Replication of porcine circovirus: induction by glucosamine and cell cycle dependence

Multiplication of porcine circovirus (PCV) was found to be inducible by treatment of infected cell cultures with 300 mM glucosamine. One day after glucosamine treatment and after growth in fresh medium, an increase in the number of cells containing virus antigen of up to 50 times as compared to mock-treated cultures was observed. Analysis of this phenomenon revealed that replication of PCV DNA was induced. Only aminohexoses but not hexoses and acetylated aminohexoses were efficacious. The course of PCV replication in synchronized cell cultures infected at different periods of the cell cycle showed that PCV DNA synthesis depends on cellular enzymes expressed during S phase growth of cells. However, whereas in cell cultures treated with glucosamine after infection in G0 or during G1, the start of PCV replication was observed during the first S phase after growth stimulation, the latent period in mock-treated cultures lasted until the second S phase. Also in cell cultures transfected with PCV DNA in G0 or during G1 using DEAE-dextran as mediator, PCV replication started during the first S phase after growth release of the cells. From these findings the conclusion is drawn that glucosamine and DEAE-dextran initiate PCV replication by enabling the PCV genome to get entry to the cell nucleus that normally can be achieved only by inclusion in the daughter nuclei at the end of mitosis.