Users Online: 6081
Home Print this page Email this page
Home About us Editorial board Search Browse articles Submit article Ahead of Print Instructions Subscribe Contacts Special issues Login 

Previous article Browse articles Next article 
Adv Biomed Res 2015,  4:139

SIX1 overexpression in diffuse-type and grade III gastric tumors: Features that are associated with poor prognosis

1 Department of Genetics, Research Institute of Biotechnology, Shahrekord University, Shahrekord, Iran
2 Department of Genetics and Molecular Biology; Pediatric Inherited Diseases Research Center; Child Growth and Development Research Center, Isfahan University of Medical Sciences, Isfahan, Iran
3 Department of Genetics and Molecular Biology, Isfahan University of Medical Sciences, Isfahan, Iran

Date of Submission12-Mar-2014
Date of Acceptance30-Jun-2014
Date of Web Publication27-Jul-2015

Correspondence Address:
Dr. Parvaneh Nikpour
Department of Genetics and Molecular Biology, Faculty of Medicine, Isfahan University of Medical Sciences, Isfahan
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2277-9175.161540

Rights and Permissions

Background: Gastric cancer is the second most common cancer worldwide. In Iran, the incidence of gastric cancer is well above the world average, and is the first common cancer in Iranian men and the third one in women. Located at chromosome 14q23, SIX1 is a homolog of the Drosophila 'sine oculis' (so) gene and is highly conserved in numerous species. In addition to the role of SIX1 in the development, its expression is frequently dysregulated in multiple cancers. This study aimed to evaluate the clinicopathological features of the expression of SIX1 gene in gastric adenocarcinoma.
Materials and Methods: Thirty pairs of gastric tissue samples from patients with gastric adenocarcinoma were evaluated for SIX1 gene expression using quantitative real-time polymerase chain reaction. A paired t-test or one-way ANOVA with post hoc multiple comparisons were used to analyze the differences between groups. Statistical significance was defined as P ≤ 0.05.
Results: SIX1 expression was decreased in tumoral samples. However, its expression increased significantly in diffuse-type gastric cancer. Furthermore, there was a trend toward statistical significance in increasing SIX1 gene expression with higher grades. Of note, the difference was significant between grades I and III.
Conclusions: The results suggest that SIX1 gene expression might be used in the future as a potential biomarker to predict the outcome of the disease as diffuse-type and grade III of gastric tumors are associated with poor prognosis.

Keywords: Diffuse-type gastric cancer, gene expression, poor prognosis SIX1, tumor grades

How to cite this article:
Emadi-Baygi M, Nikpour P, Emadi-Andani E. SIX1 overexpression in diffuse-type and grade III gastric tumors: Features that are associated with poor prognosis. Adv Biomed Res 2015;4:139

How to cite this URL:
Emadi-Baygi M, Nikpour P, Emadi-Andani E. SIX1 overexpression in diffuse-type and grade III gastric tumors: Features that are associated with poor prognosis. Adv Biomed Res [serial online] 2015 [cited 2023 Sep 21];4:139. Available from:

  Introduction Top

Gastric cancer is the second most common cancer worldwide, with an estimated 900,000 new cases and 700,000 gastric cancer-related deaths in the world. [1] In Iran, the incidence rate of gastric cancer is well above the world average, and is the first common cancer in Iranian men and the third one in women. [2] Because of the lack of trustworthy early diagnostic methods and effective treatment, more than 80% of patients with advanced gastric cancer die of the disease or recurrent disease within 1 year after diagnosis. The majority of patients with gastric cancer are being diagnosed in advanced stages of the disease such that usual treatment protocols are ineffective in a remarkable number of cases. [3] Therefore, elucidation of the molecular characteristics of gastric tumors is an essential need to develop methods of early cancer detection and reduce its mortality.

Located at chromosome 14q23, [4] SIX1 (sineoculis homeobox homolog 1), a member of the Six gene superfamily, is a homolog of the Drosophila 'sine oculis' (so) gene and is highly conserved in numerous species from Drosophila to human. [5],[6] The SIX1 gene product functions in concert with Eya1, [6] Pax and Dac in DNA binding [7] and regulates the expression of many downstream target genes. [8] Therefore, the SIX1 homeoprotein organizes a variety of cellular processes during normal development of some tissues and organs such as promoting progenitor cell population proliferation and their invasion before cell differentiation and specification, survival, migration and apoptosis. However, after development, expression of SIX1 changes and decreases in most normal adult tissues. [9],[10],[11] Furthermore, SIX1 indirectly affects cell movement and adhesion between cells and the extracellular matrix (ECM) by regulating the expression of Ezrin. [7]

In addition to the role of SIX1 in the development, its expression is frequently dysregulated in multiple cancers including breast cancer, [12] Wilms' tumors, [13] ovarian cancer, [14] hepatocellular carcinoma, [15] alveolar rhabdomyosarcomas, [16] and cervical cancer. [17] The misexpression of SIX1 in cancer can enhance cancer cell proliferation and survival and lead to tumor inception and progression. [8],[18],[19] These findings explain that unsuitable SIX1 expression in adult differentiated tissues results in cell proliferation stimulus and, in turn, leads to initiation and progression of numerous cancers. [11]

Considering the dysregulation of SIX1 gene expression in various tumors, in this study, we studied the expression of SIX1 gene in gastric tumors.

  Materials and methods Top

Tumor and non-tumor tissues

Thirty pairs of gastric tissue samples (tumor and their adjacent non-tumor tissues) from patients with gastric adenocarcinoma were provided from the Iran Tumoural Bank (Tehran, Iran) as described previously. [20] The clinicopathological characteristics of the specimens are shown in [Table 1]. Written informed consent from all subjects was obtained by the Iran Tumoral Bank. The experimental procedures were approved by the Ethics Committee of the Isfahan University of Medical Sciences. The samples were frozen in liquid nitrogen and kept at -80°C until analysis.
Table 1: Clinicopathological parameters of gastric cancer samples

Click here to view

RNA isolation and reverse transcription

Total RNAs from frozen gastric cancer tissue samples were extracted using Qiazol reagent and RNeasy columns (Qiagen, Hilden, Germany) following the manufacturer's protocol. RNA integrity was examined by running on a 1% agarose gel and total RNA concentrations determined spectrophotometrically. Two micrograms of total RNA were reverse transcribed using random hexamer primers (TAG Copenhagen) and MMLV Reverse Transcriptase (Fermentas, Vilnius, Lithuania) according to the manufacturer's instructions.

Quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR)

Synthesized cDNAs were subjected to quantitative real-time PCR using the Maxima SYBR Green/ROX qPCR Master Mix (Fermentas, Vilnius, Lithuania) and specific primers for SIX1 and TBP[21] as an endogenous control in a total volume of 20 μL reaction mixture and were run on the Rotor-gene 6000 system. The following primers were used to amplify SIX1:

SIX1 forward primer: 5'- TAAGAACCGGAGGCAAAGAG -3'

SIX1 reverse primer: 5'- AGTTTGAGCTCCTGGCGTG -3'

The amplification conditions for SIX1 were as follows: An initial denaturation step at 95 ° C for 10 min followed by 45 amplification cycles consisting of denaturation at 95 ° C for 20 s, annealing for 20 s at 55 ° C and an extension at 72 ° C for 20 s. For each sample, measurements were performed at least in triplicate. The standard curve method was used to calculate relative gene expression. For further verification of the identity of the PCR products, agarose gel electrophoresis was performed.

Statistical analysis

Data are represented as means ± standard error of mean (SEM) from at least three separate experiments. To compare the gene expression levels between the tumor and non-tumor tissues and associated clinicopathological characteristics with gene expression, Student's t test and ANOVA statistical tests were performed. The SPSS program, version 20.0, was utilized for statistical analyses, and differences were considered significant if P < 0.05.

  Results Top

SIX1 is underexpressed in human gastric adenocarcinoma tissues

Relative quantitation of the expression levels of SIX1 in gastric adenocarcinomas showed that the relative levels of SIX1 transcripts were significantly decreased (around 1.5-fold, P value = 0.018) in cancerous tissues compared with adjacent non-cancerous tissues: 0.48 ± 0.03 versus 0.64 ± 0.06, respectively, as shown in [Figure 1].
Figure 1: The relative expression levels of SIX1 in tumoral versus non-tumoral gastric samples. Error bars represent standard error of mean (SEM)

Click here to view

Association of SIX1 expression with clinicopathological parameters in gastric adenocarcinoma tissues

Next, we analyzed the association of SIX1 relative gene expression with the reported clinicopathological characteristics of the tumors (histological classifications and grade). As shown in [Figure 2], the expression level of SIX1 was different in both diffuse- and intestinal-type tumors. We found that SIX1 overexpressed in diffuse-type gastric tumors (mean: 0.56) compared with intestinal-type tumors (mean: 0.40) (P value: 0.025). Furthermore, there was no significant association between the expression levels of SIX1 and different grades of the tumors (P value: 0.09). However, SIX1 was overexpressed in grade III of gastric tumors compared with grade I (P value: 0.03) [Figure 3].
Figure 2: Relationship of the relative expression levels of SIX1 with the histological classifications of the gastric tumors (diffuse vs. intestinal types)

Click here to view
Figure 3: The SIX1 relative expression stratified according to different tumor grades. The difference between grades I and III was statistically significant (P = 0.03)

Click here to view

  Discussion Top

To the best of our knowledge, this is the first study that evaluates the expression of SIX1 gene in gastric adenocarcinoma using quantitative real-time RT-PCR. Our study showed that the relative expression of SIX1 is significantly downregulated in tumoral tissues compared with the adjacent non-tumoral tissues (P = 0.018). However, our results showed that expression of SIX1 increased significantly in diffuse-type gastric tumors in comparison with the intestinal-type gastric tumors (P = 0.025). Furthermore, SIX1 expression significantly increased in grade III gastric tumors in comparison with grade I gastric tumors (P = 0.03).

SIX1 is an important developmental regulator in several diverse tissues/organs, [10],[22],[23],[24],[25] and induces the expression of diverse genes (e.g. Cyclin D1, Cyclin A1 and c-myc) in various cell types. [8] It has been postulated that dysregulation of SIX1 leads to cancer. [7],[26]

Overexpression of SIX1 has been documented in several types of cancer, including breast cancer, [12] Wilms' tumors, [13] ovarian cancer, [14] hepatocellular carcinoma, [15] alveolar rhabdomyosarcomas [16] and cervical cancer, [17] where it facilitates proliferation and metastasis of the cancerous cells. [26] In the same vein, we observed that SIX1 expression increased significantly in diffuse type and grade III gastric cancer. Of note, microarray analyses have also shown that SIX1 overexpresses in diffuse-type gastric tumors versus intestinal-type gastric tumors. [27],[28] However, Matsusaka et al. recently reported that EYA1, a Six 1 coactivator, is often methylated in both EBV + and EBV - /high methylation gastric cancers. [29] As EYA1 interacts with and functions upstream of the homeobox gene Six 1 in the development of some organs including ear and kidney, [24],[30] it is plausible that SIX1 was co-underexpressed with EYA1 in gastric cancer. Furthermore, microarray analysis performed by Cui et al. showed that SIX1 expression decreases in gastric tumors versus normal gastric tissues. [31]

Located within a critical interval on chromosome 14q23, Ruf et al. identified a 3-bp deletion in the SIX1 gene in branchio-otic syndrome. [32] Furthermore, a loss of 14q23 has been reported in breast cancer, [33] gastrointestinal stromal tumors [34] and neuroblastomas. [35] In the same vein, deletions have been observed in 14q in gastric cancer. [36] Moreover, Gόmόs-Akay et al. recently reported that the most common losses in gastric adenocarcinomas were found on arms 18q (26%), 5q (21%) and 14q (21%). [37] Taken together, the overall underexpression of SIX1 in gastric cancer may be attributed to the loss of 14q.

In conclusion, this is the first report that evaluates the expression of SIX1 in gastric cancer. Our results showed that SIX1 is significantly downregulated in gastric tumors. However, our results showed that expression of SIX1 increased significantly in diffuse-type and grade III gastric tumors. Taken together, this gene might be used in the future as a potential biomarker to predict the outcome of the disease as diffuse-type and grade III gastric tumors are associated with poor prognosis. [38] Further studies should be carried out to elucidate the mechanisms which cause SIX1 underexpression in gastric tumors and to find out how SIX1 and EYA1 function in gastric cancer.

  References Top

Gomceli I, Demiriz B, Tez M. Gastric carcinogenesis. World J Gastroenterol 2012;18:5164-70.  Back to cited text no. 1
Kolahdoozan S, Sadjadi A, Radmard AR, Khademi H. Five common cancers in Iran. Arch Iran Med 2010;13:143-6.  Back to cited text no. 2
Malekzadeh R, Derakhshan MH, Malekzadeh Z. Gastric cancer in Iran: Epidemiology and risk factors. Arch Iran Med 2009;12:576-83.  Back to cited text no. 3
Boucher CA, Carey N, Edwards YH, Siciliano MJ, Johnson KJ. Cloning of the human SIX1 gene and its assignment to chromosome 14. Genomics 1996;33:140-2.  Back to cited text no. 4
Seo HC, Curtiss J, Mlodzik M, Fjose A. Six class homeobox genes in drosophila belong to three distinct families and are involved in head development. Mech Dev 1999;83:127-39.  Back to cited text no. 5
Buller C, Xu X, Marquis V, Schwanke R, Xu PX. Molecular effects of Eya1 domain mutations causing organ defects in BOR syndrome. Hum Mol Genet 2001;10:2775-81.  Back to cited text no. 6
Yu Y, Davicioni E, Triche TJ, Merlino G. The homeoprotein six 1 transcriptionally activates multiple protumorigenic genes but requires ezrin to promote metastasis. Cancer Res 2006;66:1982-9.  Back to cited text no. 7
Coletta RD, Christensen KL, Micalizzi DS, Jedlicka P, Varella-Garcia M, Ford HL. Six 1 overexpression in mammary cells induces genomic instability and is sufficient for malignant transformation. Cancer Res 2008;68:2204-13.  Back to cited text no. 8
McCoy EL, Iwanaga R, Jedlicka P, Abbey NS, Chodosh LA, Heichman KA, et al. Six 1 expands the mouse mammary epithelial stem/progenitor cell pool and induces mammary tumors that undergo epithelial-mesenchymal transition. J Clin Invest 2009;119:2663-77.  Back to cited text no. 9
Christensen KL, Patrick AN, McCoy EL, Ford HL. The six family of homeobox genes in development and cancer. Adv Cancer Res 2008;101:93-126.  Back to cited text no. 10
Kumar JP. The sine oculis homeobox (SIX) family of transcription factors as regulators of development and disease. Cell Mol Life Sci 2009;66:565-83.  Back to cited text no. 11
Ford HL, Kabingu EN, Bump EA, Mutter GL, Pardee AB. Abrogation of the G2 cell cycle checkpoint associated with overexpression of HSIX 1: A possible mechanism of breast carcinogenesis. Proc Natl Acad Sci U S A 1998;95:12608-13.  Back to cited text no. 12
Li CM, Guo M, Borczuk A, Powell CA, Wei M, Thaker HM, et al. Gene expression in Wilms' tumor mimics the earliest committed stage in the metanephric mesenchymal-epithelial transition. Am J Pathol 2002;160:2181-90.  Back to cited text no. 13
Behbakht K, Qamar L, Aldridge CS, Coletta RD, Davidson SA, Thorburn A, et al. Six 1 overexpression in ovarian carcinoma causes resistance to TRAIL-mediated apoptosis and is associated with poor survival. Cancer Res 2007;67:3036-42.  Back to cited text no. 14
Ng KT, Man K, Sun CK, Lee TK, Poon RT, Lo CM, et al. Clinicopathological significance of homeoprotein Six 1 in hepatocellular carcinoma. Br J Cancer 2006;95:1050-5.  Back to cited text no. 15
Yu Y, Khan J, Khanna C, Helman L, Meltzer PS, Merlino G. Expression profiling identifies the cytoskeletal organizer ezrin and the developmental homeoprotein Six-1 as key metastatic regulators. Nat Med 2004;10:175-81.  Back to cited text no. 16
Wan F, Miao X, Quraishi I, Kennedy V, Creek KE, Pirisi L. Gene expression changes during HPV-mediated carcinogenesis: A comparison between an in vitro cell model and cervical cancer. Int J Cancer 2008;123:32-40.  Back to cited text no. 17
Coletta RD, Christensen K, Reichenberger KJ, Lamb J, Micomonaco D, Huang L, et al. The Six 1 homeoprotein stimulates tumorigenesis by reactivation of cyclin A1. Proc Natl Acad Sci U S A. 2004;101:6478-83.  Back to cited text no. 18
Li Z, Tian T, Lv F, Chang Y, Wang X, Zhang L, et al. Six 1 promotes proliferation of pancreatic cancer cells via upregulation of cyclin D1 expression. PLos One 2013;8:e59203.  Back to cited text no. 19
Nikpour P, Emadi-Baygi M, Mohammad-Hashem F, Maracy MR, Haghjooy-Javanmard S. Differential expression of ZFX gene in gastric cancer. J Biosci 2012;37:85-90.  Back to cited text no. 20
Nikpour P, Baygi ME, Steinhoff C, Hader C, Luca AC, Mowla SJ, et al. The RNA binding protein Musashi1 regulates apoptosis, gene expression and stress granule formation in urothelial carcinoma cells. J Cell Mol Med 2011;15:1210-24.  Back to cited text no. 21
Li Z, Deng D, Huang H, Tian L, Chen Z, Zou Y, et al. Overexpression of Six 1 leads to retardation of myogenic differentiation in C2C12 myoblasts. Mol Biol Rep 2013;40:217-23.  Back to cited text no. 22
Zheng W, Huang L, Wei ZB, Silvius D, Tang B, Xu Px. The role of Six 1 in mammalian auditory system development. Development 2003;130:3989-4000.  Back to cited text no. 23
Xu PX, Zheng W, Huang L, Maire P, Laclef C, Silvius D. Six 1 is required for the early organogenesis of mammalian kidney. Development 2003;130:3085-94.  Back to cited text no. 24
Zou D, Silvius D, Fritzsch B, Xu Px. Eya1 and Six 1 are essential for early steps of sensory neurogenesis in mammalian cranial placodes. Development 2004;131:5561-72.  Back to cited text no. 25
Abate-Shen C. Deregulated homeobox gene expression in cancer: Cause or consequence? Nat Rev Cancer 2002;2:777-85.  Back to cited text no. 26
Ooi CH, Ivanova T, Wu J, Lee M, Tan IB, Tao J, et al. Oncogenic pathway combinations predict clinical prognosis in gastric cancer. PLoS Genet 2009;5:e1000676.  Back to cited text no. 27
Förster S, Gretschel S, Jons T, Yashiro M, Kemmner W. THBS4, a novel stromal molecule of diffuse-type gastric adenocarcinomas, identified by transcriptome-wide expression profiling. Mod Pathol 2011;24:1390-403.  Back to cited text no. 28
Matsusaka K, Kaneda A, Nagae G, Ushiku T, Kikuchi Y, Hino R, et al. Classification of Epstein-Barr virus-positive gastric cancers by definition of DNA methylation epigenotypes. Cancer Res 2011;71:7187-97.  Back to cited text no. 29
Ahmed M, Wong EY, Sun J, Xu J, Wang F, Xu PX. Eya1-Six 1 interaction is sufficient to induce hair cell fate in the cochlea by activating Atoh1 expression in cooperation with Sox 2. Dev Cell 2012;22:377-90.  Back to cited text no. 30
Cui J, Chen Y, Chou WC, Sun L, Chen L, Suo J, et al. An integrated transcriptomic and computational analysis for biomarker identification in gastric cancer. Nucleic Acids Res 2011;39:1197-207.  Back to cited text no. 31
Ruf RG, Xu PX, Silvius D, Otto EA, Beekmann F, Muerb UT, et al. SIX1 mutations cause branchio-oto-renal syndrome by disruption of EYA1-SIX1-DNA complexes. Proc Natl Acad Sci U S A 2004;101:8090-5.  Back to cited text no. 32
Tanner MM, Karhu RA, Nupponen NN, Borg A, Baldetorp B, Pejovic T, et al. Genetic aberrations in hypodiploid breast cancer: Frequent loss of chromosome 4 and amplification of cyclin D1 oncogene. Am J Pathol 1998;153:191-9.  Back to cited text no. 33
El-Rifai W, Sarlomo-Rikala M, Andersson LC, Miettinen M, Knuutila S. High-resolution deletion mapping of chromosome 14 in stromal tumors of the gastrointestinal tract suggests two distinct tumor suppressor loci. Genes Chromosomes Cancer 2000;27:387-91.  Back to cited text no. 34
Thompson PM, Seifried BA, Kyemba SK, Jensen SJ, Guo C, Maris JM, et al. Loss of heterozygosity for chromosome 14q in neuroblastoma. Med Pediatr Oncol 2001;36:28-31.  Back to cited text no. 35
Koo SH, Kwon KC, Shin SY, Jeon YM, Park JW, Kim SH, et al. Genetic alterations of gastric cancer: Comparative genomic hybridization and fluorescence In situ hybridization studies. Cancer Genet Cytogenet 2000;117:97-103.  Back to cited text no. 36
Gümüs -Akay G, Unal AE, Elhan AH, Bayar S, Karadayt K, Sunguroglu A, et al. DNA copy number changes in gastric adenocarcinomas: High resolution-comparative genomic hybridization study in Turkey. Arch Med Res 2009;40:551-60.  Back to cited text no. 37
Dicken BJ, Bigam DL, Cass C, Mackey JR, Joy AA, Hamilton SM. Gastric adenocarcinoma: Review and considerations for future directions. Ann Surg 2005;241:27-39.  Back to cited text no. 38


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1]

This article has been cited by
1 Depressing hsa_circ_0058092 functions an integrated anti-proliferation and anti-motility role in gastric cancer partially through targeting miR-1294/SIX1 axis
Jianming Fang, Jianxin Huang, Xiaodong Zhang
Applied Biological Chemistry. 2022; 65(1)
[Pubmed] | [DOI]
2 Ginsenoside Rh4 Suppresses Metastasis of Gastric Cancer via SIX1-Dependent TGF-/Smad2/3 Signaling Pathway
Hongbo Jiang, Pei Ma, Zhiguang Duan, Yannan Liu, Shihong Shen, Yu Mi, Daidi Fan
Nutrients. 2022; 14(8): 1564
[Pubmed] | [DOI]
3 Silencing SIX1 inhibits epithelial mesenchymal transition through regulating TGF-/Smad2/3 signaling pathway in papillary thyroid carcinoma
Wen-Pu Min,Xiao-Feng Wei
Auris Nasus Larynx. 2020;
[Pubmed] | [DOI]
4 Correlations between Histological and Array Comparative Genomic Hybridization Characterizations of Wilms Tumor
Ming-Ru Chiang,Chi-Wen Kuo,Wen-Chung Wang,Tai-Cheng Hou,Chen-Yun Kuo,Meng-Yao Lu,Yen-Chein Lai
Pathology & Oncology Research. 2019;
[Pubmed] | [DOI]
5 Metabolomic alterations and chromosomal instability status in gastric cancer
Cheng-Kun Tsai,Ta-Sen Yeh,Ren-Chin Wu,Ying-Chieh Lai,Meng-Han Chiang,Kuan-Ying Lu,Cheng-Yu Hung,Hung-Yao Ho,Mei-Ling Cheng,Gigin Lin
World Journal of Gastroenterology. 2018; 24(33): 3760
[Pubmed] | [DOI]
6 Expression profile of SIX family members correlates with clinic-pathological features and prognosis of breast cancer
Han-Xiao Xu,Kong-Ju Wu,Yi-Jun Tian,Qian Liu,Na Han,Xue-Lian He,Xun Yuan,Gen Sheng Wu,Kong-Ming Wu
Medicine. 2016; 95(27): e4085
[Pubmed] | [DOI]
7 Potential Biomarkers in Diagnosis of Human Gastric Cancer
Zhihao Zhang,Mengmeng Dou,Xiaofang Yao,Hao Tang,Zhubo Li,Xiaoyan Zhao
Cancer Investigation. 2016; 34(3): 115
[Pubmed] | [DOI]


Previous article  Next article
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

  In this article
Materials and me...
Article Figures
Article Tables

 Article Access Statistics
    PDF Downloaded227    
    Comments [Add]    
    Cited by others 7    

Recommend this journal