Amplification of Mdmx (or Mdm4) Directly Contributes to Tumor Formation by Inhibiting p53 Tumor Suppressor Activity

Abstract

Human tumors are believed to harbor a disabled p53 tumor suppressor pathway, either through direct mutation of the p53 gene or through aberrant expression of proteins acting in the p53 pathway, such as p14^ARF or Mdm2. A role for Mdmx (or Mdm4) as a key negative regulator of p53 function in vivo has been established. However, a direct contribution of Mdmx to tumor formation remains to be demonstrated. Here we show that retrovirus-mediated Mdmx overexpression allows primary mouse embryonic fibroblast immortalization and leads to neoplastic transformation in combination with HRas^V12. Furthermore, the human Mdmx ortholog, Hdmx, was found to be overexpressed in a significant percentage of various human tumors and amplified in 5% of primary breast tumors, all of which retained wild-type p53. Hdmx was also amplified and highly expressed in MCF-7, a breast cancer cell line harboring wild-type p53, and interfering RNA-mediated reduction of Hdmx markedly inhibited the growth potential of these cells in a p53-dependent manner. Together, these results make Hdmx a new putative drug target for cancer therapy.

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Correction for Danovi et al., “Amplification of Mdmx (or Mdm4) Directly Contributes to Tumor Formation by Inhibiting p53 Tumor Suppressor Activity”

We thank Micaela Quarto and Marco Bianchi for generation of the TMAs and for ISH and IHC analyses; Manuela Nebuloni, Renzo Boldorini, and Giuseppe Viale for providing tumor material; Giuseppe Ossolengo and Daniele Piccini for antibody purification; Manuela Capillo for help with mice; Elena Belloni for bioinformatics; and Adrian Bracken for helpful discussions. We also thank E. Appella for providing the agarose-conjugated PAb421 and PabLys(Ac)379m antibodies and R. Agami for the gifts of plasmids pS and pS-p53.

J.-C. Marine is a Chercheur Qualifié from the Fonds National pour la Recherche Scientifique. D. Danovi is a recipient of a fellowship from Fondazione Italiana per la Ricerca sul Cancro (FIRC). P. de Graaf and E. Meulmeester were supported by grants from the Association for International Cancer Research and the Dutch Cancer Society, respectively. This work was supported in part by grants from FB Insurance, FIRC, AICR, Fédération Belge contre le Cancer, and the Flanders Interuniversity Institute for Biotechnology.