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Journal of Virology, October 2000, p. 9441-9450, Vol. 74, No. 20
Laboratory of Biochemical Genetics, National
Heart, Lung, and Blood Institute, National Institutes of Health,
Bethesda, Maryland 20892
Received 16 May 2000/Accepted 25 July 2000
Adeno-associated virus (AAV) type 2 Rep78 is a multifunctional
protein required for AAV DNA replication, integration, and gene
regulation. The biochemical activities of Rep78 have been described,
but the effects of Rep proteins on the cell have not been
characterized. We have analyzed Rep-mediated cytotoxicity. We
demonstrated that Rep78 expression is sufficient to induce cell death
and disruption of the cell cycle. Cell death was found to be mediated
by apoptosis. Rep78 expression resulted in the activation of caspase-3,
a terminal caspase directly involved in the execution of cell death. A
peptidic inhibitor of caspase-3, Z-Asp-Glu-Val-Asp-fluoromethylketone
(Z-DEVD-FMK), abrogated Rep78-induced apoptosis, indicating that
Rep78-mediated apoptosis is caspase-3 dependent. Rep78 induced
apoptosis in wild-type p53-containing human embryonal carcinoma NT-2
cells and in p53-null promyelocytic human HL-60 cells, indicating that
at least one pathway of Rep78-induced apoptosis is p53 independent.
Apoptosis was shown to occur during the G1 and early S
phases of the cell cycle. By analyzing the effects of Rep78 mutations
on cell viability, the cause of cell death was attributed in part to
two biochemical activities of Rep78, DNA binding and ATPase/helicase
activity. The endonuclease activity of Rep78 did not contribute to
apoptosis induction.
0022-538X/00/$04.00+0
Adeno-Associated Virus Type 2 Rep78 Induces
Apoptosis through Caspase Activation Independently of p53
*
Corresponding author. Mailing address: LBG, NHLBI,
Bldg. 10, Rm. 7D05, Bethesda, MD 20892-1654. Phone: (301) 496-1594. Fax: (301) 496-9985. E-mail: KotinR{at}NHLBI.NIH.GOV.
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