Defective synthesis of early region 4 mRNAs during abortive adenovirus infections in monkey cells

Abstract

Human adenovirus 2 grows poorly in monkey cells, partly because of defects in late gene expression. Since deletions in early region 4 (E4) cause similar defects in late gene expression, we examined E4 mRNA expression in abortive infections. Processing of E4 mRNAs was defective during abortive infections, most likely at the level of splicing. At early times in productive infections in HeLa cells, the major E4 species produced is a 2-kb mRNA; at late times, a shift occurs so that smaller spliced E4 mRNAs are also produced. In CV-1 cells, a nonpermissive monkey cell line, this shift did not take place and only the 2-kb species was produced at late times, suggesting a defect in E4 mRNA splicing during abortive infections. The adenovirus DNA-binding protein (DBP) was required for normal processing of E4 mRNAs, since a host range mutant (hr602) containing an altered DBP gene showed a normal late E4 mRNA pattern in CV-1 cells; in addition, DBP was required during infections in HeLa cells for late E4 mRNA expression. DBP was not required for production of the late E4 pattern in transient expression assays in HeLa or 293 cells, suggesting that a second factor in addition to the DBP, present during infection but not transfection, modulates E4 mRNA processing.

Regulated splicing of adenovirus type 5 E4 transcripts and regulated cytoplasmic accumulation of E4 mRNA

“…This donor-acceptor combination is utilized in mRNAs of the late class to produce a family of shorter mRNAs. The usage of these sites is therefore temporally regulated during the course of Ad5 infection; recent studies of E4 expression in abortively infected monkey cells suggested that the E2a DNA-binding protein was important for this regulation (27). As with other examples of regulated adenovirus splicing, in expression of the Ela, Elb, and Li genes (1,8,19,22,31), processing in E4 moves toward more heavily spliced, shorter mRNAs in the late phase of infection.…”

“…Previous studies of E4 mRNAs indicated some degree of temporal regulation of the pattern of splicing (27,32), although individual mRNA species were not identified. To characterize the pattern of expression of the known and putative E4 products in more detail, a systematic study of the levels of individual mRNAs during the infectious cycle was undertaken, revealing distinct early and late classes of E4 mRNA.…”

Adenovirus type 40 and 41 growth in vitro: host range diversity reflected by differences in patterns of DNA replication

“…Ad4O, on the other hand, undergoes DNA replication on a reduced scale (compared with Ad2) in both semipermissive and nonpermissive cells, suggesting that any early defect in replication in this virus may not be as important to the final outcome of infection as the existence of one or more defects which prevent the expression of newly synthesized DNA. Such defects may be related to the decreased levels of late proteins expressed from the late transcription unit in abortive infections of monkey cells by human adenoviruses (7,16,20).…”

Virus Vectors for use in the Central Nervous System

“…It is also important to consider that many experiments are performed in non-permissive or semipermissive species (Ginsberg et al, 1991;Ross and Ziff, 1992), e.g., mice, rats, and nonhuman primates. In such systems, Ad E1 recombinants are unable to replicate due to a "species block."…”