Adenovirus early region 1A protein activates transcription of a nonviral gene introduced into mammalian cells by infection or transfection.

Transcription from all early adenovirus promoters is stimulated by a 289 amino acid phosphoprotein encoded in the pre-early transcription unit E1A. To determine if this protein could act on a nonviral gene placed on the viral chromosome, adenovirus recombinants were constructed in which the rat preproinsulin I gene, including its promoter region, was substituted in both orientations for E1A. Preproinsulin mRNA synthesis from these recombinants was greatly stimulated after infection of line 293 cells, which constitutively express E1A protein, compared to HeLa cells, which do not. Expression of the preproinsulin gene was also greatly stimulated when HeLa cells were coinfected with the recombinants and wild-type adenovirus or a mutant defective in a second E1A protein, but much less so by coinfection with a mutant defective in the 289 amino acid phosphoprotein. Much of the E1A-induced preproinsulin mRNA had a 5' end at the same position as the preproinsulin mRNA isolated from insulinoma cells, but a considerable fraction had 5' ends mapping heterogeneously within several hundred nucleotides of this site. Preproinsulin mRNA was also detected in 293 cells but not HeLa or HEK cells after transfection of a plasmid containing the preproinsulin gene with no adenovirus sequence. This indicates that there is no cis-acting adenovirus sequence required for E1A protein stimulation of preproinsulin transcription. Infection of rat cells with adenovirus did not induce detectable mRNA synthesis from the endogenous preproinsulin I gene. These results demonstrate that the E1A protein can induce expression of a nonviral gene when it is newly introduced into mammalian cells by viral infection or transfection, but it does not induce the endogenous cellular gene.