Common surface receptors on both mouse and rat cells distinguish different classes of mouse mammary tumor viruses

Cell surface receptors which bind mouse mammary tumor virus (MMTV) were detected on mouse and rat cells. Virus binding was quantitated by measuring ¹²⁵T-protein A binding to immune complexes composed of a C3H MMTV gp52 type-specific monoclonal antibody and receptor-bound MMTV. C3H MMTV binding to normal mouse mammary epithelial cells (NMuMG) was dose dependent and was ≥50% inhibited by GR MMTV, but not by endogenous C3Hf MMTV or Gross murine leukemia virus. These results were confirmed in [³H]leucine MMTV binding inhibition assays in which GR MMTV and C3H MMTV blocked C3H [³H]MMTV binding while C3Hf MMTV did not block. The affinities of C3H [³H]MMTV binding to receptors on NMuMG, NIH Swiss (SLP), and Fischer rat embryo (FRE) cells were identical by Scatchard analysis. C3Hf [³H]MMTV also bound these cells, but with an affinity approximately 10 times weaker than the C3H [³H]MMTV binding. Interference assays using a Kirsten sarcoma virus (C3H MMTV) pseudotype confirmed the importance of C3H MMTV specific binding to viral penetration and expression. Pretreatment of SLP or FRE cells with 100 μg of C3H MMTV or GR MMTV inhibited focus formation by ≥50% while C3Hf MMTV and RIII MMTV did not inhibit. Therefore, the functional C3H MMTV cell receptors on mouse and rat cells were related and were able to distinguish C3H MMTV and GR MMTV from C3Hf MMTV and RIII MMTV. These comparable receptors may represent evolutionarily conserved surface components of murine cells.