Infectious Entry by Amphotropic as well as Ecotropic Murine Leukemia Viruses Occurs through an Endocytic Pathway

In general, enveloped viruses use two different entry strategies and are classified accordingly into pHdependent and pH-independent viruses. Different members of the retrovirus family use one or the other strategy. Little is known about the uptake of foamy viruses (FV), a special group of retroviruses, into the target cells. In this study, we examined the pH dependence of FV entry by analyzing FV envelope glycoprotein (Env)-mediated infection of target cells with murine leukemia virus or FV vector pseudotypes in the presence of various lysosomotropic agents. Similar to vesicular stomatitis virus glycoprotein G (VSV-G)-mediated uptake, FV Env-mediated entry was inhibited by various lysosomotropic agents, suggesting a pH-dependent endocytic pathway. However, in contrast to its effect on VSV-G pseudotypes, chloroquine failed to reduce the infectivity of FV Env pseudotypes, implying that the pathway is different from that of VSV-G. Glycoproteins of various other FV species showed inhibition profiles similar to that of the prototype FV (PFV) Env. Analysis of the pH dependence of the FV Env-mediated fusion process in a cell-to-cell fusion assay revealed an induction of syncytium formation by a short exposure to acidic pH, peaking around pH 5.5. Interestingly, of all FV Env species analyzed, only the PFV Env had a significant fusion activity at neutral pH. Taken together, these data suggest a pH-dependent endocytic pathway for infection of target cells by FV.

Section: Resultsmentioning

confidence: 54%

“…Infection is thought to occur by direct fusion at the plasma membrane. However, a recent study suggests that MuLV-A might employ a pH-independent receptor-mediated endocytic pathway for infection (9). Other mammalian retroviruses, such as ecotropic MuLV and mouse mammary tumor virus, are thought to use a pH-dependent mode of entry (16,24).…”

mentioning

confidence: 99%

Foamy Virus Envelope Glycoprotein-Mediated Entry Involves a pH-Dependent Fusion Process

Picard‐Maureau

Jarmy

Berg

et al. 2003

“…Bafilomycin A1, an inhibitor of the vacuolar H ϩ -ATPase that is responsible for acidification of endosomal vesicles, inhibited AAV2 and rAAV12 transduction by 65% at a 5 nM concentration. NH 4 Cl, a lysosomotropic weak base, which raises the pHs within vesicles by functioning as a proton sink (15), also inhibited over 70% of rAAV2 and rAAV12 transduction activity (Fig. 5).…”

Section: Identification Of Aav Contaminations In Atcc Virus Isolatesmentioning

confidence: 99%

Adeno-Associated Virus Type 12 (AAV12): a Novel AAV Serotype with Sialic Acid- and Heparan Sulfate Proteoglycan-Independent Transduction Activity

Schmidt

Voutetakis

Afione

et al. 2008

135

Recombinant adeno-associated virus (rAAV) is a promising vector for gene therapy. Recent isolations of novel AAV serotypes have led to significant advances by broadening the tropism and increasing the efficiency of gene transfer to the desired target cell. However, a major concern that remains is the strong preexisting immune responses to several vectors. In this paper, we describe the isolation and characterization of AAV12, an AAV serotype with unique biological and immunological properties. In contrast to those of all other reported AAVs, AAV12 cell attachment and transduction do not require cell surface sialic acids or heparan sulfate proteoglycans. Furthermore, rAAV12 is resistant to neutralization by circulating antibodies from human serum. The feasibility of rAAV12 as a vector was demonstrated in a mouse model in which muscle and salivary glands were transduced. These characteristics make rAAV12 an interesting candidate for gene transfer applications.

“…The pH-dependent pathway is utilized by enveloped viruses such as Semliki Forest virus (29), West Nile virus (11), Hantaan virus (32), vesicular stomatitis virus (41), influenza virus (25), avian leukosis virus (16), and salmon anemia virus (19). Viral entry of amphotropic and ecotropic murine leukemia viruses can be both pH dependent and pH independent, conditional on the virus strain (34,41,43). Interestingly, some enveloped viruses, like herpes simplex virus, may enter target cells via more than one pathway (3).…”

mentioning

confidence: 99%

Receptor-Mediated Entry by Equine Infectious Anemia Virus Utilizes a pH-Dependent Endocytic Pathway

Jin

Zhang²,

Weisz

et al. 2005

Previous studies of human and nonhuman primate lentiviral entry mechanisms indicate a predominant use of pH-independent pathways, although more recent studies of human immunodeficiency virus type 1 entry appear to reveal the use of a low-pH-dependent entry pathway in certain target cells. To expand the characterization of the specificity of lentiviral entry mechanisms, we have in the current study examined the entry pathway of equine infectious anemia virus (EIAV) during infection of its natural target, equine macrophages, permissive equine fibroblastic cell lines, and an engineered mouse cell line expressing the recently defined equine lentivirus receptor-1. The specificity of EIAV entry into these various cells was determined by assaying the effects of specific drug treatments on the level of virus entry as measured by quantitative real-time PCR assay of early reverse transcripts or by measurements of virion production. The results of these studies demonstrated that EIAV entry into all cell types was substantially inhibited in a dose-dependent manner by treatment with the vacuolar H ؉ -ATPase inhibitors concanamycin A and bafilomycin A1 or the lysosomotropic weak base ammonium chloride. In contrast, treatments with sucrose to block clathrin-mediated endocytosis or with chloroquine to block organelle acidification failed to inhibit EIAV entry into the same target cells. The observed inhibition of EIAV entry was shown not to be related to cytotoxicity. Taken together, these experiments reveal for the first time that EIAV receptor-mediated entry into target cells is via a low-pH-dependent endocytic pathway.