ADENOVIRUS TRANSCRIPTIONAL CONTROL 
Thomas Shenk, Ph.D., Investigator 
L Transcriptional Activation by Adenovirus ElA 
Gene Products. 
The ElA gene is the first adenovirus gene to be ex- 
pressed when the viral chromosome reaches the nu- 
cleus of the infected cell. ElA gene products then ac- 
tivate transcription of all the remaining early viral 
genes and further activate expression of the ElA gene 
itself The mechanism by which ElA products activate 
gene expression remains unclear. However, several 
cellular transcription factors that play roles in the 
process have now been identified. 
Insight to the factors involved in transcriptional 
activation came initially from the identification of 
specific factor binding sites within the control re- 
gions of early viral genes. One such binding site is 
the cAMP response element (CRE). This is the rec- 
ognition site for transcription factors that have 
been termed CRE-binding protein (CREB) and acti- 
vating transcription factor (ATE). CREB/ATF activi- 
ties probably represent a family of DNA-binding 
proteins that recognize the same DNA sequence. 
Binding sites for these activities were shown to be 
present in the adenovirus ElA, E2, E3, and E4 tran- 
scriptional control regions. 
The presence of CREB/ATE-binding sites predicted 
that early viral transcription should be responsive to 
cAMP This proved to be the case. ElA gene products 
and cAMP acted in synergy to induce transcription in 
virus-infected cells. For example, if the level of E4 
gene transcription in the absence of either cAMP or 
ElA gene products is set to 1, addition of either cAMP 
or ElA products alone induced transcription by fac- 
tors of ~5 or 10, respectively, while addition of both 
induced transcription by a factor of —200. 
Transfection experiments demonstrated that the 
transcriptional response to cAMP plus ElA prod- 
ucts required a functional CREB/ATF-binding site. 
Point mutations within the binding site markedly 
reduced the response to the activators. Curiously, 
however, cAMP plus ElA products did not induce 
any detectable quantitative or qualitative change in 
CREB/ATF-binding activity. A different transcription 
factor, AP-1, was altered. The level of AP-1 activity 
was modestly induced by cAMP alone, and it in- 
creased to significantly higher levels upon treat- 
ment with cAMP in the presence of ElA products. 
The consensus AP-l-binding site [5'-TGA(C/G)TCA- 
3'] differs from the recognition sequence for 
CREB/ATF (5'-TGACGTCA-3') by only 1 base pair. 
The induced AP-1 activity bound efficiently to a vari- 
ety of both AP-1- and CREB/ATE-binding sites pres- 
ent in ElA-inducible promoters. The maximal in- 
duction of AP-1 DNA-binding activity in infected 
cells required ElA proteins, cAMP, functional pro- 
tein kinase A, and active transcription. The 
cytoplasmic levels of both c-fos and junB mRNAs 
were rapidly increased by cAMP treatment and in- 
creased to substantially higher levels by cAMP treat- 
ment in the presence of ElA proteins. It is likely 
that the AP-1 activity under study comprises c-fos 
and junB polypeptides. 
These results suggest that ElA products in the 
presence of cAMP induce transcription of early viral 
genes in part by causing an increase in the level of 
AP-1 activity within infected cells. The mechanism 
underlying the increase in AP-1 activity is presently 
under study. 
II. Modification of a Transcription Factor in Re- 
sponse to an Adenovirus E4 Gene Product. 
E2F is a cellular, sequence-specific DNA-binding 
factor that was originally identified in adenovirus- 
infected cells and shown to interact with pairs of 
sites that occur upstream of the adenovirus ElA 
and E2 early mRNA cap sites. The laboratory has 
demonstrated that substantial quantities of E2F 
activity are present in uninfected as well as infect- 
ed cells. The binding properties of E2F were altered 
by adenovirus infection. E2F from infected cells 
bound cooperatively to the pair of sites within 
the E2 control region, while the factor from un- 
infected cells bound to each of the two sites in- 
dependently. Cooperative binding was sensitive to 
the spacing between the sites and their relative 
orientation. 
Production of the infection-specific E2F activity was 
dependent on a product of the adenovirus E4 gene. 
Analysis of E2F activity in cells infected with mutant 
viruses revealed that the E4 6/7 ORF, which encodes a 
17 kDa polypeptide, was essential for modification of 
E2F activity to permit cooperative binding. 
The infection-induced change in E2F activity 
proved to be important for maximal E2 early mRNA 
accumulation in some cell lines but not others. Ap- 
parently the E4-induced alteration in E2F activity 
provides an alternative activation pathway, in addi- 
tion to that mediated by ElA products, for the E2 
early gene. That is, both ElA and E4 gene products 
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