Somatic cell hybrids between human lymphoma and human myeloid leukemia cells I. Induction of resident viral genome transcription and viral antigen formation by IUDR and TPA

We have determined the number of resident EBV DNA copies per cell and the extent of viral DNA transcription in two hybrid cell lines. The Putko line was derived from the fusion of a Burkitt lymphoma line (P3HR-1) and a myeloid leukemia line (K562) [Klein et al., J. Nat. Cancer Inst. 64, 725-735 (1980)]. Dutko is a hybrid of the Daudi lymphoma line and K562 (Klein, Zeuthen, and Ber, in preparation). These two cell lines differ significantly in their inducibility by IUDR or TPA (Klein et al., 1980; Zeuthen, Klein, and Ber, in preparation). Only Dutko can be induced to synthesize early antigen (EA), whereas Putko is noninducible altogether. Putko and Dutko contained 25 and 84 copies of EBV DNA per cell, respectively, as shown by DNA-DNA reassociation kinetics. The expression of the resident EBV genomes was restricted in both lines. Putko cells contained viral RNA transcribed from about 10% of the EBV DNA, whereas in Dutko cells at least 20% of the viral DNA was transcribed. After iododeoxyuridine (IUDR) exposure, viral RNA increased from 10 to 25% in Putko, and from 20 to more than 40% in Dutko cells. IUDR induction of Putko and Dutko cells did not increase the normally low level of viral transcripts found in the polysomal fraction. The tumor promoter, 12-0-tetradecanoylphorbol-13-acetate (TPA) had no detectable effect on viral transcription. Possible molecular mechanisms that might be responsible for the differential inducibility of the two hybrid cell lines by IUDR are discussed.