Keratinocyte-Secreted Laminin 5 Can Function as a Transient Receptor for Human Papillomaviruses by Binding Virions and Transferring Them to Adjacent Cells

Abstract

Human papillomaviruses (HPVs) replicate only in the terminally differentiating epithelium of the skin and mucosa. While infection of basal keratinocytes is considered a requirement for permissive infection, it remains unclear whether virions can specifically target basal cells for adsorption and uptake following epithelial wounding. We present evidence that HPV binds specifically to laminin 5 (LN5), a component of the extracellular matrix (ECM) secreted by migrating and basal keratinocytes. HPV type 11 capsids colocalized with LN5 in the ECM secreted by vaginal keratinocytes. Binding of both virions and virus-like particles to purified LN5 and to the LN5-rich ECM secreted by cultured keratinocytes was effectively blocked by pretreatment with anti-LN5 antibodies. HPV capsid binding to human cervical mucosa sections included the basement membrane which contains LN5. Cultured keratinocytes expressing ␣6 integrin, a transmembrane protein known to bind LN5, were readily infected by virions preadsorbed to LN5-containing substrates, whereas mutant keratinocytes lacking ␣6 integrin were relatively resistant to infection via this route. These findings suggest a model of natural HPV infection in which proliferating keratinocytes expressing ␣6 integrin at the site of epithelial wounding might be targeted by virions adsorbed transiently to LN5 secreted by migrating keratinocytes.Human papillomavirus (HPV) particles have been shown to adsorb to the plasma membranes of cultured cells via membrane-associated heparan sulfate proteoglycans (HSPGs) (18,20,33) or ␣6 integrin (CD49f) (15,26). Multiple HSPGs including CD44, syndecans and glypicans are expressed on the membranes of keratinocytes throughout the epidermis and mucosa (22,29). ␣6 integrin expression is generally restricted to basal keratinocytes where this transmembrane protein pairs with ␤4 integrin and contributes to the nucleation of hemidesmosomes connecting the keratin cytoskeleton to the basement membrane (BM) (reviewed in reference 28). Results from experiments utilizing several in vitro infection models suggest that the importance of a particular receptor in HPV adsorption/infection may differ between cell lines and viral genotypes (12,30,33).In addition to binding directly to membrane-associated glycoproteins, we recently found that HPV capsids are also capable of binding a component of the extracellular matrix (ECM) secreted by keratinocytes, but not by nonkeratinocyte cell lines (12). Here we show evidence that this secreted HPV adsorption receptor is laminin 5 (LN5), an epithelial laminin secreted by migrating keratinocytes as they invade wounded epithelium (reviewed in reference 27). In the context of the ECM secreted by cultured keratinocytes, HPV virions can use LN5 as an extracellular "transreceptor" by transiently binding LN5 and subsequently transferring to entry receptors on adjacent cells. In another viral system, human immunodeficiency virus (HIV) is hypothesized to transiently bind DC-SIGN (CD209) on immature dendritic cells within the epithelium an...

Human papillomavirus type 16 reduces the expression of microRNA-218 in cervical carcinoma cells

“…LAMB3 increases cell migration and tumorigenicity in severe combined immunodeficient mice, and in collaboration with its ligand a6b4-integrin promotes tumorigenesis in human keratinocytes (Dajee et al, 2003;Calaluce et al, 2004). A recent study suggests that secreted laminin-5 can be used by HPV as a transient receptor to aid the virus in the infection of basal cells that express a6b4-integrin (Culp et al, 2006). Thus, downregulation of miR-218 by E6 and the consequent overexpression of LAMB3 may promote viral infection of the surrounding tissue and contribute to eventual tumorigenesis.…”

Biology and natural history of human papillomavirus infection

“…Spliced viral mRNA was first detected at 12 hours postinfection, and in most assay systems infection is not robustly detected until at least 24 hours after capsid binding. 46,51 The pathway involved in internalization and intracellular trafficking is still unclear, but it seems to occur slowly and asynchronously over a span of several hours. 50 Clathrin-mediated endocytosis has been pointed out to be like the endocytotic pathway for the majority of HPV types.…”

“…Laminin-5 can also contribute to the binding of viral capsids to the extracellular matrix in the epithelial cell lines. 9,46,47 In vivo, the viral particles bind efficiently to regions of the basement membrane (BM) only after these regions have been exposed to mechanical or chemical trauma of the epithelium. The L1 capsid protein binds to heparan sulfate proteoglycans in segments of the BM exposed after epithelial trauma.…”

DNA-tumor virus entry—From plasma membrane to the nucleus

“…Some HPVs bind to heparansulfate-proteoglycans (183) and possibly secondary receptor(s), such as alpha-6 integrin, laminin or tetraspanin proteins (184,185). Factors and signals that lead to nuclear import of nonstructural and structural HPV proteins are listed in Tab.…”