Human papillomavirus (HPV)
infection is a multi-step process that implies complex interactions of the viral particles with cellular
proteins. The HPV capsid includes the two structural
proteins L1 and L2, that play crucial roles on infectious viral entry. L2 is particularly relevant for the intracellular trafficking of the
viral DNA towards the nucleus. Here, using proteomic studies we identified CCT
proteins as novel interaction partners of HPV-16 L2. The CCT multimeric complex is an essential
chaperonin which interacts with a large number of
protein targets. We analysed the binding of different components of the CCT complex to L2. We confirmed the interaction of this structural
viral protein with the CCT subunit 3 (CCT3) and we found that this interaction requires the N-terminal region of L2. Defects in HPV-16 pseudoviral particle (PsVs)
infection were revealed by
siRNA-mediated knockdown of some CCT subunits. While a substantial drop in the
viral infection was associated with the ablation of CCT component 2, even more pronounced effects on infectivity were observed upon depletion of CCT component 3. Using confocal immunofluorescence assays, CCT3 co-localised with HPV PsVs at early times after
infection, with L2 being required for this to occur. Further analysis showed the colocalization of several other subunits of CCT with the PsVs. Moreover, we observed a defect in capsid uncoating and a change in PsVs intracellular normal processing when ablating CCT3. Taken together, these studies demonstrate the importance of CCT
chaperonin during HPV infectious entry.ImportanceSeveral of the mechanisms that function during the
infection of target cells by HPV particles have been previously described. However, many aspects of this process remain unknown. In particular, the role of cellular
proteins functioning as
molecular chaperones during
HPV infections has been only partially investigated. To the best of our knowledge, we describe here for the first time, a requirement of the CCT
chaperonin for
HPV infection. The role of this cellular complex seems to be determined by the binding of its component 3 to the viral structural
protein L2. However, CCT's effect on
HPV infection most probably comprises the whole
chaperonin complex. Altogether, these studies define an important role for the CCT
chaperonin in the processing and intracellular trafficking of HPV particles and in subsequent viral infectious entry.