CancerTranslMed3387-6022009_164340.pdf

[Downloaded free from http://www.cancertm.com on Monday, March 12, 2018, IP: 65.96.222.254] CTM Cancer Transl Med 2017;3(3):87–95 doi: 10.4103/ctm.ctm_69_16 Cancer Translational Medicine Mini Review Stemness-related Markers in Cancer Wenxiu Zhao1, Yvonne Li2, Xun Zhang1 1 Neuroendocrine Unit, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA; 2Department of Medical Oncology, Dana-Farber Institute and Harvard Medical School, Boston, MA, USA Address for correspondence: Dr. Xun Zhang, Neuroendocrine Unit, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, BUL457, Boston, MA 02114, USA. E-mail: xzhang5@mgh.harvard.edu Received December 21, 2016; Accepted March 16, 2017 Cancer stem cells (CSCs), with their self‑renewal ability and multilineage differentiation potential, are a critical subpopulation of tumor cells that can drive tumor initiation, growth, and resistance to therapy. Like embryonic and adult stem cells, CSCs express markers that are not expressed in normal somatic cells and are thus thought to contribute toward a “stemness” phenotype. This review summarizes the current knowledge of stemness‑related markers in human cancers, with a particular focus on important transcription factors, protein surface markers, and signaling pathways. Key words: Cancer stem cells, cell surface stemness markers, stemness-related signaling pathways, stemness-related transcriptional factors INTRODUCTION Individual tumors consist of a mixed cell population that difers in function, morphology, and molecular signatures. hese tumors reside in and interact with their microenvironment, which consists of a wide variety of cell types and cellular structures, such as immune cells, ibroblasts, blood vessels, and extracellular matrix. Tumor cells themselves can be of multiple clonal populations, each having accumulated unique molecular alterations over the course of tumor development and growth. In addition, tumor cells that are similar at genetic level may have distinct modes of epigenetic regulation, further increasing the functional heterogeneity. It has been hypothesized that only a small subset of tumor cells are capable of initiating and sustaining tumor growth; they have been termed cancer stem cells (CSCs).1 To date, CSCs have been isolated from many organs and conirmed to have stem cell‑like abilities such as self‑renewal, multilineage diferentiation, and expression of stemness‑related markers;2,3 some of these features are even conirmed by single‑cell analysis.4 hese cells may also play a role in disease recurrence ater treatment and remission. As such, targeting of CSCs is currently an active area of therapeutic development. CSCs are classiied by the expression of stemness‑related markers, which have been identiied in embryonic stem cells (ESCs) and adult stem cells, the two main types of human stem cells. Here, we summarize the current knowledge about molecular markers and pathways that are not only involved in normal stem‑cell maintenance and self‑renewal but also regulate the stemness of CSCs. Investigation of these features may help elucidate the mechanism of CSC‑driven tumorigenesis and lead to novel approaches for CSC‑targeted cancer therapies. STEMNESS‑RELATED TRANSCRIPTIONAL FACTORS IN CANCERS Takahashi and Yamanaka5 showed in 2006 that pluripotent stem cells could be obtained from mouse embryonic ibroblasts by combined expression of four transcriptional factors (TFs) – now named the Yamanaka factors (OCT4, c‑Myc, SOX2, and KLF4). Induced pluripotent stem cells can now be derived from a wide range of somatic cells through the overexpression of a cocktail of TFs6 or a combination of TF expression with chemical compounds.7,8 Moreover, somatic cells can now be directly reprogrammed into entirely diferent cell types9 through the expression of lineage‑speciic sets of transcription factors. Yamanaka’s seminal discovery has introduced the concept that the fate of adult somatic cells can be controlled through TF expression. From another perspective, expression of stem‑cell‑speciic TFs can provide a signature for characterizing cell type as well as indicating their functional roles. here are currently approximately 25 TFs that have been reported to be expressed in stem cells. Of them, OCT4, SOX2, KLF4, Nanog, and SALL4 comprise a core regulatory network for ESC maintenance and self‑renewal. hese TFs are highly expressed in ESCs; in contrast, they are mainly silenced in normal somatic cells, This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms. For reprints contact: reprints@medknow.com How to cite this article: Zhao W, Li Y, Zhang X. Stemness‑related markers in cancer. Cancer Transl Med 2017;3(3):87‑95. © 2017 Cancer Translational Medicine | Published by Wolters Kluwer - Medknow 87 [Downloaded free from http://www.cancertm.com on Monday, March 12, 2018, IP: 65.96.222.254] Cancer Transl Med 2017;3(3) except in small groups of adult stem‑cell populations. Increasing evidence has shown that embryonic‑speciic TFs are abnormally expressed in human tumor samples,10,11 suggesting the presence of CSCs. Retrospective studies on patient cohorts have also associated TF expression with survival outcomes in speciic tumor types, suggesting that TF expression levels may also be useful for assessing patient prognosis.12 hus, detecting the expression level of these TFs, for example, by immunohistochemistry staining, can aid in tumor diagnosis, classiication, and therapeutic strategies. A summary of these CSC TFs is shown in Table 1. hese TF markers are also classiied by tissue type as shown in Table 2. A few examples are listed here. OCT4 OCT4 expression has been detected in human brain, lung, bladder, ovarian, prostate, renal, testicular tumors, and leukemia,12 by both reverse transcription‑polymerase chain reaction and immunohistochemistry. Furthermore, high expression of OCT4 has been associated with poor prognosis in bladder cancer,13,14 prostate cancer,15 medulloblastoma,16 and esophageal squamous cell carcinoma (ESCC).17 SOX2 SOX2 has been found in brain, breast, lung, liver, prostate, and testicular tumors,12,18,19 and its expression has been correlated with poor prognosis in stage I lung adenocarcinoma,18 squamous cell carcinoma,20,21 gastric carcinoma,22‑24 small cell lung cancer,25‑28 and ovarian carcinoma.29,30 KFL4 KLF4 has been found to be expressed in brain, breast, head and neck, oral, prostate, and testis tumors, as well as in leukemia and myeloma.12 Expression of KLF4 can also be a prognostic predictor for colon cancer31 and head‑neck squamous cell carcinoma.24,32 In addition, nuclear localization of KLF4 has been associated with the aggressive phenotype of early stage of breast cancer,33 as well as worse prognosis in nasopharyngeal34 and oral cancers.53 Nanog Nanog has been shown to be expressed in brain, breast, prostate, colon, liver, and ovarian tumors.40 High expression of Nanog promotes the epithelial‑mesenchymal transition (EMT),41 which Table 1. Stemness‑related transcriptional factor markers in cancer Marker Other names Function in stem cell Characteristics Expressed in tumor types Poor prognosis for tumor types Selected references OCT4 Oct3/4 or POU5F1 Stem‑cell self‑renew and pluripotency maintenance Oct family of POU transcription factor Leukemia, brain, lung, bladder, ovarian, pancreas, prostate, renal, seminoma, testis Esophageal squamous cell carcinoma Medulloblastoma Prostate cancer Bladder cancer 11–16 SOX2 Stem‑cell self‑renew and pluripotency maintenance POU family binder transcription factor Brain, breast, lung, liver, prostate, seminoma, testis Stage I lung adenocarcinoma Squamous cell carcinoma Gastric carcinoma Small cell lung cancer Ovarian carcinoma 11,17–29 KLF4 Stem‑cell self‑renew and pluripotency maintenance Zinc‑inger transcription factor Leukemia, myeloma, brain, breast, head and neck, oral, prostate, testis Breast cancer Nasopharyngeal carcinoma Colon cancer Head and neck squamous cell carcinoma Oral cancer 27,30–34 C‑MYC Stem‑cell self‑renewal Transcription factor and an oncogene Leukemia, lymphoma, myeloma, brain, breast, colon, head and neck, pancreas, prostate, renal, salivary gland, testis Hepatocellular carcinoma Early carcinoma of uterine cervix 11,35–39 Nanog Stem‑cell self‑renew and pluripotency maintenance Transcription factor Brain, breast, prostate, colon, liver, ovarian Breast cancer Colorectal cancer Gastric adenocarcinoma Nonsmall cell lung cancer Ovarian serous carcinoma Liver cancer 40–48 SALL4 Stem‑cell self‑renew and pluripotency maintenance Diferentiation regulation Zinc‑inger transcription factor and an oncogene Leukemia, breast, liver, colon, ovarian, testis Hepatocellular carcinoma Gliomas Myelodysplastic syndromes 49–52 POU: Pit‑Oct‑Unc 88 CD34 Bladder Breast ALDH1A1 ALDH1A1 ALDH1A1 ALDH1A1 CD47 CD49f/ integrin alpha 6 CD166 CD24 CD24 CD44 CD44 CD133 CD133 CD90 CD26 CD38 CD44 CD44 CD47 CD96 Colon Gastric Glioma/ Head and Liver medulloblastoma neck ALDH1A1 CD49f/integrin alpha 6 TNFRSF16 CD27/TNFRSF7 CD24 CD38 CD44 CD44 CD133 CD133 CD15/ Lewis X CD15/Lewis X CD13 CD90/hy1 CD90/hy1 CD44 CD133 Lgr5/ GPR49 EpCAM/ TROP1 BMI‑1 Lgr5/ GPR49 c‑Myc EpCAM/ TROP1 CXCR1/ IL‑8 RA CX3CR1 c‑Myc SALL4 CD24 CD151 CD44 CD44 CD133 CD133 CD133 CD20/MS4A1 CD166 CD19 TRA‑1‑60 (R) CD138Syndecan‑1 ALCAM/ CD166 EpCAM/ TROP1 CXCR4 BMI‑1 EpCAM/ TROP1 CXCR4 BMI‑1 Musashi‑1 Musashi‑1 c‑Myc c‑Myc SOX2 CD24 CD44 Lgr5/ GPR49 CXCR4 BMI‑1 CD49f/ integrin alpha 6 CD117/ c‑kit CD166/ ALCAM BMI‑1 Nestin TIM3 CD133 CD90/ hy1 Aminopeptidase N/ CD13 Pancreatic Prostate Endoglin/ CD24 CD105 CD117/ c‑kit CD123/IL‑3 CEACAM‑6/ R alpha CD66c KLF4 Osteosarcoma Ovarian ALDH1A1 ALDH1A1 CD45 CD117/c‑kit OCT4 Melanoma Myeloma ALDH1A1 CD44 CD29 Lung SOX2 Nestin Nestin c‑Myc SOX2 OCT4 BMI‑1 Nestin SOX2 c‑Myc SOX2 OCT4 KLF4 OCT4 OCT4 KLF4 Nanog Nanog Nanog Nanog Nanog SALL4 SALL4 SALL4 SALL4 SALL4 Rex1 [Downloaded free from http://www.cancertm.com on Monday, March 12, 2018, IP: 65.96.222.254] Leukemia Cancer stemness markers Table 2. Stemness‑related markers in diferent cancer types 89 [Downloaded free from http://www.cancertm.com on Monday, March 12, 2018, IP: 65.96.222.254] Cancer Transl Med 2017;3(3) is an important developmental process for cancer cells to obtain stem‑cell characteristics. Nanog has also been associated with poor prognosis in breast,42 colorectal,43,44 gastric,45 lung,46,47 ovarian,48 and liver cancers.54 SALL4 SALL4 expression has been detected in breast, liver, colon, ovarian, and testis cancers and leukemia.49,55 he expression of SALL4 has been studied as a poor prognosis marker in hepatocellular carcinoma,50,51 gliomas,52 and myelodysplastic syndromes.35 C‑Myc C‑Myc is an important TF both in stem cells and cancers. As one of the most studied oncogenes, overexpression of C‑Myc has been shown to cause tumorigenesis in mouse models. Up to 70% of human cancers exhibit c‑Myc overexpression, including brain, breast, colon, head and neck, pancreas, prostate, renal, salivary gland, and testis tumors, as well as leukemia and lymphoma.12,36,37 C‑Myc expression has also been correlated with poor prognosis in hepatocellular carcinoma38 and early carcinoma of uterine cervix.39,56 STEMNESS‑RELATED SURFACE MARKERS IN CANCERS Cell surface proteins provide a feasible way for isolating and studying diferent cell types by low cytometry or magnetic sorting. In addition, they are amenable for speciic targeting, which is useful for disease monitoring and therapeutic delivery. Similar to stemness‑related transcription factors, many surface markers that are highly expressed in stem cells are also expressed in human cancers as TRA‑1‑60, SSEA‑1, EpCAM, ALDH1A1, Lgr5, CD13, CD19, CD20, CD24, CD26, CD27, CD34, CD38, CD44, CD45, CD47, CD49f, CD66c, CD90, CD166, TNFRSF16, CD105, CD133, CD117/c‑kit, CD138, CD151, and CD166. Table 2 describes most of the stemness‑related surface markers and the tumor types they have been found to be expressed in. Among them, CD44 and CD133 are the most widely used markers in CSC research and are also therapeutic targets in cancers. CD44 is a transmembrane glycoprotein that plays diferent roles in cell division, migration, adhesion, and signaling.57 It is normally expressed in both fetal and adult hematopoietic stem cells, and on binding to hyaluronic acid, its primary ligand, CD44 mediates cell‑cell communication and signal transaction. CD44 is highly expressed in many types of cancers including bladder, breast, colon, gastric, glioma, head and neck, osteosarcoma, ovarian, pancreatic, and prostate cancers, as well as leukemia.58,59 CD44 is being studied as a therapeutic target in metastasizing tumors such as breast and colon cancer60,61 and also in leukemia.62 CD133 is another transmembrane glycoprotein and speciically localizes to cellular protrusions. CD133 is reported to be expressed in hematopoietic stem cells, endothelial progenitor cells, glioblastoma, and neuronal and glial stem cells,63,64 and it is also involved in cell growth and development.65 Almost all tumor types can be detected with CD133 expression, and CD133+ tumor cells show stem‑cell‑speciic characteristics such as self‑renewal, diferentiation, and tumor formation in NOD‑SCID mouse model.66 Ater injection into immune‑compromised mice, 90 CD133+ cells also show chemo‑ and radio‑resistance.66 Studies have been performed to use CD133 as a potential therapeutic target in colon cancer,67 ovary cancers,68 and metastatic melanoma.69 CD133 has also been used as a target for drug delivery.70 here are a number of other CSC surface markers that appear to function in speciic types of tumors. For examples, SSEA‑1 has been shown to be expressed in human colonic adenocarcinoma and glioblastoma.71,72 Similarly, TRA‑1‑60 has been associated with prostate tumors.73 Lgr5 has been shown to be expressed in head and neck, colon, and gastric tumors.74,75 CD90 has been detected in high‑grade human glioma,76,77 as well as liver 78 and lung tumors;79,80 while CD117 has been used as a CSC marker in leukemia81,82 and gastrointestinal stromal tumor,83 as well as oral squamous cell carcinomas84,85 and ovarian tumors.86,87 CD117 has been shown to be overexpressed in hepatocellular88 and pancreatic carcinoma.89 CD24 has been used in combination with CD44 in breast cancer cell lines to show that CD44+/CD24‑ cancer cells exhibit drug resistance and invasive properties.90‑92 Studies have also shown that CD24 can be used as an independent prognostic marker nonsmall cell lung cancer93,94 and ovarian cancer.95 OTHER IMPORTANT STEMNESS‑RELATED MARKERS here are a number of stemness‑related markers that are neither TFs nor cell surface proteins, which include aldehyde dehydrogenase (ALDH), Bmi‑1, Nestin, Musashi‑1, TIM‑3, and CXCR. he ubiquitous family of ALDH enzymes catalyzes the irreversible oxidation of cellular aldehydes in the cytoplasm. High activity of ALDH enzymes has been found in ESCs, adult hematopoietic and neural stem cells, as well as CSCs. ALDH activity in CSCs has been attributed to ALDH1A1 expression, which can regulate stem‑cell self‑protection, diferentiation, and population expansion. ALDH has been reported to have prognostic signiicance in head and neck squamous cell96 and ESCC.97 It is also being pursued as a therapeutic target in ovarian98,99 and nonsmall cell lung cancers.100 BMI1 is a protein required for hematopoietic stem‑cell self‑renewal101 and neural stem cells.102 Drug‑induced expression of BMI1 has been shown to enhance stem‑cell populations in head and neck cancer models.103 BMI1 has been reported as a marker for poor prognosis in oligodendroglial tumors104 and breast cancer.105,106 Nestin and Musashi‑1 have been detected in neural stem cells,107 where they both play an important role in stem‑cell self‑renewal and maintenance. Nestin expression has been shown in transformed cells of various human malignancies, correlating with the clinical course of some diseases.108 Furthermore, coexpression of Nestin with other stem‑cell markers was described as a CSC phenotype.109 Nestin was reported as a potential target for tumor angiogenesis.110,111 Musashi‑1 signaling was also detected in hematopoietic stem cells, and it is being investigated as a potential therapeutic target and diagnostic marker for lung cancer.112 Chemokines are small peptide molecules secreted by cells that afect the movement of neighboring cells, thus mediating cellular homing and migration. hey are crucial for normal physiological functions and are found to be dysregulated in cancers. he chemokine CXCL12 (SDF‑1) and its receptor CXCR4 regulate cellular chemotaxis, cell adhesion, survival, proliferation, and gene transcription through multiple divergent pathways. CXCL12/ CXCR4 interactions were shown to play an important role in the [Downloaded free from http://www.cancertm.com on Monday, March 12, 2018, IP: 65.96.222.254] Cancer stemness markers migration of hematopoietic stem cells.113 CXCR4 is overexpressed in more than twenty cancer types, with discovered roles in tumor growth, invasion, angiogenesis, metastasis, relapse, and therapeutic resistance.114 CXCR4 antagonists have been shown to disrupt tumor‑stromal cell interactions, sensitize cancer cells to cytotoxic drugs, and reduce tumor growth and metastasis. herefore, CXCR4 is considered as a target for therapeutic intervention of lung115,116 and breast cancer.117,118 It has also been used for noninvasive monitoring of disease progression and therapeutic guidance.114 STEMNESS‑RELATED PATHWAYS Stem‑cell maintenance, self‑renewal, and diferentiation pathways are involved in embryonic development and adult tissue homeostasis. Cancers commonly display aberrant activities within these pathways, oten in a cell‑context‑dependent manner. Here, we discuss current evidence for Hedgehog (HH), Notch, JAK/ STAT, phosphatidylinositol‑3‑kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR), and Wnt/β‑catenin pathway regulation in CSCs. Hedgehog pathway he HH pathway is a major regulator in vertebrate embryonic development, playing critical roles in stem‑cell maintenance, cell diferentiation, tissue polarity, and cell proliferation, as well as EMT.119 HH ligands (Desert HH, Sonic HH, and Indian HH) bind to Ptch, activating a cascade of downstream signals that lead to the activation and nuclear localization of TFs, consequently followed by expression of genes that are involved in survival, proliferation, and angiogenesis.120 HH signaling has been widely implicated in CSC self‑renewal and cell fate determination120 and is considered a potential therapeutic target in breast cancer and pancreatic cancer.121‑123 control of stem‑cell maintenance in the male germline stem‑cell microenvironment.130,131 Tightly controlled JAK‑STAT signaling is required for stem‑cell maintenance and self‑renewal. Furthermore, JAK‑STAT activity is essential for anchoring the stem cells in their respective niches by regulating diferent adhesion molecules. Phosphatidylinositol‑3‑kinase/Akt/mammalian rapamycin pathway target of he PI3K/Akt and the mTOR signaling pathways are crucial to stem‑cell proliferation, metabolism, and diferentiation. his pathway is oten improperly regulated in human cancers.132 Over 70% of ovarian cancers have active PI3K/Akt/mTOR pathway, making it a therapeutic target in this cancer type.133,134 It is also a therapeutic target for neuroblastoma,135 endometrial cancer,136 and acute myeloid leukemia.137 Wnt/β‑catenin pathway Pathways induced by Wnt ligands are highly evolutionarily conserved. Given their strong conservation in phylogeny, it is not surprising that Wnt pathways also play key roles in regulating stem‑cell diferentiation and pluripotency. Consistently in many tissue types, dysregulation of Wnt pathway has been strongly associated with expansion of stem and/or progenitor cell lineages, as well as carcinogenesis.138 Hence, therapies targeting Wnt pathway may lead to treatment options in hematological malignancies,139 liver cancer,140 and other type of tumors.141 CONCLUSION Notch signaling is a critical part of stem‑cell fate determination and angiogenesis. Notch signaling is predominantly involved in cell‑cell communication between adjacent cells through transmembrane receptors and ligands. In human ESCs, Notch signaling governs cell fate determination in the developing embryo and is required for undiferentiated ESCs to develop all three embryonic germ layers.124 In CSCs, it controls tumor immunity and CSC population maintenance.125,126 Notch signaling is frequently dysregulated in cancers, providing a survival advantage for tumors. In certain tumor types, activation of Notch signaling aids CSCs in maintaining their population in tumors, inducing EMT, and acquiring chemoresistance.127 Notch signaling is a potential target for cancers.128,129 A primary goal of cancer research is to identify mechanisms driving drug resistance, and recent studies have implicated CSCs in intrinsic resistance models. Similar to normal stem cells, the abilities of self‑renewal, maintenance, and diferentiation of CSCs make it serve as a core reservoir for cancer initiation, development, and growth. he overexpression of stem‑cell‑speciic TFs may contribute to the pathologic self‑renewal characteristics of CSCs while the surface molecules mediate interactions between cells and their microenvironment. Other stemness‑related markers and pathways may promote cancer cell proliferation, progression, and metastasis. Our summary of stem cell markers by tissue types and cellular locations in Table 2 and Figure 1 highlights the complex nature of CSC regulation, which appears to utilize diferent pathways in diferent cell or tissue types. his context dependency makes it hard to ind overarching CSC pathways and makers. Understanding the stemness‑related features in cancers will not only provide important knowledge on molecular mechanisms for cancer pathogenesis but also shed new light on the development of efective therapeutic approaches, speciically targeting these stemness‑related features. JAK/STAT pathway Financial support and sponsorship he JAK‑STAT signaling pathway is important in cytokine‑mediated immune responses and known to be involved in many biological processes such as proliferation, apoptosis, and migration, as well as the regulation of stem cells. Cancer cells also show frequent dysregulation of the JAK/STAT. Studies in Drosophila irst implicated JAK‑STAT signaling in the his work was supported in part by NIH (R01CA193520‑01A1) and the Jarislowsky Foundation. Notch pathway Grant Conlicts of interest here are no conlicts of interest. 91 [Downloaded free from http://www.cancertm.com on Monday, March 12, 2018, IP: 65.96.222.254] Cancer Transl Med 2017;3(3) 17. 18. 19. 20. Figure 1. Categories of cancer stem‑cell markers 21. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 92 Pardal R, Clarke MF, Morrison SJ. Applying the principles of stem‑cell biology to cancer. Nat Rev Cancer 2003; 3 (12): 895–902. Medema JP. Cancer stem cells: the challenges ahead. Nat Cell Biol 2013; 15 (4): 338–44. Pattabiraman DR, Weinberg RA. Tackling the cancer stem cells – What challenges do they pose? Nat Rev Drug Discov 2014; 13 (7): 497–512. 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