavioral variant frontotemporal dementia and semantic dementia, often respond to treatment with selective serotonin reuptake inhibitors. Memantine also holds promise to treat neuropsychiatric symptoms, but more prospective trials are needed.With better understanding of pathogenic molecular pathways involving microtubule-associated protein tau, progranulin and TDP-43, potential disease-modifying therapies are being studied in animal models and approaching human trials.

PGK1, the gene encoding the glycolitic enzyme phosphoglycerate kinase, acts as a multicopy suppressor of apoptotic phenotypes in S. cerevisiae

In a previous paper we reported the construction of a S. cerevisiae strain lacking the essential gene LSM4, which could survive by the introduction of a truncated form of the orthologous gene from Kluyveromyces lactis. This strain showed apoptotic hallmarks and other phenotypes, including an increased sensitivity to caffeine and acetic acid. The suppression of the latter phenotype by overexpressing yeast genes allowed the isolation of PGK1, the gene encoding the glycolytic enzyme phosphoglycerate kinase. This gene restored normal ageing, oxygen peroxide resistance and nuclear integrity in the mutant. Other phenotypes, such as caffeine sensitivity and glycerol utilization, were also suppressed.

Human initiator caspases trigger apoptotic and autophagic phenotypes in Saccharomyces cerevisiae

Caspases are a family of proteases that participate in the progression and execution of the apoptotic program. However, regulation of the caspase activation and their substrates has not yet been fully elucidated. Here we explore the effect of the ectopic expression of the human initiator caspases-8 and -10 in Saccharomyces cerevisiae. Our results showed that the expression of human CASP10 and CASP8 triggers certain apoptotic markers such as a massive production of reactive oxygen species (ROS), chromatin condensation and phosphatidylserine externalization, finally leading to cell death. In response to hydroxyurea (HU), yeast cells expressing caspase-10 did not reduce the replication of DNA and escaped to the intra-S checkpoint of the cell cycle. In addition, caspase-10 expression induced yeast vacuolization and a vacuole-associated phenotype resembling autophagy. Other intracellular alterations such as disorganization of the actin cytoskeleton, cell wall damage, and aberrations within the endoplasmic reticulum lumen were also associated with caspase-10 expression. Furthermore, caspase-induced cell death was completely dependent on the proteolytic activation of the enzyme but, in contrast, was not dependent on either of the endogenous yeast apoptotic proteins Aif1 and Mca1 or the mitochondria.

AAA ATPase p97/VCP: cellular functions, disease and therapeutic potential

p97/VCP, a member of the AAA-ATPase super family, has been associated with a wide variety of essential cellular protein pathways com prising: (i) nuclear envelope reconstruction, (ii) cell cycle, (iii) Golgi reassembly, (iv) suppression of apoptosis and (v) DNA-damage response [1-6]. In addition, vasolin-containing protein (VCP) dislodges the ubiquitinated proteins from the endoplasmic reticulum (ER) and chaperones them to the cytosol for proteasomal degradation by endoplasmic reticulum-associated degradation (ERAD) [7]. The interactions of VCP in the endoplasmic reticulum-associated degradation (ERAD) pathway determine the substrate selection for proteasomal degradation. Moreover, the interaction with VCP is also required for the ubiquitination of substrate. VCP is phosphorylated by the master cellular kinase, Akt as a mechanism to regulate ERAD [8]. These multiple interactions in protein degradation pathways points to central role of VCP in misfolded protein degradation. VCP has a poly-glutamine and ubiquitin-binding capacity and is involved in proteasomal degradation, cytosolic aggregation and processing of polyQ and polyUb aggregates in neurodegenerative and other misfolded protein diseases [9, 10]. Mutations in VCP gene are also linked to a protein deposition disorder, IBMFD [11]. We propose VCP as a therapeutic target for diseases caused by cytosolic protein aggregation or degradation of misfolded protein. We predict that selective interference of VCP interaction(s) with aberrant protein or its ERAD function will be an effective therapeutic site to rescue functional misfolded protein in diseases like cystic fibrosis and alpha-1-trypsin deficiency. The control of VCP expression is also proposed to be a potential therapeutic target in ex-polyQ-induced neurodegenerative diseases [12]. The further functional characterization of VCP and associated proteins in these diseases will help in designing of selective therapeutics.