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Trypsin cleavage has been used to probe structure-function relationships of the Escherichia coli ATP synthase (ECF1F0). Trypsin cleaved all five subunits, alpha, beta, gamma, delta, and epsilon, in isolated ECF1. Cleavage of the alpha subunit involved the removal of the N-terminal 15 residues, the beta subunit was cleaved near the C-terminus, the gamma subunit was cleaved near Ser202, and the delta and epsilon subunits appeared to be cleaved at several sites to yield small peptide fragments. Trypsin cleavage of ECF1 enhanced the ATPase activity between 6- and 8-fold in different preparations, in a time course that followed the cleavage of the epsilon subunit. This removal of the epsilon subunit increased multisite ATPase activity but not unisite ATPase activity, showing that the inhibitory role of the epsilon subunit is due to an effect on cooperativity. The detergent lauryldimethylamine oxide was found to increase multisite catalysis and also increase unisite catalysis more than 2-fold. Prolonged trypsin cleavage left a highly active ATPase containing only the alpha and beta subunits along with two fragments of the gamma subunit. All of the subunits of ECF1 were cleaved by trypsin in preparations of ECF1F0 at the same sites as in isolated ECF1. Two subunits, the beta and epsilon subunits, were cleaved at the same rate in ECF1F0 as in ECF1 alone. The alpha, gamma, and delta subunits were cleaved significantly more slowly in ECF1F0.(ABSTRACT TRUNCATED AT 250 WORDS)

In the present study, E6E7 and E6 proteins of human papillomaviruses (HPVs) associated with skin warts and cancer were compared for their transforming and carcinogenic abilities in primary human keratinocytes (PHKs). We show that E6E7 of cancer associated beta HPV types, notably 49 and 24, were able to extend the life span and enhance the clonogenic efficiency of PHKs when maintained in serum free/low calcium medium. Activities of the beta HPV E6E7 were lower than those of HPV16 E6E7. In contrast, E6 proteins from HPV types detected in skin warts or cancer, notably 10, 49 and 38, attenuated UVB induced protective responses in PHKs including cell death, proliferation arrest and accumulation of the proapoptotic proteins, p53, bax or bak. Together, this investigation revealed functional differences and commonalities between HPVs associated with skin warts and cancer, and allowed the identification of specific properties of beta HPVs supporting their involvement in skin carcinogenesis.

The protein which can be labelled by low concentrations of dicyclohexylcarbodiimide in the Mr region of 30 000-35 000 has been purified from pig heart mitochondria with a high yield and as a single band of apparent Mr 35 000 in dodecyl sulphate-containing gels. The protein is not identical with the phosphate carrier as suggested before, since the two proteins behave differently during isolation. Incorporation of the isolated 35 kDa dicyclohexylcarbodiimide-binding protein into lipid bilayer membranes causes an increase of the membrane conductance in definite steps, due to the formation of pores. The specific pore-forming activity increases during the purification procedure. The single pore conductance is about 4.0 nS, suggesting a diameter of 1.7 nm of the open pore. The pore conductance is dependent on the voltage across the membrane. Anion permeability of the pore is higher than cation permeability. These properties are similar to those described for isolated mitochondrial and bacterial porins. It is concluded that the 35 kDa dicyclohexylcarbodiimide-binding protein from pig heart mitochondria is identical with porin from outer mitochondrial membrane.

In this study we investigate the mechanism of intracellular pH change and its role in malignant transformation using the E7 oncogene of human papillomavirus type 16 (HPV16). Infecting NIH3T3 cells with recombinant retroviruses expressing the HPV16 E7 or a transformation deficient mutant we show that alkalinization is transformation specific. In NIH3T3 cells in which transformation can be turned on and followed by induction of the HPV16 E7 oncogene expression, we demonstrate that cytoplasmic alkalinization is an early event and was driven by stimulation of Na+/H+ exchanger activity via an increase in the affinity of the intracellular NHE-1 proton regulatory site. Annulment of the E7-induced cytoplasmic alkalinization by specific inhibition of the NHE-1, acidification of culture medium, or clamping the pHi to nontransformed levels prevented the development of later transformed phenotypes such as increased growth rate, serum-independent growth, anchorage-independent growth, and glycolytic metabolism. These findings were verified in human keratinocytes (HPKIA), the natural host of HPV. Results from both NIH3T3 and HPKIA cells show that alkalinization acts on pathways that are independent of the E2F-mediated transcriptional activation of cell cycle regulator genes. Moreover, we show that the transformation-dependent increase in proliferation is independent of the concomitant stimulation of glycolysis. Finally, treatment of nude mice with the specific inhibitor of NHE-1, DMA, delayed the development of HPV16-keratinocyte tumors. Our data confirm that activation of the NHE-1 and resulting cellular alkalinization is a key mechanism in oncogenic transformation and is necessary for the development and maintenance of the transformed phenotype.

It has previously been shown that the E7 protein from the cutaneous human papillomavirus type 1 (HPV1), which is associated with benign skin lesions, binds the product of the tumor suppressor gene retinoblastoma (pRb) with an efficiency similar to that of the E7 protein from the oncogenic HPV type 16. Despite this ability, HPV1 E7 does not display any activity in transforming primary cells. In addition, the two viral proteins differ in their mechanisms of targeting pRb. HPV16 E7 promotes pRb destabilization, while cells expressing HPV1 E7 do not show any decrease in pRb levels. In this study, we show that HPV1 E7, in contrast to HPV16 E7, has only a weak activity to neutralize the effect of cyclin-dependent kinase inhibitor p16 INK4a . By generation of HPV1/16 E7 chimeric proteins, we have identified a central motif in the two E7 proteins, which determines their different abilities to overcome the p16 INK4a -mediated cell cycle arrest. This motif is located downstream of the pRb-binding domain and comprises only three amino acids in HPV16 E7. Swapping this central motif in the two viral proteins causes an exchange of their activities involved in circumventing the inhibitory function of p16 INK4a . Most importantly, our data show that the efficiency of the E7 proteins in neutralizing the inhibitory effect of p16 INK4a correlates with their ability to promote pRb degradation.

Background The role of Merkel cell polyomavirus (MCV) infection in the etiology of non-melanoma skin cancers, other than Merkel cell carcinoma, is unclear. Previously, we reported a significant association between seropositivity to MCV capsid antigen and MCV DNA-positive cutaneous squamous cell carcinoma (SCC). Here we present associations between SCC and seroreactivity to MCV T-antigen (T-Ag) oncoprotein, as well as MCV DNA detected in eyebrow hairs. Findings A clinic-based case–control study, including 171 SCC cases and 300 controls without skin cancer, was conducted at Moffitt Cancer Center in Tampa, Florida. Multiplex assays were used to measure serum antibodies against MCV small and large T-Ag and MCV DNA in both eyebrow hairs and SCC tumors (n = 144). Odds ratios (ORs) and 95 % confidence intervals (CIs) were estimated using logistic regression to evaluate the associations between MCV and SCC. No significant association was observed between seroreactivity to MCV full-length large or small T-Ag and SCC, overall [ORlarge T-Ag = 0.99 (0.48-2.08), ORsmall T-Ag = 0.31 (0.06–1.62)] or when comparing tumor MCV DNA-positive cases to controls [ORlarge T-Ag = 1.06 (0.38–2.93)]. Only presence of MCV DNA in eyebrow hairs was significantly associated with MCV DNA-positive SCC [OR = 4.05 (2.01–8.18)]. Conclusion MCV infection is unlikely to play a direct role in SCC.

To investigate how adenovirus E1A controls cell proliferation, we have fused E1A to the hormone-binding domain of the human estrogen receptor (ER) and introduced the E1A-ER chimeric gene together with an activated ras gene into primary rat embryo fibroblasts. Cell lines derived from this transfection proliferate in an estrogen-dependent manner. Estrogen-dependent activation of E1A-ER led to a rapid induction of both cyclin E and cyclin A gene expression. In contrast, levels of cyclin D1 were strongly reduced by activation of E1A-ER. Similar changes in cyclin gene expression were observed when primary human fibroblasts were infected with wild-type adenovirus and when adenovirus E1A was stably expressed in NIH 3T3 cells. Our findings suggest that activation of cyclin A and E, but not D1, gene expression by E1A precedes and may be responsible for E1A-dependent cell proliferation. In contrast, we found that quantitative disruption of complexes between the E2F transcription factor and the retinoblastoma protein is not required for E1A-dependent S-phase entry.

A total of 21 squamous-cell carcinoma of the conjunctiva (SCC) and 22 control subjects had conjunctival samples tested for human papillomavirus (HPV) types using PCR-based assays. Epidermodysplasia verruciformis HPV types were found in 86% of SCC cases and 36% of control subjects (Odds ratio=12.0), suggesting a role of HPVs in the aetiology of SCC.

Studies on human papillomavirus type 16 have demonstrated that the product of the early gene, E7, plays a key role in the immortalization and malignant transformation of the host cell. Several of the biological activities of HPV16 E7 are mediated by inactivation of the members of the pocket protein family, pRb, p107 and p130. In this study, we have characterized the in vitro properties of five E7 proteins from benign and malignant HPV types (10, 32, 48, 54, 77). We show that these E7 proteins associate with pRb and p107 with different efficiencies. All E7s increased the proliferative rate of immortalized rodent fibroblasts cultured in 10% calf serum containing medium. This property is completely independent of their ability to associate with the pocket proteins. Furthermore, all E7s, except HPV10 E7, stimulate G1/S progression and activated the cyclin E and cyclin A promoter in the absence of growth factors. This activity also does not correlate with the E7-efficiency of binding the pocket proteins. Together these data provide evidence that different E7s alter the regulation of the cell cycle by diverse mechanism(s). Finally, this comparative analysis of the different E7 proteins demonstrates that the oncogenicity of a HPV type is not determined by the ability of E7 to associate with the pocket proteins.

To test the use of recombinant streptococci as live vaccine vectors, colonizationl immunization experiments were performed with Streptococcus gordonii expressing heterologous cell-surface antigens. Three isogenic strains of S. gordonii were used: a wildtype, a recombinant expressing the M6 protein of Streptococcus pyogenes, and a recombinant expressing the E7 protein of human papillomavirus type 16 as a fusion with the M6 protein. A single dose of live bacteria was used to inoculate outbred mice, and it was found that: (i) mice were stably colonized by a single intranasalloral inoculum of S. gordonii; (ii) recombinant strains were equally effective as wild-type in colonizing mice; (iii) two months after the inoculum, orallpharyngeal swabs of 83.3% of animals were still positive for isolation of S. gordonii; (iv) recombinant S. gordonii isolated from colonized mice were always positive for expression of the heterologous antigens; (v) live bacteria induced a systemic immune response, since sera of mice colonized with recombinant S. gordonii contained IgG specific for the heterologous cell-surface antigens; (vi) this immune response depended upon the effective colonization by live bacteria, since killed bacteria did not induce such a response.

Background "High risk" Human Papillomavirus strains are the causative agents of the vast majority of carcinomas of the uterine cervix. In these tumors, the physical integration of the HPV genome is a frequent, though not invariable occurrence, but the constitutive expression of the E6 and E7 viral genes is always observed, suggesting key roles for the E6 and E7 oncoproteins in the process of malignant transformation. The "intracellular antibody" technology using recombinant antibodies in single-chain format offers the possibility of targeting a protein in its intracellular environment even at the level of definite domains thus representing a valuable strategy to "knock out" the function of specific proteins. Methods In this study, we investigate the in vitro activity of two single-chain antibody fragments directed against the "high-risk" HPV 16 E7 oncoprotein, scFv 43M2 and scFv 51. These scFvs were expressed by retroviral system in different cell compartments of the HPV16-positive SiHa cells, and cell proliferation was analyzed by Colony Formation Assay and EZ4U assay. The binding of these scFvs to E7, and their possible interference with the interaction between E7 and its main target, the tumor suppressor pRb protein, were then investigated by immunoassays, PepSet™technology and Surface Plasmon Resonance. Results The expression of the two scFvs in the nucleus and the endoplasmic reticulum of SiHa cells resulted in the selective growth inhibition of these cells. Analysis of binding showed that both scFvs bind E7 via distinct but overlapping epitopes not corresponding to the pRb binding site. Nevertheless, the binding of scFv 43M2 to E7 was inhibited by pRb in a non-competitive manner. Conclusions Based on the overall results, the observed inhibition of HPV-positive SiHa cells proliferation could be ascribed to an interaction between scFv and E7, involving non-pRb targets. The study paves the way for the employment of specific scFvs in immunotherapeutic approaches against the HPV-associated lesions.

Background Only a small portion of HPV 16 infections persist and can lead to cervical intraepithelial lesions and cancer. Factors that favour HPV persistence versus clearance are still poorly understood, but several studies have suggested that HPV intra-type variants may influence persistence and clinical outcome. The aim of this study was to assess the possible association between HPV 16 variants and the risk for viral persistence in the general population of France. Methods One hundred and forty two women infected with HPV 16 with normal cytology, without previous treatment for cervical lesions, and with a valid second follow-up visit 4 to 16 months later, were selected from patients participating in routine cervical cancer screening in the Reims HPV Primary Screening Cohort Study. HPV intra-type variants were determined by sequencing the HPV 16 E6 open reading frame, and were compared for viral persistence at the second visit using odds ratios (OR) to estimate relative risk. Results Although no statistically significant differences in risk for persistence were observed by the HPV 16 variant lineage, European variants containing the polymorphism 350 T (EUR-350 T) appeared to persist more often than those containing 350 G (EUR-350 G) (OR = 1.6, 95% CI = 0.8-3.4). Conclusions No strong differences were observed in the risk of viral persistence for the HPV 16 variants that predominate in France.

Several independent studies have presented evidence for the involvement of human papillomaviruses (HPV) in the aetiology of human breast cancer, while others have reported the opposite findings. Here, we have analysed by a high sensitive multiplex PCR-based method the prevalence of alpha mucosal and beta cutaneous HPV DNA in 90 ductal lavages, colostrum and milk. Ten of the 70 DLs analyzed (14%) contained a single or multiple beta HPV types, while DNA from mucosal high-risk HPV types was detected in only one sample (1/70). A strong reduction of HPV positivity in DL fluids was observed in 45 specimens collected after removal of the superficial layers of the nipple epidermis. All DLs were negative for the mucosal low-risk HPV types 6 and 11. Finally, HPV positivity was low in colostrum and milk. Our data show that DNA of alpha mucosa and beta cutaneous HPV types are rarely present in the breast fluids and suggest that a direct role of HPV in breast carcinogenesis is unlikely.

Human papillomaviruses (HPV) are small non-enveloped icosahedral viruses with double-stranded circular DNA. More than 200 different human papillomaviruses have been identified so far. The classification of the papillomaviridae family is based on pairwise nucleotide sequence identity across the L1 ORF, as it is well conserved and can allowa genome-based approach to PV classification. The discovery of new HPVs is of paramount importance to expand our knowledge on the role of these viruses in human diseases. In particular, while a subgroup of alphapapillomaviruses, referred to as high-risk HPV types, have been related to anogenital cancer and a subset of head and neck cancers, less is known about the role of HPVs from the other genera, such as beta and gamma types, in human cancers. Recent studies show a potential role of betapapillomaviruses in cutaneous squamous cell carcinoma (cSCC) together with ultraviolet (UV) radiation, but further studies are required. The methods used so far for the identification of novel HPVs in human specimens are based on PCR and Sanger sequencing, and several specific and broad-spectrum PCR primers, targeting the L1 ORF, have been designed for the amplification of HPV sequences. Nowadays, with the advent of high-throughput sequencing methods (i.e., NGS, ONT), we can expand this viral family with a more straightforward approach. Additionally, the large amount of data, generated by these new sequencing methods, requires the development of specific bioinformatics analyses for the identification and reconstruction of the viral sequences. The aim of this work was the development of an effective strategy for the identification and full genomic characterization of novel HPV types in human samples. In this work, known and new broad-spectrum PCR primers, all targeting a portion of the HPV L1 ORF, were used to amplify the HPV sequence on human skin (n=119) and oral (n=147) samples from healthy individuals. After, NGS analysis allowed the identification of 105 putative novel HPV types in addition to 296 known types. A specific workflow was developed to analyze the NGS sequencing data. In the second step of this work, starting from the NGS data, the whole genome of HPV227, a novel beta-2 papillomavirus, was obtained using a primer-walking strategy and Sanger sequencing. Finally, the MinION sequencing technology was used to obtain the whole genome of HPV227, directly from the original skin sample where this virus was discovered. A bioinformatics analysis was developed for the reconstruction of HPV genomes using MinION sequencing data. The entire genome of HPV227 was reconstructed, confirming the effectiveness of this strategy. Overall, this thesis describes a valid approach for the identification and full characterization of novel HPV genomes. Moreover, the discovery of 105 putative novel PV types expands our knowledge on this family of viruses, although further analyses are required for a complete characterization of these new viruses, Les papillomavirus humains (HPV) sont de petits virus icosaédriques non-enveloppés à ADN circulaire double brin. À ce jour, plus de 200 HPV ont été identifiés. La classification des Papillomaviridae est basée sur les identités de séquence nucléotidique du gène L1. La découverte de nouveaux HPV est d'une importance cruciale pour élargir nos connaissances sur ces virus. Alors qu'un sous-groupe HPV du genre alpha communément appelé "à haut risque", a été clairement associé aux cancers anogénitaux, et à certains cancers de la tête et du cou, il existe peu d’informations sur le rôle des HPV des genres bêta et gamma-HPVs dans les cancers humains. Des études récentes montrent que des bêta-HPVs pourraient jouer un rôle dans les cancers de la peau de type non-mélanome (NMSC), en association avec le rayonnement ultraviolet (UV). Toutefois, des études supplémentaires sont nécessaires pour confirmer cette hypothèse chez l’homme. Jusqu’à présent, les méthodes de choix utilisées pour l'identification de nouveaux HPVs dans des échantillons humains reposaient sur l’utilisation de la PCR et le séquençage de Sanger. Plusieurs amorces spécifiques ou à large spectre ciblant le gène L1, ont été développées pour l'amplification de séquences de HPV. De nos jours, avec l'avènement des méthodes de séquençage à haut débit (NGS), la possibilité d’élargir ces familles virales s’est accrue. Cependant, de grandes quantités de données sont générées par ces nouvelles méthodes de séquençage nécessitant le développement de méthodes bioinformatiques d'analyse spécifiques pour une identification et une reconstruction efficaces des séquences virales. Le but de ce travail de thèse a été de développer une stratégie pour l'identification des HPV, ainsi que la caractérisation du génome complet de nouveaux types, dans des échantillons humains. Au cours de ce travail de thèse, l’utilisation d’amorces à large spectre connues et validées, mais aussi l’utilisation d’amorces améliorées par notre laboratoire, toutes ciblant une portion du gène L1, ont été utilisées pour la recherche de séquences HPV dans des échantillons cutanés et oraux. L'analyse des données NGS a permis l'identification de 105 possible nouvelles séquences de PVs, ainsi que l’identification de 296 HPV connus. Une méthode d’analyse bioinformatique a été développée pour l’analyse des données de séquençage. La deuxième partie de ma thèse a consisté, à partir des données NGS précédemment obtenues, d’obtenir le génome entier de plusieurs HPVs. Ainsi, le génome entier de HPV227, un nouveau bêta-HPV, a été obtenu, en combinant plusieurs méthodes c.à.d. l'amplification par cercle roulant (ou rolling circle amplification - RCA), PCR pour amplification de longs fragments (ou “Long Range PCR”), le séquençage de Sanger par “primer walking”, et le clonage. Enfin, la technologie de séquençage par nanopores (MinION, Oxford Nanopore Technologies) a été utilisée afin d’obtenir le génome entier du HPV227, directement à partir de l'échantillon cutané d'origine et ainsi permettre un gain de temps important dans la caractérisation du génome complet des HPV. Pour ce faire, une méthode d’analyse bioinformatique des données de séquençage MinION pour la reconstruction des génomes de HPV a été développée. L'ensemble du génome du HPV227 a été reconstruit, confirmant l'efficacité de cette stratégie. Dans l'ensemble, cette thèse décrit et valide plusieurs approches pour l'identification et la caractérisation complète de nouveaux génomes de HPV. De plus, la découverte de 105 possible nouveaux PVs élargit nos connaissances sur cette famille de virus, bien que pour des analyses supplémentaires soient nécessaires pour la caractérisation complète de ces nouveaux virus

Human Papillomaviruses (HPV) are a family of small double-stranded DNA viruses that have a tropism for the mucosal and cutaneous epithelia. More than 200 types of HPV have been discovered so far and are classified into several genera based on their DNA sequence. Due to the role of some HPV types in human disease, ranging from benign anogenital warts to cancer, methods to detect and characterize HPV population in DNA sample have been developed. These detection methods are needed to clarify the implications of HPV at the various stages of the disease. The detection of HPV from targeted wet-lab approaches has traditionally used PCR- based methods coupled with cloning and Sanger sequencing. With the introduction of next generation sequencing (NGS) these approaches can be improved by integrating the sequencing power of NGS. While computational tools have been developed for metagenomic approaches to search for known or novel viruses in NGS data, no appropriate bioinformatic tool has been available for the classification and identification of novel viral sequences from data produced by amplicon-based methods. In this thesis, we initially describe five fully reconstructed novel HPV genomes detected from skin samples after amplification using degenerate L1 primers. Then, is the second part, we present PVAmpliconFinder, a data analysis workflow designed to rapidly identify and classify known and potentially new Papillomaviridae sequences from NGS amplicon sequencing with degenerate PV primers. This thesis describes the features of PVAmpliconFinder and presents several applications using biological data obtained from amplicon sequencing of human specimens, leading to the identification of new HPV types, Les papillomavirus humains (HPV) constituent une famille de petits virus à double brin d’ADN qui ont un tropisme pour les cellules épithéliales de la peau et des muqueuses. Plus de 200 types d’HPV ont été découverts, et classifiés en plusieurs genres taxonomiques en fonction de la constitution de leur séquence ADN. De part le rôle de certains HPV dans les maladies affectant les humains, allant de l’apparition de verrues anogénitales bénignes jusqu’au développement d’un cancer, il est nécessaire de développer des méthodes de détection et de caractérisation de la population d’HPV dans un échantillon d’ADN. Elles sont nécessaires à la clarification du rôle de l’HPV dans les différentes étapes de la progression de la maladie. Cette détection d’HPV lors d’approches ciblées en laboratoire a principalement reposé sur des méthodes de PCR couplées avec du séquençage Sanger. Avec l’introduction des nouvelles technologies de séquençage haut débit (NGS), ces approches peuvent être revisitées afin d’intégrer la puissance de séquençage de ces technologies. Alors que des outils d’analyse in-silico ont été développés pour la recherche de virus, connus ou nouveaux, à partir de données de NGS, aucun outil approprié n’est disponible pour la classification et l’identification de nouvelles séquences virales à partir de données produites par des méthodes de séquençage d’amplicons. Dans cette thèse, la première partie présente cinq nouveaux génomes d’HPV isolés via l’utilisation d’amorces d’amplification dégénérées ciblant le gène L1 à partir d’échantillons de peau humaine. Puis, dans une seconde partie, nous présentons PVAmpliconFinder, un outil d’analyse de données conçu pour identifier et classifier rapidement des séquences connues et potentiellement nouvelles de la famille Papillomaviridae, à partir de données de NGS d’amplicons générées par PCR via l’utilisation d’oligonucleotides dégénérés ciblants les HPV. Enfin, les caractéristiques de PVAmpliconFinder sont présentées, ainsi que plusieurs applications sur des données biologiques obtenues lors du séquençage d’amplicons de spécimens humains. Ces applications ont permis la découverte de nouveaux types d’HPV

Cancer represents the second most common cause of death in industrialized countries. Epidemiological and biological studies have now conclusively proved that a variety of infectious agents constitute one of the main causes of cancer worldwide. It has been pointed out that more than 20% of cancers are from infectious origin. HPV high-risk mucosal types are associated to 98% of all cervical cancer cases. Regarding EBV, over 90% of the world’s population is infected and can give rise to malignancies such as Burkitt lymphoma or Hodgkin disease.(Young and Rickinson 2004) Keys features for oncoviruses to induce cancer are firstly to per¬sist by dampening host immune responses and to induce genomic instability in the host by altering the regulation of the cell cycle leading the infected cells to an uncontrolled proliferation. The purpose of this thesis was to find new mechanisms by which EBV and HPV can promote carcinogenesis. We have shown that EBV can alter the regulation and expression of TLRs, the key effectors molecules of the innate immune response. EBV infection of human primary B cells resulted in the inhibition of TLR9 functionality. Our study described a mechanism used by EBV to suppress the host immune response by deregulating the TLR9 transcript through LMP1-mediated NF-κB activation. As TLR was found deregulated in many cancers, we hypothesized that TLR9 may also a direct role in the process of cell cycle control and that loss of its expression may lead to transformation of the cell. Our overall objective here was to study the role of TLR9 in suppressing the events that initiates transformation of epithelial cells in the setting of cervical cancer (virus-associated) and in head and neck cancer (non–virus-associated). A third project dealt with the mechanism cell cycle deregulation by the oncoprotein E6 which expressed during infection with HPV16. We reported that HPV16E6 targets the cellular factor p150Sal2, which positively regulates p21 transcription. HPV16E6 associates with p150Sal2, inducing its functional inhibition by preventing its binding to cis elements on the p21 promoter. These data described a novel mechanism by which HPV16E6 induces cell cycle deregulation with a p53-independent pathway preventing G1/S arrest and allowing cellular proliferation and efficient viral DNA replication, Le cancer représente la deuxième cause de mortalité dans les pays industrialisés. Il a été démontré que 20% des cancers sont d'origine infectieuse. Nous nous sommes intéressés à deux oncovirus HPV (virus du papillome humain) et EBV (Epstein-Barr Virus) responsable du cancer de l'utérus et de divers lymphome B réciproquement. Les événements clés pour le développement d'un cancer viro-induit sont la persistance du virus via la dérégulation des réponses immunitaires et l'induction d'une instabilité gé¬nomique via une dérégulation du cycle cellulaire. Nous avons donc cherché si EBV était capable d'altérer la réponse immunitaire innée. Nous avons montré que EBV était capable d'inhiber TLR9 un acteur clef de la réponse immunitaire innée. Comme TLR9 est inhibé dans un certain nombre de cancers, nous nous sommes demandé si ce récepteur pouvait également, avoir un rôle dans l'oncogenèse. Nous avons montré que la réexpression de TLR9 induisait un ralentissement transitoire de la prolifération cellulaire. Nous nous sommes par la suite intéressés aux mécanismes de dérégulation du cycle cellulaire induits par E6 une oncoprotéine de HPV16. Nous avons trouvé un nouveau mécanisme d'inhibition de l'inhibiteur du cycle cellulaire, p21. HPV16E6 se lie et inhibe les fonctions de du facteur de transcription p150Sal2, ce qui induit une inhibition de p21 dans un contexte p53 indépendant