Étude de la sortie du virus herpès simplex de type 1 (HSV 1) hors du noyau

Herpes simplex virus type 1 (HSV 1) affects the majority of the world population. HSV 1 causes various deleterious symptoms with the most common being facial mucosal lesions usually named cold sores. The virus can also contribute to more serious effects such as corneal blindness and neurological problems. The virus is permanently residing in the host body. Despite the existence of several treatments against HSV 1 symptoms, no drug is able to eliminate the virus. In order to improve knowledge of the viral cycle of HSV 1, this project focuses on the transport of the virus in the host cell. During this project we collect data to detail the modus operandi used by HSV 1 to leave cellular compartments such as the nucleus and the TGN. The different experimentations achieved during this PhD allowed the publication of three articles, including one selected as worthy of note by the editors of “Journal of virology” and a fourth article that has been submitted.  Firstly, an in vitro assay that reproduces the exit of HSV 1 virus from nuclei was established via the isolation of nuclei from infected cells. We found that, as in intact cells, capsids escaped the isolated nuclei in the in vitro assay by budding through the inner nuclear membrane, accumulated as enveloped capsids between the two nuclear membranes, and were released in cytoplasm exclusively as unenveloped capsids. These observations support the de-envelopment / re-envelopment model of transport.  Secondly, to identify viral players implicated in the nuclear egress of HSV 1, viral proteins associated with nuclear released capsids were investigated. HSV 1 has a multilayered morphology that includes a DNA genome, a capsid, a tegument and an envelope. The tegument represents viral proteins added sequentially on the viral particle. The sequential order and intracellular compartments where the tegument is added are the subject of intense research. The in vitro assay was used to investigate this tegumentation process. The acquired data suggest a sequential process that involved the acquisition of viral proteins UL36, UL37, ICP0, ICP8, UL41, UL42, US3 and possibly ICP4 on capsids released by the nucleus. Thirdly, to obtain information regarding another process of egress of HSV 1 from a membranous cellular organelle, the egress of HSV 1 from the TGN was also studied. The study revealed the implication of the cellular protein kinase D (PKD) in HSV 1 post-TGN transport. The involvement of this kinase, known to regulate the transport of small cargos, highlights the post TGN trafficking of both small and large entities (such as HSV 1) by a common machinery, in sharp contrast to earlier steps of transport. This indicates that the TGN is not only a sorting station but also a meeting point where different intracellular routes can meet.  All these outcomes contribute to a better understanding of the complex maturation process of HSV 1 that could lead to the development of better tools to fight the virus. Results acquired concerning HSV 1 could also be applied to other viruses. Besides their relevance in the virology field, findings provided by this project also supply new details about cellular biology concerning intracellular transport.

Keyphrases: PKD, capsid, egress, herpesvirus, intracellular transport, nuclear membrane, PKD, tegument, tegumentation, trans Golgi network, virus assembly