GENE REGULATION IN ANIMAL CELLS 
Joseph R. Nevins, Ph.D., Investigator 
The research in Dr. Nevins's laboratory is focused 
on three aspects of gene regulation in animal cells: 
1 ) the mechanism of action of viral oncoproteins, 2) 
use of viral systems to elucidate mechanisms of tran- 
scriptional regulation, and 3) molecular mecha- 
nisms of regulation of RNA processing at polyadenyl- 
ation sites. 
Molecular Mechanisms for Oncogenesis 
by Viral Proteins 
In 1988, Dr. Ed Harlow and his colleagues demon- 
strated that the adenovirus ElA oncoprotein is able 
to bind to the retinoblastoma-susceptibiliry gene 
product (Rb) and that this interaction is dependent 
on ElA sequences that are essential for oncogenic 
activity. This finding, and the subsequent realiza- 
tion that the interaction w^as also a property of the 
oncoproteins of the other DNA tumor viruses, such 
as simian virus 40 (SV40) T antigen, and human pa- 
pillomavirus (HPV) E7, strongly suggested that 
these viral proteins elicited cellular transformation 
by inactivating the Rb tumor-suppressor protein. Dr. 
Nevins and his colleagues have now demonstrated 
that the cellular transcription factor E2F is a target 
for control by the Rb tumor-suppressor protein and 
that the interaction of the viral oncoproteins with 
Rb disrupts this control. 
Moreover, the relevance of these events to human 
cancer is indicated by Dr. Nevins's findings that the 
E2F-Rb interaction is absent in various human cervi- 
cal carcinoma cell lines that either express the HPV 
E7 protein or that harbor an inactivating mutation in 
the RBI gene, suggesting that the loss of the E2F-Rb 
interaction is an important aspect of human cervical 
carcinogenesis. It thus appears that the ability of 
ElA, SV40 T antigen, and HPV E7 to dissociate the 
E2F-Rb complex is a common activity of these viral 
proteins that has evolved to stimulate quiescent 
cells into a proliferating state. 
Further analyses of the interaction of E2F with reg- 
ulatory proteins such as Rb have shown that the 
transcriptional activity of E2F is inhibited. Since E2F 
likely controls the transcription of cellular genes 
that are important for S-phase events, this control 
appears to be an integral part of cellular prolifera- 
tion regulation. In this regard, an additional E2F in- 
teraction has been identified that is regulated at the 
transition from Gl to S phase. This complex con- 
tains the Rb-related pi 07 protein in association 
with E2F. Moreover, like the Rb protein, pi 07 in- 
hibits E2F-dependent transcription in a cotransfec- 
tion assay. This result, together with the observation 
that free, uncomplexed E2F accumulates as cells 
leave Gl and enter S phase, suggests that the pi 07 
protein may regulate E2F-dependent transcription 
during Gl. 
Mechanisms of Transcriptional Regulation 
in Virus-infected Cells 
Complex cellular events are often simplified 
through the use of model systems provided by vi- 
ruses that infect these cells. The mediation of tran- 
scription control by the adenovirus ElA gene prod- 
uct has proved valuable in deciphering mechanisms 
that control transcription in animal cells. 
Recent studies have shown that the adenovirus 
ElAi2s protein (the oncogenic ElA product) can 
trans-activate transcription by releasing the E2F 
transcription factor from inhibitory complexes with 
proteins such as Rb. However, E2F cannot be the 
only target for ElA activation, since several cellular 
promoters have been found to be activated by the 
ElA protein despite the fact that they lack E2F sites. 
Indeed, activation of the hsp70 promoter by ElA 
requires the TATAA sequence. Moreover, ElA pro- 
tein domains that are required for activation of E2 
transcription via E2F are not required for activation 
of the hsp70 promoter. Rather, a distinct protein 
domain facilitates TATAA-dependent transcriptional 
activation. It appears that the targeting of distinct 
transcription factors, leading to trans-activation of 
transcription of multiple promoters, involves dis- 
tinct domains of the ElA proteins that are also re- 
quired for oncogenic activity. 
Given the fact that the TATAA element is a target 
for the activation of the hsp70 promoter, Dr. Nevins 
and his colleagues have addressed the possibility 
that interactions with the TATAA-binding protein 
(TBP) might be altered by ElA. Recent experiments 
in the laboratory of Dr. Danny Reinberg and his col- 
leagues have identified an activity termed Drl that 
interacts with and inhibits the transcriptional activ- 
ity of TBP. Dr. Nevins's work now demonstrates that 
the ElA protein can disrupt the interaction of Drl 
with TBP, allowing TBP to then interact with the 
TFIIA transcription factor. This disruption depends 
on the amino-terminal ElA sequences that are also 
essential for trans-activation of the hsp70 promoter. 
It would thus appear that the activation of hsp70 
through the TATAA element may be mechanistically 
GENETICS 237 
