GLYCOSYLATION-DEPENDENT INACTIVATION OF THE ECOTROPIC MURINE LEUKEMIA-VIRUS RECEPTOR

The ecotropic murine leukemia virus (E-MuLV) receptor expressed on Mus dunni tail fibroblast (MDTF) cells is a receptor for all E-MuLVs with the notable exception of Moloney murine leukemia virus (Mo-MuLV). Sub stitution of isoleucine for valine at position 214 in the third extrac ellular region (the putative E-MuLV binding site) of the MDTF receptor molecule allows this molecule to function as a Mo-MuLV receptor (M. V . Eiden, K. Farrell, J. Warsowe, L.A. Mahan, and C.A. Wilson, J. Virol . 67:4056-4061, 1993). We have now determined that treating MDTF cells with tunicamycin, an inhibitor of N-linked glycosylation, also render s them susceptible to Mo-MuLV infection. Two potential N-linked glycos ylation sites are present in the third extracellular regions of both t he NIH 3T3 and MDTF ecotropic receptors. The glycosylation site at pos ition 229 of the MDTF receptor cDNA was eliminated by substituting a t hreonine codon for the asparagine codon. Mo-MuLV-resistant human HOS c ells, expressing this form of the receptor, are susceptible to Mo-MuLV infection. Thus, our studies suggest that without a glycan moiety at position 229, the valine residue at 214 is no longer restrictive for M o-MuLV infection. BHK-21 and CHO K1 hamster cells also express glycosy lation-inactivated forms of the ecotropic receptor. Sequence analysis of these receptors together with our analysis of MDTF receptor functio n suggests that a single asparagine-linked glycosylation site is respo nsible for glycosylation inactivation of these receptors.