Human Papillomavirus Types 16, 18, and 31 Share Similar Endocytic Requirements for Entry

Abstract

Human papillomavirus type 18 (HPV18), one of the HPVs with malignant potential, enters cells by an unknown endocytic mechanism. The key cellular requirements for HPV18 endocytosis were tested in comparison to those for HPV16 and -31 endocytoses. HPV18 (like HPV16 and -31) entry was independent of clathrin, caveolin, dynamin, and lipid rafts but required actin polymerization and tetraspanin CD151, and the viruses were routed to the same LAMP-1-positive compartment. Hence, the viruses shared similar cellular requirements for endocytic entry. The human papillomaviruses (HPVs) are a family of nonenveloped DNA viruses with transforming potential. A particular subgroup of HPVs, the high-risk types, are additionally associated with cervical and anogenital cancers. Of those high-risk types, HPV type 16 (HPV16) is the most prevalent and the best studied. HPVs enter the basal cells of squamous epithelia by endocytosis during initial infection (1). For cell entry, most viruses employ one of several existing pathways for endocytosis (2, 3). These pathways are typically differentiated by the cellular proteins mediating endocytic vacuole formation, by the ultrastructural morphology of endocytic pits, and by the timing of vesicle formation (2-4). Although HPV16 cell entry was originally attributed to clathrinmediated endocytosis (CME) in various cell types (5-8), it has recently been shown that HPV16 enters cells by a novel ligandinduced endocytic pathway that is clathrin, caveolin, lipid raft, and dynamin independent but that depends on highly regulated actin dynamics and an association with CD151-containing tetraspanin-enriched microdomains (9-11) The high-risk-type HPV31 may differ in the mode of endocytosis from HPV16, as it has been described to enter into human keratinocytes by a caveolin/lipid raft-mediated mechanism (12). However, in COS-7 cells and 293TT cells, HPV16 and -31 endocytoses appear to occur by a similar mechanism that is independent of lipid rafts (5).One of the more-prevalent high-risk types, which has not been analyzed for its mode of endocytic entry, is HPV18. Here, we aimed to delineate the general endocytic requirements for infectious HPV18 endocytosis. In particular, we aimed to analyze whether HPV18 exhibits requirements similar to those of HPV16 or -31 for endocytic entry into host cells. Therefore, we compared the efficacy of cell entry after cell perturbation for the main determinants of several endocytic pathways in HeLa and HaCaT cells. The cell biological determinants that allow differentiation of the different endocytic pathways include clathrin for CME, caveolin for caveolin-mediated mechanisms, cholesterol depletion for lipid raft-dependent mechanisms (e.g., caveolar/lipid raft endocytosis or glycosphingolipid-enriched endocytic carriers), dynamin-2 for dynamin-mediated endocytic processes (e.g., CME, caveolar endocytosis, and the interleukin-2 pathway), and actin polymerization dynamics for actin-mediated endocytic processes (macropinocytosis, caveolar endocytosis, and HPV16 endocytosis) (...

The Cytoskeletal Adaptor Obscurin-Like 1 Interacts with the Human Papillomavirus 16 (HPV16) Capsid Protein L2 and Is Required for HPV16 Endocytosis

“…These data suggest a specific function for the cytoskeletal adaptor protein OBSL1 in HPV16 infection. Since HPV16, HPV18, and HPV31 share similar endocytic requirements for entry (33), the influence of OBSL1 depletion was investigated for HPV18 and HPV31 in both cell lines (Fig. 3C and D).…”

“…HPV16, -18, and -31 pseudoviruses (PsVs) and HPV16 L1-only PsV were prepared as previously described and published (33,53,64). Quantification of the reporter gene plasmid was performed as published before (28,53,65).…”

“…Endocytosis of viral particles is mediated by a clathrin-, dynamin-, and caveolin-independent mechanism but requires tetraspanin CD151 and the actin cytoskeleton (10,27,28,(31)(32)(33)(34). Following internalization, viral particles are found in CD63-positive endosomes recruiting syntenin-1, a CD63-interacting adaptor protein (35).…”

Distribution of high-risk types of human papillomavirus compared to histopathological findings in cervical biopsies in women

“…Virus ulazi u bazalni i parabazalni sloj epitela kroz oštećenja epitela u zoni transformacije grlića materice (12)(13)(14)(15). Virion se vezuje za ćelijski receptor α6 integrin (16)(17)(18)(19). Različiti tipovi HPV-a prodiru u ćelije različitim mehanizmima (17).…”

“…Različiti tipovi HPV-a prodiru u ćelije različitim mehanizmima (17). Većina tipova HPV-a inficira ćeliju mehanizmom klatrin zavisne endocitoze (17,18), drugi koriste alternativni način putem kaveolarne endocitoze (17,19), dok se za HPV 16 smatra da ulazi u ćeliju mehanizmom nezavisnim od klatrina i kaveola (18,20). Maligni potencijal HPV zavisi od frekvence integracije virusa i različit je kod različitih tipova HPV (21).…”