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L'endoribonucléase RNase L est essentiellement connu comme étant un acteur critique de l'immunité innée pour enrayer la progression d'une infection virale en clivant les ARN cellulaires. Son activité est régulée par de nombreux facteurs tels que la 2-5A et son inhibiteur, la RLI. Au cours de cette étude, nous avons démontré une implication de l'activité de la RNase L dans la régulation de la structure du domaine centromérique. Nous présentons dans ce manuscrit, les perturbations majeures engendrées par une augmentation ou une inhibition de l'activité de la RNase L représentées par une délocalisation de HP1-alpha et de CENP-C causant une déstructuration générale des chromosomes. Ces délocalisations de protéines centrales de la structure chromatinienne seraient causées par un défaut de la maturation des transcrits majeures péricentromériques lors d'une modulation de l'activité de la RNase L. Pour terminer, nous avons également identifié un potentiel trafic cyto-nucléaire empreinté par la RNase L. Nous proposons ainsi une fonction nucléaire inattendue de la RNase L par son implication dans la régulation des transcrits péricentromériques assurant l'intégrité structurale de la chromatine. / The endoribonuclease Latente (RNase L) is mostly known as a critical factor in the innate immunity during the cell's defence against a viral infection. The antiviral activity of RNase L which is characterize by it capacity of cleavage of viral RNA, is regulated by several factors like it activator the oligoadénylates 2-5A and his inhibitor RLI. In this manuscript, we have studied the role of the activity of RNase L in the regulation of the structure of centromeric domains. Our results show a general destructuration of chromosomes observed in cells over-expressing RNase L or RLI. These major aberrations are demonstrated by a delocalization of essentials proteins for the structure of chromatin: HP1-alpha and CENP-C. The mislocalization of these proteins could be provoked by a default in the maturation of major transcripts due to a modulation of the activity of RNase L. moreover, in this study, we have identified a mechanism regulating the cyto-nuclear shuttling of RNase L. therefore, we propose that a new nuclear function of RNase L: it's implication in the regulation of pericentromeric transcripts needed to stabilize the integrity of the structure of chromatin.

Human papillomavirus (HPV) related cervical cancer is still the most common gynaecological malignancy in developing countries and, as yet, there is no alternative to surgery for the treatment of HPV-associated pre-malignant lesions. HPV 'hijacks' the host-cell ubiquitin-proteasome system to degrade the p53 and Rb tumour suppressor proteins which in turn, leads to the development of cancer. Previous studies have shown that the HIV protease inhibitor lopinavir selectively inhibits the chymotryptic-like activity of the 26S proteasome which stabilises p53 and induces the apoptosis of HPV positive cervical carcinoma cells. Based on this it was hypothesised that lopinavir treatment of HPV positive cervical carcinoma cells would produce changes in the levels of a wide range of cellular proteins that are dis-regulated by HPV-related activation of the proteasome. In order to address this, antibody microarray screening was carried out on lopinavir treated and control untreated HPV positive SiHa cervical carcinoma cells. This showed lopinavir induced alterations in 51 proteins including the cellular antiviral defence protein RNase L. Lopinavir induced both a dose and time dependent increase in RNase L which was subsequently confirmed by western blotting. Transient siRNA silencing of RNase L expression reduced the lopinavir-dependent toxicity in SiHa cells, suggesting an important role for this protein in the toxicity of lopinavir in HPV infected cells. SiHa cells were much more sensitive to lopinavir than CaSKi cervical carcinoma cells which had much higher levels of the E6 protein and did not up regulate RNase L. Furthermore, lopinavir treated HPV16 E6/E7 immortalised keratinocytes were also shown to up regulate RNase L protein expression and these cells were much more sensitive to lopinavir induced apoptosis than mortal control keratinocytes. In addition, transient expression of RNase L in RNase L-deficient C33A cells and the same cells stably transfected with HPV16 E6 (C33AE6) demonstrated that E6 protected these cells from RNaseL-induced cell death. Surprisingly, analysis of RNase L protein levels in these cells demonstrated that E6 did not induce the degradation of the RNase L protein. Instead it was found that E6 stabilised the interaction between RNase L and its endogenous inhibitor protein, ABCE1, and that lopinavir de-stabilised this interaction. Given that C33A tumour cells, E6/E7 immortalised keratinocytes and hTert immortalised keratinocytes are all sensitive to lopinavir, this implies that this compound does not specifically target HPV immortalised cells but rather targets immortalised cells in general, regardless of how this was achieved. The optimum concentration of lopinavir for all these effects was 25 μM, which is 15-fold higher than is observed in cervico-vaginal secretions following oral dosing with the drug Kaletra. In conclusion these results have confirmed the potential of lopinavir to treat HPV related pre-cancerous cervical lesions and provided at least part of the mode-of-action. Indeed they strongly support the use of lopinavir as a low-cost, self-applied topical alternative to surgery for this disease which will be of particular benefit in low-resource countries. Finally, the ability of lopinavir to induce apoptosis of non-HPV related immortalised cells merits further investigation since this indicates this drug may be useful for the treatment of other non HPV related pre-malignant conditions.

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L'insulinorésistance, caractérisée par l'incapacité des organes impliqués dans le métabolisme énergétique (tissu adipeux, muscles squelettiques et foie) à répondre à l'insuline, tient une place centrale dans la physiopathologie des complications métaboliques de l'obésité. L'apparition d'une insulinorésistance chez un sujet obèse est plurifactorielle et les mécanismes moléculaires impliqués ne sont à ce jour pas complètement élucidés.L'expansion majoritairement hyperplasique du tissu adipeux conduit à une hypoxie et un stress des adipocytes, induisant un relargage accru de cytokines inflammatoires et d'acides gras libres (AGL). Les AGL se fixent eux-mêmes sur les récepteurs toll-like (TLRs) de l'immunité innée, dont l'activation aboutit également à la sécrétion de cytokines inflammatoires. Ces AGL et cytokines, véhiculés par la circulation systémique, contribuent, avec la coopération des macrophages infiltrant le tissu adipeux, au développement d'une inflammation chronique de bas grade. Ainsi, les perturbations de l'homéostasie énergétique, associées à une activation du système immunitaire sont à l'origine d'une atteinte globale de la sensibilité à l'insuline de l'organisme, particulièrement délétère au métabolisme musculaire.Cette étude porte sur le rôle d'un effecteur de l'immunité innée, l'endoribonucléase latente (RNase L), dont l'expression est régulée par les interférons de type I et l'activation, par un oligoadénylate, le 2-5A. La RNase L clive les ARNs cellulaires conduisant à l'inhibition spécifique de l'expression de certains gènes. Nous montrons par ce travail l'implication de la RNase L dans le contrôle de la différenciation cellulaire et la pathogenèse de l'insulinorésistance associée à l'obésité, via la régulation des voies de l'inflammation au niveau des tissus adipeux et musculaire. / Insulin resistance, which is characterized by the incapacity of organs involved in the energetic metabolism (adipose tissue, skeletal muscles and liver) to respond to insulin, has a central place in the pathophysiology of the metabolic complications associated to obesity. The onset of insulin resistance in obese subjects is multifactorial and the molecular mechanisms involved have not yet been completely elucidated.The mainly hyperplasic expansion of white adipose tissue leads to hypoxia and stress in adipocytes, inducing an increased release of inflammatory cytokines and free fatty acids (FFA). FFA bind and activate the toll-like receptors (TLR) of the innate immunity system, leading to the secretion of inflammatory cytokines. These FFA and cytokines, taken by the systemic circulation, contribute, with the cooperation of macrophages infiltrating the adipose tissue, to the development of a chronic low-grade inflammation. Thus, the disturbances of the energetic homeostasis, associated with an activation of the immune system cause a global impairment of insulin sensitivity of the body, with particularly deleterious effects on muscular metabolism.This study focuses on the role of an effector of innate immunity, the latent endoribonuclease (RNase L). RNase L expression is regulated by type I interferons and is activated by the 2-5A oligoadenylate. RNase L splits cellular RNA, thus leading to the specific inhibition of the expression of certain genes. In this study, we demonstrate the implication of RNase L in the control of cell differentiation and the pathogenesis of obesity-associated insulin resistance, via the regulation of inflammatory pathways in the adipose and muscular tissues.

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