title: CD4-independent human immunodeficiency virus infection involves participation of endocytosis and cathepsin B.
abstract: During a comparison of the infectivity of mNDK, a CD4-independent human immunodeficiency virus type 1 (HIV-1) strain, to various cell lines, we found that HeLa cells were much less susceptible than 293T and TE671 cells. Hybridoma cells between HeLa and 293T cells were as susceptible as 293T cells, suggesting that cellular factors enhance the mNDK infection in 293T cells. By screening a cDNA expression library in HeLa cells, cystatin C was isolated as an enhancer of the mNDK infection. Because cathepsin B protease, a natural ligand of cystatin C, was upregulated in HeLa cells, we speculated that the high levels of cathepsin B activities were inhibitory to the CD4-independent infection and that cystatin C enhanced the infection by impairing the excessive cathepsin B activity. Consistent with this idea, pretreatment of HeLa cells with 125 µM of CA-074Me, a cathepsin B inhibitor, resulted in an 8-fold enhancement of the mNDK infectivity. Because cathepsin B is activated by low pH in acidic endosomes, we further examined the potential roles of endosomes in the CD4-independent infection. Suppression of endosome acidification or endocytosis by inhibitors or by an Eps15 dominant negative mutant reduced the infectivity of mNDK in which CD4-dependent infections were not significantly impaired. Taken together, these results suggest that endocytosis, endosomal acidification, and cathepsin B activity are involved in the CD4-independent entry of HIV-1.
authors.affiliation: Department of AIDS Research, Institute of Tropical Medicine, Global Center of Excellence, Nagasaki University, Nagasaki, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Yoshii
authors.forename: Haruka
authors.initials: H
authors.lastname: Kamiyama
authors.forename: Kensuke
authors.initials: K
authors.lastname: Goto
authors.forename: Kazunori
authors.initials: K
authors.lastname: Oishi
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Katunuma
authors.forename: Yuetsu
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Hideki
authors.initials: H
authors.lastname: Hayashi
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Matsuyama
authors.forename: Hironori
authors.initials: H
authors.lastname: Sato
authors.forename: Naoki
authors.initials: N
authors.lastname: Yamamoto
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Kubo
mesh_terms: D000143:Acids; D015704:CD4 Antigens / Q000378:metabolism; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002738:Chloroquine / Q000494:pharmacology; D055316:Cystatin C / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D005799:Genes, Dominant; D005822:Genetic Vectors / Q000235:genetics; D057809:HEK293 Cells; D015658:HIV Infections / Q000473:pathology* / Q000821:virology; D015497:HIV-1 / Q000187:drug effects / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D006835:Hydrazones / Q000494:pharmacology; D007113:Immunity, Innate / Q000187:drug effects; D018942:Macrolides / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D051197:Toll-Like Receptor 4 / Q000378:metabolism
chemical_list: D000143:Acids; D015704:CD4 Antigens; D055316:Cystatin C; D006835:Hydrazones; D018942:Macrolides; C511794:N'-(3,4-dihydroxybenzylidene)-3-hydroxy-2-naphthahydrazide; D011480:Protease Inhibitors; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D002738:Chloroquine; C040929:bafilomycin A1; C533912:CTSB protein, human; D002401:Cathepsin B