Entry of human papillomavirus type 16 by actin-dependent,clathrin- and lipid raft-independent endocytosis

Infectious endocytosis of incoming human papillomavirus type 16 (hpv-16),the main etiological agent of cervical cancer,is poorly characterized in terms of cellular requirements and pathways. conflicting reports attribute hpv-16 entry to clathrin-dependent and -independent mechanisms. to comprehensively describe the cell biological features of hpv-16 entry into human epithelial cells,we compared hpv-16 pseudovirion (psv) infection in the context of cell perturbations (drug inhibition,sirna silencing,overexpression of dominant mutants) to five other viruses (influenza a virus,semliki forest virus,simian virus 40,vesicular stomatitis virus,and vaccinia virus) with defined endocytic requirements. our analysis included infection data,i.e. gfp expression after plasmid delivery by hpv-16 psv,and endocytosis assays in combination with electron,immunofluorescence,and video microscopy. the results indicated that hpv-16 entry into hela and hacat cells was clathrin-,caveolin-,cholesterol- and dynamin-independent. the virus made use of a potentially novel ligand-induced endocytic pathway related to macropinocytosis. this pathway was distinct from classical macropinocytosis in regards to vesicle size,cholesterol-sensitivity,and gtpase requirements,but similar in respect to the need for tyrosine kinase signaling,actin dynamics,na+/h+ exchangers,pak-1 and pkc. after internalization the virus was transported to late endosomes and/or endolysosomes,and activated through exposure to low ph.