Cancer Letters

Cancer Letters

Volume 336, Issue 2, 19 August 2013, Pages 379-389
Cancer Letters

SOX2 promotes tumor metastasis by stimulating epithelial-to-mesenchymal transition via regulation of WNT/β-catenin signal network

https://doi.org/10.1016/j.canlet.2013.03.027Get rights and content

Highlights

  • SOX2 improves metastasis by promoting epithelial-to-mesenchymal transition through WNT/β-catenin.

  • We reveal activation and binding of SOX2 on promoter region of β-catenin.

  • SOX2 affects the protein expression levels of DKK3, DVL1 and DVL3.

Abstract

SOX2 was reported to promote metastasis in various tumor tissues; however the underlying mechanisms remain elusive. Here, we disclosed that SOX2 improves metastasis of breast and prostate cancer cells by promoting epithelial-to-mesenchymal transition (EMT) through WNT/β-catenin, but not TGF-β or Snail1 signaling. Dual luciferase assay and chromatin immunoprecipitation revealed activation and binding of SOX2 on promoter region of β-catenin. In addition, SOX2 affects the protein expression levels of DKK3, DVL1 and DVL3, which are regulators or downstream molecules of WNT signaling. Taken together, our findings demonstrated β-catenin as one of vital downstream molecules that mediate the EMT induced by SOX2.

Introduction

Tumor metastasis is the key factor that compromises the prognosis of tumor patients and accounts for 90% of tumor death [1], [2]. Metastasis is a multistep process by which a percentage of primary tumor cells acquire the ability to spread from their initial site to the surrounding normal tissues in the local areas or to secondary tissues/organs [3], [4]. It is comprised of multiple steps, which include penetrating the walls of lymphatic and/or blood vessels, infiltration into the circulation system, re-penetration through the vessels, docking and proliferation in the distant organs to form a metastatic tumor. Failure at any one of these steps can block the entire metastatic process. Since tumor metastasis is responsible for the majority of deaths for cancer patients, a better understanding of the molecular mechanism involved in tumor spreading process is important for specific targeting of the tumor metastasis.

Recent studies demonstrated that breast cancer cells with stem/progenitor cell properties exhibit enhanced invasive properties [5], [6], supporting the concept that cancer stem cells (CSCs) may play an important role in tumor metastasis. SOX2 is one of the key transcriptional factors that control the unique properties of stem cells, for example self-renewal and pluripotency [7], [8], [9], [10]. Recently, additional studies reported the contribution of SOX2 to tumorigenesis and its correlation with clinical progression of various types of tumors, including human breast cancer, rectal cancer and prostate cancer [11], [12], [13]. Although these reports revealed the contribution of SOX2 to the metastasis properties of tumor cells, the underlying mechanisms involved in this phenomenon still needed to be explored.

EMT is an important development process in which immotile epithelial cells lose their polarity, tight cell–cell contacts and acquire mesenchymal characters [14], [15]. EMT always happens when tumor cells penetrate the lymphatic and/or blood vessels. During this process, tumor cells acquire a migratory behavior and gain more invasive properties to facilitate their departure from the epithelial cell community and to integrate into surrounding tissues, or remote organs. Therefore, EMT plays an important role in tumor migration. The process of EMT can be marked by the decrease in expression levels of epithelial junction proteins, such as E-cadherin, Claudins and Occludin [16], [17], [18], as well as increased expression of mesenchymal proteins, such as α-smooth actin, vimentin and fibronectin [19]. It is also embodied in transform of zonula occludens-1 (ZO-1), which functions as an essential tight junctional protein that directly links tight junction and cytoskeleton [20], from cell–cell contact region to intracellular distribution [21], [22], [23]. EMT can be induced by several signal pathways, among them, transforming growth factor (TGF-β) was extensively investigated and demonstrated to regulate EMT through activation of three families of transcriptional factors, including the snail, zinc finger E-box-binding homeobox (ZEB) and basic helix-loop-helix (bHLH) families to control the expression level of epithelial or mesenchymal marker genes [15].

Another important signaling pathway is Wingless (WNT)/β-catenin [24]. Upon activation, the WNT signals will be transduced to cytoplasmic proteins such as Dishevelled (Dvl) et al. One important consequence was the inhibited activity of glycogen synthase kinase-3β (GSK-3β), which phosphorylates and induces the degradation of β-catenin in the absence of WNT signals. Therefore, activation of WNT signals will stabilize and finally lead to accumulation of β-catenin [25]. It was reported that the cytoplasmic domain of E-cadherin interacts with the catenin complex (α-catenin, β-catenin and γ-catenin/plakoglobin) to form a cadherin–catenin complex [26], which binds to the cytoskeleton and contributes critically to the formation of strong cell–cell adhesion. Upon activation, β-catenin dissociates with E-cadherin, dissembling the adherens and enters the nucleus to turn on the expression of target genes, most of which show stemness-promotion functions [27].

Here we investigated the function of SOX2 in tumor metastasis and found the expression of SOX2 to be closely correlated with the TNM (tumor, lymph node and metastasis) stage and histological grade, as well as dominant overexpression in lymph nodes with tumor metastasis. Overexpression of SOX2 in MCF-7 and DU145 cells stimulated EMT and also enhanced their EMT process under stimulation of TGF-β1. Exploration of the underlying mechanism demonstrated that SOX2 may regulate the EMT through WNT/β-catenin signal pathway. Our research revealed that targeting of SOX2 may be a promising strategy for prevention of tumor metastasis.

Section snippets

Immunohistochemistry (IHC)

Immunostaining was performed on three pieces of paraffin human breast tissue array (BR1002, BR1005, BR2086, Alenabio Company, Shanxi, China) and the lung and tumor tissues of NOD/SCID mice. Expressions of SOX2, β-catenin and WNT1 in these tissues were detected separately with monoclonal antibody against SOX2 (ab75485, Abcam Inc., Cambridge, UK), polyclonal anti-β-catenin (ab47426, Abcam Inc., Cambridge, UK) and polyclonal anti-WNT1 antibody (ab85060, Abcam Inc., Cambridge, UK) at a 1:100

Expression of SOX2 correlates with TNM stage and histological grade of human breast cancer

To determine whether SOX2 plays a role in metastasis of breast carcinomas, we performed immunohistochemical analyses with a SOX2-specific antibody in tissue microarrays containing 319 samples of human normal/paracarcinomal breast tissues and breast tumors with different clinical degrees. We also tested the expression of SOX2 in 115 samples of normal lymph nodes and those with cancer metastasis. It was interesting to find that strong expression of SOX2 is only detectable in breast cancer tissues

Discussion

In this study, we disclosed the regulatory effect of SOX2 on EMT in human breast and prostate cancer cells and demonstrated the important function of β-catenin in mediating the metastasis promotion effect of SOX2, in addition, the profound transcriptional regulatory effect of SOX2 on WNT signal network was also identified. To our knowledge, we are the first to demonstrate the binding of SOX2 on the promoter region of β-catenin by ChIP, thus revealing the directly transcriptional regulation

Conflict of Interest

All authors declare that no conflict of interest exists.

Acknowledgments

We thank Dr. Ralph A. Reisfeld (Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA, USA) for helpful discussion and comments for this study.

This work was funded by: China 973 Program 2013CB967201 (to R. Xiang), NSFC (31000616 to N. Li, 81273331 to R. Xiang,), China International Cooperation Research Program 2012DFA10650 (to R. Xiang), China Junior Faculty Funds 20090031120044 (to N. Li). The funders had no role in study design, data collection and

References (39)

  • V.G. Cooke et al.

    Pericyte depletion results in hypoxia-associated epithelial-to-mesenchymal transition and metastasis mediated by met signaling pathway

    Cancer Cell

    (2012)
  • G. Christofori

    New signals from the invasive front

    Nature

    (2006)
  • I.J. Fidler

    The pathogenesis of cancer metastasis: the ‘seed and soil’ hypothesis revisited

    Nat. Rev. Cancer

    (2003)
  • L. Weiss

    Metastasis of cancer: a conceptual history from antiquity to the 1990s

    Cancer Metastasis Rev.

    (2000)
  • C. Sheridan et al.

    CD44+/CD24− breast cancer cells exhibit enhanced invasive properties: an early step necessary for metastasis

    Breast Cancer Res.

    (2006)
  • M. Wernig et al.

    In vitro reprogramming of fibroblasts into a pluripotent ES-cell-like state

    Nature

    (2007)
  • I.H. Park et al.

    Reprogramming of human somatic cells to pluripotency with defined factors

    Nature

    (2008)
  • S. Masui et al.

    Pluripotency governed by Sox2 via regulation of Oct3/4 expression in mouse embryonic stem cells

    Nat. Cell Biol.

    (2007)
  • S. Saigusa et al.

    Correlation of CD133, OCT4, and SOX2 in rectal cancer and their association with distant recurrence after chemoradiotherapy

    Ann. Surg. Oncol.

    (2009)
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