Noncanonical control of C. elegans germline apoptosis by the insulin/IGF-1 and Ras/MAPK signaling pathways

Neuronal IL-17 controls Caenorhabditis elegans developmental diapause through CEP-1/p53

During metazoan development, how cell division and metabolic programs are coordinated with nutrient availability remains unclear. Here, we show that nutrient availability signaled by the neuronal cytokine, ILC-17.1, switches Caenorhabditis elegans development between reproductive growth and dormancy by controlling the activity of the tumor suppressor p53 ortholog, CEP-1. Specifically, upon food availability, ILC-17.1 signaling by amphid neurons promotes glucose utilization and suppresses CEP-1/p53 to allow growth. In the absence of ILC-17.1, CEP-1/p53 is activated, up-regulates cell-cycle inhibitors, decreases phosphofructokinase and cytochrome C expression, and causes larvae to arrest as stress-resistant, quiescent dauers. We propose a model whereby ILC-17.1 signaling links nutrient availability and energy metabolism to cell cycle progression through CEP-1/p53. These studies describe ancestral functions of IL-17 s and the p53 family of proteins and are relevant to our understanding of neuroimmune mechanisms in cancer. They also reveal a DNA damage-independent function of CEP-1/p53 in invertebrate development and support the existence of a previously undescribed C. elegans dauer pathway.

SIN-3 functions through multi-protein interaction to regulate apoptosis, autophagy, and longevity in Caenorhabditis elegans

SIN3/HDAC is a multi-protein complex that acts as a regulatory unit and functions as a co-repressor/co-activator and a general transcription factor. SIN3 acts as a scaffold in the complex, binding directly to HDAC1/2 and other proteins and plays crucial roles in regulating apoptosis, differentiation, cell proliferation, development, and cell cycle. However, its exact mechanism of action remains elusive. Using the Caenorhabditis elegans (C. elegans) model, we can surpass the challenges posed by the functional redundancy of SIN3 isoforms. In this regard, we have previously demonstrated the role of SIN-3 in uncoupling autophagy and longevity in C. elegans. In order to understand the mechanism of action of SIN3 in these processes, we carried out a comparative analysis of the SIN3 protein interactome from model organisms of different phyla. We identified conserved, expanded, and contracted gene classes. The C. elegans SIN-3 interactome -revealed the presence of  well-known proteins, such as DAF-16, SIR-2.1, SGK-1, and AKT-1/2, involved in autophagy, apoptosis, and longevity. Overall, our analyses propose  potential mechanisms by which SIN3 participates in multiple biological processes and their conservation across species and identifies candidate genes for further experimental analysis.

Alternative polyadenylation is a determinant of oncogenic Ras function

Alternative polyadenylation of mRNA has important but poorly understood roles in development and cancer. Activating mutations in the Ras oncogene are common drivers of many human cancers. From a screen for enhancers of activated Ras (let-60) in Caenorhabditis elegans, we identified cfim-1, a subunit of the alternative polyadenylation machinery. Ablation of cfim-1 increased penetrance of the multivulva phenotype in let-60/Ras gain-of-function (gf) mutants. Depletion of the human cfim-1 ortholog CFIm25/NUDT21 in cancer cells with KRAS mutations increased their migration and stimulated an epithelial-to-mesenchymal transition. CFIm25-depleted cells and cfim-1 mutants displayed biased placement of poly(A) tails to more proximal sites in many conserved transcripts. Functional analysis of these transcripts identified the multidrug resistance protein mrp-5/ABCC1 as a previously unidentified regulator of C. elegans vulva development and cell migration in human cells through alternative 3′UTR usage. Our observations demonstrate a conserved functional role for alternative polyadenylation in oncogenic Ras function.

Oocyte aging is controlled by mitogen-activated protein kinase signaling

Oogenesis is one of the first processes to fail during aging. In women, most oocytes cannot successfully complete meiotic divisions already during the fourth decade of life. Studies of the nematode Caenorhabditis elegans have uncovered conserved genetic pathways that control lifespan, but our knowledge regarding reproductive aging in worms and humans is limited. Specifically, little is known about germline internal signals that dictate the oogonial biological clock. Here, we report a thorough characterization of the changes in the worm germline during aging. We found that shortly after ovulation halts, germline proliferation declines, while apoptosis continues, leading to a gradual reduction in germ cell numbers. In late aging stages, we observed that meiotic progression is disturbed and crossover designation and DNA double-strand break repair decrease. In addition, we detected a decline in the quality of mature oocytes during aging, as reflected by decreasing size and elongation of interhomolog distance, a phenotype also observed in human oocytes. Many of these altered processes were previously attributed to MAPK signaling variations in young worms. In support of this, we observed changes in activation dynamics of MPK-1 during aging. We therefore tested the hypothesis that MAPK controls oocyte quality in aged worms using both genetic and pharmacological tools. We found that in mutants with high levels of activated MPK-1, oocyte quality deteriorates more rapidly than in wild-type worms, whereas reduction of MPK-1 levels enhances quality. Thus, our data suggest that MAPK signaling controls germline aging and could be used to attenuate the rate of oogenesis quality decline.

Modeling human brain tumors in flies, worms, and zebrafish: From proof of principle to novel therapeutic targets

For decades, cell biologists and cancer researchers have taken advantage of non-murine species to increase our understanding of the molecular processes that drive normal cell and tissue development, and when perturbed, cause cancer. The advent of whole-genome sequencing has revealed the high genetic homology of these organisms to humans. Seminal studies in non-murine organisms such as Drosophila melanogaster, Caenorhabditis elegans, and Danio rerio identified many of the signaling pathways involved in cancer. Studies in these organisms offer distinct advantages over mammalian cell or murine systems. Compared to murine models, these three species have shorter lifespans, are less resource intense, and are amenable to high-throughput drug and RNA interference screening to test a myriad of promising drugs against novel targets. In this review, we introduce species-specific breeding strategies, highlight the advantages of modeling brain tumors in each non-mammalian species, and underscore the successes attributed to scientific investigation using these models. We conclude with an optimistic proposal that discoveries in the fields of cancer research, and in particular neuro-oncology, may be expedited using these powerful screening tools and strategies.

RPA complexes in Caenorhabditis elegans meiosis; unique roles in replication, meiotic recombination and apoptosis

Replication Protein A (RPA) is a critical complex that acts in replication and promotes homologous recombination by allowing recombinase recruitment to processed DSB ends. Most organisms possess three RPA subunits (RPA1, RPA2, RPA3) that form a trimeric complex critical for viability. The Caenorhabditis elegans genome encodes RPA-1, RPA-2 and an RPA-2 paralog RPA-4. In our analysis, we determined that RPA-2 is critical for germline replication and normal repair of meiotic DSBs. Interestingly, RPA-1 but not RPA-2 is essential for somatic replication, in contrast to other organisms that require both subunits. Six different hetero- and homodimeric complexes containing permutations of RPA-1, RPA-2 and RPA-4 can be detected in whole animal extracts. Our in vivo studies indicate that RPA-1/4 dimer is less abundant in the nucleus and its formation is inhibited by RPA-2. While RPA-4 does not participate in replication or recombination, we find that RPA-4 inhibits RAD-51 filament formation and promotes apoptosis of a subset of damaged nuclei. Altogether these findings point to sub-functionalization and antagonistic roles of RPA complexes in C. elegans.

DNA repair, recombination, and damage signaling

DNA must be accurately copied and propagated from one cell division to the next, and from one generation to the next. To ensure the faithful transmission of the genome, a plethora of distinct as well as overlapping DNA repair and recombination pathways have evolved. These pathways repair a large variety of lesions, including alterations to single nucleotides and DNA single and double-strand breaks, that are generated as a consequence of normal cellular function or by external DNA damaging agents. In addition to the proteins that mediate DNA repair, checkpoint pathways have also evolved to monitor the genome and coordinate the action of various repair pathways. Checkpoints facilitate repair by mediating a transient cell cycle arrest, or through initiation of cell suicide if DNA damage has overwhelmed repair capacity. In this chapter, we describe the attributes of Caenorhabditis elegans that facilitate analyses of DNA repair, recombination, and checkpoint signaling in the context of a whole animal. We review the current knowledge of C. elegans DNA repair, recombination, and DNA damage response pathways, and their role during development, growth, and in the germ line. We also discuss how the analysis of mutational signatures in C. elegans is helping to inform cancer mutational signatures in humans.

DNA Damaged Induced Cell Death in Oocytes

The production of haploid gametes through meiosis is central to the principle of sexual reproduction. The genetic diversity is further enhanced by exchange of genetic material between homologous chromosomes by the crossover mechanism. This mechanism not only requires correct pairing of homologous chromosomes but also efficient repair of the induced DNA double-strand breaks. Oocytes have evolved a unique quality control system that eliminates cells if chromosomes do not correctly align or if DNA repair is not possible. Central to this monitoring system that is conserved from nematodes and fruit fly to humans is the p53 protein family, and in vertebrates in particular p63. In mammals, oocytes are stored for a long time in the prophase of meiosis I which, in humans, can last more than 50 years. During the entire time of this arrest phase, the DNA damage checkpoint remains active. The treatment of female cancer patients with DNA damaging irradiation or chemotherapeutics activates this checkpoint and results in elimination of the oocyte pool causing premature menopause and infertility. Here, we review the molecular mechanisms of this quality control system and discuss potential therapeutic intervention for the preservation of the oocyte pool during chemotherapy.

The Function of NM23-H1/NME1 and Its Homologs in Major Processes Linked to Metastasis

Metastasis suppressor genes (MSGs) inhibit different biological processes during metastatic progression without globally influencing development of the primary tumor. The first MSG, NM23 (non-metastatic clone 23, isoform H1) or now called NME1 (stands for non-metastatic) was identified some decades ago. Since then, ten human NM23 paralogs forming two groups have been discovered. Group I NM23 genes encode enzymes with evolutionarily highly conserved nucleoside diphosphate kinase (NDPK) activity. In this review we summarize how results from NDPKs in model organisms converged on human NM23 studies. Next, we examine the role of NM23-H1 and its homologs within the metastatic cascade, e.g. cell migration and invasion, proliferation and apoptosis. NM23-H1 homologs are well known inhibitors of cell migration. Drosophila studies revealed that AWD, the fly counterpart of NM23-H1 is a negative regulator of cell motility by modulating endocytosis of chemotactic receptors on the surface of migrating cells in cooperation with Shibire/Dynamin; this mechanism has been recently confirmed by human studies. NM23-H1 inhibits proliferation of tumor cells by phosphorylating the MAPK scaffold, kinase suppressor of Ras (KSR), resulting in suppression of MAPK signalling. This mechanism was also observed with the C. elegans homolog, NDK-1, albeit with an inverse effect on MAPK activation. Both NM23-H1 and NDK-1 promote apoptotic cell death. In addition, NDK-1, NM23-H1 and their mouse counterpart NM23-M1 were shown to promote phagocytosis in an evolutionarily conserved manner. In summary, inhibition of cell migration and proliferation, alongside actions in apoptosis and phagocytosis are all mechanisms through which NM23-H1 acts against metastatic progression.

MPK-1/ERK pathway regulates DNA damage response during development through DAF-16/FOXO

Ultraviolet (UV) induces distorting lesions to the DNA that can lead to stalling of the RNA polymerase II (RNAP II) and that are removed by transcription-coupled nucleotide excision repair (TC-NER). In humans, mutations in the TC-NER genes CSA and CSB lead to severe postnatal developmental defects in Cockayne syndrome patients. In Caenorhabditis elegans, mutations in the TC-NER genes csa-1 and csb-1, lead to developmental growth arrest upon UV treatment. We conducted a genetic suppressor screen in the nematode to identify mutations that could suppress the developmental defects in csb-1 mutants. We found that mutations in the ERK1/2 MAP kinase mpk-1 alleviate the developmental retardation in TC-NER mutants, while constitutive activation of the RAS-MAPK pathway exacerbates the DNA damage-induced growth arrest. We show that MPK-1 act via insulin/insulin-like signaling pathway and regulates the FOXO transcription factor DAF-16 to mediate the developmental DNA damage response.

A conserved CCM complex promotes apoptosis non-autonomously by regulating zinc homeostasis

Apoptotic death of cells damaged by genotoxic stress requires regulatory input from surrounding tissues. The C. elegans scaffold protein KRI-1, ortholog of mammalian KRIT1/CCM1, permits DNA damage-induced apoptosis of cells in the germline by an unknown cell non-autonomous mechanism. We reveal that KRI-1 exists in a complex with CCM-2 in the intestine to negatively regulate the ERK-5/MAPK pathway. This allows the KLF-3 transcription factor to facilitate expression of the SLC39 zinc transporter gene zipt-2.3, which functions to sequester zinc in the intestine. Ablation of KRI-1 results in reduced zinc sequestration in the intestine, inhibition of IR-induced MPK-1/ERK1 activation, and apoptosis in the germline. Zinc localization is also perturbed in the vasculature of krit1-/- zebrafish, and SLC39 zinc transporters are mis-expressed in Cerebral Cavernous Malformations (CCM) patient tissues. This study provides new insights into the regulation of apoptosis by cross-tissue communication, and suggests a link between zinc localization and CCM disease.

MiR-35 buffers apoptosis thresholds in the C. elegans germline by antagonizing both MAPK and core apoptosis pathways

Apoptosis is a genetically programmed cell death process with profound roles in development and disease. MicroRNAs modulate the expression of many proteins and are often deregulated in human diseases, such as cancer. C. elegans germ cells undergo apoptosis in response to genotoxic stress by the combined activities of the core apoptosis and MAPK pathways, but how their signalling thresholds are buffered is an open question. Here we show mir-35–42 miRNA family play a dual role in antagonizing both NDK-1, a positive regulator of MAPK signalling, and the BH3-only pro-apoptotic protein EGL-1 to regulate the magnitude of DNA damage-induced apoptosis in the C. elegans germline. We show that while miR-35 represses EGL-1 by promoting transcript degradation, repression of NDK-1 may be through sequestration of the transcript to inhibit translation. Importantly, dramatic increase in NDK-1 expression was observed in cells about to die. In the absence of miR-35, increased NDK-1 activity enhanced MAPK signalling that lead to significant increases in germ cell death. Our findings demonstrate that NDK-1 acts upstream of (or in parallel to) EGL-1, and that miR-35 targets both egl-1 and ndk-1 to fine-tune cell killing in response to genotoxic stress.

A miR-511-binding site SNP in the 3'UTR of IGF-1 gene is associated with proliferation and apoptosis of PK-15 cells

Insulin-like growth factor-1 (IGF-1) is a functional candidate gene for pig growth and development due to its crucial role in the growth axis of growth hormone-IGF-1. Considering that the 3' untranslated region (3'UTR) of gene may affect its expression, we analyzed the effect of a single-nucleotide polymorphism (SNP) (rs34142920, c.674C > T) on gene expression, cell proliferation, and apoptosis and the possible related molecular mechanisms in PK-15 cells. The SNP was found in the 3'UTR of IGF-1 in Bama Xiang pig in previous investigations. Results showed that the SNP was located at the target site binding to microRNA (miR-511). The 3'UTR of IGF-1 gene with C allele significantly downregulated the expression of IGF-1 gene compared with that of the gene with T allele by luciferase assay. miR-511 was transfected into porcine kidney cell line (PK-15 cells) to reveal its effects on cells and whether or not it targets IGF-1. The expression levels of IGF-1 at mRNA and protein levels were remarkably downregulated. miR-511 significantly inhibited cell proliferation and promoted cell apoptosis by downregulating the phosphorylation level of AKT and ERK1/2. This finding confirmed that miR-511 inhibits proliferation and promotes apoptosis by downregulating the IGF-1 in PK-15 cells.

BRAP-2 promotes DNA damage induced germline apoptosis in C. elegans through the regulation of SKN-1 and AKT-1

As part of the DNA damage response (DDR) network, the tumour suppressor Breast cancer susceptibility gene 1 (BRCA1) is activated to facilitate DNA repair, transcription and cell cycle control. BRC-1, the Caenorhabditis elegans ortholog of BRCA1, has conserved function in DNA double strand break repair, wherein a loss of brc-1 results in high levels of germline apoptosis. BRAP2/IMP was initially identified as a BRCA1 associated binding protein and previously we have shown that the C. elegans brap-2 deletion mutant experiences BRC-1 dependent larval arrest when exposed to low concentrations of paraquat. Since BRC-1 function in the germline is conserved, we wanted to determine the role of BRAP-2 in DNA damage induced germline apoptosis in C. elegans. We examined levels of germ cell death following DNA damage and found that brap-2(ok1492) mutants display reduced levels of germline apoptosis when compared to the wild type, and the loss of brap-2 significantly reduced germ cell death in brc-1 mutant animals. We also found increased mRNA levels of skn-1 following DNA damage in brap-2 mutants and that skn-1 RNAi knockdown in brap-2;brc-1 double mutants and a loss of pmk-1 mutation in brap-2 mutants increased apoptosis to wild type levels, indicating that brap-2 promotion of cell survival requires PMK-1 and SKN-1. Since mammalian BRAP2 has been shown to bind the AKT phosphatase PHLPP1/2, it suggests that BRAP2 could be involved in the Insulin/Insulin-like growth factor Signaling (IIS) pathway. We found that this interaction is conserved between the C. elegans homologs and that a loss of akt-1 in brap-2 mutants increased germline apoptosis. Thus in response to DNA damage, our findings suggest that BRAP-2 is required to attenuate the pro-cell survival signals of AKT-1 and PMK-1/SKN-1 to promote DNA damage induced germline apoptosis.

Cysteine protease cathepsin B mediates radiation-induced bystander effects

Radiation-induced bystander effects (RIBE) refer to a unique process, in which factors released by irradiated cells or tissues exert effects on other parts of the animal not exposed to radiation, causing genomic instability, stress responses, and altered apoptosis or cell proliferation^1–3. Despite important implications in radioprotection, radiation safety and radiotherapy, the molecular identities of RIBE factors and their mechanisms of action remain elusive. Here we use C. elegans as an animal model to study RIBE and have identified a cysteine protease CPR-4, a human cathepsin B homolog, as the first RIBE factor in nematodes. CPR-4 is secreted from animals irradiated with ultraviolet (UV) or ionizing gamma rays (IR) and is the major factor in the conditioned medium that leads to inhibition of cell death and increased embryonic lethality in unirradiated animals. Moreover, CPR-4 causes these effects and stress response at unexposed sites distal to the irradiated tissue. The activity of CPR-4 is regulated by the p53 homolog cep-1 in response to radiation and CPR-4 appears to act through the insulin-like growth factor receptor, DAF-2, to exert RIBE. Our study provides critical insights into the elusive RIBE and will facilitate identification of additional RIBE factors and their mechanisms of action.

Worms on the spectrum - C. elegans models in autism research

The small non-parasitic nematode Caenorhabditis elegans is widely used in neuroscience thanks to its well-understood development and lineage of the nervous system. Furthermore, C. elegans has been used to model many human developmental and neurological conditions to better understand disease mechanisms and identify potential therapeutic strategies. Autism spectrum disorder (ASD) is the most prevalent of all neurodevelopmental disorders, and the C. elegans system may provide opportunities to learn more about this complex disorder. Since basic cell biology and biochemistry of the C. elegans nervous system is generally very similar to mammals, cellular or molecular phenotypes can be investigated, along with a repertoire of behaviours. For instance, worms have contributed greatly to the understanding of mechanisms underlying mutations in genes coding for synaptic proteins such as neuroligin and neurexin. Using worms to model neurodevelopmental disorders like ASD is an emerging topic that harbours great, untapped potential. This review summarizes the numerous contributions of C. elegans to the field of neurodevelopment and introduces the nematode system as a potential research tool to study essential roles of genes associated with ASD.

The Adverse Effects of Triptolide on the Reproductive System of Caenorhabditis elegans: Oogenesis Impairment and Decreased Oocyte Quality

Previous studies have revealed that Triptolide damages female reproductive capacity, but the mechanism is unclear. In this study, we used Caenorhabditis elegans to investigate the effects of Triptolide on the germline and explore its possible mechanisms. Our data show that exposure for 4 h to 50 and 100 mg/L Triptolide reduced C. elegans fertility, led to depletion and inactivation of spermatids with the changes in the expression levels of related genes, and increased the number of unfertilized oocytes through damaging chromosomes and DNA damage repair mechanisms. After 24 and 48 h of the 4 h exposure to 50 and 100 mg/L Triptolide, we observed shrink in distal tip cells, an increase in the number of apoptotic cells, a decrease in the number of mitotic germ cells and oocytes in diakinesis stage, and chromatin aggregates in -1 oocytes. Moreover, expression patterns of the genes associated with mitotic germ cell proliferation, apoptosis, and oocyte quality were altered after Triptolide exposure. Therefore, Triptolide may damage fertility of nematodes by hampering the development of oocytes at different developmental stages. Alterations in the expression patterns of genes involved in oocyte development may explain the corresponding changes in oocyte development in nematodes exposed to Triptolide.

Bisphenol A exposure triggers apoptosis via three signaling pathways in Caenorhabditis elegans

Bisphenol A can trigger germline apoptosis via three signaling pathways including DNA damage response (DDR) pathway, mitogen-activated protein kinase (MAPK) cascades and insulin-like growth factor-1 (IGF-1) network in Caenorhabditis elegans.

Establishment of Time- and Cell-Specific RNAi in Caenorhabditis elegans

The nematode worm Caenorhabditis elegans, in which loss-of-function mutants and RNA interference (RNAi) models are available, is a model organism useful for analyzing effects of genes on various life phenomena. In particular, RNAi is a powerful tool that enables time- or cell-specific knockdown via heat shock-inducible RNAi or cell-specific RNAi. However, the conventional RNAi methods are insufficient for investigating pleiotropic genes with various sites of action and life stage-dependent functions. To investigate the temporal- and cell-specific profiles of multifunctional genes, we established a new RNAi method that enables simultaneous time- and cell-specific knockdown (T.C.RNAi) in C. elegans. In this method, one RNA strand is expressed by a cell-specific promoter and the other by a heat shock promoter, resulting in only expression of double-stranded RNA in the target cell when heat shock is induced. We confirmed the effect of T.C.RNAi by the knockdown of GFP and the odr-3 gene which encodes Gα and is essential for olfaction. Further, this technique revealed that the control of glutamate receptors GLR-1 localization in RMD motor neurons requires Ras at the adult stage to regulate locomotion behavior.

Run-on of germline apoptosis promotes gonad senescence in C. elegans

Aging (senescence) includes causal mechanisms (etiologies) of late-life disease, which remain poorly understood. According to the recently proposed hyperfunction theory, based on the older theory of antagonistic pleiotropy, senescent pathologies can arise from futile, post-reproductive run-on of processes that in early life promote fitness. Here we apply this idea to investigate the etiology of senescent pathologies in the reproductive system of Caenorhabditis elegans hermaphrodites, particularly distal gonad degeneration and disintegration. Hermaphrodite germ cells frequently undergo "physiological" (non-damage-induced) apoptosis (PA) to provision growing oocytes. Run-on of such PA is a potential cause of age-related gonad degeneration. We document the continuation of germline apoptosis in later life, and report that genetically blocking or increasing PA retards or accelerates degeneration, respectively. In wild-type males, which lack germ line apoptosis, gonad disintegration does not occur. However, mutational induction of PA in males does not lead to gonad disintegration. These results suggest that as germ-cell proliferation rate declines markedly in aging hermaphrodites (but not males), run-on of PA becomes a pathogenic mechanism that promotes gonad degeneration. This illustrates how hyperfunction, or non-adaptive run-on in later life of a process that promotes fitness in early life, can promote atrophic senescent pathology in C. elegans.

Your neighbours matter - non-autonomous control of apoptosis in development and disease

Traditionally, the regulation of apoptosis has been thought of as an autonomous process in which the dying cell dictates its own demise. However, emerging studies in genetically tractable multicellular organisms, such as Caenorhabditis elegans and Drosophila, have revealed that death is often a communal event. Here, we review the current literature on non-autonomous mechanisms governing apoptosis in multiple cellular contexts. The importance of the cellular community in dictating the funeral arrangements of apoptotic cells has profound implications in development and disease.

Helicobacter pylori modulates host cell survival regulation through the serine-threonine kinase, 3-phosphoinositide dependent kinase 1 (PDK-1)

BACKGROUND

Helicobacter pylori (H. pylori) infection affects cell survival signaling pathways including cell apoptosis and proliferation, which are considered risk factors for the development of gastric cancer when unregulated. In the present study, we investigated the effect of H. pylori infection on the phosphorylation state of 3-phosphoinositide-dependent kinase-1 (PDK-1), a master kinase that regulates phosphorylation of Akt (also known as protein kinase B, PKB) and cell survival.

METHODS

The activity of PDK-1 was examined in human gastric epithelial cells incubated in the presence or absence of different H. pylori strains. In addition, the role of H. pylori type IV secretion system and the mechanism of H. pylori effect on PDK-1 activity was examined.

RESULTS

In the presence of H. pylori, phosphorylation of the activation loop (serine 241) PDK-1 was rapidly lost suggesting that dephosphorylation of PDK-1 is a target for H. pylori to modulate cell survival. The extent of dephosphorylation was strain dependent with H. pylori 60190 being the most effective. H. pylori infection of gastric epithelial cells resulted in altered phosphorylation and degradation of Akt, suggesting that PDK-1 dephosphorylation affects cell survival pathways and thereby may contribute to disease pathogenesis.

CONCLUSION

We propose that dephosphorylation of PDK-1 and the resulting changes to Akt phosphorylation is one of the mechanisms by which infection with H. pylori alter the balance between apoptosis and cell proliferation and identify a host molecular mechanism regulated by H. pylori that ultimately contributes to carcinogenesis. Our studies therefore provide insights into one of the mechanisms by which H. pylori infection contributes to gastric cancer by regulating the activity of a cell survival signaling pathway.

Developmental Coordination of Gamete Differentiation with Programmed Cell Death in Sporulating Yeast

The gametogenesis program of the budding yeast Saccharomyces cerevisiae, also known as sporulation, employs unusual internal meiotic divisions, after which all four meiotic products differentiate within the parental cell. We showed previously that sporulation is typically accompanied by the destruction of discarded immature meiotic products through their exposure to proteases released from the mother cell vacuole, which undergoes an apparent programmed rupture. Here we demonstrate that vacuolar rupture contributes to de facto programmed cell death (PCD) of the meiotic mother cell itself. Meiotic mother cell PCD is accompanied by an accumulation of depolarized mitochondria, organelle swelling, altered plasma membrane characteristics, and cytoplasmic clearance. To ensure that the gametes survive the destructive consequences of developing within a cell that is executing PCD, we hypothesized that PCD is restrained from occurring until spores have attained a threshold degree of differentiation. Consistent with this hypothesis, gene deletions that perturb all but the most terminal postmeiotic spore developmental stages are associated with altered PCD. In these mutants, meiotic mother cells exhibit a delay in vacuolar rupture and then appear to undergo an alternative form of PCD associated with catastrophic consequences for the underdeveloped spores. Our findings reveal yeast sporulation as a context of bona fide PCD that is developmentally coordinated with gamete differentiation.

Effects of microgravity on DNA damage response in Caenorhabditis elegans during Shenzhou-8 spaceflight

PURPOSE

Space radiations and microgravity both could cause DNA damage in cells, but the effects of microgravity on DNA damage response to space radiations are still controversial.

MATERIALS AND METHODS

A mRNA microarray and microRNA micro- array in dauer larvae of Caenorhabditis elegans (C. elegans) that endured spaceflight environment and space radiations environment during 16.5-day Shenzhou-8 space mission was performed.

RESULTS

Twice as many transcripts significantly altered in the spaceflight environment than space radiations alone. The majority of alterations were related to protein amino acid dephosphorylation and histidine metabolic and catabolic processes. From about 900 genes related to DNA damage response, 38 differentially expressed genes were extracted; most of them differentially expressed under spaceflight environment but not space radiations, although the identical directions of alteration were observed in both cases. cel-miR-81, cel- miR-82, cel-miR-124 and cel-miR-795 were predicted to regulate DNA damage response through four different anti-correlated genes.

CONCLUSIONS

Evidence was provided that, in the presence of space radiations, microgravity probably enhanced the DNA damage response in C. elegans by integrating the transcriptome and microRNome.

Effects of PLCE1 gene silencing by RNA interference on cell cycling and apoptosis in esophageal carcinoma cells

Esophageal squamous cell carcinoma (ESCC) is one of the most malignancies with a poor prognosis. The phospholipase C? gene (PLCE1) encodes a novel ras-related protein effector mediating the effects of R-Ras on the actin cytoskeleton and membrane protrusion. However, molecular mechanisms pertinent to ESCC are unclear. We therefore designed PLCE1-special small interfering RNA and transfected to esophageal squamous cell (EC) 9706 cells to investigate the effects of PLCE1 gene silencing on the cell cycle and apoptosis of ESCC and indicate its important role in the development of ESCC. Esophageal cancer tissue specimens and normal esophageal mucosa were obtained and assayed by immunohistochemical staining to confirm overexpression of PLCE1 in neoplasias. Fluorescence microscopy was used to examine transfection efficiency, while the result of PLCE1 silencing was examined by reverse transcription (RT-PCR). Flow cytometry and annexin V apoptosis assays were used to assess the cell cycle and apoptosis, respectively. Expression of cyclin D1 and caspase-3 was detected by Western-blotting. The level of PLCE1 protein in esophageal cancer tissue was significantly higher than that in normal tissue. After transfection, the expression of PLCE1 mRNA in EC 9706 was significantly reduced, compared with the control group. Furthermore, flow cytometry results suggested that the PLCE1 gene silencing arrested the cell cycle in the G0/G1 phase; apoptosis was significantly higher than in the negative control group and mock group. PLCE1 gene silencing by RNAi resulted in decreased expression of cyclin D1 and increased expression of caspase-3. Our study suggests that PLCE1 may be an oncogene and play an important role in esophageal carcinogenesis through regulating proteins which control cell cycling and apoptosis.

A role for Ras in inhibiting circular foraging behavior as revealed by a new method for time and cell-specific RNAi

BACKGROUND

The nematode worm Caenorhabditis elegans, in which loss-of-function mutants and RNA interference (RNAi) models are available, is a model organism useful for analyzing effects of genes on various life phenomena, including behavior. In particular, RNAi is a powerful tool that enables time- or cell-specific knockdown via heat shock-inducible RNAi or cell-specific RNAi. However, conventional RNAi is insufficient for investigating pleiotropic genes with various sites of action and life stage-dependent functions.

RESULTS

Here, we investigated the Ras gene for its role in exploratory behavior in C. elegans. We found that, under poor environmental conditions, mutations in the Ras-MAPK signaling pathway lead to circular locomotion instead of normal exploratory foraging. Spontaneous foraging is regulated by a neural circuit composed of three classes of neurons: IL1, OLQ, and RMD, and we found that Ras functions in this neural circuit to modulate the direction of locomotion. We further observed that Ras plays an essential role in the regulation of GLR-1 glutamate receptor localization in RMD neurons. To investigate the temporal- and cell-specific profiles of the functions of Ras, we developed a new RNAi method that enables simultaneous time- and cell-specific knockdown. In this method, one RNA strand is expressed by a cell-specific promoter and the other by a heat shock promoter, resulting in only expression of double-stranded RNA in the target cell when heat shock is induced. This technique revealed that control of GLR-1 localization in RMD neurons requires Ras at the adult stage. Further, we demonstrated the application of this method to other genes.

CONCLUSIONS

We have established a new RNAi method that performs simultaneous time- and cell-specific knockdown and have applied this to reveal temporal profiles of the Ras-MAPK pathway in the control of exploratory behavior under poor environmental conditions.

Caspase-activated phosphoinositide binding by CNT-1 promotes apoptosis by inhibiting the AKT pathway

Inactivation of cell survival factors is a crucial step in apoptosis. The phosphoinositide 3 kinase (PI3K) and AKT signaling pathway promotes cell growth, proliferation and survival and its deregulation causes cancer. How this pathway is suppressed to promote apoptosis is poorly understood. Here we report the identification of a CED-3 caspase substrate in C. elegans, CNT-1, that upon cleavage by CED-3 during apoptosis activates an N-terminal phosphoinositide-binding fragment (tCNT-1), which translocates from cytoplasm to plasma membrane to block AKT binding to phosphatidylinositol (3,4,5)-triphosphate (PIP₃), thereby disabling AKT activation and its pro-survival activity. Our findings reveal a new mechanism that negatively regulates AKT cell signaling to promote apoptosis and that may restrict cell growth and proliferation in normal cells.

Molecular control of arsenite-induced apoptosis in Caenorhabditis elegans: roles of insulin-like growth factor-1 signaling pathway

Apoptosis is one of the main cellular processes in responses to arsenic, the well known environmental carcinogen. By using the nematode Caenorhabditis elegans as an in vivo model, we found that insulin-like growth factor-1 networks and their target protein DAF-16/FOXO, known as key regulators of energy metabolism and growth, played important roles in arsenite-induced apoptosis. Inactivation of DAF-2, AGE-1 and AKT-1 caused worms more susceptible to arsenite-induced apoptosis, which could be attenuated by DAF-16 knockout. Worms with inactivated AKT-2 and SGK-1 or with constitutively activated PDK-1 and AKT-1 showed low levels of apoptosis, which could be elevated by DAF-16 mutation. Our results demonstrated that DAF-2/IGF-1R, AGE-1/PI3K, PDK-1/PDK1 and AKT-1/PKB negatively regulated the arsenite-induced apoptosis, whereas AKT-2 and SGK-1 acted proapoptotically. DAF-16/FOXO antagonized IGF-1 signals in signaling the arsenite-induced apoptosis, and apoptosis promoted by DAF-16 inactivation was attributed to its higher sensitivity to oxidative stress.

LIN-3/EGF promotes the programmed cell death of specific cells in Caenorhabditis elegans by transcriptional activation of the pro-apoptotic gene egl-1

Programmed cell death (PCD) is the physiological death of a cell mediated by an intracellular suicide program. Although key components of the PCD execution pathway have been identified, how PCD is regulated during development is poorly understood. Here, we report that the epidermal growth factor (EGF)-like ligand LIN-3 acts as an extrinsic signal to promote the death of specific cells in Caenorhabditis elegans. The loss of LIN-3 or its receptor, LET-23, reduced the death of these cells, while excess LIN-3 or LET-23 signaling resulted in an increase in cell deaths. Our molecular and genetic data support the model that the LIN-3 signal is transduced through LET-23 to activate the LET-60/RAS-MPK-1/ERK MAPK pathway and the downstream ETS domain-containing transcription factor LIN-1. LIN-1 binds to, and activates transcription of, the key pro-apoptotic gene egl-1, which leads to the death of specific cells. Our results provide the first evidence that EGF induces PCD at the whole organism level and reveal the molecular basis for the death-promoting function of LIN-3/EGF. In addition, the level of LIN-3/EGF signaling is important for the precise fine-tuning of the life-versus-death fate. Our data and the previous cell culture studies that say EGF triggers apoptosis in some cell lines suggest that the EGF-mediated modulation of PCD is likely conserved in C. elegans and humans.

Programmed cell death (PCD) is an evolutionarily conserved cellular process that is important for metazoan development and homeostasis. The epidermal growth factor (EGF) promotes cell proliferation, differentiation and survival during animal development. Surprisingly, we found that the EGF-like ligand LIN-3 also promotes the death of specific cells in Caenorhabditis elegans. We found that the LIN-3/EGF signal can be secreted from a cell to facilitate the demise of cells at a distance by activating the transcription of the PCD-promoting gene egl-1 in the doomed cells through the transcription factor LIN-1. LIN-1 binds to the egl-1 promoter in vitro and is positively regulated by the LIN-3/EGF, LET-23/EGF receptor, and the downstream MAPK signaling pathway. To our knowledge, LIN-3/EGF is the first extrinsic signal that has been shown to regulate the intrinsic PCD machinery during C. elegans development. In addition, the transcription factor LIN-31, which binds to LIN-1 and acts downstream of LIN-3/EGF, LET-23/EGF receptor, and the MAPK signaling pathway during vulval development, is dispensable for PCD. Thus, LIN-3/EGF promotes cell proliferation, differentiation, and PCD through common downstream signaling molecules but acts via distinct sets of transcription factors for different target gene expression.

Analysis of apoptosis in Caenorhabditis elegans

The nematode worm Caenorhabditis elegans has provided researchers with a wealth of information on the molecular mechanisms controlling programmed cell death (apoptosis). Its genetic tractability, optical clarity, and relatively short lifespan are key advantages for rapid assessment of apoptosis in vivo. The use of forward and reverse genetics methodology, coupled with in vivo imaging, has provided deep insights into how a multicellular organism orchestrates the self-destruction of specific cells during development and in response to exogenous stresses. Strains of C. elegans carrying mutations in the core elements of the apoptotic pathway, or in tissue-specific regulators of apoptosis, can be used for genetic analyses to reveal conserved mechanisms by which apoptosis is regulated in the somatic and reproductive (germline) tissue. Here we present an introduction to the study of apoptosis in C. elegans, including current techniques for visualization, analysis, and screening.

Immunostaining for markers of apoptosis in the Caenorhabditis elegans germline

The transparency of Caenorhabditis elegans makes it an ideal organism for visualizing proteins by immunofluorescence microscopy; however, the tough cuticle of worms and the egg shell surrounding embryos pose challenges in achieving effective fixation so that antibodies can diffuse into cells. In this protocol, we describe immunostaining of apoptosis-related proteins in the C. elegans adult germline using fluorescent reagents. Protein localization and abundance can be determined in various mutant backgrounds and under a variety of conditions, such as exposure to genotoxic stress. The number of antibodies specific to C. elegans proteins is quite limited compared with other organisms, but there is a growing list of immunological reagents directed against proteins in other organisms that cross-react with the homologous C. elegans proteins.

Ribosome synthesis and MAPK activity modulate ionizing radiation-induced germ cell apoptosis in Caenorhabditis elegans

Synthesis of ribosomal RNA by RNA polymerase I (RNA pol I) is an elemental biological process and is key for cellular homeostasis. In a forward genetic screen in C. elegans designed to identify DNA damage-response factors, we isolated a point mutation of RNA pol I, rpoa-2(op259), that leads to altered rRNA synthesis and a concomitant resistance to ionizing radiation (IR)-induced germ cell apoptosis. This weak apoptotic IR response could be phenocopied when interfering with other factors of ribosome synthesis. Surprisingly, despite their resistance to DNA damage, rpoa-2(op259) mutants present a normal CEP-1/p53 response to IR and increased basal CEP-1 activity under normal growth conditions. In parallel, rpoa-2(op259) leads to reduced Ras/MAPK pathway activity, which is required for germ cell progression and physiological germ cell death. Ras/MAPK gain-of-function conditions could rescue the IR response defect in rpoa-2(op259), pointing to a function for Ras/MAPK in modulating DNA damage-induced apoptosis downstream of CEP-1. Our data demonstrate that a single point mutation in an RNA pol I subunit can interfere with multiple key signalling pathways. Ribosome synthesis and growth-factor signalling are perturbed in many cancer cells; such an interplay between basic cellular processes and signalling might be critical for how tumours evolve or respond to treatment.

Methods for detection and analysis of apoptosis signaling in the C. elegans germline

This review assesses current and emerging methods for the detection, and analysis of apoptosis in the Caenorhabditis elegans germline. The nematode worm C. elegans is highly tractable to genetic manipulation, making it an excellent model for elucidating mechanisms of apoptosis signaling in a multicellular setting. Here we profile the most efficacious fluorescent tools to visualize and quantify germline apoptosis. We focus specifically on the application of fluorescent markers to screen by RNAi for genes and pathways that regulate germline apoptosis under normal conditions or in response to genotoxic stress. We also present the limitations of these methods, and suggest complimentary techniques in order that researchers new to the field can comprehensively assess apoptosis phenotypes in the C. elegans germline.

Autophagy induced by silibinin protects human epidermoid carcinoma A431 cells from UVB-induced apoptosis

Ultraviolet B (UVB) in the sun light is a major cause of skin damage, which accompanies complex alterations in irradiated skin cells, including DNA lesions, oxidative stress, inflammation and caspase activation. The protection against UVB damage requires multiple interruptions such as repair of the DNA lesions, scavenging of the reactive oxygen species (ROS), repression of the inflammation and others. Silibinin is suggested as an anti-UVB reagent, but the underlying mechanisms have not been fully elucidated. In this study, we found a role of autophagy in the anti-UVB effect of silibinin in A431 cells. Autophagy was reduced after UVB-irradiation while restored by silibinin through the suppression of the IGF-1R signalling pathway. The protective effect of silibinin in UVB-irradiated A431 cells was further enhanced by pre-treatment with an autophagy inducer, rapamycin, while it was reversed by an autophagy inhibitor, wortmannin, indicating that elevated autophagy contributed to the cell survival. Consistently, cell apoptosis was augmented by siRNAs targeting Beclin 1 and Atg5, supporting the hypothesis that autophagy induced by silibinin plays a protective role against UVB-induced epidermal apoptosis.

Interference of silibinin with IGF-1R signalling pathways protects human epidermoid carcinoma A431 cells from UVB-induced apoptosis

Ultraviolet B (UVB) from sunlight is a major cause of cutaneous lesion. Silibinin, a traditional hepatic protectant, elicits protective effects against UVB-induced cellular damage. In A431 cells, the insulin-like growth factor-1 receptor (IGF-1R) was markedly up-regulated by UVB irradiation. The activation of the IGF-1R signalling pathways contributed to apoptosis of the cells rather than rescuing the cells from death. Up-regulated IGF-1R stimulated downstream mitogen-activated protein kinases (MAPKs), such as c-Jun N-terminal kinases (JNK) and extracellular signal-regulated protein kinases 1/2 (ERK1/2). The subsequent activation of caspase-8 and caspase-3 led to apoptosis. The activation of IGF-1R signalling pathways is the cause of A431 cell death. The pharmacological inhibitors and the small interfering RNA (siRNA) targeting IGF-1R suppressed the downstream activation of JNK/ERK-caspases to help the survival of the UVB-irradiated A431 cells. Indeed, silibinin treatment suppressed the IGF-1R-JNK/ERK pathways and thus protected the cells from UVB-induced apoptosis.