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The steady-state level of CDK4 protein is regulated by antagonistic actions between PAQR4 and SKP2 and involved in tumorigenesis Free
Lin Wang1,†, Rui Zhang2,†, Xue You3, Huanhuan Zhang3, Siying Wei1, Tingting Cheng4, Qianqian Cao1, Zhenzhen Wang1, and Yan Chen1,3,*
1 CAS Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China
2 Cancer Molecular Diagnostic Core Laboratory, Tianjin Medical University Cancer Institute and Hospital, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Immunology and Biotherapy, Tianjin 300060, China
3 School of Life Sciences and Technology, ShanghaiTech University, Shanghai 200031, China
4 Department of Clinical Medicine, Tongji University, Shanghai 200092, China † These authors contributed equally to the work. *Correspondence to:Yan Chen, E-mail: ychen3@sibs.ac.cn
J Mol Cell Biol, Volume 9, Issue 5, October 2017, Pages 409-421  https://doi.org/10.1093/jmcb/mjx028
Keyword: CDK4, PAQR4, SKP2, ubiquitination, protein degradation, tumorigenesis

CDK4 is crucial for G1-to-S transition of cell cycle. It is well established that ubiquitin-mediated degradations of CDK inhibitors and cyclins are pivotal for the timely and unidirectional progression of cell cycle. However, how CDK4 itself is modulated by ubiquitin-mediated degradation has been elusive. Here we report that the steady state level of CDK4 is controlled by PAQR4, a member of the progestin and adipoQ receptor family, and SKP2, an E3 ubiquitin ligase. Knockdown of PAQR4 leads to reduction of cell proliferation, accompanied by reduced protein level of CDK4. PAQR4 reduces polyubiquitination and degradation of CDK4. PAQR4 interacts with the C-terminal lobe of CDK4. On the other hand, SKP2 also interacts with the C-terminal lobe of CDK4 and enhances polyubiquitination and degradation of CDK4. Importantly, PAQR4 and SKP2 bind to the same region in CDK4, and PAQR4 competes with SKP2 for the binding, thereby abrogating SKP2-mediated ubiquitination of CDK4. Using a two-stage DMBA/TPA-induced skin cancer model, we find that PAQR4-deleted mice are resistant to chemical carcinogen-induced tumor formation. Collectively, our findings reveal that the steady-state level of CDK4 is controlled by the antagonistic actions between PAQR4 and SKP2, contributing to modulation of cell proliferation and tumorigenesis.