A rapid transfer of virions coated with heparan sulfate from the ECM to cell surface CD151 defines a step in the human papillomavirus infection cascade

Human Papillomaviruses (HPVs) are the underlying cause of several types of cancer, albeit they are mostly known for their association with cervical carcinoma. The virions must reach their target cells through a break in the epithelial barrier. After binding to heparan sulfate (HS) of the extracellular matrix (ECM), they translocate to the cell surface and co-internalize with the entry factor CD151. The in vivo occurring translocation from the ECM to entry factors at the cell membrane may be bypassed in nonpolarized cells with low ECM secretion. To specifically investigate these early events of the infection cascade, we use polarized keratinocytes. They produce a robust ECM and have a restricted expression of entry receptors primarily to the substrate-adhered basal membrane. Virion access to the basal membrane by diffusion is strongly limited, such that translocation from the ECM is the main pathway used for infection. We block the translocation from ECM attachment sites to the cell body, release the blocking, and monitor the association of virions with CD151 or HS. We observe quick virion translocation from the ECM to the cell body within 15 min. During translocation, virions associate with the tetraspanin CD151 present at the cell border or at filopodia. Translocating virions are decorated with HS, which they lose in the next few hours, presumably prior to endocytosis. Our observations reveal a rapid step in the HPV infection cascade: the transfer of HS-coated virions from the ECM to CD151. This step is too fast to account for the asynchronous uptake of HPVs which is likely driven by glycan-and capsid processing.