Transition metal bis(thiosemicarbazone) complexes have been of great interest in the last five decades. One of the most striking features of these complexes is that they possess a wide range of biological properties including antimalarial, antibacterial and anticancer activity. Zinc and copper bis(thiosemicarbazone) complexes have recently attracted attention due to their intracellular fluorescence and anticancer activity, respectively. The present work “Targeting Cancer Cells and Live Cell Imaging Using Bis(thiosemicarbazone) Complexes of Copper and Zinc” is an effort to target cancer cells using folic acid or biotin linked anticancer active copper bis(thiosemicarbazone) complexes. Interestingly, bis(thiosemicarbazone) ligands form zinc complexes that could be used to image cancer cells and one of the ligands could be used for imaging zinc in the cells. Chapter 1, provides a brief introduction to metal complexes in medicine. Different classes of metallodrugs and their mechanism of action are listed. A short discussion on different types of diagnostic drugs and transition metal complexes possessing anticancer activity is presented. An overview of the strategies available to target cancer cells is included. Furthermore, the use of thiosemicarbazone compounds for anticancer activity is reviewed in detail. Recent examples of bis(thiosemicarbazone) compounds in medicinal studies is briefly mentioned. This section ends with the scope of the present work which involves bis(thiosemicarbazone) complexes of zinc and copper. Chapter 2, “Zinc bis(thiosemicarbazone) complexes for live cell imaging and anticancer activity” deals with the synthesis and characterization of a series of mononuclear and binuclear zinc bis(thiosemicarbazone) complexes by varying substituents at the diketone moiety or at the thiosemicarbazide fragment of the ligand. The crystal structures of mononuclear ligand benzil-bis(4-pyrrolidine-3-thiosemicarbazone) (BTSCH2), zinc glyoxal-bis(4-methyl-4-phenyl-3-thiosemicarbazone) [Zn(GTSC)]3 and [Zn(BTSC)(DMSO)] complexes were determined using single-crystal X-ray crystallography. Here, the mononuclear zinc complexes were utilized as live cell imaging agents whereas binuclear zinc complexes proved to be anticancer agents. Among the many mononuclear complexes prepared, the trimeric zinc complex derived from glyoxal- bis(4-methyl-4-phenyl-3¬thiosemicarbazone) was found to be the most fluorescent complex owing to its unique structure. This permitted live cell imaging in a number of cancer cell lines. In comparison with the well studied zinc biacetyl-bis(4-methyl-3-thiosemicarbazone) Zn(ATSM) complex, which was used as a reference, [Zn(GTSC)]3 had a 2.5 fold higher fluorescence quantum yield in DMSO. The cellular fluorescence was measured in collaboration with Prof. K.Somasundaram’s laboratory at MCBL using flow cytometry. It was observed that [Zn(GTSC)]3 had 3 to 12 fold higher fluorescence than Zn(ATSM) in various cell lines (n = 9) of different tissue origin. Confocal fluorescence microscopy studies established that [Zn(GTSC)]3 localizes in the nucleus of human breast cancer MCF-7 and MDA-MB-231 cells within 30 minutes of addition. Moreover, [Zn(GTSC)]3 showed relatively less cytotoxicity compared to the Zn(ATSM) complex in all the cancer cell lines tested. DNA interaction studies such as binding and cleavage showed that [Zn(GTSC)]3 was less harmful to DNA as well. All these features make [Zn(GTSC)]3 a good fluorescent imaging agent for live cells. Binuclear zinc bis(thiosemicarbazone) complexes were also synthesized and their cytotoxicity was evaluated in different cancer cells. One of the ligands, 1,3-bis{biacetyl-2′-"-N-pyrrolidinethiosemicarbazide)-3′-(4"-N-thiosemicarbazide)} propane (ProBATpyrH4), and its zinc complex were found to show excellent anticancer activity against human hepatocellular cancer (HepG2) cell line. However, the cellular uptake studies as followed by flow cytometry revealed that these compounds do not fluoresce inside the cells. However, the DNA interaction studies using ethidium bromide displacement assay revealed that these complexes have better binding ability to DNA than mononuclear zinc complexes and the viscometric titrations suggested the binding mode to DNA is through partial intercalation. Apparently, these complexes do not induce DNA cleavage as evident from the cleavage experiments performed on pBR322 DNA. It is likely that their anticancer activity is due to unique DNA binding properties. Imaging zinc is important in the field of metallomics as alteration of zinc concentration in cells is associated with, or attributed to various diseases. In this regard, bis(thiosemicarbazone) ligands are useful. Chapter 3, “Imaging intracellular zinc using glyoxal-bis(4-methyl-4-phenyl-3-thiosemicarbazone) ligand” deals with imaging zinc in live cells using the bis(thiosemicarbazone) ligand, GTSCH2. Since the trimeric zinc complex is fluorescent, the corresponding ligand, GTSCH2, was utilized to visualize the zinc present within cells. The ligand GTSCH2 is found to be a selective fluorescence “turn-on” sensor for zinc. This sensor exhibited excellent sensitivity and selectivity towards zinc over other physiologically relevant cations. The binding affinity of GTSCH2 to zinc was estimated to be 0.59 nM in an aqueous MOPS (50 mM, NaCl; 100 mM; pH 7.3) buffer containing 30% DMSO, from competitive binding experiments carried out with ethylene glycol tetraacetic acid (EGTA). The sensor displayed maximal fluorescence response to zinc ion when present in the ratio of 1:1 and displayed stable fluoresence in the pH range 5.0 to 7.8, which suggests that the probe may be suitable for imaging zinc in both normal and cancer cells. The potential of GTSCH2 to image zinc inside the cell has been demonstrated in two human breast cancer cell lines using confocal fluorescence microscopy. Unlike mononuclear zinc complexes, the mononuclear copper bis(thiosemicarbazone) complexes are cytotoxic. Chapter 4, “Anticancer activity of copper bis(thiosemicarbazone) complexes” deals with the synthesis, characterization and anticancer activity of mononuclear copper bis(thiosemicarbazone) complexes. All of them were characterized by spectroscopic methods and in three cases by single crystal X-ray diffraction. The redox properties, studied by cyclic voltammetry, showed reversible one electron- reduction process that varied from –0.53 V to –0.18 V vsSCE. Anticancer activity for the synthesized complexes and their ligands were tested against many human cancer cell lines where the complexes Cu(GTSC) and Cu(GTSCHCl) derived from glyoxal-bis(4-methyl-4-phenyl-3-thiosemicarbazone) are found to be most cytotoxic (GI50 <0.1 µM to 2.1 µM) in five cancer cell lines tested. Moreover, the cytotoxicity is similar to that of adriamycin, a known anticancer drug, in all cell lines. However, it is less potent than a copper bis(thiosemicarbazone) analog, copper biacetyl-bis(4-methyl-3-thiosemicarbazone) Cu(ATSM), a well studied anticancer agent in many cell lines. Cellular studies were carried out for the selected complexes Cu(GTSC) and Cu(GTSCHCl) along with Cu(ATSM) on HCT116 colon cancer cells. The order of lipophilicity and cellular uptake as studied by ICP-OES are correlated with their cytotoxicity. Based on the interaction of these complexes with DNA using the ethidium bromide displacement assay, DNA -melting, -viscosity and -cleavage studies, it is suggested that these complexes intercalate partially with DNA. DNA cleavage studies using pBR322 DNA revealed that only Cu(GTSCHCl) complex cleaves DNA. Mechanistic discrimination studies suggest that the complex cleaves DNA through the hydrolytic pathway. Since the topoisomerase IIα (Topo IIα), a nuclear enzyme resolving topological problems of DNA, is considered as one of the possible molecular targets for a number of anticancer drugs including some of the copper thiosemicarbazone complexes, Topo IIαinhibition studies were carried out in human Topo IIα. Interestingly, many copper bis(thiosemicarbazone) complexes are able to inhibit Topo IIα activity by acting as Topo IIα poison. Cu(GTSCHCl) complex was found to be the most active in this series of complexes (90 % inhibition at 100 µM) and it inhibits the enzyme in a dose dependant manner. Based on the results, it was concluded that the cell death may be mediated, at least in part, through DNA cleavage and Topo IIαinhibition. Severe side effects, poor distribution profiles and or organ specific toxicity make the conventional chemotherapy of limited value with metal based drugs. Therefore, developing cancer-specific drug delivery systems is an urgent need in cancer therapy. Among the many strategies available to target cancer, targeting the receptors that are overexpressed in the cancer cell membrane is a novel strategy being used in recent studies. Therefore the last part my work, “Copper bis(thiosemicarbazone) complexes linked to poly(ethylene glycol) and multiwalled carbon nanotubes for targeted delivery to cancer cells ” was designed to target cancer cells. Here, copper complexes (therapeutic molecule) were attached with PEG and MWCNT (carrier) along with folic acid or biotin (targeting molecule). First, CuATSM–A was functionalized with a disulfide linker and connected with folic acid via a poly(ethylene glycol) (PEG600) linker. This was synthesized to target KB (human nasopharyngeal carcinoma) cells, a cell line that overexpresses the folate receptor on the cell surface. In order to investigate the targeting efficacy, the corresponding fluorescent labeled analogs and non-targeted PEG conjugates were synthesized. Flow cytometry studies with fluorescent marker (fluorescein isothiocyanate) labeled PEG analogs showed the targeting efficacy on KB cells. The copper complex, CuATSM–A, attached with biotin–PEG2000 also was synthesized to target high-biotin-using HeLa (human cervical carcinoma) cells. Multiwalled carbon nanotubes (MWCNT) were also used as nanocarriers. Here, the MWCNT was decorated with PEG600 diamine and then functionalized with the copper complex (therapeutic molecule), folic acid (targeting molecule), and FITC (fluorescent molecule). The conjugation of all the molecules with MWCNT is characterized by various spectroscopic techniques.

Please find the referenced videos attached / The physical ends of eukaryotic chromosomes consist of repetitive DNA sequences, which are associated with specialized proteins forming a nucleoprotein structure essential for the integrity of the linear chromosomes, and are known as telomeres. Telomerase is an enzyme responsible for the maintenance of the telomeric repeats at the end of the chromosomes. Telomerase is a ribonucleoprotein, which contains a catalytic subunit that possesses reverse transcriptase activity, and a RNA subunit that acts as a template, since it possess the telomeric repeat sequences necessary to amplify telomere ends. Telomeres are transcribed in most eukaryotes into a non-coding RNA know as TERRA (Telomeric repeats-containing RNA). It has been proposed that TERRA may act as a regulator of telomere homeostasis, and as an inhibitor of telomerase, however, its specific function is still unknown. In Saccharomyces cerevisiae, TERRA is rapidly degraded by the 5’-3’ Rat1 exonuclease, which has hampered its study by classic biochemical experiments in yeast. In this thesis, we report the use of cytological approaches to study TERRA in budding yeast. Two different approaches were used for this purpose: the fluorescent in-situ hybridization (FISH) and the labeling of TERRA by the MS2-GFP system, which allow the visualization of TERRA transcripts form a single telomere in living cells. With these two approaches, we observed that TERRA is expressed from a single telomere and accumulates as a single perinuclear foci, in a small percentage of cells population. We also demonstrate that TERRA expression occurs due to telomere shortening. We demonstrate that TERRA interacts in vivo with the telomerase RNA (TLC1) in yeast. Telomere elongation depends on the action of several telomerase molecules that are visible as clusters, which associate with telomeres in late S phase in yeast, and mammalian cells. In adidition, we show that TERRA stimulates the nucleation of telomerase clusters. By performing time course experiments of TERRA and TLC1 RNA in live cells, we observed that TERRA acts as a scaffold for generating telomerase clusters, which are then recruited in late S phase to the telomere from which TERRA molecules originated. The recruitment of TERRA to its telomere of origin is dependent on factors that control telomerase recruitment at telomeres like: Mre11, Tel1 and the yKu complex. We propose that a short telomere expresses TERRA to assemble and organize telomerase molecules, which later on allows their recruitment at the short telomere, where elongation is needed. Finally we showed an up-regulation of TERRA, and telomerase RNA TLC1, accompanied by a predominant cytoplasmic localization as cell growth progresses from exponential growth to diauxic shift, and stationary phase. In these conditions, TERRA foci co-localize with TLC1 RNA foci, suggesting that the function of TERRA as a scaffold molecule to generate telomerase cluster is necessary for this yeast cell growth phases. / Les télomères à l’extrémité des chromosomes constituent une structure d’ADN et de protéines essentielle à l’intégrité de ces chromosomes. La télomérase est l’enzyme responsable du maintien des répétitions télomériques à l’extrémité des chromosomes. Cette enzyme est constituée d’une sous-unité catalytique, qui possède une activité de transcriptase réverse, et d’une sous-unité d’ARN, qui fourni la matrice nécessaire à la synthèse des répétitions télomériques. Les ARN contenant des répétions télomériques (ou Telomeric repeats-containing RNA; TERRA) constitue une nouvelle classe d’ARN non-codants transcrits à partir des télomères et conservée chez la plupart des eucaryotes. TERRA a été proposé d’agir comme un régulateur de l‘homéostasie des télomères et comme inhibiteur de la télomérase, mais sa fonction spécifique reste inconnue. De plus, chez la levure Saccharomyces cerevisiae, TERRA est rapidement dégradé par l’exonucléase 5’-3’ Rat1, ce qui complique l’étude de cet ARN par les méthodes biochimiques classiques. Dans cette thèse, nous rapportons l‘utilisation d’une approche cytologique pour étudier TERRA dans les cellules de levures. Deux approches sont utilisées : l’hybridation in situ en fluorescence (FISH) et l’étiquetage de TERRA à l’aide du système MS2-GFP, qui nous permet de visualiser l’expression de TERRA transcrit d’un seul télomère dans des cellules vivantes. Avec ces deux approches, nous observons que TERRA exprimé à partir d’un seul télomère s’accumule dans un faible nombre de cellules, sous la forme d’un focus périnucléaire. De plus, nous montrons que TERRA est exprimé lorsque son télomère raccourcit. Par immunoprécipitation, nous montrons que TERRA interagit in vivo avec l’ARN de la télomérase de levure, TLC1. L’élongation des télomères dépend de l‘action de multiples molécules de télomérase, qui sont visibles sous la forme de clusters de télomérases, qui s‘associent en phase S avec les télomères chez la levure et les cellules de mammifère. Nous démontrons que TERRA stimule la nucléation de ces clusters de télomérase. Par imagerie en temps réel de TERRA et de l’ARN TLC1, nous observons que TERRA agit comme molécule d’échafaudage pour générer des clusters de télomérases, qui sont par la suite recrutés, en phase S, au télomère duquel TERRA a été exprimé. Le recrutement d’un focus de TERRA à son télomère d’origine dépend des facteurs contrôlant le recrutement de la télomérase aux télomères : Mre11, Tel1 et le complexe yKu. Nous proposons qu’un télomère court exprime TERRA pour assembler et organiser les molécules de télomérase, afin que celles-ci soit puissent être recrutées au télomère court pour permettre son élongation. Enfin, nous observons une surexpression de l’ARN de la télomérase TLC1 et de TERRA, ainsi qu’une accumulation cytoplasmique de ceux-ci sous la forme de foci, lorsque la cellule passe de la phase de croissance exponentiel à la phase diauxique, puis à la phase stationnaire. Dans ces conditions, les foci d’ARN TLC1 colocalisent avec les foci de TERRA, suggérant que la fonction de TERRA comme molécule d’échafaudage pour générer des foci de télomérase est aussi nécessaire durant ces phases du cycle de croissance des levures.

Chlamydien sind obligat intrazelluläre Bakterien, die sich in einem membranumschlossenen Kompartiment namens Inklusion vermehren. Nach Infektion fragmentiert der Golgi-Apparat der Wirtszelle in kleine Membranstapel. Dies verbessert die Aufnahme von Sphingolipiden und ist deshalb für die chlamydiale Vermehrung essentiell. Die infektionsinduzierte Golgi-Fragmentierung geschieht nach Spaltung des Golgi-Matrix-Proteins Golgin-84. In dieser Arbeit konnte, durch den Vergleich mit bekannten Substraten und Inhibitorstudien, die chlamydiale Protease CPAF (Chlamydia protease-like activity factor) als das Enzym identifiziert werden, das diese Spaltung induziert, abhängig von der Anwesenheit zweier Rab-Proteine, Rab6 und Rab11, die den zellulären Vesikeltransport kontrollieren und zur Inklusion rekrutiert werden. Die Fragmentierung des Golgi-Apparates verhinderte dessen Relokalisierung während der Zellpolarisierung nach Einbringen eines migratorischen Stimulus. Sowohl infizierte als auch Golgin-84-depletierte Zellen migrierten langsamer und randomisiert in einem Motilitätsassay. Die Relokalisierung des Golgi-Apparates konnte durch seine Stabilisierung mittels WEHD oder Rab-Depletion wieder gewonnen werden, was die Zellmotilität teilweise wieder herstellte. Darüber hinaus konnte gezeigt werden, dass die Infektion außer der Golgi-Reorientierung die Signaltransduktion durch GTPasen beeinflusst. Die Aktivität von Cdc42 in infizierten Zellen war erhöht und die Interaktionen mit vielen ihrer Effektoren laut quantitativer Massenspektrometrie stark verändert. Die Ergebnisse dieser Arbeit zeigen, dass CPAF die für Chlamydien lebenswichtige Golgin-84 Prozessierung und Fragmentierung des Golgi-Apparates auslöst. Dies verringert die Mobilität der Wirtszelle, vor allem da der Golgi-Apparat während der Polarisierung nicht mehr ausgerichtet werden kann, des Weiteren durch Modulierung der Protein-Protein-Interaktionen von Cdc42. / Chlamydia are obligate intracellular human pathogens that proliferate inside a membrane-bound compartment called the inclusion. In infected cells, the Golgi apparatus is fragmented into small ministacks that are aligned around the inclusion. This facilitates uptake of host cell sphingolipids and is essential for chlamydial development. Infection-induced Golgi fragmentation happens after processing of the Golgi matrix protein golgin-84. This work could, via comparison with well-known substrates and inhibitor studies, identify the chlamydial protease CPAF (Chlamydia protease-like activity factor) as the enzyme accountable for this cleavage. Golgi Fragmentation depended on two Rab proteins, Rab6 and Rab11, which control vesicle transport and are recruited to the Chlamydia inclusion. As a consequence of Golgi fragmentation, cells lost the capacity to reorient the Golgi apparatus during polarization after a migratory stimulus. Both infected and golgin-84 depleted cells with a permanently fragmented Golgi apparatus displayed decelerated and furthermore randomized migration in a motility assay. Relocalization of the Golgi apparatus could be restored via stabilizing WEHD treatment or Rab depletion which partly rescued cell motility. Moreover, it could be shown that migration signaling via small GTPases was influenced by Chlamydia infection. Infected cells exhibited activation of the small polarity GTPase Cdc42. Numerous interactions with downstream effectors were strongly altered in infected cells according to quantitative mass spectrometry. Particularly, the binding of Cdc42 to migration-associated effectors was decreased. The results of this work show that CPAF, by processing of golgin-84, induces Golgi fragmentation which is vitally important for Chlamydia. This disturbs host cell motility because the Golgi apparatus cannot be reoriented during polarization and, additionally, via the modulation of protein-protein-interactions of Cdc42.

No description available.

Abstract Desmoglein 3 (Dsg3) is an adhesion receptor in desmosomes, but relatively little is known about its role in cancer. In this study, the function of Dsg3 was investigated in oral squamous cell carcinoma (SCC) cell lines in vitro using locally established human leiomyoma tumor microenvironment (TME) matrices. Since Dsg3 has been identified as a key regulator in cell adhesion, we hypothesized that it may play a role in oral SCC cells adhesion and motility. Thus, one aim of the study was to explore this hypothesis by both gain and loss of function methods in four human buccal mucosa SCC SqCC/Y1 cell lines: transduction of vector control (Ct), full-length (FL) or two different C-terminally truncated Dsg3 mutants (&#916;238 and &#916;560). Live cell imaging was performed for 2D migration and 3D sandwich, alongside other assays. In 3D sandwich, we tested the effects of the monoclonal antibody, AK23, targeting the extracellular domain of Dsg3 in SqCC/Y1 cells. Our results showed that loss of Dsg3 disrupted cell adhesion and protein expression. In 2D assays, FL and Dsg3 mutants migrated faster with higher accumulated distances than Ct. In contrast with 2D, mutants showed accelerated invasion over the Ct in 3D models. The AK23 antibody inhibited only the invasion of FL cells. The TME in vivo consists of cellular and matrix elements playing a leading role in carcinoma progression. To study carcinoma cells invasion in vitro, mouse Matrigel® and rat type 1 collagen are the most commonly used matrices in 3D models. Since they are non-human in origin, they do not perfectly mimic human TME. To address this, we have developed a solid organotypic myoma disc model derived from human uterus leiomyoma tumor. Here, we introduce a novel Myogel, prepared from leiomyoma similar to Matrigel®. We validated Myogel for cell-TME interactions in 3D models, using SqCC/Y1 and HSC-3 cell lines. Compared with Matrigel® and type I collagen, oral SCC cell lines invaded more efficiently in Myogel containing matrices. This study describes promising 3D models using human TME mimicking Myogel which is suitable to analyze oral SCC cells both in carcinoma monocultures and in co-cultures, such as with TME fibroblasts. We also introduce a possible novel therapeutic target against Dsg3 to suppress cancer cell invasion. / Tiivistelmä Desmogleiini 3 (Dsg3) on desmosomien adheesioreseptori, jonka merkityksestä syövässä tiedetään vähän. Koska Dsg3 on tärkeä epiteelisolujen välisissä liitoksissa, oletimme sillä olevan vaikutusta myös suun karsinoomasolujen tarttumisessa ja niiden liikkuvuudessa. Testasimme hypoteesiamme muuttamalla Dsg3:n toimintaa ihmisen posken karsinoomasolulinjassa SqCC/Y1, josta oli aiemmin valmistettu neljä erilaista muunnosta: tyhjän vektorin sisältävä kontrollisolulinja (Ct), kokopitkää Dsg3 tuottava solulinja (FL), sekä kaksi Dsg3 C-päästä lyhennettyä mutanttisolulinjaa (&#916;238 ja &#916;560). Immunofluoresenssi-menetelmää käyttäen analysoimme solulinjoissamme solujen välisiä liitoksia. Lisäksi mittasimme solujen liikkeitä 2D-migraatio- ja 3D-sandwich-kokeissa. Testasimme myös Dsg3:n solunulkoista osaa tunnistavan monoklonaalisen vasta-aineen (AK23) vaikutusta solujen invaasioon. Osoitimme, että Dsg3:n rakenteen muuttaminen ja toiminnan estyminen häiritsi solujen tarttumista. 2D-kokeissa sekä FL että mutanttilinjat (&#916;238 ja &#916;560) migroivat kontrollisoluja nopeammin ja pidemmälle, mutta 3D-kokeissa vain mutanttilinjat invasoituivat kontrollisoluja tehokkaammin. AK23-vasta-aine esti vain FL-solujen invaasiota. Syöpäsolujen 3D-invaasiota mittaavissa kokeissa käytetään yleensä hiiren kasvaimesta valmistettua kaupallista Matrigeeliä® tai rotan kudoksista eristettyä tyypin I kollageenia. Tutkimusryhmämme on jo aiemmin kehittänyt organotyyppisen myoomamallin, jossa valmistamme myoomakudosnapit ihmisen kohdun leiomyoomakasvaimista. Tässä työssä valmistimme leiomyoomasta Myogeelia, vertasimme sitä Matrigeeliin®, sekä tutkimme tarkemmin Myogeeli-valmisteen soveltuvuutta 3D-tutkimuksiin. Totesimme, että kielen (HSC-3) ja posken (SqCC/Y1) karsinoomasolut invasoituivat tehokkaimmin Myogeeli-pitoisissa matrikseissa kuin Matrigeeliä® tai kollageeniä sisältävissä kasvatusalustoissa. Tutkimustulostemme perusteella Myogeeli-pohjaiset 3D-mallit soveltuvat hyvin sekä syöpäsolulinjojen invaasiotutkimuksiin että yhteisviljelmiin, joissa syöpäsoluja viljellään yhdessä syöpäkasvaimen ympärillä olevien solujen, kuten fibroblastien, kanssa.

No description available.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Approximately 2.8% of the world population is currently infected with hepatitis C virus (HCV). Neutralizing antibodies (nAbs) are often generated in chronic hepatitis C patients yet fail to control the infection. In the first two chapters of this study, we focused on two alternative routes of HCV transmission, which may contribute to HCV’s immune evasion and establishment of chronic infection. HCV was transmitted via a cell-cell contact-mediated (CCCM) route and in the form of exosomes. Formation of HCV infection foci resulted from CCCM HCV transfer and was cell density-dependent. Moreover, CCCM HCV transfer occurred rapidly, involved all four known HCV receptors and intact actin cytoskeleton, and led to productive HCV infection. Furthermore, live cell imaging revealed the temporal and spatial details of the transfer process. Lastly, HCV from HCV-infected hepatocytes and patient plasma occurred in both exosome-free and exosome-associated forms and the exosome-associated HCV remained infectious, even though HCV infection did not significantly alter exosome secretion. In the third chapter, we characterized HCV interaction with astrocytes, one of the putative HCV target cells in the brain. HCV infection causes the central nervous system (CNS) abnormalities in more than 50% of chronically infected subjects but the underlying mechanisms are largely unknown. We showed that primary human astrocytes (PHA) were very inefficiently infected by HCV, either in the free virus form or through cell-cell contact. PHA expressed all known HCV receptors but failed to support HCV entry. HCV IRES-mediated translation was functional in PHA and further enhanced by miR122 expression. Nevertheless, PHA did not support HCV replication regardless of miR122 expression. To our great surprise, HCV exposure induced robust IL-18 expression in PHA and exhibited direct neurotoxicity. In summary, we showed that CCCM HCV transfer and exosome-mediated HCV infection constituted important routes for HCV infection and dissemination and that astrocytes did not support productive HCV infection and replication, but HCV interactions with astrocytes and neurons alone might be sufficient to cause CNS dysfunction. These findings provide new insights into HCV infection of hepatocytes and astrocytes and shall aid in the development of new and effective strategies for preventing and treating HCV infection.