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  • The EMBO Journal (2006) 25, 1207 - 1218
  • doi:10.1038/sj.emboj.7601010

Published online: 2 March 2006

14-3-3big gamma binds to MDMX that is phosphorylated by UV-activated Chk1, resulting in p53 activation

Yetao Jin1, Mu-Shui Dai1, Steven Z Lu1, Yingda Xu2, Zhijun Luo3, Yingming Zhao2 and Hua Lu1

  1. Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR, USA
  2. Department of Biochemistry, UT Southwestern Medical Center, Dallas, TX, USA
  3. Department of Medicine, Boston University, Boston, MA, USA

Correspondence to:

Hua Lu, Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA. Tel.: +1 503 494 7414; Fax: +1 503 494 8393; E-mail: luh@ohsu.edu

Received 5 September 2005; Accepted 27 January 2006

It has been shown that MDMX inhibits the activity of the tumor suppressor p53 by primarily cooperating with the p53 feedback regulator MDM2. Here, our study shows that this inhibition can be overcome by 14-3-3gamma and Chk1. 14-3-3gamma was identified as an MDMX-associated protein via an immuno-affinity purification-coupled mass spectrometry. Consistently, 14-3-3gamma directly interacted with MDMX in vitro, and this interaction was stimulated by MDMX phosphorylation in vitro and in cells. Interestingly, in response to UV irradiation, the wild-type, but not the kinase-dead mutant, Chk1 phosphorylated MDMX at serine 367, enhanced the 14-3-3gamma-MDMX binding and the cytoplasmic retaining of MDMX. The Chk1 specific inhibitor UCN-01 repressed all of these effects. Moreover, overexpression of 14-3-3gamma, but not its mutant K50E, which did not bind to MDMX, suppressed MDMX-enhanced p53 ubiquitination, leading to p53 stabilization and activation. Finally, ablation of 14-3-3gamma by siRNA reduced UV-induced p53 level and G1 arrest. Thus, these results demonstrate 14-3-3gamma and Chk1 as two novel regulators of MDMX in response to UV irradiation.

  • Keywords:

    • 14-3-3gamma,
    • Chk1,
    • MDMX,
    • p53,
    • UV response