As a transcription factor critical for embryonic and adult stem cell self-renewal and function, SOX2 gene amplification has been recognized as a driving factor for various cancers including esophageal cancer. SOX2 overexpression occurs more broadly in cancer than gene amplification, but the mechanism is poorly understood. Here we showed that in esophageal cancer cell lines the levels of SOX2 proteins are not directly correlated to the copy numbers of SOX2 genes and are strongly influenced by proteostasis. We showed that AKT is a major determinant for SOX2 overexpression and does so by protecting SOX2 from ubiquitin-dependent protein degradation. We identified UBR5 as a major ubiquitin E3 ligase that induces SOX2 degradation through ubiquitinating SOX2 at lysine 115. Phosphorylation of SOX2 at threonine 116 by AKT inhibits the interaction of UBR5 with SOX2 and thus stabilizes SOX2. We provided evidence that AKT inhibitor can effectively downregulate SOX2 and suppress esopheageal cancer cell proliferation and stemness. Taken together, our study provides new insight into the mechanism of SOX2 overexpression in cancer and evidence for targeting AKT as a potential therapeutic strategy for SOX2-positive cancers.
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Sarkar A, Hochedlinger K. The sox family of transcription factors: versatile regulators of stem and progenitor cell fate. Cell Stem Cell. 2013;12:15–30.
Lefebvre V, Dumitriu B, Penzo-Mendez A, Han Y, Pallavi B. Control of cell fate and differentiation by Sry-related high-mobility-group box (Sox) transcription factors. Int J Biochem Cell Biol. 2007;39:2195–214.
Masui S, Nakatake Y, Toyooka Y, Shimosato D, Yagi R, Takahashi K, et al. Pluripotency governed by Sox2 via regulation of Oct3/4 expression in mouse embryonic stem cells. Nat Cell Biol. 2007;9:625–35.
Arnold K, Sarkar A, Yram MA, Polo JM, Bronson R, Sengupta S, et al. Sox2(+) adult stem and progenitor cells are important for tissue regeneration and survival of mice. Cell Stem Cell. 2011;9:317–29.
Wuebben EL, Rizzino A. The dark side of SOX2: cancer - a comprehensive overview. Oncotarget. 2017;8:44917–43.
Weina K, Utikal J. SOX2 and cancer: current research and its implications in the clinic. Clin Transl Med. 2014;3:19.
Bass AJ, Watanabe H, Mermel CH, Yu S, Perner S, Verhaak RG, et al. SOX2 is an amplified lineage-survival oncogene in lung and esophageal squamous cell carcinomas. Nat Genet. 2009;41:1238–42.
Hussenet T, Dali S, Exinger J, Monga B, Jost B, Dembele D, et al. SOX2 is an oncogene activated by recurrent 3q26.3 amplifications in human lung squamous cell carcinomas. PLoS ONE. 2010;5:e8960.
Gen Y, Yasui K, Zen Y, Zen K, Dohi O, Endo M, et al. SOX2 identified as a target gene for the amplification at 3q26 that is frequently detected in esophageal squamous cell carcinoma. Cancer Genet Cytogenet. 2010;202:82–93.
Cancer Genome Atlas Research Network; Analysis Working Group; Asan University; BC Cancer Agency; Brigham and Women’s Hospital; Broad Institute et al. Integrated genomic characterization of oesophageal carcinoma. Nature. 2017;541:169–75.
Maier S, Wilbertz T, Braun M, Scheble V, Reischl M, Mikut R, et al. SOX2 amplification is a common event in squamous cell carcinomas of different organ sites. Hum Pathol. 2011;42:1078–88.
Alonso MM, Diez-Valle R, Manterola L, Rubio A, Liu D, Cortes-Santiago N, et al. Genetic and epigenetic modifications of Sox2 contribute to the invasive phenotype of malignant gliomas. PLoS ONE. 2011;6:e26740.
Tam WL, Ng HH. Sox2: masterminding the root of cancer. Cancer Cell. 2014;26:3–5.
Vanner RJ, Remke M, Gallo M, Selvadurai HJ, Coutinho F, Lee L, et al. Quiescent sox2(+) cells drive hierarchical growth and relapse in sonic hedgehog subgroup medulloblastoma. Cancer Cell. 2014;26:33–47.
Gangemi RM, Griffero F, Marubbi D, Perera M, Capra MC, Malatesta P, et al. SOX2 silencing in glioblastoma tumor-initiating cells causes stop of proliferation and loss of tumorigenicity. Stem Cells. 2009;27:40–48.
Mu P, Zhang Z, Benelli M, Karthaus WR, Hoover E, Chen CC, et al. SOX2 promotes lineage plasticity and antiandrogen resistance in TP53- and RB1-deficient prostate cancer. Science. 2017;355:84–88.
Liu K, Jiang M, Lu Y, Chen H, Sun J, Wu S, et al. Sox2 cooperates with inflammation-mediated Stat3 activation in the malignant transformation of foregut basal progenitor cells. Cell Stem Cell. 2013;12:304–15.
Gen Y, Yasui K, Nishikawa T, Yoshikawa T. SOX2 promotes tumor growth of esophageal squamous cell carcinoma through the AKT/mammalian target of rapamycin complex 1 signaling pathway. Cancer Sci. 2013;104:810–6.
Boumahdi S, Driessens G, Lapouge G, Rorive S, Nassar D, Le Mercier M, et al. SOX2 controls tumour initiation and cancer stem-cell functions in squamous-cell carcinoma. Nature. 2014;511:246–50.
Riggi N, Suva ML, De Vito C, Provero P, Stehle JC, Baumer K, et al. EWS-FLI-1 modulates miRNA145 and SOX2 expression to initiate mesenchymal stem cell reprogramming toward Ewing sarcoma cancer stem cells. Genes Dev. 2010;24:916–32.
Mayer IA, Arteaga CL. The PI3K/AKT pathway as a target for cancer treatment. Annu Rev Med. 2016;67:11–28.
Jeong CH, Cho YY, Kim MO, Kim SH, Cho EJ, Lee SY, et al. Phosphorylation of Sox2 cooperates in reprogramming to pluripotent stem cells. Stem Cells. 2010;28:2141–50.
Fang L, Zhang L, Wei W, Jin X, Wang P, Tong Y, et al. A methylation-phosphorylation switch determines Sox2 stability and function in ESC maintenance or differentiation. Mol Cell. 2014;55:537–51.
Siegel RL, Miller KD, Jemal A. Cancer Statistics, 2017. CA Cancer J Clin. 2017;67:7–30.
Hirai H, Sootome H, Nakatsuru Y, Miyama K, Taguchi S, Tsujioka K, et al. MK-2206, an allosteric Akt inhibitor, enhances antitumor efficacy by standard chemotherapeutic agents or molecular targeted drugs in vitro and in vivo. Mol Cancer Ther. 2010;9:1956–67.
Barsyte-Lovejoy D, Li F, Oudhoff MJ, Tatlock JH, Dong A, Zeng H, et al. (R)-PFI-2 is a potent and selective inhibitor of SETD7 methyltransferase activity in cells. Proc Natl Acad Sci USA. 2014;111:12853–8.
Cox JL, Wilder PJ, Gilmore JM, Wuebben EL, Washburn MP, Rizzino A. The SOX2-interactome in brain cancer cells identifies the requirement of MSI2 and USP9X for the growth of brain tumor cells. PLoS ONE. 2013;8:e62857.
Wang H, Paczulla AM, Konantz M, Lengerke C. In vitro tumorigenic assay: the tumor spheres assay. Methods Mol Biol. 2018;1692:77–87.
Lu YX, Yuan L, Xue XL, Zhou M, Liu Y, Zhang C, et al. Regulation of colorectal carcinoma stemness, growth, and metastasis by an miR-200c-Sox2-negative feedback loop mechanism. Clin Cancer Res. 2014;20:2631–42.
Ozen M, Karatas OF, Gulluoglu S, Bayrak OF, Sevli S, Guzel E, et al. Overexpression of miR-145-5p inhibits proliferation of prostate cancer cells and reduces SOX2 expression. Cancer Invest. 2015;33:251–8.
Xu N, Papagiannakopoulos T, Pan G, Thomson JA, Kosik KS. MicroRNA-145 regulates OCT4, SOX2, and KLF4 and represses pluripotency in human embryonic stem cells. Cell. 2009;137:647–58.
Singh S, Trevino J, Bora-Singhal N, Coppola D, Haura E, Altiok S, et al. EGFR/Src/Akt signaling modulates Sox2 expression and self-renewal of stem-like side-population cells in non-small cell lung cancer. Mol Cancer. 2012;11:73.
Peltier J, Conway A, Keung AJ, Schaffer DV. Akt increases sox2 expression in adult hippocampal neural progenitor cells, but increased sox2 does not promote proliferation. Stem Cells Dev. 2011;20:1153–61.
Zhang HF, Wu C, Alshareef A, Gupta N, Zhao Q, Xu XE, et al. The PI3K/AKT/c-MYC axis promotes the acquisition of cancer stem-like features in esophageal squamous cell carcinoma. Stem Cells. 2016;34:2040–51.
Fang X, Yoon JG, Li L, Tsai YS, Zheng S, Hood L, et al. Landscape of the SOX2 protein-protein interactome. Proteomics. 2011;11:921–34.
Callaghan MJ, Russell AJ, Woollatt E, Sutherland GR, Sutherland RL, Watts CK. Identification of a human HECT family protein with homology to the Drosophila tumor suppressor gene hyperplastic discs. Oncogene. 1998;17:3479–91.
Saunders DN, Hird SL, Withington SL, Dunwoodie SL, Henderson MJ, Biben C, et al. Edd, the murine hyperplastic disc gene, is essential for yolk sac vascularization and chorioallantoic fusion. Mol Cell Biol. 2004;24:7225–34.
Shearer RF, Iconomou M, Watts CK, Saunders DN. Functional roles of the E3 ubiquitin ligase UBR5 in cancer. Mol Cancer Res. 2015;13:1523–32.
Meissner B, Kridel R, Lim RS, Rogic S, Tse K, Scott DW, et al. The E3 ubiquitin ligase UBR5 is recurrently mutated in mantle cell lymphoma. Blood. 2013;121:3161–4.
Ikushima H, Todo T, Ino Y, Takahashi M, Saito N, Miyazawa K, et al. Glioma-initiating cells retain their tumorigenicity through integration of the Sox axis and Oct4 protein. J Biol Chem. 2011;286:41434–41.
Basu-Roy U, Seo E, Ramanathapuram L, Rapp TB, Perry JA, Orkin SH, et al. Sox2 maintains self renewal of tumor-initiating cells in osteosarcomas. Oncogene. 2012;31:2270–82.
Leis O, Eguiara A, Lopez-Arribillaga E, Alberdi MJ, Hernandez-Garcia S, Elorriaga K, et al. Sox2 expression in breast tumours and activation in breast cancer stem cells. Oncogene. 2012;31:1354–65.
Gupta N, Gopal K, Wu C, Alshareef A, Chow A, Wu F, et al. Phosphorylation of Sox2 at threonine 116 is a potential marker to identify a subset of breast cancer cells with high tumorigenecity and stem-like features. Cancers (Basel). 2018; 10. https://doi.org/10.3990/cancers10020041.
Zhang J, Gao Q, Li P, Liu X, Jia Y, Wu W, et al. S phase-dependent interaction with DNMT1 dictates the role of UHRF1 but not UHRF2 in DNA methylation maintenance. Cell Res. 2011;21:1723–39.
We thank Dr. Shimin Zhao from Fudan University for providing expression plasmids for UBR5C, Dr. Tianbang Kang from SUN YAT-SEN University (Guangzhou, China) for providing K30, K140, K410 and K520 cells and Dr. Zhihua Liu at Cancer Hospital Chinese Academy of Medical Sciences (Beijing, China) for providing K70, K150, K450 and K510 cells. We also thank members of Wong’s lab for valuable discussion. This study is supported by grants from the National Natural Science Foundation of China (81530078), the Ministry of Science and Technology of China (2017YFA0504201 and 2015CB910402 to J.W.) and the Grants from the State Key Laboratory of Oncogenes and Related Genes (No. 90-17-05).
Conflict of interest
The authors declare that they have no conflict of interest.
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