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CRAC channel activity in C. elegans is mediated by Orai1 and STIM1 homologues and is essential for ovulation and fertility.

The Ca(2+) release-activated Ca(2+) (CRAC) channel is a plasma membrane Ca(2+) entry pathway activated by endoplasmic reticulum (ER) Ca(2+) store depletion. STIM1 proteins function as ER Ca(2+) sensors and regulate CRAC channel activation. Recent studies have demonstrated that CRAC channels are encoded by the human Orai1 gene and a homologous Drosophila gene. C. elegans intestinal cells express a store-operated Ca(2+) channel (SOCC) regulated by STIM-1. We cloned a full-length C. elegans cDNA that encodes a 293 amino acid protein, ORAI-1, homologous to human and Drosophila Orai1 proteins. ORAI-1 GFP reporters are co-expressed with STIM-1 in the gonad and intestine. Inositol 1,4,5-trisphosphate (IP(3))-dependent Ca(2+) signalling regulates C. elegans gonad function, fertility and rhythmic posterior body wall muscle contraction (pBoc) required for defecation. RNA interference (RNAi) silencing of orai-1 expression phenocopies stim-1 knockdown and causes sterility and prevents intestinal cell SOCC activation, but has no effect on pBoc or intestinal Ca(2+) signalling. Orai-1 RNAi suppresses pBoc defects induced by intestinal expression of a STIM-1 Ca(2+)-binding mutant, indicating that the proteins function in a common pathway. Co-expression of stim-1 and orai-1 cDNAs in HEK293 cells induces large inwardly rectifying cation currents activated by ER Ca(2+) depletion. The properties of this current recapitulate those of the native SOCC current. We conclude that C. elegans expresses bona fide CRAC channels that require the function of Orai1- and STIM1-related proteins. CRAC channels thus arose very early in animal evolution. In C. elegans, CRAC channels do not play obligate roles in all IP(3)-dependent signalling processes and ER Ca(2+) homeostasis. Instead, we suggest that CRAC channels carry out highly specialized and cell-specific signalling roles and that they may function as a failsafe mechanism to prevent Ca(2+) store depletion under pathophysiological and stress conditions.

Amino Acid Sequence↗

Polycation-mediated delivery of siRNAs for prophylaxis and treatment of influenza virus infection.

Influenza A virus causes one of the most prevalent infections in humans. In a typical year, 10-20% of the population of the US is infected by influenza virus, resulting in up to 40,000 deaths and 200,000 hospitalisations. Vaccination is the most effective preventative measure that can protect 70-90% of healthy adults aged < 65; however, the protection rate is much lower in those most susceptible to infection, namely infants, the elderly and individuals with weakened immune systems. Although four drugs have been approved by the FDA for use as prophylaxis and/or treatment of influenza, concerns about their side effects and the emergence of drug-resistant viruses persist. RNA interference (RNAi), an emerging method of post transcriptional gene silencing, appears ideal for the prevention and treatment of influenza. RNAi in mammals can be mediated by short interfering RNAs (siRNAs) of approximately 21-27 nucleotides in length. The authors have previously shown that siRNAs specific for conserved regions of the influenza virus genome are potent inhibitors of influenza virus replication in both cell lines and chicken embryos. This review discusses the recent progress in the in vivo inhibition of influenza virus by the delivery of siRNAs mediated by non-viral vectors, and the prospects of this strategy for prophylaxis and treatment of influenza infection in humans.

Animals↗

RNA interference machinery regulates chromosome dynamics during mitosis and meiosis in fission yeast.

The regulation of higher-order chromosome structure is central to cell division and sexual reproduction. Heterochromatin assembly at the centromeres facilitates both kinetochore formation and sister chromatid cohesion, and the formation of specialized chromatin structures at telomeres serves to maintain the length of telomeric repeats, to suppress recombination, and to aid in formation of a bouquet-like structure that facilitates homologous chromosome pairing during meiosis. In fission yeast, genes encoding the Argonaute, Dicer, and RNA-dependent RNA polymerase factors involved in RNA interference (RNAi) are required for heterochromatin formation at the centromeres and mating type region. In this study, we examine the effects of deletions of the fission yeast RNAi machinery on chromosome dynamics during mitosis and meiosis. We find that the RNAi machinery is required for the accurate segregation of chromosomes. Defects in mitotic chromosome segregation are correlated with loss of cohesin at centromeres. Although the telomeres of RNAi mutants maintain silencing, length, and localization of the heterochromatin protein Swi6, we discovered defects in the proper clustering of telomeres in interphase mitotic cells. Furthermore, a small proportion of RNAi mutant cells display aberrant telomere clustering during meiotic prophase. This study demonstrates that the fission yeast RNAi machinery is required for the proper regulation of chromosome architecture during mitosis and meiosis.

Chromosomes, Fungal↗

Potent and specific inhibition of human immunodeficiency virus type 1 replication by RNA interference.

Synthetic small interfering RNAs (siRNAs) have been shown to induce the degradation of specific mRNA targets in human cells by inducing RNA interference (RNAi). Here, we demonstrate that siRNA duplexes targeted against the essential Tat and Rev regulatory proteins encoded by human immunodeficiency virus type 1 (HIV-1) can specifically block Tat and Rev expression and function. More importantly, we show that these same siRNAs can effectively inhibit HIV-1 gene expression and replication in cell cultures, including those of human T-cell lines and primary lymphocytes. These observations demonstrate that RNAi can effectively block virus replication in human cells and raise the possibility that RNAi could provide an important innate protective response, particularly against viruses that express double-stranded RNAs as part of their replication cycle.

Cell Line↗

Dehydroascorbate transport in human chondrocytes is regulated by hypoxia and is a physiologically relevant source of ascorbic acid in the joint.

OBJECTIVE: To evaluate the dehydroascorbate (DHA) transport mechanisms in human chondrocytes. METHODS: The transport of L-(14)C-DHA in human chondrocytes was analyzed under various conditions, including the use of RNA interference (RNAi), to determine the role of glucose transporter 1 (GLUT-1) and GLUT-3 in L-14C-DHA transport and to evaluate the effects of physiologically relevant oxygen tensions on L-14C-DHA transport. In order to estimate the contributions of reduced ascorbic acid (AA) and DHA to intracellular ascorbic acid (Asc), the quantities of AA and DHA were measured in synovial fluid samples from osteoarthritis (OA) patients and compared with the reported levels in rheumatoid arthritis (RA) patients. RESULTS: DHA transport in human chondrocytes was glucose-sensitive, temperature-dependent, cytochalasin B-inhibitable, modestly stereoselective for L-DHA, and up-regulated by low oxygen tension. Based on the RNAi results, GLUT-1 mediated, at least in part, the uptake of DHA, whereas GLUT-3 had a minimal effect on DHA transport. DHA constituted a mean 8% of the total Asc in the synovial fluid of OA joints, in contrast to 80% of the reported total Asc in RA joints. CONCLUSION: We provide the first evidence that chondrocytes transport DHA via the GLUTs and that this transport mechanism is modestly selective for L-DHA. In the setting of up-regulated DHA transport at low oxygen tensions, DHA would contribute 26% of the total intracellular Asc in OA chondrocytes and 94% of that in RA chondrocytes. These results demonstrate that DHA is a physiologically relevant source of Asc for chondrocytes, particularly in the setting of an inflammatory arthritis, such as RA.

Arthritis, Rheumatoid↗

Inhibition of respiratory viruses by nasally administered siRNA.

Respiratory syncytial virus (RSV) and parainfluenza virus (PIV) are two respiratory pathogens of paramount medical significance that exert high mortality. At present, there is no reliable vaccine or antiviral drug against either virus. Using an RNA interference (RNAi) approach, we show that individual as well as joint infection by RSV and PIV can be specifically prevented and inhibited by short interfering RNAs (siRNAs), instilled intranasally in the mouse, with or without transfection reagents. The degree of protection matched the antiviral activity of the siRNA in cell culture, allowing an avenue for quick screening of an efficacious siRNA. When targeting both viruses in a joint infection, excess of one siRNA moderated the inhibitory effect of the other, suggesting competition for the RNAi machinery. Our results suggest that, if properly designed, low dosages of inhaled siRNA might offer a fast, potent and easily administrable antiviral regimen against respiratory viral diseases in humans.

Animals↗

Silencing expression of UO-44 (CUZD1) using small interfering RNA sensitizes human ovarian cancer cells to cisplatin in vitro.

Ovarian cancer is currently the second leading cause of gynecological malignancy and cisplatin or cisplatin-based regimens have been the standard of care for the treatment of advance epithelial ovarian cancers. However, the efficacy of cisplatin treatment is often limited by the development of drug resistance either through the inhibition of apoptotic genes or activation of antiapoptotic genes. We have previously reported the overexpression of human UO-44 (HuUO-44) in ovarian cancers and the HuUO-44 antisera markedly inhibited NIH-OVCAR3 ovarian cancer cell attachment and proliferation (Oncogene 23: 5707-5718, 2004). In the present study, we observed through the cancer cell line profiling array that the expression of HuUO-44 was suppressed in the ovarian cancer cell line (SKOV-3) after treatment with several chemotherapeutic drugs. Similarly, this suppression in HuUO-44 expression was also correlated to the cisplatin sensitivity in two other ovarian cancer cell lines NIH-OVCAR3 and OV-90 in a dose-dependent manner. To elucidate the function of HuUO-44 in cisplatin chemoresistance in ovarian cancer cell, small interfering RNAs (siRNAs) were employed to mediate HuUO-44 silencing in ovarian cancer cell line, NIH-OVCAR3. HuUO-44 RNA interference (RNAi) resulted in the inhibition of cell growth and proliferation. Importantly, HuUO-44 RNAi significantly increased sensitivity of NIH-OVCAR3 to cytotoxic stress induced by cisplatin (P<0.01). Strikingly, we have also demonstrated that overexpression of HuUO-44 significantly conferred cisplatin resistance in NIH-OVCAR3 cells (P<0.05). Taken together, UO-44 is involved in conferring cisplatin resistance; the described HuUO-44-specific siRNA oligonucleotides that can potently silence HuUO-44 gene expression may prove to be valuable pretreatment targets for antitumor therapy or other pathological conditions that involves aberrant HuUO-44 expression.

Base Sequence↗

The Trypanosoma brucei cyclin, CYC2, is required for cell cycle progression through G1 phase and for maintenance of procyclic form cell morphology.

CYC2 is an essential PHO80-like cyclin that forms a complex with the cdc2-related kinase CRK3 in Trypanosoma brucei. In both procyclic and bloodstream form T. brucei, knock-down of CYC2 by RNA interference (RNAi) led to an accumulation of cells in G(1) phase. Additionally, in procyclic cells, but not in bloodstream form cells, CYC2 RNAi induced a specific cell elongation at the posterior end. The G(1) block, as well as the posterior end elongation in the procyclic form, was irreversible once established. Staining for tyrosinated alpha-tubulin and morphometric analyses showed that the posterior end elongation occurred through active microtubule extension, with no repositioning of the kinetoplast. Hence, these cells can be classified as exhibiting the "nozzle" phenotype as has been described for cells that ectopically express TbZFP2, a zinc finger protein that is involved in the differentiation of the bloodstream form to procyclic form. Within the tsetse fly, procyclic trypanosomes differentiate to elongated mesocyclic cells. However, although mesocyclic trypanosomes isolated from tsetse flies also show active microtubule extension at the posterior end, the kinetoplast is coincidentally repositioned such that it always lies approximately midway between the nucleus and posterior end of the cell. Thus, in the procyclic form CYC2 has dual functionality and is required for both cell cycle progression through G(1) and for the maintenance of correct cell morphology, whereas in the bloodstream form only a role for CYC2 in G(1) progression is evident.

Animals↗

Altered expression of G(q/11alpha) protein shapes mGlu1 and mGlu5 receptor-mediated single cell inositol 1,4,5-trisphosphate and Ca(2+) signaling.

The metabotropic glutamate (mGlu) receptors mGlu1 and mGlu5 mediate distinct inositol 1,4,5-trisphosphate (IP(3)) and Ca(2+) signaling patterns, governed in part by differential mechanisms of feedback regulation after activation. Single cell imaging has shown that mGlu1 receptors initiate sustained elevations in IP(3) and Ca(2+), which are sensitive to agonist concentration. In contrast, mGlu5 receptors are subject to cyclical PKC-dependent uncoupling and consequently mediate coincident IP(3) and Ca(2+) oscillations that are largely independent of agonist concentration. In this study, we investigated the contribution of G(q/11)alpha protein expression levels in shaping mGlu1/5 receptor-mediated IP(3) and Ca(2+) signals, using RNA interference (RNAi). RNAi-mediated knockdown of G(q/11)alpha almost abolished the single-cell increase in IP(3) caused by mGlu1 and mGlu5 receptor activation. For the mGlu1 receptor, this unmasked baseline Ca(2+) oscillations that persisted even at maximal agonist concentrations. mGlu5 receptor-activated Ca(2+) oscillations were still observed but were only initiated at high agonist concentrations. Recombinant overexpression of G(q)alpha enhanced IP(3) signals after mGlu1 and mGlu5 receptor activation. It is noteworthy that although mGlu5 receptor-mediated IP(3) and Ca(2+) oscillations in control cells were largely insensitive to agonist concentration, increasing G(q)alpha expression converted these oscillatory signatures to sustained plateau responses in a high proportion of cells. In addition to modulating temporal Ca(2+) signals, up- or down-regulation of G(q/11)alpha expression alters the threshold for the concentration of glutamate at which a measurable Ca(2+) signal could be detected. These experiments indicate that altering G(q/11)alpha expression levels differentially affects spatiotemporal aspects of IP(3) and Ca(2+) signaling mediated by the mGlu1 and mGlu5 receptors.

Animals↗

MicroRNA-dependent localization of targeted mRNAs to mammalian P-bodies.

Small RNAs, including small interfering RNAs (siRNAs) and microRNAs (miRNAs) can silence target genes through several different effector mechanisms. Whereas siRNA-directed mRNA cleavage is increasingly understood, the mechanisms by which miRNAs repress protein synthesis are obscure. Recent studies have revealed the existence of specific cytoplasmic foci, referred to herein as processing bodies (P-bodies), which contain untranslated mRNAs and can serve as sites of mRNA degradation. Here we demonstrate that Argonaute proteins--the signature components of the RNA interference (RNAi) effector complex, RISC--localize to mammalian P-bodies. Moreover, reporter mRNAs that are targeted for translational repression by endogenous or exogenous miRNAs become concentrated in P-bodies in a miRNA-dependent manner. These results provide a link between miRNA function and mammalian P-bodies and suggest that translation repression by RISC delivers mRNAs to P-bodies, either as a cause or as a consequence of inhibiting protein synthesis.

3' Untranslated Regions↗

Spindle dynamics and the role of gamma-tubulin in early Caenorhabditis elegans embryos.

gamma-Tubulin is a ubiquitous and highly conserved component of centrosomes in eukaryotic cells. Genetic and biochemical studies have demonstrated that gamma-tubulin functions as part of a complex to nucleate microtubule polymerization from centrosomes. We show that, as in other organisms, Caenorhabditis elegans gamma-tubulin is concentrated in centrosomes. To study centrosome dynamics in embryos, we generated transgenic worms that express GFP::gamma-tubulin or GFP::beta-tubulin in the maternal germ line and early embryos. Multiphoton microscopy of embryos produced by these worms revealed the time course of daughter centrosome appearance and growth and the differential behavior of centrosomes destined for germ line and somatic blastomeres. To study the role of gamma-tubulin in nucleation and organization of spindle microtubules, we used RNA interference (RNAi) to deplete C. elegans embryos of gamma-tubulin. gamma-Tubulin (RNAi) embryos failed in chromosome segregation, but surprisingly, they contained extensive microtubule arrays. Moderately affected embryos contained bipolar spindles with dense and long astral microtubule arrays but with poorly organized kinetochore and interpolar microtubules. Severely affected embryos contained collapsed spindles with numerous long astral microtubules. Our results suggest that gamma-tubulin is not absolutely required for microtubule nucleation in C. elegans but is required for the normal organization and function of kinetochore and interpolar microtubules.

Amino Acid Sequence↗

Germline and developmental roles of the nuclear transport factor importin alpha3 in C. elegans.

The importin alpha family of transport factors mediates the nuclear import of classical nuclear localization signal-containing proteins. In order to understand how multiple importin alpha proteins are regulated both in individual cells and in a whole organism, the three importin alpha (ima) genes of Caenorhabditis elegans have been identified and studied. All three IMAs are expressed in the germline; however, only IMA-3 is expressed in the soma. RNA interference (RNAi) experiments demonstrate that IMA-3 is required for the progression of meiotic prophase I during oocyte development. Loss of IMA-3 expression leads also to a disruption of the nuclear pore complex accompanied by the mis-localization of P granules. A range of defects occurring in ima-3(RNAi) F1 progeny further supports a role for IMA-3 during embryonic and larval development. The functional association of IMA-3 with distinct cellular events, its expression pattern and intracellular localization indicate that regulation of the nuclear transport machinery is involved in the control of developmental pathways.

Amino Acid Sequence↗

Stearylated octaarginine and artificial virus-like particles for transfection of siRNA into primary rat neurons.

RNA interference (RNAi) provides a powerful experimental tool for sequence-specific gene silencing, allowing efficient analysis of gene function in a multitude of cell types. However, application of RNAi in primary mammalian neurons has been limited by low-transfection efficiency and considerable toxicity of conventional transfection methods. In this study, we evaluated a peptide-mediated and a polymer/lipid-based cellular delivery method for siRNA into rat primary neurons and compared the results with a commonly used liposomal transfection reagent. Stearylated octaarginine (Stearyl-R8) was used as polypeptide and artificial virus-like particles (AVPs) were used as a combined liposomal-polymeric vector, since both reagents have been previously shown to successfully transfect DNA into cell lines. Stearyl-R8 and AVPs both promoted siRNA transfection into primary hippocampal neurons via the endosomal pathway. SiRNA-mediated gene silencing could be effectively induced in primary neuron cultures. In comparison with the commonly used cationic liposome transfection agent, both novel reagents were less detrimental to cell metabolic activity. We conclude that these novel transfection methods yield performances comparable to cationic liposome-mediated transfection for siRNA, while being less cytotoxic in primary neurons. Stearyl-R8 and AVPs may therefore represent novel and more cost-efficient alternatives to conventional siRNA-transfection reagents.

Animals↗

The hematopoietic isoform of Cas-Hef1-associated signal transducer regulates chemokine-induced inside-out signaling and T cell trafficking.

Leukocyte migration and trafficking is dynamically regulated by various chemokine and adhesion molecules and is vital to the proper function of the immune system. We describe a role for the Cas and Hef-1-associated signal transducer in hematopoietic cells (Chat-H) as a critical regulator of T lymphocyte migration, by using lentivirus-mediated RNA interference (RNAi). Impaired migration of Chat-H-depleted cells coincided with defective inside-out signaling shown by diminished chemokine-induced activation of the Rap-1 GTPase and integrin-mediated adhesion. Localization of Chat-H to the plasma membrane, association with its binding partner Crk-associated substrate in lymphocytes (CasL), and Chat-H-mediated CasL serine-threonine phosphorylation were required for T cell migration. These results identify Chat-H as a critical signaling intermediate acting upstream of Rap1 to regulate chemokine-induced adhesion and migration.

Adaptor Proteins, Signal Transducing↗

Poly(A) binding protein (PABP) homeostasis is mediated by the stability of its inhibitor, Paip2.

The poly(A)-binding protein (PABP) is a unique translation initiation factor in that it binds to the mRNA 3' poly(A) tail and stimulates recruitment of the ribosome to the mRNA at the 5' end. PABP activity is tightly controlled by the PABP-interacting protein 2 (Paip2), which inhibits translation by displacing PABP from the mRNA. Here, we describe a close interplay between PABP and Paip2 protein levels in the cell. We demonstrate a mechanism for this co-regulation that involves an E3 ubiquitin ligase, EDD, which targets Paip2 for degradation. PABP depletion by RNA interference (RNAi) causes co-depletion of Paip2 protein without affecting Paip2 mRNA levels. Upon PABP knockdown, Paip2 interacts with EDD, which leads to Paip2 ubiquitination. Supporting a critical role for EDD in Paip2 degradation, knockdown of EDD expression by siRNA leads to an increase in Paip2 protein stability. Thus, we demonstrate that the turnover of Paip2 in the cell is mediated by EDD and is regulated by PABP. This mechanism serves as a homeostatic feedback to control the activity of PABP in cells.

Feedback, Physiological↗

Dicer-deficient mouse embryonic stem cells are defective in differentiation and centromeric silencing.

Dicer is the enzyme that cleaves double-stranded RNA (dsRNA) into 21-25-nt-long species responsible for sequence-specific RNA-induced gene silencing at the transcriptional, post-transcriptional, or translational level. We disrupted the dicer-1 (dcr-1) gene in mouse embryonic stem (ES) cells by conditional gene targeting and generated Dicer-null ES cells. These cells were viable, despite being completely defective in RNA interference (RNAi) and the generation of microRNAs (miRNAs). However, the mutant ES cells displayed severe defects in differentiation both in vitro and in vivo. Epigenetic silencing of centromeric repeat sequences and the expression of homologous small dsRNAs were markedly reduced. Re-expression of Dicer in the knockout cells rescued these phenotypes. Our data suggest that Dicer participates in multiple, fundamental biological processes in a mammalian organism, ranging from stem cell differentiation to the maintenance of centromeric heterochromatin structure and centromeric silencing.

Animals↗

Translation of a small subset of Caenorhabditis elegans mRNAs is dependent on a specific eukaryotic translation initiation factor 4E isoform.

The mRNA cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) participates in protein synthesis initiation, translational repression of specific mRNAs, and nucleocytoplasmic shuttling. Multiple isoforms of eIF4E are expressed in a variety of organisms, but their specific roles are poorly understood. We investigated one Caenorhabditis elegans isoform, IFE-4, which has homologues in plants and mammals. IFE-4::green fluorescent protein (GFP) was expressed in pharyngeal and tail neurons, body wall muscle, spermatheca, and vulva. Knockout of ife-4 by RNA interference (RNAi) or a null mutation produced a pleiotropic phenotype that included egg-laying defects. Sedimentation analysis demonstrated that IFE-4, but not IFE-1, was present in 48S initiation complexes, indicating that it participates in protein synthesis initiation. mRNAs affected by ife-4 knockout were determined by DNA microarray analysis of polysomal distribution. Polysome shifts, in the absence of total mRNA changes, were observed for only 33 of the 18,967 C. elegans mRNAs tested, of which a disproportionate number were related to egg laying and were expressed in neurons and/or muscle. Translational regulation was confirmed by reduced levels of DAF-12, EGL-15, and KIN-29. The functions of these proteins can explain some phenotypes observed in ife-4 knockout mutants. These results indicate that translation of a limited subset of mRNAs is dependent on a specific isoform of eIF4E.

Alleles↗

Loss of the human polycomb group protein BMI1 promotes cancer-specific cell death.

The polycomb group protein BMI1 has been shown to support normal stem cell proliferation via its putative stem cell factor function, but it is not known if BMI1 may also act as a cancer stem cell factor to promote cancer development. To determine the role of human BMI1 in cancer growth and survival, we performed a loss-of-function analysis of BMI1 by RNA interference (RNAi) in both normal and malignant human cells. Our results indicate that BMI1 is crucial for the short-term survival of cancer cells but not of normal cells. We also demonstrated that loss of BMI1 was more effective in suppressing cancer cell growth than retinoid-treatment, and surviving cancer cells showed significantly reduced tumorigenicity. The cancer-specific growth retardation was mediated by an increased level of apoptosis and a delayed cell cycle progression due to the loss of BMI1. By comparison, BMI1 deficiency caused only a moderate inhibition of the cell cycle progression in normal lung cells. In both normal and cancer cells, the loss of BMI1 led to an upregulation of INK4A-ARF, but with no significant effect on the level of telomerase gene expression, suggesting that other BMI1-cooperative factors in addition to INK4A-ARF activation may be involved in the BMI1-dependent cancer-specific growth retardation. Thus, human BMI1 is critical for the short-term survival of cancer cells, and inhibition of BMI1 has minimal effect on the survival of normal cells. These findings provide a foundation for developing a cancer-specific therapy targeting BMI1.

Apoptosis↗