The data also suggest find more that the replication kinetics of PML-type JCV DNA differ among COS-tat cell clones. In the current study, we examined the propagation characteristics of PML-type JCV in COS-7 derived cell lines
expressing HIV-1 Tat protein. In COS-tat cells, production of virus progenies and replication of viral genomic DNA were increased compared to those in parental COS-7 cells, as judged by data from HA and real-time PCR assays. Based on the results obtained in the present and previous studies (8), we have demonstrated that stable expression of HIV-1 Tat facilitates propagation of, not only archetype, but also PML-type, JCV. In COS-tat cells, HIV-1 Tat-mediated JCV propagation can be examined without transfecting the cells with Tat click here expression plasmid or stimulating them with exogenous Tat. Thus, these cell lines may provide a useful model system for studying HIV-1 Tat-mediated propagation of
both archetype and PML-type JCV. When examining the characteristics of COS-tat cells, we found that stable expression of HIV-1 Tat resulted in down-regulation of cell proliferation. This reduction of the cell growth of COS-tat cells is consistent with earlier results indicating that Tat prevents proliferation of human intestinal epithelial cells (15). A growing body of evidence suggests that HIV-1 Tat regulates numerous cellular genes that are involved in cell signaling and translation, thereby controlling Carnitine palmitoyltransferase II the proliferation of host cells (16). The precise mechanism by which Tat protein represses the proliferation of COS-tat cells is unclear; however, previous investigations suggest that HIV-1 Tat induces the expression of Purα, a single-stranded DNA binding protein which inhibits cell growth (16, 17). Therefore, it might be that the decreased proliferation of COS-tat cells is associated with Tat-induced expression of Purα. In our previous study, archetype JCV efficiently propagated in COS-tat7, COS-tat15, and COS-tat22 (8). Among the COS-tat cell clones tested, COS-tat22 cells exhibited a marked increase in the propagation of
archetype JCV at about 30 days after transfection with viral DNA (8). Consistent with earlier results, amounts of HA and viral DNA in COS-tat22 cells were greater than those in other COS-tat cell clones at 30 days following transfection with PML-type JCV DNA. It is likely that production of Tat protein leads to increased propagation of archetype and PML-type JCV in three COS-tat cell clones, although the extent of its expression varies between these clones (8). It has been reported by others that Tat protein can enhance late-promoter transcription of JCV through interaction with a sequence similar to TAR in the JCV control region (3, 4). It has also been demonstrated that Tat protein forms a complex with Purα, thereby stimulating viral DNA replication initiated at the JCV origin (5, 6).