Cell type specific regulation of expression from the Ad40 E1b promoter in recombinant Ad5/Ad40 viruses

The defective growth of the enteric adenovirus type 40 (Ad40) in HeLa cells can only be overcome by supplying an E1B 55K function in trans, and it has been demonstrated that expression of Ad40 E1B mRNA is poor in these cells (V. Mautner et al., 1990, Virology 171, 618-622). To study the control of expression from the Ad40 E1B region in greater detail, two Ad5/Ad40 recombinant viruses were constructed containing the Ad40 E1B region in place of the equivalent Ad5 region, under either the control of the Ad40 E1B promoter (sub40P) or that of Ad5 (sub5P). For both recombinants, E1B mRNAs similar to those seen in a wt Ad40 infection were detected, with late splicing (post DNA replication) occurring predominantly via the Ad40 14S splice acceptor. However, the level of expression from the substituted E1B region differs markedly between the two recombinants, and synthesis of E1B mRNA and proteins was impaired in sub40P-infected cells. In 293 and KB16 cells, expression from the Ad40 E1B promoter was reduced 10- to 20-fold compared with the Ad5 promoter. In HeLa cells, the reduction was 80-fold and mirrored the poor expression of E1B mRNA in Ad40-infected HeLa cells. Furthermore, in contrast to the 293 cells, early expression of E1B proteins could not be detected in sub40P- or wt Ad40-infected HeLa cells. The experiments demonstrate the low activity of the Ad40 E1B promoter and that this promoter is regulated in a cell type specific manner.