STUDIO DEI MECCANISMI MOLECOLARI ALLA BASE DEL COINVOLGIMENTO DEI MULTIVESICULAR BODY NEL CICLO REPLICATIVO DEL CITOMEGALOVIRUS UMANO

The eucaryotic endosomal system is a complex network of vesicles and organelles surrounded by membranes which coordinates protein transport between the plasma membrane, the trans-Golgi network (TGN) and the lysosomes. A central role at this level is played by an organelle named multivesicular body (MVB). Several proteins involved in the MVB biogenesis are essential for budding of RNA-enveloped viruses, like retroviruses (Göttlinger et al., 1991), rhabdoviruses, filoviruses (Strack et al., 2000), arenaviruses and paramyxovirus (Strack et al., 2003). More recently it has been clarified that also some DNA-enveloped viruses, and in particular Herpes simplex virus type 1 (HSV-1) (Calistri et al., 2007; Crump et al., 2007), Hepatitis B Virus (HBV) (Lambert et al., 2007; Watanabe et al., 2007), Human Herpes Virus type 6 (HHV-6) (Mori et al., 2008) and Human Cytomegalovirus (HCMV) (Tandom et al., 2009), exploit the MVB membranes for their assembly and budding. The more accredited view concerning herpesviruses envelopment and budding is the ‘double envelopment theory’, envisioning that virion acquires at the level of the inner leaflet of the nuclear membrane a primary envelope, that it is lost by budding from the outer nuclear membrane. Finally, virions acquire the secondary and final envelope at the level of intracytoplasmic membranous organelles. HCMV morphogenesis is completed in a virally induced perinuclear compartment, referred as ́assembly compartment’ or ‘assembly complex’ (AC). This project moves from the data obtained in our laboratory regarding HSV-1 gB as one of the protein linking the virus to the MVB pathway. Indeed, the glycoprotein colocalizes with well-known MVB markers and its intracellular trafficking and maturation require the correct biogenesis of these organelles. Furthermore, gB is ubiquitinated in the C-terminal tail at the level of residues involved in endocytosis and trafficking between endosomes, TGN and lysosomes (Calistri et al., 2007). The aim of this work was to contribute to elucidate ...