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J. Biol. Chem., Vol. 282, Issue 52, 37492-37500, December 28, 2007

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Human Papillomavirus E7 Requires the Protease Calpain to Degrade the Retinoblastoma Protein^*

Grant A. Darnell, Wayne A. Schroder, Toni M. Antalis, Eleanore Lambley, Lee Major, Joy Gardner, Geoff Birrell^¶, Angel Cid-Arregui^||, and Andreas Suhrbier¹

From the Immunovirology Laboratory, Queensland Institute of Medical Research, Brisbane, Queensland 4029, Australia, Center for Vascular Biology and Inflammatory Diseases and the Department of Physiology, University of Maryland School of Medicine, Maryland 21201, ^¶Radiation Biology and Oncology Laboratory, Queensland Institute of Medical Research, Brisbane, Queensland 4029, Australia, and ^||Angewandte Tumorvirologie, Deutsches Krebsforschungszentrum, Heidelberg D-69012, Germany

Cervical cancers transformed by high risk human papilloma virus (HPV) express the E7 oncoprotein, which accelerates the degradation of the retinoblastoma protein (Rb). Here we show that the E7-mediated degradation of Rb requires the calcium-activated cysteine protease, calpain. E7 bound and activated µ-calpain and promoted cleavage at Rb⁸¹⁰, with mutation of this residue preventing E7-mediated degradation. The calpain cleavage product, Rb^1–810, was unable to mediate cell cycle arrest but retained the ability to repress E6/E7 transcription. E7 also promoted the accelerated proteasomal degradation of Rb^1–810. Calpain inhibitors reduced the viability of HPV-transformed cells and synergized with cisplatin. Calpain, thus, emerges as a central player in E7-mediated degradation of Rb and represents a potential new drug target for the treatment of HPV-associated lesions.

Received for publication, August 17, 2007 , and in revised form, October 4, 2007.

^* This work was funded by the National Health and Medical Research Council, Australia (to A. S. and G. A. D.) and National Institutes of Health Grant R01 CA098369 (to T. M. A. and A. S.). 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–S3.

¹ To whom correspondence should be addressed: Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Queensland 4029, Australia. Tel.: 61-7-33620415; Fax: 61-7-33620107; E-mail: Andreas.Suhrbier{at}qimr.edu.au.

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