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PubMed2005

Establishment of a screening system for selection of siRNA target sites directed against hepatitis B virus surface gene.

To study the inhibitory effects of plasmid-derived small interfering RNA (siRNA) and synthetic siRNA on the expression of the hepatitis B virus surface (HBs) gene, three plasmid-derived siRNAs and one synthetic siRNA that complement the coding region of the HBs gene were prepared. The HBs expression plasmid pHBs-EGFP was also constructed. HeLa cells were co-transfected with pHBs-EGFP and the above siRNAs. The HBs mRNA quantities were measured by reverse-transcription PCR, and the level of HBs-EGFP fusion protein was quantified by fluorescent microscope. The concentrations of the hepatitis B virus surface antigen (HBsAg) derived from the culture supernatant of transfected HepG2.2.15 cells were measured by an enzyme-linked immunosorbent assay (ELISA) kit. The results showed that the three plasmid-derived siRNAs and the synthetic siRNA can effectively reduce the quantities of HBs mRNA and protein. The plasmid-derived siRNA psiRNA1 was found to be the most effective inhibitor of HBs expression. It can inhibit HBs-EGFP expression by 63.3% and suppress HBs mRNA by 75.6%. To further substantiate the above observations, psiRNA1 was transfected into HepG2.2.15 cells (an HBV secreting cell line). The transfections resulted in almost complete blockage of HBsAg production, whereas control vector-transfected cells secreted high levels of HBsAg 7 days post-transfection. In conclusion, our data suggests that RNA interference (RNAi) is an efficient approach for reducing the level of HBs transcripts and proteins and for suppressing HBsAg production.

Base Sequence↗
PubMed2006

[Mitosis arrest caused by inhibition of PLK1 expression in gastric cancer MKN45 cells].

OBJECTIVE: To observe the effect of polo-like kinase 1 (PLK1) gene depletion on mitosis phenotype and elucidate its vital role in gastric cancer cell line (MKN45) mitosis. METHODS: The PLK1 expression in MKN45 cells was blocked by RNA interference (RNAi), the expression level of PLK1 mRNA and protein were measured by real-time quantitative PCR and Western blot, respectively. The morphological change of microtubules and mitosis phenotype in MKN45 cells were observed by immunofluorescence staining and laser confocal microscopy, the morphological changes of cells were observed by reverse microscopy, the variation of cell cycle distribution was detected by flow-cytometry. RESULTS: After RNAi targeting PLK1, PLK1 mRNA and protein level decreased obviously, the cell microtubules became obscure and lost cohesiveness, the mitosis phenotype also varied substantially (P < 0.05), more gastric cancer cells became rounded and showed G(2) phase cell DNA content (P < 0.05). CONCLUSION: PLK1 gene plays a key role in mitosis and its inhibition can lead to mitosis arrest in MKN45 cells.

Adenocarcinoma↗
PubMed2005

Effects on proliferation and melanogenesis by inhibition of mutant BRAF and expression of wild-type INK4A in melanoma cells.

Activating BRAF mutations and loss of wild-type INK4A expression both occur at high frequencies in melanomas. Here, we present evidence that BRAF and INK4A have different effects on melanogenesis, a marker of melanocytic differentiation. Human melanoma cell line 624Mel harbors mutations in both BRAF and INK4A. The in vitro and in vivo growth of these cells was inhibited by either reduced expression of mutant BRAF using stable retroviral RNA interference (RNAi) or retrovirus-mediated stable expression of wild-type INK4A cDNA. Consistent with the observed growth inhibition, phosphorylation of S780 and S795 in pRB, both CDK4/6 targets, was suppressed in cells expressing either mutant BRAF RNAi or wild-type INK4A. Interestingly, melanoma cells expressing mutant BRAF RNAi had increased pigmentation, produced more mature melanosomes and melanin and expressed higher levels of tyrosinase and tyrosinase-related protein-1, whereas melanogenesis was not induced by wild-type INK4A. We found that the melanocyte lineage-specific master control protein microphthalmia-associated transcription factor was upregulated by inhibition of mutant BRAF, which may be the cause for the melanogenic effect of BRAF RNAi. The results suggest that, although both BRAF and INK4A lesions promote cell growth and tumor formation, mutant BRAF may also induce dedifferentiation in melanoma cells.

Animals↗
PubMed2004

Interplay between Drosophila Bloom's syndrome helicase and Ku autoantigen during nonhomologous end joining repair of P element-induced DNA breaks.

P transposable elements in Drosophila are mobilized via a cut-and-paste mechanism. The broken DNA ends generated during transposition can be repaired via the homology-directed synthesis-dependent strand annealing or by nonhomologous end joining (NHEJ). Genetic studies have demonstrated an interaction between the gene (mus309, for mutagen-sensitive) encoding the Drosophila Bloom's syndrome helicase homolog (DmBLM) and the Ku70 gene, which is involved in NHEJ. We have used RNA interference (RNAi) to knock down expression of DmBLM and one or both of the Drosophila Ku subunits, DmKu70 or DmKu80. Our results show that upon reduction of DmKu, an increase in small deletions (1-49 bp) and large deletions (>/=50 bp) flanking the site of P element-induced breaks is observed, and a reduction in large deletions at these sites is found upon reduction of DmBLM. Moreover, double RNAi of DmKu and DmBLM results in an increase in small deletions characteristic of the DmKu RNAi and also partially suppresses the reduction in repair efficiency observed with DmKu RNAi. These results suggest that there are DNA double-strand break recognition and/or processing events involving DmKu and DmBLM that, when eliminated by RNAi, lead to deletions. Finally, these results raise the possibility that, unlike the situation in mammals, where BLM appears to function exclusively in the homologous repair pathway, in Drosophila, DmBLM may be directly involved in, or at least influence the double-strand break recognition that leads to the NHEJ repair pathway.

Adenosine Triphosphatases↗
PubMed2006

Identification of genes regulated by Wnt/beta-catenin pathway and involved in apoptosis via microarray analysis.

BACKGROUND: Wnt/beta-catenin pathway has critical roles in development and oncogenesis. Although significant progress has been made in understanding the downstream signaling cascade of this pathway, little is known regarding Wnt/beta-catenin pathway modification of the cellular apoptosis. METHODS: To identify potential genes regulated by Wnt/beta-catenin pathway and involved in apoptosis, we used a stably integrated, inducible RNA interference (RNAi) vector to specific inhibit the expression and the transcriptional activity of beta-catenin in HeLa cells. Meanwhile, we designed an oligonucleotide microarray covering 1384 apoptosis-related genes. Using oligonucleotide microarrays, a series of differential expression of genes was identified and further confirmed by RT-PCR. RESULTS: Stably integrated inducible RNAi vector could effectively suppress beta-catenin expression and the transcriptional activity of beta-catenin/TCF. Meanwhile, depletion of beta-catenin in this manner made the cells more sensitive to apoptosis. 130 genes involved in some important cell-apoptotic pathways, such as PTEN-PI3K-AKT pathway, NF-kappaB pathway and p53 pathway, showed significant alteration in their expression level after the knockdown of beta-catenin. CONCLUSION: Coupling RNAi knockdown with microarray and RT-PCR analyses proves to be a versatile strategy for identifying genes regulated by Wnt/beta-catenin pathway and for a better understanding the role of this pathway in apoptosis. Some of the identified beta-catenin/TCF directed or indirected target genes may represent excellent targets to limit tumor growth.

Apoptosis↗
PubMed2005

RNA interference-mediated silencing of X11alpha and X11beta attenuates amyloid beta-protein levels via differential effects on beta-amyloid precursor protein processing.

Processing of the beta-amyloid precursor protein (APP) plays a key role in Alzheimer disease neuropathogenesis. APP is cleaved by beta- and alpha-secretase to produce APP-C99 and APP-C83, which are further cleaved by gamma-secretase to produce amyloid beta-protein (Abeta) and p3, respectively. APP adaptor proteins with phosphotyrosine-binding domains, including X11alpha (MINT1, encoded by gene APBA1) and X11beta (MINT2, encoded by gene APBA2), can bind to the conserved YENPTY motif in the APP C terminus. Overexpression of X11alpha and X11beta alters APP processing and Abeta production. Here, for the first time, we have described the effects of RNA interference (RNAi) silencing of X11alpha and X11beta expression on APP processing and Abeta production. RNAi silencing of APBA1 in H4 human neuroglioma cells stably transfected to express either full-length APP or APP-C99 increased APP C-terminal fragment levels and lowered Abeta levels in both cell lines by inhibiting gamma-secretase cleavage of APP. RNAi silencing of APBA2 also lowered Abeta levels, but apparently not via attenuation of gamma-secretase cleavage of APP. The notion of attenuating gamma-secretase cleavage of APP via the APP adaptor protein X11alpha is particularly attractive with regard to therapeutic potential given that side effects of gamma-secretase inhibition due to impaired proteolysis of other gamma-secretase substrates, e.g. Notch, might be avoided.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Hypoxia-induced resistance to cisplatin and doxorubicin in non-small cell lung cancer is inhibited by silencing of HIF-1alpha gene.

OBJECTIVES: Hypoxia is associated with human non-small cell lung cancers (NSCLC), which are highly resistant to chemotherapy. The hypoxia inducible factor (HIF) as a transcription factor in response to hypoxia indicates that it could be a novel, tumor-specific target for anticancer therapy. We hypothesized that disruption of HIF pathway through lentiviral vector-mediated HIF-1alpha RNA interference (RNAi) could reverse the hypoxia-induced resistance to chemotherapy. METHODS: We transfected Human NSCLC cell lines, SPCA1 and A549 with HIF-1alpha specific RNAi lentiviral vectors as well as controls. HIF-1alpha silenced cells [SPCA1/HIF-1alpha(-) and A549/HIF-1alpha(-)] were screened by blasticidin. They were incubated in 19 or 0.5% O2 for 16 h followed by the assessment of chemosensitivity to cisplatin and doxorubicin with MTT and clonogenic assays. Quantitative RT-PCR and Western blot analysis were used to detect the expressions of HIF-1alpha mRNA and protein, respectively. Moreover, flow cytometry was used to monitor the expression of P-glycoprotein. RESULTS: Exposure of SPCA1 and A549 cells to 0.5% O2 significantly increased resistance to cisplatin and doxorubicin, in contrast to cells incubated in normoxia. Transduction of SPCA1 with HIF-1alpha RNAi vector resulted in sequence specific silencing with 87.2 and 84.6% decreases of HIF-1alpha mRNA transcription and 97.3 and 94.8% of protein expressions in normoxia and hypoxia, respectively. Correspondingly, they are 89.2, 89.9% and 97.2, 88.4% decreases in A549 cells. Hypoxia-induced resistance to cisplatin and doxorubicin were reversed in SPCA1/HIF-1alpha(-) and A549/HIF-1alpha(-) cells. There was no significant P-glycoprotein increase induced by hypoxia in NSCLC cells. CONCLUSIONS: Our studies demonstrated that hypoxia-induced chemoresistance to cisplatin and doxorubicin in NSCLC cells is through the HIF pathway. MDR1 regulation may not be involved in hypoxia-induced chemoresistance. Combining delivery of HIF-1alpha RNAi lentiviral vector with cisplatin-related chemotherapy regimens may enable us to develop more effective strategy for NSCLC therapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2004

Functional comparison of single- and double-stranded siRNAs in mammalian cells.

The concept of small interfering RNA (siRNA) has been extended to include not only short double-stranded RNA of 19-25bp, but also single-stranded antisense RNA of the same length, since such single-stranded antisense siRNAs were recently found to be able to inhibit gene expression as well. We made comprehensive comparison of double- and single-stranded siRNA functions in RNA interference (RNAi), targeting multiple sites and different mRNAs, measuring RNAi effects at different time-points and in different cell lines, and examining response curves. Duplex siRNAs were found to be more potent than single-stranded antisense siRNAs. This was verified by the observation that single-stranded antisense siRNAs, which were inefficient in some cases when used alone, could be rescued from inefficiency by sequentially transfecting with the sense siRNAs. This result suggests that the structural character of siRNA molecules might be a more important determinant of siRNA efficiency than the cellular persistence of them.

Animals↗
PubMed2005

Specific anti-viral effects of RNA interference on replication and expression of hepatitis B virus in mice.

BACKGROUND: RNA interference (RNAi) is a powerful tool to silence gene expression post-transcriptionally. Our previous study has demonstrated that small interfering RNAs (siRNAs) have sufficiently inhibited hepatitis B virus (HBV) replication and expression in vitro. In this study we observed the RNAi-mediated inhibitory effects on HBV replication in mice models and accessed the specificity of these effects. METHODS: A mutant RNAi vector (pSI-C mut) with two base pairs different from the original target gene sequence at the RNAi vector (pSI-C) was constructed according to the method described in this study. A mouse model of acute hepatitis B virus infection was established by injecting naked plasmid pHBV1.3 via the tail vein with acute circulatory overload. pSI-C, pSI-C mut and the irrelevant RNAi control plasmid for green fluorescent protein (GFP) gene, pSIGFP were respectively delivered with pHBV1.3 by tail vein injection method. Six days post injection, enzyme-linked immunosorbent assay (ELISA) assay was used to measure the concentration of HBV surface antigen (HBsAg) in mouse serum, immunohistochemical straining method was used to visualize the expression of HBV core protein (HBcAg) in liver tissues, and the transcriptional level of HBV C mRNA in liver tissues was detected by reverse transcriptase PCR (RT-PCR) analysis. RESULTS: Injection of pSI-C exerted magnificent and specific inhibitory effects on the replication and expression of HBV in the murine model. After 6-day post-injection (p.i.), the OD values were shown to be 5.07 +/- 1.07 in infecting group and 0.62 +/- 0.59 in pSI-C group. The concentration of HBsAg in pSI-C group was significantly lower than that in infecting group (P < 0.01). Liver intracellular synthesis of viral core protein was sharply reduced to 0.9% +/- 0.1%, compared with 5.4% +/- 1.2% of positive hepatocytes in infecting group (P < 0.01), and the transcriptional level of HBV C mRNA was greatly reduced by 84.7%. However, the irrelevant RNAi control plasmid (pSIGFP), and the pSI-C mut did not show the same robust inhibitory effects as pSI-C. CONCLUSION: pSI-C exert efficient and specific inhibitory effects on HBV replication and expression in mice models.

Animals↗
PubMed2005

RNA interference-mediated silencing of the acetyl-CoA-carboxylase-alpha gene induces growth inhibition and apoptosis of prostate cancer cells.

Overexpression of lipogenic enzymes is a common characteristic of many cancers. Thus far, studies aimed at the exploration of lipogenic enzymes as targets for cancer intervention have focused on fatty acid synthase (FAS), the enzyme catalyzing the terminal steps in fatty acid synthesis. Chemical inhibition or RNA interference (RNAi)-mediated knockdown of FAS consistently inhibits the growth and induces death of cancer cells. Accumulation of the FAS substrate malonyl-CoA has been implicated in the mechanism of cytotoxicity of FAS inhibition. Here, using RNAi technology, we have knocked down the expression of acetyl-CoA carboxylase-alpha (ACC-alpha), the enzyme providing the malonyl-CoA substrate. Silencing of the ACC-alpha gene resulted in a similar inhibition of cell proliferation and induction of caspase-mediated apoptosis of highly lipogenic LNCaP prostate cancer cells as observed after FAS RNAi. In nonmalignant cells with low lipogenic activity, no cytotoxic effects of knockdown of ACC-alpha or FAS were observed. These findings indicate that accumulation of malonyl-CoA is not a prerequisite for cytotoxicity induced by inhibition of tumor-associated lipogenesis and suggest that in addition to FAS, ACC-alpha is a potential target for cancer intervention.

Acetyl-CoA Carboxylase↗
PubMed2006

Golgi alkaline ceramidase regulates cell proliferation and survival by controlling levels of sphingosine and S1P.

Sphingosine-1-phosphate (S1P), a sphingolipid metabolite, promotes cell proliferation and survival whereas its precursor, sphingosine, has the opposite effects. However, much remains unknown about their regulation. Here we identify a novel human ceramidase (haCER2) that regulates the levels of both sphingosine and S1P by controlling the hydrolysis of ceramides. haCER2 is localized to the Golgi complex and is highly expressed in the placenta. High ectopic expression of haCER2 caused fragmentation of the Golgi complex and growth arrest in HeLa cells due to sphingosine accumulation. Low ectopic expression of haCER2 increased S1P without sphingosine accumulation, promoting cell proliferation in serum-free medium. This proliferative effect was suppressed by dimethylsphingosine, an inhibitor of the S1P formation, or by the RNA interference (RNAi) -mediated inhibition of S1P(1,) a G-protein-coupled receptor for S1P. The RNAi-mediated down-regulation of haCER2 enhanced the serum deprivation-induced growth arrest and apoptosis of HeLa cells, which was inhibited by addition of exogenous S1P. Serum deprivation up-regulated both haCER2 mRNA and activity in HeLa cells. haCER2 mRNA is also up-regulated in some tumors. Taken together, these results suggest that haCER2 is important for the generation of S1P and S1P-mediated cell proliferation and survival, but that its overexpression may cause cell growth arrest due to an accumulation of sphingosine.

Alkaline Ceramidase↗
PubMed2004

Effects of RNA interference-mediated silencing of gamma-secretase complex components on cell sensitivity to caspase-3 activation.

Familial Alzheimer's disease mutations in the presenilin 1 gene (PSEN1) have been previously shown to potentiate caspase activation and apoptosis in transfected cells and transgenic mice. However, the mechanism underlying this effect is not known. We set out to determine whether cellular sensitivity to caspase activation could be affected by modulating presenilin 1 (PS1) processing. PS1 processing was altered using RNA interference (RNAi) aimed at silencing the expression of the genes encoding the four components of the gamma-secretase complex, PSEN1, APH-1, PEN-2, and nicastrin. RNAi for these genes was carried out in naive H4 human neuroglioma cells, as well as H4 cell lines overexpressing either wild-type PSEN1 or the Familial Alzheimer's disease mutant PSEN1-Delta9 (PS1-mutant), that were induced to undergo apoptosis. In wild-type PSEN1 cells, RNAi for PEN-2, as expected, increased levels of full-length PS1 (PS1-FL) and decreased PS1 endoproteolysis. This was accompanied by potentiated caspase-3 activation in response to an apoptotic stimulus. In contrast, nicastrin RNAi, which only decreased levels of PS1-amino-terminal fragment and did not affect PS1-FL levels, had no effect on caspase-3 activation during apoptosis. Surprisingly, in the PS1-mutant cells, RNAi for PEN-2 (and APH-1) did not increase but instead reduced the levels of PS1-FL deleted for exon 9. In turn, this was accompanied by attenuated caspase-3 activation in response to an apoptotic stimulus. Finally, in naive H4 cells, PSEN1 RNAi also attenuated caspase-3 activation in response to an apoptotic stimulus. Collectively, these findings indicate that cellular sensitivity to caspase activation correlates with overall PS1 protein levels, particularly with levels of FL-PS1.

Amyloid Precursor Protein Secretases↗
PubMed2005

Differential regulation of strand-specific transcripts from Arabidopsis centromeric satellite repeats.

Centromeres interact with the spindle apparatus to enable chromosome disjunction and typically contain thousands of tandemly arranged satellite repeats interspersed with retrotransposons. While their role has been obscure, centromeric repeats are epigenetically modified and centromere specification has a strong epigenetic component. In the yeast Schizosaccharomyces pombe, long heterochromatic repeats are transcribed and contribute to centromere function via RNA interference (RNAi). In the higher plant Arabidopsis thaliana, as in mammalian cells, centromeric satellite repeats are short (180 base pairs), are found in thousands of tandem copies, and are methylated. We have found transcripts from both strands of canonical, bulk Arabidopsis repeats. At least one subfamily of 180-base pair repeats is transcribed from only one strand and regulated by RNAi and histone modification. A second subfamily of repeats is also silenced, but silencing is lost on both strands in mutants in the CpG DNA methyltransferase MET1, the histone deacetylase HDA6/SIL1, or the chromatin remodeling ATPase DDM1. This regulation is due to transcription from Athila2 retrotransposons, which integrate in both orientations relative to the repeats, and differs between strains of Arabidopsis. Silencing lost in met1 or hda6 is reestablished in backcrosses to wild-type, but silencing lost in RNAi mutants and ddm1 is not. Twenty-four-nucleotide small interfering RNAs from centromeric repeats are retained in met1 and hda6, but not in ddm1, and may have a role in this epigenetic inheritance. Histone H3 lysine-9 dimethylation is associated with both classes of repeats. We propose roles for transcribed repeats in the epigenetic inheritance and evolution of centromeres.

Arabidopsis↗
PubMed2006

Valosin-containing protein (p97) is a regulator of endoplasmic reticulum stress and of the degradation of N-end rule and ubiquitin-fusion degradation pathway substrates in mammalian cells.

Valosin-containing protein (VCP; p97; cdc48 in yeast) is a hexameric ATPase of the AAA family (ATPases with multiple cellular activities) involved in multiple cellular functions, including degradation of proteins by the ubiquitin (Ub)-proteasome system (UPS). We examined the consequences of the reduction of VCP levels after RNA interference (RNAi) of VCP. A new stringent method of microarray analysis demonstrated that only four transcripts were nonspecifically affected by RNAi, whereas approximately 30 transcripts were affected in response to reduced VCP levels in a sequence-independent manner. These transcripts encoded proteins involved in endoplasmic reticulum (ER) stress, apoptosis, and amino acid starvation. RNAi of VCP promoted the unfolded protein response, without eliciting a cytosolic stress response. RNAi of VCP inhibited the degradation of R-GFP (green fluorescent protein) and Ub-(G76V)-GFP, two cytoplasmic reporter proteins degraded by the UPS, and of alpha chain of the T-cell receptor, an established substrate of the ER-associated degradation (ERAD) pathway. Surprisingly, RNAi of VCP had no detectable effect on the degradation of two other ERAD substrates, alpha1-antitrypsin and deltaCD3. These results indicate that VCP is required for maintenance of normal ER structure and function and mediates the degradation of some proteins via the UPS, but is dispensable for the UPS-dependent degradation of some ERAD substrates.

Adenosine Triphosphatases↗
PubMedDate not supplied

The use of small interfering RNA to elucidate the activity and function of ion channel genes in an intact tissue.

Small interfering RNA (siRNA) directs the targeted destruction of mRNA encoding a specific protein, in a process known as RNA interference (RNAi). This stops translation of the targeted mRNA into protein, effectively silencing the gene. RNAi is a recent discovery, identified in mammalian cells in 2001, but it has rapidly advanced into a practical technique and is being used increasingly to investigate mammalian gene function. Tools are available to induce RNAi in cell lines, intact tissue preparations and even in vivo. Depending on the method used, loss of gene expression may be transient or sustained, enabling a wide range of functions to be investigated. RNAi therefore offers a powerful technique that can be used to produce targeted knockout of ion channel genes in mammalian cells. Its applications potentially include identification of ion channel function in health and disease, identification of novel channel genes and drug target validation. This paper outlines our current understanding of siRNA and the experimental requirements for producing efficient RNAi and gene silencing. Effective RNAi requires an appropriate siRNA sequence to be designed and an efficient method for delivering the siRNA to the cells of interest. Since not all potential siRNA sequences are effective, it is also important to verify the loss of gene expression by measuring the level of channel protein remaining. Limitations of the methods available for delivering siRNA are one of the main obstacles to producing efficient RNAi, especially in intact tissue preparations. Here we describe an in vitro method for targeted RNAi against the TASK-1 potassium channel gene in an isolated vascular preparation, using a DNA construct to direct the expression of siRNA, along with a non-viral method for transfecting cells within the vessel. Successful silencing of the TASK-1 gene is verified by immunostaining with an antibody directed against the TASK-1 protein.

Blood Vessels↗
PubMed2005

Cytoplasmic and nuclear retained DMPK mRNAs are targets for RNA interference in myotonic dystrophy cells.

Small interfering RNA (siRNA) duplexes induce the specific cleavage of target RNAs in mammalian cells. Their involvement in down-regulation of gene expression is termed RNA interference (RNAi). It is widely believed that RNAi predominates in the cytoplasm. We report here the co-existence of cytoplasmic and nuclear RNAi phenomena in primary human myotonic dystrophy type 1 (DM1) cells by targeting myotonic dystrophy protein kinase (DMPK) mRNAs. Heterozygote DM1 myoblasts from a human DM1 fetus produce a nuclear retained mutant DMPK transcript with large CUG repeats ( approximately 3,200) from one allele of the DMPK gene and a wild type transcript with 18 CUG repeats, thus providing for both a nuclear and cytoplasmic expression profile to be evaluated. We demonstrate here for the first time down-regulation of the endogenous nuclear retained mutant DMPK mRNAs targeted with lentivirus-delivered short hairpin RNAs (shRNAs). This nuclear RNAi(-like) phenomenon was not observed when synthetic siRNAs were delivered by cationic lipids, suggesting either a link between processing of the shRNA and nuclear import or a separate pathway for processing shRNAs in the nuclei. Our observation of simultaneous RNAi on both cytoplasmic and nuclear retained DMPK has important implications for post-transcriptional gene regulation in both compartments of mammalian cells.

Active Transport, Cell Nucleus↗
PubMed2004

The hereditary spastic paraplegia gene, spastin, regulates microtubule stability to modulate synaptic structure and function.

BACKGROUND: Hereditary Spastic Paraplegia (HSP) is a devastating neurological disease causing spastic weakness of the lower extremities and eventual axonal degeneration. Over 20 genes have been linked to HSP in humans; however, mutations in one gene, spastin (SPG4), are the cause of >40% of all cases. Spastin is a member of the ATPases associated with diverse cellular activities (AAA) protein family, and contains a microtubule interacting and organelle transport (MIT) domain. Previous work in cell culture has proposed a role for Spastin in regulating microtubules. RESULTS: Employing Drosophila transgenic methods for overexpression and RNA interference (RNAi), we have investigated the role of Spastin in vivo. We show that Drosophila Spastin (D-Spastin) is enriched in axons and synaptic connections. At neuromuscular junctions (NMJ), Dspastin RNAi causes morphological undergrowth and reduced synaptic area. Moreover, Dspastin overexpression reduces synaptic strength, whereas Dspastin RNAi elevates synaptic currents. By using antibodies against posttranslationally modified alpha-Tubulin, we find that Dspastin regulates microtubule stability. Functional synaptic defects caused by Dspastin RNAi and overexpression were pharmacologically alleviated by agents that destabilize and stabilize microtubules, respectively. CONCLUSIONS: Loss of Dspastin in Drosophila causes an aberrantly stabilized microtubule cytoskeleton in neurons and defects in synaptic growth and neurotransmission. These in vivo data strongly support previous reports, providing a probable cause for the neuronal dysfunction in spastin-linked HSP disease. The role of Spastin in regulating neuronal microtubule stability suggests therapeutic targets for HSP treatment and may provide insight into neurological disorders linked to microtubule dysfunction.

Animals↗
PubMed2005

Acute reduction of an origin recognition complex (ORC) subunit in human cells reveals a requirement of ORC for Cdk2 activation.

The origin recognition complex (ORC) is involved in formation of prereplicative complexes (pre-RCs) on replication origins in the G1 phase. At the G1/S transition, elevated cyclin E-CDK2 activity triggers 1DNA replication to enter S phase. The CDK cycle works as an engine that drives progression of cell cycle events by successive activation of different types of cyclin-CDK. However, how the CDK cycle is coordinated with replication initiation remains elusive. Here we report that acute depletion of ORC2 by RNA interference (RNAi) arrests cells with low cyclin E-CDK2 activity. This result suggests that loss of a replication initiation protein prevents progression of the CDK cycle in G1. p27 and p21 proteins accumulate following ORC2 RNAi and are required for the CDK2 inhibition. Restoration of CDK activity by co-depletion of p27 and p21 allows many ORC2-depleted cells to enter S phase and go on to mitosis. However, in some cells the release of the CDK2 block caused catastrophic events like apoptosis. Therefore, the CDK2 inhibition observed following ORC2 RNAi seems to protect cells from premature S phase entry and crisis in DNA replication. These results demonstrate an unexpected role of ORC2 in CDK2 activation, a linkage that could be important for maintaining genomic stability.

Apoptosis↗