Ruolo della proteina arginin-metiltrasferasi-5 (PRMT5) nella linfomagenesi B: implicazioni terapeutiche

Numerosi studi hanno mostrato come i meccanismi epigenetici di regolazione della cromatina svolgano un ruolo centrale nel controllare la trascrizione genica. E’ stato infatti dimostrato che complessi inibitori come SWI/SNF e gli enzimi ad esso associati quali istone deacetilasi (HDAC) e protein arginin-metiltrasferasi (PRMT), siano coinvolti nel controllo della crescita, differenziazione e proliferazione cellulare. Diversi studi hanno mostrato come i meccanismi epigenetici di controllo della trascrizione genica svolgano un ruolo di primo piano nel promuovere la sopravvivenza cellulare in leucemie/linfomi di derivazione dai linfociti B come la leucemia linfatica cronica, il linfoma mantellare ed i linfomi associati al virus di Epstein-Barr (EBV). Tuttavia, molto poco e’ conosciuto circa i meccanismi epigenetici di controllo della trascrizione che divengono operativi e che contribuiscono al processo di trasformazione dei linfociti B. PRMT5 e’ un enzima che di-metila specificamente residui argininici sugli istoni (H) 3 (H3R8) ed 4 (H4R3). PRMT5 ed HDAC lavorano in concerto per reprimere la trascrizione di specifici geni oncosoppressori. In questo progetto sono stati studiati i meccanismi e le conseguenze dell’iperespressione di PRMT5 durante il processo di trasformazione dei linfociti B indotto da EBV, e’ stata dimostrata l’importanza di questo enzima nel processo di trasformazione, e sono stati studiati nuovi metodi per inibirne l’espressione/attivita’. In particolare si e’ dimostrato che l’espressione di PRMT5 e’ ridotta o assente in linfociti B normali (o attivati da stimoli fisiologici) ed elevata in linee cellulari linfoblastoidi immortalizzate o completamente trasformate. Elevati livelli citosolici di PRMT5 sono detectabili dopo 4 giorni dall’infezione di linfociti B normali con EBV, PRMT5 e’ detectabile a livello nucleare, dove esercita la sua funzione repressoria la trascrizione, a partire dal giorno 8. L’utilizzo di specifici small interference RNAs (siRNA) in linee cellulari linfoblastoidi ha permesso di dimostrare la riduzione dell’espressione di PRMT5, la riduzione della metilazione degli istoni target di PRMT5, inibizione della proliferazione cellulare e abbassamento della soglia di sensibilita’ cellulare a stimoli pro-apoptotici. Esperimenti di co-immunoprecipitazione cromatinica hanno permesso di evidenziare che in queste cellule PRMT5 e’ parte di un complesso proteico a funzione inibitoria e che questo complesso si lega alla regione promotrice di specifici geni oncosoppressori quali ST7, GAS e NM23, inibendone la trascrizione. Si e’ inoltre provveduto a sviluppare una categoria di inibitori allosterici di PRMT5: l’attivita’ terapeutica/la specificita’ in vitro e la modalita’ di somministrazione ottimale in modelli murini di linfoma non-Hodgkin, sono in corso di valutazione.

Identification and characterization of the sRNA network in Neisseria meningitidis

Bacterial small regulatory RNAs (sRNAs) are posttranscriptional regulators involved in stress responses. These short non-coding transcripts are synthesised in response to a signal, and control gene expression of their regulons by modulating the translation or stability of the target mRNAs, often in concert with the RNA chaperone Hfq. Characterization of a Hfq knock out mutant in Neisseria meningitidis revealed that it has a pleiotropic phenotype, suggesting a major role for Hfq in adaptation to stresses and virulence and the presence of Hfq-dependent sRNA activity. Global gene expression analysis of regulated transcripts in the Hfq mutant revealed the presence of a regulated sRNA, incorrectly annotated as an open reading frame, which we renamed AniS. The synthesis of this novel sRNA is anaerobically induced through activation of its promoter by the FNR global regulator and through global gene expression analyses we identified at least two predicted mRNA targets of AniS. We also performed a detailed molecular analysis of the action of the sRNA NrrF,. We demonstrated that NrrF regulates succinate dehydrogenase by forming a duplex with a region of complementarity within the sdhDA region of the succinate dehydrogenase transcript, and Hfq enhances the binding of this sRNA to the identified target in the sdhCDAB mRNA; this is likely to result in rapid turnover of the transcript in vivo. In addition, in order to globally investigate other possible sRNAs of N. meningitdis we Deep-sequenced the transcriptome of this bacterium under both standard in vitro and iron-depleted conditions. This analysis revealed genes that were actively transcribed under the two conditions. We focused our attention on the transcribed non-coding regions of the genome and, along with 5’ and 3’ untranslated regions, 19 novel candidate sRNAs were identified. Further studies will be focused on the identification of the regulatory networks of these sRNAs, and their targets.

Tetracycline-inducible RNAi Knockdown of SCL (Stem Cell Leukaemia) in Mice

RNAi (RNA interference) is a powerful technology for sequence-specific targeting of mRNAs. This thesis was aimed at establishing conditions for conditional RNAi-mediated silencing first in vitro and subsequently also in transgenic mice. As a target the basic helix-loop-helix transcription factor encoding gene SCL (stem cell leukaemia also known as Tal-1 or TCL5) was used. SCL is a key regulator for haematopoietic development and ectopic expression of SCL is correlated with acute T-lymphoblastic leukaemias. Loss of SCL function studies demonstrated that ab initio deletion of SCL resulted in embryonic lethality around day E9 in gestation. To be able to conditionally inactivate SCL, RNAi technology was combined with the tetracycline-dependent regulatory system. This strategy allowed to exogenously control the induction of RNAi in a reversible fashion and consequently the generation of a completely switchable RNAi knockdown. First a suitable vector allowing for co-expression of tetracycline-controlled shRNAs (small hairpin RNAs) and constitutively active EGFP (enhanced green fluorescent protein) was generated. This novel vector, pRNAi-EGFP, was then evaluated for EGFP expression and tetracycline-mediated expression of shRNAs. Four sequences targeting different regions within the SCL mRNA were tested for their efficiency to specifically knockdown SCL. These experiments were performed in M1 murine leukaemia cells and subsequently in the HEK 293 cell line, expressing an engineered HA-tagged SCL protein. The second assay provided a solid experimental method for determining the efficiency of different SCL-siRNA knockdown constructs in tissue culture. Western blotting analyses revealed a down regulation of SCL protein for all four tested SCL-specific target sequences albeit with different knockdown efficiencies (between 25% and 100%). Furthermore, stringent tetracycline-dependent switchability of shRNA expression was confirmed by co-transfecting the SCL-specific pRNAi-EGFP vector (SCL-siRNA) together with the HA-tagged SCL expression plasmid into the HEK 293TR /T-REx cell line constitutively expressing the tetracycline repressor (TetR). These series of experiments demonstrated tight regulation of siRNA expression without background activity. To be able to control the SCL knockdown in vivo and especially to circumvent any possible embryonic lethality a transgenic mouse line with general expression of a tetracycline repressor was needed. Two alternative methods were used to generate TetR mice. The first approach was to co-inject the tetracycline-regulated RNAi vector together with a commercially available and here specifically modified T-REx expression vector (SCL-siRNA T-REx FRT LoxP mouse line). The second method involved the generation of a TetR expressor mouse line, which was then used for donating TetR-positive oocytes for pronuclear injection of the RNAi vector (SCL-siRNA T-REx mouse line). As expected, and in agreement with data from conditional Cre-controlled adult SCL knockout mice, post-transcriptional silencing of SCL by RNAi caused a shift in the maturation of red blood cell populations. This was shown in the bone marrow and peripheral blood by FACS analysis with the red blood cell-specific TER119 and CD71 markers which can be used to define erythrocyte differentiation (Lodish plot technique). In conclusion this study established conditions for effective SCL RNAi-mediated silencing in vitro and in vivo providing an important tool for further investigations into the role of SCL and, more generally, of its in vivo function in haematopoiesis and leukaemia. Most importantly, the here acquired knowledge will now allow the establishment of other completely conditional and reversible knockdown phenotypes in mice.

Trascriptome analysis and functional genomics of Neisseria meningitidis in human blood

Neisseria meningitidis (Nm) is the major cause of septicemia and meningococcal meningitis. During the course of infection, it must adapt to different host environments as a crucial factor for survival. Despite the severity of meningococcal sepsis, little is known about how Nm adapts to permit survival and growth in human blood. A previous time-course transcriptome analysis, using an ex vivo model of human whole blood infection, showed that Nm alters the expression of nearly 30% of ORFs of the genome: major dynamic changes were observed in the expression of transcriptional regulators, transport and binding proteins, energy metabolism, and surface-exposed virulence factors. Starting from these data, mutagenesis studies of a subset of up-regulated genes were performed and the mutants were tested for the ability to survive in human whole blood; Nm mutant strains lacking the genes encoding NMB1483, NalP, Mip, NspA, Fur, TbpB, and LctP were sensitive to killing by human blood. Then, the analysis was extended to the whole Nm transcriptome in human blood, using a customized 60-mer oligonucleotide tiling microarray. The application of specifically developed software combined with this new tiling array allowed the identification of different types of regulated transcripts: small intergenic RNAs, antisense RNAs, 5’ and 3’ untranslated regions and operons. The expression of these RNA molecules was confirmed by 5’-3’RACE protocol and specific RT-PCR. Here we describe the complete transcriptome of Nm during incubation in human blood; we were able to identify new proteins important for survival in human blood and also to identify additional roles of previously known virulence factors in aiding survival in blood. In addition the tiling array analysis demonstrated that Nm expresses a set of new transcripts, not previously identified, and suggests the presence of a circuit of regulatory RNA elements used by Nm to adapt to proliferate in human blood.

Untersuchungen zur Rolle des BH3-only-Proteins Bid bei der Stress-induzierten Apoptose in Karzinomzelllinien

Als BH3-only Protein gehört Bid zu den proapoptotischen Mitgliedern der Bcl-2 Familie, die während der Apoptose die Freisetzung Caspase-aktivierender Proteine aus den Mitochondrien kontrollieren. Bid zählt zu den potentesten BH3-only Proteinen und wird von vielen transformierten und nichttransformierten Zellen konstitutiv exprimiert. Ziel dieser Arbeit war es, Bid durch RNA-Interferenz stabil zu depletieren, um Bid-abhängige Apoptosewege in HeLa Zervixkarzinomzellen zu identifizieren, die von intrinsischen Stressstimuli sowie von konventionellen und neuartigen Chemotherapeutika induziert werden. Da Bid im Todesrezeptor-vermittelten Signalweg der Apoptose durch Caspase-8 gespalten und aktiviert wird, waren die Bid-depletierten Zellen signifikant vor der Fas/CD95-, TRAIL- oder TNF-α-induzierten Apoptose geschützt und zeigten nach Exposition mit allen drei Todesrezeptorliganden eine drastisch reduzierte Effektorcaspase-Aktivität und eine höhere Proliferationsrate als die Kontrollzellen. Eine ektopische Bidexpression in Bid knock down (kd) Zellen hob die Protektion vor der Fas- und TRAIL-induzierten Apoptose auf. Der Proteasominhibitor Epoxomicin, der Proteinkinase-Inhibitor Staurosporin oder die ER Stress-induzierenden Agenzien Tunicamycin, Thapsigargin und Brefeldin A lösten hingegen einen Bid-unabhängigen Zelltod aus. Allerdings konnten subletale Tunicamycin- oder Thapsigarginkonzentrationen HeLa Zellen für die TRAIL-induzierte Apoptose sensitivieren. Da der Synergieeffekt auf einer ER Stress-vermittelten Amplifizierung des Todesrezeptorwegs beruhte, zu der eine Tunicamycin-induzierte Steigerung der Expression des Todesrezeptors DR5 signifikant beitrug, erfolgte diese Sensitivierung nur in Bid-profizienten Zellen. Bid war in HeLa Zellen außerdem an der apoptotischen Signalkaskade beteiligt, die von den DNA-schädigenden Agenzien Etoposid, Doxorubicin und Oxaliplatin (Oxa) ausgelöst wird. Nach Behandlung mit Oxa zeigten die Bid kd Zellen eine verzögerte Caspase-2, -3, -8 und -9 Aktivierung, einen geringeren Verlust des mitochondrialen Membranpotentials sowie eine reduzierte Apoptose- und eine höhere Proliferationsrate als Bid-profiziente Zellen. Neben Bid war ein weiteres BH3-only Protein, Puma, an der Oxa-induzierten Effektorcaspase-Aktivierung beteiligt, da eine Puma-spezifische siRNA unabhängig vom Bidstatus der Zellen antiapoptotisch wirkte. Im letzten Teil der Arbeit wurde untersucht, welche Proteasen für die durch gentoxische Agenzien induzierte Spaltung und Aktivierung von Bid verantwortlich sind. Obwohl Caspasen für die Exekutionphase der Oxa-induzierten Apoptose notwendig waren, trugen sie weder zur initialen Bidaktivierung noch zur mitochondrialen Depolarisierung bei, da sie erst postmitochondrial aktiviert wurden. Konventionelle Calpaine hingegen wurden nach DNA-Schädigung bereits stromaufwärts der Mitochondrien aktiviert und der Calpaininhibitor Calpeptin reduzierte nicht nur die Bid- und Caspasespaltung, sondern auch die mitochondriale Depolarisierung signifikant. Diese Protektion durch Calpeptin fiel in Bid-depletierten Zellen signifikant geringer als in Bid-profizienten Kontrollzellen aus. Auch war in Oxa-behandelten Bid kd Zellen, die eine durch Caspase-2, -3 und -8 nicht spaltbare Bidmutante exprimierten, trunkiertes Bid nachweisbar, dessen Generierung durch Calpain-, aber nicht durch Caspaseinhibierung verhindert werden konnte. Zusammenfassend deuten diese Ergebnisse auf eine Calpain-abhängige Bidaktivierung stromaufwärts der Mitochondrien hin und zeigen, dass die BH3-only Proteine Bid und Puma wichtige Vermittler der Oxa-induzierten Apoptose in HeLa Zellen darstellen.

Posttranskriptionale Regulation von Myelin-mRNAs

Die Myelinisierung neuronaler Axone ermöglicht eine schnelle und energieeffiziente Weiterleitung von Informationen im Nervensystem. Durch lokale Synthese von Myelinproteinen kann die Myelinschicht, zeitlich und räumlich reguliert, gebildet werden. Dieser Prozess ist abhängig von verschiedensten axonalen Eigenschaften und muss damit lokal reguliert werden. Die Myelinisierung im zentralen sowie im peripheren Nervensystem hängt unter anderem stark von kleinen regulatorischen RNA Molekülen ab. In Oligodendrozyten wird das Myelin Basische Protein (MBP) von der sncRNA715 translational reguliert, indem diese direkt innerhalb der 3’UTR der Mbp mRNA bindet und damit die Proteinsynthese verhindert. Mbp mRNA wird in hnRNP A2‐enthaltenen RNA Granula in die Zellperipherie transportiert, wo in Antwort auf axonale Signale die membranständige Tyrosin‐ Kinase Fyn aktiviert wird, welche Granula‐Komponenten wie hnRNP A2 und F phosphoryliert wodurch die lokale Translation initiiert wird. Während des Transports wird die mRNA durch die Bindung der sncRNA715 translational reprimiert. SncRNAs bilden zusammen mit Argonaut‐Proteinen den microRNA induced silencing complex (miRISC), welcher die translationale Inhibition oder den Abbau von mRNAs vermittelt. In der vorliegenden Arbeit sollte zum einen die Regulation der sncRNA715‐abhängigen translationalen Repression der Mbp mRNA in oligodendroglialen Zellen genauer untersucht werden und im zweiten Teil wurde die Rolle der sncRNA715 in den myelinbildenden Zellen des peripheren Nervensystems, den Schwann Zellen, analysiert. Es konnte in oligodendroglialen Zellen die mRNA‐Expression der vier, in Säugern bekannten Argonaut‐Proteinen nachgewiesen werden. Außerdem konnten die beiden Proteine Ago1 und Ago2 in vitro sowie in vivo detektiert werden. Ago2 interagiert mit hnRNP A2, Mbp mRNA und sncRNA715, womit es als neue Komponente des Mbp mRNA Transportgranulas identifiziert werden konnte. Des Weiteren colokalisiert Ago2 mit der Fyn‐Kinase und alle vier Argonaut‐Proteine werden Fyn‐abhängig Tyrosin‐phosphoryliert. Die Fyn‐abhängige Phosphorylierung der Granula‐Komponenten in Antwort auf axo‐glialen Kontakt führt zum Zerfall des RNA‐Granulas und zur gesteigerten MBP Proteinsynthese. Dies wird möglicherweise durch Abstoßungskräfte der negativ geladenen phosphorylierten Proteine vermittelt, wodurch diese sich voneinander und von der mRNA entfernen. Durch die Ablösung des miRISCs von der Mbp mRNA wird die Translation möglicherweise reaktiviert und die Myelinisierung kann starten. Mit der Identifizierung von Ago2 als neuer Mbp mRNA Transportgranula‐Komponente konnte ein weiterer Einblick in die Regulation der lokalen Translation von MBP gewährt werden. Das Verständnis dieses Prozesses ist entscheidend für die Entwicklung neuer Therapien von demyelinisierenden Erkrankungen, da neue Faktoren als eventuelle Ziele für pharmakologische Manipulationen identifiziert und möglichweise neue Therapiemöglichkeiten entstehen könnten. Im zweiten Teil der Arbeit wurde die translationale Regulation von Mbp mRNA in Schwann Zellen untersucht. Auch Schwann Zell‐Mbp wird als mRNA translational inaktiviert zur axo‐glialen Kontaktstelle transportiert, wo vermutlich auch lokale Translation in Antwort auf spezifische Signale stattfindet. Allerdings bleiben die genauen Mechanismen der mRNA‐Lokalisation und damit verbundenen translationalen Repression bislang ungeklärt. Es konnte hier gezeigt werden, dass auch in Schwann Zellen die sncRNA715 exprimiert wird und die Translation von Mbp reguliert. Überexpression der synthetischen sncRNA715 führt zu einer signifikanten Reduktion der MBP Proteinmengen in differenzierten primären Schwann Zellen. Damit kann vermutet werden, dass die Regulation der lokalen MBP Proteinsynthese in Schwann Zellen der in Oligodendrozyten ähnelt

Homeodomain-only protein HOP is a novel modulator of late differentiation in keratinocytes

The homeodomain-only protein (HOP) contains an atypical homeodomain which is unable to bind to DNA due to mutations in residues important for DNA binding. Recently, HOP was reported to regulate proliferation/differentiation homeostasis in different cell types. In the present study, we performed transcriptional profiling of cultured primary human keratinocytes and noted a robust induction of HOP upon calcium-induced cell differentiation. Immunohistochemistry of human skin localized HOP to the granular layer in the epidermis. Overexpression of HOP using a lentiviral vector up-regulated FLG and LOR expression during keratinocyte differentiation. Conversely, decreasing HOP expression using small interfering RNA markedly reduced the calcium-induced expression of late markers of differentiation in vitro, with the most prominent effect on profilaggrin (FLG) mRNA. Moreover, mRNA levels of profilaggrin and loricrin were downregulated in the epidermis of HOP knockout mice. Analysis of skin disorders revealed altered HOP expression in lichen planus, psoriasis and squamous cell carcinoma (SCC). Our data indicate that HOP is a novel modulator of late terminal differentiation in keratinocytes.

MicroRNA-381 Represses ID1 and is Deregulated in Lung Adenocarcinoma

MicroRNAs are small, noncoding RNAs that suppress gene expression by binding to the 3' untranslated region (UTR) and thereby repress translation or decrease messenger RNA stability. Inhibitor of differentiation 1 (ID1) is a putative stem-cell gene involved in invasion and angiogenesis. We previously showed that ID1 is regulated by Src kinases, overexpressed in human lung adenocarcinoma, and targeted by Src-dependent microRNAs. The current study focused on the association between miR-381 and ID1 in lung adenocarcinoma.

A sensitized RNA interference screen identifies a novel role for the PI3K p110γ isoform in medulloblastoma cell proliferation and chemoresistance

Medulloblastoma is the most common malignant brain tumor in children and is associated with a poor outcome. We were interested in gaining further insight into the potential of targeting the human kinome as a novel approach to sensitize medulloblastoma to chemotherapeutic agents. A library of small interfering RNA (siRNA) was used to downregulate the known human protein and lipid kinases in medulloblastoma cell lines. The analysis of cell proliferation, in the presence or absence of a low dose of cisplatin after siRNA transfection, identified new protein and lipid kinases involved in medulloblastoma chemoresistance. PLK1 (polo-like kinase 1) was identified as a kinase involved in proliferation in medulloblastoma cell lines. Moreover, a set of 6 genes comprising ATR, LYK5, MPP2, PIK3CG, PIK4CA, and WNK4 were identified as contributing to both cell proliferation and resistance to cisplatin treatment in medulloblastoma cells. An analysis of the expression of the 6 target genes in primary medulloblastoma tumor samples and cell lines revealed overexpression of LYK5 and PIK3CG. The results of the siRNA screen were validated by target inhibition with specific pharmacological inhibitors. A pharmacological inhibitor of p110γ (encoded by PIK3CG) impaired cell proliferation in medulloblastoma cell lines and sensitized the cells to cisplatin treatment. Together, our data show that the p110γ phosphoinositide 3-kinase isoform is a novel target for combinatorial therapies in medulloblastoma.

Bone morphogenetic protein-7 is a MYC target with prosurvival functions in childhood medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor in children. It is known that overexpression and/or amplification of the MYC oncogene is associated with poor clinical outcome, but the molecular mechanisms and the MYC downstream effectors in MB remain still elusive. Besides contributing to elucidate how progression of MB takes place, most importantly, the identification of novel MYC-target genes will suggest novel candidates for targeted therapy in MB. A group of 209 MYC-responsive genes was obtained from a complementary DNA microarray analysis of a MB-derived cell line, following MYC overexpression and silencing. Among the MYC-responsive genes, we identified the members of the bone morphogenetic protein (BMP) signaling pathway, which have a crucial role during the development of the cerebellum. In particular, the gene BMP7 was identified as a direct target of MYC. A positive correlation between MYC and BMP7 expression was documented by analyzing two distinct sets of primary MB samples. Functional studies in vitro using a small-molecule inhibitor of the BMP/SMAD signaling pathway reproduced the effect of the small interfering RNA-mediated silencing of BMP7. Both approaches led to a block of proliferation in a panel of MB cells and to inhibition of SMAD phosphorylation. Altogether, our findings indicate that high MYC levels drive BMP7 overexpression, promoting cell survival in MB cells. This observation suggests the potential relevance of targeting the BMP/SMAD pathway as a novel therapeutic approach for the treatment of childhood MB.

Secretin receptor promotes the proliferation of endocrine tumor cells via the PI3K/AKT pathway

The secretin receptor (SR), a G protein-coupled receptor, mediates the effects of the gastrointestinal hormone secretin on digestion and water homeostasis. Recently, high SR expression has been observed in pancreatic ductal adenocarcinomas, cholangiocellular carcinomas, gastrinomas, and bronchopulmonary carcinoid tumors. Receptor overexpression associates with enhanced secretin-mediated signaling, but whether this molecule plays an independent role in tumorigenesis is currently unknown. We recently discovered that pheochromocytomas developing in rats affected by the MENX (multiple endocrine neoplasia-like) syndrome express at very high-level Sctr, encoding SR. We here report that SR are also highly abundant on the membranes of rat adrenal and extraadrenal pheochromocytoma, starting from early stages of tumor development, and are functional. PC12 cells, the best characterized in vitro pheochromocytoma model, also express Sctr at high level. Thus, we used them as model to study the role of SR in neoplastic transformation. Small interfering RNA-mediated knockdown of Sctr decreases PC12 cells proliferation and increases p27 levels. The proproliferative effect of SR in PC12 cells is mediated, in part, by the phosphatidylinositol 3 kinase (PI3K)/serine-threonine protein kinase (AKT) pathway. Transfection of Sctr in Y1 adrenocortical carcinoma cells, expressing low endogenous levels of Sctr, stimulates cell proliferation also, in part, via the PI3K/AKT signaling cascade. Because of the link between SR and PI3K/AKT signaling, tumor cells expressing high levels of the receptor (MENX-associated primary pheochromocytoma and NCI-H727 human bronchopulmonary carcinoid cells) respond well and in a SR-dependent manner to PI3K inhibitors, such as NVP-BEZ235. The association between SR levels and response to PI3K inhibition might open new avenues for the treatment of tumors overexpressing this receptor.

SiRNA inhibits replication of Langat virus, a member of the tick-borne encephalitis virus complex in organotypic rat brain slices

Tick-borne encephalitis virus is the causative agent of tick-borne encephalitis, a potentially fatal neurological infection. Tick-borne encephalitis virus belongs to the family of flaviviruses and is transmitted by infected ticks. Despite the availability of vaccines, approximately 2000-3000 cases of tick-borne encephalitis occur annually in Europe for which no curative therapy is available. The antiviral effects of RNA mediated interference by small interfering RNA (siRNA) was evaluated in cell culture and organotypic hippocampal cultures. Langat virus, a flavivirus highly related to Tick-borne encephalitis virus exhibits low pathogenicity for humans but retains neurovirulence for rodents. Langat virus was used for the establishment of an in vitro model of tick-borne encephalitis. We analyzed the efficacy of 19 siRNA sequences targeting different regions of the Langat genome to inhibit virus replication in the two in vitro systems. The most efficient suppression of virus replication was achieved by siRNA sequences targeting structural genes and the 3' untranslated region. When siRNA was administered to HeLa cells before the infection with Langat virus, a 96.5% reduction of viral RNA and more than 98% reduction of infectious virus particles was observed on day 6 post infection, while treatment after infection decreased the viral replication by more than 98%. In organotypic hippocampal cultures the replication of Langat virus was reduced by 99.7% by siRNA sequence D3. Organotypic hippocampal cultures represent a suitable in vitro model to investigate neuronal infection mechanisms and treatment strategies in a preserved three-dimensional tissue architecture. Our results demonstrate that siRNA is an efficient approach to limit Langat virus replication in vitro.

Phosphatase and tensin homolog regulates stability and activity of EphB1 receptor

Deregulation of receptor tyrosine kinases (RTKs) is linked to a broad range of cancers, stressing the necessity of studying their regulatory pathways. We and others demonstrated previously that c-Cbl is necessary for the lysosomal degradation of erythropoietin-producing hepatocellular B1 (EphB1) carcinoma and epidermal growth factor receptor (EGFR) RTKs. Moreover, the tumor suppressor phosphatase and tensin homolog (PTEN) was shown to modulate c-Cbl-dependent EGFR degradation. We therefore investigated the involvement of PTEN in EphB1 signaling and degradation. We used PTEN mutants, PTEN, and NHERF1 small interfering RNA in CHO-EphB1 and SW480 cells endogenously expressing EphB1 to delineate EphB1-PTEN interactions. PTEN was constitutively associated with c-Cbl, protecting it from degradation. EphB1 stimulation triggered ∼50% serine-threonine PTEN dephosphorylation and PTEN-Cbl complex disruption, a process requiring PTEN protein phosphatase activity. Both proteins independently translocated to EphB1, with PTEN in association with the scaffold protein NHERF1. Biologically, PTEN lipid phosphatase activity impairs EphB1-dependent cell adhesion and chemotaxis. This study demonstrates for the first time in mammalian cells that the Eph receptor and PTEN associate and influence their signaling. Moreover, it contributes to the emerging concept that PTEN regulates expression of RTKs through modulation of their degradation. Finally, it reveals a new role for PTEN protein phosphatase activity involved in this process.

DOCK2 is required for chemokine-promoted human T lymphocyte adhesion under shear stress mediated by the integrin alpha4beta1

The alpha4beta1 integrin is an essential adhesion molecule for recruitment of circulating lymphocytes into lymphoid organs and peripheral sites of inflammation. Chemokines stimulate alpha4beta1 adhesive activity allowing lymphocyte arrest on endothelium and subsequent diapedesis. Activation of the GTPase Rac by the guanine-nucleotide exchange factor Vav1 promoted by CXCL12 controls T lymphocyte adhesion mediated by alpha4beta1. In this study, we investigated the role of DOCK2, a lymphocyte guanine-nucleotide exchange factor also involved in Rac activation, in CXCL12-stimulated human T lymphocyte adhesion mediated by alpha4beta1. Using T cells transfected with DOCK2 mutant forms defective in Rac activation or with DOCK2 small interfering RNA, we demonstrate that DOCK2 is needed for efficient chemokine-stimulated lymphocyte attachment to VCAM-1 under shear stress. Flow chamber, soluble binding, and cell spreading assays identified the strengthening of alpha4beta1-VCAM-1 interaction, involving high affinity alpha4beta1 conformations, as the adhesion step mainly controlled by DOCK2 activity. The comparison of DOCK2 and Vav1 involvement in CXCL12-promoted Rac activation and alpha4beta1-dependent human T cell adhesion indicated a more prominent role of Vav1 than DOCK2. These results suggest that DOCK2-mediated signaling regulates chemokine-stimulated human T lymphocyte alpha4beta1 adhesive activity, and that cooperation with Vav1 might be required to induce sufficient Rac activation for efficient adhesion. In contrast, flow chamber experiments using lymph node and spleen T cells from DOCK2(-/-) mice revealed no significant alterations in CXCL12-promoted adhesion mediated by alpha4beta1, indicating that DOCK2 activity is dispensable for triggering of this adhesion in mouse T cells, and suggesting that Rac activation plays minor roles in this process.

Histamine increases sphingosine kinase-1 expression and activity in the human arterial endothelial cell line EA.hy 926 by a PKC-alpha-dependent mechanism

Sphingosine 1-phosphate (S1P) is a potent mitogenic signal generated from sphingosine by the action of sphingosine kinases (SKs). In this study, we show that in the human arterial endothelial cell line EA.hy 926 histamine induces a time-dependent upregulation of the SK-1 mRNA and protein expression which is followed by increased SK-1 activity. A similar upregulation of SK-1 is also observed with the direct protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate (TPA). In contrast, SK-2 activity is not affected by neither histamine nor TPA. The increased SK-1 protein expression is due to stimulated de novo synthesis since cycloheximide inhibited the delayed SK-1 protein upregulation. Moreover, the increased SK-1 mRNA expression results from an increased promoter activation by histamine and TPA. In mechanistic terms, the transcriptional upregulation of SK-1 is dependent on PKC and the extracellular signal-regulated protein kinase (ERK) cascade since staurosporine and the MEK inhibitor U0126 abolish the TPA-induced SK-1 induction. Furthermore, the histamine effect is abolished by the H1-receptor antagonist diphenhydramine, but not by the H2-receptor antagonist cimetidine. Parallel to the induction of SK-1, histamine and TPA stimulate an increased migration of endothelial cells, which is prevented by depletion of the SK-1 by small interfering RNA (siRNA). To appoint this specific cell response to a specific PKC isoenzyme, siRNA of PKC-alpha, -delta, and -epsilon were used to selectively downregulate the respective isoforms. Interestingly, only depletion of PKC-alpha leads to a complete loss of TPA- and histamine-triggered SK-1 induction and cell migration. In summary, these data show that PKC-alpha activation in endothelial cells by histamine-activated H1-receptors, or by direct PKC activators leads to a sustained upregulation of the SK-1 protein expression and activity which, in turn, is critically involved in the mechanism of endothelial cell migration.