THE ENVELOPE GLYCOPROTEIN OF AN AMPHOTROPIC MURINE RETROVIRUS BINDS SPECIFICALLY TO THE CELLULAR RECEPTOR PHOSPHATE TRANSPORTER OF SUSCEPTIBLE SPECIES

A rat cDNA (rRam-1); which was cloned on the basis that it enables Chi nese hamster ovary (CHO) cells to be infected by amphotropic host rang e murine retroviruses, was recently found to encode a widely expressed Naf phosphate symporter (M. P, Kavanaugh, D. G, Miller, W. Zhang, W. Law, S. L, Kozak, D, Kabat, and A, D, Miller, Proc, Natl, Acad, Sci. U SA 91:7071-7075, 1994), CHO cells express the hamster homolog of Ram-1 but are resistant to amphotropic retroviruses, Although the amphotrop ic envelope glycoprotein gp70 bound weakly onto control CHO cells, CHO /rRam-1 cells had novel high-affinity binding sites, and the resulting strongly adsorbed gp70 was only slowly removed from cell surfaces, wi th a half-life of greater than 6 h. CHO/rRam-1 cells were also specifi cally and efficiently killed by exposure to amphotropic gp70 followed by antiserum to gp70 in the presence of complement. Infection with an appropriately pseudotyped form of amphotropic retrovirus 4070A did not perturb control CHO cells or inhibit their phosphate transport, In co ntrast, 4070A infection of CHO/rRam-1 cells caused major alterations i ncluding cell-cell fusions, a specific 40% down-modulation of the rRam -1 component of phosphate transport, and complete interference to supe rinfection by amphotropic viruses, The 4070A virus-infected CHO/rRam-1 cells retained a substantial cell surface pool of rRam-1 that functio ned as a phosphate transporter but not as a viral receptor, We conclud e that amphotropic gp70 binds more strongly to rRam-1 than to the homo logous hamster protein and that this stable attachment is necessary fo r infection, interference, membrane fusion, and pathogenesis.