Release of simian virus 40 virions from epithelial cells is polarized and occurs without cell lysis

We have investigated the process of release of simian virus 40 (SV40) virions from several monkey kidney cell lines. High levels of virus release were observed prior to any significantly cytopathic effects in all cell lines examined, indicating that SV40 utilizes a mechanism for escape from the host cell which does not involve cell lysis. We demonstrate that SV40 release was polarized in two epithelial cell types (Vero C1008 and primary African green monkey kidney cells) grown on permeable supports; release of virus occurs almost exclusively at apical surfaces. In contrast, equivalent amounts of SV40 virions were recovered from apical and basal culture fluids of nonpolarized CV-1 cells. SV40 virions were observed in large numbers on apical surfaces of epithelial cells and in cytoplasmic smooth membrane vesicles. The sodium ionophore monensin, an inhibitor of vesicular transport, was found to inhibit SV40 release without altering viral protein synthesis or infectious virus production.