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J. Virol., Aug 1997, 5861-5870, Vol 71, No. 8
LR Bonin and JK McDougall
Physical interactions between human cytomegalovirus (HCMV) immediate- early
(IE) proteins and key cell cycle regulatory proteins have been suggested as
a mechanism whereby this herpesvirus modifies cellular control of
proliferation. Observed similarities to interactions of other DNA virus
proteins (human papillomavirus type 16 E6 and E7, simian virus 40 large T
antigen, and adenovirus type 5 E1A and E1B) with cell cycle modulatory
proteins such as p53 and Rb have suggested that HCMV IE proteins may
likewise alter the G1-to-S phase transition. The IE2 region gene product
IE86 has been shown to specifically bind p53, potentially modifying p53 G1
checkpoint function. To examine this possibility, p53-mediated G1 arrest in
the presence of IE86 was assessed. Retroviral constructs were created to
facilitate the stable expression of IE86 and IE72, another IE protein
implicated in HCMV- mediated alteration of cell cycle progression. Western
analysis and immunoprecipitation confirmed IE protein expression and
binding of IE86 to p53, respectively. Chloramphenicol acetyltransferase
assays examining the ability of IE86 to repress activity from the HCMV
major IE promoter or activate the HCMV early promoter for the 2.2-kb class
of RNAs demonstrated the functional integrity of the IE86 protein.
Induction of DNA damage in normal, uninfected fibroblasts (FB) or FB
expressing IE86 by actinomycin D (Act D) resulted in increased p53 levels,
a predominance of the hypophosphorylated form of Rb, and increased
expression of both p21(CIP1/WAF1) and mdm-2. Fluorescence- activated cell
sorting revealed that both uninfected and IE86- expressing FB experienced
dramatic G1 arrest following exposure to Act D. The clear demonstration of
these p53-dependent responses in the presence of IE86 indicates that
binding to this viral protein does not compromise the ability of p53 to
elicit growth arrest following DNA damage.
Copyright © 1997, American Society for Microbiology
Human cytomegalovirus IE2 86-kilodalton protein binds p53 but does not abrogate G1 checkpoint function
Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA.
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