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J. Biol. Chem., Vol. 283, Issue 45, 30788-30795, November 7, 2008

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Selective Targeting of Leukemic Cell Growth in Vivo and in Vitro Using a Gene Silencing Approach to Diminish S-Adenosylmethionine Synthesis^*

Ramy R. Attia, Lidia A. Gardner, Engy Mahrous, Debra J. Taxman^¶, Leighton LeGros, Sarah Rowe, Jenny P.-Y. Ting^¶, Arthur Geller^||, and Malak Kotb^||1

From the University of Tennessee Health Science Center and the Research Service, Veterans Affairs Medical Center², Memphis, Tennessee 38104, the ^¶Department of Microbiology and Immunology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, and the ^||Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524

We exploited the fact that leukemic cells utilize significantly higher levels of S-adenosylmethionine (SAMe) than normal lymphocytes and developed tools that selectively diminished their survival under physiologic conditions. Using RNA interference gene silencing technology, we modulated the kinetics of methionine adenosyltransferase-II (MAT-II), which catalyzes SAMe synthesis from ATP and L-Met. Specifically, we silenced the expression of the regulatory MAT-IIβ subunit in Jurkat cells and accordingly shifted the of the enzyme 10–15-fold above the physiologic levels of L-Met, thereby reducing enzyme activity and SAMe pools, inducing excessive apoptosis and diminishing leukemic cell growth in vitro and in vivo. These effects were reversed at unphysiologically high L-Met (>50 µM), indicating that diminished leukemic cell growth at physiologic L-Met levels was a direct result of the increase in MAT-II due to MAT-IIβ ablation and the consequent reduction in SAMe synthesis. In our NOD/Scid IL-2R^null humanized mouse model of leukemia, control shRNA-transduced Jurkat cells exhibited heightened engraftment, whereas cells lacking MAT-IIβ failed to engraft for up to 5 weeks post-transplant. These stark differences in malignant cell survival, effected by MAT-IIβ ablation, suggest that it may be possible to use this approach to disadvantage leukemic cell survival in vivo with little to no harm to normal cells.

Received for publication, May 30, 2008 , and in revised form, August 21, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grant R01CA108792. This work was also supported by a Veterans Affairs Merit Review Award and a Senior Research Career Scientist Award (to M. K.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1 and S2 and Table S1.

² The abbreviations used are: MAT, methionine adenosyltransferase; SAMe, S-adenosylmethionine; GFP, green fluorescence protein; shRNA, short hairpin RNA; HPLC, high pressure liquid chromatography; BM, bone marrow.

¹ To whom correspondence should be addressed: Dept. of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, 231 Albert Sabin Way, P.O. Box 670524, 2938 CVC Mail Loc-0524, Cincinnati, OH 45267-0524. Tel.: 513-558-5231; Fax: 513-558-1190; E-mail: mscbskotb{at}gmail.com.

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