As loss of PTEN tumor suppressive function resulting in aberrant Akt activation is a prevalent event in human cancers and associated with cancer metastasis, it is important to identify the key effector downstream of the PTEN/PI3K/Akt pathway that drives cancer progression and metastasis. Using the biochemical approaches and mouse genetic models, we identified Skp2 as an important Akt substrate that plays a critical for PTEN/Akt-mediated tumorigenesis. Skp2 (S-phase kinase associated protein-2), an F-box protein, is an E3 ligase component of Skp2 SCF complex responsible for substrate recognition. Skp2 overexpression induces cell cycle entry, and the degradation of p27 is responsible for Skp2-mediated cell cycle progression. Although Skp2 is overexpressed in numerous human cancers and associates with cancer metastasis 1,2, it remains unclear how Skp2 overexpression occurs during cancer progression and how its oncogenic activity is regulated. Our study provides for the first time that Akt kinase phosphorylates Skp2 at S72 and Skp2 S72 phosphorylation is a molecular switch that orchestrates Skp2 E3 ligase activity and oncogenic functions. The objective of this application is to determine the functional crosstalk between PTEN/PI3K/Akt signal and Skp2 S72 phosphorylation in prostate cancer progression and metastasis. The central hypothesis of the application is that Skp2 S72 phosphorylation by PI3K/Akt is critical for prostate cancer progression and metastasis. Our central hypothesis has been formulated on the basis of our strong preliminary data. The rationale of the proposed research is that, once the important role of Skp2 S72 phosphorylation is confirmed and established in prostate cancer progression and metastasis, the better treatment or target for prostate cancer can be achieved. We plan to test our central hypothesis and accomplish the objective of this application by pursuing the following specific aims:
Aim 1) To determine the molecular mechanism by which Skp2 gene expression and activity are regulated by the PI3K/Akt pathway.
Aim 2) To determine the potential role of Skp2 S72 phosphorylation in prostate cancer progression.
Aim 3) To determine the functional crosstalk between Akt and Skp2 in cell migration and invasion.
Aim 4) To determine the potential role of Skp2 and Skp2 S72 phosphorylation in prostate cancer metastasis. This proposal work is innovative, because it provides for the first time that Akt is a kinase for Skp2 and that Skp2 S72 phosphorylation by Akt is critical for Skp2 E3 ligase activity, cytosolic localization, and oncogenic functions. Importantly, our study reveals that Skp2 is a critical downstream effector for the PTEN/PI3K/Akt signal in animal models of prostate cancers. With respected outcomes, the combination of work in this proposal is collectively expected to uncover the critical role Skp2 S72 phosphorylation in prostate cancer progression and metastasis. Such results will have an important positive impact and may therefore provide a potentially therapeutic target for prostate cancer treatment. Our results will also fundamentally advance our current understandings of how prostate cancer develops and further progresses into the metastasis stage.

Public Health Relevance

Although the extensive studies have been made in the field of prostate cancer, how prostate cancer develops and further progresses into metastatic prostate cancer is still unclear. Our study reveals that the S72 phopshorylation of Skp2, an oncoprotein overexpressed in prostate cancer, is induced by the PI3K/Akt signal and is critical for its E3 ligase activity and oncogenic functions. Understanding the important role of Skp2 and Skp2 S72 phopshorylation in prostate cancer progression and metastasis may provide an important therapeutic implication for human prostate cancers.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA136787-05
Application #
8606824
Study Section
Cancer Genetics Study Section (CG)
Program Officer
Ault, Grace S
Project Start
2010-04-01
Project End
2015-01-31
Budget Start
2014-02-01
Budget End
2015-01-31
Support Year
5
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Texas MD Anderson Cancer Center
Department
Microbiology/Immun/Virology
Type
Hospitals
DUNS #
City
Houston
State
TX
Country
United States
Zip Code
77030
Rezaeian, Abdol-Hossein; Li, Chien-Feng; Wu, Ching-Yuan et al. (2017) A hypoxia-responsive TRAF6-ATM-H2AX signalling axis promotes HIF1? activation, tumorigenesis and metastasis. Nat Cell Biol 19:38-51
Xu, Dazhi; Li, Chien-Feng; Zhang, Xian et al. (2015) Skp2-macroH2A1-CDK8 axis orchestrates G2/M transition and tumorigenesis. Nat Commun 6:6641
Jin, Guoxiang; Lee, Szu-Wei; Zhang, Xian et al. (2015) Skp2-Mediated RagA Ubiquitination Elicits a Negative Feedback to Prevent Amino-Acid-Dependent mTORC1 Hyperactivation by Recruiting GATOR1. Mol Cell 58:989-1000
Feng, Haizhong; Lopez, Giselle Y; Kim, Chung Kwon et al. (2014) EGFR phosphorylation of DCBLD2 recruits TRAF6 and stimulates AKT-promoted tumorigenesis. J Clin Invest 124:3741-56
Yang, Wei-Lei; Jin, Guoxiang; Li, Chien-Feng et al. (2013) Cycles of ubiquitination and deubiquitination critically regulate growth factor-mediated activation of Akt signaling. Sci Signal 6:ra3
Chan, Chia-Hsin; Morrow, John Kenneth; Li, Chien-Feng et al. (2013) Pharmacological inactivation of Skp2 SCF ubiquitin ligase restricts cancer stem cell traits and cancer progression. Cell 154:556-68
Wu, J; Lee, S-W; Zhang, X et al. (2013) Foxo3a transcription factor is a negative regulator of Skp2 and Skp2 SCF complex. Oncogene 32:78-85
Jin, Guoxiang; Wang, Ying-Jan; Lin, Hui-Kuan (2013) Emerging Cellular Functions of Cytoplasmic PML. Front Oncol 3:147
Chan, Chia-Hsin; Li, Chien-Feng; Yang, Wei-Lei et al. (2012) The Skp2-SCF E3 ligase regulates Akt ubiquitination, glycolysis, herceptin sensitivity, and tumorigenesis. Cell 149:1098-111
Wu, Juan; Zhang, Xian; Zhang, Ling et al. (2012) Skp2 E3 ligase integrates ATM activation and homologous recombination repair by ubiquitinating NBS1. Mol Cell 46:351-61

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