Analysis of the Infectious Entry Pathway of Human Papillomavirus Type 33 Pseudovirions

Human papillomavirus type 33 (HPV-33) pseudovirus infection is a slow process dependent on the initial interaction with cell-surface heparan sulfate (T. Giroglou, L. Florin, F. Schafer, R. E. Streeck, and M. Sapp, 2001a, J. Virol. 75, 1565–1570). We have now further dissected the initial steps of pseudovirus uptake using removal of cell-surface proteoglycans and selective inhibition of entry pathways. Treatment of cells with heparinase I, but not with phosphoinositol-specific phospholipase C (PIPLC), prevented binding of papillomavirus-like particles and infection with HPV-33 pseudovirions, indicating that GPI-linked proteoglycans (glypicans) are not required for productive infection. The slow entry of pseudovirions was inhibited by cytochalasin D and nocodazole in a concentration-dependent manner, suggesting actin polymerization and intact microtubuli be required. Inhibitors of the caveolae-mediated uptake did not significantly affect pseudoinfection. Interestingly, pseudoinfection was blocked by selective inhibitors of endosomal acidification up to 12 h postinfection. Together, our results suggest that binding of HPV pseudovirions to heparan sulfate proteoglycans, most likely syndecans, is followed by delayed internalization via the endosomal pathway.