Heparin Binds to Murine Leukemia Virus and Inhibits Env-Independent Attachment and Infection

Abstract

Certain glycosaminoglycans (GAGs), including heparin, inhibit infection by murine leukemia virus (MLV).We now show that this is due to inhibition of virus attachment independent of the interaction between viral envelope proteins (Env) and their cellular receptors. Heparin blocked the binding of both Env-deficient and amphotropic MLV (MLV-A) particles to NIH 3T3 fibroblasts, CHO cells which lack the amphotropic retroviral receptor Pit-2, and CHO cells transfected with Pit-2 (CHO-Pit-2). Heparin also inhibited the transduction of NIH 3T3 cells by MLV-A over a similar concentration range. This effect was observed within 15 min of exposure to retrovirus. Preloading target cells with heparin had no effect on transduction and both MLV-A and Env-deficient retrovirus bound efficiently to heparin-coated agarose beads, suggesting that heparin interacts with the virus rather than the target cell. This requires both a strong negative charge and a specific structure since GAGs with different charge and carbohydrate composition inhibited virus infection variably. The specificity of GAG-virus interaction also depends on the producer cells, since virus packaged by murine GP؉EnvAM12 cells was 1,000-fold more sensitive to inhibition by chondroitin sulfate A than was virus packaged by human FLYA13 packaging cells. No evidence for an interaction between MLV and cell surface proteoglycans was found, however, since the attachment of MLV-A and envelope-defective virus to proteoglycan-deficient CHOpgsA-745 cells was similar to that seen with both wild-type and CHO-Pit-2 cells. Although the molecular mechanism is unclear, this study presents evidence that Env receptor-independent attachment is an important step in MLV infection.

Directional Spread of Surface-Associated Retroviruses Regulated by Differential Virus-Cell Interactions

“…Previously it was demonstrated that infection by HIV-1 is promoted by GAGs on target cells but only for HIV-1 isolates carrying a viral Env protein with a highly positively charged V3-loop (38). In our system, we observed virus surfacing even for cells generating Gag-CFP in the absence of MLV Env (data not shown), consistent with the notion that MLV's association with GAGs or alternative receptors on infected XC cells is not necessarily Env dependent (11,24,25,35). Polybrene treatment switches surfacing to surfing on infected cells.…”

“…Retroviruses including MLV and HIV are able to bind to cells through interactions with cell surface glycosaminoglycans (GAGs) (34,35), notably heparan sulfate (7,11), even in the absence of specific viral receptor molecules. To test if the retention and motility of assembled viruses at the infected-cell surface reflected an association with GAGs, we initiated live-cell imaging prior to the addition of heparinase II, which cleaves heparan FIG.…”

Identification of Host Proteins Associated with Retroviral Vector Particles by Proteomic Analysis of Highly Purified Vector Preparations

“…For retroviruses, this initial step in the virus life cycle was for a long time believed to be mediated solely by the viral Env protein. However, the presence of cellular components on the MMLV surface responsible for promoting viruscell attachment has been proposed (17,53,69). To date, these components remain unidentified.…”

Induction of Human T Cell Leukemia Virus Type I Receptors on Quiescent Naive T Lymphocytes by TGF-β

“…Heparan sulfates, which are widely expressed on the surface of cells, have been shown to be used by a number of viruses including the retroviruses HIV-1 and murine leukemia virus (24,25). More recent studies have revealed that heparan sulfate proteoglycans (HSPG) can also specifically bind soluble HTLV SU and enhance entry of HTLV-I pseudotypes (26,27).…”