SAG (Sensitive to Apoptosis Gone), also known as RBX2IROC2, or RNF7 (RING finger protein 7), is a stress-responsive component of SCF (Skp1, Cullins, F-box proteins) E3 ubiquitin ligase. Our previous work has shown that SAG promotes cell proliferation and Inhibits apoptosis under stressed conditions. The role of SAG in regulation of angiogenesis and carcinogenesis is, however, largely unknown. Our long-range goal is to achieve cancer therapy through inhibition of angiogenesis and tumorigenesis by targeting SAG. Our strong preliminary data showed that SAG knockout causes mouse embryonic lethality at E1O.5-12.5, largely due to the failure in vasculogenesis and angiogenesis. Embryoid bodies derived from SAG-null embryonic stem (ES) cells are unable to differentiate into endothelial cells to form the interior of blood islands, which is associated with the failure in VEGF induction and in RAS/ERK activation. The teratomas derived from SAG-null ES cells are smaller in size with reduced density of blood vessels and reduced rate of proliferation. We also found that transgenic expression of SAG accelerates the growth of mouse skin tumors induced by chemical carcinogens, whereas SAG knock-down by siRNA inhibits the growth of human cancer cells both in vitro and in vivo. The objectives of this application are 1) to define the role of SAG in angiogenesis and 2) to elucidate its mechanism of action, using mouse ES cells arid human cancer cells. The central hypothesis is that SAG promotes angiogenesis by inducing degradation of 1KB to activate NFKB and degradation of neurofibromin, a NF-1 gene product, to activate RAS. SAG deletion causes the accumulation of 1) lKBa to inactivate NFKB, and 2) neurofibromin to inactivate RAS, resulting in inhibition of angiogenesis.
The specific aims to test the hypothesis are 1) to define the role of SAG in regulation of angiogenesis in mouse ES cells and in human cancer cells and 2) to define the mechanism of action by which SAG regulates endothelial differentiation of embryoid bodies. We expect that successful completion of this proposed study will demonstrate that blockade of SAG inhibits angiogenesis through NFKB inactivation by accumulated 1KB and RAS inactivation by accumulated neurofibromin. Targeting SAG in cancer cells, via siRNA silencing or small molecule inhibitors, would, therefore, be a valid antianglogenesis therapy.

Public Health Relevance

SAG (Sensitive to Apoptosis Gene) E3 ubiquitin ligase has been previously shown to promote cell proliferation and inhibit apoptosis under stressed conditions. This proposed study is to test our working hypothesis that SAG inhibition via genetic and molecular biological approaches will inhibit angiogenesis and angiogenesis-associated carcinogenesis, and sensitize cancer cells to radiation through the use of mouse ES cells and embryos, mouse transgenic models, and human xenograft tumor models. The ultimate goal is to achieve cancer therapy through inhibiting angiogenesis and carcinogenesis by targeting SAG via genetic and small molecule approaches.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA111554-06
Application #
7894931
Study Section
Molecular Oncogenesis Study Section (MONC)
Program Officer
Bernhard, Eric J
Project Start
2005-02-01
Project End
2011-07-31
Budget Start
2010-08-01
Budget End
2011-07-31
Support Year
6
Fiscal Year
2010
Total Cost
$298,007
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
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
Jia, Lijun; Bickel, Jeremy S; Wu, Jiaxue et al. (2011) RBX1 (RING box protein 1) E3 ubiquitin ligase is required for genomic integrity by modulating DNA replication licensing proteins. J Biol Chem 286:3379-86
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

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