S-PHASE-DEPENDENT CELL-CYCLE DISTURBANCES CAUSED BY ALEUTIAN MINK DISEASE PARVOVIRUS

We examined replication of the autonomous parovirus Aleutian mink dise ase parovirus (ADV) in relation to cell cycle progression of permissiv e Crandell feline kidney (CRFK) cells. Flow cytometric analysis showed that ADV caused a composite, binary pattern of cell cycle arrest. ADV -induced cell cycle arrest occurred exclusively in cells containing de novo-synthesized viral nonstructural (NS) proteins. Production of ADV NS proteins, indicative of ADV replication, was triggered during S-ph ase traverse. The NS+ cells that were generated during later parts of S phase did not undergo cytokinesis and formed a distinct population, termed population A. Formation of population A was not prevented by VM -26, indicating that these cells were arrested in late S or G(2) phase . Cells in population A continued to support high-level ADV DNA replic ation and production of infectious virus after the normal S phase had ceased. A second, postmitotic, NS+ population (termed population B) ar ose in G(0)/G(1), downstream of population A. Population B cells were unable to traverse S phase but did exhibit low-level DNA synthesis. Si nce the nature of this DNA synthesis was not examined, we cannot at pr esent differentiate between G(1) and early S arrest in population B. C ells that became NS+ during S phase entered population A, whereas popu lation B cells apparently remained NS- during S phase and expressed hi gh NS levels postmitosis in G(0)/G(1). This suggested that population B resulted from leakage of cells with subthreshold levels of ADV produ cts through the late S/G(2) block and, consequently, that the binary p attern of ADV-induced cell cycle arrest may be governed merely by vira l replication levels within a single S phase. Flow cytometric analysis of propidium iodide fluorescence and bromodeoxyuridine uptake showed that population A cells sustained significantly higher levels of DNA r eplication than population B cells during the ADV-induced cell cycle a rrest. Therefore, the type of ADV-induced cell cycle arrest was not tr ivial and could have implications for subsequent viral replication in the target cell.