Endogenous Type C Retrovirus Expression in Epithelial Cells of a Rhesus Monkey (Macaca mulatta): Analysis of Viral Antigens and Virus Release in Clonal Cell Lines

Abstract

Expression of Macaca mulatta type C virus, first isolate (MMC-1) from a rhesus monkey epithelial cell line was investigated by analyzing cellassociated viral antigen and virus release in clonal cell lines. Clonal lines were generated in microtiter plates using homologous feeder layers. The clones were expanded and cell stocks for thirty-three separate lines were established. Cell extracts were assayed for MMC-1 antigen expression using an homologous double antibody radioimmunoassay, developed to detect the major protein component of the virion. Clones with varying levels of antigen expression were selected for the characterization of intracellular antigen by radioimmunoprecipitation followed by sodium dodecyl sulfatepolyacrylamide gel electrophoresis. The clones assayed contained a single detectable immunologically specific polypeptide with a molecular weight of ~ 65,000 daltons. A canine thymus cell line, used to amplify virus replication, was similarly analyzed. In the canine cells, additional immunologically specific proteins were identified. Pulse-chase experiments indicated that the 65,000 dalton molecule is a precursor, to a final polypeptide product of ~ 26,000 daltons. Extracellular antigen was detected in some but not all of the clones. Virus particles were observed by electron microscopy in five out of eight clones viewed. However, intracellular processing of the 65,000 dalton precursor was not detected as it was in the high producer canine cells, indicating that the rate of posttranslational cleavage of this precursor is limiting and/or controlling the level of virus expression by the rhesus epithelial cell line, 816A.