Control of Adenovirus Gene Expression: Cellular Gene Products Restrict Expression of Adenovirus Host Range Mutants in Nonpermissive Cells

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Abstract
Adenovirus type 5 (Ad5) host range mutants dl312 and hr-1, with lesions in region E1A (0 to 4.5 map units) of the viral genome, fail to accumulate virus-specific early RNA during infection in human cervical carcinoma HeLa cells. The addition of anisomycin, a stringent inhibitor of protein synthesis, at 1 h after infection of HeLa cells with hr-1 virus resulted in the accumulation of properly spliced and translatable mRNA from all early regions. Based on these results a model was proposed in which expression of early mutant RNA was achieved through inactivation of a cellular protein normally causing a reduction in the amount of viral RNA. These studies have been extended in the present report, which shows that early viral proteins can be detected in Ad5 dl312- and Ad5 hr-1-infected HeLa cells which have been treated for several hours with anisomycin either shortly after infection or before infection. A pulse of drug treatment also resulted in expression of substantial amounts of adenovirus structural proteins after infection with both Ad5 hr-1 and Ad5 dl312; in drug-free controls, no late proteins were detected. The Ad5 hr-1 virus previously reported to be DNA replication negative in nonprermissive HeLa cells was found to replicate its DNA, albeit at low levels, when anisomycin was present either from 1 to 5 h postinfection or for 5 h before infection. When infectious virus production was examined in mutant-infected cells, the titer of Ad5 dl312 virus was found to increase at least 500-fold in anisomycin-treated HeLa cells. Evidently, the block in gene expression characteristic for complementation group I Ad5 host range mutants in HeLa cells can be overcome by inactivating cellular gene products serving as negative regulators of viral gene expression.