Identification of a role for the trans-Golgi network in human papillomavirus 16 pseudovirus infection

Human papillomavirus 16 (HPV16) enters its host cells by a process that most closely resembles macropinocytosis. Uncoating occurs during passage through the endosomal compartment, and the low pH encountered in this environment is essential for infection. Furin cleavage of the minor capsid protein, L2, and cyclophilin B-mediated separation of L2 and the viral genome from the major capsid protein, L1, are necessary for escape from the late endosome (LE). Following this exodus, L2 and the genome are found colocalized at the ND10 nuclear subdomain, which is essential for efficient pseudogenome expression. However, the route by which L2 and the genome traverse the intervening cytoplasm between these two subcellular compartments has not been determined. This study extends our understanding of this phase in PV entry in demonstrating the involvement of the Golgi complex. With confocal microscopic analyses involving 5-ethynyl-2'-deoxyuridine (EdU)-labeled pseudogenomes and antibodies to virion and cellular proteins, we found that the viral pseudogenome and L2 travel to the trans-Golgi network (TGN) following exit from the LE, while L1 is retained. This transit is dependent upon furin cleavage of L2 and can be prevented pharmacologically with either brefeldin A or golgicide A, inhibitors of anterograde and retrograde Golgi trafficking. Additionally, Rab9a and Rab7b were determined to be mediators of this transit, as expression of dominant negative versions of these proteins, but not Rab7a, significantly inhibited HPV16 pseudovirus infection.