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Originally published In Press as doi:10.1074/jbc.M701085200 on February 21, 2007
J. Biol. Chem., Vol. 282, Issue 16, 11715-11721, April 20, 2007
MADD/DENN Splice Variant of the IG20 Gene Is a Negative Regulator of Caspase-8 ActivationKNOCKDOWN ENHANCES TRAIL-INDUCED APOPTOSIS OF CANCER CELLS*
Nirupama Mulherkar1,
Kanteti V. Prasad, and
Bellur S. Prabhakar2
From the
Department of Microbiology and Immunology, College of Medicine, University of Illinois, Chicago, Illinois 60612
The MADD variant of the IG20 gene is necessary and sufficient for cancer cell survival. Abrogation of MADD, but not the other IG20 splice variants, can render cancer cells more susceptible to spontaneous as well as TRAIL (tumor necrosis factor -related apoptosis-inducing ligand)-induced apoptosis. Both types of apoptosis in cells devoid of MADD can be inhibited by expression of CrmA or dominant-negative FADD, thereby suggesting that endogenous MADD may be targeting caspase-8 activation. Immunoprecipitation studies showed that MADD down-modulation could lead to caspase-8 activation at the death receptors without an apparent increase in the recruitment of death-inducing signaling complex components such as FADD. Further, we found that MADD can directly interact with death receptors, but not with either caspase-8 or FADD, and can inhibit caspase-8 activation. These results clearly demonstrate the importance of MADD in the control of cancer cell survival/death and in conferring significant resistance to TRAIL-induced apoptosis. In addition, our results indicate the therapeutic potential of MADD abrogation in enhancing TRAIL-induced selective apoptosis of cancer cells.
Received for publication, February 5, 2007
, and in revised form, February 20, 2007.
* This work was supported by Grant 5R01CA107506 from the National Institutes of Health, Bethesda, MD. 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.
1 Current address: Inst. for Cancer Genetics, Columbia University, New York, NY 10032.
2 To whom correspondence should be addressed: Rm. E-705, 835 South Wolcott Ave. (M/C 790), Chicago, IL 60612. Tel.: 312-996-4945; Fax: 312-996-6415; E-mail: bprabhak{at}uic.edu.

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Copyright © 2007 by the American Society for Biochemistry and Molecular Biology.
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