Skip to main content
NCBI home page
Protein & Cell logoLink to Protein & Cell
. 2012 Nov 8;4(2):103–116. doi: 10.1007/s13238-012-2105-7

Functional characterization of SAG/RBX2/ROC2/RNF7, an antioxidant protein and an E3 ubiquitin ligase

Yi Sun 1,✉, Hua Li 1
PMCID: PMC3888511  NIHMSID: NIHMS536243  PMID: 23136067

Abstract

SAG (Sensitive to Apoptosis Gene), also known as RBX2 (RING box protein 2), ROC2 (Regulator of Cullins 2), or RNF7 (RING Finger Protein 7), was originally cloned in our laboratory as a redox inducible antioxidant protein and later characterized as the second member of the RBX/ROC RING component of the SCF (SKP1-CUL-F-box Proteins) E3 ubiquitin ligase. When acting alone, SAG scavenges oxygen radicals by forming inter- and intra-molecular disulfide bonds, whereas by forming a complex with other components of the SCF E3 ligase, SAG promotes ubiquitination and degradation of a number of protein substrates, including c-JUN, DEPTOR, HIF-1α, IκBα, NF1, NOXA, p27, and procaspase-3, thus regulating various signaling pathways and biological processes. Specifically, SAG protects cells from apoptosis, confers radioresistance, and plays an essential and non-redundant role in mouse embryogenesis and vasculogenesis. Furthermore, stress-inducible SAG is overexpressed in a number of human cancers and SAG overexpression correlates with poor patient prognosis. Finally, SAG transgenic expression in epidermis causes an early stage inhibition, but later stage promotion, of skin tumorigenesis triggered by DMBA/TPA. Given its major role in promoting targeted degradation of tumor suppressive proteins, leading to apoptosis suppression and accelerated tumorigenesis, SAG E3 ligase appears to be an attractive anticancer target.

Keywords: antioxidant, angiogenesis, apoptosis, Cullin-RING ligases, radiation resistance, reactive oxygen species, SAG/RBX2/ROC2/RNF7, SCF E3 ligases, tumorigenesis, ubiquitin ligase, vasculogenesis

References

  1. Ahmed KM, Li JJ. NF-kappa B-mediated adaptive resistance to ionizing radiation. Free Radic Biol Med. 2008;44:1–13. doi: 10.1016/j.freeradbiomed.2007.09.022. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Angel P, Karin M. The role of Jun, Fos and the AP-1 complex in cell-proliferation and transformation. Biochim Biophys Acta. 1991;1072:129–157. doi: 10.1016/0304-419x(91)90011-9. [DOI] [PubMed] [Google Scholar]
  3. Baeuerle PA, Baltimore D. Activation of DNA-binding activity in an apparently cytoplasmic precursor of the NF-kappa B transcription factor. Cell. 1988;53:211–217. doi: 10.1016/0092-8674(88)90382-0. [DOI] [PubMed] [Google Scholar]
  4. Baeuerle PA, Baltimore D. I kappa B: a specific inhibitor of the NF-kappa B transcription factor. Science. 1988;242:540–546. doi: 10.1126/science.3140380. [DOI] [PubMed] [Google Scholar]
  5. Bello NF, Lamsoul I, Heuze ML, Metais A, Moreaux G, Calderwood DA, Duprez D, Moog-Lutz C, Lutz PG. The E3 ubiquitin ligase specificity subunit ASB2beta is a novel regulator of muscle differentiation that targets filamin B to proteasomal degradation. Cell Death Differ. 2009;16:921–932. doi: 10.1038/cdd.2009.27. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Brownell JE, Sintchak MD, Gavin JM, Liao H, Bruzzese FJ, Bump NJ, Soucy TA, Milhollen MA, Yang X, Burkhardt AL, et al. Substrate-assisted inhibition of ubiquitin-like protein-activating enzymes: the NEDD8 E1 inhibitor MLN4924 forms a NEDD8-AMP mimetic in situ. Mol Cell. 2010;37:102–111. doi: 10.1016/j.molcel.2009.12.024. [DOI] [PubMed] [Google Scholar]
  7. Cai QL, Knight JS, Verma SC, Zald P, Robertson ES. EC5S ubiquitin complex is recruited by KSHV latent antigen LANA for degradation of the VHL and p53 tumor suppressors. PLoS Pathog. 2006;2:e116. doi: 10.1371/journal.ppat.0020116. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Carrano AC, Eytan E, Hershko A, Pagano M. SKP2 is required for ubiquitin-mediated degradation of the CDK inhibitor p27. Nat Cell Biol. 1999;1:193–199. doi: 10.1038/12013. [DOI] [PubMed] [Google Scholar]
  9. Chanalaris A, Sun Y, Latchman DS, Stephanou A. SAG attenuates apoptotic cell death caused by simulated ischaemia/reoxygenation in rat cardiomyocytes. J Mol Cell Cardiol. 2003;35:257–264. doi: 10.1016/s0022-2828(03)00003-8. [DOI] [PubMed] [Google Scholar]
  10. Chen L, Willis SN, Wei A, Smith BJ, Fletcher JI, Hinds MG, Colman PM, Day CL, Adams JM, Huang DC. Differential targeting of prosurvival Bcl-2 proteins by their BH3-only ligands allows complementary apoptotic function. Mol Cell. 2005;17:393–403. doi: 10.1016/j.molcel.2004.12.030. [DOI] [PubMed] [Google Scholar]
  11. Cichowski K, Jacks T. NF1 tumor suppressor gene function: narrowing the GAP. Cell. 2001;104:593–604. doi: 10.1016/s0092-8674(01)00245-8. [DOI] [PubMed] [Google Scholar]
  12. Ciechanover A. The ubiquitin-proteasome pathway: on protein death and cell life. EMBO J. 1998;17:7151–7160. doi: 10.1093/emboj/17.24.7151. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Cook JA, Gius D, Wink DA, Krishna MC, Russo A, Mitchell JB. Oxidative stress, redox, and the tumor microenvironment. Semin Radiat Oncol. 2004;14:259–266. doi: 10.1016/j.semradonc.2004.04.001. [DOI] [PubMed] [Google Scholar]
  14. Cryns V, Yuan J. Proteases to die for. Genes Dev. 1998;12:1551–1570. doi: 10.1101/gad.12.11.1551. [DOI] [PubMed] [Google Scholar]
  15. Deneke SM. Thiol-based antioxidants. Curr Top Cell Regul. 2000;36:151–180. doi: 10.1016/s0070-2137(01)80007-8. [DOI] [PubMed] [Google Scholar]
  16. Deshaies RJ, Joazeiro CA. RING domain E3 ubiquitin ligases. Annu Rev Biochem. 2009;78:399–434. doi: 10.1146/annurev.biochem.78.101807.093809. [DOI] [PubMed] [Google Scholar]
  17. Dhillon AS, Hagan S, Rath O, Kolch W. MAP kinase signalling pathways in cancer. Oncogene. 2007;26:3279–3290. doi: 10.1038/sj.onc.1210421. [DOI] [PubMed] [Google Scholar]
  18. Duan H, Tsvetkov LM, Liu Y, Song Y, Swaroop M, Wen R, Kung HF, Zhang H, Sun Y. Promotion of S-phase entry and cell growth under serum starvation by SAG/ROC2/Rbx2/Hrt2, an E3 ubiquitin ligase component: association with inhibition of p27 accumulation. Mol Carcinog. 2001;30:37–46. doi: 10.1002/1098-2744(200101)30:1<37::aid-mc1011>3.0.co;2-7. [DOI] [PubMed] [Google Scholar]
  19. Duan H, Wang Y, Aviram M, Swaroop M, Loo JA, Bian J, Tian Y, Mueller T, Bisgaier CL, Sun Y. SAG, a novel zinc RING finger protein that protects cells from apoptosis induced by redox agents. Mol Cell Biol. 1999;19:3145–3155. doi: 10.1128/mcb.19.4.3145. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Duan S, Skaar JR, Kuchay S, Toschi A, Kanarek N, Ben-Neriah Y, Pagano M. mTOR Generates an auto-amplification loop by triggering the betaTrCP- and CK1alpha-dependent degradation of DEPTOR. Mol Cell. 2011;44:317–324. doi: 10.1016/j.molcel.2011.09.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Earnshaw WC, Martins LM, Kaufmann SH. Mammalian caspases: structure, activation, substrates, and functions during apoptosis. Annu Rev Biochem. 1999;68:383–424. doi: 10.1146/annurev.biochem.68.1.383. [DOI] [PubMed] [Google Scholar]
  22. Feng L, Allen NS, Simo S, Cooper JA. Cullin 5 regulates Dab1 protein levels and neuron positioning during cortical development. Genes Dev. 2007;21:2717–2730. doi: 10.1101/gad.1604207. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Fenner BJ, Scannell M, Prehn JH. Expanding the substantial interactome of NEMO using protein microarrays. PLoS One. 2010;5:e8799. doi: 10.1371/journal.pone.0008799. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Frei B, Stocker R, Ames BN. Antioxidant defenses and lipid peroxidation in human blood plasma. Proc Natl Acad Sci U S A. 1988;85:9748–9752. doi: 10.1073/pnas.85.24.9748. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Fuchs SY, Chen A, Xiong Y, Pan ZQ, Ronai Z. HOS, a human homolog of Slimb, forms an SCF complex with Skp1 and Cullin1 and targets the phosphorylation-dependent degradation of IkappaB and beta-catenin. Oncogene. 1999;18:2039–2046. doi: 10.1038/sj.onc.1202760. [DOI] [PubMed] [Google Scholar]
  26. Gao D, Inuzuka H, Tan MK, Fukushima H, Locasale JW, Liu P, Wan L, Zhai B, Chin YR, Shaik S, et al. mTOR drives its own activation via SCF(betaTrCP)-dependent degradation of the mTOR inhibitor DEPTOR. Mol Cell. 2011;44:290–303. doi: 10.1016/j.molcel.2011.08.030. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Gu Q, Bowden GT, Normolle D, Sun Y. SAG/ROC2 E3 ligase regulates skin carcinogenesis by stage-dependent targeting of c-Jun/AP1 and IkappaB-alpha/ NF-kappaB. J Cell Biol. 2007;178:1009–1023. doi: 10.1083/jcb.200612067. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Gu Q, Tan M, Sun Y. SAG/ROC2/Rbx2 is a novel activator protein-1 target that promotes c-Jun degradation and inhibits 12-O-tetradecanoylphorbol-13-acetate-induced neoplastic transformation. Cancer Res. 2007;67:3616–3625. doi: 10.1158/0008-5472.CAN-06-4020. [DOI] [PubMed] [Google Scholar]
  29. He H, Gu Q, Zheng M, Normolle D, Sun Y. SAG/ROC2/RBX2 E3 ligase promotes UVB-induced skin hyperplasia, but not skin tumors, by simultaneously targeting c-Jun/AP-1 and p27. Carcinogenesis. 2008;29:858–865. doi: 10.1093/carcin/bgn021. [DOI] [PubMed] [Google Scholar]
  30. He H, Tan M, Pamarthy D, Wang G, Ahmed K, Sun Y. CK2 phosphorylation of SAG at Thr10 regulates SAG stability, but not its E3 ligase activity. Mol Cell Biochem. 2007;295:179–188. doi: 10.1007/s11010-006-9287-3. [DOI] [PubMed] [Google Scholar]
  31. Hershko A, Ciechanover A. The ubiquitin system. Annu Rev Biochem. 1998;67:425–479. doi: 10.1146/annurev.biochem.67.1.425. [DOI] [PubMed] [Google Scholar]
  32. Hershko A, Ciechanover A, Varshavsky A. Basic Medical Research Award. The ubiquitin system. Nat Med. 2000;6:1073–1081. doi: 10.1038/80384. [DOI] [PubMed] [Google Scholar]
  33. Huang Y, Duan H, Sun Y. Elevated expression of SAG/ROC2/Rbx2/Hrt2 in human colon carcinomas: SAG does not induce neoplastic transformation, but its antisense transfection inhibits tumor cell growth. Mol Carcinog. 2001;30:62–70. [PubMed] [Google Scholar]
  34. Ivan M, Kondo K, Yang H, Kim W, Valiando J, Ohh M, Salic A, Asara JM, Lane WS, Kaelin WG., Jr. HIFalpha targeted for VHL-mediated destruction by proline hydroxylation: implications for O2 sensing. Science. 2001;292:464–468. doi: 10.1126/science.1059817. [DOI] [PubMed] [Google Scholar]
  35. Jaakkola P, Mole DR, Tian YM, Wilson MI, Gielbert J, Gaskell SJ, Kriegsheim A, Hebestreit HF, Mukherji M, Schofield CJ, et al. Targeting of HIF-alpha to the von Hippel-Lindau ubiquitylation complex by O2-regulated prolyl hydroxylation. Science. 2001;292:468–472. doi: 10.1126/science.1059796. [DOI] [PubMed] [Google Scholar]
  36. Jackson EL, Willis N, Mercer K, Bronson RT, Crowley D, Montoya R, Jacks T, Tuveson DA. Analysis of lung tumor initiation and progression using conditional expression of oncogenic K-ras. Genes Dev. 2001;15:3243–3248. doi: 10.1101/gad.943001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Jia L, Li H, Sun Y. Induction of p21-Dependent Senescence by an NAE Inhibitor, MLN4924, as a Mechanism of Growth Suppression. Neoplasia. 2011;13:561–569. doi: 10.1593/neo.11420. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Jia L, Sun Y. SCF E3 ubiquitin ligases as anticancer targets. Curr Cancer Drug Targets. 2011;11:347–356. doi: 10.2174/156800911794519734. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Jia L, Yang J, Hao X, Zheng M, He H, Xiong X, Xu L, Sun Y. Validation of SAG/RBX2/ROC2 E3 Ubiquitin Ligase as an Anticancer and Radiosensitizing Target. Clin Cancer Res. 2010;16:814–824. doi: 10.1158/1078-0432.CCR-09-1592. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Jin J, Cardozo T, Lovering RC, Elledge SJ, Pagano M, Harper JW. Systematic analysis and nomenclature of mammalian F-box proteins. Genes Dev. 2004;18:2573–2580. doi: 10.1101/gad.1255304. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Kamura T, Maenaka K, Kotoshiba S, Matsumoto M, Kohda D, Conaway RC, Conaway JW, Nakayama KI. VHL-box and SOCS-box domains determine binding specificity for Cul2-Rbx1 and Cul5-Rbx2 modules of ubiquitin ligases. Genes Dev. 2004;18:3055–3065. doi: 10.1101/gad.1252404. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Kim DW, Lee SH, Jeong MS, Sohn EJ, Kim MJ, Jeong HJ, An JJ, Jang SH, Won MH, Hwang IK, et al. Transduced Tat-SAG fusion protein protects against oxidative stress and brain ischemic insult. Free Radic Biol Med. 2010;48:969–977. doi: 10.1016/j.freeradbiomed.2010.01.023. [DOI] [PubMed] [Google Scholar]
  43. Kim H, Rafiuddin-Shah M, Tu HC, Jeffers JR, Zambetti GP, Hsieh JJ, Cheng EH. Hierarchical regulation of mitochondrion-dependent apoptosis by BCL-2 subfamilies. Nat Cell Biol. 2006;8:1348–1358. doi: 10.1038/ncb1499. [DOI] [PubMed] [Google Scholar]
  44. Kim SY, Bae Y S, Park J W. Thio-linked peroxidase activity of human sensitive to apoptosis gene (SAG) protein. Free Radic Res. 2002;36:73–78. doi: 10.1080/10715760210164. [DOI] [PubMed] [Google Scholar]
  45. Kim SY, Kim MY, Mo JS, Park JW, Park HS. SAG protects human neuroblastoma SH-SY5Y cells against 1-methyl-4-phenylpyridinium ion (MPP+)-induced cytotoxicity via the downregulation of ROS generation and JNK signaling. Neurosci Lett. 2007;413:132–136. doi: 10.1016/j.neulet.2006.11.074. [DOI] [PubMed] [Google Scholar]
  46. Kim SY, Lee J H, Yang E S, Kil I S, Bae Y S. Human sensitive to apoptosis gene protein inhibits peroxynitrite-induced DNA damage. Biochem Biophys Res Commun. 2003;301:671–674. doi: 10.1016/s0006-291x(03)00018-4. [DOI] [PubMed] [Google Scholar]
  47. Kim SY, Yang ES, Lee YS, Lee J, Park JW. Sensitive to apoptosis gene protein regulates ionizing radiation-induced apoptosis. Biochimie. 2011;93:269–276. doi: 10.1016/j.biochi.2010.09.020. [DOI] [PubMed] [Google Scholar]
  48. Kim YS, Lee J Y, Son M Y, Park W, Bae YS. Phosphorylation of threonine-10 on CKBBP1/SAG/ROC2/Rbx2 by protein kinase CKII promotes the degradation of IkBa and p27kip1. J. Biol. Chem. 2003;278:28462–28469. doi: 10.1074/jbc.M302584200. [DOI] [PubMed] [Google Scholar]
  49. Kohroki J, Nishiyama T, Nakamura T, Masuho Y. ASB proteins interact with Cullin5 and Rbx2 to form E3 ubiquitin ligase complexes. FEBS Lett. 2005;579:6796–6802. doi: 10.1016/j.febslet.2005.11.016. [DOI] [PubMed] [Google Scholar]
  50. Kranenburg O, Gebbink MF, Voest EE. Stimulation of angiogenesis by Ras proteins. Biochim Biophys Acta. 2004;1654:23–37. doi: 10.1016/j.bbcan.2003.09.004. [DOI] [PubMed] [Google Scholar]
  51. Kuang Z, Yao S, Xu Y, Lewis RS, Low A, Masters SL, Willson TA, Kolesnik TB, Nicholson SE, Garrett TJ, et al. SPRY domain-containing SOCS box protein 2: crystal structure and residues critical for protein binding. J Mol Biol. 2009;386:662–674. doi: 10.1016/j.jmb.2008.12.078. [DOI] [PubMed] [Google Scholar]
  52. Laszlo GS, Cooper JA. Restriction of Src activity by Cullin-5. Curr Biol. 2009;19:157–162. doi: 10.1016/j.cub.2008.12.007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  53. Le LQ, Parada LF. Tumor microenvironment and neurofibromatosis type I: connecting the GAPs. Oncogene. 2007;26:4609–4616. doi: 10.1038/sj.onc.1210261. [DOI] [PMC free article] [PubMed] [Google Scholar]
  54. Lee J, Zhou P. Cullins and cancer. Genes Cancer. 2010;1:690–699. doi: 10.1177/1947601910382899. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Lee SJ, Yang ES, Kim SY, Shin SW, Park JW. Regulation of heat shock-induced apoptosis by sensitive to apoptosis gene protein. Free Radic Biol Med. 2008;45:167–176. doi: 10.1016/j.freeradbiomed.2008.03.026. [DOI] [PubMed] [Google Scholar]
  56. Li W, Bengtson MH, Ulbrich A, Matsuda A, Reddy VA, Orth A, Chanda SK, Batalov S, Joazeiro CA. Genome-wide and functional annotation of human E3 ubiquitin ligases identifies MULAN, a mitochondrial E3 that regulates the organelle’s dynamics and signaling. PLoS One. 2008;3:e1487. doi: 10.1371/journal.pone.0001487. [DOI] [PMC free article] [PubMed] [Google Scholar]
  57. Liang P, Pardee AB. Differential display of eukaryotic messenger RNA by means of the polymerase chain reaction [see comments] Science. 1992;257:967–971. doi: 10.1126/science.1354393. [DOI] [PubMed] [Google Scholar]
  58. Lin HK, Chen Z, Wang G, Nardella C, Lee SW, Chan CH, Yang WL, Wang J, Egia A, Nakayama KI, et al. Skp2 targeting suppresses tumorigenesis by Arf-p53-independent cellular senescence. Nature. 2010;464:374–379. doi: 10.1038/nature08815. [DOI] [PMC free article] [PubMed] [Google Scholar]
  59. Lin JJ, Milhollen MA, Smith PG, Narayanan U, Dutta A. NEDD8-targeting drug MLN4924 elicits DNA rereplication by stabilizing Cdt1 in S phase, triggering checkpoint activation, apoptosis, and senescence in cancer cells. Cancer Res. 2010;70:10310–10320. doi: 10.1158/0008-5472.CAN-10-2062. [DOI] [PMC free article] [PubMed] [Google Scholar]
  60. Lipkowitz S, Weissman AM. RINGs of good and evil: RING finger ubiquitin ligases at the crossroads of tumour suppression and oncogenesis. Nat Rev Cancer. 2011;11:629–643. doi: 10.1038/nrc3120. [DOI] [PMC free article] [PubMed] [Google Scholar]
  61. Luo Z, Yu G, Lee HW, Li L, Wang L, Yang D, Pan Y, Ding C, Qian J, Wu L, et al. The Nedd8-activating enzyme inhibitor MLN4924 induces autophagy and apoptosis to suppress liver cancer cell growth. Cancer Res. 2012;72:3360–3371. doi: 10.1158/0008-5472.CAN-12-0388. [DOI] [PubMed] [Google Scholar]
  62. Maxwell PH, Wiesener MS, Chang GW, Clifford SC, Vaux EC, Cockman ME, Wykoff CC, Pugh CW, Maher ER, Ratcliffe PJ. The tumour suppressor protein VHL targets hypoxia-inducible factors for oxygen-dependent proteolysis. Nature. 1999;399:271–275. doi: 10.1038/20459. [DOI] [PubMed] [Google Scholar]
  63. Milhollen MA, Narayanan U, Soucy TA, Veiby PO, Smith PG, Amidon B. Inhibition of NEDD8-activating enzyme induces rereplication and apoptosis in human tumor cells consistent with deregulating CDT1 turnover. Cancer Res. 2011;71:3042–3051. doi: 10.1158/0008-5472.CAN-10-2122. [DOI] [PubMed] [Google Scholar]
  64. Milhollen MA, Traore T, Adams-Duffy J, Thomas MP, Berger AJ, Dang L, Dick LR, Garnsey JJ, Koenig E, Langston SP, et al. MLN4924, a NEDD8-activating enzyme inhibitor, is active in diffuse large B-cell lymphoma models: rationale for treatment of NF-{kappa}B-dependent lymphoma. Blood. 2010;116:1515–1523. doi: 10.1182/blood-2010-03-272567. [DOI] [PubMed] [Google Scholar]
  65. Moore R, Boyd L. Analysis of RING finger genes required for embryogenesis in C. elegans. Genesis. 2004;38:1–12. doi: 10.1002/gene.10243. [DOI] [PubMed] [Google Scholar]
  66. Nakayama KI, Nakayama K. Ubiquitin ligases: cell-cycle control and cancer. Nat Rev Cancer. 2006;6:369–381. doi: 10.1038/nrc1881. [DOI] [PubMed] [Google Scholar]
  67. Nateri AS, Riera-Sans L, Da Costa C, Behrens A. The ubiquitin ligase SCFFbw7 antagonizes apoptotic JNK signaling. Science. 2004;303:1374–1378. doi: 10.1126/science.1092880. [DOI] [PubMed] [Google Scholar]
  68. Nawrocki ST, Griffin P, Kelly KR, Carew JS. MLN4924: a novel first-in-class inhibitor of NEDD8-activating enzyme for cancer therapy. Expert Opin Investig Drugs. 2012;21:1563–1573. doi: 10.1517/13543784.2012.707192. [DOI] [PubMed] [Google Scholar]
  69. Ohta T, Michel JJ, Schottelius AJ, Xiong Y. ROC1, a homolog of APC11, represents a family of cullin partners with an associated ubiquitin ligase activity. Mol Cell. 1999;3:535–541. doi: 10.1016/s1097-2765(00)80482-7. [DOI] [PubMed] [Google Scholar]
  70. Ozden SA, Ozyurt H, Ozgen Z, Kilinc O, Oncel M, Gul AE, Karadayi N, Serakinci N, Kan B, Orun O. Prognostic role of sensitive-to-apoptosis gene expression in rectal cancer. World J Gastroenterol. 2011;17:4905–4910. doi: 10.3748/wjg.v17.i44.4905. [DOI] [PMC free article] [PubMed] [Google Scholar]
  71. Pan Q, Qiao F, Gao C, Norman B, Optican L, Zelenka PS. Cdk5 targets active Src for ubiquitin-dependent degradation by phosphorylating Src(S75) Cell Mol Life Sci. 2011;68:3425–3436. doi: 10.1007/s00018-011-0638-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  72. Persaud A, Alberts P, Amsen EM, Xiong X, Wasmuth J, Saadon Z, Fladd C, Parkinson J, Rotin D. Comparison of substrate specificity of the ubiquitin ligases Nedd4 and Nedd4-2 using proteome arrays. Mol Syst Biol. 2009;5:333. doi: 10.1038/msb.2009.85. [DOI] [PMC free article] [PubMed] [Google Scholar]
  73. Peterson TR, Laplante M, Thoreen CC, Sancak Y, Kang SA, Kuehl WM, Gray NS, Sabatini DM. DEPTOR is an mTOR inhibitor frequently overexpressed in multiple myeloma cells and required for their survival. Cell. 2009;137:873–886. doi: 10.1016/j.cell.2009.03.046. [DOI] [PMC free article] [PubMed] [Google Scholar]
  74. Querido E, Blanchette P, Yan Q, Kamura T, Morrison M, Boivin D, Kaelin WG, Conaway RC, Conaway JW, Branton PE. Degradation of p53 by adenovirus E4orf6 and E1B55K proteins occurs via a novel mechanism involving a Cullin-containing complex. Genes Dev. 2001;15:3104–3117. doi: 10.1101/gad.926401. [DOI] [PMC free article] [PubMed] [Google Scholar]
  75. Reynolds PJ, Simms JR, Duronio RJ. Identifying determinants of cullin binding specificity among the three functionally different Drosophila melanogaster Roc proteins via domain swapping. PLoS One. 2008;3:e2918. doi: 10.1371/journal.pone.0002918. [DOI] [PMC free article] [PubMed] [Google Scholar]
  76. Sarikas A, Hartmann T, Pan ZQ. The cullin protein family. Genome Biol. 2011;12:220. doi: 10.1186/gb-2011-12-4-220. [DOI] [PMC free article] [PubMed] [Google Scholar]
  77. Sasaki H, Yukiue H, Kobayashi Y, Moriyama S, Nakashima Y, Kaji M, Fukai I, Kiriyama M, Yamakawa Y, Fujii Y. Expression of the sensitive to apoptosis gene, SAG, as a prognostic marker in nonsmall cell lung cancer. Int J Cancer. 2001;95:375–377. doi: 10.1002/1097-0215(20011120)95:6<375::aid-ijc1066>3.0.co;2-l. [DOI] [PubMed] [Google Scholar]
  78. Sato M, Bremner I. Oxygen free radicals and metallothionein. Free Radic Biol Med. 1993;14:325–337. doi: 10.1016/0891-5849(93)90029-t. [DOI] [PubMed] [Google Scholar]
  79. Semenza GL. Targeting HIF-1 for cancer therapy. Nat Rev Cancer. 2003;3:721–732. doi: 10.1038/nrc1187. [DOI] [PubMed] [Google Scholar]
  80. Seol JH, Feldman RMR, Zachariae WZ, Shevchenko A, Correll CC, Lyapina S, Chi Y, Galova M, Claypool J, Sandmeyer S, et al. Cdc53/cullin and the essential Hrt1 RING-H2 subunit of SCF define a ubiquitin ligase module that activates the E2 enzyme Cdc34. Genes & Dev. 1999;13:1614–1626. doi: 10.1101/gad.13.12.1614. [DOI] [PMC free article] [PubMed] [Google Scholar]
  81. Shaulian E, Karin M. AP-1 as a regulator of cell life and death. Nat Cell Biol. 2002;4:E131–136. doi: 10.1038/ncb0502-e131. [DOI] [PubMed] [Google Scholar]
  82. Sherr CJ, Roberts JM. Inhibitors of mammalian G1 cyclin-dependent kinases. Genes Dev. 1995;9:1149–1163. doi: 10.1101/gad.9.10.1149. [DOI] [PubMed] [Google Scholar]
  83. Sherr CJ, Roberts JM. CDK inhibitors: positive and negative regulators of G1-phase progression. Genes Dev. 1999;13:1501–1512. doi: 10.1101/gad.13.12.1501. [DOI] [PubMed] [Google Scholar]
  84. Simo S, Jossin Y, Cooper JA. Cullin 5 regulates cortical layering by modulating the speed and duration of Dab1-dependent neuronal migration. J Neurosci. 2010;30:5668–5676. doi: 10.1523/JNEUROSCI.0035-10.2010. [DOI] [PMC free article] [PubMed] [Google Scholar]
  85. Son MY, Park JW, Kim YS, Kang SW, Marshak DR, Park W, Bae YS. Protein kinase CKII interacts with and phosphorylates the SAG protein containing ring-H2 finger motif. Biochem Biophys Res Commun. 1999;263:743–748. doi: 10.1006/bbrc.1999.1460. [DOI] [PubMed] [Google Scholar]
  86. Soucy TA, Dick LR, Smith PG, Milhollen MA, Brownell JE. The NEDD8 conjugation pathway and its relevance in cancer biology and therapy. Genes Cancer. 2010;1:708–716. doi: 10.1177/1947601910382898. [DOI] [PMC free article] [PubMed] [Google Scholar]
  87. Soucy TA, Smith PG, Milhollen MA, Berger AJ, Gavin JM, Adhikari S, Brownell JE, Burke KE, Cardin DP, Critchley S, et al. An inhibitor of NEDD8-activating enzyme as a new approach to treat cancer. Nature. 2009;458:732–736. doi: 10.1038/nature07884. [DOI] [PubMed] [Google Scholar]
  88. Soucy TA, Smith PG, Rolfe M. Targeting NEDD8-activated cullin-RING ligases for the treatment of cancer. Clin Cancer Res. 2009;15:3912–3916. doi: 10.1158/1078-0432.CCR-09-0343. [DOI] [PubMed] [Google Scholar]
  89. Sun Y. Free radicals, antioxidant enzymes, and carcinogenesis. Free Radic Biol Med. 1990;8:583–599. doi: 10.1016/0891-5849(90)90156-d. [DOI] [PubMed] [Google Scholar]
  90. Sun Y. Induction of glutathione synthetase by 1,10-phenanthroline. FEBS Lett. 1997;408:16–20. doi: 10.1016/s0014-5793(97)00380-3. [DOI] [PubMed] [Google Scholar]
  91. Sun Y. Alteration of SAG mRNA in human cancer cell lines: requirement for the RING finger domain for apoptosis protection. Carcinogenesis. 1999;20:1899–1903. doi: 10.1093/carcin/20.10.1899. [DOI] [PubMed] [Google Scholar]
  92. Sun Y. Identification and characterization of genes responsive to apoptosis: Application of DNA chip technology and mRNA differential display. Histol Histopathol. 2000;15:1271–1284. doi: 10.14670/HH-15.1271. [DOI] [PubMed] [Google Scholar]
  93. Sun Y. Targeting E3 ubiquitin ligases for cancer therapy. Cancer Biol Therapy. 2003;2:623–629. [PubMed] [Google Scholar]
  94. Sun Y. E3 ubiquitin ligases as cancer targets and biomarkers. Neoplasia. 2006;8:645–654. doi: 10.1593/neo.06376. [DOI] [PMC free article] [PubMed] [Google Scholar]
  95. Sun Y. RNF7 (RING finger protein-7) Atlas Genet Cytogenet Oncol Haematol. 2008;12:289–291. [Google Scholar]
  96. Sun Y, Bian J, Wang Y, Jacobs C. Activation of p53 transcriptional activity by 1,10-phenanthroline, a metal chelator and redox sensitive compound. Oncogene. 1997;14:385–393. doi: 10.1038/sj.onc.1200834. [DOI] [PubMed] [Google Scholar]
  97. Sun Y, Tan M, Duan H, Swaroop M. SAG/ROC/Rbx/Hrt, a zinc RING finger gene family: molecular cloning, biochemical properties, and biological functions. Antioxid Redox Signal. 2001;3:635–650. doi: 10.1089/15230860152542989. [DOI] [PubMed] [Google Scholar]
  98. Sutterluty H, Chatelain E, Marti A, Wirbelauer C, Senften M, Muller U, Krek W. p45SKP2 promotes p27Kip1 degradation and induces S phase in quiescent cells. Nature Cell Biol. 1999;1:207–214. doi: 10.1038/12027. [DOI] [PubMed] [Google Scholar]
  99. Swaroop M, Bian J, Aviram M, Duan H, Bisgaier CL, Loo JA, Sun Y. Expression, purification, and biochemical characterization of SAG, a RING finger redox sensitive protein. Free Radicals Biol Med. 1999;27:193–202. doi: 10.1016/s0891-5849(99)00078-7. [DOI] [PubMed] [Google Scholar]
  100. Swaroop M, Gosink M, Sun Y. SAG/ROC2/Rbx2/Hrt2, a component of SCF E3 ubiquitin ligase: genomic structure, a splicing variant, and two family pseudogenes. DNA Cell Biol. 2001;20:425–434. doi: 10.1089/104454901750361488. [DOI] [PubMed] [Google Scholar]
  101. Swaroop M, Wang Y, Miller P, Duan H, Jatkoe T, Madore S, Sun Y. Yeast homolog of human SAG/ROC2/Rbx2/ Hrt2 is essential for cell growth, but not for germination: Chip profiling implicates its role in cell cycle regulation. Oncogene. 2000;19:2855–2866. doi: 10.1038/sj.onc.1203635. [DOI] [PubMed] [Google Scholar]
  102. Swords RT, Kelly KR, Smith PG, Garnsey JJ, Mahalingam D, Medina E, Oberheu K, Padmanabhan S, O’Dwyer M, Nawrocki ST, et al. Inhibition of NEDD8-activating enzyme: a novel approach for the treatment of acute myeloid leukemia. Blood. 2010;115:3796–3800. doi: 10.1182/blood-2009-11-254862. [DOI] [PubMed] [Google Scholar]
  103. Tan M, Davis SW, Saunders TL, Zhu Y, Sun Y. RBX1/ROC1 disruption results in early embryonic lethality due to proliferation failure, partially rescued by simultaneous loss of p27. Proc Natl Acad Sci U S A. 2009;106:6203–6208. doi: 10.1073/pnas.0812425106. [DOI] [PMC free article] [PubMed] [Google Scholar]
  104. Tan M, Gallegos JR, Gu Q, Huang Y, Li J, Jin Y, Lu H, Sun Y. SAG/ROC-SCFbeta-TrCP E3 ubiquitin ligase promotes pro-caspase-3 degradation as a mechanism of apoptosis protection. Neoplasia. 2006;8:1042–1054. doi: 10.1593/neo.06568. [DOI] [PMC free article] [PubMed] [Google Scholar]
  105. Tan M, Gu Q, He H, Pamarthy D, Semenza GL, Sun Y. SAG/ROC2/RBX2 is a HIF-1 target gene that promotes HIF-1alpha ubiquitination and degradation. Oncogene. 2008;27:1404–1411. doi: 10.1038/sj.onc.1210780. [DOI] [PubMed] [Google Scholar]
  106. Tan M, Li Y, Yang R, Xi N, Sun Y. Inactivation of SAG E3 ubiquitin ligase blocks embryonic stem cell differentiation and sensitizes leukemia cells to retinoid acid. PLoS One. 2011;6:e27726. doi: 10.1371/journal.pone.0027726. [DOI] [PMC free article] [PubMed] [Google Scholar]
  107. Tan M, Zhao Y, Kim SJ, Liu M, Jia L, Saunders TL, Zhu Y, Sun Y. SAG/RBX2/ROC2 E3 Ubiquitin Ligase Is Essential for Vascular and Neural Development by Targeting NF1 for Degradation. Dev Cell. 2011;21:1062–1076. doi: 10.1016/j.devcel.2011.09.014. [DOI] [PMC free article] [PubMed] [Google Scholar]
  108. Tan M., Zhu Y., Kovacev J., Zhao Y., Pan Z.Q., Spitz D.R., Sun Y. Disruption of Sag/Rbx2/Roc2 induces radiosensitization by increasing ROS levels and blocking NF-kB activation in mouse embryonic stem cells. Free Radic Biol Med. 2010;49:976–983. doi: 10.1016/j.freeradbiomed.2010.05.030. [DOI] [PMC free article] [PubMed] [Google Scholar]
  109. Tsvetkov LM, Yeh K-H, Lee S-J, Sun H, Zhang H. p27kip1ubiquitination and degradation is regulated by the SCFskp2 complex through phosphorylated Thr187 in p27. Cur Biol. 1999;9:661–664. doi: 10.1016/s0960-9822(99)80290-5. [DOI] [PubMed] [Google Scholar]
  110. Vesterlund M, Zadjali F, Persson T, Nielsen ML, Kessler BM, Norstedt G, Flores-Morales A. The SOCS2 ubiquitin ligase complex regulates growth hormone receptor levels. PLoS One. 2011;6:e25358. doi: 10.1371/journal.pone.0025358. [DOI] [PMC free article] [PubMed] [Google Scholar]
  111. Viarengo A, Burlando B, Ceratto N, Panfoli I. Antioxidant role of metallothioneins: a comparative overview. Cell Mol Biol. 2000;46:407–417. [PubMed] [Google Scholar]
  112. Wei D, Li H, Yu J, Sebolt JT, Zhao L, Lawrence TS, Smith PG, Morgan MA, Sun Y. Radiosensitization of human pancreatic cancer cells by MLN4924, an investigational NEDD8-activating enzyme inhibitor. Cancer Res. 2012;72:282–293. doi: 10.1158/0008-5472.CAN-11-2866. [DOI] [PMC free article] [PubMed] [Google Scholar]
  113. Wei D, Morgan MA, Sun Y. Radiosensitization of cancer cells by inactivation of cullin-RING E3 ubiquitin ligases. Transl Oncol. 2012;5:305–312. doi: 10.1593/tlo.12229. [DOI] [PMC free article] [PubMed] [Google Scholar]
  114. Wei D, Sun Y. Small RING finger proteins RBX1 and RBX2 of SCF E3 ubiquitin ligases: the role in cancer and as cancer targets. Genes Cancer. 2010;1:700–707. doi: 10.1177/1947601910382776. [DOI] [PMC free article] [PubMed] [Google Scholar]
  115. Wei W, Jin J, Schlisio S, Harper JW, Kaelin WG., Jr. The v-Jun point mutation allows c-Jun to escape GSK3-dependent recognition and destruction by the Fbw7 ubiquitin ligase. Cancer Cell. 2005;8:25–33. doi: 10.1016/j.ccr.2005.06.005. [DOI] [PubMed] [Google Scholar]
  116. Welcker M, Clurman BE. FBW7 ubiquitin ligase: a tumour suppressor at the crossroads of cell division, growth and differentiation. Nat Rev Cancer. 2008;8:83–93. doi: 10.1038/nrc2290. [DOI] [PubMed] [Google Scholar]
  117. Willems AR, Schwab M, Tyers M. A hitchhiker’s guide to the cullin ubiquitin ligases: SCF and its kin. Biochim Biophys Acta. 2004;1695:133–170. doi: 10.1016/j.bbamcr.2004.09.027. [DOI] [PubMed] [Google Scholar]
  118. Winston JT, Strack P, Beer-Romero P, Chu CY, Elledge SJ, Harper JW. The SCFbeta-TRCP-ubiquitin ligase complex associates specifically with phosphorylated destruction motifs in IkappaBalpha and beta-catenin and stimulates IkappaBalpha ubiquitination in vitro. Genes Dev. 1999;13:270–283. doi: 10.1101/gad.13.3.270. [DOI] [PMC free article] [PubMed] [Google Scholar]
  119. Wrighton KH. Cell signalling: mTOR targets its own inhibitor. Nat Rev Mol Cell Biol. 2011;12:769. doi: 10.1038/nrm3229. [DOI] [PubMed] [Google Scholar]
  120. Wu K, Fuchs SY, Chen A, Tan P, Gomez C, Ronai Z, Pan ZQ. The SCF(HOS/beta-TRCP)-ROC1 E3 ubiquitin ligase utilizes two distinct domains within CUL1 for substrate targeting and ubiquitin ligation. Mol Cell Biol. 2000;20:1382–1393. doi: 10.1128/mcb.20.4.1382-1393.2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  121. Wu K, Fuchs SY, Chen G, Tan P, Gomez C, Ronai Z, Pan Z-Q. The SCFHOS/b-TRCP-ROC1 E3 ubiquitin ligase utilizes two distinct domains within CUL1 for substrate targeting and ubiquitin ligation. Mol. Cell. Biol. 2000;20:1382–1393. doi: 10.1128/mcb.20.4.1382-1393.2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  122. Yamaoka S, Courtois G, Bessia C, Whiteside ST, Weil R, Agou F, Kirk HE, Kay RJ, Israel A. Complementation cloning of NEMO, a component of the IkappaB kinase complex essential for NF-kappaB activation. Cell. 1998;93:1231–1240. doi: 10.1016/s0092-8674(00)81466-x. [DOI] [PubMed] [Google Scholar]
  123. Yang D, Tan M, Wang G, Sun Y. The p21-dependent radiosensitization of human breast cancer cells by MLN4924, an investigational inhibitor of NEDD8 activating enzyme. PLoS One. 2012;7:e34079. doi: 10.1371/journal.pone.0034079. [DOI] [PMC free article] [PubMed] [Google Scholar]
  124. Yang ES, Huh YJ, Park JW. Knockdown of sensitive to apoptosis gene by small interfering RNA enhances the sensitivity of PC3 cells toward actinomycin D and etoposide. Free Radic Res. 2010;44:864–870. doi: 10.3109/10715762.2010.485996. [DOI] [PubMed] [Google Scholar]
  125. Yang ES, Park JW. Regulation of nitric oxide-induced apoptosis by sensitive to apoptosis gene protein. Free Radic Res. 2006;40:279–284. doi: 10.1080/10715760500511500. [DOI] [PubMed] [Google Scholar]
  126. Yang GY, Pang L, Ge HL, Tan M, Ye W, Liu XH, Huang FP, Wu DC, Che XM, Song Y, et al. Attenuation of ischemia-induced mouse brain injury by SAG, a redox-inducible antioxidant protein. J Cereb Blood Flow Metab. 2001;21:722–733. doi: 10.1097/00004647-200106000-00010. [DOI] [PubMed] [Google Scholar]
  127. Yasukawa T, Kamura T, Kitajima S, Conaway RC, Conaway JW, Aso T. Mammalian Elongin A complex mediates DNA-damage-induced ubiquitylation and degradation of Rpb1. EMBO J. 2008;27:3256–3266. doi: 10.1038/emboj.2008.249. [DOI] [PMC free article] [PubMed] [Google Scholar]
  128. Yoo DY, Shin BN, Kim IH, Kim DW, Yoo KY, Kim W, Lee CH, Choi JH, Yoon YS, Choi SY, et al. Effects of sensitive to apoptosis gene protein on cell proliferation, neuroblast differentiation, and oxidative stress in the mouse dentate gyrus. Neurochem Res. 2012;37:495–502. doi: 10.1007/s11064-011-0634-8. [DOI] [PubMed] [Google Scholar]
  129. Yu X, Yu Y, Liu B, Luo K, Kong W, Mao P, Yu XF. Induction of APOBEC3G ubiquitination and degradation by an HIV-1 Vif-Cul5-SCF complex. Science. 2003;302:1056–1060. doi: 10.1126/science.1089591. [DOI] [PubMed] [Google Scholar]
  130. Zhao L, Yue P, Lonial S, Khuri FR, Sun SY. The NEDD8-activating enzyme inhibitor, MLN4924, cooperates with TRAIL to augment apoptosis through facilitating c-FLIP degradation in head and neck cancer cells. Mol Cancer Ther. 2011;10:2415–2425. doi: 10.1158/1535-7163.MCT-11-0401. [DOI] [PMC free article] [PubMed] [Google Scholar]
  131. Zhao Y, Sun Y. Targeting the mTOR-DEPTOR Pathway by CRL E3 Ubiquitin Ligases: Therapeutic Application. Neoplasia. 2012;14:360–367. doi: 10.1593/neo.12532. [DOI] [PMC free article] [PubMed] [Google Scholar]
  132. Zhao Y, Xiong X, Jia L, Sun Y. Targeting Cullin-RING ligases by MLN4924 induces autophagy via modulating the HIF1-REDD1-TSC1-mTORC1-DEPTOR axis. Cell Death Dis. 2012;3:e386. doi: 10.1038/cddis.2012.125. [DOI] [PMC free article] [PubMed] [Google Scholar]
  133. Zhao Y, Xiong X, Sun Y. DEPTOR, an mTOR inhibitor, is a physiological substrate of SCFβTrCP E3 ubiquitin ligase and regulates survival and autophagy. Mol Cell. 2011;44:304–316. doi: 10.1016/j.molcel.2011.08.029. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Protein & Cell are provided here courtesy of Oxford University Press

RESOURCES