Hypoxia is known to confer resistance of cancer cells to radio- and chemo-therapies leading to treatment failure. Our long-range goal is to induce apoptosis of hypoxic cancer cells through targeting the molecules that confer such a resistance. SAG (Sensitive to Apoptosis Gene) or ROC2/Rbx2 is a cysteine-rich antioxidant protein and a RING component of SCF (skp1, Cullins, F-box proteins) and possibly VCB (VHL-Cul2-Elongin B and C) E3 ubiquitin ligases. We found that SAG is induced under hypoxia and when over-expressed, inhibits hypoxiainduced apoptosis both in vitro and in vivo. SAG also binds to caspase 3 and promotes caspase 3 ubiquitination when complexed with SCF E3 ubiquitin ligase. The objective of this application is to elucidate the mechanism of SAG induction and apoptosis protection under hypoxia. The central hypothesis is that hypoxia induces HIF-1 which transactivates SAG expression through a direct binding to its consensus elements in the SAG promoter. Hypoxia also induces activity of protein kinase CKII which activates SAG via phosphorylation. Upon its induction and activation, SAG complexes with other components of SCF and VCB E3 ubiquitin ligases to promote the ubiquitination and degradation of caspase 3 and HIF-1alpha, respectively. Targeted caspase 3 degradation blocks caspase-dependent apoptosis, whereas targeted HIF-1alpha degradation prevents HIF-1alpha induced apoptosis through p53 stabilization. The rationale for the proposed research is to identify and characterize SAG and CKII as novel hypoxic cancer targets with ultimate goal in pharmaceutical intervention through their inhibition to sensitize hypoxic cancer cells to current cancer therapies.
Specific aims to test the hypothesis are 1) to elucidate the mechanism of SAG induction through HIF-1alpha transcriptional activation under hypoxia, 2) to elucidate the mechanism by which SAG protects against apoptosis in manners of ligase independence (scavenging reactive oxygen species) and ligase dependence (caspase 3 and HIF-1alpha ubiquitination and degradation), 3) to determine the sensitization of hypoxic cancer cells to radio-therapy through targeting SAG and CKII, and 4) to differentiate SAG from ROC1/Rbx1 in their stress responses. Through this proposed research, we will demonstrate, for the first time, a feedback loop between SAG and HIF-1alpha and reveal a mechanism by which SAG inhibits apoptosis under hypoxia via promoting the ubiquitination/degradation of caspase 3 and HIF-1alpha. We will also demonstrate a radio-sensitizing effect achieved by SAG silencing and CKII inhibition and provide a molecular basis for future discovery of novel radio-sensitizers through targeting SAG, or SAG-associated E3 ligases, and/or CKII kinase.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA111554-04
Application #
7340430
Study Section
Cancer Etiology Study Section (CE)
Program Officer
Stone, Helen B
Project Start
2005-02-01
Project End
2009-07-31
Budget Start
2008-02-01
Budget End
2009-07-31
Support Year
4
Fiscal Year
2008
Total Cost
$286,517
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Radiation-Diagnostic/Oncology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Zhou, Weihua; Xu, Jie; Li, Haomin et al. (2017) Neddylation E2 UBE2F Promotes the Survival of Lung Cancer Cells by Activating CRL5 to Degrade NOXA via the K11 Linkage. Clin Cancer Res 23:1104-1116
Yang, Dong; Zhao, Yongchao; Li, Amy Y et al. (2012) Smac-mimetic compound SM-164 induces radiosensitization in breast cancer cells through activation of caspases and induction of apoptosis. Breast Cancer Res Treat 133:189-99
Wei, Dongping; Li, Hua; Yu, Jie et al. (2012) Radiosensitization of human pancreatic cancer cells by MLN4924, an investigational NEDD8-activating enzyme inhibitor. Cancer Res 72:282-93
Tan, Mingjia; Li, Yun; Yang, Ruiguo et al. (2011) Inactivation of SAG E3 ubiquitin ligase blocks embryonic stem cell differentiation and sensitizes leukemia cells to retinoid acid. PLoS One 6:e27726
Tan, Mingjia; Zhao, Yongchao; Kim, Sun-Jung et al. (2011) SAG/RBX2/ROC2 E3 ubiquitin ligase is essential for vascular and neural development by targeting NF1 for degradation. Dev Cell 21:1062-76
Xiong, X; Zhao, Y; He, H et al. (2011) Ribosomal protein S27-like and S27 interplay with p53-MDM2 axis as a target, a substrate and a regulator. Oncogene 30:1798-811
Jia, L; Sun, Y (2011) SCF E3 ubiquitin ligases as anticancer targets. Curr Cancer Drug Targets 11:347-56
Jia, Lijun; Li, Hua; Sun, Yi (2011) Induction of p21-dependent senescence by an NAE inhibitor, MLN4924, as a mechanism of growth suppression. Neoplasia 13:561-9
Zhao, Yongchao; Xiong, Xiufang; Sun, Yi (2011) DEPTOR, an mTOR inhibitor, is a physiological substrate of SCF(?TrCP) E3 ubiquitin ligase and regulates survival and autophagy. Mol Cell 44:304-16
Yang, Jie; McEachern, Donna; Li, Wenyan et al. (2011) Radiosensitization of head and neck squamous cell carcinoma by a SMAC-mimetic compound, SM-164, requires activation of caspases. Mol Cancer Ther 10:658-69

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