Oncogenic Herpesviruses of Non-Human Primates — Persistence of Viral DNA in Transformed Lymphoid Cells

Abstract

Herpesvirus (H.) saimiri and H. ateles are highly oncogenic in various non-human primates and in rabbits, causing rapidly progressing maligmant T-cell lymphomas upon experimental infection. Cell lines derived from virus-induced tumors and in vitro transformed lymphoid cells contain non-integrated circular viral DNA in high multiplicity. Persisting viral DNA molecules of cell lines that do not produce infectious virus are highly methylated in the unique L-DNA and repetitive (H) DNA sequences. Partial denaturation mapping has shown that some DNA circles contain duplications of L-DNA segments; however all non-producer cell lines investigated so far have L-DNA segments that are considerably shorter than the L-DNA region of virion DNA (110 kbp). The deletions in the circular molecules of H. saimiri transformed cells were mapped by hybridizations with cloned probes of virion L-DNA. In the circular DNA of two cell lines derived from virus induced marmoset lymphomas (1670, 70N2), a 20 kbp segment of L-DNA is missing which corresponds to the virion L-DNA between map coordinates 0,52 and 0,70. The rabbit tumor cell line 7710 bears an L-DNA deletion of about 30 kbp (L-DNA map units 0.23 to 0.50). Two sublines of the in vitro immortalized H1591 cells were investigated. The circular DNA of one line is missing about 42 kbp of virion DNA; in the circles of the other H1591 subline at least 47% of the viral genetic information was found to be absent. The L-DNA missing in the circular viral genomes could not be found in the linear fraction of each cellular DNA at the sensitivity level where 0.5 single copy gene/cell would have been clearly detected. Apparently, an internal L-DNA stretch of at least 63 kbp, representing 56% of the total viral genetic information, does not code for viral gene functions that would be consistently required to guarantee continuous extrachromosomal persistence or to maintain the state of growth transformation in lymphoid cells. The high amount of persisting viral DNA stands in remarkable contrast to low concentration of viral RNA and virus-coded proteins. The Herpesvirus ateles-associated nuclear antigen (HATNA) was detected in transformed lymphoid cells with very high genome copy number; but no trace of viral protein synthesis was found in other non-producer cell lines.