title: Entry of tiger frog virus (an Iridovirus) into HepG2 cells via a pH-dependent, atypical, caveola-mediated endocytosis pathway.
abstract: Tiger frog virus (TFV), in the genus Ranavirus of the family Iridoviridae, causes high mortality of cultured tiger frog tadpoles in China. To explore the cellular entry mechanism of TFV, HepG2 cells were treated with drugs that inhibit the main endocytic pathways. We observed that TFV entry was inhibited by NH(4)Cl, chloroquine, and bafilomycin, which can all elevate the pH of acidic organelles. In contrast, TFV entry was not influenced by chlorpromazine or overexpression of a dominant-negative form of Esp15, which inhibit the assembly of clathrin-coated pits. These results suggested that TFV entry was not associated with clathrin-mediated endocytosis, but was related to the pH of acidic organelles. Subsequently, we found that endocytosis of TFV was dependent on membrane cholesterol and was inhibited by the caveolin-1 scaffolding domain peptide. Dynamin and actin were also required for TFV entry. In addition, TFV virions colocalized with the cholera toxin subunit B, indicating that TFV enters as caveola-internalized cargo into the Golgi complex. Taken together, our results demonstrated that TFV entry occurs by caveola-mediated endocytosis with a pH-dependent step. This atypical caveola-mediated endocytosis is different from the clathrin-mediated endocytosis of frog virus 3 (FV3) by BHK cells, which has been recognized as a model for iridoviruses. Thus, our work may help further the understanding of the initial steps of iridovirus infection in lower vertebrates.
authors.affiliation: State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, 135 Xingang Road West, Guangzhou 510275, People's Republic of China.
authors.forename: Chang-Jun
authors.initials: CJ
authors.lastname: Guo
authors.forename: Dong
authors.initials: D
authors.lastname: Liu
authors.forename: Yan-Yan
authors.initials: YY
authors.lastname: Wu
authors.forename: Xiao-Bo
authors.initials: XB
authors.lastname: Yang
authors.forename: Li-Shi
authors.initials: LS
authors.lastname: Yang
authors.forename: Shu
authors.initials: S
authors.lastname: Mi
authors.forename: Yu-Xin
authors.initials: YX
authors.lastname: Huang
authors.forename: Yong-Wen
authors.initials: YW
authors.lastname: Luo
authors.forename: Kun-Tong
authors.initials: KT
authors.lastname: Jia
authors.forename: Zhao-Yu
authors.initials: ZY
authors.lastname: Liu
authors.forename: Wei-Jian
authors.initials: WJ
authors.lastname: Chen
authors.forename: Shao-Ping
authors.initials: SP
authors.lastname: Weng
authors.forename: Xiao-Qiang
authors.initials: XQ
authors.lastname: Yu
authors.forename: Jian-Guo
authors.initials: JG
authors.lastname: He
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D021941:Caveolae / Q000502:physiology*; D002784:Cholesterol / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D056945:Hep G2 Cells / Q000821:virology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000166:cytology / Q000821:virology*; D017995:Ranavirus / Q000472:pathogenicity*; D053586:Virus Internalization
chemical_list: D000199:Actins; D002784:Cholesterol; D034281:Dynamins