Subunit 6 of the COP9 signalosome promotes tumorigenesis in mice through stabilization of MDM2 and is upregulated in human cancers
Ruiying Zhao, … , Guillermina Lozano, Mong-Hong Lee
Ruiying Zhao, … , Guillermina Lozano, Mong-Hong Lee
Published February 7, 2011
Citation Information: J Clin Invest. 2011;121(3):851-865. https://doi.org/10.1172/JCI44111.
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Research Article Oncology

Subunit 6 of the COP9 signalosome promotes tumorigenesis in mice through stabilization of MDM2 and is upregulated in human cancers

Abstract

The mammalian constitutive photomorphogenesis 9 (COP9) signalosome (CSN), a protein complex involved in embryonic development, is implicated in cell cycle regulation and the DNA damage response. Its role in tumor development, however, remains unclear. Here, we have shown that the COP9 subunit 6 (CSN6) gene is amplified in human breast cancer specimens, and the CSN6 protein is upregulated in human breast and thyroid tumors. CSN6 expression positively correlated with expression of murine double minute 2 (MDM2), a potent negative regulator of the p53 tumor suppressor. Expression of CSN6 appeared to prevent MDM2 autoubiquitination at lysine 364, resulting in stabilization of MDM2 and degradation of p53. Mice in which Csn6 was deleted died early in embryogenesis (E7.5). Embryos lacking both Csn6 and p53 survived to later in embryonic development (E10.5), which suggests that loss of p53 could partially rescue the effect of loss of Csn6. Mice heterozygous for Csn6 were sensitized to γ-irradiation–induced, p53-dependent apoptosis in both the thymus and the developing CNS. These mice were also less susceptible than wild-type mice to γ-irradiation–induced tumorigenesis. These results suggest that loss of CSN6 enhances p53-mediated tumor suppression in vivo and that CSN6 plays an important role in regulating DNA damage–associated apoptosis and tumorigenesis through control of the MDM2-p53 signaling pathway.

Authors

Ruiying Zhao, Sai-Ching J. Yeung, Jian Chen, Tomoo Iwakuma, Chun-Hui Su, Bo Chen, Changju Qu, Fanmao Zhang, You-Tzung Chen, Yu-Li Lin, Dung-Fang Lee, Feng Jin, Rui Zhu, Tattym Shaikenov, Dos Sarbassov, Aysegul Sahin, Huamin Wang, Hua Wang, Chien-Chen Lai, Fuu-Jen Tsai, Guillermina Lozano, Mong-Hong Lee

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Figure 5

CSN6 facilitates the degradation of p53.

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CSN6 facilitates the degradation of p53. (A) CSN6 reduces the steady-sta...
(A) CSN6 reduces the steady-state protein level of p53. Equal amounts of protein were analyzed with the indicated antibodies. (B) p53 protein level was upregulated with loss of CSN6. Protein levels of p53 and CSN6 were analyzed in various cells subjected to CSN6 shRNA or control shRNA. (C) Proteasome inhibitor blocked CSN6-mediated degradation of p53. H1299 cells were treated with or without proteasome inhibitor MG132 (50 μg/ml, 6 hours), then immunoblotted with the indicated antibodies. (D) CSN6 enhanced MDM2-mediated p53 ubiquitination. HA-ubiquitinated p53 was immunoprecipitated with anti-HA and probed with anti-p53. Equal amounts of TCE were immunoblotted with indicated antibodies. (E) CSN6-mediated destabilization of p53 is MDM2 dependent. p53–/– or p53–/–Mdm2–/– MEFs were transfected with the indicated plasmids, then analyzed with the indicated antibodies. (F) CSN6 increased the turnover rate of p53. H1299 cells were transfected with the indicated plasmids, then checked with the indicated antibodies. (G) CSN6 knockdown increased MDM2 turnover but reduced p53 turnover. U2OS cells were subjected to control shRNA or CSN6 shRNA. MDM2 or p53 remaining is indicated. (H) Enhanced expression of CSN6 impaired p53 transcriptional activation, as determined by quantitative RT-PCR in the presence or absence of DOX (1 μg/ml). Expression levels of the indicated p53 target genes were quantitated and presented as a heat map. (I) Knockdown of CSN6 potentiated p53 transcriptional activation, as determined by quantitative RT-PCR in the presence or absence of DOX (1 μg/ml). Expression levels of the indicated p53 target genes were quantitated and presented as a heat map.