Recombinant adenoviral vectors can induce expression of p73 via the E4-orf6/7 protein.
Despite the utility of recombinant adenoviral vectors in basic research, their therapeutic promise remains unfulfilled. Most engineered adenoviral vectors use a heterologous promoter to transcribe a foreign gene. We show that adenoviruses containing the cytomegalovirus immediate-early promoter induce the expression of the proapoptotic cellular protein TAp73 via the cyclin-dependent kinase-retinoblastoma protein-E2F pathway in murine embryonic fibroblasts. Cells transduced with these vectors also expressed high levels of the adenoviral E4-orf6/7 and E2A proteins. By contrast, adenoviruses containing the ubiquitin C promoter failed to elicit these effects. E4-orf6/7 is necessary and sufficient for increased TAp73 expression, as shown by using retrovirus-mediated E4-orf6/7 expression and adenovirus with the E4-orf6/7 gene deleted. Activation of TAp73 likely occurs via E4-orf6/7-induced dimerization of E2F and subsequent binding to the inverted E2F-responsive elements within the TAp73 promoter. In addition, adenoviral vectors containing the cytomegalovirus immediate-early promoter, but not the ubiquitin C promoter, cooperated with chemotherapeutic agents to decrease cellularity in vitro. In contrast to murine embryonic fibroblasts, adenoviruses containing the ubiquitin C promoter, but not the cytomegalovirus immediate-early promoter, induced both E4-orf6/7 and TAp73 in human foreskin fibroblasts, emphasizing the importance of cellular context for promoter-dependent effects. Because TAp73 is important for the efficacy of chemotherapy, adenoviruses that increase TAp73 expression may enhance cancer therapies by promoting apoptosis. However, such adenoviruses may impair the long-term survival of transduced cells during gene replacement therapies. Our findings reveal previously unknown effects of foreign promoters in recombinant adenoviral vectors and suggest means to improve the utility of engineered adenoviruses by better controlling their impact on viral and cellular gene expression.
Shapiro
Gary S
GS
Department of Biochemistry and Molecular Genetics, Mail Stop 8101, Aurora, CO 80045, USA.
Van Peursem
Crystal
C
Ornelles
David A
DA
Schaack
Jerome
J
DeGregori
James
J
D017500:Adenovirus E1A Proteins / Q000235:genetics / Q000502:physiology*; D017504:Adenovirus E4 Proteins / Q000235:genetics / Q000502:physiology*; D000260:Adenoviruses, Human / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000378:metabolism; D015870:Gene Expression; D005822:Genetic Vectors; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000502:physiology; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis* / Q000378:metabolism
D017500:Adenovirus E1A Proteins; D017504:Adenovirus E4 Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; C000606460:TP73 protein, human; C000606368:Trp73 protein, mouse; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins