Efficient replication of plasmids containing the SV40 origin in N-myc overexpressing human neuroblastoma cells.

Using test plasmids containing the SV40 origin, we found a wide spectrum of permissiveness to their replication in different human cell lines. N-myc overexpressing neuroblastoma cells were highly permissive. LA-N-1 neuroblastoma cells were the most permissive of all the cell lines that we tested including the homologous CV-1 or COS-1 monkey kidney cells. Other human cell lines expressing various amounts of c-myc, and the 293 cell line expressing adenovirus E1A and E1B exhibited intermediate levels of permissiveness. T24 and EJ bladder carcinoma cells, which do not express the myc genes, were nonpermissive. Transient expression of c-myc or N-myc from plasmid vectors resulted in a modest stimulation of replication. Replication of test plasmids containing different configurations of the SV40 origin region was activated by the myc proteins. The high efficiency of replication in LA-N-1 cells is due to a combination of reasons including the overproduction of N-myc, high efficiency of expression of the SV40 replication initiator protein large T antigen from a cotransfected expression plasmid (containing the T antigen gene under the RSV LTR control), and other unknown host cell replication stimulatory factors. Replication of test plasmids was not detected in N-myc or c-myc overexpressing cells when the T antigen expression plasmid was not provided, showing that the myc proteins cannot substitute for T antigen in SV40 DNA replication.