Monitoring foreign gene expression by a human adenovirus-based vector using the firefly luciferase gene as a reporter
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We have constructed a helper-independent adenovirus type 5-luciferase recombinant (Ad5-Luc 3) containing the firefly luciferase gene flanked by simian virus 40 (SV40) regulatory sequences inserted in the early region 3 (E3) of the Ad5 genome. Expression of luciferase in cells infected with Ad5-Luc3 was relatively efficient. In HeLa cells approximately 20 micrograms luciferase per 10(6) cells was made by 36 h post-infection and a 62 kilo-Dalton (kDa) luciferase band was clearly visible in a [35S]methionine-labeled Ad5-Luc 3-infected cell extract analyzed directly by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The results of experiments in which cultured cells were infected with Ad5-Luc 3 in the presence or absence of 1-beta-D-arabinofuranosyl cytosine (AraC) showed that the majority of luciferase expression was dependent on viral DNA replication. This suggested that the enzyme was probably translated primarily from mRNA derived from transcripts expressed from the major late promoter of Ad5. An anti-luciferase antibody was raised in a rabbit and used to further characterize the luciferase expressed in HeLa cells infected with Ad5-Luc 3 by immunoprecipitations and Western blot analyses. The half-life of luciferase expressed in HeLa cells infected with Ad5-Luc 3 was calculated to be approximately 6-8 h by pulse chase analysis. Luciferase is likely to be a useful marker for monitoring virus dissemination and gene expression in experimental animals because assays for enzymatic activity are extremely sensitive and backgrounds are low in all tissues. In mice inoculated intraperitoneally (i.p.) with Ad5-Luc 3, luciferase activity was detected in the liver, spleen, kidney, and lung. A single i.p. inoculation of mice with Ad5-Luc 3 was sufficient to raise anti-luciferase antibody and Ad5 neutralizing antibody which persisted for at least 8 weeks. Even in the presence of circulating anti-luciferase and Ad5 neutralizing antibodies, luciferase activity could be detected in the livers, spleens, and kidneys of mice inoculated i.p. a second time with Ad5-Luc 3.
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