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E2F1 Enhances 8-Chloro-adenosine-Induced G2/M Arrest and Apoptosis in A549 and H1299 Lung Cancer Cells

Hong-Ying Duan1,2, Ji-Xiang Cao1, Jun-Juan Qi1, Guo-Sheng Wu1, Shu-Yan Li1, Guo-Shun An1, Hong-Ti Jia1,3, Wang-Wei Cai2, and Ju-Hua Ni1*

1Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Peking University Health Science Center, Xue Yuan Road 38, Beijing 100191, PR China; fax: 86-10-82801434; E-mail: juhuani@bjmu.edu.cn

2Department of Biochemistry, Hainan Medical College, Haikou 571101, PR China

3Department of Biochemistry and Molecular Biology, Capital University of Medical Sciences, You An Men Xitoutiao 8, Beijing 100054, PR China

* To whom correspondence should be addressed.

Received July 30, 2011; Revision received October 29, 2011
The E2F1 transcription factor is a well known regulator of cell proliferation and apoptosis, but its role in response to DNA damage is less clear. 8-Chloro-adenosine (8-Cl-Ado), a nucleoside analog, can inhibit proliferation in a variety of human tumor cells. However, it is still elusive how the agent acts on tumors. Here we show that A549 and H1299 cells formed DNA double-strand breaks after 8-Cl-Ado exposure, accompanied by E2F1 upregulation at protein level. Overexpressed wild-type (E2F1-wt) colocalized with double-strand break marker γ-H2AX and promoted G2/M arrest in 8-Cl-Ado-exposed A549 and H1299, while expressed S31A mutant of E2F1 (E2F1-mu) significantly reduced ability to accumulate at sites of DNA damage and G2/M arrest, suggesting that E2F1 is required for activating G2/M checkpoint pathway upon DNA damage. Transfection of either E2F1-wt or E2F1-mu plasmid promoted apoptosis in 8-Cl-Ado-exposed cells, indicating that 8-Cl-Ado may induce apoptosis in E2F1-dependent and E2F1-independent ways. These findings demonstrate that E2F1 plays a crucial role in 8-Cl-Ado-induced G2/M arrest but is dispensable for 8-Cl-Ado-induced apoptosis. These data also suggest that the mechanism of 8-Cl-Ado action is complicated.
KEY WORDS: E2F1, 8-chloro-adenosine, DNA double-stranded breaks, G2/M arrest, apoptosis

DOI: 10.1134/S0006297912030042