“Hit-and-Run” Transformation by Adenovirus Oncogenes

Abstract

According to classical concepts of viral oncogenesis, the persistence of virus-specific oncogenes is required to maintain the transformed cellular phenotype. In contrast, the "hit-and-run" hypothesis claims that viruses can mediate cellular transformation through an initial "hit," while maintenance of the transformed state is compatible with the loss ("run") of viral molecules. It is well established that the adenovirus E1A and E1B gene products can cooperatively transform primary human and rodent cells to a tumorigenic phenotype and that these cells permanently express the viral oncogenes. Additionally, recent studies have shown that the adenovirus E4 region encodes two novel oncoproteins, the products of E4orf6 and E4orf3, which cooperate with the viral E1A proteins to transform primary rat cells in an E1B-like fashion. Unexpectedly, however, cells transformed by E1A and either E4orf6 or E4orf3 fail to express the viral E4 gene products, and only a subset contain E1A proteins. In fact, the majority of these cells lack E4-and E1A-specific DNA sequences, indicating that transformation occurred through a hit-and-run mechanism. We provide evidence that the unusual transforming activities of the adenoviral oncoproteins may be due to their mutagenic potential. Our results strongly support the possibility that even tumors that lack any detectable virus-specific molecules can be of viral origin, which could have a significant impact on the use of adenoviral vectors for gene therapy.The observation that a number of viral oncogenes are recurrently expressed in virus-transformed cells and in the corresponding tumors led to the general view that the persistence of virus-specific genes is required to maintain the transformed cellular phenotype (21). In contrast to this conventional concept of viral oncogenesis, the "hit-and-run" hypothesis, originally proposed by Skinner (31), claims that viruses can mediate cellular transformation through an initial "hit," while maintenance of the transformed state is compatible with the loss ("run") of viral molecules. The hit-and-run concept raises the intriguing possibility of an etiological role of viral agents in tumors that lack any viral genes and proteins.It is well established that cellular transformation by adenovirus type 5 (Ad5) is initiated through expression of the E1A oncogene, which is sufficient to immortalize cells, although transformation by E1A alone is inefficient and often incomplete (reviewed in references 6 and 29). The 19-and 55-kDa proteins expressed from the E1B transcription unit of Ad5 (E1B-19 kDa and E1B-55 kDa) can individually cooperate with Ad5 E1A proteins to increase transformation efficiency and to convert primary human and rodent cells to a fully transformed tumorigenic phenotype (6, 29). We and others have recently shown that two early region 4 (E4) gene products of Ad5, the E4orf6 (E4-34 kDa) and E4orf3 (E4-11 kDa) proteins, can also cooperate with E1A and E1A plus E1B to substantially enhance transformation (16,(18)(19)(20). Consistent with the conv...

Adenovirus DNA is detected at increased frequency in Guthrie cards from children who develop acute lymphoblastic leukaemia

“…Gene products of adenovirus can transform cells in culture by a hit-and-run mechanism that leaves no viral DNA in the transformed cells (Nevels et al, 2001). Because species C adenoviruses profoundly block double-stranded DNA-break repair (Weitzman and Ornelles, 2005), it is conceivable that infection with species C adenovirus could lead to the acquisition of genomic mutations common to childhood ALL.…”

Human retinoblastoma is not caused by known pRb‐inactivating human DNA tumor viruses

“…Although most cell lines transformed by adenovirus maintain the presence of viral DNA through integration into the host cell genome, cells transformed by HAdV5 E1A and E4orf6 or E4orf3 can maintain a transformed phenotype after loss of adenoviral DNA in long-term culture, possibly because of cumulative viral-induced mutations and genetic instability. 48 However, the absence of any viral sequences in samples argues against a role for adenovirus in retinoblastoma, given that adenovirus-negative cell lines arise from adenovirus-containing, transformed precursors.…”

“…Although most cell lines transformed by adenovirus maintain the presence of viral DNA through integration into the host cell genome, cells transformed by HAdV5 E1A and E4orf6 or E4orf3 can maintain a transformed phenotype after loss of adenoviral DNA in long-term culture, possibly because of cumulative viral-induced mutations and genetic instability. 48 However, the absence of any viral sequences in samples argues against a role for adenovirus in retinoblastoma, given that adenovirus-negative cell lines arise from adenovirus-containing, transformed precursors.Whether SV40 circulates in the human population as a result of contamination of the polio vaccine and contributes to the pathogenesis of human malignancies is a matter of considerable controversy. 49,50 Although we detected SV40 genomic DNA sequences in a small proportion of retinoblastomas using a single primer pair targeted to the SV40 large T-antigen exon, the low viral copy number, the uniform absence of the SV40 large T-antigen intron and the detection of plasmid-specific sequences in samples, argue that the sequences were derived from contaminating plasmid DNA.…”

“…Furthermore, in contrast to HPV, recent data suggest that HAdV may be able to act by a ''hit and run'' mechanism. 48 The pRb inactivating oncoprotein of adenovirus E1A together with E1B or E4orf6/E4orf3 are necessary for the development of the transformed phenotype. Although most cell lines transformed by adenovirus maintain the presence of viral DNA through integration into the host cell genome, cells transformed by HAdV5 E1A and E4orf6 or E4orf3 can maintain a transformed phenotype after loss of adenoviral DNA in long-term culture, possibly because of cumulative viral-induced mutations and genetic instability.…”

SUMO modification of E1B-55K oncoprotein regulates isoform-specific binding to the tumour suppressor protein PML

“…HAdV5 E1B-55K-wt (Nevels et al, 2001), the E1B mutant proteins E1B-55K-NES (L83/87/91A), E1B-55K-V103D and E1B-55K-K104R (Endter et al, 2001(Endter et al, , 2005 were expressed from pcDNA3 vector. N-terminal flag-tagged human PML isoforms I-VI were expressed from pLKO.1-puro vector (kindly provided by R Everett).…”