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Molecular and Cellular Biology, December 2003, p. 8902-8912, Vol. 23, No. 23
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.23.8902-8912.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Ribosomal Protein L11 Negatively Regulates Oncoprotein MDM2 and Mediates a p53-Dependent Ribosomal-Stress Checkpoint Pathway

Yanping Zhang,1* Gabrielle White Wolf,2 Krishna Bhat,1 Aiwen Jin,1 Theresa Allio,2 William A. Burkhart,3 and Yue Xiong2,4,5*

Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030,1 Curriculum in Genetics and Molecular Biology,2 Lineberger Comprehensive Cancer Center,4 Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295,5 Department of Chemistry and Department of Functional Genetics, GlaxoSmithKline Inc., Research Triangle Park, North Carolina 277093

Received 27 June 2003/ Returned for modification 11 August 2003/ Accepted 21 August 2003

The gene encoding p53 mediates a major tumor suppression pathway that is frequently altered in human cancers. p53 function is kept at a low level during normal cell growth and is activated in response to various cellular stresses. The MDM2 oncoprotein plays a key role in negatively regulating p53 activity by either direct repression of p53 transactivation activity in the nucleus or promotion of p53 degradation in the cytoplasm. DNA damage and oncogenic insults, the two best-characterized p53-dependent checkpoint pathways, both activate p53 through inhibition of MDM2. Here we report that the human homologue of MDM2, HDM2, binds to ribosomal protein L11. L11 binds a central region in HDM2 that is distinct from the ARF binding site. We show that the functional consequence of L11-HDM2 association, like that with ARF, results in the prevention of HDM2-mediated p53 ubiquitination and degradation, subsequently restoring p53-mediated transactivation, accumulating p21 protein levels, and inducing a p53-dependent cell cycle arrest by canceling the inhibitory function of HDM2. Interference with ribosomal biogenesis by a low concentration of actinomycin D is associated with an increased L11-HDM2 interaction and subsequent p53 stabilization. We suggest that L11 functions as a negative regulator of HDM2 and that there might exist in vivo an L11-HDM2-p53 pathway for monitoring ribosomal integrity.


* Corresponding author. Mailing address for Y. Xiong: Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7295. Phone: (919) 962-2142. Fax: (919) 966-8799. E-mail: yxiong{at}email.unc.edu Mailing address for Y. Zhang: Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030. E-mail: ypzhang{at}mdanderson.org.


Molecular and Cellular Biology, December 2003, p. 8902-8912, Vol. 23, No. 23
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.23.8902-8912.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.




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