PAPILLOMAVIRUS CAPSID BINDING AND UPTAKE BY CELLS FROM DIFFERENT TISSUES AND SPECIES

The inability of papillomaviruses (PV) to replicate in tissue culture cells has hampered the study of the PV life cycle. We investigated vir us-cell interactions by the following two methods: (i) using purified bovine PV virions or human PV type 11 (HPV type 11) virus-like particl es (VLP) to test the binding to eukaryotic cells and (ii) using differ ent VLP-reporter plasmid complexes of HPV6b, HPV11 L1 or HPV11 L1/L2, and HPV16 L1 or HPV16 L1/L2 to study uptake of particles into differen t cell lines. Our studies showed that PV capsids bind to a broad range of cells in culture in a dose-dependent manner. Binding of PV capsids to cells can be blocked by pretreating the cells with the protease tr ypsin. Penetration of PV into cells was monitored by using complexes i n which the purified PV capsids were physically linked to DNA containi ng the gene for beta-galactosidase driven by the human cytomegalovirus promoter. Expression of beta-galactosidase occurred in <1% of the cel ls, and the efficiency of PV receptor-mediated gene delivery was great ly enhanced (up to 10 to 20% positive cells) by the use of a replicati on-defective adenovirus which promotes endosomal lysis. The data gener ated by this approach further confirmed the results obtained from the binding assays, showing that PV enter a wide range of cells and that t hese cells have all functions required for the uptake of PV. Binding a nd uptake of PV particles can be blocked by PV-specific antisera, and different PV particles compete for particle uptake. Our results sugges t that the PV receptor is a conserved cell surface molecule(s) used by different PV and that the tropism of infection by different PV is con trolled by events downstream of the initial binding and uptake.