Research Papers:

Flavokawain A induces deNEDDylation and Skp2 degradation leading to inhibition of tumorigenesis and cancer progression in the TRAMP transgenic mouse model

Xuesen Li, Noriko N. Yokoyama, Saiyang Zhang, Lina Ding, Hong-min Liu, Michael B. Lilly, Dan Mercola and Xiaolin Zi _

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Oncotarget. 2015; 6:41809-41824. https://doi.org/10.18632/oncotarget.6166

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Xuesen Li1,2, Noriko N. Yokoyama1, Saiyang Zhang1, Lina Ding3, Hong-min Liu3, Michael B. Lilly4, Dan Mercola5,6 and Xiaolin Zi1,6,7

1 Departments of Urology, University of California, Irvine, Orange, CA, USA

2 Institutes for Cancer Medicine, Sichuan Medical University, Luzhou, Sichuan, China

3 Co-innovation Center of Henan Province for New Drug R & D and Preclinical Safety, Zhengzhou University, Zhengzhou, Henan, China

4 Division of Hematology-Oncology, Medical University of South Carolina, Charleston, SC, USA

5 Pathology and Laboratory Medicine, University of California, Irvine, Orange, CA, USA

6 Chao Family Comprehensive Cancer Center, University of California, Irvine, Orange, CA, USA

7 Pharmacology, University of California, Irvine, Orange, CA, USA

Correspondence to:

Xiaolin Zi, email:

Keywords: kava, NEDDylation, Skp2, prostate cancer, TRAMP

Received: July 31, 2015 Accepted: October 04, 2015 Published: October 19, 2015


S phase kinase-associated protein 2 (Skp2) has been shown to be required for spontaneous tumor development that occurs in the retinoblastoma protein (pRb) deficient mice. Here we have demonstrated that flavokawain A (FKA), a novel chalcone from the kava plant, selectively inhibited the growth of pRb deficient cell lines and resulted in a proteasome-dependent and ubiquitination-mediated Skp2 degradation. Degradation of Skp2 by FKA was found to be involved in a functional Cullin1, but independent of Cdh1 expression. Further studies have demonstrated that FKA docked into the ATP binding pocket of the precursor cell-expressed developmentally down-regulated 8 (NEDD8)-activating enzyme (NAE) complex, inhibited NEDD8 conjugations to both Cullin1 and Ubc12 in PC3 cells and Ubc12 NEDDylation in an in vitro assay. Finally, dietary feeding of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) mice with FKA inhibited the formation of high-grade prostatic intra-epithelial neoplasia lesions (HG-PIN) and prostate adenocarcinomas, reduced the tumor burden and completely abolished distant organ metastasis. Immunohistochemistry studies revealed that dietary FKA feeding resulted in marked anti-proliferative and apoptotic effects via down-regulation of Skp2 and NEDD8 and up-regulation of p27/Kip1 in the prostate of TRAMP mice. Our findings therefore provide evidence that FKA is a promising NEDDylation inhibitor for targeting Skp2 degradation in prostate cancer prevention and treatment.

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