Impaired Phosphorylation and Ubiquitination by p70 S6 Kinase (p70S6K) and Smad Ubiquitination Regulatory Factor 1 (Smurf1) Promote Tribbles Homolog 2 (TRIB2) Stability and Carcinogenic Property in Liver Cancer*
- Jiayi Wang‡1,
- Yue Zhang§1,
- Wenhao Weng‡1,
- Yongxia Qiao¶,
- Lifang Ma‡,
- Weifan Xiao§,
- Yongchun Yu§,
- Qiuhui Pan§2 and
- Fenyong Sun‡3
- From the Departments of ‡Clinical Laboratory Medicine and
- §Central Laboratory, Shanghai Tenth People's Hospital of Tongji University, 200072 Shanghai, China and
- ¶School of Public Health, Shanghai Jiaotong University School of Medicine, 200025 Shanghai, China
- ↵2 To whom correspondence may be addressed: Dept. of Central Laboratory, Shanghai Tenth People's Hospital of Tongji University, No. 301 Middle Yanchang Rd., 200072 Shanghai, China. Tel.: 86-21-66313245; Fax: 86-21-66313245; E-mail: panqiuhui{at}263.net.
- ↵3 To whom correspondence may be addressed: Dept. of Clinical Laboratory Medicine, Shanghai Tenth People's Hospital of Tongji University, No. 301 Middle Yanchang Rd., 200072 Shanghai, China. Tel.: 86-21-66300588; Fax: 86-21-66300588; E-mail: sunfenyong{at}126.com.
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↵1 These authors contributed equally to this work.
Abstract
Tribbles homolog 2 (TRIB2) is critical for both solid and non-solid malignancies. Recently, TRIB2 was identified as a liver cancer-specific Wnt/β-catenin signaling downstream target and is functionally important for liver cancer cell survival and transformation. TRIB2 functions as a protein that interacts with E3 ubiquitin ligases and thereby modulates protein stability of downstream effectors. However, the regulation underlying TRIB2 protein stability per se has not yet been reported. In this study, we found that TRIB2 was up-regulated and exhibited high stability in liver cancer cells compared with other cells. We performed a structure-function analysis of TRIB2 and identified a domain (amino acids 1–5) at the N terminus that interacted with the E3 ubiquitin ligase Smurf1 and was critical for protein stability. Deletion of this domain extended TRIB2 half-life time accompanied with a more significant malignant property compared with wild type TRIB2. Furthermore, Smurf1-mediated ubiquitination required phosphorylation of TRIB2 by p70 S6 kinase (p70S6K) via another domain (amino acids 69–85) that is also essential for correct TRIB2 subcellular localization. Mutation of Ser-83 diminished p70S6K-induced phosphorylation of TRIB2. Moreover, the high stability of TRIB2 may be due to the fact that both p70S6K and Smurf1 were down-regulated and negatively correlated with TRIB2 expression in both liver cancer tissues and established liver cancer cell lines. Taken together, impaired phosphorylation and ubiquitination by p70S6K and Smurf1 increase the protein stability of TRIB2 in liver cancer and thus may be helpful in the development of diagnosis and treatment strategies against this malignant disease.
- E3 Ubiquitin Ligase
- Gene Regulation
- Hepatocellular Carcinoma
- Phosphorylation
- Post-translational Modification
Footnotes
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↵* This work was supported by 973 Program Grants 2011CBA01100 and 2012CB966900; Natural Science Foundation of China Grants 81272292, 81071524, and 81201884; and the 5810 Training Program (to J. W.) from Shanghai Tenth People's Hospital.
- Received July 19, 2013.
- Revision received September 30, 2013.
- © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.
