Clathrin- and caveolin-independent entry of human papillomavirus type 16--involvement of tetraspanin-enriched microdomains (TEMs).
BACKGROUND
Infectious entry of human papillomaviruses into their host cells is an important step in the viral life cycle. For cell binding these viruses use proteoglycans as initial attachment sites. Subsequent transfer to a secondary receptor molecule seems to be involved in virus uptake. Depending on the papillomavirus subtype, it has been reported that entry occurs by clathrin- or caveolin-mediated mechanisms. Regarding human papillomavirus type 16 (HPV16), the primary etiologic agent for development of cervical cancer, clathrin-mediated endocytosis was described as infectious entry pathway.


RESULTS
Using immunofluorescence and infection studies we show in contrast to published data that infectious entry of HPV16 occurs in a clathrin- and caveolin-independent manner. Inhibition of clathrin- and caveolin/raft-dependent endocytic pathways by dominant-negative mutants and siRNA-mediated knockdown, as well as inhibition of dynamin function, did not impair infection. Rather, we provide evidence for involvement of tetraspanin-enriched microdomains (TEMs) in HPV16 endocytosis. Following cell attachment, HPV16 particles colocalized with the tetraspanins CD63 and CD151 on the cell surface. Notably, tetraspanin-specific antibodies and siRNA inhibited HPV16 cell entry and infection, confirming the importance of TEMs for infectious endocytosis of HPV16.


CONCLUSIONS
Tetraspanins fulfill various roles in the life cycle of a number of important viral pathogens, including human immunodeficiency virus (HIV) and hepatitis C virus (HCV). However, their involvement in endocytosis of viral particles has not been proven. Our data indicate TEMs as a novel clathrin- and caveolin-independent invasion route for viral pathogens and especially HPV16.
Spoden
Gilles
G
Institute for Medical Microbiology and Hygiene, University of Mainz, Mainz, Germany.
Freitag
Kirsten
K
Husmann
Matthias
M
Boller
Klaus
K
Sapp
Martin
M
Lambert
Carsten
C
Florin
Luise
L
D015703:Antigens, CD / Q000378:metabolism / Q000648:ultrastructure; D021941:Caveolae / Q000378:metabolism / Q000821:virology; D002460:Cell Line; D002966:Clathrin / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis; D005260:Female; D006367:HeLa Cells; D052162:Human papillomavirus 16 / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity / Q000648:ultrastructure; D006801:Humans; D007668:Kidney / Q000166:cytology; D021962:Membrane Microdomains / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism* / Q000648:ultrastructure; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism / Q000648:ultrastructure; D060185:Tetraspanin 24; D060149:Tetraspanin 30; D014771:Virion / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D053586:Virus Internalization
D015703:Antigens, CD; C554715:CD151 protein, human; C554586:CD63 protein, human; D002966:Clathrin; D008565:Membrane Proteins; D010980:Platelet Membrane Glycoproteins; D060185:Tetraspanin 24; D060149:Tetraspanin 30