Mouse lymphoma cell variants with genetically dominant alterations in the maturation of viral glycoproteins

The appearance of Mouse Mammary Tumor Virus (MMTV) glycoproteins on the surface of infected mouse lymphoma cells is regulated by glucocorticoid hormones. The hormone stimulates transcription of the proviral genes and is also required for maturation of viral proteins. We have reported earlier the isolation of variant cell lines with altered patterns of cell-surface expression of the MMTV antigens. One type of variant expresses high levels of viral glycoproteins on the cell surface in a constitutive or hormone-independent manner. Another type of variant expresses reduced levels of viral glycoproteins on the cell surface compared with wild-type cells, both in the presence and in the absence of glucocorticoids. In this report pulse-chase studies demonstrate that the variant phenotypes are caused by changes in the efficiency of processing the envelope polyprotein precursor into the mature glycoproteins. In addition, both variant phenotypes are dominant over the wild-type phenotype in stable hybrid cell lines produced by cell fusion.