INCREASED FREQUENCY OF SPECIFIC-LOCUS MUTATION FOLLOWING HUMAN CYTOMEGALOVIRUS-INFECTION

The effect of human cytomegalovirus (HCMV) infection on the frequency of mutations at the hypoxanthine-guanine phosphoribosyl transferase (h prt) locus was studied in Chinese hamster lung V79 cells. When V79 cel ls were infected with HCMV (strain AD169) at multiplicities of 0.1 to 50 plaque forming units (PFU) per cell the presumptive mutation freque ncy, as determined by the number of 6-thioguanine-resistant (TG(r)) co lonies, was increased up to 16.8-fold (P < 0.005), depending on the mu ltiplicity of infection. Increases in the mutation frequency at the hp rt locus were also observed for other laboratory-adapted HCMV strains (C-87, Davis) and for low passage clinical isolates (82-1, 84-2). The expression time required for the maximum increase in TG(r) colonies wa s 3 days and was consistent among the HCMV strains evaluated in this s tudy. UV-irradiation of HCMV stock up to a dose of 9.6 x 10(4) ergs/mm (2) increased the mutation frequency, but further exposure to UV light or to heat (56 degrees for 30 min) significantly decreased the freque ncy of TG(r)-resistant colonies, suggesting that expression of HCMV ge nes was involved in the mutation process. HCMV-induced TG(r) cells dem onstrated substantially reduced (>96%) incorporation of [H-3]hypoxanth ine. PCR analysis of the hprt locus demonstrated deletions in 9 of 19 HCMV-induced TG(r) colonies randomly selected for further study, while 2 of 17 spontaneously developed TG(r) colonies demonstrated deletions . Although insertions were not detected in spontaneously developed clo nes, 3 of 19 HCMV-induced TG(r) clones had insertions in the hprt gene . Neither HCMV-specific DNA sequences nor HCMV-specific proteins were detected in the TG(r) clones obtained after HCMV infection. infection of V79 cells with HCMV also increased their sensitivity to mutation wi th N-methyl-N'-nitro-N-nitrosoguanidine, giving a synergistic enhancem ent of the mutation frequency. These results indicate that HCMV infect ion has the capacity to induce mutations in the cellular genome and in crease the sensitivity of infected cells to mutation by genotoxic chem icals. Although inactivated HCMV particles are responsible for a modes t increase in the mutation frequency, expression of HCMV genes is asso ciated with a substantial enhancement of the mutation frequency. (C) 1 997 Academic Press.